Occlusion, Orthodontic Treatment, and Temporomandibular … · 2010. 3. 12. · Occlusion, Orthodontic Treatment, and Temporomandibular Disorders: A Review James A, McNamara, Jr,

Occlusion, Orthodontic Treatment, andTemporomandibular Disorders: A Review

James A, McNamara, Jr, DDS, PhDProfessorDepartment of Orthodoxies and

Pédiatrie Dentistryand Research ScientistCenter for Human Growth and

DevelopmentThe University of MichiganAnn Arbor, Michigan

Donald A. Seligman, DDSAdjunct Assistant ProfessorSection of Orofaoial Pain and

OcclusionUniversity of California at Los AngelesSchool of DentistryLos Angeles, California

Jeffrey P. Okeson, DMDProfessorDepartment of Oral Health Practice

and Orofaeial Pain CenterUniversity of KentuckyOollege of DentistryLexington, Kentucky

Corresporiderice to:Dr James A McNamara, JrDepartment of Orthodontics and

Pédiatrie DentistryUniversity of MichiganAnn Arbor, Michigan 48109-1078

TTiis artide is based in part on a paperprssenied at the international Workshopon the TMDs and Reiated Pain Conditions,sponsored by Che National Institutes ofHealtti, heid in Hunt Vaiiey, Maryiand. Aprii17-20, 1994 Ttie paper wiil be pubiishsdas. McNamara JA Jr. Seiigman DA,Okeson JP The relationship ofocdusaifactors and orthodontic treatment to tem-poromandibuiar disorders. In: Sessle BJ,Bryant PS. Dionne RA. TemporomandibuiarDisorders and Related Pam Conditions. Vol4: Progress in pain research and manage-ment. Seattie, Washington: lASP Press (inpress).

A review of the current literature regardmg the interaction of mor-phologic and functional occlusal factors relative to TMD indicatestbat tbere is a relatively low association of occlusal factors m char-acterizmg TMD. Skeletal anterior open hite, overjets greater than 6to 7 7nm, retruded cuspal posttion/intercuspal position slidesgreater than 4 mm, unilateral lingual crossbite, and five or moremissing posterior teeth are the five occlusal features that have heenassociated with specific diagnostic groups of TMD conditions. Thefirst three factors often are associated with TMJ arthropathies andmay be the result of osseous or ligamentous changes within thetemporomandibular articulation. With regard to tbe relationship oforthodontic treatment to TMD, the current literature indicates thatorthodontic treatment performed during adolescence generally doesnot increase or decrease the odds of developing TMD later in life.There is no elevated risk of TMD associated with any particulartype of orthodontic mechanics or with extraction protocols.Althougb a stable occlusion is a reasonable orthodontic treatmentgoal, not achieving a specific gnathologically ideal occlusion doesnot result in TMD signs and symptoms. Thus, according to tbeexisting literature, the relationship of TMD to occlusion andorthodontic treatment is minor. Signs and symptoms of TMDoccur in healthy individuals and increase with age, particularly dur-ing adolescence: thus, TM disorders that originate during varioustypes of dental treatment may not be related to the treatment butmay be a naturally occurring phenomenon.J OROFACIAL PAIN 199S;9:73-90,

Occlusion is cited as one of the major etiologic factors withinthe acknowledged multifactorial origin of temporo-mandibular disorders (TMD),' This emphasis on occlusion

is carried over to the most recent US Medicare guidelines, whichlist "malocclusion" as one of rhe covered temporomandibuiar joint(TMJ) diagnoses,- implying that the occurrence of occlusal varia-tion is itself a disease. Despite much recent debate that suggests amore limited role for occlusal factors in TMJ pain and dysfunction,the question remains open for many in the field,̂

The assumed strong association between TMD and occlusion hasbeen a major reason that the diagnosis and treatment of these dis-orders has remained within the purview of dentistry. Numerous eti-ologic and therapeutic theories are based either partly or com-pletely on this presumed connection and have justified many of themost common treatment approaches such as occlusal appliancetherapy, anterior repositioning apphances, occlusal adjustment,restorative procedures, and orthodontic/orthognathic treatment.

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Conversely, many types of dental interventions,including routine orthodontic treatment, have beenalleged to be causes of TMD,

Despite agreement among TMD experts thatocclusion actually only has a relatively small role inthe etiologically diverse and multifactorial origitis ofTMD, the influence of occlusion continues to begreatly overrated in companson by practicing den-tists and specialists outside tbe TMD expert circle.'This considerable discrepancy between the opinionsof practicing dentists and TMD experts on tbe roleof occlusion in tbe pathopbysiology of TMD bas agreat impact on tbe contemporary quality of diag-nosis and trearment for these cbronic conditions.The ptirpose of tbis article is to correct occlusal mis-conceptions about TMD and orthodontics/ortbog-natbtc treatment maintained by popular beliefs thatare not sustained in current literature, and to putocclusion into its proper perspective relative to cur-rent knowledge about its role in TMD.

Occlusal Factors and TMD

Numerous clinical studies have investigated therelationship of occlusal factors and the signs andsymptoms associated witb TMD in relatively largepatient and nonpatient populations. Some studiesreported statistically significant associations, whileothers did not, and few cotnmon trends wereapparent. For example, Nilner' examined 749 juve-niles and adolescents and reported tbat TMD signsand symptoms were associated with centric slidesand balancing-side contacts. Egermark-Erikssonand colleagues,' after examining a random sampleof 402 cbildren, reported tbat occlusal supracon-tacts as well as many cbaracteristics of unusualtypes of occlusion (ie, anterior crossbite, anterioropen bite, Class II malocclusion. Class III malocciu-sion) were associated witb signs and symptoms ofTMD. Similarly, Brandt,' in a study of 1,342 cbil-dren, noted a positive correlation of overbite, over-jet, and anterior open bite witb TMD,

In contrast, otber investigators bave reported nosuch associations, including DeBocver andAdriaens* in 135 TMD patients, Gunn andcoworkers' in 151 migrant cbildren, and Dworkinand colleagues'" upon examining 592 subjects in ahealth maintenance organization.

Evaluation of Previous Studies

As can be seen from the above-mentioned studies,there is no universal agreement as to tbe relation-sbip of occiusa] factors to TMD. Tbese differences

in findings can be explained in part by problems instudy design. According to Seligman," some of tbeproblems are as follows:

Symptoms Are Not Disease States. Tbe mostcommon type of study used in TMD research is aninvestigation of symptoms. Thjs approach is prob-lematic because isolated symptoms are not thesame as disease. Any actual association of a symp-tom to a specific disease state may be obscuredwben only isolated symptoms are monitored. Forexample, tbe report of joint clicking would not dif-ferentiate disc displacement due to osteoarthrosisfrom simple soft tissue internal derangement.Similarly, latent muscle tenderness to palpationmay reflect problems witbin a speciftt musclegroup or may he an tndication of global chronicfibromyalgia. If tbe differences among symptomsare subtle, overlapping symptoms can mask distin-guishing morpbologic differences hy including toomany different patbologic processes m the analysis.

