Ebook Shafer''s textbook of oral pathology (7th edition): Part 2

(BQ) Part 2 book Shafer''s textbook of oral pathology presentation of content: Physical and chemical injuries of the oral cavity, regressive alterations of the teeth, healing of oral wounds, oral aspects of metabolic diseases, allergic and immunologic diseases of the oral cavity, diseases of specific systems, forensic odontology,... and other contents.

Section III

Injuries and Repair

Chapter 12

Injuries of the Oral Cavity

Effect of Restorative Materials

Physical Injuries of the Teeth

Physical Injuries of the Bone

Physical Injuries of Soft Tissues

Nonallergic Reactions to Drugs and Chemicals usedSystemically

Occupational Injuries of the Oral Cavity

Occlusal Trauma

Injuries of the oral cavity may be caused by physical orchemical causes Physical injuries may be iatrogenic,self-inflicted, traumatic, or occupational The most importantiatrogenic cause is the repair of tooth affected by dental caries

or other developmental defects and restoration of missing

tooth Iatrogenic cause also includes X radiation and laser

radiation Self-induced or factitious injuries are due tooverzealous oral hygiene practices, caused by psychotic orneurotic condition, or habitual Traumatic causes include afall, fight, road traffic accidents, and sports injuries

Although chemical injuries are caused by environmentalelements such as toxic levels of chemicals in the water, air, orconsumables, the restorative and endodontic materials used inthe routine dental practice play an important role

Injuries of Teeth Associated with Tooth Preparation

The teeth, particularly the dentin and pulp, may be injured notonly by dental caries, but also from those proceduresnecessary for the repair of lesions involving dental hardtissues Preparation of the teeth for receiving the restorationsinclude cutting, grinding, and etching with acids etc Thesephysical and chemical methods of tooth preparation as well asthe various medicaments and filling materials which areinserted into the prepared tooth, have their own effects

Effect of Tooth Preparation

The effect upon the dental pulp of restorative procedure alone

is difficult to assess except in the sound tooth, since thecarious lesion itself produces demonstrable changes in boththe dentin and the pulp Even when a sound tooth is preparedfor experimental purpose, care must be taken in observing theeffects to separate those which are due solely to the toothpreparation from those which are due to the restorativematerials applied

Tooth preparation is usually done by rotary instruments such

as tungsten carbide burs and diamond burs of different sizesand shapes Lasers and air abrasion are also usedalternatively Pulpal responses to these various proceduresdepend on the heat generated by friction, cutting ofodontoblastic processes and drying of dentinal tubules,thickness of remaining dentin, vibration, removal of mineralsand exposure of the organic matrix of dentin, and formation

of smear layer

Reaction to Rotary Instrumentation

Stainless steel burs revolving at low speed were used in thepast for cavity and crown preparation As the hardness of theenamel is high, these burs could not abrade instead they cut orchip away the tooth material Also a considerable amount ofpressure is applied during the procedure, which results inexcessive heat production and evaporation of the contents ofthe dentinal tubules High speed rotary instrumentation withtungsten carbide and diamond burs has replaced the steel burs

in recent years Nevertheless stainless steel burs are used inprocedures involving bone

The reaction of the dental pulp to cutting of dentin with adental bur has been studied by Fish in both dogs andmonkeys When dentin is injured, there is stasis of thecontents of the dentinal tubules, which lose their fluidcommunication with the pulp because of the formation ofsecondary dentin Involved dentinal tubules are occluded bythe deposition of calcium which separates these scleroseddentinal tubules physiologically from the rest of the tooth.The cavities prepared by Fish in the teeth of dogs or monkeyswere cut with steel burs which were kept wet to prevent thecomplication of heat-induced damage to the pulp In somecases the cavities were then filled with copper oxyphosphatecement and in other instances they were left open andexposed to the oral fluids The animals were sacrificed aftervarying periods of time, and sections of the filled teeth wereprepared for microscopic study Three general reactions tocavity preparation were noted: (1) the production ofsecondary dentin, (2) changes in the odontoblasts associatedwith injured tubules, and (3) general changes in the pulp Fishcarefully pointed out that the reaction of the tooth with theformation of a calcified barrier and secondary dentinproduction is always strictly confined to the pulp surface ofthe injured dentinal tubules There is never overlap ofuninjured tubules, and for this reason the changes may beregarded as a specific reaction to injury of the dentinaltubules.

The pulp reaction to superficial injury of the dentin varies indegree of severity, depending partially upon the depth of theprepared cavity and partially upon the elapsed time betweencutting the cavity and extraction of the tooth for study Inmild reactions the odontoblasts become distorted and reduced

in number Small vacuoles may appear between them,probably lymph exudate Capillaries in the damaged area may

be prominent In more severe injuries, there may be completedisorganization of and hemorrhage in the odontoblastic layer(Fig 12-1) The bulk of the pulp tissue away from the cuttubules may exhibit little or no reaction

Figure 12-1

Effect on dental pulp of cavity preparation by steel bur.Cavities were prepared in human teeth and filled withgutta-percha A section of pulp from an intact normal tooth is

shown in (A), while the injured area in the pulp six days after cavity preparation is seen in (B) Courtesy of Drs David F

Mitchell and Jensen JH J Am Dent Assoc, 55:57, 1957

In more serious injuries there is a greater infiltration of theinjured locus by polymorphonuclear leukocytes, whichgradually become replaced by lymphocytes The majority ofthe severe pulp injuries are probably associated with irritationbrought about by the open cavities, with the sudden exposure

of large numbers of open dentinal tubules to oral fluids andbacteria

Even after such severe injuries the majority of damaged pulpsundergo spontaneous healing or at least enter a quiescentphase and produce no signs or symptoms of persistingdamage (Fig 12-2) The factors responsible for thisphenomenon, especially from the clinical aspect, areunknown.

