Ebook Handbook of research on computerized occlusal analysis technology applications in dental medicine: Part 2

Part 2 book “Handbook of research on computerized occlusal analysis technology applications in dental medicine” has contents: The clinical applications of computerized occlusal analysis, new occlusal concepts based on computerized occlusal analysis.

The Clinical Applications of Computerized Occlusal Analysis

Chapter 11 Orthodontic T-Scan

Applications

ABSTRACT

This chapter reviews T-Scan use in Orthodontics, defines normal T-Scan recordings for orthodontically treated subjects versus untreated subjects, and explains T-Scan use in the case-finishing process After orthodontic appliance removal changes in the occlusion result from “settling,” because teeth can move freely within the periodontium Despite a post treatment, visually “perfect” Angle’s Class I relation- ship, ideal occlusal contacts often do not result solely from tooth movement Creating simultaneous and equal contacts following fixed appliance removal can be accomplished using T-Scan data to optimize the end-result occlusal contact pattern The software’s force distribution and timing indicators (the 2 and 3-Dimensional ForceViews, force percentage per tooth and arch half, the Center of Force, and the Occlusion and Disclusion Times) aid in obtaining an ideal occlusal force distribution during case- finishing Several case reports highlight combining lingual orthodontic treatment with Orthognathic surgery, where each presented case utilized T-Scan data during active treatment and retention.

INTRODUCTION

The dental occlusion develops progressively, under

the guidance of functional and genetic influences

throughout the differing stages of dental arch

morphogenesis, and then subsequently through a

variety of adaptations made notably to the

Tem-poromandibular joint and the masticatory muscles

When dealing with complex malocclusions,

Orthodontists modify all dental contacts to achieve

a new position of occlusal equilibrium, and take

responsibility for its functional integration Fully

aware of these implications, they devote special attention to the quality of the final occlusion of their treated cases, whatever the therapeutic oc-clusal philosophy is that they ascribe to follow

It is uniformly understood and agreed upon, that at the completion of orthodontic treatment the occlusal contacts of all teeth should demonstrate simultaneous contact timing and be of equal force intensity, thereby creating a uniform and symmetrical distribution of masticatory force It has been recommended that the anterior teeth be

Julia Cohen-Levy, DDS, MS, PhD

Private Practice, France

slightly less loaded than the posterior teeth (Roth,

1970; Dawson, 2006)

In Orthodontics, and other dental medicine

disciplines as well, such as Prosthodontics and

Periodontics, the assessment of occlusal quality

has relied mostly on the visual inspection of

oc-clusal contacts, by using:

• The intercuspation of stone dental casts

• Subjectively Interpreting articulating

pa-per marks

• Listening to oral patient “feel” feedback

Alternative, but more time-consuming

oc-clusal indicator techniques have been described,

that are often employed within research studies

These alternative occlusal indicator methods are:

• Observing imprints in high fluidity

impres-sion materials

• Analyzing force distribution statically

within pressure sensitive wax - Dental

Prescale 50H (Fuji Photo Film Corporation,

Tokyo, Japan) and its analyzing apparatus

(Occluzer ™ FPD703, Fuji Photo Film

Corporation, Tokyo, Japan)

After the patient imprints the above static

dental material indicators, the indicators require

digital scanning, followed later by computer

pro-cessing to retrieve and analyze their force data

Unfortunately, their effectiveness in generating

force distribution representations is offset by the

significant chair time used to complete data

re-trieval Furthermore, neither of these techniques

gives the clinician information about the “timing”

of the contacts They offer no indication as to

the location of the first contact, the sequence of

contacts from 1st contact through until maximum

intercuspation, nor the distribution of contacts

within the maximum intercuspated position

Therefore with these methods, the clinician does

not have the required tools to properly evaluate the

‘simultaneity’ or ‘timing’ of the post orthodontic occlusal contact result

Orthodontic End-Result Occlusal Function

Several questions have arisen about orthodontic treatment completion and the established end-result occlusal function:

• Should Orthodontists assume that ing ideal positional tooth-to-tooth relation-ships is enough to obtain a measurably bal-anced occlusion?

achiev-• Do the occlusal contacts spontaneously improve the overall occlusal force balance resultant from settling, after appliance removal?

• Is post treatment occlusal force distribution

of the teeth symmetrically obtained when a pre treatment dental asymmetry has been corrected, orthodontically?

The T-Scan III (T-Scan III Version 7, Tekscan Inc S Boston, MA, USA) is an occlusal analysis system available to Orthodontists, that records

in real-time, the contact force distribution as it changes functionally throughout the progression

of occlusal contacts from 1st contact through til maximum intercuspation during closure, and quantifies the time durations of any frictional occlusal surface engagements that posterior teeth make in protrusive or lateral excursions This very detailed occlusal analysis can be played back in increments of 0.01 seconds, or when in the much faster Turbo-mode, 0.003 second-long increments.This chapter will initially review the literature describing orthodontic norms and post-orthodon-tic functional occlusion Then, the clinical use

un-of the T-Scan III system in Orthodontics will be explained by highlighting the force distribution indicators for closure contacts leading to maximum intercuspation (the 2-Dimensional and 3-Dimen-sional ForceViews; the percentage of force per

tooth, arch-half, quadrant; the COF trajectory

path and the symmetry of its final position), and

detailing within dynamic mandibular excursive

function, the Disclusion Times Computer-aided

orthodontic case finishing and follow-up protocols

employing the T-Scan III are illustrated within

case studies, which discuss how best to improve

the quality of a post-orthodontic occlusal contact

pattern end-result

BACKGROUND

Occlusal Finishing in Orthodontics

According to the American Board of

Orthodon-tists (Casko, Vaden, Kokich, Damone, James,

Cangialosi, Riolo, Owens, & Bills, 1998;

Dyk-house, Moffitt, Grubb, Greco, English, Briss,

Jamieson, Kastrop, & Owens, 2006), occlusal

finishing quality can be evaluated on stone dental

casts, by visually assessing the proper alignment

of incisal borders and marginal ridges, the

buc-colingual inclinations of the individual teeth, the

occlusal relationships (achieving Angle’s Class I

is considered ideal), the overjet, and the occlusal

contacts Interproximal contacts should be tight

with complete space closure

Class I is considered the normal

antero-poste-rior relationship of the mandible to the maxilla

Following Angle’s classification (Angle, 1899),

the mesio-buccal cusp of the permanent

maxil-lary first molar ideally should occlude within the

buccal groove of the permanent mandibular first

molar, between the mesial and mid-buccal cusp

(Figure 1a) Andrews added other “keys” to achieve

an ideal occlusion, among which were a mesial

angulation of the maxillary first molar crown, so

that the distal buccal cusp of the maxillary first

molar is placed in close contact with the mesial

cusp of the mandibular 2nd molar (Andrews,

1972) (Figure 1b)

In 1969, Ricketts highlighted the major role of the maxillary second premolar position (Ricketts, 1969) He also recommended there be a special inclination of the canines, attained with a posi-tive torque value, in order to free the mandible in excursive movements He additionally described

an ideal contact distribution for the Class I patient that contained a theoretical “24 points” of occlu-sion per half-arch, in maximal intercuspation In

Figure 1a Ideal ‘Class I’ molar relationships according to Angle

Figure 1b Ideal ‘Class I’ molar relationships according to Andrews, where there is a recom- mended mesial angulation of the maxillary first molar crown

Figure 2a Maxillary ideal contacts to be obtained in a Class I occlusion with no extractions, as described

by Ricketts Note the actual contacts illustrated by the blue articulating paper marks versus the ideal contacts noted in dark blue There are less blue paper marks showing contacts than is the presented ideal.