Lack of Differential Diagnosis. Most investiga-tions bave grouped subjects into a single diseasecategory witbout differentially diagnosing eachpatient. Thus, often it is unclear as to which dis-ease process is being studied, Fnrther, manypatient studies are purely descriptive and do notcompare patient populations with equivalent pop-ulations of bealtby individuals.

Unrepresentative Samples. In some studies, thesample population does not represent the targetpopulation, particularly with regard to age andgender. For example, it is inappropriate to extrap-olate to adults with osteoarthritis or fihromyalgiafindings from children who rarely appear aspatients with tbese conditions. The sample sbouldmatcb the target population as mnch as possible,especially witb regard to age and sex.

Lack of Factor Definition. The definitions ofthe factors being stndied must be made clear inoperational terms, witb specific criteria establishedfor each variable. For instance, when multipleocclnsal factors are grouped together into an over-all variable termed "malocclusion," it is difficult todetermine exactly wbicb factors are being investi-gated. A factor sucb as posterior crosshite in onepatient must he shown to bave the same impact ontbe analysis as does a deep overbite in anotherpatient. And if tbe efficacy of poorly definedocclusal treatments is examined (eg, occlusal equi-libration) and tbe treatment is focused on tbe cor-rection of a wide range of occlnsal conditionsratber than on tbe elimination of a single condition(eg, slides between centric occltision and centricrelation), tbe interpretation of tbe results of tbetreatment will be difficult.

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Multi factorial Analysis Not Used. Combina-tions of factors must be studied together in a mul-tifactorial analysis, rather than separately,"Isolated pairwise or sensitivity-specificity analysesattribute either major responsibility or no signifi-cant role to the occlusal factors that they examine.It is obvious that individual occlusal factors do notact in isolation from one another, and to suggestotherwise is inappropriate. With multiple factoranalysis, an estimate can be made of the relativecontribution of each factor in characterizing thepatient.

Inappropriate Groupings of Data. Everyattempt should be made to consider continuousvariables over the entire range of their occurrence.Otherwise there may be an artificial or arbitraryskewing of the resulrs. Further, the transformationof real data to unvalidated severity scales shouldbe avoided. If a ttansformation is to be performed,rhe individual measures in the severity scale mustbe shown to be roughly equivalent. For example,the number of muscles tender to palpation can bequantified. To deem this information useful, itmust be shown that a certain number of tendermuscles is of greater concern than another num-ber, and that there is no threshold of a minimumnumber of muscles before an effect is noted.

If a number of unrelated symptoms are includedin a severity scale (eg, clicking, crepitus, muscletenderness), the investigator must prove that theweighted input ascribed ro each variable is valid.In addition, if one sign or symptom is emphasizedin a given scoring system (eg, muscle tendernessover clicking), this preference for one type of fac-tor also must be shown to be valid.

Conclusions. The observations of Seligman"illustrate the necessity of examining previous stud-!es not necessarily on the basis of the conclusionsstated by the authors, but ratber by the groupsstudied, the criteria used, and the methods of anal-ysis employed.

Critical Reviews of the Literature

Two of the most comprehensive rev!ews that haveconsidered the relat!onship of occlus!on to TMDhave been published by Seligman and Pullinger,one considering morphologic occlusal relation-ships'- and the second functional occlusal relation-ships." These reviews were compiled in an attemptto determine consensus on the roles of variousocclusal factors on the pathophysiology of TMD.These investigators considered only originalresearch articles and emphasized those that usedappropriate methodology, m particular, research

that evaluated diagnostic groups or disease statesrather than symptoms. The reader is referred tothese articles for an in-depth literature review oneach subject.

Morphologic Occlusal Relationships. Seligmanand Pullinger" evaluated five identifiable factorsrelated to the static occlusion.

Overhite/Open Bite. The vertical overlap ofthe teeth should be considered as a continuousvariable. Large overbite is common in nonpatientpopulations, and thus this variable cannot be usedto define a patient population. Studies that do notconsider overbite as a continuous variable reportmixed results, W!th a majority reporting no or veryselective associations. If overbite is considered as acontinuous vanable, there is consensus that mim-mal overbtte in adults is associated with osteo-arthrosis, A reduced overbite may be a result ofosseous changes in the joint, rather than vice versa.Skeletal anterior open bite is of particular signifi-cance. This condition is characterized as a negativevertical overlap of rhe anterior teeth that often iscombined with occlusa! contacts only m tbe molarregion. Skeleral open bite is not common inasymptomatic nonpatients and usually is associ-ated with disease states demonstrating intracapsu-lar changes (eg, osteoarthrosis), Larnheim andcoworkers" among others have noted that theseocclusal changes may be a result of, rather thanthe cause of, these osseous changes. Skeletal ante-rior open bite in adults should be distinguishedfrom anterior open bite in children, as the latrermay arise from different causes (eg, rhumb suck-ing, abnormal tongue posture),

Overjet. The horizontal overlap of the teethdoes not seem to be associated with TMJ symp-toms or disease. Seligman and Pulhnger" note oneexception, namely the higher prevalence of largeoverjet in patients with osteoarthropathies of theTMJ. Pullinger and Seligman" found that althoughlarger overjets were associated with osteoarthrosispatients having a pr!or history of disc derange-ment, no such association was evident in derange-ment patients without osteoarthrosis. Despire theassociation with osteoarthrosis, large overjet iscommon in nonpatient populations as well, andthus this measure lacks specificity in def!ningpatient groups,

Crossbite. Most previous studies of crossbitehave considered younger patient populations,"'"Although asymmetric muscle activity has beenreported in children with unilateral posteriorcrossbite,"-" there is little evidence that this type ofmorphologic relationsh!p leads to TMJ symptoma-tology,"''"' Most patient studies report no greater


McMamara et al

prevalence of crosshite in patients as compared tostudies of non patients.-'•^•' Crossbites persisting inadults typically are skeletal in origin and do notappear to provoke TMD symptoms or disease. Thus,the correction of crossbites in adults to preventpotential TMD problems does not seem warranted.

Posterior Occlusal Support. Loss of posteriortooth support has been associated withosteoarthrosis,-'"' but this association becomesquestionable when tiie evaluation is controlled forage effects.-" Research on this topic, however, isscant with regard to other patient populations.One of the few studies to consider the longitudinalrelationship of the loss of posterior teeth to thehealth of the masticatory systetn has been con-ducted by Käyser-* and Witter.'' They have shownover the years that the adaptive capacity of themasticatory system is great, and that most peoplewith loss of molar support have acceptable masti-catory ftinction and no increased amount of TMDsigns and symptoms. Thus, no conclusions can bedrawn regardmg the benefits of prosthecicallyreplacing missing posterior teeth as a preventativemeasure for TMD.