Figure 12-2

Effect of cavity preparation by steel bur on dental pulp

A calciotraumatic line (1) and reparative dentin (2) are foundbeneath the cavity nine weeks after preparation Courtesy ofDrs David F Mitchell, JH Jensen J Am Dent Assoc, 55: 57,1957

It appears that dentin has a heat-dissipating action whichreduces the temperature rise within the pulp to only a fraction

of the actual temperature applied to the tooth

This is due to the low thermal conductivity of dentin, whichacts as an effective insulating medium Nevertheless theapplication of heat to a dental pulp already injured from a

carious lesion of the dentin, but not an actual pulp exposure,may be sufficient to affect adversely the repair or healing ofthe pulp even though an apparently successful restoration isgiven to the tooth.

The preparation of tooth under the constant application ofwater to cool the cutting instrument and tooth will preventmany of the serious consequences due to heat, and thisprocedure is strongly recommended

High-Speed Instrumentation

The development of high-speed dental engines andhand-pieces necessitated investigation of the possible effectswhich their use might have on pulp tissue, and numerousreports of such studies have been published

Bernier and Knapp reported a study on high-speedinstrumentation utilizing various speeds up to 100,000 rpm.They found evidence of mild pulpal damage, but, in addition,observed a new type of lesion which they termed the ‘reboundresponse’ This consisted variously in: (1) an alteration inground substance, (2) edema, (3) fibrosis, (4) odontoblasticdisruption, and (5) reduced predentin formation in a regiondirectly across the pulp opposite the cavity site or at a distantpulpal site, and thought to be caused by waves of energytransmitted to the pulp focused into a certain region by thepulpal walls The significance of this phenomenon is still notclear

Swerdlow and Stanley in their study involving 450 humanteeth found that speeds over 50,000 rpm with coolants were

less injurious to the pulp than lower speeds They concludedthat the combination of high speed, controlled temperature,and light load produced minimal pathologic pulpal alteration.When heavy loads were used, even coolants did not minimizeinflammatory responses Extending this investigation to 13operative techniques, Diamond and his coworkers found thatthe 300,000 rpm air-water spray—No 35 carbide burtechnique—provided all the cutting efficiency of a high-speedinstrument without producing extended or burn lesions andcaused the highest incidence of reparative dentin formation, afavorable protective reaction A speed of 250,000 rpm withwater coolant was reported by Nygaard-Ostby to produceeven less pulpal reaction than the conventional (6,000 rpm)machine without water-spray Caviedes-Bucheli andcoworkers in their study found that substance P expression isincreased in tooth where cavity preparation is done andconcluded that it may have an important clinical significance

in terms of inflammation and pain experience

The practicability of use of accelerated hand-piece speeds hasbeen accurately summarized by Stanley and Swerdlow, whostated: ‘In principle, high speed techniques approach the idealbut at the same time these methods can be easily abused…properly used, ultraspeed is an extremely safe and efficientmethod of reducing tooth structure’

Effect of Air Abrasive Technique

In the air abrasive technique, aluminum oxide sprayed underpressure is used as an abrasive for the cavity preparation andsurface treatment The main drawback of this procedure is, itdoes not allow the operators’ stereognostic ability to control

the depth of cutting However Ferrazzano et al, based on theirstudy in 60 mandibular third molar concluded that themacroscopic size and shape of cavities is connected toworking distance, while working time is important todetermine the depth of preparation Also the abrasive dust is apotential health hazard to the operator and the patient.Nowadays it is used only to clean the pit and fissures prior tothe application of sealants.

Effect of Ultrasonic Technique

The use of ultrasonic equipment for cutting cavities in teethhas been advocated because it involves less heat, noise, andvibration in contrast to rotary instruments Essentially, thetechnique consists in the conversion of electrical energy intomechanical energy in the form of vibration of a tiny cutting

tip, approximately 29,000 vibrations per second with an

amplitude of about 0.0014 inch Aluminum oxide abrasive in

a liquid carrier is washed across this tip, and the vibration ofthe particles in turn results in a rapid reduction of toothsubstance

The effects of this technique, as used in cavity preparation, onthe tooth and dental pulp have been evaluated by a number ofinvestigators whose results are in essential agreement Zachand Brown, Healey and his coworkers, and Lefkowitz amongothers have found that there are no remarkable differences inthe reaction of the dental pulp to the preparation of cavities bythe steel bur, the diamond stone or the ultrasonic instrument.This again emphasizes that only the dentinal injury itself isimportant, not how this injury is produced

Mitchell and Jensen, studying the effect of steel bur andultrasonic cavity preparation on the human tooth, alsoreported that no differences could be observed in the reaction

of the pulp to these two techniques Mild hyperemia,hemorrhage and a slight neutrophilic and lymphocyticinfiltration of the pulp tissue immediately below the cutdentinal tubules were noted during the 6–12 day periodfollowing cavity preparation by either means After severalweeks the late reaction consisted in slight, irregular secondarydentin deposition and the formation of a ‘calciotraumatic’line, a hematoxyphilic line between the regular dentin and thepostoperative dentin apparently representing a disturbance indentin formation at the time of the operative procedure

