Ebook Textbook of endodontology (3/E): Part 2

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Part 3

Endodontic Treatment Procedures

169

Chapter 10

Endodontic emergencies

Peter Jonasson, Maria Pigg, and Lars Bjørndal

Introduction

The most frequent causes of tooth-related pain are pulpal

and periapical inflammation due to bacterial infection

Notably, the underlying major etiological mechanisms

behind a painful inflamed pulp or apical periodontitis

are not different from “cases” without pain The focus

is still on the bacterial infection, but an acute clinical

expression has appeared and needs immediate attention

Very often, the dentist has to consider management of

emergencies under time pressure, either as unscheduled

consultations squeezed in between regular patients, or

due to a sudden complication This requires clinical skill,

not least regarding proper diagnostics to ascertain that

the source of pain has been correctly identified

Emer-gency treatment is often a compromise and a temporary

solution, and needs to include information to the patient

about the need for later completion of the treatment and

expected outcome

The aim of emergency treatment is to achieve pain

relief and/or infection control while at the same time

maintaining good prognosis for the subsequent

treat-ment, and to prevent adverse sequelae This usually

includes removing the cause of pain but may also

include drainage in case of purulent infection and

swelling (see Core concept 10.1)

After a general introduction on diagnostics and

emer-gency principles, this chapter will cover the

manage-ment of patients with acute pain or complications

origi-nating from the tooth or the surrounding tissues

General diagnostic considerations and

emergency principles

A general medical and local dental anamnesis and a

careful clinical examination is the basis for diagnosis

and treatment (see Chapter 4), and should in the gency situation focus on the chief complaint (Fig 10.1).The pain history often provides important informa-tion regarding endodontic conditions, and the patient’sdescription is a vital part of diagnosis The type andduration of symptoms may give some indication of theconditions (see Core concept 10.2)

emer-Pain varies in intensity and may be mild, ate, or severe Pain quality also varies along a spec-trum from sharp, intermittent attacks over pulsating orthrobbing sensations to a continuous dull ache How-ever, the intensity and quality of pain per se wasreported to have poor correlation to the diagnosis [1],and the evidence that symptoms are useful as markers

moder-of disease severity is insufficient overall [2] Caution isthus needed when the information is used to make adiagnosis

Correct diagnosis is fundamental for adequate ment, but is not always easy to achieve in the acute situ-ation Several teeth may display pathosis, but to achievesymptom relief the offending tooth must be identified(see Core concept 10.3)

treat-The etiology and pathogenesis behind emergency scenarios

A high proportion of patients seeking emergency dentalappointments because of pain have symptoms of pul-pal or periapical disease [3] In one study it was foundthat the most frequent reason for performing root canaltreatment was vital symptomatic carious teeth (Fig 10.2)[4, 5], but fractures or cracks in the tooth substance(Fig 10.3) from traumatic injuries or leakage in gapsalong the margins of restorations or from chemical orthermal insult subsequent to dental treatment are othercauses (see Core concept 10.4)

Textbook of Endodontology, Third Edition Edited by Lars Bjørndal, Lise-Lotte Kirkevang, and John Whitworth.

© 2018 John Wiley & Sons Ltd Published 2018 by John Wiley & Sons Ltd.

Companion Website: www.wiley.com/go/bjorndal/endodontology

171

172 Endodontic Treatment Procedures

Core concept 10.1 Overall strategy for emergency

visits

An overall strategy for handling emergency visits includes the

following:

r Identify the pain cause (diagnosis, location)

r Eliminate the pain cause (infection, inflammation)

r Consider need of drainage

r Consider risk of infection spreading (need for antibiotics)

r Consider need for further pain relief (analgesics) and later

treatment

Once the carious bacterial front reaches the innermost

dentin and the pulp [6], the dentin barrier function is

lost and the pulp is no longer able to resist bacterial

invasion Consequently, microorganisms will enter the

pulp space and over time advance in apical direction, as

the pulp tissue gradually breaks down and the necrotic

zone progresses Bacterial products induce an

inflam-matory reaction in the periradicular tissues (apical

peri-odontitis) adjacent to canal orifices, mainly in the apical

part of the tooth The degree of inflammation and the

presence and character of symptoms will depend on the

Core concept 10.2 Taking a pain history

A thorough pain history should include the following information:

r Exacerbating or relieving factors

quantitative (number) and qualitative (virulence) nature

of the microorganisms as well as the host inflammatoryresponse (see Chapter 7)

Most acute endodontic conditions develop neously, but in conjunction with certain treatments theremay be a higher risk of postoperative pain (flare-up) Ifthe host defense is insufficient to contain the infectionwithin the root, bacteria may enter the periapical tis-sues and cause a massive acute inflammatory response,which usually includes pain and swelling The process

sponta-of swelling can be categorized as either an abscess or

Diagnosis and treatment

Vital pulp and apical periodontitisNecrotic, infected pulp

Caries excavation (- pulp exposure)

Systemic infection spread

(- pus - swelling) Access cavity preparation and cleaning of pulp chamber

(+/- pus +/- swelling) Complete chemomechanical cleaning of root canal system +/- incision for drainage

(- moderate swelling,

- signs of spread to deeper structures) Removal of source of infection + systemic antibiotics (+ severe swelling, breathing difficulties, + signs of spread to deeper structures) Removal of source of infection + systemic antibiotics Hospitalization +/- surgical drainage

Paraclinical examination:

Radiology

Fig 10.1 Flowchart of the emergency diagnostic process and endodontic treatment modalities.

Endodontic emergencies 173

Core concept 10.3 Clinical assessment of tooth

pain and the potential parameters involved Extraoral

r Pulp vitality (cold, electricity)

r Pain provocation (percussion, apical palpation, temperature)

cellulitis (see later) An abscess is a localized

accumula-tion of pus and swelling within the soft tissue and the

pathway follows the route of least resistance (Fig 10.4)

It is usually very painful If the amount of pus increases,

the pressure in the tissue rises and the abscess may

eventually perforate the bone and periosteum (Fig 10.5)

and burst, or establish a fistula through the oral mucosa

or skin, allowing drainage of the infection and

dimin-ishing the risk of infectious spread A fistula may also

advance along the periodontal space mimicking a deep

periodontal pocket The choice of endodontic emergency

treatment should be based on location of the infection

and consideration of the risk for systemic spreading

Although this is rare, it is important to diagnose and treat

deep infections of dental origin early, since they may

lead to serious conditions and even, in very rare cases,

death The influence of local anatomy is well

under-stood, but there is limited literature describing other

risk factors contributing to the spread of odontogenic

infections

Acute pain from pulpitis

Two types of primary nociceptors are responsible for

pulpal pain: A- and C-fibers The A-fibers have free

nerve endings in the peripheral pulp and inner dentin,

and normally respond to thermal or mechanical

stim-uli (when pulp or dentin is exposed) with sharp and

intense pain The C-fibers are located deeper in the

pulp, and are mainly sensitive to extreme temperaturesand chemical stimulation During pulpal inflammation,particularly in late stages, release of proinflammatorymediators such as bradykinin and histamine activate theC-fibers, resulting in dull, aching pain [7] (see Chap-ter 3) Presence of such pain can thus be considered a sign

of pulpitis During inflammation, the excitation olds of pain neurons drop due to central and periph-eral changes [8–10] and inflamed teeth are overall moresensitive The inflammation is further potentiated by therelease of neuropeptides from the nociceptive neuronsthemselves, often referred to as neurogenic inflamma-tion [11, 12] Since the inflammatory reaction in pulpitislargely occurs inside the tooth, it is mainly factors able

thresh-to directly stimulate the pulpal nerves that will inducepain, such as changes in temperature (cold/hot), osmoticpressure (sweetness), or mechanical manipulation of anopen carious lesion (chewing)

Acute pain from apical periodontitisSensory trigeminal nerves innervate the periradiculartissues Periodontal mechanoreceptors are responsiblefor tactile sensation and the ability to sense tooth load(e.g., objects between the teeth) and do not normally sig-nal pain However, in an inflammatory state, normallypainless activities, such as chewing or tooth brushing,become painful Perception of pain on stimulation that

is normally nonpainful in nature (such as light sion, pressure, or touch) is known as allodynia Hyper-algesia, a decrease in pain threshold to, for example,heat, is another example of how the nociceptive responseincreases in the presence of bacteria-induced inflamma-tion Functional plasticity on peripheral and central lev-els of the nervous system explains these phenomena[13, 14]

percus-Since the sensitized nociceptors in apical periodontitisare located outside the tooth, pain is usually provoked

by activities stimulating the periodontal tissues, such asbiting or chewing Palpation of the alveolar process close

to the tooth apex will also elicit pain, especially whenthere is local spread of infection with extreme inflamma-tory activity (e.g., an abscess)

Symptomatic pulpitis – vital pulp

Anamnesis and pain history

In an emergency situation patients will be in differentdegrees of pain and thus needing different urgency fortreatment A situation suggestive of a progressing pulpinflammation is when the tooth first becomes increas-ingly more sensitive to cold air or cold drinks andfood products, which subsequently turns into shorter

174 Endodontic Treatment Procedures

Fig 10.2 Mandibular molar with (a) extremely deep caries, (b) penetrating radiographically into the pulp, and with apical radiolucency, (c) pronounced bleeding

of the pulp and the focal presence of pus is noted (d) prior to preparation of an endodontic working restoration and an aseptic working field Source: Reproduced from [4] with permission from Springer.

or longer periods of lingering pain elicited by the same

stimuli The intermittent character of the pain

experi-ence is a characteristic feature and contributes in the

dif-ferential diagnosis from other painful conditions In the

most severe case, excruciating pain may linger for hours

Pain may occur spontaneously or be provoked by hot or

cold drinks and foods In the end stage, prior to

com-plete breakdown of the pulp, patients may find that cold

water alleviates the symptoms However, symptoms and

circumstances vary widely and careful examination is

necessary to confirm the diagnosis and match findings

to the pain description (Table 10.1)

Relevant examination – clinical and radiographic

If the pain history indicates a vital inflamed pulp,the examination should focus on confirming this andlocalizing the tooth Deep caries, fracture of tooth orrestoration, and cracks may be observations that sup-port the diagnosis, as well as pain provocation of air

Core concept 10.4 Reasons for emergency

r Pulp exposure because of caries, iatrogenic injury, or trauma in an

otherwise nonpainful tooth

r Symptomatic apical periodontitis

r Midtreatment or posttreatment pain associated with pulpectomy,

root canal disinfection or retreatment

r Flare-up subsequent to root canal treatment

blasting or careful probing of the defect, to which a vitalpulp should respond Pain can sometimes be provoked

by tooth percussion [1, 15] Prolonged spontaneous painattacks and lingering pain sensations after pulp provo-cation are regarded as signs of severe inflammation,but the scientific support for this is weak [2] If a toothcrack is suspected (sometimes referred to as “crackedtooth syndrome”; see Chapter 3), transillumination andselective loading of cusps by biting on a wooden spat-ula, cotton roll, or instrument specially designed for thepurpose (FracFinderTM, Tooth Slooth®) can be helpful(Fig 10.6) Typically, sharp pain is elicited when the pres-sure is released after biting with moderate force Injury

to the pulp may also be caused by restorative treatment,

176 Endodontic Treatment Procedures

Mylohyoid muscle

Sublingual space,

in sublingual tissue above mylohyoid muscle (1)

Palatal abscess (6) Maxillary sinus

Vestibule

Buccal space between buccinator muscle and overlying skin (3)

Submandibular space below mylohyoid muscle (2)

Buccinator muscle

(4) (5)

Fig 10.4 Common pathways of an

api-cal abscess The route depends on the

location of the infection process in

rela-tion to the surrounding anatomical

struc-tures: (1) sublingual space in the

sublin-gual tissue above the mylohyoid muscle; (2)

submandibular space below the mylohyoid

muscle; (3) buccal space between

buccina-tor muscle and overlying skin; (4) vestibule;

(5) maxillary sinus; (6) palatal abscess.

typically carried out within a fairly short period of time

(weeks) prior to the onset of symptoms

Identifying the offending tooth is an important

pri-mary task but may be a demanding diagnostic challenge

(see Chapter 4) The primary reason is that findings other

than the patient’s report of pain are rarely present If

there is no overt deep carious lesion (the most common

cause of painful pulpitis) the clinician may be faced with

the difficult task of assessing which one of several teeth

is affected (see Case study 10.1)

Radiographic examination should focus on

identify-ing possible compromise of the pulp If the pain is in

(c)

Fig 10.5 Acute and chronic apical abscess (a) Drainage through the

alve-olar bone, subperiostal/submucosal abscess (b) Drainage by fistula formation.