Figure 2b Mandibular ideal contacts to be obtained in a Class I occlusion with no extractions, as scribed by Ricketts Note the actual contacts illustrated by the red articulating paper marks versus the ideal contacts noted in dark red There are less red paper marks showing contacts than is the presented ideal.

de-this proposed ideal contact pattern, the “centric

point” contacts were to be placed on the lingual

cusp tips of the maxillary posterior teeth, the

buccal cusp tips of mandibular posterior teeth,

within the central fossa and upon the marginal

ridges of the posterior teeth, and the incisal edges

of mandibular anterior teeth were to make contact

with lingual surfaces of the maxillary anterior

teeth (Figures 2a and b) When wisdom teeth are

present, a maximum of 30 occlusal contact points

could be obtained And, if first premolars were

removed during orthodontic treatment, then only

21 points of contact could be established

Conversely, Tweed and Merrifield (Tweed

& Merrifield, 1986) stated that at the end of

edgewise orthodontic treatment, a slight

poste-rior open-occlusion should be left to allow for

an overcorrection This posterior “open bite” is

created during the leveling phase with directional

force mechanics, by sequential tip back bends in

the orthodontic wire applied to maxillary first

and second molars A “transitional occlusion”

remains at appliance removal, which is

character-ized by a disclusion of the second molars and the

distal cusps of the first molars (Figure 3) This

arrangement was suggested to allow the muscles

of mastication to affect the greatest force on the primary chewing table located within the mid-arch area (Klonz, 1996) During this “denture recovery” phase that followed orthodontic appli-ance removal, it has been postulated that the non-contacting teeth would spontaneously come into ideal contact, resultant from applied pressure from the surrounding muscles and the periodontium.With the development of straight wire appli-ances in Orthodontics, different authors described for each tooth, their own bracket prescription for proper angulation and torque values Differences according the type of appliance employed are significant, especially for the maxillary anterior teeth Below are three differing author’s recom-mendations that describe the maxillary canines:

• According Andrews (Andrews, 1989) and Roth (Roth, 1970), the canines should be inclined towards the palatal (with negative torque, of -7° and -2° values, respectively)

• According McLaughlin, Benett and Trevisi (McLaughlin, Bennett & Trevisi, 2001), who described the widely used MBT™ straight-wire technique, the canines should

be straight with 00 torque value

• According to Ricketts (Ricketts, 1978) and Hilgers (Hilgers, 1987), the canines should

be inclined towards the buccal with a tive torque value of +7°

posi-In relation to the malocclusion type or the facial pattern, where reinforced anchorage may

or not be required, most authors advocated some variability in the incisor’s torque values Several sets of pre-adjusted brackets then were created that all demonstrated different levels of torque, for different treatment needs

The chosen orthodontic appliance design will have a major consequence on the morphology of the anterior guidance because the slope of the

Figure 3 The sequential tip-back on the maxillary

molars to create a slight posterior open-occlusion

at the completion of edgewise orthodontic

treat-ment

maxillary lingual surfaces guide the mandibular

teeth Maxillary incisor and canine torque, together

with the overjet and overbite measurements,

di-rectly influences the amount of vertical mandibular

opening that occurs during protrusive and lateral

movements Slavicek in the early 1980’s suggested

that the anterior guidance should not be too sharp,

so as to avoid distalizing the mandible constrain

free movement of the mandible (Slavicek, 1982;

Slavicek, 1988)

Despite the differences in orthodontic ance type used, and any major variability in patient occlusal morphology, most authors describe an occlusal scheme that was to be representative of

appli-an ‘ideal’ functional occlusion, which should be present at orthodontic treatment completion When

an excellent static occlusion was achieved, it has been assumed in Orthodontics, that a balanced

Figure 5a Visible maxillary incisor positive torque

in maximum intercuspation Figure 5b Influence of maxillary incisor’s positive torque on the amount of mandibular opening

dur-ing protrusion Lesser posterior tooth separation is achieved with positive torque vs negative torque, combined with a flat mandibular curve of Spee.

Figure 4a Visible maxillary incisor negative

torque in maximum intercuspation Figure 4b Influence of maxillary incisor’s nega- tive torque on the amount of mandibular opening

present in protrusion Significant posterior tooth separation is achieved with negative torque and

a flat mandibular curve of Spee.

functional occlusion was also obtained, except in

cases of major sagittal divergence or significant

tooth-size discrepancies Additionally, it has also

been assumed that when excellent static occlusion

was achieved orthodontically, the lateral excursive

and protrusive movements also functioned

prop-erly Nevertheless, despite these assumptions made

on visual inspection of the final contacts, some

authors have suggested that this is not always the

case (King, 2010; Morton & Pancherz, 2009)

Is There a Need for Computerized

Occlusal Analysis in

Orthodontic Case-Finishing?

Does Achieving an Ideal Angle’s Class I

Result, Ensure a Balanced Occlusion?

In order to achieve functional occlusal equilibrium,

several occlusal functional features should be

achieved (Timm, Herremans, & As, 1976; Morton

& Pancherz, 2009; Clark & Evans, 2001; Clark

& Evans, 1998):

• Bilateral, symmetrical occlusal contacts

developed in the retruded contact position

(RCP)

• Coincidence between the retruded contact

position and the intercuspal contact

posi-tion, or only a short slide of < 1mm should

exist between the two positions

• Contacts on the working side during

lat-eral mandibular movements that may be

limited to the canines (canine protection),

or may extend posteriorly to include one

or more pairs of adjacent posterior teeth

(group function)

• Teeth in group function should be in

pre-cise harmony with anterior and condylar

guidance

• No contact should be present between

op-posing posterior teeth on the non-working

side during lateral excursions

In a post treatment stone cast analysis formed on 37 patients, where the casts were evaluated immediately after orthodontic appliance removal, most subjects had only unilateral contacts present upon initial closure in the retruded axis position, and exhibited a slide between the retruded contact position and the intercuspal position In addition, most subjects demonstrated non-working side contact between opposing second molars at the end of treatment (Clark & Evans, 1998) In a similar study performed on 230 patients the au-thors found non-working side contact was present

per-in 30% of subjects, posterior contacts on sion present in 20% of the subjects, and RCP-ICP prematurities in 18% of the subjects (Milosevic

protru-& Samuels, 2000)

The influence of the appliance type and the experience of the orthodontist, have been sug-gested as critical factors in obtaining varying orthodontic end-results In a recent study using articular ribbon (8 microns thick), patients treated

with edgewise appliances were found not to exhibit

ideal functional occlusal contact relationships, despite being finished in Class I canine and molar relationships However, most individuals who

underwent straight-wire appliance orthodontic

treatment better demonstrated a mutually protected occlusion (Akhoundi, Hashem, & Noroozi, 2009)

Do Contacts Spontaneously Improve With Time by the ’Settling’ of the Occlusion?

Settling, or the reinstatement of functional occlusion, has been likened to a tooth’s physi-ologic eruption process, and considered as an adaptation phenomenon that occurs once the teeth are freed from the stresses exerted by the orthodontic appliances Settling must be ac-counted for, both in the orthodontic finishing process and in the retention phase, where settling can allow occlusal contacts to improve Some authors suggest functional occlusal relation-ships be examined after retention has ceased,

ment attempting to achieve “ideal” functional

occlusal goals (Clark & Evans, 2001) But, is

there definitive published evidence that Nature

spontanenously improves the occlusion

follow-ing orthodontic treatment?