Lasers

Laser is an acronym for Light Amplification by StimulatedEmission of Radiation It is an electro-optical device which,upon stimulation, can convert jumbles of light waves into anintense, concentrated, uniform, narrow beam ofmonochromatic light with an energy source of great intensityand exceptional flexibility The radiation may be continuous

or modulated, or the emission may occur in short pulses Thishigh-intensity radiation can be focused on an extremely smallarea, approximately 1 micron in diameter, because of thesmall angle of divergence and coherency of the beam Lightphotons of characteristic wavelengths are produced,amplified, and filtered to produce the laser beam Carbondioxide and neodymium:yttrium-aluminum-garnet (Nd:YAG)lasers are most commonly used The main problem with lasercutting of hard dental tissues is the generation of heat andforbidden tactile control

Lasers are used in dental practice to coalesce pits and fissures

to eliminate retention sites for bacteria, to desensitize theexposed root surfaces, to make the hard tissue surfaces rough

to promote bonding as an alternative to acid etching, tovaporize the carious tissue, to vaporize the organic tissues inthe root canal in endodontic procedures, cavity preparation,restoration removal, treatment of dentinal sensitivity, cariesprevention and bleaching

Effects on Teeth

The effects of laser on teeth were first reported by Stern andSognnaes, who found that exposure of intact enamel, caused aglass like fusion of the enamel, whereas dentin exposed tolaser exhibited a definitive charred crater Chalky spots,craters, or small holes in enamel may also be produced underother conditions Scanning electron microscopic analysisshowed the effects of laser on dentin vary from no effects todisruption of the smeared layer to actual melting andrecrystallization of the dentin, depending on power level,duration of exposure, and color of the dentin Although it hasbeen shown that selective deep destruction of carious toothsubstance can be accomplished, the practicality of its use inremoving carious lesions is still questionable Laserirradiation alters the dentin structure and produces surfacelayers that give the appearance of being more enamel-like.The laser-modified surface may be more resistant todemineralization; hence, many investigators are proposingcontinued development of the laser for caries prevention

Open dentin surface exposed to laser results in melting andclosure of the orifices of the dentin and this property is used

to treat dentin hypersensitivity

Bleaching of stained teeth has also been accomplished bylasing

Effects on Pulp

The pulps of teeth in animals subjected to laser radiation havebeen described by Taylor and his associates as showingsevere pathologic changes, including hemorrhagic necrosiswith acute and chronic inflammatory cell infiltration Theodontoblastic layer also underwent coagulation necrosis,although the severity of the response varied with the amount

Thermal change may be influenced by: (1) the size, shape,and composition of the bur or stone, (2) the speed of the bur

or stone, (3) the amount and direction of pressure applied, (4)the amount of moisture in the field of operation, (5) the length

of time that the bur or stone is in contact with the tooth, and

(6) the type of tissue being cut, enamel or dentin Of furthersignificance is the heat generated during the setting of various

restorative materials, particularly the direct resins In in vitro

experiments, Wolcott and his associates showed that thetemperature at the dentin-resin junction may reach 212° F,and they recorded a temperature of 133° F in the pulpchamber

Smear layer

Smear layer is an amorphous micro layer deposited on theprepared tooth surfaces and consists of inorganic enamel anddentin debris, organic pulp materials, dentinal fluid, bacteria,and saliva The thickness of smear layer may vary from 1μm

to 5μm Its morphology, composition, and biological behaviorstill remain controversial Smear layer has the protectiveeffect by forming a physical barrier, which reduces thepermeability of dentin and prevents the exit of dentinal fluid

On the other hand it also acts as a barrier against themicrooraganisms, which already penetrated before thetreatment, may flow back and express their pathogenicity.Many investigators advocate the removal of smear layer as itinterferes with the bonding between the restorative materialand the tooth structure in restorative treatment and affects theaction of irrigants and disinfectants and penetration andadhesion of sealers in endodontic treatment

Effect of Restorative Materials

The dentist has at his/her disposal a great many materialsprepared commercially to restore the original contour of thetooth attacked by dental caries and other lesions of the tooth

including trauma The dentist must be familiar with theadvantages and disadvantages of each material from the point

of view of its physical and chemical properties and its ability

to fulfil the purpose for which it is intended In addition, hemust be acquainted with the biologic effects of the restorativematerials on the tooth, especially on the dental pulp

A great many experimental studies have been carried out toinvestigate the effects of the different restorative materials onthe dental pulp, and today such testing is routine before newrestorative materials are released by ethical manufacturers foruse by dentists It should be obvious that a restorativematerial applied to a prepared tooth is in contact with morethan just a mass of inert calcified material The dentinaltubules, containing odontoblastic processes which have beenfreshly cut, form a series of passage ways leading directly tothe pulp through which a fluid or soluble material may reachthe pulp tissue If this material is irritating, it may lead toserious injury For this reason a comparison of the effects ofthe various common restorative materials is important

Remaining dentin thickness

It is generally agreed that if the cavity depth is shallow, with2.0 mm or more of primary dentin remaining between thefloor of the cavity preparation and the dental pulp, dentinprobably provides its own insulation against traumatic,thermal or restorative material irritation However, if theremaining thickness of primary dentin is less than 2.0 mm, it

is necessary that a cement base of one type or another beutilized

Zinc Oxide and Eugenol

It is used routinely as a temporary filling material or rootcanal sealer Eugenol of this cement fixes cells, depresses the

cell respiration, and reduces the neural transmission in vitro.

