Orthodontics

The importance of the seated condylar positionin orthodontic correctionFrank E. Cordray, DDS, MS'

It has been proposed that the discrepancy between the seated and unseated condyiar position be identi-fied and eliminated when the ooolusion is reorganized. Identification ot this discrepancy is most accuratelyaccomplished through the use ol diagnostic casts that haue been taken trom a deprogrammed patient andmounted in the seated condylar position on a se m i adjustable articulator through an estimated facebowtransler. The amount and direction ol any discrepancy is determined three dimensionally with condylarposition instrumentation, (Quintessence int 2002:33:284-293)

Key words: articulator, oondylar dispiacement, condylar distraction, orthodontics, seated condyiar

position, unseated condyiar position

Aprevious article outlined steps that orthodontistsmust take to advance the specialty into the new

millennium';

1. Specific, comprehensive, and universal treatmentgoals must be developed.

2. Occlusion, temporomandibular joint function,facial esthetics, and periodontics must receivegreater emphasis in graduate orthodontic programs.

3. The quality of orthodontic records must beupgraded to include diagnostic study casts mountedin the seated condylar position.

4. A comprehensive orthodontic classification systemmust be developed.

5. Orthodontic diagnosis must become more accurate.6. Orthodontic treatment time must be minimized.

These issues constitute the foundation for state-of-the-arf orthodontic treatment in the 21st century,which will include the following:

1. The use of a repositioning splint to ehminate mus-cle symptoms and attain a comfortable, stable, andrepeatable seated condylar position

2. Instrumental anaiysis of diagnostic study casts:mounting of diagnostic study casts in the seatedcondylar position on a semiadjustable articulatorthrough the use of af least an estimated facebowtransfer

'Assistant Cliriical Proiessoi, Department of Orthodonlics, Ohio SlateUniversity, Colurrbus, Ohio,

Reprinl requesis: Dr Frank E. Cordray, 96 Northwoods Boulevard, Worth-irglon, Ohio 43235. E-mail: kcord74385@aol.com

Presented at the 100th Annual Session of the Arrerican Association ofOrlhodontists, Chicago, May 2000.

3. Measurements of jaw deflections caused by tooth-dictated positions (currently measurahle with theCondylar Path Indicator [CPI] [Panadent], theIVIandibular Position Indicator [MPI] [SAM], andCranio-Mandibular Fosition [CMF] [Denar]instrumentation)

4. Computer-assisted treatment planning, includingcorrected cephalometrics (conversion of lateralcephalograms from maximum intercuspation-centric occlusion (IVIIC-CO) to the seated condylarposition); comptiterized cephaiometric analysescorrected for jaw deflections; computerized growthdeterminations; and computer-aided treatmentforecasts (Visualized Treatment Objectives [VTOs])

5. Video imaging as an aid to optimizing dental, skele-tal, and soft tissue esthetics

Howaf et aP have stated, "Orthodontic assessment ofpatients has evolved as treatment goals have changed,"which ieads to the discussion of a fundamental aspect oforthodontic treatment: What are the goals of orthodonticcorrection? Ultimately it comes down to clinical results.Two overriding concerns for those delivering orthodonticcare are improved esthetics (facial and dental) andincreased longevity of the dentition and associated stmc-tures (periodontium and temporomandihular joints).

How are these goals accomplished? Consistentlyexcellent resuits are achieved by the application cfsophisticated treatment goals and utilization of asophisticated appliance system. Two areas of primeimportance for both the practitioner (from a practicemanagement standpoint) and the patient (from a satis-faction standpoint} are satisfying the patient's chiefconcern and treating the patient in the shortest timepossible, to achieve the desired result.

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Fig 1 Seated condyiar position, superior, anterior, andmidsagittai

Fig 2 Prematuie occlusai molar contact visible on castsmounted on an articulator in the seated condylar position.

ORTHODONTIC TREATMENT GOALS

The application of specific, comprehensive orthodon-tic treatment goals is paramount to the execution ofthe aforementioned principles.

Facial esthetics

Improved esthetics is what drives most patients toseek orthodontic care. The importance of esthetics forself-image cannot be overstated. The psychologicaland social development of patients is related inincreasing amounts to attractiveness and a favorableself-image. A sensitivity to patient expectations andmotivations, as well as treatment possibilities, must bedeveloped if the orthodontist is to end up with consis-tently satisfied patients.