Lyotard’s study was the first to quantitatively

assess the short-term occlusal changes that took

place from a total absence of retention

follow-ing multi-bracket orthodontic treatment in a

group of adolescents (Lyotard, Hans, Nelson,

& Valiathan, 2010) This study reported that an

improvement to the buccolingual inclination and

leveling of the marginal ridges was observed,

while the overjet and the irregularity index

tended to worsen As a consequence, a lack of

retainer cannot be recommended

Neverthe-less, the chosen type of retainer can potentially

influence the occlusion, as well (fixed anterior

retainers, Hawley plates, thermoformed splints

with full or partial coverage), depending upon

the amount of relative vertical tooth

move-ment allowed by the type of retainer employed

(Başçiftçi, Uysal, Sari, & Inan, 2007; Aslan,

Dinçer, Salmanli, & Qasem, 2013; Hoybjerg,

Currier, & Kadioglu, 2013)

Conversely, other studies that analyzed the

settling process found that no spontaneous

im-provements occurred in dynamic occlusal

con-tacts (Dinçer, Meral, & Tümer, 2003) Although

the number of contacts in centric occlusion

increased significantly during the retention

pe-riod, no significant difference was observed with

regard to the location of the contacts In a more

recent study, the authors were able to establish

that at debanding, nearly half of their subjects

(44.3%) presented with unsatisfactory functional

occlusion, and after 2 years of retention 34.7%

of subjects still presented with interferences in

protrusion and lateral excursions, where many

subjects demonstrated a > 2 mm discrepancy

between maximum intercuspation and Centric

Relation The occlusion remained comparable to

that which was observed at orthodontic bracket

removal in 72.3% of cases, while the occlusion improved in only 20% of patients, and worsened

in 10% of the cases (Morton & Pancherz, 2009)

In conclusion, it seems that the settling process does exist, but its result is unpredict-able (Greco, English, Briss, Jamieson, Kastrop, Castelein, DeLeon, Dugoni, & Chung, 2010) The increase in number of contacts continues

to evolve beyond 3 months folowing appliance removal, and can extend for up to 21 months (Gazit & Lieberman, 1985; Razdolsky, Sad-owsky, & BeGole, 1989) Most authors agree that orthodontic treatment should not be ter-minated before a proper dynamic evaluation is accomplished It has also been recommended that a 6-month period of observation should pass, prior to performing any proposed occlu-sal equilibration because the most significant occlusal alterations from settling, take place primarily in the first 2 months following orth-odontic appliance removal (Bauer, Behrent, Olivier, & Bushang, 2010)

Evaluating ‘Visually Perfect’

Contact Distribution with the T-Scan III System

In the last few years, a few studies have been taken with orthodontic subjects that were recorded with the T-Scan III Computerized Occlusal Analy-sis System (Tekscan, Inc S Boston, MA, USA),

under-to assess the post orthodontic contacts present in both maximum intercuspation and during lateral movements In a clinical edgewise therapy study where 14 adolescents were compared to a control group with normal occlusion, the authors found no differences in contact surfaces on the back teeth between the 2 groups (An, Wang, & Bai, 2009) However, they did find a more anterior Center of Force in the treated group, implying the anterior teeth received more occlusal force following edgewise treatment, than did the control untreated subjects This finding could indicate that edgewise

treatment resulted in Tweed’s ‘recovery phase

in-termediate occlusion’ where there is a purposeful

2nd molar disclusion in closure (Figure 3), or that

during the incisor retraction phase of tooth

move-ment, a lack of maxillary incisor torque control

resulted in increased load on the anterior teeth

One published study about the occlusal changes

that took place during the 12 month period

follow-ing orthodontic treatment, reported that there was

an overall dynamic occlusion improvement, where

the Disclusion Times during protrusion, and the

right and left lateral excursive movements, were

reduced significantly over time (He, Li, Gao &

An, 2010) They divided the sample into 2 groups;

a “no interference group”, and an “interference

group”, and concluded “the presence of occlusal

interferences affected the self-improvement

pro-cess, and increased the chance of post-treatment

disorders of the Stomatognathic system, such as

mandibular abnormal movements”

In another dynamic occlusion, post

orthodon-tic treatment study, when compared to a control

group of young adults with normal occlusions,

the orthodontic patients had a high prevalence of

posterior occlusal interferences, mostly located

on the second molars such that their Disclusion

Times were also longer (p < 0.01) (An, Wang,

& Bai, 2011)

In a sample of dental students (young adults),

previously orthodontically treated during

child-hood, Le found numerous prematurities present

that were mainly located in the second molar region

(Le, 2013) She suggested that orthodontic

treat-ment was possibly completed before the second

molars were fully erupted into the mouth, or that

because these teeth are difficult to reach clinically,

the pre-adjusted orthodontic bracket or tube might

not have been correctly bonded, resulting in a poor

3- Dimensional tooth position control

In a study made on a sample of adult patients,

whose adaptation potential was known to be

reduced because adult subjects have no residual

growth potential, the authors found an increase in contact surface occurred during retention, without any change occurring in the contact locations (Cohen-Levy & Cohen, 2011) Moreover, most subjects demonstrated overall symmetry improve-ment during settling, with a tendency over passing time towards 50% of the force being supported

on each side (Figure 6) But some patients did develop a significant functional asymmetry, where these patients demonstrated an extremely unequal right side-left side arch-half force imbalance, without exhibiting any significant dysfunctional symptoms (Figure 7)

The existence of a possible asymmetry in clusal force distribution, recorded in the maximal intercuspation position, was previously described

oc-by a Japanese team (Mizui, Nabeshima, Tosa, Tanaka, & Kawazoe, 1994), using the T-Scan

II system (Tekscan Inc S Boston, MA, USA) The authors noted there was a difference between patients that were affected by TMD (n = 5) and those of an asymptomatic control group (n = 60)

In the control group, the duration and distribution

of contacts were symmetrical with the Center of Force clustered around the first molar In the TMD group, the force and duration of contacts were asymmetrical, with Center of Force appearing

in varied locations This study did not command

a great deal of academic impact because of merous study design methodological flaws (low subject numbers, failure to randomize groups and maintain their anonymity, and an unclear definition

nu-of the subject inclusion/exclusion factors) ever, similar results were found in another, more recent T-Scan study that reported TMD subjects demonstrated a significantly higher frequency of premature contacts (half of the studied subjects; 16 out of 32 subjects), and greater bilateral asymmetry

How-in the occlusal force distribution, than compared

to the control subjects (Wang & Yin, 2012)

SECTION II

Treating an Unbalanced Static

Occlusion during Orthodontic

Case-Finishing and Retention

Evaluating Occlusal

Contact Distribution

The chosen mandibular reference for the evaluation

of occlusal contacts is the maximum intercuspal

position (MIP) Maximally intercuspating teeth

are a fundamental key of general masticatory

function The engagement of all the teeth guides

the mandible to a unique, precise and reproducible

position that allows the patient to make simple and

repetitive muscular contraction schemes that move

the mandible in and out of the teeth During active contraction of elevator muscles when in maximum intercuspation, the mandible should be centered and stabilized, thanks to bilateral contacts evenly distributed within the dental arches

From an Orthodontist’s point of view, when occlusal forces in maximum intercuspation are distributed unevenly around the arch, tooth move-ment most likely will occur

Qualitative Occlusal Evaluation with a T-Scan III Recording

It has been suggested as being absolutely necessary

to know the occlusal force levels when analyzing contacts, because the number of contacts, their surface area, and their pressure gradients gradu-

Figure 6 A Force graph where the left vertical axis that ranges from 0 to 100%, describes the percentage

of force supported by the right arch half during 2 years of settling that was observed in a case series

of adult patients Each line represents a different patient The horizontal axis represents the Time In Retention, with T1 = 1 month after orthodontic appliance removal, T2 = just past 6 months, T3 = over one year, and T4 = at two years Note the general tendency for the sides to equalize and approach equi- librium approximating 50% at T2 and T3 Only a few patients were recorded with the T–Scan III after T2, but they were maintaining nearly 50% equality.

ally increase with rising occlusal force (Kumagai,

Suzuki, Hamada, Sondang, Fujitani, & Nikawa,

1999) Rather than initially analyzing the post

orth-odontic contact locations and surface area between

the arches with articulating paper, the “quality”

of a patient’s occlusion can first be analyzed with

the T-Scan (Throckmorton, Rasmussen & Caloss,

2009) Only after the T-Scan sensor records a

proper, firm and repeatable intercuspation, should

the actual occlusal contacts be studied

• First, the sensitivity of the sensor needs to

be calibrated to match an individual

pa-tient’s occlusal strength In this manner,

the T-Scan system can detect very light

contacts without becoming saturated by the heavier contacts One or two pink col-umns present at maximum intercuspation patient force in the both the 2-Dimensional and 3-Dimensional ForceViews, is all that should be ideally visible