Asymmetric Contact in Retruded CuspatPosition. Ii imbalances of tooth contacts exist inretruded cuspal position (RCP)/centric relation,they may be most obvious in younger patient pop-ulations,' and as with a loss of posterior dentalsupport, may be associated with age. No associa-tions of this type of disorder and TMD have beenreported in older populations. Prophylactic adjust-ment of the natural occlusion is not indicated onthe basis of published studies, but the establish-ment of bilateral contact in RCP may be a prudentrestorative goal.

Functional Occlusal Relationships. Sehgmanand Pullinger'- reviewed similar published researchconcerning the relationship of the functionalmovements of the mandible to TMD.

Balancing and Working Occlusal Contacts.Most controlled surveys fail to demonstrate anyassociation between occlusal supracontacts andTMD signs or symptoms in symptomatic nonpa-tients or in populations of TMD patients. Occlusalsupracontacts are so common and variable'" thatrhey lack the sensitivity and specificity for defining apresent or potential TMD population. Further, aprecise and reproducible method for determining thepresence of occlusal sopracontacts does not exist.

Slides Between Centric Occlusion and CentricRelation. According to Seligman and Pullinger,"the majority of past research reports little associa-tion between the length of the slide betweenRCP/centric relation and intercuspal position

(lCP)/centric occlusion and signs or symptoms ofdisorders in asymptomatic individuals. Studies ofpatients with radlographically determinedosteoarthrosis report longer slides in arthrosispatients than in controls,*'''- a finding that indi-cates that osseous remodeling or condylar lysis canbe accompanied by an increased slide. In none ofthe studies is the amount of the slide handled as acontinuous variable, thus adding bias to the inter-pretation of the data.

Occiusa! Guidance Pattern. While there is evi-dence that occlusal guidance patterns can altermuscle activity levels,̂ '̂̂ '' there is little evidence tosuggest that a given guidance pattern can provokeTMD symptomatology. Little is known concerningthe role of specific guidance patterns in particularpatient populations.

Farafunction. Bruxistn and clenching often arecited as etiologic factors in the development ofTMD, but similar to occlusal interferences, theseactivities (especially bruxism) seem to be endemicin the general population.'* Furthermore, compar-isons of groups identified according to self-reportsof parafunctional activities are suspect because ofthe universality of this activity and the lack of defi-nition as to the quantification of severity measures.Seligman and Pullinger'- state that there is increas-ing evidence that parafunction is not associatedwith chronic occlusai factors, and thus reversiblerather than nonreversible treatment should be pro-vided in attempts to prevent or minimize possibleharmful effects of this activity."

Dental Attrition. There is no evidence frommost nonpatient studies that dental attrition isassociated with signs or symptoms of TMD. Menshow greater attrition severity than women, yetthey have fewer TMD symptoms. Once again,patients with osteoarthrosis have the mostnotable occlusal changes, often demonstratingadvanced rates of attrition. These changes may besecondary to the occlusal changes resulting fromthe arthrosis.

Multiple Analysis of Occlusal Factors

The studies cited above considered the significanceor nonsignificance of occlusal factors relative toTMD as isolated factors. Pullinger and colleagues''used a blinded multifactorial analysis to determinethe weighted influence of each factor acting incombination with the other factors. The interac-tion of the following 11 occlusal factors" was con-sidered in randomly collected but strictly defineddiagnostic groups compared to asymptomatic con-trols;

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1. Anterior open bite2. Maxillary lingual posterior crossbite3. RCP-ICP slide length4. RCP-ICP slide asymmetry5. Unilateral RCP contact6. Overbite7. OverjetS. Dental midlme discrepancy9. Number uf missing posterior teeth

10. First molar relationships (the greater of themesiodistal maxillary discrepancies at thefirst molar location)

11. Right versus !eft first molar position asymmetry

The following are the diagnostic groups of Pullingerandcoworkers'":

1. Disc displacement with redtiction (n = 81)2. Disc displacement without reduction (n = 48)3. TMJ osteoarthrosis with disc displacement

hisrory (n = 75)4. Primary osteoarthrosis {n = 85)5. Myalgia only (n = 124)6. Asymptomatic normals (n = 147)

The asymptomatic control subjects were consid-ered the goid standard because they were withoutsigns and symptoms and had no history of TMD.The samples were demographic ally representative,and the occlusal factors studied were collectedblindly and were strictly defined. A multiple logisticregression model was used for simultaneous assess-ment of the relative odds of each potential occlusalfactor. The outcome was always the disease classi-fication versus che asymptomatic control subjects.

To control for age and gender, possible associa-tions with each continuous occlusal variable weretested using the regression analysis and nominalvariables by an unpaired t test. Of the 22 possibleassociations, only four were significant, and threeof the four variables {overjet being the only excep-tion) were not contributing factors in differentiat-ing patients from controls. Thus, genders and ageswere combined in this analysis.

Findings in Healthy Subjects. Wide variationsin occlusal features were noted in the asymp-tomatic control group, including overjct from -1to 6 mm, overbite from —2 to 10 mm, midline dis-crepancies to 5 mm, anteroposterior molar rela-tionsbips from -6 to 6 mm, molar asymmetriesfrom 0 to 6 mm, and RCP-ICP slides up to 2 mmin length. In addition, a wide variety of crossbites,asymmetric slides, retruded posterior contacts, andsevere attrition facets were observed. Skeletal ante-rior open bite relationships were not observed.Thus, variations in occlusal morphology are the

norm in healthy individuals, indicating the capacityof the human masticatory system to adapt to a widevariety of morphologic and functional features.

Pullinger and coworkers'" proposed a new defi-nition of "normal" within the context of TMD,that being those occlusal features that exist with-out significant elevated risk of disease. Such "nor-mal" features include RCP-ICP slides of 2 mm orless, deep overbite, minimal overjet, midline dis-crepancies, all Angle classifications of occlusion,unilateral RCP contacts, and less than five missingposterior teeth. These factors alone cannot defineeither TMD patients or asymptomatic individuals.

Findings in Patient Populations. No singleocclusai factor was able ro differentiate patientsfrom healthy subjects. There were four occlusa!features, however, that occurred mainly in TMDpatients and were rare in asymptomatic individu-als: rhe presence of a skeletal anterior open bite,RCP-ICP slides of greater than 2 mm, ovcrjets ofgreater than 4 mm, and five or more missing andunreplaced posterior teeth. Unfortunately, all ofthese signs are not only rare in healthy individuals,but also in patient populations, indicating hmiteddiagnostic usefulness of these features.