There is almost universal agreement that zinc oxide andeugenol is the least injurious of all filling materials to thedental pulp Not only is there no irritation produced by thissubstance, but actually it exerts a palliative and sedative effect

on the mildly damaged pulp, since it inhibits synthesis ofprostaglandins and leukotrienes It seems to be such a blandsubstance that it may lack even the necessary irritatingproperties requisite to the stimulation of secondary dentinformation In view of these findings, zinc oxide and eugenol

is the material of choice for use over injured pulps or as abase in deep cavity preparations

Zinc Phosphate (Oxyphosphate) Cement

This particular cement is widely used in dentistry both as aprotective base in deep cavities before the insertion of therestoration and also in cementing cast inlays, crowns, andother similar restorations The majority of investigators havereported significant deleterious effects on the pulp when thematerial is placed in cavities, the actual injurious agentsupposedly being the phosphoric acid

Gurley and Van Huysen prepared cavities in teeth of youngdogs and filled them with zinc phosphate cement Afterapproximately 1½ months they found hyperemia andinflammatory cell infiltration of the pulp with disarrangement

of the odontoblastic layer Secondary dentin had formedunder the shallower cavities The more severe pulpalreactions occurred under the deeper cavities

Studies on human teeth, such as those by Manley, by Shroff,and by Kramer and McLean, show that hyperemia orhemorrhage with inflammatory cell infiltration of the pulpaccompanied by reduction in the size and number of theodontoblasts occurs after placement of this cement inprepared cavities.

The studies generally indicate that zinc oxyphosphate cement

is an irritant when placed in the base of a deep cavity,particularly in bulk, although the human pulp may be able tolocalize this reaction in most instances When this cement isused in shallow cavities, it is relatively innocuous andreportedly serves a useful function in the stimulation ofsecondary dentin formation

Polycarboxylate or polyacrylate cements have propertiescomparable to those of the phosphate cements, but have a lowdegree of pulpal irritation similar to that of the zincoxide-eugenol cements

Silver Amalgam

Silver amalgam is used as a filling material in dentistry It is

an innocuous material, particularly in shallow cavities.Beneath deep cavities filled with amalgam, Manley found adecrease in the number of odontoblasts, as well as mildinflammatory cell infiltration of the pulp The complication ofthermal shock transmitted by deep amalgam restorations isdifficult to evaluate, but is a source of potential damage

In contrast, Swerdlow and Stanley studied the pulpalresponses in 73 intact human teeth with cavities prepared at

speed of 20,000–300,000 rpm and filled with either amalgam

or zinc oxide and eugenol They reported that the amalgamincreased the intensity of mild pulpal response to cavitypreparation and that this appeared to be due, in part at least, tothe mechanical aspects of amalgam condensation Brännströmstudied the effect of amalgam restorations on pulp tissue, andconcluded that any damage to the pulp was due to leakagearound the restoration, not to the filling material itself Darkcolored metallic components of the silver alloy turn the dentindark gray and tooth may appear discolored

Amalgam restorations when in contact with gingiva causeinflammation because of corrosion products and dentalplaque

Relationship between oral lichenoid reactions and silveramalgam fillings is a matter of controversy A number ofstudies have been published with respect to amalgam fillingand lichenoid reactions A Dunsche and coworkers suggestthe removal of amalgam fillings in all patients withsymptomatic oral lichenoid reactions associated withamalgam fillings if no cutaneous lichen planus is present

Glass-ionomer

Glass-ionomer cement is considered as biocompatible and iswidely used as filling and lining material and as a lutingagent It consists of fluoroaluminosilicate glass powder andpolycarboxylic acid Glass-ionomers are water-based, and theset materials are composed of an inorganic-organic complexwith high molecular weight In contrast to other cements,

glass-ionomer has the advantages of chemically bonding tomineralized tissues and release of fluorides.

Glass-ionomer cement bonds to the dentin by chemical andmechanical means The chemical bonding is based on theexchange of ions between carboxylic groups of the substrateand calcium ions derived from partially dissolved apatitecrystallites The mechanical interlocking is based on thedemineralization of exposed dentin by polycarboxylic acidtreatment Collagen fibers can be exposed and an intermediatelayer can be formed between glass-ionomer material andundemineralized dentin

Biocompatibility of glass-ionomer cement is due to the weaknature of polyacrylic acid Histologically there is minimal orabsence of inflammation in pulp after a month Pulpal painmay be present for a short period after the filling of cervicalcavities, and is due to the increased dentin permeability afteracid etching

Self-polymerizing Acrylic Resin

Self-curing resins were extensively used as restorativematerials, particularly in anterior teeth There is evidence toindicate, however, that these resins may cause serious damage

to the dental pulp Still, not all investigations are in completeagreement

Conventional Composite Resins

These are restorative materials developed chiefly becausemethyl methacrylate or unfilled acrylic resins have restrictivecharacteristics such as low hardness and strength, a highcoefficient of thermal expansion and a lack of adhesion totooth structure The resin matrix is a compromise betweenepoxy and methacrylate resins This resin is combined with afiller of dispersed particles of varying types in relatively highconcentration While most

conventional composite resins are chemically activated, someare now marketed whose cure is based on light activation

The biologic properties of the composite resins show thesame irritational characteristics as the unfilled acrylic resins.For this reason, the same measures should be taken to protectthe pulp from possible injury, especially when the cavitypreparation is deep A calcium hydroxide base is preferable to

a zinc oxide and eugenol base because of the possibleinteraction of eugenol and resin