• Repeatedly occluding into the sensor can indicate whether the patient understands how to reliably occlude into it, to record useful T-Scan data for analysis However,

it is important to limit patient closure peatability pre testing, as it can tire a patient’s musculature before recording actual T-Scan data for analysis In clini-cal practice, it is recommended that three

re-Figure 7 T-Scan III recording of an adult patient 12 months after orthodontic appliance removal, ing a significant force imbalance of 66.5% left - 36.5% right exits between the arch halves This large orthodontic result force imbalance was recorded from a symmetrical Class I relationship.

show-consecutive patient self-intercuspations be

performed in MIP, to check the patient’s

reproducibility in consistently loading the

sensor

• The qualitative evaluation of how occlusal

contact forces load the sensor over elapsed

time, can illustrate not only the changing

occlusal forces, but also the functional

strength of the accompanying muscular

function

The Total Force Line

The Total Force Line, the black line within the

T-Scan III’s Force vs Time Graph, which is located

beneath the 2-Dimensional and 3-Dimensional

ForceView windows (Figure 8), illustrates the

changing amount of total force the patient can

generate when occluding through the sensor into

maximum intercuspation, and trying to firmly

hold their teeth intercuspated By observing the

shape of the Total Force Line, it is possible to see

whether the patient can reach their maximum force

quickly, and whether they can maintain a stable

muscle contraction at this maximal force levels,

for some time

The other colored graph lines in the Graph

(Figure 8), represent different sub-sectors of

the dental arch, as the T-Scan 2-Dimensional

ForceView can be divided into right (red) and left

(green) denoted arch-halves, and into four

differ-ent colored quadrants, as well During a patidiffer-ent

self-intercuspation, note that the different colored

graph lines and the Total Force Line, all show an

initial phase of growing occlusal force beginning

at first contact, which then rises to a plateau phase

that is reached at maximum intercuspation,

fol-lowed by a diminishing force phase as the patient

opens their teeth out of maximum intercuspation

In Figure 8, the first closure is incomplete

only reaching 33% of Total Force It should not

be used for occlusal analysis, whereas the

fol-lowing three closures show a similar pattern of

loading, indicating some of these can be used

for diagnosis The Occlusion Time (OT), which

is calculated by the software (between the A-B vertical lines) to measure the time from 1st contact until static intercuspation is reached, is directly influenced by not only the mandibular closure contact scheme, but also the patient’s ability to clench on the sensor In this case, only the third and fourth closures are well reproduced and should represent the patient’s actual OT

In Figure 9, which was recorded a few weeks after a different patient underwent maxillofacial surgery, the pattern of force loading appears very irregular, but demonstrates some of the same features of when a patient repeats their intercuspa-tion (as seen in Figure 8) This is likely a sign of muscular weakness during post surgical healing, indicating that the patient should have their oc-clusion recorded at a future appointment Physi-cal therapy should be prescribed after an initial observation period, if there is no spontaneous reduction in the patient’s mandibular discomfort, post treatment

To obtain a more accurate functional analysis

of masticatory muscles, in addition to the data provided within the shape of the Total Force line, The T-Scan system has been synchronized with surface electromyography recordings (EMG),

as has been described in several publications (T-Scan/BioEMG; Tekscan Inc, S Boston, MA, USA; Bioresearch Assoc., Milwaukee, WI, USA) (Kerstein, 2004; Kerstein & Radke, 2006; Kerstein

& Radke 2012) The simultaneous recording of these two occlusal/muscle analysis systems, al-lows the operator to objectively correlate specific occlusal contacts that occur at precise moments

in closure and excursive movements, to specific electromyographic changes These synchronized systems could be used in Orthodontics to refine the finishing process, and might enhance long-term occlusal stability (Mahony, 2005)

Figure 8 The Total Force line (black), and the left (green) side, and right (red) side force lines within the Force vs Time Graph, illustrate four consecutive self-intercuspations performed by an asymptomatic Class

I patient In this case, only the third and fourth closures are well reproduced and should be analyzed.

Figure 9 The Total Force line (black), and the left (green) side, and right (red) side force lines within the Force vs Time Graph, illustrate four consecutive self-intercuspations from a patient who underwent facial mandibular asymmetry surgery Note the irregularity of the 4 intercuspations suggesting further healing is needed before the patient will be able to repeatedly intercuspate.

3-Dimensional ForceView Columns,

2-Dimensional Occlusal ForceView,

and Force Percentage per Tooth

The principles of a mutually protective occlusion

involve establishing light contacts on the

inci-sors in maximum intercuspation (0.0005”

infra-occlusion, Roth, 1970) with the more forceful

contacts placed on the posterior teeth This allows

the posterior to support heavy occlusal loads along

their long axis Only during anterior and lateral

movements should the incisors and canines support

the majority of the loading, generating rapid and

immediate posterior disclusion It is expected, that

in normal occlusion, the first and second molars

receive the most relative force, whereas premolars

receive on average half as much relative force (Le,

2013) Weak contacts in the anterior portion of the

arch are not a sign of non-ideal occlusal finishing,

as they are often found in T-Scan recordings from

untreated subjects, with the lateral incisor being

sometimes difficult to create contact on during

intercuspation

When treating adolescents and young adults

patients, the morphologies of natural teeth are

almost completely intact, with minimal wear or

restorations present These orthodontic candidates

should result in ideal occlusal contacts at the

Figure 10a Occlusal views of the maxillary arch

Figure 11a The corresponding T-Scan III recording at appliance removal, where only posterior tooth contact exists with no anterior occlusal contact visible There is an extreme posterior right side overload present, as denoted by the position of the Center of Force (COF) trajectory.

Figure 11b During the retention period at 3 months the T-Scan showed some settling had occurred, resulting in new anterior occlusal contacts that demonstrated lighter occlusal force content

Figure 11c At the 6 th month follow-up examination, the occlusal amalgam filling in the maxillary right

2 nd molar was reshaped to relieve high force, but ideal overall case balance was not achieved tion did not resolve the occlusal balance to 50% bilaterally, as the 6-month force imbalance was 62.6% right - 37.4% left

Reten-end of treatment, except when there are major

dental discrepancies present, (conditions where

peg shaped incisors and premolar hypoplasia

compromise space, or the agenesis of teeth, or

asymmetric extraction protocols create uneven

numbers of bilateral teeth)

When treating adult patients, the condition is

quite different as these patients may demonstrate

wear facets, and fillings and/or prosthetic tooth

replacements, which are adapted to the existing

malocclusion As a consequence, when moving

these teeth, the pre treatment occlusal

morpholo-gies might not occlusally match in their new tooth

positions

Figures 10a, 10b, and 10c, illustrate an adult

female patient, who was treated orthodontically

to resolve a Class II Division 2 malocclusion,

where on the day the braces were removed, an

anterior lingual retention wire was bonded into

place (Figure 10c) Within the T-Scan recording

most of the occlusal forces were exerted

primar-ily on the molar teeth, weakly on the premolars,

and more forcibly on the right side than on the

left (Figure 11a) The sensor detected that the

maxillary and mandibular right second molars

combined, concentrated 41% of the total force

This initial distribution signified a slight anterior

open occlusion existed that was derived from the

differential in thickness between the maxillary

lingual brackets and that of the bonded retention

wire that replaced them Accordingly, the paper

marks made by the articulating paper on the

canines were false positive marks (Figure 10c)

At the 3-month follow-up visit, the patient

described a feeling of there being uneven

molar-region contact between the right and left arch

halves This reported ”unevenness” sensation was

not apparent from the articulating paper markings

(shown on the intraoral view of the maxillary arch

in Figure 10c) However, the T-Scan detected that,

despite post-orthodontic physiological extrusion,

bringing the maxillary and mandibular anterior

teeth into contact, the force of their occlusion

remained weak, and the right side occlusion still

accounted for 66% of the total contact forces (Figure 11b) This was denoted by The Center of Force maintaining its shift to the right arch-half, that was also present at debanding (Figure 11a)

