Download pdf - Computerized occlusal analysis in Dentofacial orthopedics ... · DOI: 10.1051/odfen/2012103 J Dentofacial Anom Orthod 2012;15:203 RODF / EDP Sciences 1 Conflicts of interest declared

DOI: 10.1051/odfen/2012103 J Dentofacial Anom Orthod 2012;15:203� RODF / EDP Sciences

1

Conflicts of interest declared by the author: NONEArticle Received: 09-2011.Article Accepted: 11-2011.

Computerized occlusal analysisin Dentofacial orthopedics:indications and clinical use theT-scan III system

Julia COHEN-LEVY, Nicolas COHEN

ABSTRACT

By definition, orthodontists take special care in achieving a high qualityocclusion when finishing cases, believing good contacts are essential tomaintain dental health, function, and insure stable long-term of results.The T-scan III system provides a real-time digitized analysis of occlusion, in bothstatic and dynamic modes, and records the distribution of occlusal forces withinthe dental arches in different clinical situations. While the first T-Scangenerations versions showed weaknesses, recent technical improvementshave made T-scan a reliable and reproducible tool, whose findings areindependent of the operator. It is now possible to calibrate the sensitivity of thesensor for individual patients, and to evaluate the quality of records so thatcomparisons can be made between various stages of a patient’s treatment, aswell as between patients. In addition to the accuracy of occlusal diagnosis, thatoften exceed clinical requirements, the T-scan III also can help understandingbetter each patient’s functional pattern. This article describes the T-scan IIIocclusal analysis system, reviews current literature that evaluated its clinicaluse, and outlines its principal indications in dentofacial orthopedics. Four clinicalcases treated with full bonded lingual appliance will illustrate how the Tscan IIIinfluences orthodontic case finishing : one case of ‘‘occlusal discomfort’’ aftercompletion of surgical and orthodontic treatments, a case of cervical abfractionlesions, a case of anterior deep bite restored with an implant-supportedprosthesis, and a case of severe facial hemiatrophy treated with a complexprotocol.

KEY WORDS

Occlusion

Lingual orthodontics

Diagnosis

Dental implant

Address for correspondence:

J. COHEN-LEVY255, rue St-Honore75001 [email protected]

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Asymmetry1 – INTRODUCTION

Dental occlusion develops progres-sively, under the guidance of func-tional and genetic influencesthroughout dental arch morphogen-esis and subsequently through a vari-ety of adaptations, notably posturaland articular. Dealing with complexmalocclusions with fixed appliances,orthodontists modify dental contactsto achieve a new position of occlusalequilibrium. Fully aware of the re-sponsibility that this implies, ortho-dontists devote a special attention tothe quality of the final occlusion oftheir treated cases, irrespective ofthe therapeutic philosophy to whichthey adhere (Planas, Ricketts, Roth,Tweed-Merrifield. . .). Common to allorthodontic philosophies is the de-mand for esthetics and the restora-tion of good masticatory and posturalfunction. Many practitioners considergood occlusion to be a bulwark ofstable results.

Orthodontists have traditionallyevaluated the quality of dental con-tacts by direct visual inspection sup-plemented by articulating papermarks. Most do not now routinelyemploy the time-consuming techni-

que of mounting models on articula-tors, except for some complex casesor for the construction of customizedpositioner-type retainers.

However, by using new digitizedtools like the T-scan III system, ortho-dontists can now evaluate and regis-ter occlusal forces throughout thearches in real time, dynamically, indiffering clinical situations.

In this article we describe this ana-lysis system, review the literature de-tailing studies that have used it,compare its efficacy with articulatingpaper records, and present an outlineof its fundamental principles and ap-plications in dentofacial orthope-dics. We illustrate our account withfour clinical cases, each treated witha customized bonded lingual appli-ance: one case of ‘‘occlusal discom-fort’’ after combined orthodontic andsurgical treatment; a case of cervicalabfraction lesions; a case of treat-ment of anterior deep-bite with animplanted-supported prosthesis; anda case of severe facial hemiatrophytreated with a complex protocol.

2 – THE T-SCAN III SYSTEM

2 – 1 – Presenting theT-scan III system

In 1984, Tekscan Inc29 introducedthe Windows-compatible, digitizedocclusal analysis T-scan system as amethod for registering inter-arch oc-

clusal contacts dynamically duringvarious mandibular movements, andfor representing these in a graphicform in real time, giving informationabout their duration and their relativeforce. The system was designed tofacilitate diagnosis of occlusal dys-

JULIA COHEN-LEVY, NICOLAS COHEN

2 Cohen-Levy J., Cohen N. Computerized occlusal analysis in Dentofacial orthopedics:indications and clinical use the T-scan III system

function and to guide practitioners indelivering occlusal equilibration ofnatural and prosthetic teeth and,especially, of implant-supported pros-theses23,29.