Microfilled Composite Resins

These are a newer group of resins which contain the sameresin matrix as the conventional composite resins but differ inthat the size of the filler is much smaller than in theconventional resin The biologic properties of the microfilledresins, including their irritational effects on the pulp, arecomparable to those of the conventional composite resins.Thus, some pulpal protection is necessary under deep cavities.Acid etching

Resin based restorative materials are mechanically bonded tothe tooth structure by creating micropores, a procedure known

as acid etching This process demineralizes hard tissues andexposes the organic matrix Phosphoric acid is the mostcommonly used etchant in clinical practice

In contrast to the scanty organic matrix of enamel which islost during the demineralization and subsequent washing, thecomponents of dentin are demineralized selectively.Peritubular dentin demineralizes quicker than does theintertubular matrix Demineralization of dentin widens thetubules, makes them funnel shaped towards the surface Itexposes the collagen in the wall of the tubules and alsouncovers the openings of a large number of lateral branches.The exposed collagen forms an interwoven mesh of fibers inwhich the resin infiltrates This collagen mesh infiltrated byresin is referred to as the hybrid layer After polymerization,the resin-impregnated collagen, together with the resin in thedentinal tubules and their branches, constitutes the adhesionbetween the dentin and the resin If the hybrid layer becomestoo dry, the collagen mesh will collapse and penetration ofresin will be impaired Adequate moisture content of thesurface is a must to prevent collapse of the collagen mesh for

an optimal bonding between the resin and the hybrid layer

The many experimental studies cited would indicatesuperficially that the majority of restorative materials used indentistry today are dangerous because of the serious effects

on the dental pulp which they often induce It is true thatmany of these materials are potentially injurious.Nevertheless, literally millions of restorations with thesesubstances are placed each year, and clinical experience hasshown that, unless actual pulp exposure has occurred, the

death rate of dental pulps directly attributable to therestorative material is extremely low Even the occurrence ofclinical symptoms of pulp injury is uncommon Although thisseems contradictory to experimental evidence, it should beappreciated that most cavities prepared by the dentist inwhich these materials are inserted are to repair a destructivecarious lesion The presence of this carious lesion, in contrast

to the experimental cavities prepared in sound human andanimal teeth, has usually induced the deposition of secondarydentin and has caused a certain amount of dentinal sclerosis,and these reactions offer considerable protection to the pulp

It is on this basis that the dentist is justified in continuing touse these filling materials There is a need, however, forcontinued study of this general problem

Effect of Cement Bases, Cavity Liners, Varnishes and Primers

A variety of materials commonly used in dental practice areinserted in a cavity preparation between the tooth and therestoration for the following purposes:

To prevent discoloration of tooth structure adjacent to certaintypes of restorative materials.

•

To prevent the penetration of deleterious constituents ofrestorative materials into the dentin and pulp

•

To improve the marginal seal of certain restorative materials

by preventing microleakage and the ingress of saliva anddebris along the tooth-restoration interface

These materials are generally classified as cement bases,cavity liners, cavity varnishes and cavity primers, and theyare important because of their possible effects on the dentalpulp

Cement Bases

A cement base is a layer of cement commonly used beneaththe dental restoration either to encourage recovery of theinjured pulp or to protect the pulp against the injuries.Intermediary base materials that are commonly used underpermanent restorations include zinc phosphate cement, zincoxide-eugenol cement, and calcium hydroxide cement.Ideally, a cement base should be biologically compatible withthe dental pulp and such is the case with zinc oxide-eugenoland calcium hydroxide However, zinc phosphate cement,when placed against dentin, acts as an irritant to the dentalpulp because of the acid content which varies between pH 3.5and 6.6, as discussed previously

Cavity Liners

Cavity liners are aqueous or volatile organic liquidsuspensions or dispersions of zinc oxide or calcium hydroxidethat can be applied in a relatively thin film to the surface of acavity They may also be solutions of resins in an organicsolvent to which has been added calcium hydroxide or zincoxide, or aqueous suspensions of calcium hydroxide inmethylcellulose The cavity liner provides the beneficialeffects of zinc oxide and calcium hydroxide as thin films inshallow cavities and, in addition, neutralizes the free acid ofzinc phosphate and silicate cements The cavity linersthemselves have no effect on dental pulp and, in fact, actuallyform a chemical barrier to provide reliable protection for thepulp under certain deep restorations

Stanley has compared the protective effect of reparativedentin with cavity liners and bases, and generally concludedthat: (1) pulpal tissue beneath preoperatively formedreparative dentin is safe from most subsequent procedures; (2)cavity liners and/or bases, should be employed since thecompleteness of the reparative dentin barrier cannot beascertained; (3) the unrestored tooth being utilized as anabutment lacks reparative dentin and is more subject to thedamaging effects of chemical agents because of patentdentinal tubules; (4) although 2 mm of primary dentinbetween the floor of the cavity preparation and the dental pulp

is usually a sufficient protective barrier, the condensation ofamalgam or gold foil, as well as the chemical irritation ofcements and self-curing resins, may render this thickness ofprotection insufficient; (5) age changes in the tooth, with theproduction of reparative dentin in the involved area, are of no

recognizable benefit regarding pulp protection; (6)high-speed, water-cooled cutting techniques produce anaverage incidence of reparative dentin formation of under20%; even less reparative dentin formation is produced ifmore than 1 mm of primary dentin remains beneath the cavitypreparation; (7) if reparative dentin does not form within thefirst 50 days following a restorative procedure, then there will

be none; (8) nearly 20 postoperative days are required for newodontoblasts to differentiate and produce reparative dentin,and it has been shown that an average of 100 productive days

of matrix formation is required to produce a reparative dentinbarrier of 0.15 mm; (9) final cementation of restorations neednot be delayed in allowing time for reparative dentin to form,since the use of cavity-lining materials is a reasonablesubstitute; and (10) cavity varnish and calcium hydroxidelining materials appear capable of protecting pulp if usedappropriately

as a semipermeable membrane so that certain types of ionspenetrate it, while others do not It has been found also thatvarnishes are effective in reducing the microleakage of fluidsaround the margins of restorations