At the 6 month follow-up examination, the occlusal amalgam filling present on the maxil-lary right 2nd molar was reshaped to relieve the high force contacts sustained by this single tooth, since debanding (the 2-Dimensional Force View tracings of the forces exactly followed the shape

of the occlusal portion of the amalgam tion) (Figure 11c) When the patient felt more occlusal uniformity, corrective adjustments were suspended without having reached an ideal force distribution In this case, retention itself did not resolve the occlusal balance to 50% bilaterally, as the 6 month force imbalance was significant at 62.6% right - 37.4% left A clinical advantage of using the T-Scan is that the patient can follow the on-screen improvements made, due to changes in the desktop color- graphics

restora-The Center of Force

Within the 2-Dimensional ForceView, the red and white diamond-shaped icon represents the position of the Center of Force, and the adjoining redline trajectory illustrates its movements during the elapsed time of the recorded occlusal force data This Center of Force (COF) summates the total contact forces of all occluding teeth at any given moment within the T-Scan recording The COF therefore, is not an indicator of mandibular position; it describes where the occlusal forces are gathered together from all contacting teeth, and not where the mandible sits relative to the maxilla.For recordings made of maximum intercuspa-tion, ideally, the COF icon and trajectory should

be positioned along the median sagittal sional ForceView axis (which indicates near-equal right-left force distribution), and within the middle

2-Dimen-of the distribution 2-Dimen-of contacting teeth

There is a scientific basis for this “summation of” occlusal force to act as an indicator of func-

tional occlusal balance, which has been described

by several research teams, using different research

methods that obtained similar overall results:

• In the early 1980’s, two studies determined

the physiologic equilibrium point of the

mandible, when Class I subjects clenched

their teeth in centric relation with an

ap-plied force of 24 pounds Using electronic

means, the equilibrium point was

estimat-ed to lie within the mesial third of the

man-dibular first molar while being close to the

mid-sagittal plane (Tradowsky & Dworkin,

1982; Tradowsky & Kubicek, 1981)

• Using the Dental Prescale System™,

an-other group determined that the Center

of Force was not influenced by ethnicity,

gender or age, of the studied subjects In

populations presenting with full sets of natural teeth, the Center of Force was situ-ated slightly more posterior, to lie within the middle of the maxillary first molar (Shinogaya, Bakke, Thomsen, Sodeyama,

& Matsumoto, 2001)

• A Chinese T-Scan study performed on 123 subjects with normal intact dentitions, who occluded with maximal occlusal force in the intercuspal position, determined that

in 98.4% of subjects, the COF was

locat-ed in the posterior region No statistically significant difference was found between the occlusal contacts observed on the left and right arch-halves when biting with maximal force in intercuspal position (Hu, Cheng, Zheng, Zheng, & Ma, 2006)

• Maness described there was a tendency towards bilateral equality in normal occlu-

Figure 12a On the day of appliance removal, there

existed asymmetry in the occlusal force

distribu-tion (64% right to 36% left) with the Center of

Force deviated to the right side, and its trajectory

being non-centered

Figure 12b After several months of settling, the Center of Force is near-perfectly centered resultant from improved bilateral contact symmetry and arch-half force equality (51.5% left - 49.5% right)

sions (n = 93), and that the center of effort

was located in the region of the first molar

(Maness & Podoloff, 1989)

In Figure 12, the T-Scan III data was recorded

just after orthodontic appliance removal (Figure

12a), and 24 months later using the same level

of recording Sensitivity (Figure 12b) These two

figures illustrate the COF positional change that

occurred with passing time, where it became

centered, and was ideally located near the second

premolar and first molar area This new COF

po-sition indicated a better equilibrium was present

after some settling had transpired (Figure 12b)

The COF trajectory, which tracks the changing

total force summation history from the first

con-tact until maximum intercuspation, after 2 years

of settling, was reduced in length, did not extend

beyond the COF target (the grey and white oval

within the 2-Dimensional ForceView), with the

COF icon located near the middle of the COF

target The settling improved the force distribution

to 51.5% left - 49.5% right

In conclusion, the COF provides a visual means

of discerning occlusal force balance anomalies

It illustrates an immediate answer to the question

of whether contact symmetry and force equality,

exists following orthodontic treatment Ideally, it

has been suggested that the COF icon be placed

in the sagittal median axis, approximately in line

with the 1st molar to the premolar area (depending

of the presence of wisdom teeth and/or the

pres-ence or abspres-ence of some premolars)

Improving the Center of Force

Position upon Completion of

Orthodontic Treatment

A post-treatment imbalance in Center of Force

can be improved during the finishing process by

several means:

• Employing vertical elastics on the half that demonstrates weaker occlusal contacts (Figures 13a, b, and c)

arch-• Adding composite bonded restorations to increase contact force on arch-half that demonstrates weaker occlusal contacts (es-pecially applicable in cases of restored or hypoplastic teeth (Figure 14)

• Prescribing functional training, which sists of the patient performing bilateral chewing exercises and swallowing exercis-

con-es, absent of any anterior or lateral tongue thrust

This physical therapy helps to reprogram the cortical engrams that were adapted to the initial malocclusion, as these forces are prone to move teeth back to their pretreatment position When

a lateral tongue thrust persists, it can open the occlusion unilaterally This same open occlusion problem can result when an anterior overjet is combined with an anterior tongue thrust

Figure 14a-d illustrates a patient that was afflicted with Parry-Romberg hemifacial hypot-rophy syndrome, which is a strong disfiguring facial asymmetry that involves skeletal structures, muscles, and the dental arches Figure 14a is a preoperative panoramic radiograph that illustrates both the skeletal asymmetry and the lack of root structure in the lower left premolar area, while Fig-ure 14b shows the patient’s preoperative left side.The rendered treatment combined surgical and orthodontic maxillomandibular interven-tions (Figure 14c), which were supplemented by physical therapy, and subcutaneous lipo-filling,

to restore balance to the distorted facial features Orthodontic treatment employed a mixed, fixed orthodontic technique with individualized (cast as custom per each lingual surface) lingual bonded attachments on the maxillary arch, and buccal bonded ceramic brackets on the mandibular arch, adapting our treatment to accommodate the pos-sible loss of some teeth that, at the beginning of therapy had almost no root structure After orthog-

Figure 13a In this case, no sign of asymmetry could be noted on the articulating papers marks, but the T-Scan III records showed the post orthodontic occlusion was very asymmetric (67% right - 33% left) leading to reported patient occlusal discomfort

Figure 13b Maxillary-mandibular elastics were

worn between labial bonded buttons, solely on the

left side to improve the left side occlusal contact

interdigitation

Figure 13c Improvement within the overall clusal balance and force uniformity was attained after 2 months of elastic use

oc-nathic and orthodontic treatment was complete,

composite build-ups were employed to obtain

bilaterally symmetrical contacts (Figure 14d)

Figures 15a and b depict the distribution of

inter-arch contact points at the time of appliance

removal (Figure 15a), and then two years post

orthodontic treatment (Figure 15b) The occlusal

forces were highly imbalanced, with 80% of the

occlusal force concentrated on the patient’s right

side at de-banding The composite additions were

bonded to the hypoplastic premolars, to bring

the inter-arch contacts into improved balance At

the end of the 2-year retention period, the teeth

affected with phantom roots were still in place,

and exhibited negligible mobility The patient

was advised that these might imminently need

to be replaced with implants, but currently were

maintaining space and preserving alveolar bone The inter-arch contacts still exhibit some right-sided dominance as the occlusal loading increased becoming more regular and uniform throughout the arches (Figure 15b) Considering the serious effect this syndrome had on the patient’s muscu-lature, it was very important to ensure that nearly symmetric occlusal function was achieved along with symmetric tooth morphology

It has been shown in a dentate population, that chewing side preference is related to both occlusal force lateral asymmetry and occlusal contact area asymmetry present in the intercuspal position, and not to handedness (Martinez-Gomis, Lujan-Climent, Palau, Bizar, Salsench, & Peraire, 2009) Therefore, it is possible that physical therapy, em-ployed in association with patient education about