Pulhnger and coworkers^" concluded that manyocclusal parameters that traditionally were believedto be influential contribute only minor amounts tothe change in risk in rhe multiple factor analysisused in their study. They reported that although therelative odds for disease were elevated with severalocclusal variables, clear definition of disease groupswas evident only in selective extreme ranges andinvolved only a few subjects. Thus, they concludedthat occlusion cannot be considered the mostimportant factor in the definition of TMD.

Puilinger and colleagues" noted, however, thatthe results of their study indicated that occlusalfactors do contribute to TMD. Combinations oftwo to five of the occlusal parameters, involvingeight of the 11 factors, contributed to risk for dis-ease. These investigators stated that more com-monly used statistical methods, such as robustpairwise testing, would have ignored some of thesevariables. The minor elevation in odds ratiorevealed by tbe multiple factor analysis indicatesthat specific occlusal factors are making some bio-logic contribution and thus cannot be ignored.They state further that a biologic system mustadapt to its various morphologic features until sta-bility is achieved, and some occlusa! features mayplace greater adaptive demands on the system.While most individuals compensate without prob-lems, adaptation in others may lead to a greaterrisk of dysfunction.

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Some occlusal differences between diagnosticgroups were reported," For a clinically perceptibleinfluence to be significant, Pullinger and cowork-ers'' stated that an occlusal feature would need toat least double the risk of disease (at least a 2:1mean odds ratio). Only five occlusal conditionsreached this threshold:

Anterior Open Bite. The highest odds ratiowas for anterior open bite, and this occlusal mani-festation was seen predominantly in hoth theosteoatthrosis and the myalgia-only groups, anobservation noted previously by Seligman andPullinger" and Stegenga,'" For anterior open bite tobe shown as an etiologic factor in rhe developmentof osteoarthritis, some evidence of this occlusal fac-tor should exist in other diagnostic groups thoughtto be conditions often preceding osteoarthrosis.However, anterior open bite was not common indisc displacement disorders, with or without reduc-tion. Further, Pullinger and coworkers*' noted thatmost osteoarthrosis and myalgia patents did notpresent with anterior open bite,

Overjets Greater Than 6 to 7 mm. Over|ets ofgreater than 4 mm were associated with the likeli-hood of osteoarthrosis, the same disease groups asthe anterior open bite populations. There was nocontribution to the TMJ derangement patients,Pullinger and coworkers'' stated that some largeoverjers in adults can be secondary to the condylarrepositioning seen with advanced osteoarthrosis.An overjet of 6 mm or larger was needed for asubjecr ro be assigned to one of these disease clas-sifications with an odds ratio of at least 2:1, Theoccurrence of a progressively increasing overjet inaduirs should alert the clinician to evaluate apatient for other signs of TMD disease.

RCP-ICP Occlusal Slides. Small occlusalslides, mostly under 1 mm, were common in allpatient groups and normals, but sagittal slideslonger than 2 mm were found in the diseasegroups only. None of the asymptomatic subjectshad occlusal slides greater than 2 mm, and only6% had slides longer than 1 mm, Puilinger andcoworkers" found that larger slides occasionallywere associated with degenerative changes withinthe TMJ. A slide of 5 mm or greater would be nec-essary to reach a 2:1 odds ratio threshold fornotable risk, and this ratio never was observed inthe patients. Thus, the effective clinical contribu-tion of this factor was determined to be minimal.

Because an occlusal slide has not been shown tobe a contributor to the TMD equation, the pro-phylactic elimination of most slides through clini-cally relevant occlusal equilibration procedures isnot indicated. Even in the presence of what may

appear to be symptoms associated with an occlusalslide, the removal of a large discrepancy betweencentric occlusion and centric relation may not beadvisable because the slide may be a consequenceof an articular disorder (eg, primary arthrosis)rather than as a result of occlusal factors. It shouldbe noted that the above three factors that haveemerged from the multiple factor analysis have aprimary association with osseous and ligamentouschanges within the articular compartments of thetemporomandibular joints. These occlusal factorsmay in fact be a result of, rather than a cause of,these joint changes.

Unilateral Maxillary Lingual Crossbite. Thisocclusal feature, occurring in about 10% of theadult population, has a greater risk for assignmentto the TM] derangement groups. Nearly one fourthof the nonreducing disc displacement patientsincluded this feature, and the odds ratio that anindividual with this type of crossbite also wouldhave TMJ disc displacement with reduction wasover 3:1,'' Similar odds ratios were seen for the discdisplacement group without reduction (2.6:1) andalso In the osteoarthrosis with disc displacement his-tory group (1,96:1), Pullinger and coworkers'* notethat the persistence of an odds ratio for diseaseassociation into adulthood indicates that the adap-tive response in a small percentage of subjects mayhe less than optimal and leads to the suggestion thatfunctional adaptation to a unilateral posterior cross-bite in childhood may be made at the expense of thearticular disc through the development of internalderangement, including a few that eventuallyprogress to arthrosis. These investigators believethat a case can be made for the treatment of chil-dren with unilateral crossbites to reduce the adap-tive demands on the masticatory system.Conversely, the orthodontic correction of unilateralcrossbite in adults to prevent TMJ derangementdevelopment probably is not warranted, becauseskeletal adaptation already has occurred.

Missing Posterior Teeth. In the samples stud-ied by Pullinger and coworkers,'* extensive poste-rior tooth loss was not common. Five or more pos-terior reeth needed to be missing before rhe oddsratio of assignment to disease groups assumed aminimal critical ratio of 2:1 for osteoarthrosis withdisc displacemetit history and primary osteoarthro-sis and also for disc displacement with reduction.Age is associated with both osteoarthrosis" andtooth loss," indicating that the increase in oddsratio in patients with osteoarthrosis and more thanfour missing teeth also may be a reflection of age.Much of the increase in tooth loss in the patientscharacterized by disc displacement with reduction.

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a group of patients that generally was youngertban tbe osteoartbrosis groups, was premolarextraction as parr of an orthodontic treatmentPulhnger and coworkers" noted tbat tbe contribu-tion of tbe extraction of two to four teeth per se,for example, as part of an orthodontic treatmentprotocol, was neghgible in most cases wben otbervariables were conrrolled. As mentioned earlier,longitudinal studies of patients with multiple miss-ing posterior teeth bave sbown acceptable mastica-tory function witbout increased signs and symp-toms of TMD.-'--'

Conclusions. Tbe multifactorial analysis ofPullinger and coworkers" bas shown tbat, exceptfor a few defined occlusal conditions, tbere is a rel-atively low risk of occlusal factors associared withTMD. In a subsequent reanalysis of these data,Seligman" has estimated that overall contributionof occlusal factors m defining TMD patients prob-ably is from 10% to 20%, wbich leaves 80% to90% of tbe TMD patient characteristics unex-plained by tbeir occlusion. None of these studiescan identify a cause and effect relationship ofocclusal factors to TMD. However, tbe fact tbattbe correlation coefficients usually are in the .3range explains less tban 10% of the variation. In aspecific disease state, the causative agent usuallyexplains 80% to 90% of tbe variation.