The T-scan system consists of athin flexible sensor inserted into anautoclavable sensor handle that isplugged into the USB port of a perso-nal computer (Fig. 1a).

The slim horseshoe-shaped sen-sors, which can be used repeatedlyfor a single patient, are made up of1370 active pressure sensing loca-tions (1122 pressure sensing locationsfor small sensors). Eighty-five micronsthick (Fig. 1b), it encloses a doublelayer of Mylar, a special ink. A forceapplied to each of these cells modifiesthe electric conductivity of the Mylar.The program records and analyzes thedifferentials of applied voltage, andgives relative values of the force andduration of occlusal contacts, with atime precision of 10 ms.

The results are delivered in theform of graphs describing force varia-tion with time; force histograms areprojected on an individualized dental

arch (that can be modified accordingmesio-distal tooth dimensions ormissing teeth) allowing the praction-ner to picture the location and dura-tion of inter-arch contacts over time.

Before bite registration, one mustcalibrate the sensitivity of the T-scanto accommodate the patient’s mus-cular force such that the system candetect very light contacts without be-coming saturated by heavier con-tacts.

In the first example, we presentthe case of a patient who was ex-periencing ‘‘occlusal discomfort’’after the removal of orthodontic appli-ances. We had treated her with acombined surgical and orthodonticnon-extraction approach for a Class IIdivision 2 malocclusion (Figs. 2a–3cand 3a–3c. Dr. O. Esnault, Paris, wasthe maxillofacial surgeon). The pa-tient was included in a clinicalstudy7. We made various T-scan re-gistrations for this patient, first onthe day on which the lingual attach-ments were removed, and then at 3and 6 months into the retention peri-od (Fig. 4a–4c).

Figures 1a and 1bThe T-scan III system.

a: The T scan III system consists of a disposable sensor, an autoclavable occlusal adaptor, connected to anelectronic sleeve to the USB port of a laptop computer.b: the sensor is 85 lm thick and flexible.

COMPUTERIZED OCCLUSAL ANALYSIS IN DENTOFACIAL ORTHOPEDICS: INDICATIONS AND CLINICAL USE THE T-SCAN III SYSTEM

Rev Orthop Dento Faciale 2012;15:203. 3

Immediately after appliance re-moval, we bonded an anterior lingualretention wire and proceeded to thefirst registration; there were no con-tacts in the anterior region of thearch, so that occlusal forces were ex-erted primarily on the molar teeth,weakly on the bicuspids, and mostforcibly on the right side. The upperand lower right second molars sup-

ported 41% of the total force dis-cerned by the sensor. This initialdistribution signified a slight anterioropen bite that we interpret as resul-tant from the differential in thicknessbetween the upper lingual attach-ments and that of the bonded reten-tion wire that replaced them.Accordingly, the marks made by ar-

Figures 2a to 2cClinical case 1: Intraoral views of a Class II division 2 malocclusion treated by a com-bined surgical-orthodontic protocol with a customized lingual appliance technique.a: Before treatment. The extruded position of the mandibular anterior teeth seems to bethe principle component of the anterior overbite.b: Pre-surgical situation showing clear bonded buttons in place on both arches.c: Post-treatment. Note the slight canines’s infra-occlusion.



ticulating paper on the canines werefalse positives.

At the 3-month check-up visit, thepatient described a feeling of unevencontact between the upper and lowermolar teeth on the right and leftsides that was not apparent from ar-ticulating paper markings (as shownin the intraoral view of the maxillaryarch in Figure 3c). Even though post-orthodontic physiological eruption(‘‘settling’’) brought the upper andlower anterior teeth into contact, theforce of their occlusion remainedweak, and the right side occlusiontook 66% of the total contact forces,demonstrating its dominance. Thecenter of force, depicted by a dia-mond, has clearly shifted to the right.

At 6 months (Fig. 4c), we relievedhigh spots on the amalgam filling inthe upper right second molar to re-duce the force sustained by this sin-gle tooth and to encourage a betterdistribution of occlusal forces. Wehad noted how the histogramtracings of forces exactly followedthe shape of the occlusal portion ofthe amalgam restoration. However,the asymmetry of inter-arch contactspersisted and their distributionthroughout the maxillary arch re-mained unchanged.

Because of the absence of clinicalsigns and the eradication of occlusaldiscomfort, we undertook no furtherequilibration despite the residualasymmetry in the occlusal forces.We encouraged the patient to con-tinue the physiotherapy exercisesprescribed after her maxillofacial sur-gery, and asked her to balance hermastication between the right andleft sides to eliminate functionalasymmetry.