Figure 14a Panoramic radiograph showing

man-dibular skeletal asymmetry and “ghost roots” on

several mandibular left premolar teeth

Figure 14b Pre treatment clinical photographs

of patient’s left side

Figure 14c Patient’s left side during orthodontic

treatment

Figure 14d Patient’s left side during retention with composite build-ups occluding the small, hypoplastic teeth

Figure 15a T-Scan recording after appliance removal with 80% of the occlusal force concentrated on the patient’s right side

Figure 15b T-Scan recording following composite build-ups and physical therapy showing improved overall occlusal balance and significantly more occlusal contacts present, than at debanding (Figure 15a)

the need to use both sides of their mouth when

chewing, could help to obtain a more balanced

force distribution This would work in parallel

with balanced muscular function for both the

symptomatic TMD patient, and with the skeletal

and dental asymmetry cases

Evaluating Contact Time

Simultaneity Using the Occlusion

Movies and the Occlusion Time

A powerful tool offered by the T-Scan III system is

the ability to play back, in as fast as 3 milliseconds

(via turbo-mode), the “movies” of contact order occurrence This capability gives a precise idea

of how early, and how important each contact is

in the overall process of intercuspating The erator can follow the time line, or choose a force percentage value (25%, 50%, 75%, or 100%) to check contact occurrence from first contact to com-plete intercuspation, and contact symmetry within 2-Dimensional and 3-Dimensional ForceViews,

op-by observing contact intensity using the column heights and the range of force level colors

Figure 16c The mandibular occlusal view showing natural teeth with tooth #19 (#36) partially restored with a composite restoration

Figure 16a Right lateral view of a complete set

of natural teeth in a Class I relationship Figure 16b Left lateral view of a complete set of natural teeth in a Class I relationship

Figure 17a When looking at 100% of total force

at orthodontic treatment completion, the contacts

seem equal However, if a clinician assesses only

the 100% point within a T-Scan recording, he/

she will miss some early uneven force moments.

Figure 17b The T-Scan III data recorded at 60%

of total force The contacts are equally distributed but appear earlier on the left side, resulting in higher left side column heights.

Figure 17d Same T-Scan recording at 75% of total force The Center of Force finishes centered, and the column heights are nearly equal on both sides of the arch.

Figure 17c The T-Scan III data visualized at 50%

of total force, following the selective adjustment

to the forceful composite filling present on molar

#19 (#36)

In the following case report, shown in clinical

pictures (Figures 16a, 16b and 16c) and the

com-panion T-Scan data (Figures 17a, 16b, 16c, and

16d), it becomes clear that a very small change

of even less than 1mm2 in a precise occlusal

con-tact, can have major consequences on the overall

contact symmetry

An initial T-Scan evaluation that only assesses

the 100% point within a T-Scan recording, will

likely miss some earlier critical, uneven force

moments that occur during closure An example

of this can be seen in Figure 17a, at 98.2% of

total force, the contacts seem even within the

arch, despite the T-Scan data showing some left

side overall force dominance However, when the

movie is played to 50-75% of total force (Figure

17b), some contacts on the left side rise to higher

force earlier than those on the right side After

adjusting a new composite restoration that was

placed into the left first mandibular molar central

fossa, the force columns became almost equal in

height when analyzed at 50-60% of total force

(Figure 17c) Later, at 75% of total force (Figure

17d), there is a more centered COF, with nearly

equal force column heights present, bilaterally

The Occlusion Time measurement (OT) is

defined as the elapsed time from the first contact

until static intercuspation, which precedes

maxi-mum intercuspation To be ideal, the OT should

be short, and not exceed 0.2 seconds duration

(Kerstein & Grundset, 2001) This measurement is

a time-based indicator of contact time

simultane-ity, but does not describe force intensity equality

of individual tooth-to-tooth contact

Dealing With an Unbalanced

Dynamic Occlusion

An important and useful feature of the T-Scan

is its ability to register in real-time, the occlusal

contacts present during mandibular excursive

movements, which often eliminates the need for

mounting casts on an articulator This traditional method for obtaining excursive function informa-tion, which is the “gold standard” of prosthetic treatment, is a time-consuming method to employ during Orthodontics, because teeth are being moved from one appointment to another Hence,

to study the lateral excursive function traditionally, new stone casts would need to be obtained from the patient at every treatment session

When orthodontic leveling has been completed, during the finishing process excursive move-ments should be evaluated using the T-Scan III,

to localize protrusive, working, and non-working interferences, that are often found on the maxillary first and second molars

During overjet reduction or space closure, the maxillary incisor’s torque can easily be lost, where the occlusal plane might rotate in a clockwise direction, resulting in a potentially steep anterior guidance When transversal expansion has been performed, the crowns of posterior teeth might rotate in the buccal direction, and their palatal cusps step down (excessive buccal torque) Should this occur when these tooth movement mechanics are employed, protrusive posterior interferences should be carefully evaluated At this stage, the anterior torque correction can be easily added into the finishing process by utilizing full-size archwires, thereby reducing the need to couple the posterior teeth with subtractive equilibration.The difficulty in controlling and expressing torque with the pre-adjusted orthodontic appli-ance, is widely observed in the maxillary canines, which have the longest roots of all teeth Slavicek’s functional angle should be checked during lateral excursions (Slavicek, 1982; Slavicek, 1988), as it might be too steep, especially in extraction cases,

or too shallow when major lateral arch expansion has been done

Similarly to the Occlusion Time, a ment known as the Disclusion Time (left, right, and protrusive) can be determined when record-

measure-ing patient excursive movements The Disclusion

Time is defined as the “elapsed time required for

a patient to exit from intercuspation and totally

disclude the posterior teeth with only incisor and/

or canines in contact (Kerstein &Wright, 1991)

It should be kept to a minimum of < 0.5 seconds,

so that periodontal stimuli can be reduced and

masticatory muscular contractions lessened

(Ker-stein &Wright, 1991; Ker(Ker-stein, 1993; Ker(Ker-stein &

Radke, 2012) For further detailed information on

the Disclusion Time can be found in Chapter 7

The T-Scan III analysis can be helpful when

dealing with specific cases like the Class II

cam-ouflage treatments Angle’s Class II relationships

selected for maxillary premolar extraction (with no

mandibular premolar compensatory extractions),

can create major interferences that frequently

ap-pear on the maxillary first molars When excessive

buccal torque or distal rotation of these molars

was established from orthodontic treatment,

centric closure interferences are often found on

the mesiolingual cusps (Nangia & Darendeliler,

2001; Lejoyeux E 1983)

All of the previously presented T-Scan

registra-tions were made with no mandibular manipulation

by the clinician The objective was to find a free

expression of occlusal forces by eliminating, as

much as possible, any iatrogenic interference from

within natural mandibular movements However,

the search for interferences in the mandibular

closing pathway between the terminal hinge axis

(Centric Relation) and a convenience habitual

occlusion (Maximum Intercuspation) requires

practitioners exert a gentle manipulating pressure

of weak amplitude on the mandible, through which

the patient is to “feel” the first contact For this

kind of contact determination, T-Scan III has a

special application, known as the CR Mode, which

is more sensitive than non-CR Mode recordings,

such that it is designed to record weak occlusal

contact pressure values

The T-Scan Computerized Occlusal Analysis system is easy to use, in that many consecutive mandibular movements can be made, concentrat-ing on tactile sensations, with no insertion and removal of the recording sensor required between closures Only after the recording is accomplished can the repetitive character of the patient results

be determined However, when using the T-Scan system, the need for articulating paper is not com-pletely eradicated, as the paper markings are used

to visualize effectively upon the teeth, the desired occlusal contacts to treat, once the problematic contacts have been located and clearly quantified,

by the T-Scan software

SECTION III: SPECIFIC CLINICAL SITUATIONS Lingual Orthodontics

The orthodontic norms previously described serve

as both a diagnostic aid, and a guide for creating pretreatment set-ups, which are used in lingual Orthodontics Maxillary and mandibular models are mounted on an articulator and the stone teeth are moved within a wax model, respecting an ideal, customized arch-form, following Andrew’s Keys (Figures 18a, 18b, and 18c) (Andrews, 1972) Here, the orthodontist can easily visualize Bolton’s tooth-size discrepancies (Bolton, 1958), and if proximal enamel reduction (stripping) is required within the treatment plan to establish ideal occlusal relationships

However, once treatment objectives have been achieved, where the final full size archwires have been placed intraorally, the occlusal contacts are not always assessable, despite appearing ideal in theory This occurs because during lingual ortho-dontics, the palatal position of brackets or bases may interfere with the patient’s closure pathway into complete intercuspation resulting in an an-

terior open occlusion, while limiting posterior tooth engagement (Figure 19a) Only when the lingual appliances are removed and the patient can fully intercuspate, should the final lingual orthodontic treatment result be evaluated with the T-Scan (Figure 19b).