Orthodontic Treatment and TMD

Although long recognized by orthodontists as aclinical problem, little emphasis was placed on thediagnosis and treatment of TMD within rbe spe-cialty until about tbe mid-1980s. Traditionally,scant mention was made of Tt.lD treatment in tbecurricula of graduate programs in orthodontics,and only cursory examinations of tbe TMJ regionwere conducted in routine ortbodontic clinicalexaminations.

However, the interest of the orthodontic com-munity was awakened abruptly in tbe late 1980sfollowing litigation that alleged tbat orthodontictreatment was tbe proximal cause of TMD inortbodontic patients, witb substantial monetaryjudgments being awarded to several plaintiffs.'"This litigious climate stimulated the AmericanAssociation of Orthodontists not only to sponsor aseries of risk management teleconferences andnewsletters, btit also to underwrite researcb con-cerning the relationsbip of ortbodontic treatmentto TMD. Tbis series of clinical studies, tbe resultsof wbicb were publisbed in tbe January 1992 issueof tbe American Journal of Orthodontics and

Dentofacial Orthopedics, reported that ortbodon-tic treatment generally is not a primary factor inTMD, Yet, this controversy is not sertled, as isindicated by tbe recent viewpoint article ofThompson" that once again cites faulty intercus-pation of tbe teetb and dental intrusions into tbefreeway space as two of the many etiologic factorsthat may lead to TMJ dysfunction and its sequelae.

Review of tbe Literature

Prior to 10 years ago, surprisingly few method-ologically sound clinical studies regarding therelationsbip between ortbodontic treatment andTMD had heen publisbed. In a comprehensivereview of the literature on this subject that waspublished between 1966 and 1988, Reynders"divided 91 publications into three categories:viewpoint articles, case reports, and samplestudies. The most numerous were viewpointarticles {n = 55), publications that usually wereanecdotal in nature, stating the opinion of theauthor regarding tbe orthodontic-TMD relation-sbip. Little (or more commonly no) data werepresented to support the opinion. Further,Reynders" notes tbat 23 of the 55 viewpointarticles were published in The FunctionalOrthodontist, with articles advancing the con-cepts that ortbodontic treatmenr can eithercause or cure TMD. The second most frequenttype of article (n = 30) was tbe case report, acategory of publicarion that described the influ-ence of certain orthodontic treatment modalitiesused in one or more patients on the signs andsymptoms of TMD, Tbe least numerous (n = 6)were in tbe tbird category of sample studies,investigations tbat reported data from largesample groups. Tbese studies were of variablequality, often baving tbe same méthodologieproblems and limitations as discussed previouslyfor studies of occlusal factors. Since 1988, asubstantial number of clinical investigationsbave considered the association of orthodonticsand TMD (Table 1),

Viewpoint articles, of course, are not suitablefor critical evaluation of associations between twoentities sucb as orthodontic treatment and TMD;tbey are, however, useful in identifying questionstbat may be wortby of scientific investigation.Some of tbese questions are as follows:

1. Wbat is the prevalence of signs and symptoms ofTMD in orthodontically untreated populations?

2, Does orthodontic treatment lead to a greaterincidence of signs and symptoms of TMD?

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Table 1 Major Studies of the Relationship Between Orthodontic Trearment and Signs andSymptoms of TMD

Author

Sadowsky and BeGole, 1980^

Larsson and Rönnerman, 1981"

Jandon ani Hasund, 1981='

Sadowsky and Poison, 1984"

Ranchera,1985"DibbBts and van der Weele,19a78'

Dahletal, 1988''

Smith and Freer, 1989"

Sadowsky el al, 1991'^Dibbets and van der Weele, 1992«

Lu ecke and Johnston, 1992'-Artunelal, 19928=

Kremenak et al, 1992a''Kremenaketal, 1992b^'Egermark and Thilarder, 1992'™

Paquette el al, 1992"Luppanapornlarp and Johnston, 1993"

Beattieetal, 1994'=

Sample

75 treated75 untreated

23 treated60 treated30 untreated207 treated214 untreated

22 treated135 treated

51 treated47 untreated

87 treated28 untreated! 60 treated92 treated

42 patients63 treated65 treated109 treated402 mixed

63 orthodontic patients62 orthodontic patients63 orthodontic patients

Appliance

Fixed

FiKedFinedFunctionalFixed

FunctionalFixed 172)Functional 163)

FixedFunctionalFixed

RxedFixed

FunctionalFixedFixedFixedFixedFixedFunctionalFixedFixedFixed

Tooth extraction

No

NoYes

No

NoYes

No

No

YesYes

YesYes

YesNo

No

YesYesYes

Relationship

No

Improve rrertImprovement

No

NoNo

No

No

NoNo

NoNoNoNoImp rove merit

NoNoNo

7.

Does the type of appliance (eg, fixed versusfunctional; orthodontic versus orthopedic)make a dtfference?Does the removal of teeth as part of anorthodontic protocol lead to a greater inci-dence of TMD?Can orthodontic treatnient lead to a posteriordisplacement of the mandibular condyle?Should the occlusions of orthodontic patientshe treated to specific gnathologic standards?Does orthodontic treatment prevent TMD?

Although the literature is not as extensive on therelationship of orthodontics to TMD as it is to theocclusal/TMD relationship, the questions outlinedabove have been addressed in a substantial numberof recent studies. These reports are discussed indetail below, wirh many of rhe investigations con-sidering more than one question.

Occurrence of Signs and Sytnptoms of TMD inHealthy Individuals. We previously have seen theimportance of studying healthy asymptomatic pop-ulations in assessing the reiat!onship of occlusalfactors to TMD. Such is the case when orthodonticpopulations are considered.

Numerous epidemiologic studies have examinedthe prevalence of signs and symptoms associatedwith TMD in a wide variety of subject populations(Table 2), In general, the prevalence has beenshown to be statistically significant, with an aver-age of 32% reporting at least one symptom ofTMD, and an average of 55% demonstrating atleast one clinical sign.