Figures 3a to 3cClinical case 1: Occlusal views of the maxillary arch.a: Before treatment.b: Pre-surgical. Note the bite planes incorporated inthe canine lingual attachments to help leveling of themandibular arch.c: Appearance on the day of appliance removal, witha lingual retention arch wire bonded between themaxillary canine, and the occlusal marks made byBausch two-sided articulating paper. Note the clearmarks on the molars and the weaker marks on theleft second bicuspid and the right cuspid. The incisalmarks appear to be false positives caused by foldingover of the articulating paper.



Figures 4a to 4cClinical case 1: T-scan III registration, occlusal view.

a: On the day of appliance removal only posterior teeth, primarily the molars, are in con-tact with their antagonists. Contact between upper and lower bicuspids is weaker. Thered diamond shows clearly that the center of force has drifted to the right, and showsoscillations.b: Three-month recall visit. Note that the upper and lower anterior teeth have begun tocome into contact because of physiological extrusion. The center of forces is still locatedon the right but with fewer oscillations. The contact between the upper and lower sec-ond molars is still strong.c: Six-month recall visit. The patient’s sense of occlusal discomfort was eradicated byequilibrating the amalgam filling on the occlusal surface of the maxillary right secondmolar. The occlusal forces are more balanced but still somewhat heavier on the right.The upper right lateral incisor and canine teeth are still out of contact with their lowerantagonists.



2 – 2 – Scientific validation of theT scan system

The first generation of T-scan sen-sors had certain weaknesses, princi-pally high variability in their physicalproperties, with sensitivity not distrib-uted uniformly across the sensor.Consequently, they often disclosedfewer contacts than were revealedby articulating paper. Reliability andsensitivity studies reported disap-pointing clinical results for early T-scans17,18. The next two generationsof sensors were thinner and hadgreatly improved resolution and sen-sitivity, especially for extreme pres-sure values22. Other studies showedthat these much-needed improve-ments had made the instrumentmore reproducible and sensitive22,23.

A German research team validatedthe clinical use of the T-scan on 42adult subjects24, estimating its errorof measurement as 1%, its precisionerror as 2%, and its reliability error as2.8%. They also asserted that chan-ging the sensor or repeating thetests had no effect on the measure-ments obtained.

2 – 3 – A comparative analysisbetween digitizedocclusal force resultsand results fromtraditional methods

Clinicians have traditionally used ar-ticulating paper and patient’s feed-back to guide occlusal equilibration.Despite widespread use, these meth-

ods had limitations, as illustrated inseveral clinical and research articles.

Articulating paper can pinpoint thelocation of contacts between antago-nistic teeth if the ink transfers cor-rectly from paper to tooth. However,as we have noted, this inevitably pro-duces a number of false positives.

Marks made by articulating papercan vary in size and shape, in deep-ness of color, or appear as a ringwith a clear center like a halo20, andcan be interpreted in multiple ways.Differences in the intensity of marksmay represent differences in force in-tensity or could simply reflect thespecific occlusal morphology or thecondition of the occlusal enamel orrestoration surface. Variations in ar-ticulating paper marking may alsoarise from differences in paper thick-ness, the extent to which it is im-pregnated with saliva, and the forceof the patient’s bite. Because ofthese types of variation, many re-searchers have been able to demon-strate that contact profilesdetermined using articulating paperare not reproducible, even whenmade under apparently identicalconditions9,20,31,38,39. Furthermore,Rozencweig et al. 37 have shown thatthe storage conditions of articulatingpaper in the dental office can contri-bute to variation in markings.Repeated utilization, probably be-cause of saliva impregnation, can sig-nificantly reduce its precision andsensitivity, regardless of the type ofsupport employed39. In contrast, T-scan is totally unaffected by moist-ure39.



Dentists often interpret largemarks as an indication of strongforces, which is a false conclusion inmost cases. In a pilot experimentalstudy on the subject9, researchersmounted models on articulators andsubjected them to forces of increas-ing intensity. They found only a 21%probability that two similar markswere generated by the same force(between 25 N and 450 N). Anotherstudy, conducted in 2008, comparingthe effect of articulating paper thick-ness (25 lm or 60 lm) on contactmarking at pressures ranging from100 N to 200 N, found there was nosignificant increase in the number orsize of the marks with increasedpressure for either thickness of pa-per. As expected, the thicker papercreated more marks, which weregenerally of larger size than with thinpaper38.

In summary, the marks made byocclusal articulating paper are difficultto reproduce and should no longer beconsidered as accurate reporters ofgenerated occlusal force, their pri-mary purpose now being the qualita-tive location of contacts or nearcontacts between opposing teeth.