Two studies have shown that the static sal balance can change in the post-orthodontic retention phase following lingual treatment (Cohen-Levy & Cohen, 2011; Cohen-Levy & Cohen, 2012) In most cases analyzed, there was

occlu-an observed general trend towards improving the relative balance of the right and left occlusal force

Figure 18a The pre treatment right side clinical

view, illustrating major maxillary arch

crowd-ing, a lateral cross-bite, and mandibular molar

hypoplasia

Figure 18b A wax set-up where the maxillary first

premolars were removed, the maxillary arch was

expanded, and interproximal enamel stripping in

the mandibular arch was accomplished

Figure 18c The right side clinical view at

orth-odontic treatment completion

Figure 19a Nearing orthodontic completion, the lingual brackets can interfere with complete ante- rior intercuspation (note the slight overjet present)

Figure 19b Immediately after lingual appliance removal, the patient can completely close and intercuspate both anteriorly and posteriorly

distribution However, in some of the studied cases,

there was observed a sustained unevenness, and a

clear non-improved, asymmetric contact

distribu-tion The authors reported that a non-improving

occlusal imbalance could signal a tongue thrust

existed, that would interfere with physiologic

tooth extrusion, thereby preventing some teeth

from contacting uniformly

It also has been suggested that an unbalanced

occlusion could be more prone to relapse resultant

from undetected muscular or articular factors

(de Freitas et al., 2007), and that asymmetrical

contacts could be associated with the

occur-rence of craniomandibular dysfunction (Mizui,

Nabeshima, Tosa, Tanaka, & Kawazoe, 1994;

Wang & Yin, 2012) The clinical significance of

these findings remains to be determined, because

in studies performed to date, the prior existence of

functional asymmetry was not statistically

evalu-ated before orthodontic treatment was initievalu-ated

Regardless, all of these studies indicate occlusal

balance and precise contact quality is not

read-ily obtained by tooth movement alone, such that

there is a definitive need for occlusal balancing

following orthodontic treatment

Combined Orthodontic and

Surgical Treatments

Maxillofacial surgery dramatically changes the

geometry of the masticatory system, by altering

the dental arches, the muscular insertions, which

modifies the TMJ anatomical relationships The

T-Scan III is an ideal tool to track post-surgical

occlusal force changes, and to evaluate the need

for post-surgical occlusal adjustment, to control

abnormal occlusal force distributions that result

from surgical corrections

It is important to understand that normal

mas-ticatory force changes after maxillofacial surgery

• Both the occlusal force levels and the clusal contact area are affected by orthog-nathic surgery

oc-With bilateral sagittal split osteotomy dures, both occlusal force and occlusal contact area recover to their preoperative levels between 2

proce-to 3 months post operatively (Harada, Watanabe, Ohkura & Enemoto, 2000) Initially, occlusal force levels and contact area increase slowly, but later exceed the preoperative levels at 6 months following surgery In one study, occlusal pressure returned close to the value exhibited in control subjects, 12 months after surgery (Nagai et al., 2001) In another study, occlusal force steadily increased, approaching normal values after 2 to

3 years (Ellis et al., 1996)

• The preoperative vertical pattern

influenc-es the occlusal force levels

Dolichofacial (high mandibular angle) subjects show reduced occlusal force when compared to brachyfacial subjects, during maximal clenching, chewing, or swallowing (Proffit, Fields, & Nixon, 1983) It was postulated that individuals with a long facial pattern fail to gain strength normally

in the mandibular elevator muscles Brachyfacial subjects have also been shown to demonstrate significantly higher electromyographic temporal activities than dolichofacial subjects (Custodio

et al., 2011)

Craniofacial dimensions also play a role in clusal force asymmetry, as dolichofacial subjects also exhibited occlusal force lateral asymmetry (Gomes et al., 2011) When comparing asym-metrical and symmetrical skeletal deformities, the balance of occlusal force deviates to the side which demonstrates the observed mandibular

oc-skeletal asymmetry (Goto et al., 2008).

• The correction of mandibular skeletal

deformities might not correct functional

dysfunction

Combined Orthodontic and surgical treatments

do not significantly change the chewing pattern

(Ueki et al., 2005), which means that despite a

major deformity correction being performed, the

patient may maintain any previously acquired oral

functional movements A previously asymmetric

facial skeleton, with the associated long-term

asymmetric muscular function, could encourage

the patient to develop a unilateral chewing habit

In the same manner, a patient with a previously

prognathic mandible who presents with an anterior

cross-bite (under-bite), the establishment of

nor-mal anterior guidance control surgically, might not

function naturally despite there being a skeletal and

dental correction back into a more normal anterior

tooth interarch relationship Learning a reversed

chewing cycle has been suggested for class III

patients following maxillofacial surgery, as a

way to instill a functional chewing improvement

in non-responding surgical patients (Piancino,

Frongia, Dalessandri, Bracco & Ramieri, 2013)

To illustrate the complexity of evaluating T-Scan recordings for these types of patients, an example of a “perfectly visually appearing” Class

I occlusion established with maxillofacial surgery, can be seen in Figures 20a, 20b, 20c, and 20d The pretreatment asymmetrical high mandibular angle condition (Figure 20a) was treated surgically Then during orthodontic finishing, vertical elastics were used for six weeks on bilaterally, to guide proper mandibular healing (Figure 20b) At debanding, the occlusion appeared as a normal Class I (Figure 20c), that demonstrated widespread and uniform articulating paper marks that are suggestive of ideal occlusal balance (Figure 20d)

However, this case does not appear “perfect”

at all, within the T-Scan data (Figure 21a, 21b, and 21c) When observing the measured oc-clusal contact and force distribution, the patient demonstrated an inability to maintain total force showing weak muscular contraction capability And, when carefully observing the post retention photographs, it is possible to observe the begin-nings of a unilateral open occlusion developing within the canine-premolar area of the right side, indicating a partial relapse has occurred (compare Figure 20d to Figure 21c)

Figure 20a An asymmetrical high angle Class III surgical case, pre-treatment

Figure 20b The post operative surgical result with vertical elastics bilaterally, guiding the healing of the mandible (lingual customized appliances were used in this case)

Figure 20c Class I established at orthodontic appliance removal

Figure 20d After ten months of retention, note the widespread articulating paper marks that suggest there exists ideal occlusal balance

Figure 21a T-Scan recording of the case presented

in Figure 21 a-d, at appliance removal There is a

severe left side occlusal imbalance present (70.5%

left - 29.5% right), despite the Class I appearance

(Figure 20c).