Cross-sectional epidemiologic studies of specificadult nonpatient populations indicate that at anygiven time, between 40% and 75% have at leastone sign, and ahout one third report at least onesymptom of TMD,"""" According to Montegi andcoworkers,"" the point prevalence of symptoms inchildren and teenagers is lower, about 12% to 20%,

Because of the longitudinal nature of orthodon-tic treatment (eg, 2 to 3 years for adolescents; 5 to7 years for patients starting a two-phase treatmentprotocol in the early mixed dentition], an under-standing of the changes in the signs and symptomsof TMD in a healthy population is essential.Several investigators have noted that signs andsymptonis of TMD generally increase in frequencyand severity, beginning in the second decade oflife."'""''" Wanman and Agerberg"^ have noted that

8 0 Volume 9, Number 1, 1995

íicNamara et al

Table 2 Epidemiologie Studies of the Signs and Sympto

Author

Nilnerand Lassing, 1981'°'Egemiark.Enksson et al. 1981""

Gazitet al, 1984'°'Nilner 1986^Swanljung and Rantanen, 1979'"Solberg et al. 1979'°"

Pullinger et al, 1988 '̂

Rieder et al, 1983"^

Ingervallet al, 1980'*Osterberg and Carlsson. 1979'°'Agerberg and Inkapoöl, 1990'^De Kanter et al, 1993"Magnussen et al, 1993"

Glass et al, 1993'°»Tanne et ai, 1993"°

Totals*:

No. ofindividuals

440136131

135369309583739

222

1.040

389334637

3,463293

534

323

No. offemales/ma les

218/22274/6261/7059/76

181/188162/147341/256370/369

102/120

653/387

0/389198/186323/314

1815/1653164/129

317/217146/86

n ^ 10.032 (symptoms)n= 9,205 (signs)

Age(years)

7-147

111510-1815-1818-6419-25

19-40

13-86

21-547018-6415-7417-25

18-653-29

Population

Swedish childrenSwedish childrenSwedish childrenSwedish childrenIsraeli childrenSwedish childrenFinnish workersAmericanuniversity studentsDenial hygiene anddental sludentsAmerican privatepracticeSwedish reservistsSwedish retireesSwedish adultsDutch nationalsSwedish youngadultsKansas City aduitsProspectiveorthodonlic patients

Prevalence

At least onesymptom

3639677456415826

39

33

1559142243 (only!

46 loniy)16

n = 3.254= 32%

At least oneclinical sign

7233466144773676

48

50

6037SB45

15

n = 5.023= 55%

AdaplEd and eitparäsu from OkesoiThe rumbers of subjects with symfol sub|ects exhibiting al least one sjsymptom and 55% had at ieast one

itoms and clmicai signs were determined for each study by multipiying the totai number of subjects by the percentage•mptom and at ieast one ciinicai sign For the total number ol sut^ects considered in tiie tabie. 32% had at least one

the incidence of joint sounds in young adults intheir late teens can be as high as 17.5% over a 2-year period. Thus, the occurrence of joint soundsduring orthodontic treatment must be consideredwithin the context of longittjdina! changes in acomparable untreated population studied duringthe same time interval.

Orthodontic Treatment Versus No Treatment.Two of the first investigations sponsored by theNational Institutes of Health to consider the rela-tionship between orthodontics and TMD were ini-tiated about 15 years ago (Table 1). These researchefforts considered the prevalence of TMD and thestatus of the "functional occltision" (to be dis-cussed later) in large groups of subjects who hadundergone orthodontic treatment at least 10 yearspreviously.

Sadowsky and BeGole'" reported on the findingsfrom a University of Illinois study of 75 adult sub-jects who, at least 10 years previously, had beentreated with full orthodontic appliances as adoles-cents. The treated group was compared to a group

of 75 adults with untreated malocclusions. In asubsequent article by Sadowsky and Poison,*' thesample from the Illinois study (increased to 96treated and 103 controls) was compared co a treat-ment group of 111 subjects who had been createdat least 10 years previously at the Eastman DentalCenter and a control group of 111 individualswith untreated malocclusions. In the two studies,15% to 21% of the subjects presented with one otmore sign of TMD and 29% to 42% had at leastone or more symptom of TMD, usually jointsounds. There were no statistically significant dif-ferences between the treated and untreatedgroups." The results of these two studies provideevidence in support of the concept that orthodon-tic treatment performed during adolescence gener-ally did not increase or decrease the risk of devel-oping TMD later in life.

Another study of the long-term effects oforthodontic treatment was conducted by Larssonand Rönnerman.'' They evaluated 23 adolescentpatients who had been treated orthodontically at

Joumal of Orofacial Pain 8 1

McNamara et al

least 10 years earlier. Eighteen of the patients weretreated with fixed appliances, while five patientsreceived activator treatment. Using the Helkimoindex" as an evaluative tool, mild dysfunction wasrecorded in eight patients, while one patient hadsevere dysfunction. Comparing their results topublished epidemiologic studies, Larsson andRönnerman'^ stated that comprehensive orthodon-tic treatment can be undertaken without fear ofcreating TMD problems.

Dahl and coworkers'* examined 51 suhjects 5years after the completion of orthodontic treat-ment. Signs and symptoms of TMD were notedand compared to the findings from a similar groupof 47 untreated individuals. According to theauthors, "nobody really bad craniomandibular dis-orders" in either group. Severe symptoms (eg, dif-ficulties in wide opening, locking, pain onmandibular movement) typically were notobserved; however, mild symptoms (eg, jointsounds, muscle fatigue, stiffness of the lower jaw)were observed more frequently in the untreatedgroup than in the treated group, a difference thatwas statistically significant. Dahl and coworkers"noted thar the number of subjects in both grotipswho had at least one mild symptom was relativelyhigh (70% in the treated group, 90% in theuntreated group), especially in comparison to thepreviously mentioned investigation of Larsson andRönnerman,*' which reported a 27% occurrence ofmild dysfunction in their treated patients. Theyreported that differences between samples may bedue as much to measuring differences (eg, lack offactor definition, differences in the interpretationof the criteria of the Helkimo index) as to a truereflection of differences between groups.

Rendell and colleagues* examined 462 patientsreceiving treatment in an orthodontic graduate clinic(90% adolescents, 10% adults), using a modificationof the Helkimo'"' index. Eleven of the patients pre-sented with TMD signs/symptoms prior to treat-ment. During the 18-month study period, none ofthe patients who had been free from signs/symptomsat the beginning of treatment developed signs orsymptoms of TMD. No clear or consistent changesin the levels of pain and dysfunction occurred duringthe treatment period in those patients with preexist-ing signs or symptoms. Rendell and coworkers™ con-cluded that a relationship could not be established intheit patient population between orthodontic treat-ment and either the onset or the change in severity ofTMD signs and symptoms.

One of the few clinical studies to report positivefindings is the investigation of Smith and Freer, '̂which examined S7 patients treated with full

orthodontic appliances in adolescence. About twothirds of rhe sample had permanent teeth removedas part of the treatment protocol. The treatedgroup was compared to an untreated controlgroup of 28 individuals. Four years following theend of retention, symptoms were found in 21% ofthe treated group and 14% of the control subjects,a difference that was not significant statistically.However, the investigators noted a single sign thatwas statistically significant, the exception being theassociation between what they termed "softclicks" and previous treatment. Soft clicks werefound in 64% of the treatment group and 36% ofthe untreated group. They, however, did not findany difference in joint sounds (ie, crepitus as deter-mined by stethoscopic examination) between thetwo groups. Interestingly, the authors concludedthe article by stating: "The null hypothesis thatthere is a significant association betweenorthodontic treatment and occlusal or joint dys-function has been rejected by nearly all previouslyrepotted studies and continues to be rejected bythe present study."