Dental esthetics

As a result of his pioneering research on the commoncharacteristics of untreated ideal occlusions, Andrews'proposed "six keys to normal occlusion" as staticocclusal goals for orthodontic correction. These keysare the ideal for static dental alignment, thus provid-ing a guideline for the precise positioning of eachtooth in all three planes of space,

Periodontai health

Periodontal health in the context of orthodontic treat-ment goals means both adequate hard and soft tissuesupport and management of soft tissue for stabilityand esthetics.

Functional occlusion and seated condyiar position

A fundamental aspect of orthodontic correction is theneed for coordination of tooth position with jaw func-tion.''-' Roth*' added further keys that relate Andrews'static occlusal goals^ to occlusal function and devel-oped the orthodontic treatment mechanics that makeit possible to attain functional occlusion treatmentgoals orthodontically.

A number of practitioners have advocated mount-ing diagnostic study casts in the seated condylar posi-tion,'"-" while others " - "- " have outlined practicaltechniques for accomplishing condylar position treat-ment goals orthodontically. If the treatment goal iscoordinated tooth and jaw function (as is taught in alldentai schools throughout the nation), then diagnosisfrom and treatment toward the seated condylar posi-tion is of paramount importance.

SEATED CONDYLAR POSITION

Definition

The seated condylar position is defined as superior,anterior, and midsagittai, centered transversely (Fig I).This is the essence of optimal temporomandibularjoint form and function. *"-'*' It has been shown thatthe overwhelming majority of the human populationexhibits an occlusal prematurity on the most posteriortooth. '•"" ' Traditional orthodontic study casts (hand-held casts trimmed in MIC-CO) do not reflect thisfact. When a premature occlusal contact (Fig 2) ispresent, the condyle is distracted or displaced down

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and away from the optimal seated position, in order tointercuspate the teeth into MIC-CO {the occlusion-dictated condylar position),

Condylar dhti-action or displacement is defined asthe difference in condylar position between the seatedand unseated (occlusion-dictated) positions (the posi-tion of the condyle caused hy intercuspation of theteeth). Most condylar displacements arc vertical dis-placements, not horizontal displacements, because thecondyle drops inferiorly in the fossa as the mandibleshifts superiorly in the region of the incisors.

Measurement techniques

Previous attempts to measure the seated condyiarposition have utilized methods such as intraoral visualestimation,'"' measurement of the hit-and-slide at theocclusal level,"" radiographs (panoramic, transcranial,or lateral cephalometric radiography, corrected tomo-graphy, and arthrography),-' and magnetic resonanceimaging or computed tomography scans,-'' However,these do not allow measurement of the mandibularfunctional shift from the unseated (occlusion-dictated)condylar position to the seated condylar position in alltiiree planes of space to 0,2 mm. In fact, it has beenshown that condylar position cannot be accuratelydetermined radiographi cal ly,•'•'"" The new gold stan-dard for the measurement of condylar position wasproposed hy the author in 1997,*'' Only three-dimen-sional condylar graph measurements made from artic-ulated study casts that have heen mounted in theseated condylar position from a deprogrammedpatient will yield this information.

Identification of the discrepancy between the seatedand unseated (occlusion-dictated) condylar position ismost accurately accomplished with diagnostic studycasts taken from a deprogrammed patient; these castsmust be mounted in the seated condylar position on asemiadjustablc articulator through the use of at leastan estimated facebow transfer, ""'-'*'-*'*-* The amount(millimeters) and direction (anteroposterior, vertical,and transverse) of any discrepancy between the seatedand unseated condylar position can he determinedwith ease through the use of condylar position instru-mentation available today {CPI; MPI; CMP;Verichcck, Denar; modified Buhnergraph, Whip Mix).

Advantages and indications

The condylar graph measurement technique has anumber of advantages:

1, It is simple and easy to perform,2, It is available to every dental practitioner,3, It is inexpensive (the most cost-effective method

available to determine condylar position),4. It is noninvasive,5, It is highly accurate (the most accurate method for

determining condylar position in all three planes ofspace to within 0,2 mm anteroposteriorly and verti-cally and 0,1 mm transversally).

The seated condylar position is a three-dimen-sional entity that must be assessed with a three-dimensional measuring device. This is a much moresophisticated and accurate method for measuringcondylar position, '' ''' ''' -'-"

Howat et aF have stated that the discrepancybetween the seated and unseated condylar positionmust he identified and eliminated when the occlusionis to he reorganized, which is required:

1, When posterior occlusal stability is to be restoredby occlusal adjustment or tooth restoration,

2, When mandibular dysfunction is to be treated.3, Before placement of multiunit restorations,4, Before fabrication of complete dentures,5, When orthodontic treatment is planned,6, When the condyle is to be positioned during

orthognathic surgery.