The possibility of using a digitizedanalysis such as that offered by theT-scan system is extremely attractivebecause it eliminates the factor ofoperator subjectivity. Other compu-terized methods are also available in-cluding the Prescale OcclusalSystem� (Ref. 31). Alternatively, low-viscosity impression materials suchas Blu-Mousse� can be used, withthe need of a scanner and computer.

2 – 4 – Clinical use of the T-scanIII system

• Analysis of contact marks made

in intercuspation

Having chosen and calibrated asensor for an individual patient, thepractitioner begins registration of anocclusal sequence by keeping thesensor in place within the maxillaryincisors’ embrasures. It is advisableto register a number of consecutivebites on the sensor because manyhesitant patients begin by biting verytentatively.

After practitioners complete theregistration, they can visualize the di-gitized results from various perspec-tives:– a view of the arch upon which the

forces exerted are represented bycolor histograms (Fig. 4);

– a familiar occlusal view resemblingthe picture given by articulatingpaper (Fig. 4) and,

– two graphs that illustrate thedevelopment of forces over time,as shown below.Time is expressed in milliseconds

on the abscissa, while the ordinateshows the forces received by thesensor, ranging between 0 and100%. The gray graph denotes thetotality of the forces recorded by thesensor, while the color graphs repre-sent different sub-sectors of the den-tal arch that can be divided into right(pink) and left (green) or into quad-rants. Note that these differentgraphs show a phase of growing oc-clusal force upon closure and firstcontact, a plateau phase of maximal



intercuspation, and a diminishingphase as the mouth re-opens. In theocclusal view of contacts, the dia-mond represents the center of forceand the adjoining tracing shows itsmovements during the registration.

The Center of Force (COF) is thecenter of ‘‘gravity’’ of the pressuresrecorded by the sensor and not an in-dicator of mandibular position. Thetracing of mandibular movements, or‘‘oscillations’’, denotes the balance offorces between the first and last con-tacts. In theory, it should be posi-tioned in the median sagittal axis forregistrations of maximal intercuspa-tion and for patients with full den-tures.• Dynamic analysis

An important and useful feature ofthe T-scan is its ability to register oc-clusal contacts during mandibular ex-cursive movements in real time,eliminating any need for mountingmodels on an articulator (the tradi-tional method for obtaining this infor-mation).

A Chinese study40, published inAugust 2011, reported dynamic T-scan analyses of the occlusion of 85students with Class I occlusions. Inthe three positions (lateral disclusion,edge to edge canine position, andmaximum lateral amplitude), six dif-ferent occlusal schemes were de-scribed, going beyond the notions ofcanine protection and group function.It may thus be possible to formulatenew norms but new clinical applica-tions for these findings have yet tobe found.

To illustrate this analysis, we pre-sent the case of a patient treatedorthodontically for a Class I malocclu-sion with a Class III tendency, an

arch length discrepancy, an anteriorcross bite, and abfraction lesions inthe posterior area. Because ofchipped incisal edges and the smallsize of the maxillary lateral incisors,bonded veneers for the upper ante-rior teeth were included as a compo-nent of the treatment plan.

Figures 5a–d depicts the initial clini-cal situation, while Figures 6a–6dshow intraoral views of the results oforthodontic treatment. Figures 7a–7dare maxillary occlusal views at var-ious stages of treatment (before;nearing completion of treatmentwhen the bonded lingual attach-ments were still in place; after treat-ment showing articulating papermarks and a bonded cuspid-to-cuspidwire retainer; and the final appear-ance of the arch after bonding of ve-neers to the upper lateral incisors).We show an example of right lateralmovement as perceived clinically inFigure 8d on the working side and in8e on the non-working side, thephotograph illustrating canine protec-tion taking the buccal teeth well outof occlusion, at least in the finalphase.

The T-scan registration depictingthis right lateral movement is shownin three screen shots, taken at differ-ent time frames:– At the beginning of lateral move-

ment, as the upper and lowercuspids come into contact, thereis an excellent balance of occlusalforces, albeit slightly dominated bythe left side (Fig. 8a).

– Group function can be noted on theright side, with slight premolarinterference on the non-workingside at the end point of lateraldisclusion. The amplitude and dura-



tion of these premolar contactinterferences are both weak(Fig. 8b).