There have been relatively few prospective stud-ies that have examined the relationship oforthodontics to TMD. The two major investiga-tions have been conducted at the University ofGroningen in the Netherlands (to be discussedlater) and at the University of Iowa.""™ In the lat-ter ongoing study, 30 new orthodontic patientshave been enrolled annually since 1983. Themethod of Helkimo" has been used to collectTMD data prior to orthodontic treatment and atyearly intervals following the completion of treat-ment. Patients were treated using comprehensiveedgewise appliances with and without extractions.No longitudinal data on a comparable untreatedpopulation were obtained.

Kremenak and coworkers" have reported datafrom pretreatment and posttreatment examina-tions from 109 patients. Data on follow-up exami-nations from 1 to 6 years posttreatment wereavailable on declining samples sizes of 92, 56, 33,19, 11, and 7 individuals. No statistically signifi-cant differences were noted between mean pre-treatment and posttreatment Helkimo scores forany of the various groupings. Ninety percent of thepatients had Helkimo scores that remained thesame or improved, and 10% had scores that wors-ened (an increase from 2 to 5 Helkimo points).Kremenak and colleagues'*" concluded that theorthodontic treatment experienced by their samplewas not an important etiologic factor for TMD.

Hirata and coworkers" examined 102 patientsbefore and after orthodontic treatment for signs of

82 Voiume 9, Number 1, 1995

McNamara et al

TMD. Findings from this group were compared tofmdings from 41 untreated subjects matched forage. The incidence of TMD signs for the treatmentand control groups was not a statistically signifi-cant difference.

Type of Orthodontic Mechanics Used. In theother major longitudinal study of this subject,Dibbets and colleagues"^' followed 171 patients,75 of whom were treated using the Begg technique(most patients had extractions as part of theirtreatment protocol), 66 pacienrs treated using acti-vator therapy, and 30 patients treated with chincups. The pretreatment documentation revealed astrong dependence of the prevalence of signs andsymptoms on age: from 10% at age 10 years, signsincreased to 30% at 15 years, while symptomsincreased to over 40%. They also noted that at theend of treatment, the fixed apphance group had ahigher percentage of objective symptoms than didthe functional group, bur no differences existed atthe 20-year follow-up,''

Janson and Hasund'" conducted a similar studyof adolescent patients with Class II division 1 mal-occlusion examined 5 years out of retention.Thirty patients underwent a two-phase treatmentregimen (headgear/acrivator therapy followed byfixed apphances] without the removal of teeth, and30 patients were rreared using fixed appliances fol-lowing rhe removal of four premolars. An addi-rional 30 untreated subjects were used as controls.One or more symptoms were reported in about42% of the subjects overall (treated anduntreated], with similar findings for the clinicaldysfunction index,"

One prospective study examined the effect offunctional mandibular advancement in patients withClass II division 1 malocciusion, Pancherz'* used thebanded Herbst appliance only in 22 adolescentpatients with Class II division 1 malocclusion duringa treatment period of 6 months. Following an initialmcisal edge-to-edge bite registration, Pancherzreported that a number of patients complained ofmuscle tenderness dturing the first 3 months of treat-ment. However, 12 months following treatment, thenumber of subjects with symptoms was the same asbefore treatment.

Extraction and TMD. Viewpoint articles andtexts have strongly associated the extraction ofpremolars with the occurrence of TMD inorthodontic patients,'"^ These articles are long onopinion and short on data.

The clinical studies that have dealt with thisissue have not shown a relationship between pre-molar extraction and TMD, For example,Sadowsky and coworkers" reported findings on

160 patients, 54% of whom were treated usingextraction treatment strategies. Joint sounds weremonitored before and after treatment in 87 extrac-tion patients and 68 nonextraction orthodonticpatients. Before treatment, 25% of patients hadjoint sounds, whereas 16.5% had sounds afterrreatment. Similarly, 14% of patients had recipro-cal clicking; only 8% had clicking after treatment.The investigators concluded that their findings didnot indicate a progression of signs and symptoms tomore serious prohlems during treatmenr. They alsoreported no increase in the risk of developing jointsounds regardless of whether teeth were removed.

The long-term effects of extraction and nonex-traction edgewise treatments were compared iti 63patients with Class 11 division 1 malocclusionswho were identified hy discriminant analysis asbeing equally susceptible to the two treatmentstrategies,"'"* In terms of a menu of 62 signs andsymptoms (eg, muscle palpation, joint function)that commonly are thought ro be characteristic ofTMD, there were no differences between extrac-tion and non-extraction samples. A follow-upstudy by Luppanapornlarp and Johnston" thatexamined an additional 62 "clear-cut" patients(those in the tail of the distribution] also notedthat both extraction and nonextraction samplesdemonstrated similar findings.

The longitudinal studies at the University ofIowa also have addressed this quesrion, Kremenakand colleagues'' followed three groups of patients:26 patients treated without extraction, 25 patientswith four premolars extracted, and 14 patientswith two maxillary premolars extracted. No signif-icant intergroup differences between mean pre-treatment or posttreatment Helkimo scores werenoted, A small but statistically significant improve-ment in Helkimo scores was observed posttreat-ment in both the nonextraction group and thegroup with four extracted premolars.

Dibbets and van der Weele" followed 111 of theoriginal 172 orthodontic patients in the Groningenstudy over a 15-year period. In this group, anonextraction approach was used in 34% of thepatients, four premolars were extracted in 29%,and other extraction patterns were used in theremaining 37%. Functional apphances were usedin 39%, fixed appliances (Begg) were used in 44%,and chin cups in 17% of the patients. Symptomsincreased from 20% to 62%; signs of clicking andcrepitus increased from 23% to 36% after 4 yearsand then stabilized. In contrast to the finding fromthe first 10 years during which rhere was no differ-ence between the three treatment groups withregard to clicking, after 15 years this symptom was


MoNamara el al

seen more often in tbe premolar extraction group.The authors noted, bowever, tbat clicking wasbigher in tbe premolar extraction group beforetreatment was started and concluded that the orig-inal growth pattern, ratber than the extractionprotocol, was the most likely factor responsible forthe TMD complaints seen many years posttreat-ment. Tbese investigators also noted that for asubstantial number of patients, symptoms of TMDappeared and disappeared during tbe course ofstudy. In tbe 20-year follow-up, the difference haddisappeared completely." They also noted tbateven though tbe overall incidence of symptomsincreased witb time, many previously symptomaticcbildren hecame asymptomatic at tbe time of sub-sequent evaluations.