While cavity varnishes themselves appear to have nosignificant effect upon a dental pulp, neither do they have a

sedative effect Therefore, in deep restorations, it may beadvisable to utilize calcium hydroxide or zinc oxide-eugenolcements first, and then apply the varnish over this base.

Effect of Cavity-sterilizing Agents

Cavity-sterilizing agents are frequently used as a final step inroutine cavity preparation and also in an attempt to sterilizediscolored, infected dentin in the base of deep carious lesionswhen this dentin cannot be completely removed without risk

of pulp exposure It has been suggested that cavitysterilization is unnecessary, since microorganisms persisting

in the dentinal tubules after a restoration has been placed donot flourish but, rather die or exist in an inactive state.Furthermore, should the dentin be carious so near the pulpthat exposure is feared were it all to be removed, the pulptissue by this time would almost certainly have becomeinfected, and attempts at sterilization would be worthless.Mineral trioxide aggregate (MTA)

Mineral trioxide aggregate (MTA) is a moisture friendlybiocompatible material composed of refined Portland cementand bismuth oxide Portland cement is a mixture of dicalciumsilicate, tricalcium silicate, tricalcium aluminate gypsum, andtetracalcium aluminoferrate MTA has wide endodonticapplications, which include pulp-capping, pulpotomydressing, root-end filling, perforation repair, andapexification The effect of white mineral trioxide aggregate

on dental pulp was investigated by Moghaddame-Jafari andcoworkers on mouse MDPC-23 odontoblast-like cells andOD-21 undifferentiated pulp cells They found that there was

no induction of apoptosis and increased DNA synthesis In

another in vitro study where exposed pulps were covered with

MTA or calcium hydroxide, histological evaluationdemonstrated less inflammation, hyperemia and necrosis, athicker dentinal bridge, and more frequent odontoblast layerformation with MTA than with calcium hydroxide There aremany reports available comparing the effect of calciumhydroxide and MTA on pulp-capping procedures andpulpotomy dressing and most of them claim MTA is superiorover calcium hydroxide Although the overall results inhuman studies involving MTA is promising further extensive,long-term studies are needed to find out its adverse reactions

if any

Physical Injuries of the Teeth

Bruxism: (‘Night-grinding’, bruxomania)

Bruxism is the habitual grinding or clenching of the teeth,either during sleep or as an unconscious habit during wakinghours This term is generally applied both to the clenchinghabit, during which pressure is exerted on the teeth andperiodontium by the actual grinding or clamping of the teeth,and also to the repeated tapping of the teeth Bruxism is one

of the most common sleep disorders The incidence ofbruxism has been variously reported as between 5 and 20%

Etiology

In a review of the subject by Nadler and Meklas, the causes ofbruxism have been described as: (1) local, (2) systemic, (3)psychologic, and (4) occupational.

Local factors are generally associated with some form of

mild occlusal disturbance which produces mild discomfort,and chronic, even though unrecognized, tension It has beensuggested that in many cases bruxism becomes a firm habit as

a result of an unconscious attempt by the patient to establish agreater number of teeth in contact or to counteract a localirritating situation In children the habit is frequentlyassociated with the transition from the deciduous to thepermanent dentition and may result from an unconsciousattempt to place the individual tooth planes so that themusculature will be at rest

Systemic factors have been proposed as etiologically

significant, but the role of most of these is difficult to assess.Gastrointestinal disturbances, subclinical nutritionaldeficiencies, and allergy or endocrine disturbances have allbeen reported as causative factors A hereditary backgroundhas been described in some cases

Psychologic factors are believed by some investigators to be

the most common cause of bruxism High levels of anxiety,stress, and emotional tension may be expressed through anumber of nervous habits, one of which may be bruxism.Thus, when a person suffers from fear, rage, rejection, or avariety of other emotions which he/she is unable to express,these become hidden in the subconscious but are expressedperiodically by numerous means It has been observed thatbruxism is common in mental institutions Bruxism is amanifestation of nervous tension in children also and may be

related to chronic biting or chewing of toys.Polysomnographic studies suggested that sleep bruxismepisodes are part of sleep arousal response The sleep arousalresponse is nothing but sudden change in the depth of sleep.Besides the sleep bruxism appears to be a disturbance in thedopaminergic system.