(c) Drainage along the periodontal ligament.

the posterior region, the bite-wing projection has severaladvantages It is superior for detection of caries and deeprestorations, and also allows simultaneous assessment ofupper and lower jaw, which is important since referredpain is fairly frequent The inability of the patient tocorrectly locate the painful tooth is explained by thefunctional convergence of the trigeminal sensory path-ways In pulpitis cases, the patient’s report of whichtooth is painful should always be supported by clearfindings of pathology to eliminate the risk of treating thewrong tooth Since the pain originates from intradentaltissue, abnormal periapical radiographic findings are

Table 10.1 Prevalent clinical findings associated with reversible and irreversible pulpitis

Pulp condition

Diagnostic factors

Reversible pulpitis

Irreversible pulpitis

Pulp response to cold and electricity Yes Yes

Tenderness to biting/percussion Possible Yes Radiographic signs of apical bone

destruction

Possible Possible

Endodontic emergencies 177

Fig 10.6 Diagnosis of a cracked second molar (a) Pain is elicited on selective loading of cusps by biting on a specially designed instrument (FracFinder ® ) (b)

No radiographic evidence of a crack; but (c) clinically, a crack is clearly identified following removal of a superficial restoration.

not expected and thus a periapical radiograph should

not be the first choice However, it should be noted

that periapical radiolucency can be found in association

with teeth with pulpitis of various degree, and should

not be regarded as a certain sign of pulp necrosis

(see Fig 10.2b) Also, tenderness to percussion of theoffending tooth and even of the neighboring teeth may

or may not be observed in the final stages of pulpalinflammation

Case Study 10.1

Pulpitis may be accompanied by severe painful

symp-toms Although the cause is often a deep carious lesion,

painful pulpitis may also follow pulp capping or

restora-tion close to the pulp Especially in a dentirestora-tion that is

fully and properly restored the offending tooth may be

difficult to identify This case demonstrates the dilemma

the clinician may be faced with in cases like this

The emergency patient, a 55-year-old woman, had

suf-fered from excruciating pain over several days The pain

varied from none to intense, which is typical in cases of

painful pulpitis Also suggestive of pulpitis was that the

pain was poorly localized and was felt to variably

origi-nate from the lower as well as from the upper jaw on the

right hand side Occasionally, pain radiated peripherally

to involve the temporal region There was no clear

asso-ciation with intake of hot and cold drinks or food, and

pain was not aggravated by biting or chewing

Paraceta-mol gave pain relief, albeit only for a few hours

The patient, who was a regular attendant to the clinic,

was well restored and had no obvious carious lesion

(a,b,c) Tooth 47 had received a ceramic restoration

about 2 years previously Teeth 45, 47, and 48 could

be tested for pulp sensitivity but the other teeth wererestored with full cover crowns, and tests were incon-clusive The three teeth showed no response to electricityand unclear response to cold testing Periodontal condi-tions were fair with no periodontal pockets There was

no pain on percussion or apical palpation According tothe radiographs there were no signs of caries

Because of the inconclusive anamnestic, clinical, andradiographic findings, emergency treatment was post-poned because of the risk of entering the wrong tooth.Three days later the patient was seen again afterhaving been on analgesics She reported spontaneous,intermittent, and pulsating pain localized to the lowerjaw Drinking coffee induced sustained pain Tooth

47 showed some percussion sensitivity After isolatingtooth 47 with rubber dam, provocation with warm waterinduced severe persistent pain of high intensity A sub-sequent nerve block in the lower jaw gave pain relief.Upon accessing the pulp of tooth 47, the causative toothwas confirmed by the finding of abundant bleeding (d)

178 Endodontic Treatment Procedures

Emergency management of reversible

(saveable pulp)/irreversible pulpitis

(nonsaveable pulp)

Patients with pulpal pain may require a pulpectomy

pro-cedure whereby the entire pulp tissue is removed (see

Chapter 6) and replaced with a root filling, but this

deci-sion should be taken only after careful consideration of

the causes and the extent to which the pain condition

can be alleviated by a more conservative approach

aim-ing to preserve the pulp and re-establish nonpainful and

healthy conditions in the long term

Reversible pulpitis – saveable pulp

Cases where the pulp is not exposed and the pain

presents as hypersensitivity or only short-lasting pain

to external stimuli are especially amenable to a

con-servative or “wait and see” approach One example is

postoperative hypersensitivity after a restorative

proce-dure; the symptoms to temperature changes and

chew-ing are often of a temporary nature and will disappear

without active treatment, or following adjustment of

hyperocclusion If symptoms are pronounced or have

persisted for some time, removal of the composite

restoration and replacement with a temporary

restora-tion may solve the problem, by blocking exposed

denti-nal tubules and removing residual stress from composite

polymerization shrinkage

Vital teeth with exposed dentin may become

hyper-sensitive to external stimuli, most frequently

temper-ature changes and tooth brushing The patient may

experience considerable discomfort and request an

emergency appointment Exposed dentinal tubules

are susceptible to thermally induced volume changes

of fluid in the dentinal tubules, leading to nociceptor

activation Discomfort often hinders proper cleaning,

and retention of biofilm and bacterial products may

together with neurogenic inflammation induce chronic

inflammatory changes in the pulp

The treatment strategy should initially be

conserva-tive Professional cleaning and re-establishment of good

hygiene routines may in itself lead to significant and

per-manent pain relief [16] On failure to achieve pain relief,

toothpastes with strontium or potassium salts, which

block fluid movement by precipitation of salt crystals,

may be tried [1, 17] If ineffective, the next step is to seal

the dentinal tubules with fluoride varnish, dentin primer

and resin, or a composite restoration Dentin

hypersensi-tivity can be very difficult to control, indicating that the

materials either have no permanent effect and/or that

the inflammatory changes are so profound that a

natu-ral healing process is prevented Endodontic treatment

should be a last resort

Clinical procedure 10.1 Emergency pulpotomy

1 Ensure appropriate local anesthesia.

2 Prepare access cavity to the pulp and remove the coronal pulp with

a bur.

3 Irrigate with copious amounts of water or NaOCl (0.5–2.5%).

4 Control hemorrhage by pressure with cotton pellets In case of fuse bleeding, soak pellets in 3% hydrogen peroxide or an aqueous mixture of Ca(OH)2.

pro-5 Restore access cavity with a temporary filling.

6 Perform pulpectomy as soon as possible.

Irreversible pulpitis – nonsaveable pulp

If the pulp condition is deemed to be of an irreversiblenature, the first step in the emergency treatment is toexpose the pulp If there is a carious lesion, all cari-ous dentin should be excavated first From then on sev-eral options are available, although time pressure oftendecides the choice of treatment Pulpectomy with com-plete debridement of the root canals will offer a highprobability of pain relief [18–20] However, with timeconstraints pulpotomy and removal of the coronal pulptissue without penetrating into the radicular pulp tissue

is an efficient treatment with a comparable probability ofpain relief [18–22] (see Clinical procedure 10.1) Pulpo-tomy is reported to give total or partial pain relief inmore than 90% of cases [18] This is a temporary measureuntil time is available for pulpectomy; if pain from thetooth was previously not relieved by pulpotomy, pulpec-tomy should be performed

In general, a cotton pellet should not be placed inthe access cavity during temporization, as it reduces thethickness of the temporary seal, which increases the risk

of bacterial leakage and reinfection of the pulp chamber[23, 24] The patient should be made aware that postop-erative tenderness or a slight dull pain in the affectedregion can be expected for a couple of days after theemergency procedure Analgesics are usually effective,but if severe pain continues, the patient is advised to seek

a new appointment For a pharmacological approach(see Advanced concept 10.1) [25]

Advanced concept 10.1

Recently, a randomized clinical trial found that a pharmacological approach using intraosseous methylprednisolone injection relieved pain caused by acute pulpitis more effectively than did pulpotomy during a 7-day period before proper endodontic treatment was per- formed [25] The concept is interesting and could have relevance espe- cially in regions where access to dental resources is low However, adequate diagnosis is important This requires good knowledge about etiology and training in differential diagnosis of dental pain.

Endodontic emergencies 179

Symptomatic apical periodontitis with or

without acute abscess

Anamnesis and pain history

A chief complaint is localized pain, at first only present

on chewing, but eventually developing into persistent,

severe pain disturbing night sleep The patient has

usually no doubt which tooth is affected The tooth

may feel elevated or even loose, and there may be

soft-tissue swelling However, considerable variation in

symptoms should be expected, since the transition from

a necrotic pulp to acute periapical disease occurs along a

continuum

Relevant examination – clinical

and radiographical

The tooth and periradicular tissue should be tested

with palpation, percussion, periodontal probing,

mobil-ity, analysis of occlusion and articulation, and

transillu-mination It can be difficult clinically to estimate the

tran-sition between symptomatic apical periodontitis and the

initial stages of an abscess formation The tooth may be

tender to percussion and the mucosa and bone

overly-ing the apical region may be sensitive to palpation

Peri-odontal probing will reveal drainage of an abscess or

fis-tula formation through the periodontal ligament space

(Fig 10.5) Differential diagnosis in relation to localized

marginal periodontitis is important and is done by pulp

vitality assessment (see Chapter 4) In addition, a narrow

isolated periodontal pocket may be caused by a vertical

root fracture

A periapical radiographic examination of the tooth is

mandatory The apical radiolucency may be restricted

to a minor widening of the periodontal space Notably,

while inflammatory changes in soft tissue develop fast,resorption of periapical bone is a slower process, whichmay not yet be detectable in radiographs at the acutestage Radiographs in two horizontal angulations may

be helpful if one image does not show clear pathology

In case of a fistula along the periodontal pocket, graphic changes can be completely absent For morecomplicated cases when the intraoral examination isinconclusive, cone beam computed tomography may beconsidered [26], but should not be the first choice inemergency cases

radio-Emergency management of symptomatic apical periodontitis

The strategy for the biomechanical instrumentation ried out in pain cases is the same as in symptom-free cases In case of extrusion of the tooth from thesocket due to inflammatory exudate in the periodontalligament, the tooth may be very tender and even loose.Therefore, in addition to local anesthesia, it may be nec-essary to stabilize the tooth during access Pus may ormay not appear spontaneously (Fig 10.7) After accesspreparation, an aseptic working field is prepared withrubber dam and disinfection, and the standard root canaldisinfection is carried out (see Chapters 13–15) Calciumhydroxide is applied in the cleaned canal, and propertemporary sealing is mandatory A moist cotton pelletcan be used to wipe the walls of the access cavity cleanfrom calcium hydroxide, allowing a proper tight seal

car-If time is insufficient for a full root canal disinfection,

an access cavity should be performed, removing theinfected crown pulp and exposing the canal orificesfollowed by irrigation of the pulp chamber with water

or sodium hypochlorite and placement of a temporary

Fig 10.7 Symptomatic apical periodontitis in a mandibular molar (a) Temporary restoration of questionable quality is seen radiographically (b) Pus emerges spontaneously from the cavity (c) Due to a cotton pellet placed in the cavity, the temporary restoration (arrow) was insufficient and leakage of bacteria from the oral environment occurred.