– Only the right cuspids are in con-tact, which is of moderate intensity,at the end point of lateral move-ment (Fig. 8c).The trajectory of the center of

force is, not surprisingly, located onthe right side, between the canineand the first bicuspid, but is notfrankly oblique. The curves describingsensor loading on the right side (red)and left side (green) cross over, illus-trating the dis-occlusion of the leftcuspid sectors, and the sensor load-ing on the right side. With T-scan III

registrations, it is possible to followthe distribution of contacts at 10 msintervals.• Searching for interferences in

centric relation

In the preceding registrations,which were made with no manipula-tion by the practitioner, our objectivewas to find a free expression of oc-clusal forces by eliminating, as muchas possible, any interference withnatural mandibular movement. Thesearch for interferences in the man-dibular closing pathway betweenterminal axial position and a conveni-ence bite requires, however, thatpractitioners exert a gentle manipulat-

Figures 5a to 5dClinical case 2: Intraoral views of a case of Class I malocclusion with anterior cross bite,gingival recession with cervical abfraction lesions (restored on the left side, marked onthe right side) and fractures of incisor’s incisal edges.a: Frontal view,b: jaw slightly open,c: right view, teeth in occlusion,d: left view, teeth in occlusion.



ing pressure of weak amplitude onthe mandible, through which they‘‘feel’’ the first contact. However,T-scan III has a special application,more sensitive, designed for thistype of registration and that can re-cord the weakest pressure values.

This analysis system is easy to usein the sense that a dozen consecu-tive movements can be made, con-

centrating on tactile sensations, withno insertion and removal of paper,only later controlling the repetitivecharacter of the results. However,the need to use articulating paper isnot completely eradicated; it muststill be used to visualize effectivelythe desired contact once it has beenlocated and clearly quantified.

3 – INDICATIONS FOR DIGITIZED OCCLUSAL ANALYSIS IN DENTOFACIALORTHOPEDICS

3 – 1 – Temporomandibulardisorders (TMD) andT-scan III

• Diagnosis

Temporomandibular disorders aremultifactorial in origin and are now

thought to resemble chronic muscu-loskeletal pain disorders in otherparts of the body, such as the lowerback, whose etiology has a large psy-chological component1. Suppliers andmanufacturers have proposed differ-ent methods for diagnosing TMD,

Figures 6a to 6dClinical case 2: Occlusion at the end of treatment.



suggesting registrations of muscularactivity21, the rest position of themandible11 or the recording of occlu-sal interferences, an area in which T-scan III could be useful.

Analysis of the validity, reliability,and utility of these techniques4 iscurrently a controversial subject,partly because clear cost-benefit de-monstrations have yet to be made.

The issue of over-diagnosis ofTMD or, more gravely, of over-treat-ment is important because no onehas yet accurately described the clini-cal significance of different TMDanomalies. The American Association

for Dental Research1 recommendsthat practitioners essentially basetheir diagnoses on the anamnesisand clinical examination, completed ifindicated by X-ray films.

One 1994 study, published by aJapanese team32, using the T-scan IIInoted a difference between patientsaffected by TMD (n = 5) and a con-trol group (n = 60). In the controlgroup, the duration and distributionof contacts were symmetrical withcenters of force clustered around thefirst molar. In the TMD group, theforce and duration of contacts wereasymmetrical, with centers of force

Figures 7a to 7dClinical case 2: Views of the maxilla.

a: At the beginning of treatment,b: near the end of treatment, showing lingual bonded attachments,c: at the end of treatment with articulating paper markings, 3-to-3 bonded retention wire,d: after placement of anterior veneers.



in varied locations. This study, how-ever, does not provide us with a reli-able assessment of the diagnostic

value of T-scan III because of numer-ous methodological faults (e.g. lowsubject numbers, failure to randomize

Figures 8a to 8dClinical case 2: T-scan III registration.

a: Maximal intercuspation showing the well-balanced distribution of inter-arch contacts, with the center of forceon the median line;b: Beginning of lateral movement, with group protection (canines and premolars contacting on the right side) andinterference of the left premolars on the non-working side;c: Final extension of lateral movement with only canines in contact, and other teeth dis-occluded. The canineguidance facet can be seen;d: Dis-occlusion on the left side.



groups and maintain their anonymity,and inadequacy of the definition of in-clusion factors).

In summary, T-scan III provides ameans of discerning anomalies in thecentering and intensity of occlusalforces that reflect functional asym-metries and muscular spasms. How-ever, it is only to be used tosupplement, not substitute for, ana-mneses, clinical examinations, andradiographic imaging. In addition, be-cause of the visual clarity with whichits findings are presented, it constitu-tes an excellent tool for communicat-ing results and concepts withcolleagues and patients.

The vagaries of the center of forceand the irregular character of the sen-sor loading can be reviewed in laterappointments after patients have un-dergone oral health training with phy-sical therapy7, to help them resolvingtheir TMD problems through theirown efforts.• Treatment

Mechanistic thinking has for yearspersuaded many dentists that theetiology of TMD is structural, andwas caused exclusively by occlusaldiscrepancies and poor condylar posi-tioning associated with disturbancesof neuromuscular or postural balance.This mindset led them to attempt totreat TMD with orthodontic, surgical,and prosthetic therapy, the sole goalof which was to correct temporo-mandibular symptoms.