Figure 21b T-Scan recording after three months

of retention No improvement in the occlusal ance has occurred.

bal-Figure 21c T-Scan recording after 10 months of retention Note the low occlusal force levels, the regular muscular contraction, and that the Center of Force being clearly deviated to the left side This less than ideal orthodontic treatment end-result was obtained despite the “visually good” occlusion, and the widespread articulating paper marks present (Figure 20d).

ir-Solutions and Recommendations

The clinical reality described in this chapter, is

that visual assessments of the final Orthodontic

result that often appear to the clinician as being

“ideal”, when those same end-results are actually

measured by the T-Scan system for occlusal force

balance, equality of contact intensity, and the

tim-ing of occlusal contact loadtim-ing, the end-results

are frequently far from the ideal Therefore, it is

important for Orthodontists to recognize that the

appearance of good occclusal function does not

necessarily indicate that the rendered orthodontic

treatment will result in ideal occlusal function

This same reality also applies to the concept

that “Settling” will equally distribute occlusal

force bilaterally, after some time has passed from

the date of debanding Numerous studies cited

in this chapter point to the fact that traditional

post treatment orthodontic assessments at case

completion, do not inform the clinician as to the

true occlusal force imbalances present, and do

not illustrate where excess occlusal force may be

concentrated within the arches

These are realities that the modern Orthodontist

must become aware of and readily understand

What the T-Scan is illustrating about orthodontic

treatment, is that aligning the teeth to fit together

well with proper axial inclination, where the teeth

are in visually-determined or articulating

paper-confirmed contact with their opposing

counter-parts, does not ensure an optimally functioning

and well-balanced occlusion has been attained by

the orthodontic treatment

Despite that Orthodontists are often concerned

with: the interdigitation of opposing teeth, the

3-Dimensional relationships of the mandible to

the maxillae, and the relation of the dental arches

to the soft tissue frame (the lip competence and

the tongue function), it is not enough According

to Broadbent, Orthodontists “must enlarge” their

“scope of knowledge and responsibilities, to be

equally concerned and be competent as

physi-been recommended that a physiologically oriented orthodontist should consider all physiologic pa-tient aspects, which would include breathing issues, swallowing mechanics, any masticatory dysfunction, and the TMJ kinetics

Although the masticatory system is widely adaptable and tolerant, especially in young people, there are limits (Orthlieb, Deroze, Lacout & Ma-niere-Ezvan, A 2006) One should keep in mind that teeth are the hardest organs in the human body, and the adaptation of the occlusal morphology of-

ten seen as functional wear, will not be visible until

significant time has passed following orthodontic

completion occlusal interferences that may have been ignored at case completion could later result (during the long-term) in periodontal breakdown, gingival recession, abfraction formation, and tooth mobility These interferences could also lead to the appearance of TMD symptomotology, years after treatment is completed

Therefore it is this author’s recommendation that the field of Orthodontics, at this time in the digital era of Dental Medicine, seriously con-sider employing computer-guided, T-Scan based case finishing at the completion of active tooth movement, and during the retention period, so

as to measurably balance the forces bilaterally, and create uniform occlusal contact intensities throughout the arches Without taking this step forward into the modern world of digital occlusal case finishing, many orthodontic patients will be left at case completion with an unbalanced oc-clusion, that contains undetected occlusal force overload in many areas within the occlusion.Digital occlusal analysis should be performed before appliance removal, when antero-posterior corrections have been completed (i.e class II or class III mechanics), and all diastemas closed

At that stage, posterior interferences in excursive mandibular movements can be reduced by add-ing corrective bends in the orthodontic wire, (1storder - in and out bends; 2nd order - vertical bends

to level marginal ridges and incisal borders; or 3rd

have been removed, a T-Scan III analysis should

be performed to check that the settling process

together with the chosen retention method (fixed

retainer wire or removable appliance), is

improv-ing the occlusal contact quality

An interval of 6 months should be respected

before offering occlusal adjustments when needed

Moreover, a period of over one year should pass

before occlusal adjustments are performed on a

surgical case

FUTURE RESEARCH DIRECTIONS

Presently, review papers analyzing the quality of

published clinical studies such as the Cochrane

Review (Fricton, Look, Wright, Alencar, Chen,

Lang, Ouyang, & Velly, 2010; Luther, Layton, &

McDonald, 2010), emphasize the lack of

statisti-cal power and the methodologistatisti-cal flaws present

in existing published TMD studies These critics

explain based upon the current state of knowledge,

it is not yet possible to make recommendations

that approve of orthodontic or surgical treatment,

whose sole goal is to ameliorate symptoms

associ-ated with the TMD However, the same authors

admit that this position may change, should new

research provide evidence of the efficacy of such

therapy

For some authors, a significant relationship

does exists between the distribution of occlusal

contacts and TMD symptom appearance, which

could be primarily expressed by occlusal contact

pattern asymmetries present in young adults

(Ciancaglini R, Gherlone EF, Redaelli, &

Radae-lli, 2002) Deficiencies in this research area are

significant, indicating there is a definitive need

for prospective, longitudinal trials that might help

to clarify the requirements of an ideal functioning

occlusal design

The T-Scan system, because of its precise,

reliable, reproducible, and objective recordings

that can be made of many aspects of occlusal

function, appears to be the correct occlusal

docu-mentation tool for such studies There is an urgent need for well-designed, T-Scan research protocols (prospective, randomized, and controlled clinical trials), and long-term follow-up cohort studies, that highlight the role that the Center of Force, and the Occlusion and/or Disclusion Times, have

in the etiology of TMD symptomotology, and in orthodontic case relapse

CONCLUSION

The use of a digitized occlusal analysis system like the T-Scan, is extremely attractive to the Orthodontist because it eliminates the factor of operator subjectivity in the interpretation of post orthodontic occlusal contact quality Moreover,

it is the only available tool that can measurably assess orthodontic case end-result symmetry, time-simultaneity, and occlusal force equality that the differing occlusal contacts exhibit within the arches

The T-Scan III’s precision, which can be quantified in milliseconds and square millime-ters, has won it recognition, as being a reliable and reproducible clinical tool In Orthodontics, T-Scan III usage during the finishing stage gives the clinician quantifiable data describing closure prematurities and lateral excursive interferences, that requires virtually no chair-time to acquire This information can be applied to the case when tooth movement is still possible, by adding into the arch wire corrective wire bends, or by employing vertical elastics, where needed

When the orthodontic treatment has been completed, T-Scan III recordings can be used periodically to follow the settling of the occlu-sion, by observing any imbalance of the Center

of Force This is particularly important in the high mandibular angle cases For adult patients who have limited adaptation potential, and present with extensive prostheses or advanced tooth wear, further T-Scan guided occlusal adjustments could improve the orthodontic outcomes, especially

when a persistent occlusal disharmony exists

within the occlusal contact distribution, following

orthodontic treatment

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KEY TERMS AND DEFINITIONS

Lingual Orthodontics: Orthodontic

multi-bracket custom cast appliance system, where braces are placed behind the teeth on the lingual side Brackets are miniaturized and can be cus-tomized

Occlusion: Occlusion describes the

relation-ships between the maxillary and mandibular teeth Static occlusion refers to contact between teeth when the mandible is closed into complete tooth interdigitation and is stationary Dynamic occlu-sion refers to occlusal contacts made when the mandible is moving excursively Centric Occlu-sion is referred to as a person’s habitual bite, the bite of convenience, or the intercuspation position (ICP) (not to be confused with Centric Relation)

Orthodontics: Formally Orthodontics and

Dentofacial Orthopedics, is the specialty of Dental Medicine that is concerned with the study and treatment of malocclusions

Orthognathic Surgery: The correction of

abnormal skeletal and dental relationships through the surgical movement of the bones of the maxilla and/or the mandible These surgical corrections often produce ideal visual occlusal relationships that demonstrate compromised occlusal force

strength capability, and non-ideal occlusal force

balance

Vertical Pattern: Two differing terms

De-scribes the patient’s facial type Brachyfacial type

is characterized by a short and wide face, usually

presentation with a flat mandibular plane angle,

and a closed gonial angle A deep bite is frequently

associated with this facial type and Dolichofacial

type which is a facial type characterized by a

long and narrow face where the maxilla exhibits excessive vertical growth and the mandibular plane is steeper than normal This growth pat-tern results in long and narrow alveolar dental arches, and produce a clockwise rotation of the mandible during growth This is what opens the mandibular plane angle, and sometimes creates

a skeletal open occlusion