180 Endodontic Treatment Procedures

filling [20, 22] Cleaning of the pulp chamber has

shown pain relief for a large proportion, but not to the

same magnitude as complete root canal disinfection

[20, 22, 27–29] The patient should be scheduled for

completion of root canal treatment as soon as possible

to preclude recurrent pain This concept is not

recom-mended in patients with infection associated with either

pus or swelling

Drainage of pus through the root canal

If the periapical process is purulent, drainage through

the root canal (Fig 10.7) is often obtained within

min-utes, but it can be difficult to predict If pus does not

emerge from the root canal during instrumentation as

expected, once the canal has been properly cleaned it

is advisable to penetrate the apical constriction with a

handfile (size 10–15) in order to optimize drainage Care

should be taken not to overinstrument the apical

fora-men region

The tooth should never be left open between

appoint-ments [30]; it should be sealed with a tight temporary

restoration, after placement of calcium hydroxide In

very rare cases the drainage may continue, but even in

such cases the tooth can be sealed By the time of the next

appointment the initial removal of infection has usually

arrested pus formation

Acute apical abscess – incision and drainage

The classical approach to achieving drainage is by

inci-sion (Fig 10.8) The right timing of abscess inciinci-sion is

often described as “when it appears soft and fluctuant,”

that is, when the pus is located in the submucosa, as

opposed to a more diffuse increase of volume or even a

hard swelling, indicating that the periosteum has started

to elevate The decision whether to incise or not is based

on clinical assessment and experience It is advisable to

Fig 10.8 Drainage of a fluctuant submucosal abscess is provided by the

use of a scalpel Pus is released on careful incision (approx 1 cm cut).

monitor symptom development carefully, incise whenpossible, and refrain from antibiotics unless systemicspread is identified

Cellulitis

Cellulitis is an infection spreading in the connective sue with diffuse erythematous swelling Cellulitis is usu-ally painful and may be accompanied by malaise andfever Pathogens and related inflammatory exudate mayspread along the spaces of the head and neck within thefascial planes (see Fig 10.4)

tis-Such advanced systemic spread of endodontic tions is rare, but if not properly assessed and adequatelyhandled it may lead to serious complications and be life-threatening (see also Chapter 25) [31, 32]

infec-Posttreatment emergency

A painful condition may remain after emergency ment or arise postoperatively by an initially nonpainfultooth The latter condition is termed endodontic flare-up.Teeth with preoperative pain and teeth with apical peri-odontitis are more prone to developing postoperativepain and discomfort [33–35] The causes include micro-bial, mechanical, and/or chemical injury to the pulp orperiradicular tissues Contamination due to not apply-ing a rubber dam, an unsatisfactory temporary restora-tion (Fig 10.7a), or displacement of carious dentin andbacterial plaque into the pulpal or periapical tissue arekey factors [35–37] In combination with inappropriateintracanal medication, incomplete instrumentation, non-instrumented canals, and apical overinstrumentation, it

treat-is easy to comprehend that conditions for bacterial tiplication in the root canal system are created It should

mul-be emphasized that complications of this nature should

be rare in properly managed clinical practice [36, 38](see Core concept 10.5) Cracked tooth (see Fig 10.3c–e)substance and hyperocclusion are other factors to con-sider when examining a patient for causes of a post-endodontic emergency

After assessment of potential causes, the first step is toassess the need to carry out a re-entry procedure Post-operative pain often resolves spontaneously and may

be controlled simply by pain medication and a tion of the occlusal forces Re-entry is only relevant iffurther removal of inflamed or infected pulp tissue can

reduc-Core concept 10.5

Adherence to basic endodontic principles – including aseptic ment, complete removal of accessible pulpal tissue, and filling of canal to proper length – favors pain relief and precludes endodontic flare-ups.

be performed, and when it is deemed necessary, the

endodontic procedure should follow the same strictly

aseptic routine as described above, which includes

rub-ber dam application and disinfection Moreover, in cases

with abscess formation a re-entry will allow for drainage

of pus

An endodontic flare-up may also be associated with an

overfilled root canal Normally, a small extrusion of root

filling material does not cause more than slight

tender-ness, which usually subsides over a couple of days If a

severe pain condition has developed, with apical

tender-ness and some swelling, there is often a bacterial cause

where microorganisms have been pushed into the

peri-odontal tissues along with the root filling material

How-ever, a flare-up may also occur when the root filling is

short of apex (Fig 10.9)

Non-endodontic tooth pain – conditions

of differential diagnostic interest

Non-odontogenic pain presenting as toothache

chal-lenges the diagnostic ability of the clinician Although

most toothache is odontogenic and endodontic, the

den-tist needs to be aware of and able to identify other

con-ditions with similar symptoms, in order to avoid

mis-diagnosis (see Core concept 10.6) A brief description of

the most relevant differential diagnoses is given below,

but several other conditions are possible (see Chapters 4

and 22)

Marginal (periodontal) abscessMarginal periodontitis is generally not painful, butsometimes a marginal abscess occurs Symptoms andclinical findings of marginal abscess are throbbing pain,marginal swelling, tenderness to percussion and palpa-tion, and a local deep pocket The pulp is normally vital(responds to pulp testing) and bone destruction associ-ated with the tooth apex is absent (atypical, lateral bonedestruction may be seen) A history of periodontal dis-ease should be a warning sign Emergency treatmentincludes careful scaling and irrigation of the affectedpocket [39]

Referred pain from other teeth ornondental structures

Referred pain originates in a different body structurethan where it is perceived by the patient The phe-nomenon is explained by the complex innervation pat-terns of sensory nerves In the central nervous system(CNS), the afferents converge and signals from some-times quite remote tissues use the same pathways; thisleads to an inability to discriminate between pains of dif-ferent origin, such as another ipsilateral tooth, mastica-tory or neck muscles and jaw joints [40, 41], sinus dis-ease [42], neurovascular headache [43], or even cardiacmuscle ischemia [44, 45] Failure to find clinical or radio-graphic evidence of pathology in the pain region shouldresult in inquiry about muscle tenderness, ear, nose, and

182 Endodontic Treatment Procedures

Core concept 10.6 Overview of findings suggestive

of odontogenic pain (of dental origin) and non-odontogenic pain

Odontogenic pain Non-odontogenic pain

Evidence of dental or

periodontal pathosis is

present (e.g., caries, leakage,

fracture, crack, pocket,

lingering to dull, constantly

aching and throbbing

Poorly localized pain, appears at different locations at different times

Unilateral and localized pain Bilateral pain or multiple pain sites

Pain level affected by

temperature change

Pain co-occurring with headache

Pain evoked on tooth

percussion, pressure and/or

Pain level affected by changes in posture

throat infection, headaches, and heart disease, and

clin-ical examination should include assessment of

oppos-ing teeth and provocation of muscles If muscle

palpa-tion increases the tooth pain, this may indicate that the

tooth pain has a muscular origin Tender or painful teeth

are frequently reported in association with bruxism and

with sinusitis (upper premolars and first molar)

Idiopathic or neuropathic tooth pain

Patients with long-lasting pain complaints sometimes

schedule an emergency appointment, and such chronic

problems should be distinguished from acute tooth pain

Symptoms and clinical signs overlap with inflammatory

pain, and in the emergency situation it is wise to be

vig-ilant Pain that does not resolve as expected, for

exam-ple lingering pain after seemingly adequate endodontic

treatment, should signal caution The pain may be

neu-ropathic, caused by trauma or an earlier dental

proce-dure, or idiopathic (of unknown origin) In the absence

of explanatory clinical or radiographic findings, the

den-tist should avoid invasive treatment A later

appoint-ment for more comprehensive assessappoint-ment should be

scheduled, or the patient referred to an endodontist or

specialist in orofacial pain Differential diagnostic effortsmay include diagnostic anesthesia [46], a somatosensoryscreening examination [47], and extended radiographicexamination or imaging [48, 49]

Management of patients with acute dental pain

From a psychological perspectiveAcute pain is often accompanied by anxiety and emo-tional distress The experience of pain is complex innature, and the sensory input from tissue injury orinflammation is only one dimension Affective factors(such as stress, anxiety, fear, and mood) and cogni-tive factors (such as attention, control, pain beliefs, andexpectations) are other dimensions that play an impor-tant role for the total impact of pain and the patient’sability to cope Stress and fear of treatment amplify pain,and in the emergency situation the dentist should there-fore strive to inspire confidence and make the patient feelsafe If the patient is stressed and anxious, the dentistmay overestimate the severity of the condition (in terms

of tissue damage), and thus prompt a more invasive cedure than is needed A very important aspect of theemergency management is to listen carefully to the his-tory reported by the patient before any intraoral exam-ination and treatment By spending sufficient time onlistening and asking relevant questions many mistreat-ments may be avoided

pro-AntibioticsIntake of antibiotics does not provide pain relief inirreversible pulpitis [50] Use of antibiotics should berestricted to situations when the bacterial infection hasspread outside the tooth Fever, malaise, and tendernessand swelling of regional lymph nodes are signs of sys-temic spread, and thus indications for antibiotic treat-ment Abscess formation adjacent to the offending tooth

is a sign of local spread, and removal of the infectionand drainage is the recommended primary treatmentsince evidence is scarce that antibiotics have an addi-tional effect [51] Antibiotics are generally not required,but careful assessment of surrounding tissues should bedone to exclude deeper spread (see Chapter 25).Prescription of antibiotics as a solitary emergencytreatment may sometimes be necessary if it is not pos-sible to remove the infection (anesthetic failure, psycho-logical concerns, or physical obstacles) but should beavoided as far as possible to minimize the risk of devel-opment of resistant bacterial strains (both within theindividual and in the community) and must in all cases

be followed by causal treatment soon after

Endodontic emergencies 183

Analgesics

Pain relief is usually the patient’s major concern

Appro-priate management of the infection is often enough but

in some cases pharmacological supplements are needed

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the

medications of choice, since they are considered effective

and safe, and are available without prescription

Ibupro-fen in combination with acetaminophen (paracetamol)

is reported to be more effective than ibuprofen alone

[52] Patients should be encouraged to seek pain relief

whenever needed Longer duration of preoperative pain

predicts persisting pain after root canal treatment [53]

Preoperative analgesia may potentiate the effect of local

anesthesia, decrease postoperative pain, and lower the

risk of sensitization of the pain system and chronic pain

development [54–56]

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2 Mej`are IA, Axelsson S, Davidson T, Frisk F, Hakeberg

M, Kvist T, et al Diagnosis of the condition of the

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3 Hasselgren G, Calev D Endodontics emergency treatment

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4 Bjørndal L Vital Pulp Therapy for Permanent Molars Berlin:

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5 Bjørndal L, Laustsen MH, Reit C Root canal treatment in

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6 Reeves R, Stanley HR The relationship of bacterial

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7 N¨arhi MV The characteristics of intradental sensory units

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8 Byers MR, Taylor PE, Khayat BG, Kimberly CL Effects of

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9 Khayat BG, Byers MR, Taylor PE, Mecifi K, Kimberly CL.

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peri-apical lesions in rat molars demonstrated by calcitonin

gene-related peptide immunocytochemistry J Endod 1988;

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11 Brain SD Sensory neuropeptides: their role in

inflamma-tion and wound healing Immunopharmacology 1997; 37:

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12 Chiu IM, von Hehn CA, Woolf CJ Neurogenic tion and the peripheral nervous system in host defense and

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13 Hu JW Tooth pulp In: Clinical Oral Physiology (Miles

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14 Trulsson M, Essick G Mechanosensation In: Clinical Oral

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symp-toms in pulp disease Int Endod J 1980; 13: 27–35.

16 Hovgaard O Dentin hypersensibilitet: fysiologi og behandling.

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Tandsygdom-17 Poulsen S, Errboe M, Lescay Mevil Y, Glenny AM sium containing toothpastes for dentine hypersensitivity.

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18 Asgary S, Eghbal MJ A clinical trial of pulpotomy vs.

root canal therapy of mature molars J Dent Res 2010; 89:

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19 Oguntebi BR, DeSchepper EJ, Taylor TS, White CL, Pink FE Postoperative pain incidence related to the type of emer-

gency treatment of symptomatic pulpitis Oral Surg Oral

Med Oral Pathol 1992; 73: 479–83.

20 Bjerk´en E, Wennberg A, Tronstad L Endodontisk

akutbe-handling Tandl¨akartidningen 1980; 72: 314–19.

21 Hasselgren G, Reit C Emergency pulpotomy: pain

reliev-ing effect with and without the use of sedative dressreliev-ings J.

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22 Molander A, Nilsson A, Reit C Effekter av endodontisk

akutbehandling Tandl¨akartidningen 2004; 96: 48–54.

23 Beach CW, Calhoun JC, Bramwell JD, Hutter JW, Miller

GA Clinical evaluation of bacterial leakage of endodontic

temporary filling materials J Endod 1996; 22: 459–62.

24 Laustsen MH, Laren T, Reit C, Bjørndal L den af temporære endodontiske fyldningsmaterialer En

Bakterietæthe-klinisk og mikrobiologisk undersøgelse Tandlægebladet

2004; 108: 888–94.

25 Bane K, Charpentier E, Bronnec F, Descroix V,

Gaye-N’diaye F, Kane AW, et al Randomized clinical trial of

intraosseous methylprednisolone injection for acute

pulpi-tis pain J Endod 2016; 42: 2–7.

26 Patel S, Durack C, Abella F, Roig M, Shemesh H,

Lam-brechts P, et al European Society of Endodontology tion statement: the use of CBCT in endodontics Int Endod.

posi-J 2014; 47: 502–4.

27 Fouad AF, Rivera EM, Walton RE Penicillin as a

supple-ment in resolving the localized acute apical abscess Oral

Surg Oral Med Oral Pathol Oral Radiol Endod 1996; 81:

590–5.

28 Henry M, Reader A, Beck M Effect of penicillin on operative endodontic pain and swelling in symptomatic

post-necrotic teeth J Endod 2001; 27: 117–23.

29 Nusstein JM, Reader A, Beck M Effect of drainage upon access on postoperative endodontic pain and swelling in

symptomatic necrotic teeth J Endod 2002; 28: 584–8.

30 Tj¨aderhane LS, Pajari UH, Ahola RH, B¨ackman TK, Hietala

EL, Larmas MA Leaving the pulp chamber open for drainage has no effect on the complications of root canal

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184 Endodontic Treatment Procedures

31 Carter L, Starr D Alarming increase in dental sepsis Br.

Dent J 2006; 200: 243.