Occupations of certain types favor the development of this

habit Athletes engaged in physical activities often developbruxism, although the exact reason for this is uncertain.Occupations, in which the work must be unusually precise,such as that of the watchmaker, are prone to cause bruxism

Voluntary bruxism is also recognized in those persons who

habitually chew gum, tobacco, or objects such as toothpicks

or pencils Although voluntary, this too is a nervous reactionand may lead eventually to involuntary or subconsciousbruxism

Clinical Features

The person who engages in bruxism performs the typicalgrinding or clenching motions during sleep or subconsciouslywhen awake These may be associated with a grinding orgrating noise The symptomatic effects of this habit have beenreviewed by Glaros and Rao, who have divided them into sixmajor categories: (1) effects on the dentition, (2) effects onthe periodontium, (3) effects on the masticatory muscles, (4)effects on the temporomandibular joint, (5) head pain, and (6)psychologic and behavioral effects

When the habit is firmly established, severe wearing orattrition of the teeth may occur, not only occlusal wear, but

also interproximal wear which produces sensitivity On bothsurfaces actual facets may be worn in the teeth As thebruxism continues, there may be loss of integrity of theperiodontal structures, resulting in loosening or drifting ofteeth or even gingival recession with alveolar bone loss.Temporomandibular joint disturbances are also reported tooccur as a result of the traumatic injury of continuous toothimpact without normal periods of rest Hypertrophy of themasticatory muscles, particularly the masseter muscle, mayinterfere with maintenance of the rest position, cause trismus,and alter occlusion and the opening and closing pattern of thejaws.

Finally, while it has been suggested that bruxism may giverise to facial pain and headache as well as psychologic andbehavioral effects, these are very difficult manifestations toevaluate and correlate

Treatment and Prognosis

If the underlying cause of the bruxism is an emotional one,the nervous factor must be corrected if the disease is to becured Removable splints to be worn at night may beconstructed to immobilize the jaws or to guide the movement

so that periodontal damage is minimal Recently Botulinumtoxin (Botox) has been very successful in treating thegrinding and clenching of bruxism Botox when injected intothe masseter muscle, weakens the muscle enough to stop thegrinding and clenching, but not so much as to interfere withchewing or facial expressions RC DiFrancesco andcoworkers suggest that there is a positive correlation betweensleep-disordered breathing and bruxism and stated that there

was an important improvement of bruxism afteradenotonsillectomy based on their study of 69 children If thedisease is left untreated, severe periodontal and/ortemporomandibular disturbances may result.

Fractures of Teeth

Tooth fracture is a common injury which may arise in avariety of situations, the most frequent of which is suddensevere trauma This is usually a fall, a blow, an automobileaccident or any of a large number of incidents in whichchildren especially are frequently involved Some cases offracture occur when a tooth is weakened as by a largerestoration, leaving thin walls or unsupported cusps whichgive way under the stress of mastication A similar weakeningand subsequent fracture occurs also in cases of internalresorption of teeth Teeth which have had root canal therapyare often described as being somewhat brittle and susceptible

is a definite predilection for involvement of maxillary teeth,with between 75 and 90% of fractures occurring there (Fig.12-3)

Figure 12-3

Fractured teeth after traumatic injury

(A) Fracture of crown with pulp exposure (B) Root fracture.

There are several classifications of fractured teeth, thesimplest being only whether or not the fracture line involvesthe pulp A more detailed classification is that of Ellis, whodivides all traumatized anterior teeth (for these constitute thevast majority of such injuries) into nine classes:

Class 1: Simple fracture of the crown, involving little or no

dentin

Class 2: Extensive fracture of the crown, involving

considerable dentin but not the dental pulp

Class 3: Extensive fracture of the crown, involving

considerable dentin and exposing the dental pulp

Class 4: The traumatized tooth becomes nonvital, with or

without loss of crown structure

Class 5: Teeth lost as a result of trauma.

Class 6: Fracture of the root, with or without loss of crown

If the dentin over the pulp is exceedingly thin, bacteria maypenetrate the dentinal tubules, infect the pulp and producepulpitis, leading to death of the pulp When vitality ismaintained, usually a layer of secondary dentin is depositedover the involved dentinal tubules The tooth may be sore andslightly loose because of the traumatic injury, but severe pain

is usually absent

A fractured tooth crown which exposes the pulp is a moreserious problem, but pulp exposure does not necessarilyimply that death of the pulp will occur In some cases the

exposure can be capped by calcium hydroxide, and a dentinalbridge will form as a part of the healing reaction Pulpotomy

or pulpectomy may often be necessary; however, since thepulp becomes infected almost immediately after the injury

Root fractures are somewhat uncommon in young children,

since their tooth roots are not completely formed and the teethhave some resilience in their sockets It occurs in patientsbetween the ages of 10 and 20 years and most are traumatic inorigin Root fractures involve mostly the middle third of theroot and are horizontal When fracture does occur, the tooth isloose and sore and there may be displacement of the coronalportion of the tooth Most of the time tooth becomes nonvitalafter fracture Some teeth may be repaired by forming a layer

of reparative dentin along the pulp wall and cementum on theouter surface, or form granulation tissue between thefractured segments Few may remain vital with resorption ofthe sharp edges of the fractured fragments

In certain situations where the injury is sufficient to causeroot fracture, fragments of cementum may be severed fromdentin and is called cemental tear

of new cementum or bone formation There is nearly alwayssome resorption of the ends of the fragments, but these

resorption lacunae ultimately are repaired If the appositionbetween the two fragments is not close, the union is byconnective tissue alone It appears likely that the repairprocess can be organized from connective tissue cells in boththe pulp and the periodontal ligament.