Success or failure of treatment in each of theseareas is completely dependent on the ability of theoperator to attain a comfortahie, stable, repeatahleseated condylar position as a reference point.

Importance to orthodontic correction

The importance of the seated condylar position inorthodontic correction is as follows: orthodontics pro-vides the ability to move every tooth in all threeplanes of space, making orthodontic treatment compa-rable to complete-mouth restoration or a completedenture setup,"*™ Thus it is imperative to have a com-fortable, stable, and repeatable seated condylar posi-tion to work from.

It has been asserted that in 25% to 30"/o of ortho-dontic cases the decision-making process would beaffected hy an articulator mounting in the seatedcondylar position, because of the presence of a signifi-cant condylar distraction,^"-" However, the clinicalexperience of the author is that this informationaffects every orthodontic case that is treated. Sevenimportant decision-making areas are affected:

1, Diagnosis:a. Magnitude (mm) of the horizontal discrepancy

(Class II, Class III) tobe correctedb. Magnitude (mm) of the vertical discrepancy

(open bite, deep bite) to be corrected

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C, Magnitude (mm) of the transverse diserepancy tobe corrected

d. Direction of mandibular growthe. Direction of tiiandibular rotation anticipated

with treatment2, Treatment planning;

a. Extraction versus nonextractiortb, Nonsurgical versus surgical treattnent

3, Anchorage requirements (minimum, moderate, ormaximum)

4, Treatment mecbanics (dictated by all of the above,especially the diagnosis and anchorage require-ments)

5, Occlusal finishing (arch coordination in all threeplanes of space)

6, Evaluation of orthodontic treatment effects1. Evaluation of orthodontic relapse

It is faster, easier, less expensive, and tnore accurateto mount diagnostic study casts in the seated condylarposition than to trim them in MIC-CO (habitual posi-tion), -'• •'•' Diagnostic accuracy is increased becausemuscle splinting is eliminated. Muscle spiinting is partof the neurotnuscular protective mechanism and pos-tures the mandible into the best tooth fit. It does notallow the operator to detect the discrepancy betweenthe seated and unseated condylar position clinically atthe chairside wben manipulating tbe jaw. Musclesplinting may disappear during orthodontic treatment,allowing the mandible to drop back, revealing a largerdiscrepancy tban at the start of treatment (dual bite).

The problem hes in tbe fact tbat the effect of mus-cle splinting is not detectable clinically."-'-'^"

Because tbe neuromusculature is programmed toclose tbe mandible into tbe best tootb fit, it is difficultto identify tbe seated condylar position throughclinical evaluation or mandibular manipulation alone.Patients avoid interferences and occlude into the besttootb fit, even at the expense of the joints. Occlusaldisbarmonies cannot be studied (or even consistentlydetected) in tbe functioning moutb because tbe mus-cles and nerve reflexes protect tbe teetb by overridingthe joint's guidance,

Neuromuscular deprogramming is the key toreproducibility.'"'^^""-^^'*-^^ Witbout deprogram-ming, it is highly unlikely tbat the seated condylarposition will be captured clinically, Tberefore what isseen in the mouth may not be wbat is really beingtreated.'- '' ' ""' «'' ^-' ' ''' '*'-^^ When indicated, a repo-sitioning splint is an extremely valuable, reversible,and conservative appliance tbat aids in tbe therapeu-tic, diagnostic, and treatment planning phases ofortbodontic correction,326.3i).6o,í3-99

This infortnation directly affects cephaiometricevaluations as well. First, a significant condylar dis-

Fig 3 Lateral cephalogram of a patient witti severe veiticai UIK-traction of ttie condyles. resulting in a notioeable joint space("arraWE,) visible superior to ttie condyie.

placement can often be detected on a routine lateralcepbaiogram; wben tbe condyie is severely distractedvertically, a noticeable joint space is visible superior tothe outline of the condyie (Fig 3). This is not normal;typically tbese structures are superimposed when thecondyie is seated near its undistracted position. If acondylar displacement is suspected on a lateraleephalogratii or corrected tomogram, then it would bepertinent to determine the fuil extent of the condylardisplacement by mounting the dental casts and accu-rately measuring the discrepancy. In addition, it hasbeen sbown that cepbalometric measurements per-formed in the seated condylar position (rather than inthe unseated or MIC-CO condylar position) yieldmore accurate diagnostic information regarding themagnitude of the skeletal and dental discrepancies inthe horizontal and vertical plan es,'"""'"^