32 Sepp¨anen L, Rautemaa R, Lindqvist C, Lauhio A Changing

clinical features of odontogenic maxillofacial infections.

Clin Oral Invest 2010; 14: 459–65.

33 Ali A, Olivieri JG, Duran-Sindreu F, Abella F, Roig M,

Garcia-Font M Influence of preoperative pain intensity on

postoperative pain after root canal treatment: a prospective

clinical study J Dent 2015: 8.

34 Sadaf D, Ahmad MZ Factors associated with

postopera-tive pain in endodontic therapy Int J Biomed Sci: IJBS.

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35 Walton R, Fouad A Endodontic interappointment

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J Endod 1992; 18: 172–7.

36 Imura N, Zuolo ML Factors associated with endodontic

flare-ups: a prospective study Int Endod J 1995; 28: 261–5.

37 Rosenberg PA, Babick PJ, Schertzer L, Leung A The effect

of occlusal reduction on pain after endodontic

instrumen-tation J Endod 1998; 24: 492–6.

38 Trope M Flare-up rate of single-visit endodontics Int.

Endod J 1991; 24: 24–6.

39 Herrera D, Alonso B, de Arriba L, Santa Cruz I, Serrano C,

Sanz M Acute periodontal lesions Periodontol 2000 2014;

65: 149–77.

40 Simons DG, Travell JG, Simons LS Travell & Simons’

Myofas-cial Pain and Dysfunction: The Trigger Point Manual, vol 1,

2nd edn Philadelphia, PA: Lippincott Williams & Wilkins,

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41 Wright EF Referred craniofacial pain patterns in patients

with temporomandibular disorder J Am Dent Assoc 2000;

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42 Hansen JG, Højbjerg T, Rosborg J Symptoms and signs

in culture-proven acute maxillary sinusitis in a general

practice population Acta Pathol Microbiol Immunol Scand.

2009; 117: 724–9.

43 Alonso AA, Nixdorf DR Case series of four different

headache types presenting as tooth pain J Endod 2006; 32:

1110–13.

44 Kreiner M, Alvarez R, Waldenstr ¨om A, Michelis V, Mu ˜niz

R, Isberg A Craniofacial pain of cardiac origin is associated

with inferior wall ischemia J Oral Fac Pain Headache 2014;

46 List T, Leijon G, Helkimo M, ¨ Oster A, Svensson P Effect

of local anesthesia on atypical odontalgia – a randomized

controlled trial Pain 2006; 122: 306–14.

47 Baad-Hansen L, Pigg M, Ivanovic SE, Faris H, List

T, Drangsholt M, et al Chairside intraoral qualitative

somatosensory testing: reliability and comparison between

patients with atypical odontalgia and healthy controls J.

Orofac Pain 2013; 27: 165–70.

48 Pigg M, List T, Abul-Kasim K, Maly P, Petersson A A comparative analysis of magnetic resonance imaging and radiographic examinations of patients with atypical odon-

talgia J Oral Fac Pain Headache 2014; 28: 233–42.

49 Pigg M, List T, Petersson K, Lindh C, Petersson A tic yield of conventional radiographic and cone-beam com- puted tomographic images in patients with atypical odon-

Diagnos-talgia Int Endod J 2011; 44: 1092–101.

50 Nagle D, Reader A, Beck M, Weaver J Effect of systemic

penicillin on pain in untreated irreversible pulpitis Oral

Surg Oral Med Oral Pathol Oral Radiol Endod 2000; 90:

pain Cochrane Database Syst Rev 2013; 6: CD010210.

53 Nixdorf DR, Law AS, Lindquist K, Reams GJ, Cole E,

Kan-ter K, et al Frequency, impact, and predictors of

persis-tent pain after root canal treatment: a national dental PBRN

study Pain 2016; 157: 159–65.

54 Campiglia L, Consales G, De Gaudio AR Pre-emptive

anal-gesia for postoperative pain control: a review Clin Drug

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55 Dahl JB, Kehlet H Preventive analgesia Curr Opin

Anaes-thesiol 2011; 24: 331–8.

56 Reader A, Nusstei J, Drum M Successful Local

Anesthe-sia for Restorative Dentistry and Endodontics Chicago, IL:

Quintessence, 2011.

Chapter 11

Controlling the environment – the

aseptic working field

Merete Markvart and Pia Titterud Sunde

Background

The microbial etiology of pulp and periapical disease is

well established, and it is no surprise that infection

con-trol is central to effective clinical management Studies

have shown convincingly that the presence of

microor-ganisms in the root canal at the time of filling is

associ-ated with impaired periapical healing [1] and it is

cru-cial that the root canal system is protected from the oral

microflora during treatment Probably the single most

effective way of preventing contamination is to isolate

all teeth that are undergoing endodontic treatment with

a well-sealing rubber dam

History and evidence

The benefits of tooth isolation with a rubber sheet were

first described by Sanford Christie Barnum in 1864 [2],

with the rubber dam punch introduced in 1882 and

con-tinuous technological development since that time

The routine isolation of teeth with rubber dam is

recommended in professional treatment quality

guide-lines for both adults and children [3–5] and should be

considered the standard of care for all endodontic

proce-dures In common with many elements of contemporary

endodontic practice, including the choice of irrigant

solution or root canal filling material, there is little hard

evidence to prove a causal link between the use or

nonuse of rubber dam and the outcome of endodontic

treatment The established professional support for this

simple and inexpensive measure to promote asepsis and

protect patients from endodontic materials and

instru-ments, however, makes such studies both unnecessary

and unethical to perform [6] Although the data are not

strong, inferences on treatment outcome may be drawn

from a large population-based study which revealed a

small but statistically significant improvement in tooth

survival when rubber dam was employed for primary

endodontic treatment compared with non-isolated trols [7] Similar inferences have also been made for theuse of rubber dam isolation during nonsurgical retreat-ment [8] In patient-centered terms, the nonuse of rubberdam was identified as one of the risk factors for contin-ued symptoms in a small cohort of patients referred forspecialist care after commencing endodontic treatment[9], and a small retrospective review found a signifi-cant, negative impact on periapical health when teethreceiving posts were not isolated with rubber dam [10].The benefits of rubber dam isolation go beyond thecreation of an aseptic working environment Unpro-tected patients do, unfortunately, swallow and aspirateendodontic instruments from time to time [11–13] andisolation of the working environment with rubber dam

con-is the only sure protection (see Chapter 25 for more mation on the management of swallowed or inhaledendodontic instruments) The rubber dam also functions

infor-to promote the use of antimicrobial irrigants such assodium hypochlorite [14], which is foul-tasting and maydamage unprotected soft tissues [15]

The microbial content of air turbine aerosols producedduring operative procedures, including access cavitypreparation, is significantly reduced by rubber dam iso-lation, thereby reducing the risk of cross-infection in thedental practice [16–19]

Despite all of these advantages, and the routine cation of rubber dam in dental school, dentists in manycountries abandon the use of rubber dam when theyenter general practice [6, 14, 20, 21] (see Chapter 26 formore information on transition shock and the pressuresthat come to bear on professionals as they enter clini-cal practice) In a recent study with 10-year follow-upamong Danish general dental practitioners, there was

appli-an encouraging increase in the application of rubberdam for endodontic procedures from 4% to 29%, but theproportion of general dental practitioners preparing anaseptic working field was still low [22]

Textbook of Endodontology, Third Edition Edited by Lars Bjørndal, Lise-Lotte Kirkevang, and John Whitworth.

© 2018 John Wiley & Sons Ltd Published 2018 by John Wiley & Sons Ltd.

Companion Website: www.wiley.com/go/bjorndal/endodontology

185

186 Endodontic Treatment Procedures

Core concept 11.1 Advantages of establishing the

aseptic working field

r The application of rubber dam facilitates disinfection of the

work-ing field.

r The aseptic working field lowers the risk of contamination of the

root canal system.

r Contrast and vision in the working field are enhanced.

r The risk of the patient swallowing instruments is reduced.

r The patient is protected against caustic and foul-tasting irrigants

such as sodium hypochlorite.

Preparing teeth for rubber dam isolation

and the development of an aseptic

working field

The benefits of developing an aseptic working field are

summarized in Core concept 11.1

All plaque and calculus should be removed before

establishing the aseptic working field Removal of

plaque and calculus can be done with periodontal

curettes and/or ultrasound, followed by a rubber cup

with pumice All carious dentine and defective/leaking

restorations should be removed before accessing the

pulp chamber, and a new, clean bur should be used to

enter the pulp space in an effort to minimize

contamina-tion with infected material

Teeth scheduled for endodontic treatment are often

compromised by caries, large restorations, or cracks and

will require occlusal reduction and cuspal coverage aspart of their prosthodontic reconstruction (see Chapter16) Fragile, undermined cusps may be at risk of frac-ture while treatment proceeds and should be reducedfrom the outset Teeth with extensive substance loss, sub-gingival cavity margins or ingrowth of gingival tissuescan be difficult to isolate, and in such cases an endodon-tic “working restoration” is placed This may involveperforming a local gingivectomy, before rebuilding withcomposite resin or glass ionomer cement (Fig 11.1a,b) Ifthe pulp chamber has been opened during initial excava-tions, it is wise to place sterile cotton wool, foam sponge,

or a soft cement such as Cavit (3M) in the chamber beforebuilding the working restoration On occasions, it may

be difficult to place a conventional matrix and a per ring or orthodontic band may need to be cementedand filled with a hard setting material such as IRM®

cop-(Dentsply) or zinc phosphate cement, before adjustingthe occlusion On occasions, teeth with little undercutcan be modified by the addition of composite resin totheir buccal and lingual surfaces All approaches shouldallow the stable application of a rubber dam clamp andprovide the tooth with walls that will allow the accesscavity to be flooded with an appropriate volume of irri-gant during treatment

Access preparationThe timing of rubber dam isolation is contentious Manyadvocate opening the access cavity without rubber damisolation in an effort to avoid any loss of orientationand the risk of overcutting or perforation (Fig 11.2)

Fig 11.1 (a) A maxillary first molar that requires a working restoration before isolation with rubber dam and endodontic treatment (b) The same tooth after rebuilding with Ketac Molar ® and isolation with rubber dam.

Controlling the environment 187

Fig 11.2 Perforation of a maxillary molar during access cavity preparation

with the rubber dam in situ The mesiobuccal canals were also not found due

to disorientation.

Others advocate access cavity preparation to the brink

of pulp exposure before applying the dam, yet others

routinely place the rubber dam from the outset unless

the anatomy seems particularly challenging (see

Chap-ter 12) Decision-making is based on the balance of risks,

with iatrogenic damage and microbial contamination

being prominent considerations From a purely aseptic

point of view, having a disinfected rubber dam in place

before entry to the pulp chamber is probably wise

Prerequisites before rubber dam isolation are

summa-rized in Clinical procedure 11.1

Rubber dam isolation

Rubber dam isolation represents the first step in

estab-lishing an aseptic working field Rubber dam sheets

are available in thicknesses from 0.15 to 0.35 mm (often

referred to as light, medium, heavy, extra heavy), and

in individual sheets or rolls For the endodontic

treat-ment of a single tooth, sheets of 5 in × 5 in in a medium

Clinical procedure 11.1 Prerequisites before

application of rubber dam

r Local anesthesia.

r Plaque, calculus, and carious dentine should be removed.

r Insufficient restorations should be replaced.

r If there is substantial loss of tooth structure, the tooth must be

rebuilt with glass ionomer cement or composite.

r Undermined cusps must be adjusted to avoid tooth fracture

between appointments.

r Preparation of the access cavity and identification of the root

canal entrances (note that this action is not a prerequisite in all

cases).