Cracked Tooth Syndrome

Cracked tooth syndrome (CTS) is characterized by sharp pain

on chewing without any obvious reason, which is actuallycaused by a ‘hidden’ crack of the tooth These are incompletefractures that are too small to be seen on radiographs Thetypical symptom is sharp fleeting pain when releasing bitingpressure on an object This is because when biting down, thesegments are usually moving apart and thereby reduce thepressure in the nerves of the pulp When the bite is released,the ‘segments’ snap back together sharply increasing thepressure causing pain The pain is often inconsistent, andfrequently hard to reproduce Causes of CTS include attrition,bruxism, trauma, accidental bitting on a hard object, presence

of large restoration, and improper endodontic treatment TheAmerican Association of Endodontists have classified fivespecific variations of cracked teeth; craze line, fractured cusp,cracked tooth, split tooth, and vertical root fracture

Treatment and Prognosis

The site, direction, and size of the crack or fracture dictatesthe choice of the treatment It ranges from stabilization with astainless steel band or crown to endodontic treatment andrestoration If untreated, CTS can lead to severe pain, possiblepulpal necrosis and periapical abscess Unfortunately,

management of CTS is not always successful In some cases,such as in vertical root fractures (split root) in single rootedteeth, the only treatment option is tooth extraction.

Abrasion

Wearing away of tooth substance due to mechanical means isknown as abrasion The most common cause is the faultybrushing techniques Habits such as opening the hairpinconstantly using anterior teeth, holding bobby pins, andholding pipe also produce a characteristic form of abrasion.This is described in Chapter 13 on Regressive Alterations ofthe Teeth

Abuse of the teeth such as opening of beer or other bottlesusing teeth causes chipping away of enamel in incisors,canine and premolars

Injuries to the Supporting Structures of the Tooth

Concussion is produced by injury which is not strong enough

to cause serious, visible damage to the tooth and theperiodontal structures On clinical examination tooth may not

be mobile or displaced from its original position Crownappears normal and patient may not feel any difference inocclusion Pulp gives normal response to vitality test But thecharacteristic feature is the increased sensitivity of the tooth

to percussion from any direction

Treatment consists of selective grinding of the tooth toeliminate occlusal forces

Subluxation refers to abnormal loosening of tooth without

displacement due to sudden trauma Tooth is mobile onpalpation and sensitive to percussion and occlusal forces.Rupture of the periodontal tissue is usually evident bybleeding at the gingival marginal crevice In time toothbecomes nonvital due to severance of apical blood supply

Avulsion is dislocation of the tooth from its socket due to

traumatic injury It can be partial or total Partial avulsionincludes intrusion, extrusion, or facial, lingual or palatal, orlateral displacement

Avulsion is usually accompanied by fracture of the alveolarbone Partial avulsion is managed by reposition of the toothand stabilization with splints Completely avulsed tooth can

be replanted in its socket The prognosis of the replantationwill be good if the extraoral time is minimal and the avulsedtooth is kept in a suitable medium during transportation.Nevertheless many of the replanted teeth undergo ankylosis tothe alveolar bone

Tooth Ankylosis

Fusion between the tooth and bone, termed ankylosis is anuncommon phenomenon in the deciduous dentition and evenmore rare in permanent teeth The condition of deciduoustooth ankylosis (submerged tooth) has been described inChapter 1 on Developmental Disturbances of Oral andParaoral Structures

Ankylosis ensues when partial root resorption is followed byrepair with either cementum or bone that unites the tooth root

with the alveolar bone It must not be inferred that rootresorption invariably leads to ankylosis Actually, it is anuncommon sequela, and the cause for this sporadic happening

is unknown Ankylosis does occur rather frequently after atraumatic injury to a tooth, particularly occlusal trauma, but it

is also seen as a result of periapical inflammation subsequent

to pulp infection Periapical inflammation is awell-recognized cause of root resorption Ankylosissometimes also follows root canal therapy if the apicalperiodontal ligament is irritated or seriously damaged.Resorption and ankylosis is more common in replanted teeth

Clinical Features

Ankylosis of the permanent tooth seldom manifests clinicalsymptoms unless there is a concomitant pulp infection whichmay be the underlying cause If there is an extensive area ofthe root surface involved, the tooth may give a dull, muffledsound on percussion rather than the normal sharp sound Thefact that this condition exists may become apparent only atthe time of extraction of the tooth, when considerabledifficulty will be encountered, sometimes necessitatingsurgical removal

Radiographic Features

If the area of ankylosis is of sufficient size, it may be visible

on the radiograph There is loss of the normal thin radiolucentline surrounding the root that represents the periodontalligament, with a mild sclerosis of the bone and apparentblending of the bone with the tooth root

Histologic Features

Microscopic examination reveals an area of root resorptionwhich has been repaired by a calcified material, bone orcementum, which is continuous with the alveolar bone Theperiodontal ligament is completely obliterated in the area ofthe ankylosis (Fig 12-4)

There is no treatment for ankylosis Ankylosed teeth have agood prognosis and, unless removed for some other reason,should serve well indefinitely.

Physical Injuries of the Bone

The most common physical injury involving the bone isfracture

Fractures of Jaws

Fractures of the craniofacial complex occur commonly due toautomobile, industrial, and sports accidents, and fights.Fracture can occur more easily in bones, which are alreadyweakened by certain developmental and systemic disorders.Fracture may be simple, greenstick, compound, orcomminuted In simple fracture, the bone is brokencompletely; the overlying structures are intact and are notexposed to exterior Greenstick fracture common in children

is characterized by break of bone in one side and bend on theother side In compound fractures external wound isassociated with the break and is common in road trafficaccidents Bone is crushed or splintered in comminutedfractures and may or may not be exposed to the exterior.Mandible is more prone for fractures, since chin is aprominent feature of the face Fractures of the jaw are morecommon in males

Fractures of the Maxilla