The information gained from an articulator mount-ing in the seated condylar position and three-dimen-sional condylar graph measurements can be appliedacross tbe broad spectrum of cases routinely encoun-tered in clinicai practice. In a high percentage ofpatients, tbe interarcb relationships in the seated andunseated positions are substantially different. Tbis canbe evaluated by comparing the intraorai interarcb rela-tionsbip to the interarch relationship observed onmounted casts in tbe seated position. Tbus, these casescould each be treatment-planned a number of differ-ent ways, depending on tbe overriding treatrnentobjectives of the clitiieian.

For example, a basic treatment planning decisionthat is tTiade for all orthodontic patients is whether ornot to extract teeth and, if so, which teetb? In mosteases, an argument could be made for cither a nonex-traction or an extraction treatmetit plan, depending ona number of factors, one of wbicb is the magnitude oftbe borizontal, vertical, and/or transverse interarch

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discrepancy present, Tbis information is preciselyrevealed hy an articulator mounting in tbe seatedcondylar position. In addition, an articulator mount-ing may reveai an interarch discrepancy that may havea surgical treatment option as well as conventionalorthodontic treatment options.

Furthermore, the anchorage requirements andchoice of treatment mechanics is directiy affected,depending on the magnitude of the horizontal or verti-cal interarch discrepancy present pretreatment, whichis precisely revealed by an articulator mounting in theseated condylar position. However, the treatmentplanning and mechanÍL;al choices are limited if theoverriding treatment objective is to reduce the pre-treatment condylar displacement. Seating the condylewith orthodontic correction requires precise verticalcontrol. Reduction of the pretreatment condylar dis-placement can be achieved orthodontically throughthe use of various treatment methods (extraction,nonextraction, high-pull facehow, transpalatal bars,bite blocks, elastics, mounted tooth positioner, splintwear, orthognathic surgery, and equiiibration),

Occlusal flnishing can be more accurately accom-plished if the pre-dcband casts are first mounted in theseated condylar position. The mounting is then used intwo ways. First, it is used to assess the interarch rela-tionships near the end of treatment, allowing the clini-cian to adjust tooth positioning as needed (anteropos-teriorly, vertically, or transversaily). Often thismounting wiil reveal either posterior torque deficien-cies or transverse arch discrepancies (inclined planecontacts or arch coordination problems) that have tobe addressed to gain posterior intercuspation withoutcondylar displacement. Second, the mounting is usedto fabricate a tooth positioner from an ideal setupwith the condyle seated. The positioner is used tomaintain condylar seating while settling of the denti-tion is controlled vertically.

Moreover, the seated condylar position is thebenchmark from which true comparisons of treatmenteffectiveness (both skeletal and dental) can be made.It is the only valid reference point for comparison oftreatment effects in orthodontics. The unseated(occlusion-dictated) condylar position (condylar posi-tion in iVIIC-CO) bas inherent error as a referencepoint because of tbe lack of understanding of the mag-nitude of the mandibular functional shift (hit andslide) present before and after treatment. Failure tounderstand this principle has been the source of greatconfusion, misunderstanding, and miscommunicationin hoth dentistry in general and orthodontics in partic-ular, "'" To obtain precise measurements of the skele-tal and dental changes witb treatment, it is essential tobegin with a stable, repeatable condylar position andend with a stable, repeatable condylar position and

then assess the result. This Is how treatment efficacy isaccurately determined.

In the evaluation of orthodontic relapse, certainphenomena such as dual bites (both vertically andhorizontally), relapse of horizontal (anteroposterior:Class II, Class III) correction, relapse of vertical(superoinferior: open bite, deep bite) correction, andthe development of symptoms of temporomandibulardysfunction after orthodontic correction have previ-ously been explained as dental compensations toorthodontic corrections. However, it is now under-stood that they are often skeletal compensations(skeletal relapse) resulting from treatment to anunseated condylar position. '""^^- ''' "' ''-*''"' Thus it isapparent that diagnostic accuracy is enhanced hy anarticulator mounting in the seated condylar position.