Bow

Jaws Wing

Forceps hole

Contact points

Fig 11.3 The key features of a winged rubber dam clamp.

thickness are commonly used Concerns about latexallergy [23, 24] have encouraged many to switch to latex-free polyethylene or polyvinylchloride products.Rubber dam clamp

Clamps are generally designed with two jaws and fourpoints (Figs 11.3 and 11.4a–e) that are necessary to makestable and secure contact with the tooth to be isolated.Clamps with multiple points are available to make sta-ble contact with unusually shaped or damaged teeth(Fig 11.4f) The jaws may be flat (bland), for use onteeth with good undercuts, or deeply festooned (active),for use on teeth that are partially erupted or with lim-ited undercut, often engaging and gaining stability justbelow the gingival margin (Fig 11.4e) Clamps are avail-able for application to anterior teeth, premolars, andmolars, with the differences relating largely to size anddistance between the jaws Clamps specific to maxillaryand mandibular teeth are also available, as are wingedand wingless versions to accommodate different place-ment techniques (see later) Clamps with a matt finishmay avoid reflection and glare from the operating light.Even new rubber dam clamps may fracture during use[25], and many advocate tying dental floss to all rubberdam clamps before use so that fragments can be safelyretrieved Clamps usually fracture across the bow, andthe simple act of passing floss down the forceps hole onone side, and back up the hole on the other side beforetying in a loop is sufficient

Punches and forceps

A rubber dam punch is used to make holes in the rubberdam sheet (Fig 11.5a) Some punches allow the prepa-ration of a single size of hole, while others have anadjustable platform that allows holes of different diam-eters to be punched To obtain a tight seal around thetooth, the hole must be punched cleanly; a defect in thecut may cause the dam to split and tear as it is stretched

188 Endodontic Treatment Procedures

Fig 11.4 (a) An Ivory 9 clamp designed for anterior teeth (b) Winged premolar clamp (c) Winged lower molar clamp with four-point jaws (d) Wingless lower molar clamp (e) Molar clamp with deeply festooned (active) jaws (f) Molar clamp with multiple contact points.

over the tooth The hole should be made in a position

that will ensure positioning of the rubber dam sheet

cen-trally over the mouth to protect the oral opening from

instruments and materials Stamps are available to

indi-cate hole-positioning for individual teeth, or the sheet

can be offered to the mouth and marked to indicate

opti-mal hole-position

Forceps are used to expand the clamp and position

it on the tooth (Fig 11.5b) Sometimes the retaining

grooves on the beaks of the forceps are too deep, and it

(a)

(b)

Fig 11.5 (a) A multi table rubber dam punch, capable of creating holes of

different sizes for different types of teeth (b) Rubber dam forceps.

may be difficult to disengage the forceps from the clampafter placement on the tooth The tips of the forceps caneasily be thinned with a bur or stone to ensure that theywill slip smoothly off the clamp when positioned

Rubber dam frameThe rubber dam frame holds the loose ends of the rubbersheet away from the tooth during treatment, protectingthe oropharyngeal opening and retracting soft tissues.They are available in closed loop and open U-designs(Fig 11.6) and fabricated in metal or plastic The appli-cation of a frame that optimally retracts the dam and

Fig 11.6 Rubber dam frames; a closed frame in plastic and open frames in both metal and plastic.

Controlling the environment 189

Fig 11.7 Application of the DryDam ® to a lower right first premolar The

rubber bands round the ears retract the dam instead of a frame.

maximizes working space and visualization is

particu-larly important at the back of the mouth

Frameless rubber dams, such as Dry-Dam© (Directa)

are fixed with rubber bands around the patient’s ears

(Fig 11.7), and include a backing paper to limit contact of

the rubber with facial skin and to absorb small amounts

of moisture that may otherwise be uncomfortable The

hole must be carefully placed according to tooth position

if the Dry-Dam is to be worn comfortably and protect the

oropharynx

Application of the rubber dam

The clamp is usually placed with its jaws on the

buc-cal and lingual sides of the tooth and the bow

posi-tioned distally Although manufacturers suggest

pat-terns of clamp for specified types of teeth, it is important

to choose a clamp that will fit stably and securely on the

tooth, and to confirm this by trying it on the tooth before

use Sometimes creativity is called for in clamp selection

(Fig 11.8)

Winged technique

In this technique, the hole in the rubber dam is stretched

over the wings of the clamp (Fig 11.9a), before carefully

applying it the tooth with forceps, sliding the points of

the clamp below the coronal undercut and positioning

just above the gingival margin (Fig 11.9b) The rubber

is then disengaged from the wings with a blunt

instru-ment (Fig 11.9c), before flossing it through the proximal

contacts to form a tight seal around the neck of the tooth

(Fig 11.9d)

Wingless technique

Here, the bow of the clamp is engaged through the hole

in the dam (Fig 11.10), before applying it to the tooth

Fig 11.8 The aseptic working field of a first upper molar prepared to receive

a ceramic crown but afterwards needing endodontic treatment The absence

of undercuts required creative clamp selection; in this case an Ivory 9 “incisor” clamp The field is disinfected with iodine.

with forceps as before The rubber dam sheet is thenpassed over the clamp and flossed through proximalcontacts as in the winged technique

With both winged and unwinged designs, it is sible to place the clamp first, before stretching a largehole over the entire clamp, or to place the rubber damfirst before applying the clamp over the top When teethare well-approximated, and especially at the front ofthe mouth and around porcelain restorations that may

pos-be damaged by rubpos-ber dam clamps, it may pos-be ble to avoid clamps and retain the rubber dam withinterproximal stabilizing cords such as Wedjets (Coltene)(Fig 11.11) Experienced practitioners develop their ownmethods and tricks; the important thing is to find asimple method that works for you and that provides agood seal

possi-The frame is then applied, taking care not to placeunnecessary tension on the clamp If there is a risk ofleakage at the margins of the dam, small gaps can besealed with a light-curing material such as Opaldam(Ultradent) or a nonhardening putty such as Oraseal®

(Ultradent) Agents of this sort may not seal as perfectly

as an ideally placed rubber dam sheet, but may help

in challenging situations [26] Leakage can also be vented by tying tight dental floss ligatures around therubber dam at the neck of the tooth (Fig 11.12)

pre-Disinfection of the working field

Having isolated the tooth with a well-sealing rubberdam, the working field should be disinfected, includingthe tooth, clamp, and rubber dam to a radius of 2–3 cmfrom the tooth

190 Endodontic Treatment Procedures

Fig 11.9 (a) Rubber dam engaged on the clamp wings (b) Positioning the clamp and rubber dam to engage undercuts (c) Disengaging the dam with a blunt instrument (d) Flossing through the contacts secures a tight seal.

A popular method includes scrubbing with 30%

hydrogen peroxide on a cotton bud until no more

effer-vescence is seen, before scrubbing again with 10% iodine

tincture [27] Methods involving 30% hydrogen

perox-ide followed by 2.5% sodium hypochlorite [26] have

shown similar results, as have chlorhexidine/alcohol

preparations

Key steps in the development of an aseptic working

field are summarized in Clinical procedure 11.2

Fig 11.10 Engaging the rubber dam during isolation with a wingless

clamp The bow is pushed from the back of the rubber dam sheet through

the hole, allowing visualization of the jaws as they are applied to the tooth.

Aseptic working procedures

Asepsis should be maintained throughout the entireoperative procedure, and members of the dental teamshould pay attention to hand hygiene and the use ofpersonal protective equipment, including gloves

Fig 11.11 Isolation of three anterior teeth with a single floss ligature and Wedjets placed interproximally.

Controlling the environment 191

Fig 11.12 Placement of the rubber dam on the partially erupted central

incisor of a 7-year-old patient The dam was fixed with a floss ligature and two

clamps were placed over the rubber dam sheet on the first primary molars.

Although there is limited evidence on microbial

trans-mission from dental personnel to the root canal, skin

commensals including Staphylococcus aureus and

Pro-pionibacterium acnes have been identified in recent

investigations on the ecology of endodontic infections

[28, 29]

It goes without saying that endodontic instruments

should be sterilized before use, and efforts should be

made to avoid touching the parts of instruments that

will enter the root canal Equally, paper points for

dry-ing root canals should be sterile and gutta points should

be sterilized by immersion in sodium hypochlorite

or chlorhexidine/alcohol for 2 minutes before use

[30–32]

Radiographic images and rubber dam

Contamination of the working field with saliva is a

par-ticular risk during radiographic exposure, and efforts

should be made whereever possible leave the frame in

position (Fig 11.13)

The principles of aseptic working are summarized in

Clinical procedure 11.3

Clinical procedure 11.2 Application and

disinfection of rubber dam

1 Tie floss to the selected clamp before trying it on the tooth.

2 Try on the clamp on the tooth for stability Select a different clamp

if necessary.

3 Choose a frame that enhances the view of the working field.

4 Place the hole central in the rubber dam sheet.

5 Apply the rubber dam by the preferred method.

6 Disinfect the working field by scrubbing the tooth, the clamp and

2–3 cm of rubber dam surrounding the teeth with disinfectant.

Fig 11.13 Exposing a radiograph without losing control of the aseptic ronment The image sensor is held firmly in a hemostat and the dam frame only partially disengaged.

envi-Coronal sealingDue to time constraints, or an active decision to apply anintracanal medicament, root canal treatment may be con-ducted over more than one visit, and require the place-ment of a provisional coronal restoration This shouldprovide a good seal and be durable in function, butshould be readily distinguished from tooth tissue andeasily removed Some materials that are marketed forprovisional restoration expand on setting and may risktooth fracture and leakage [33, 34]

Teeth with substantial tissue loss are best managed bythe placement of a “working restoration” as describedpreviously, sometimes with the support of a copperring or orthodontic band, rather than relying on theprecarious bond of unsupported cement material Con-ventional access cavities within teeth or through work-ing restorations can then be sealed by blocking canalentrances with 2 mm thickness of a soft cement like Cavit

Clinical procedure 11.3 Working aseptically

r Both the operator and the dental nurse should pay attention to

hand hygiene and should wear gloves and a face mask.

r New, sterile burs should be used to enter the pulp chamber.

r Only sterilized instruments should be used in root canals The

working parts of instruments that will enter root canals should be handled with sterile tweezers or mosquito forceps to avoid con- tamination This includes rubber stop adjustment and exchanging rotary instruments in the handpiece.

r The rubber dam frame should not be removed for radiographic imaging.

r Paper points and tubs for irrigants should be sterile.

r Gutta-percha cones should be disinfected for 2 minutes in sodium

hypochlorite before use.

192 Endodontic Treatment Procedures

Fig 11.14 Canal plugs of Cavit to protect the root fillings from coronal

leakage if the provisional restoration is lost.

(Fig 11.14), before closing with the maximum

possi-ble thickness of well-adapted hard cement, such as

the polymer-reinforced zinc oxide eugenol cement, IRM

(Dentsply) The canal entrance plugs of Cavit will

pro-vide an additional layer of protection if the provisional

restoration is lost Similarly, canal plugs of Cavit or IRM

can also be placed in canal openings to protect

perma-nent root fillings against coronal leakage

Restorative considerations are discussed in

Chap-ter 16

References

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of infection at the time of root filling on the outcome of

endodontic treatment of teeth with apical periodontitis Int.

Endod J 1997; 30: 297–306.

2 Barnum SC Following history of the discovery of the dam.

Can J Dent Sci 1877; 4: 88–9.

3 American Association of Endodontists AAE Position

State-ment Dental Dams 2017 Available from: https://www

.aae.org/uploadedfiles/publications_and_research/

guidelines_and_position_statements/

dentaldamstatement.pdf (accessed October 13, 2017).

4 European Society of Endodontology Quality guidelines for

endodontic treatment: consensus report of the European

Society of Endodontology Int Endod J 2006; 39: 921–30.

5 American Academy of Pediatric Dentistry Guideline on

pulp therapy for primary and young permanent teeth

Pedi-atr Dent 2008; 30(7 Suppl.): 170–4.

6 Ahmed HM, Cohen S, L´evy G, Steier L, Bukiet F Rubber

dam application in endodontic practice: an update on

crit-ical educational and ethcrit-ical dilemmas Aust Dent J., 2014;

59: 457–63.

7 Lin PY, Huang SH, Chang HJ, Chi LY The effect of rubber

dam usage on the survival rate of teeth receiving initial root

canal treatment: a nationwide population-based study J.

Endod 2014; 40: 1733–7.

8 Van Nieuwenhuysen JP, Aouar M, D’Hoore W

Retreat-ment or radiographic monitoring in endodontics Int.

Endod J 1994; 27: 75–81.

9 Abbott PV Factors associated with continuing pain in

endodontics Aust Dent J 1994; 39: 157–61.

10 Goldfein J, Speirs C, Finkelman M, Amato R Rubber dam use during post placement influences the success of root

canal-treated teeth J Endod 2013; 39: 1481–4.

11 Israel HA, Leban SG Aspiration of an endodontic

instru-ment J Endod 1984; 10: 452–4.

12 Kuo SC, Chen YL Accidental swallowing of an endodontic

file Int Endod J 2008; 41: 617–22.

13 Susini G, Pommel L, Camps J Accidental ingestion and aspiration of root canal instruments and other dental for-

eign bodies in a French population Int Endod J 2007; 40:

585–9.

14 Whitworth JM, Seccombe GV, Shoker K, Steele JG Use of rubber dam and irrigant selection in UK general dental

practice Int Endod J 2000; 33: 435–41.

15 H ¨ulsmann M, Hahn W Complications during root canal

irrigation – literature review and case reports Int Endod J.

2000; 33: 186–93.