Nowadays, most practitioners rea-lize that TMD develops according toa normal cycle with active phases,when pain and discomfort can have asignificant effect on patient’s lifequality, and improvement phases,

with spontaneous remission even inthe absence of treatment.

Controlled studies, in the ‘‘evi-dence-based’’ concept, have notdrawn the conclusion that patientsneed a permanent ‘‘correction’’ oftheir occlusion or the relations oftheir condyles to be cured of TMD14.Despite their symptoms, patientswith internal defects of the TMJ donot ordinarily require treatment be-cause most respond well to physicaltherapy, 2,14 and pain management.

Published papers analyzing thequality of clinical studies, notably theCochrane Reviews, emphasize thelack of statistical power and themethodological flaws in TMD studiesso far available1,26,27. These criticsexplain that it is not yet possible tomake recommendations for clinicalpractice in this domain, and accord-ingly, in the current state of knowl-edge, they cannot approveorthodontic or surgical treatmentwhose sole goal is to amelioratesymptoms associated with the TMJ.They admit that this stance maychange should new research provideevidence of the efficacy of suchtherapy.

In parallel, however, is a broadagreement that therapy, be it ortho-dontic, restorative, or prosthetic,should favor proper intercuspation,encourage free movement of themandible, and avoid placing themandible in a distal position that cancause articular constraints35. Practi-tioners should search in their exami-nations for oral habits or behavior likebruxism that impose an unhealthyoverload on the masticatory system.



3 – 2 – Follow-up of post-orthodontic occlusalchanges

Several studies have been devotedto the quality of static and dynamicocclusion after orthodontic treatmentand to the influence of various typesof retainers7. After removing appli-ances it is tempting for orthodontiststo leave teeth unretained becausethat will allow for spontaneous im-provement of certain parameters likethe attainment of more contactpoints and the leveling of marginalridges. However, without the place-ment of fixed or removable retainers,the risk that rotations or overbitescould relapse and require retreatmentis too great to be acceptable28.

By using tooth positioners madefrom a perfected set-up mounted onarticulators, orthodontists can im-prove the equilibration and intercus-pation of cases treated withasymmetric or atypical extractionsbecause of arch length discrepan-cies13.

Weak anterior inter-arch contactsusually represent something otherthan poor finishing of an orthodonticcase (as was true in our first case,Figs. 2–4). They resemble the usualT-scan findings of individuals whohad no orthodontic treatment, wheremarkings of lateral incisors are diffi-cult to find in maximum intercuspa-tion. In a mutually protectedocclusion, it is normal to obtain weakanterior markings and much strongerposterior ones in intercuspation be-cause molars, with their broad-basedroot surfaces, are designed to accepta large proportion of the total occlu-sal load. It is only during the course

of anterior and lateral excursivemovements that incisors and caninessupport occlusal forces as molars aretaken out of occlusion.

A Chinese team3 studied inter-archcontacts at different force levels fortwo groups of subjects with normalocclusion: a group of patients whohad been treated with pre-adjustedbrackets (edgewise technique) andarch wires, and another with subjectswho had never had orthodontic treat-ment. They found that anterior forcelevels were significantly higher in thetreated subjects than in the controlgroup, although this had no clinicalsignificance.

Another (longitudinal) study, per-formed in adults who had been trea-ted with an individualized lingualappliance7, demonstrated that the oc-clusal forces of a great majority ofthese patients tended to becomesymmetrical over time. However, insome patients a marked asymmetryin the force of contacts on the rightand left sides persisted to an aston-ishing extent. Marks left by articulat-ing paper could not have discernedthese subtle distinctions, which canonly be revealed through the reliablyreproducible results from a digitizedsensor.

The clinical significance of theseobservations is obscure because noone has yet been able to associatethem with any oral disorders.However, it is unequivocal that theseresults project a surprising, differentview of functional occlusion. For ex-ample, sensors can specificallysearch out the location of the centerof force and the balance of contacts,as the following case study indicates.



This patient was afflicted with Par-ry-Romberg hemifacial hypotrophysyndrome, a strong disfiguring facialasymmetry involving skeletalstructures, muscles, and the dentalarches8 (Fig. 9). Her complex com-bined surgical and orthodontic bimax-illary treatment was supplementedby lipo-filling injections given byDr. D. Defrennes, of Paris, to restorebalance to her distorted facial fea-tures. We employed a mixed fixedorthodontic technique that used indi-vidualized lingual bonded attach-ments on the upper arch and buccalbonded ceramics on the lower jaw,adapting our treatment to accommo-date the possible loss of some ante-rior teeth that, at the start of therapy,had practically no roots (Figs. 10and 11).