This concept is further reinforced by Ackerman andProffit,'"' who have stated:

It is clear that the condyles should not be dis-placed during treatment by more than a smalldistance from their relaxed (retruded) position.In addition to the possibility of TMD symptoms,treatment methods that reposition the mandiblemore than a small amount are likely to fail in thelong run due to the musculature returning themandible to a seated condylar position. Whenthis occurs after treatment it is perceived asrelapse. ("The boundaries of dental compensa-tion for an underlying jaw discrepancy are estab-lished by,,,tbe neuromuscular influence onmandihuiar position.") Neuromuscular harmonyis at risk when the condyles are not within 1 mmor so of a seated position when the teeth are inMIC. This is an important soft tissue limitationon orthodontic treatment.

CASE REPORT

A 26-year-old woman presented with complaints ofmuscle contraction headaches, a nightly clenchinghabit, and crowding. Intraorally she presented with aCiass I moderately crowded occlusion (Figs 4a to 4c),Her mounted casts (made after deprogramming with acomplete-coverage maxillary stabilization splint withanterior guidance to relieve her symptoms) indicatedthat the magnitude of the horizontal and vertical dis-crepancies was greater when her dentition was in theseated condyiar position; Tbe horizontal relationshipchanged from Class I to Class II, and the vertical rela-tionship revealed a dental and skeletal open bite withmoderate crowding (Figs 4d to 4f), The distobuccalcusp of the mandibular second molar had been frac-tured off (Fig 4g), and tbe premature occlusal contact

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Figs 4a ío 4c Pretreatment inlraorai views ol Ihe patient in maximum inlercuspalion-centric occlusion.

Fig 4a Fig 4b Fig 4c

Figs 4d to 4f Pretreatment casts mounted in the seated condylar position (afler ihe patient hadbeen deprogrammed with a complete-coverage maxillary stabilization splint with anterior guidanceto relieve her symptoms). Note the premature contacts on itie mandibular left molars, the fractureddistobuccal cusp oí the mandibular leít second molar, and the increased magnitude ot the horizontal(Class 11] and vertical (open bite) interarcli discrepancies

Fig4d Fig4e Fig4f

Fig 4g Fractured rjisiobuccal cusp of themandibular letl second moiar (arrow).

Figs 4h to 4¡ PI•osttreatment intraoral .-lews ol the patient m maximum intercuspation-<;entric occlusion

Fig4h

Ou"

Fig4iFig4i

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Figs 4k and 41 Püsttreatment intraorai views of iaterai excursions, demonstiating theachievement of a mutualiy protected oociusion with canine guidance.

Figs 4m to 4o Postfreatment casts mounted in the seated condylar position. Note the reduction ofthe horizontal and vertical interarch discrepancies.

Fig 4m Fig4n Fig4o

VERTICAL CONOVIAR POSITtON

IRIWSVEflSE CONDYLAf) POSITION

ANTERIOR HOKOONJtí POSmON

VERTICAL CONDYLAR POSITION

RIFT

TRANSVERSE CONDYIAR POSITIONI L < R I J, ,

OPanaJent CPI

Fig 4p (ieñ) Pretreatment CPI condylargraphmeasurements.

Fig 4q irÍQÍ~\i) Posttreatment CPI condylargraph measurements. Note the reduction oícondylar distraction with orthodontic cor-rection and equilibration in the seatedcondyiar position

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was on these same mandibular second molars. Thegoal of orthodontic correction in this case was to gainideal alignment and occlusal interdigitation while atthe same time decreasing the condylar distraction towithin normal limits (within 1 mm of the seatedcondylar position).

Treatment included extraction of four second pre-molars (to decrease the vertical dimension of occlu-sion) instead of four first premolars; thus, the treat-ment mechanics and anchorage requirements for thispatient were substantially different (moderate to maxi-mum for first premolar extractions and minimum forsecond premolar extractions). Finishing was accom-plished with full-sized (21 x 25) braided rectangulararch wires, short vertical (Class II) elastics, a mountedtooth positioner, and complete-mouth equilibration.The symptoms were eliminated while function andesthetics were improved; total treatment time was 26months (Figs 4h to 4o), The pretreatment and post-treatment CPI recordings are shown in Figs 4p and4q; the pretreatment condylar distraction or displace-ment has been reduced by ortbodontic correction andcomplete-mouth equilibration.

CONCLUSION

It has heen shown in all areas of dentistry that theseated position is the most stähle, comfortable, andrepeatable condylar position from which extensiverestoration of the dentition should be diagnosed andtreatment planned. The techniques and instrumenta-tion that make assessment of this position possible aresimple and predictable and have proven to be faster,easier, less expensive, and more accurate than tradi-tional orthodontic diagnostic techniques. Diagnosticaccuracy and treatment execution are enhanced by theavailability of an articulator mounting in the seatedcondyiar position.

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