16 Wong RC The rubber dam as a means of infection control

in an era of AIDS and hepatitis J Indiana Dent Assoc 1988;

67: 41–3.

17 Forrest WR, Perez RS The rubber dam as a surgical drape:

protection against AIDS and hepatitis Gen Dent 1989; 37:

236–7.

18 Samaranayake LP, Reid J, Evans D The efficacy of rubber dam isolation in reducing atmospheric bacterial contami-

nation ASDC J Dent Child 1989; 56: 442–4.

19 Harrel SK, Molinari J Aerosols and splatter in dentistry: a brief review of the literature and infection control implica-

tions J Am Dent Assoc 2004; 135: 429–37.

20 Mala S, Lynch CD, Burke FM, Dummer PM Attitudes of

final year dental students to the use of rubber dam Int.

Endod J 2009; 42: 632–8.

21 Anabtawi MF, Gilbert GH, Bauer MR, Reams G, Makhija

SK, Benjamin PL, et al Rubber dam use during root

canal treatment: findings from The Dental Practice-Based

Research Network J Am Dent Assoc 2013; 144: 179–86.

22 Markvart M, Bjorndal L Ten year follow-up study on the adoption of endodontic technology amongst Danish

general dental practitioners Int Endod J 2016; 49: 90,

R163.

23 Burke FJ, Wilson MA, McCord JF Allergy to latex gloves in

clinical practice: case reports Quintessence Int 1995; 26(12):

859–63.

24 Hamann CP, Turjanmaa K, Rietschel R, Siew C, Owensby

D, Gruninger SE, et al Natural rubber latex

hypersensitiv-ity: incidence and prevalence of type I allergy in the dental

professional J Am Dent Assoc 1998; 129: 43–54.

25 Zinelis S, Margelos J In vivo fracture of a new rubber-dam

clamp Int Endod J 2002; 35: 720–3.

26 Ng YL, Spratt D, Sriskantharajah S, Gulabivala K ation of protocols for field decontamination before bacte- rial sampling of root canals for contemporary microbiology

Evalu-techniques J Endod 2003; 29: 317–20.

Controlling the environment 193

27 Moller AJ Microbiological examination of root canals and

periapical tissues of human teeth Methodological studies.

Odontol Tidskr 1966; 74(Suppl.): 1–380.

28 Sunde PT, Olsen I, Debelian GJ, Tronstad L Microbiota

of periapical lesions refractory to endodontic therapy.

J Endod 2002; 28: 304–10.

29 Niazi SA, Clarke D, Do T, Gilbert SC, Mannocci F,

Beighton D Propionibacterium acnes and Staphylococcus

epidermidis isolated from refractory endodontic lesions

are opportunistic pathogens J Clin Microbiol 2010; 48:

3859–69.

30 Gomes BP, Vianna ME, Matsumoto CU, Rossi Vde P,

Zaia AA, Ferraz CC, et al Disinfection of gutta-percha

cones with chlorhexidine and sodium hypochlorite Oral

Surg Oral Med Oral Pathol Oral Radiol Endod 2005; 100:

512–17.

31 Kayaoglu G, G ¨urel M, Om ¨url ¨u H, Bek ZG, Sadik B ination of gutta-percha cones for microbial contamination

Exam-during chemical use J Appl Oral Sci 2009; 17(3): 244–7.

32 Fern´andez R, Cadavid D, Zapata SM, Alvarez LG, Restrepo

FA Impact of three radiographic methods in the outcome

of nonsurgical endodontic treatment: a five-year follow-up.

J Endod 2013; 39: 1097–103.

33 Tennert C, Eismann M, Goetz F, Woelber JP, Hellwig E, Polydorou O A temporary filling material used for coro- nal sealing during endodontic treatment may cause tooth

fractures in large Class II cavities in vitro Int Endod J 2015;

Chapter 12

Access and canal negotiation: the first

key procedural steps for successful

endodontic treatment

Ove A Peters and Ana Arias

Introduction

An ideal access cavity should promote high-quality

root canal treatment, facilitating the efficient removal

of vital and necrotic pulp tissue, thorough disinfection

and complete obturation of the canal system At the

same time as much structural dentin as possible should

be preserved to maintain the mechanical strength of

the tooth Anatomical knowledge is necessary to avoid

iatrogenic errors, and practitioners should cultivate a

deep understanding of tooth development and

post-eruption reaction patterns that may influence pulp

anatomy, and carefully analyze each case individually

before and during treatment

The access cavity is a critical element of

tooth-preserving endodontic and restorative treatment, and

demands the following essential stages:

r Analysis of the tooth with preoperative radiographs,

and occasionally three-dimensional (3D) imaging

r Access cavity preparation, including conservative

entry to the pulp chamber and identification of all

canal entrances

r Initial canal negotiation, coronal flaring, and working

length determination

Principles of tooth development

and tooth anatomy

Teeth are formed by epithelial and mesenchymal tissues,

which interact sequentially during early development of

the crown (late bell stage) and later during root

devel-opment as cells from the cervical loop proliferate in an

apical direction In the crown, epithelial/mesenchymal

interactions continue throughout dental development,

and result in the external tooth surface and internal pulp

spaces having similar shapes Similarly in the root, theodontoblasts continue to deposit dentin symmetricallyaround the periphery of the pulp, and as a consequence,the inner and outer contours of the root are similar incross-section External landmarks therefore reflect inter-nal anatomy, and this can provide valuable hints foraccess cavity design [1]

The following rules provide further anatomical ance for canal location once the pulp chamber has beenunroofed [2–4]:

located in the center of the tooth at the level of thecemento-enamel junction (CEJ)

cham-ber are concentric to the external surface of thetooth at the level of the CEJ, (i.e., the external rootsurface anatomy reflects the internal pulp chamberanatomy)

of the clinical crown to the wall of the pulp chamber

is the same throughout the circumference of the tooth

at the level of the CEJ – the CEJ is the most consistent,repeatable landmark for locating the position of thepulp chamber

equidistant from a line drawn in a mesial–distaldirection, through the pulp chamber floor (exception:maxillary molars)

line perpendicular to a line drawn in a mesial–distaldirection across the center of the floor of the pulpchamber (exception: maxillary molars)

cham-ber floor is always darker than the walls Secondaryand tertiary dentin particular often has a whitishappearance

Textbook of Endodontology, Third Edition Edited by Lars Bjørndal, Lise-Lotte Kirkevang, and John Whitworth.

© 2018 John Wiley & Sons Ltd Published 2018 by John Wiley & Sons Ltd.

Companion Website: www.wiley.com/go/bjorndal/endodontology

195

196 Endodontic Treatment Procedures

are always located at the junction of the walls and the

floor

are located at the angles in the floor–wall junction

are located at the terminus of the root developmental

fusion lines

Over time, secondary and tertiary dentin deposition

may reduce the overall volume of the pulp chamber and

complicate access cavity preparation, and these

chal-lenges may be compounded by the development of pulp

stones within the diminished pulp space

In order to prepare the access cavity conservatively

and in the right place, knowledge is needed of the

number and location of canal entrances, and the

inci-dence and location of common anatomical variations

(see Chapter 13 for more information on 3D pulp

anatomy)

Individual analysis of the tooth,

preoperative radiographs, and additional

CBCT scans in complex cases

Well-angulated radiographic images are mandatory to

facilitate safe and efficient access, negotiation of the

root canal system, and to minimize the risk of mishaps

that may result from unexpected anatomical complexity

Periapical films and bite-wings (for posterior teeth)

pro-vide a first orientation of pulp chamber and root canal

location Although two radiographs with different

angu-lations are often sufficient to develop a 3D picture of the

tooth to be treated, cone beam computed tomography

(CBCT) images may occasionally be justified to

evalu-ate the potential for extra canals, complex morphologies,

and/or dental anomalies [5, 6]

Images should be studied carefully, ideally with nification, to reveal coronal interferences to canal entryand instrumentation such as:

mag-r small pulp chambers;

r canals that have narrowed or become obliterated

coronally;

r bulges of dentin covering canal entrances;

r presence of pulp stones;

r canals that narrow within the root; and

r possible bifurcations or lateral topographical exits of

the apical foramen

Anatomical complexity and potential challenges mayencourage referral to a colleague with specialist skills inendodontics

Rubber dam isolation

For optimal aseptic working, the rubber dam should be

in place before commencing access cavity preparation(see Chapter 11) Yet, there are certain clinical situations,particularly where treatment is undertaken by inexperi-enced clinicians, when accessing before rubber dam iso-lation (Fig 12.1) may have benefits:

r The height of the clinical crown and the long axis of

the tooth may be better visualized, reducing the risks

of furcal or cervical perforation

r Accessing the wrong tooth is less likely As shown

in Fig 12.1, a further recommendation to avoid thisunlikely mishap is to mark the correct tooth with

a sterile pen before starting the access preparation.This also provides information regarding the tooth’slong axis

Irrespective of the sequence, it should be kept in mindthat a well-adapted rubber dam is a key element of infec-tion control in endodontics

Fig 12.1 Markings with sterile red pen to demonstrate the tooth’s long axis before and after rubber dam placement.

Access and canal negotiation 197

Core concept 12.1 Evaluation criteria for

traditional access cavity preparations

r Root canal orifices are exposed and clearly visible

r All root canals can be scouted with an endodontic explorer (or

small hand files), in a straight line and without indicating

instru-ment deflection

r The access cavity fully unroofs the pulp chamber, including all

anatomical ramifications

Access cavity preparation

Although glossy advertisements may suggest that

suc-cessful endodontics is all about the latest instrument for

canal preparation, it should be noted that all treatment

steps may be compromised if the access cavity is not

ade-quate, and its importance cannot be overemphasized

In practical terms, access cavity preparation can be

divided in two steps:

1 External outline of the access cavity performed with

high-speed burs until the pulp chamber is

pene-trated

2 Internal refinement where canal orifices should be

identified and straight-line access to the root canal

should be achieved with the goal of maximum

dentin preservation

Standardized access cavity outlines (see Core concept

12.1) for each tooth are frequently utilized in

teach-ing and are helpful to novice students as they prepare

their first preclinical access cavities (Fig 12.2) Defining

cavity shapes in this way helps students to know where

Fig 12.2 Canal orifice locations for the preparation of access cavities.

Source: Adapted from [7].

to cut and reduces some of the risks of inappropriateand excessive tissue loss As stated before, a more tooth-specific approach may help to ultimately achieve thegoal of not sacrificing more tissue than is absolutely nec-essary In this case, 3D software tools enable the visual-ization of transparent models or images, disclosing theposition and dimensions of the pulp chamber and canalentrances in relation to crown and root morphology(Fig 12.3) Such reconstructions define a convenienceform, in which the smallest possible dimensions of theaccess cavity are dictated by the precise location of canalentrances on the pulpal floor The widest dimensionsare situated in the most coronal portion, promoting a

“straight-line” access to the orifice(s) of the root canal,including the removal of dentin to extend straight-lineaccess directly to the apical foramen, or to the primarycurvature of the root canal These concepts facilitatesubsequent treatment procedures and minimize proce-dural errors (Fig 12.3)

(a)

(b)

Fig 12.3 Microcomputed tomography renderings of access cavities in a maxillary central incisor, seen in the clinical and mesiodistal view Note the difference in angulation of the tooth long axis and the entry of the access into the crown seen in the mesio-distal view (a) Traditional access (b) Minimal invasive access.

198 Endodontic Treatment Procedures

It should be recognized that overly large access

cavi-ties eliminate crucial structural dentin and may

compro-mise the biomechanical integrity of the tooth Minimal

preparation is more readily achieved with

magnifica-tion, enhanced lighting, and highly flexible instruments,

making it possible to move from the stereotypical and

often excessive designs (round/triangular in anterior

teeth, oval in premolars and triangular/quadrilateral in

molars) illustrated in most textbooks [8, 9] Many teeth

have suffered considerable tissue loss prior to

endodon-tic intervention, and it may be even more important in

such cases to adopt a thoughtful, deliberate, and

con-servative approach to access in order to avoid further

unnecessary tissue loss and structural weakening

Figure 12.4a shows procedural steps for traditional

and conservative access to a mandibular molar (see

Clin-ical procedure 12.1) Millions of successfully preserved

teeth are testament to the fact that endodontic treatment

involving traditional access can be successful, but

con-temporary concepts are encouraging the use of

magni-fication and minimal intervention Where magnimagni-fication

is not available, as in most undergraduate programmes

and many private practices, students and practitioners

are encouraged to work as conservatively as they

rea-sonably can

The steps outlined in Fig 12.4b include the initial

preparation of a smaller version of the final access

cav-ity shape deep into dentin, and penetration into the

pulp chamber towards the largest pulp horn This may

be done with a cylindrical or slightly tapered diamond

bur The outline is then refined, unroofing the

cham-ber with a non end-cutting bur, which is unlikely to

damage the chamber floor or walls If magnification is

Clinical procedure 12.1 Access cavity preparation

Irrespective of the specific tooth and root canal anatomy, the main

steps in access cavity preparation involve the following:

1 Visualizing the pulp chamber space in three dimension and in

relation to the clinical crown.