Figure 12 depicts the surgical archwire, while the clinical change afterthe removal of appliances and at theend of the retention period (2 yearspost-operative) is shown in Figures13 and 14, respectively. Figure 15portrays the distribution of inter-archcontact points at the time of appli-ance removal and 2 years later. Theocclusal forces were highly lopsidedon the day of debonding, with 80%being concentrated on the right side.Adding composites to the hypoplasticbicuspids brought the inter-arch con-tacts into improved balance.

At the end of the 2-year retentionperiod, the teeth affected with phan-tom roots were still in place, andexhibited negligible mobility. Thepatient was advised that these mightimminently need to be replaced withimplants but are currently maintainingspace and preserving alveolar bone.Inter-arch contacts still show right

side dominance and their distributionis unchanged. The charging of thesensor is now regular as the forcesbecome uniform throughout the archas they increase in amplitude. Takinginto account the serious effect thissyndrome has on the patient’s mus-culature, we felt it was important toensure that symmetric function wasachieved as well as morphologicalsymmetry.

The necessary physiological adjust-ments of the patient’s masticatorysystem and occlusion may requirelonger than a year to become firmlyestablished following combinedorthodontic and surgical treatment19.

3 – 3 – Occlusal trauma as anetiological factor

It has been suggested that ec-centric occlusal forces could be a fac-tor in the etiology of abfractioncervical lesions and that the exis-tence of occlusal micro-trauma couldhave a deleterious effect on period-ontal tissues and osseointegrated im-plants. To prevent such undesirableoutcomes, occlusal equilibration hasbeen suggested as the treatmentmodality.• Abfraction lesions

Abfraction lesion is a type of non-carious cervical lesion that causes aloss of hard dental tissues thatsometimes require restoration ofsurrounding crown and root areas.They differ from other cervical le-sions caused by abrasion or erosionand develop in response to flexion,which is an excessive, cyclic loadingperpendicular to the long axis ofteeth. Constraints concentrate in thecervical region of the tooth where



the enamel layer is thin and readilyfractured.

Most theories explaining abfractionlesions are derived from finite ele-ment models but there is virtually noexperimental proof to substantiatethem. Clinical studies have shownthat they are associated with brux-ism, wear facets, and premature con-tacts but no investigations have been

able to confirm any causal relation-ship15,30.

In an investigation of 46 subjects5,one research group evaluated the re-lationship between premature con-tacts in centric relation and thedevelopment of abfraction lesions.The majority of both abfraction le-sions and high spots were located inthe premolar area. The teeth affectedby abfraction lesions had significantly

Figures 9a to 9dClinical case 3: Facial views of a patient with Parry-Romberg syndrome before (a and b)and after (c and d) combined surgical-orthodontic treatment and lipo-filling (autogenic fatgraft) on the hypoplastic side.



Figures 10a to 10eClinical case 3: Intraoral views at the beginning of treatment showing the asymmetric sagittal relationships andthe hypoplasia of the lower left cuspid and bicuspid teeth.

Figures 11a and 11bClinical case 3: Panoramic views.

a: Start of treatment. Note the ‘‘phantom’’ roots of the lower left cuspid and first and second bicuspids, and themarkedly short roots of the upper right central incisor, the lower left central incisor, and the lower left first molar.b: After orthodontic treatment. Both arches have been leveled. Apical resorption of 11, 41, and 36 worsened, butthe roots of 33, 34, and 35 appear stable.



more loss of buccal soft tissue at-tachment than healthy teeth. How-ever, the correlation of occlusalinterferences in centric relation to ab-fraction lesions or to a greater loss ofattachment has not been demon-strated.

In conclusion, it is no longerdeemed advisable to use selectivegrinding in an attempt to cure abfrac-tion lesions30,36. Nevertheless, in theframework of orthodontic treatment,it may be worthwhile for orthodon-tists to discern specific areas of inter-ference and to modify the values oflateral torque during finishing stagesof treatment. Furthermore, to guardagainst bruxism, orthodontists may

use thermoformed splints to affordmechanical protection to teeth thatcould be damaged by unhealthy con-straints.• Occlusal trauma and periodontal

damage

Increased mobility of teeth asso-ciated with an enlargement of theperiodontal ligament, a decrease inthe visibility of the lamina dura, a lossof alveolar bone, or a change in thetrabecular nature of maxillary or man-dibular bone, as seen on radiographs,are all signs of occlusal trauma. Theinfluence of occlusal factors in thedevelopment of periodontal diseaseis currently a controversial topic.Some authors still advocate occlusal

Figures 12a to 12cClinical case 3: Intraoral views before surgery.