2 Penetration of the enamel or restoration with an appropriate bur.

3 Mapping out a small version of the definitive access cavity shape

deep in dentin with opening of the pulp chamber towards the

largest pulp horn.

4 Refining the access:

– with a bur with a noncutting tip.

– with ultrasonic tips and under magnification for higher dentin

preservation.

5 Balancing the access cavity size between the demands for an

adequate convenience form and optimized structural strength.

The final access cavity must reveal all root canal orifices and

should function as a reservoir for irrigation solutions during

subse-quent shaping Importantly, it should provide adequate space for root

canal instruments to the canals.

available, conventional high- and low-speed burs may

be less desirable [3], and practitioners may prefer toselectively unroof the chamber with ultrasonically ener-gized tips that improve visual access, while providinghigh cutting efficiency, combined with safety and con-trol [10] Alternatives include special burs with long, nar-row shanks to enhance visualization, and small roundtips for controlled cutting (e.g., Munce discovery burs,

or Meisinger Goose-Neck burs)

In conventional access procedures, ultrasonic tips areuseful for access refinement, location of MB2 canals inupper molars and accessory canals in other teeth, loca-tion of calcified canals in any tooth, and the removal ofattached pulp stones [10–12] Micro-instruments (micro-openers, micro-debriders) were designed to facilitatesuch procedures under magnification [13] The combina-tion of the operating microscope (magnification and illu-mination together) and specifically designed ultrasonictips has allowed these steps to be optimized (Fig 12.5)[11, 14]

The concept of minimally invasiveaccess cavities

As Gluskin et al [8] have stated, “the concept of

mini-mally invasive endodontics calls for the treatment andprevention of pulpal pathoses and apical periodontitis,while causing the least amount of change to the dentalhard tissues This preserves the strength and function ofthe endodontically treated tooth with the intent that itwill last the patient’s lifetime.” Access cavity prepara-tion is the first invasive step of a root canal treatmentand therefore it plays a crucial role in this treatmentapproach

Endodontically treated teeth are more frequentlyextracted because of fracture than because of persis-tent apical pathosis [15] and, as we have seen, efforts

to maintain tooth structure are beneficial This conceptchanges access cavity design from a completely unroof-ing and coronally divergent preparation to the selectivepreservation of part of the chamber roof and pericer-vical dentin [16], prioritizing the removal of caries andrestorative material ahead of tooth structure, while con-serving dentin mainly at the cervical level [9] The finalgoal is the long-term functional survival of the tooth, rec-ognizing that no current restorative material can replacethe mechanical characteristics of dentin lost from areasthat suffer intensive stress–strain forces during mastica-tion or parafunctional activity [17]

Preserving pericervical dentin (4 mm above and belowthe crestal bone) seems to be crucial for the distri-bution of functional stresses and hence tooth strengthand long-term viability of the entire complex [17] Theconservation of the dentin in the cingulum of incisors

Access and canal negotiation 199

(a)

(b)

Fig 12.4 Two different versions of access cavity preparations in the same simulated mandibular molar (a) Traditional access (b) Minimally invasive access Note the use of ultrasonic tips and small files to scout the root canal in both (phase 1).

(pericingulum dentin) also seems to improve functional

stress distribution [9], although the conservation of

dentin has not yet been correlated with an increase in

fracture resistance in this group of teeth [18] Finite

ele-ment analysis has, however, demonstrated the reduced

masticatory stresses achieved by preserving even smallamounts of radicular dentin [19]

Although it preserves tissue, the use of minimallyinvasive endodontics [8] does not mean that treatmentgoals must be compromised, and access preparation

200 Endodontic Treatment Procedures

Fig 12.5 Microcomputed tomography of

mini-mally invasive access cavity preparation in a natural

mandibular molar Right: The same access in

transpar-ent image to show the conservation of the pulp

cham-ber walls when access to both distal canals is gained.

should not be so restrictive as to impede the location

and entry of instruments into all canal orifices or safe

and efficient cleaning and shaping procedures Balance

is needed, with judgments based on clinical

experi-ence Cavities cut within composite or amalgam can

often be slightly larger and the benefits of removing old

restorative materials in their entirety are discussed in

Chapter 11

Difficulties accessing teeth with mineralized

pulp chambers

Access may be difficult in traumatized teeth, in older

patients where pulp chambers and root canal entrances

have been reduced by dentin apposition, or where they

are obliterated by pulp stones [20] The apposition of

new hard tissue starts in the coronal portion of the root

canal and is followed by gradual narrowing of the pulp

space [21]

Pulp canal mineralization is not pathologic itself

and its identification on a radiograph does not require

endodontic intervention per se, yet pulp infection and

necrosis may subsequently develop, and require

treat-ment Occasionally, teeth may become discolored by the

apposition of dentin, and in the absence of clinical signs

or symptoms of disease, root canal treatment is again

not generally indicated If, on the other hand, signs and

symptoms of disease do develop, or if a decision is made

to attempt internal bleaching of the tooth to improve its

color, root canal treatment may in these circumstances

be justified Accessing such teeth requires great skill and

experience and there is a high risk of causing massive

tissue loss, perforating the crown or root, or promotingfracture risk Specialist referral should be considered insuch cases

The use of magnification, ideally an operative scope, often allows the visualization of a central gray,translucent area, fully embedded in darker tertiarydentin or bone-like matrix [4] These structures areindicative of the original canal orifices In other cases,there is no color change to indicate where the root canalsused to be and dyes may help to detect the fine residualfilaments of pulp tissue or tracts of organic material [22]that histology suggests are always present (Fig 12.6)

micro-Fig 12.6 Use of ophthalmic fluorescein in a calcified canal to dye organic rests in search of the root canal.

Access and canal negotiation 201

The use of long ultrasonic tips optimizes visualization

when working deep under the microscope and reduces

unnecessary dentin removal [10] Progress has

tradi-tionally been monitored by periodically exposing

peri-apical radiographs from different angles (Fig 12.7) and

this helps to control against mesiodistal or buccolingual

deviation

Three-dimensional imaging technology is

recom-mended to avoid mishaps in complex cases, with the

potential to create 3D printed templates that will guide

the access of burs into calcified root canals, analogous

to the guide sleeves used routinely during implant

placement [23–25] Virtual planning and precise

cut-ting has the potential to preserve tooth structure and

avoid iatrogenic perforations in calcified teeth (see alsoChapter 23)

Access as a diagnostic step

It is desirable to confirm not only the etiology of pal or periapical pathosis in teeth requiring endodontictreatment, but also to assess their restorability Often thisrequires the complete removal of the existing restora-tion to exclude or confirm leakage, fractures, and otherpossible causes [26] The merits of removing crownsand other restorative materials before access to identifycaries, cracks, or fractures was discussed in Chapter 11,

pul-202 Endodontic Treatment Procedures

Advanced concept 12.1

Initial coronal flaring may progress in a stepwise manner, moving

for-ward and backfor-ward between phases 1 and 2 This may be especially

helpful when shaping root canals with substantial curvatures or

S-shaped root canals, which often present their most challenge anatomy

in the apical third Here, mishaps are often avoided by flaring the

coro-nal two-thirds of the root cacoro-nal before negotiating the apical third.

This pre-enlargement procedure can be conceptualized by imagining

the root canal as two separate canals After scouting the coronal part

of the canal with an ISO 8 or 10 file (phase 1), the straight coronal

portion (first part of the curvature) is first flared as an uncomplicated

canal This will allow easier negotiation and subsequent enlargement

of a shorter but more difficult apical third after removing the

restric-tive dentin in the coronal and middle thirds.

and this process forms an important element of the

diag-nostic and treatment planning process

Canal negotiation

After selectively unroofing the canal entrances and

ensuring that instruments can approach them without

stress, it is time to begin canal negotiation The pulp

chamber may be flooded with sodium hypochlorite

to secure hemostasis, commence disinfection, and help

lubricate the path of instruments as they enter deeper

canal anatomy In uncomplicated cases, it may be

possi-ble to advance a small hand file (size ISO 10 or smaller)

with gentle watch-winding motions directly to the root

canal terminus and estimate the working length with

an electronic apex locator Many canals can then be

enlarged without special difficulty, following the

prin-ciples outlined in Chapter 13

In more complicated cases where it is not

possi-ble to advance directly to the canal terminus,

negoti-ation may be conducted in a number of phases, with

episodes of exploration and enlargement that will

facil-itate the stepwise progression of instruments to the

api-cal constriction and facilitate safe canal enlargement

(see also Advanced concept 12.1) Although this process

is distinct from the outlining and unroofing processes

described for access cavity preparation, it is

undoubt-edly an element of endodontic access, extending from

the pulp chamber to allow instrument access into the

complexities of the canal system The principles of this

often multiple-phased process are described in the

fol-lowing sections:

r Pre-flaring the superficial part of the canal (phase 1)

r Coronal flaring of the coronal half to two-thirds of the

canal (phase 2)

r Negotiation to the canal terminus and determination

of working length (phase 3)

Pre-flaring the superficial part

of the canal (phase 1)

It is tempting to open root canal entrances with driven nickel–titanium (Ni-Ti) files without first explor-ing or “scouting” the anatomy, but the temptationshould be resisted if instrument fractures and other iatro-genic errors such as ledges are to be avoided The coro-nal portion of root canals should always be exploredwith hand files, often sizes ISO 15 or 20, to determinehow deeply they can enter without force Often someapproximation can be made from the preoperative radio-graph, but in particularly narrow canals, the radiographmay not be helpful and even smaller instruments may

engine-be needed for initial exploration engine-before gently openingwith hand files to size ISO 15 or 20 The confirmationthat small instruments can enter should ensure a safepathway for the fragile tips of canal-enlarging instru-ments, and defines the apical limit of a so-called “safetyzone” which may be opened or “flared” with a range

of instruments including Ni-Ti orifice shapers, increasedtaper Ni-Ti files, or Gates Glidden drills Instrumentationshould be accompanied by copious irrigation to removecutting debris The act of pre-flaring improves straight-line access and removes interferences from the coronalpart of the canal that may impede deeper explorationand canal enlargement

Coronal flaring of the coronal half totwo-thirds of the canal (phase 2)Pre-flaring (phase 1) often allows small hand instru-ments to penetrate deeper into the canal, usually withgentle watch-winding and filing motions against thecanal walls to gain entry to the middle or apical third

of the canal Engine-driven or hand Ni-Ti instrumentsmay then be used to flare the coronal half to two-thirds

of the canal, accompanied once again by copious tion In very challenging curved or narrow canals, thisphase may itself progress in a series of steps and requiresboth patience and light touch

irriga-In common with pre-flaring, coronal flaring allowsdeeper exchange of irrigant and removes further inter-ferences that may impede entry to the apical third

Negotiation to the canal terminus anddetermination of working length (phase 3)

At this stage it is often possible to advance small, curved hand instruments to the root canal terminus withlight watch-winding and filing motions and determinethe working length with an electronic apex locator Thismay be confirmed with a working length radiograph

pre-It is then common practice to develop a “glide-path”

by progressively advancing stainless-steel hand files of

Access and canal negotiation 203

size ISO 15 or 20 to working length, and lightly opening

the space to ensure that they will “glide” smoothly in

and out of the canal without resistance This once again

ensures the safe passage of larger hand- or engine-driven

Ni-Ti instruments, which will complete the canal

flar-ing from coronal orifice to workflar-ing length Alternatively,

rotary or reciprocating instruments specifically designed

for the purpose of glide path preparation may be used

Detailed shaping protocols, including final apical

canal instrumentation (phase 4) will again be considered

in Chapter 13

References

1 Hargreaves HM, Goodis HE, Tay RT Seltzer and Bender’s

Dental Pulp, 2nd edn Chicago, IL: Quintessence, 2002.

2 Ingle JI, Bakland LK, Baumgartnet JC Endodontics, 6th edn.

Hamilton, ON: BC Decker, 2008.

3 Peters OA Accessing root canal systems: knowledge base

and clinical techniques ENDO 2008; 2: 87.

4 Krasner P, Rankow HJ Anatomy of the pulp-chamber

floor J Endod 2004; 30: 5–16.

5 Arens DE, Gluskin AH, Peters CI, Peters OA Practical

Lessons in Endodontic Treatment Chicago, IL: Quintessence,

2009.

6 AAE and AAOMR Joint position statement: Use of cone

beam computed tomography in endodontics 2015 update.

J Endod 2015; 41: 1393–6.

7 Carlsen O Dental Morphology Copenhagen: Munksgaard,

1987.

8 Gluskin AH, Peters CI, Peters OA Minimally invasive

endodontics: challenging prevailing paradigms Br Dent.

J 2014; 216: 347–53.

9 B ´oveda C, Kishen A Contracted endodontic cavities: the

foundation for less invasive alternatives in the

manage-ment of apical periodontitis Endod Topics 2015; 33: 169–86.

10 Plotino G, Pameijer CH, Grande NM, Somma F Ultrasonics

in endodontics: a review of the literature J Endod 2007; 33:

81–95.

11 Rampado ME, Tj¨aderhane L, Friedman S, Hamstra SJ.

The benefit of the operating microscope for access cavity

preparation by undergraduate students J Endod 2004; 30:

863–7.

12 G ¨orduysus MO, G ¨orduysus M, Friedman S Operating

microscope improves negotiation of second mesiobuccal

canals in maxillary molars J Endod 2001; 27: 683–6.

13 B ¨urklein S, Sch¨afer E Minimally invasive endodontics.

Quintessence Int 2015; 46: 119–24.

14 Sheets CG, Paquette JM Ultrasonic tips for conservative

restorative dentistry Dent Today 2002; 21: 102–4.

15 Bor´en LD, Jonasson P, Kvist T Long-term survival of endodontically treated teeth at a public dental specialist

clinic J Endod 2015; 41: 176–81.

16 Clark D, Khademi J Modern molar endodontic access and

directed dentin conservation Dent Clin North Am 2010;

54: 249–73.

17 Clark D, Khademi JA Case studies in modern molar

endodontic access and directed dentin conservation Dent.

Clin North Am 2010; 54: 275–89.

18 Krishan R, Paqu´e F, Ossareh A, Kishen A, Dao T, Friedman

S Impacts of conservative endodontic cavity on root canal instrumentation efficacy and resistance to fracture assessed

in incisors, premolars, and molars J Endod 2014; 40:

1160–6.

19 Bonessio N, Arias A, Lomiento G, Peters OA Effect of root canal treatment procedures with a novel rotary nickel titanium instrument (TRUShape) on stress in mandibular

molars: a comparative finite element analysis Odontology

21 Smith JW Calcific metamorphosis: a treatment dilemma.

Oral Surg Oral Med Oral Pathol 1982; 54: 441–4.

22 Malhotra N, Mala K Calcific metamorphosis

Litera-ture review and clinical strategies Dent Update 2013; 40:

48–58.

23 Zehnder MS, Connert T, Weiger R, Krastl G, K ¨uhl S Guided endodontics: accuracy of a novel method for guided access cavity preparation and root canal location.

study Int Endod J 2016; 49: 790–5.

26 Abbott PV Assessing restored teeth with pulp and periapical diseases for the presence of cracks, caries

and marginal breakdown Aust Dent J 2004; 49:

33–9.

Chapter 13

Root canal instrumentation

Lars Bergmans and Paul Lambrechts

Introduction

Accurately prepared root canals that allow effective

elimination of soft- and hard-tissue elements,

disin-fection, and obturation of the root canal system are

critical to successful endodontic treatment The

proce-dure, which is referred to as “cleaning and shaping”

[1], is often difficult and time-consuming and

there-fore requires a systematic approach to avoid errors such

as underpreparation and iatrogenic injury that may

adversely affect the clinical prognosis In this chapter

concepts for effective root canal instrumentation are

reviewed and clinical guidelines are presented, based on

root canal system anatomy and final shaping objectives

Principles of root canal instrumentation

Root canal instrumentation is accomplished by the use

of endodontic instruments and (antimicrobial)

irrigat-ing solutions under aseptic workirrigat-ing conditions A

pri-mary objective of this chemomechanical preparation in

teeth with vital or necrotic pulps is shaping the root

canal space and it is generally accepted that the most

appropriate final root canal shape is a tapered

(coni-cal) preparation with the smallest diameter near the root

tip, and the widest at the canal entrance Special

atten-tion should therefore be paid to the apical level and

the original path of the canal As a general rule, the

removal of root dentin should be centered within the

ini-tial root canal anatomy, and during canal enlargement

soft-tissue elements, which potentially provide substrate

for the growth of remaining microorganisms, will also be

removed

Root canal instrumentation may be carried out using

hand-held or engine-driven rotary or reciprocating

instruments, which come in many configurations The

quality, sizing, and physical properties of endodontic

instruments and the materials used for their facture are generally well defined according to ISO(International Organization for Standardization) andANSI (American National Standards Institute) stan-dards Instrument properties (e.g., stiffness) relate to

manu-type of alloy (stainless steel versus nickel–titanium

(Ni-Ti)), degree of taper (conicity), and cross-sectionaldesign

Stainless-steel files are inherently stiff, and thisincreases with increasing instrument size An instrumentthat is too stiff will cut more on the convex (outer) sidethan on the concave (inner) side, thereby straighteningthe curve (Fig 13.1) The resulting “hour-glass shape”and canal aberrations (e.g., ledge, zip, and perforation)leave important portions of the root canal wall uninstru-mented and create an irregular canal shape that is diffi-cult to clean, disinfect, and fill properly

Over time, researchers and clinicians have found avariety of methods to overcome the challenges cre-ated by stiff stainless-steel instruments, and as a result,various movements for instrument manipulation andapproaches to shaping the canal have been proposed.Although skillful operators can handle these demandingtechniques, shaping a curved root canal with stainless-steel hand files remains a time-consuming and challeng-ing exercise

Besides adaptations in file design and use, the problem

of instrument stiffness has been reduced by the tion of instruments manufactured from Ni-Ti alloys [2].Ni-Ti’s unique property of superelasticity allows Ni-Tifiles to be worked in curved canals with less lateral forceagainst the canal walls All such files are made from Niti-nol, an equi-atomic Ni-Ti alloy (using about 56 wt% Niand 44 wt% Ti) with a low modulus of elasticity and greatresistance to plastic deformation (Note: The symbols ofthe metals were combined with the place of invention(Naval Ordnance Laboratory, Silver Springs, MD, USA)

introduc-to create the acronym NiTiNOL.) Today, a wide array of

Textbook of Endodontology, Third Edition Edited by Lars Bjørndal, Lise-Lotte Kirkevang, and John Whitworth.

© 2018 John Wiley & Sons Ltd Published 2018 by John Wiley & Sons Ltd.

Companion Website: www.wiley.com/go/bjorndal/endodontology

205

206 Endodontic Treatment Procedures

Straighten

Fig 13.1 The stiff instrument tends to straighten within the curved root

canal (a), causing ledge formation (b), zipping (c), or perforation (d).

Ni-Ti file systems are employed in general and specialist

practices, the majority being engine-driven in

continu-ous clockwise rotation or reciprocation

The driving force behind this development is the belief

that engine-driven Ni-Ti files, applied in a crown-down

sequence (see further later) could improve both the

qual-ity and efficacy of root canal preparation Before

enter-ing the excitenter-ing field of Ni-Ti instrumentation, some

basic preparation concepts will be reviewed, including

straight-line access and the matching of shaping

objec-tives with individual tooth anatomy

Root canal system anatomy

Root canal(s) versus root canal system

The internal complexity of teeth has been investigated

by a variety of methods As early as 1917, Hess [3]

stud-ied the internal anatomy of thousands of teeth using

an impression/replica technique and concluded that

the pulp anatomy often represented a complex system

composed of a central area (root canals with round,

oval or irregular cross-sectional shape) with lateral

complexities (fins, anastomoses, and accessory canals),

which in terms of volume were greater than the central

“root canals.” This observation challenges conventional

approaches to root canal cleaning and shaping, since

much of the anatomical complexity will be

inaccessi-ble to both instruments and irrigants/medicaments, and

may therefore continue to harbor necrotic pulp tissue as

well as infectious elements (see Fig 15.35) A

postop-erative endodontic image that demonstrates a smooth,

conical shape is generally too simplistic and

underesti-mates the challenges of root canal instrumentation and

disinfection

In dental practice, complete visualization of the pulp

system is rarely possible, since even an operating

microscope is limited to the straight part of the root

canal (above the curve) Traditionally, radiographic

techniques have been considered helpful adjuncts tovisualize root morphology, but radiographs also havelimitations related to resolution, geometric distortion,and two-dimensional (2D) projection Even though theparalleling technique with orthogonal and eccentricprojections improves our three-dimensional (3D) under-standing, much of the lateral anatomy, especially in thebuccolingual plane, will remain invisible (Fig 13.2) This

Dig-Root canal instrumentation 207

Fig 13.3 (a) Digital photograph of an upper premolar with a single root that is severely curved toward its terminus (b,c) Micro-CT images showing the internal anatomy of the root (d) A detailed view on the anatomical complexity of the apical part.

limited perception of canal system anatomy may cause

procedural difficulties and may invite clinicians to

fol-low an unthinking 2D-based approach where

instru-mentation to the final working length early in the

shap-ing procedure often causes procedural mishaps

As 3D imaging (cone beam computed tomography

(CBCT)) has become established in specialist dental

practice, the unique anatomy of complex root canal

sys-tems can be observed from axial, sagittal, and coronal

perspectives [4] That is not to say that all canal

sys-tems should be 3D imaged and international guidelines

(SEDENTEXCT guidelines [5], American Association of

Endodontists (AAE)/American Academy of Oral and

Maxillofacial Radiology (AAOMR) [6], and European

Society of Endodontology (ESE) [7] recommend that this

should be reserved for teeth with a high frequency of

extra canals, and cases where complex morphology is

suspected

Even in these cases, caution should be exercised before

exposing patients, particularly young patients, to 3D

imaging; high-resolution, limited field-of-view images

are generally preferred Aside from radiation concerns,limitations for the use of CBCT as a standard procedureinclude potential artefact generation and high levels ofscatter and noise [8] Therefore, CBCT should be usedonly when the need for imaging cannot be met by lowerdose 2D radiography

Root canal curvatureMost root canals are curved and, in addition, curved rootcanals are often relatively narrow when compared totheir straight counterparts Curvatures typically becomemore pronounced and exhibit their greatest anatomi-cal complexity toward their apical terminus (Fig 13.3).Root canal curvature can be described by level (coro-nal, middle, or apical), angle and radius [9] Most cur-vatures are multiplanar and are thus expressed in bothmesiodistal and buccolingual (or buccopalatal) planes(Fig 13.4)

The fact that root canals are curved and narrow inmature teeth makes them difficult to clean and shape

208 Endodontic Treatment Procedures

(a) (b)

(c) (d)

Fig 13.5 Micro-CT data of an upper premolar (a,b) Renderings of the outer

root surface with a mesial invagination (c,d) Visualizations of the inner root

anatomy Notice that the root canals that join or diverge deviate from their

initial path, while the resulting angle is different for the canals involved.

The risks of canal straightening and the creation of errors

are related to the level and severity of the curvature, with

abrupt apical curvatures and double curvatures (the

S-shape) being especially difficult to negotiate and shape

In addition, canals that join or diverge always deviatefrom their initial path (Fig 13.5)

The creation of straight-line access, the use of flexibleendodontic instruments and the precurving of files areessential measures to prepare curved canals (see furtherlater, and Chapter 12 on canal negotiation)

Cross-sectional shape and diameterRoot canals may be round, oval, or irregular (ribbon-shaped) on cross-sectional view Oval and irregularshapes are common in the coronal two-thirds of rootcanals, whereas the round variant is often restricted tothe apical part (Fig 13.6) When two or more canalsare present in the same root, anastomoses and fins(lateral extensions) are frequently observed (Fig 13.7),while some root canals may present with extreme cross-sectional shapes This applies especially to the C-shapedcanal (Fig 13.8), which is more prevalent in certainethnic groups [10] Oval and irregular cross-sectionalshapes in particular challenge root canal cleaning andshaping since large parts of the lateral anatomy are oftenout of reach because most endodontic instruments aredesigned to stay centered (see Fig 15.35)

Root canal diameter is related to the concept of ity or “taper.” Observing the root canal diameter at con-secutive levels along the root gives an idea of its overallconicity, though the exact diameter and taper will varyfor each point along the central axis Usually root canalsare wide in the coronal part and relatively narrow api-cally Immature teeth and roots that have experiencedinternal resorption may appear different, and the deposi-tion of secondary and tertiary dentin may alter root canaldiameter generally or locally

(c)

(d)

(e)

Fig 13.6 (a,b) Visualizations of a lower

premolar scanned with micro-CT (c–e)

Corre-sponding slices at different horizontal levels

(indicated by the yellow lines) reveal the

rib-bon (c), oval (d), and round (e) cross-sectional

shape of the canal.