Figures 13a to 13cClinical case 3: Intraoral views at the close of treatment.



equilibration as a component of atreatment plan aimed at regeneratingperiodontal tissue.

The influence of dynamic occlusalinterferences on the depth of period-ontal pockets was evaluated in atransverse epidemiological study of2,980 subjects representative of aCaucasian population5. Their medicaland dental histories and the differentknown periodontal risk factors werestudied. Interferences on the non-working side were shown to be sig-nificantly associated with pocketdepth and loss of attachment(P < 0.0001), and there was an in-crease in pocket depth (P = 0.004)when a tooth had both working andnon-working side contacts, with theamplitude of these forces having

some influence on this outcome.These different relationships, eventhough clearly demonstrated, are notspecific and are of little importancecompared with other factors such aspatient age, tobacco use, and plaqueindex.

Some older studies have shownthat, despite occlusal trauma, period-ontal disease can be successfullytreated and stabilized15. However, oc-clusal trauma caused by high spotsand interferences in lateral move-ments are found in cases of severeloss of alveolar bone and are posi-tively correlated to the loss of period-ontal attachment6,10.• Occlusal trauma and implants

Dentists have not yet agreed onthe general principles that should

Figure 14Clinical case 3: Intraoral views atthe end of the retention period.

We have added composite mate-rial to the hypoplastic teeth.



guide the management of implant-supported replacements for missingteeth. For example, different authori-ties have alternative opinions onwhether occlusal interferences mightbe a causative factor in the loss ofcrestal bone around implants. Someclinicians fear that strong occlusalforces may have a deleterious effecton the long-term success of their im-plants by causing crown fracture oran osseointegration defect.

There is, however, a consensusthat bacterial infection combined withimmunosuppression are necessary tocause an implant failure and that, incertain cases, occlusal trauma couldbe an associated factor. Recent stu-dies suggest that occlusal overloadcan lead to a loss of crestal bone inthe absence of inflammation, but ran-domized prospective studies areneeded to confirm this finding.

Implants have no periodontal liga-ment and so cannot benefit from thespecific proprioceptive sensors thatprotect natural teeth against occlusaltrauma. One study16 has shown thatthe accuracy with which patients per-ceived the forces on implant-sup-ported prostheses were eight timesless reliable than their perception offorces applied to natural teeth. Inmixed situations, as illustrated byclinical case 5 (Figs. 17a and 17b),where implant-supported prosthesesare next to natural teeth, the differ-ence between their axial and lateraldepressibility could lead to the im-plant receiving greater trauma.Neither the patient nor the practi-tioner could tell that this was actuallyhappening23.

One case report25 has recountedan early-onset bone loss associatedwith a prosthesis receiving excessive

Figures 15a and 15bClinical case3: T-scan III registration

a and b: appliance removal appointment, showing the marked asymmetry of the inter-arch contacts, with 80% onthe right side.c and d: End of the 2-year retention period. The forces are almost centered, and are globally far more symmetric,with 60% on the right side and 40% on the left side.



occlusal loads. After removal of thestressed dental element, occlusalforces on the prosthesis were re-duced and radiographic evidence

showed partial repair of bone in thedefect that affected several threadsof the implant. Three years later bonelevels remained stable.

Figures 16a to 16cClinical case 4: Treatment of a Class I malocclusion with an arch length discrepancy and anterior crowding asso-ciated with deep-bite. The lower left first prosthetic crown is supported by an implant (Dr. N. Cohen).a: Lingual attachments were bonded from second bicuspid to second bicuspidb: Lingual attachments were also placed on the entire upper arch.c: Lower arch at the end of treatment. Note the mandibular tori.

Figures 17a and 17bClinical case 5.

a: Panoramic radiograph at the end of treatmentb: T-scan III registration showing the distribution and excellent centering of forces.



4 – CONCLUSION

The T-scan III system is a newcomputerized occlusal analysis toolthat can provide an abundance of in-formation, that might even exceedour present day clinical requirements.

Beyond the controversy over theeffectiveness of occlusal equilibrationas a treatment modality for abfractionlesions, periodontal defects, or boneloss around implants, the T-scan IIIsystem offers orthodontists immedi-ate access to patient’s functional oc-

clusion. They can see the static anddynamic quality of inter-arch contactsin real time in a form that can be pre-served in a record for comparison atany future date.

The T-scan III’s precision, whichcan be quantified in milliseconds andsquare millimeters, has won recogni-tion as a reliable and reproducible re-search tool.

Conflict of interest

The T-scan III sensor was graciously loaned to Dr. Cohen-Levy for clinicalresearch, the results of which were published in 2011.

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