Finally, in tbe multiple factor analysis ofocclusal factors described previously, Pullinger etaP* noted tbat the contribution of tbe extraction oftwo to four teetb per se, for example, as parr of anorthodontic treatment protocol, was negligible inmost cases when otber variables were controlled.

Ortbodontic Treatment and Posterior CondylarDisplacement. A number of viewpoint articlesbave asserted that a wide variety of tradittonalortbodontic procedures (eg, premolar extraction,extraoral traction, retraction of maxillary antenorteetb) cause TMD signs and symptoms by produc-ing a distal displacement of the condyle.'*"''"' Thisallegation is opposite to tbat of the gnathologist'sapproach to condylar position, a topic that will beconsidered in tbe next section,

Gianelly et al" used corrected tomograms toevaluate condylar position before orthodontictreatment in 37 consecutive patients aged 10 to18 years and compared them with tomogramsfrom 30 consecutively treated patients treatedwith fixed appliances (edgewise or Begg) and theremoval of four premolars. No differences incondylar position were noted between groups.Tbe position of the condyle tended to be centeredwitbin the glenoid fossa, but wide variation incondylar position was noted in both groups.

Luecke and Johnston*' evaluated the pretreat-ment and posttreatment records of 42 patientstreated with fixed appliances in conjunction witbthe removal of two maxillary premolars. Theresults of tbis study indicated that the majority ofpatients (about 70%) undergo a forward mandihu-lar displacement and a slight opening rotation ofthe mandible. The remainder of the sample haddistal movement of the condyle. Incisor changeswere essentially unrelated to condyiar displace-ment during treatment. Luecke and Johnston"stated that a change in the spatial position of the

mandible is a function of changes in tbe anteropos-terior position of tbe occluding buccal segments,rather than the relatively nonoccluding incisors.These observations also are supported by tbe find-ings of Tallents and coworkers.'*'

Tbe recall studies of Paquette and coworkers"and Luppanapornlarp and Johnston'' bave reportedno differences between groups with regard to TMDsigns and symptoms. They also noted tbat bothextraction and nonextraction treatments produceda mean mesial displacement of tbe mandible.

Arrun and colleagues" also investigated tbe rela-tionship of orthodontic treatment to posteriorcondylar displacement. Sixty-three female patientswere evaluated after routine fixed appliance treat-ment (29 with extraction and 34 witbout extrac-tion). Condylar position was measured in percentanterior and posterior displacement from absoluteconcentricity on tbe basis of sagittally correctedtomograms. The investigators did note a mean dif-ference in condylar position between the two treat-ment groups, but the difference was due mainly totbe occurrence of presumed anteriorly displacedcondyles in tbe nonextraction group (data on thepretreatment position of the condyle were notobtained). They did note that the condyles inpatients with clicking were in a more mean poste-rior position, but there was a wide variation ofcondylar position in all samples, and this variationalso extended to different tomograpbic sectionswithin the same condyle. They concluded that anyposterior condylar position was not due toortbodontic treatment,

Gnatbologic Principles and OrtbodonticTreatment. Several viewpoint articles"'"'' havemaintained tbat TMD may result from a failtire totreat orthodontic patients to gnathologic standardsthat include the establishment of a "mutually pro-tected occlusion" and proper seating of themandibular condyle witbin the glenoid fossa (incontrast to tbe more anterior position of thecondyle advocated by tbe so-called "functionalorthodontists"). The gnathologists claim tbat non-functional occlusal contacts, wben introducedthrough ortbodontic treatment, can. lead to signsand symptoms of TMD.

The discussion of the relationship of occlusionand malocclusion to TMD presented earlier in thispaper illustrates the lack of association betweenmost occlusal factors and TMD. Pullinger andcoworkers"* reported that small occlusal slides,mosriy under 1 mm, are common in asymptomaticsubjects as well as TMD patients. Only when aslide between RCP and ICP becomes extreme (5mm or greater) does the odds ratio for disease

84 Volume 9, Number 1. 1995

McNamara et al

hecome elevated. Thus, finishing orthodontic treat-ment with a modest slide typically is within theadaptive capabilities of most patients.

Sadowsky and BeGole'^ and Sadowsky andPoison" evaluated the prevalence of nonfunctionalocclusal contacts in patients at least 10 years afterorthodontic treatment. They noted a high inci-dence of such occlusal contacts in both orthodon-tic and control groups. Similar findings have beenreported by Cohen" and Rinchuse and Sassouni,"among others.

Although it probably is prudent to establishmorpholog!C treatment goals that mimic what isobserved m untreated occlusions that have beenjudged normal or ideal, such as the "six keys ofideal occlusion" advocated by Andrews,'*'"' and totreat a patient orchodontically so rhat there is aminimal (< 2 mm) slide between RCP and ICP, theestablishment of an occlusion that meets gnatho-logic ideals probably is unnecessary, particularly inadolescent parients, and sometimes the attainmentof a gnathologic ideal may be impossible in certainadult patients.

Orthodontic Treatment to Prevent TMD.This last topic probably is the most difficult toinvestigate, given the prevalence of signs andsymptoms of TMD in healthy !ndividuals and themany types of orthodontic treatment ph!loso-phies, goals, and techniques !n existence today.The quest!on of whether orthodontic treatmentcan prevent TMD is complicated further bymany of the unsubstantiated viewpoint art!clesthat claim preventive capabilities of nonextrac-tion treatment, functional appliances, and someof the more nontraditional orthodontic treat-menr protocols (eg, second molar extraction andthird molar replacement) that have been advo-cated vigorously,"-"'''""^^

As discussed above, most studies that havecompared treated and untreated populationshave found no differences between groups in theoccurrence of TMD signs and symptoms. One ofrhe few invest!gations that found improved TMDhealth in a treated group was the sample stud!edhy Magnusson and coworkers" and Egermarkand Thilander,'°^ These invest!gators reevaluatedat 5 and 10 years respectively a group of 402children and adolescents who originally had beenevaluated cross sectionally by Egermark-Er!ksson" and Egermark and Thilander,'"" Thesample originally was divided into three groupsaccording to age (7, U , and 15 years). Aboutone third of the sample had received orthodontictreatment at the end of the final examinationperiod, Bruxism awareness and subjective symp-

toms of TMD increased in all age groups, withsymptoms slightly more pronounced in untreatedindividuals. The investigators also noted thatcUcking recorded at the first examination maydisappear at subsequent examinations and thatclicking may appear at subsequent intervalsregardless of whether the subject underwentorthodontic treatment. As in many previousstudies, the Helkimo^' index was used to measureclinical signs of TMD in the oldest age group (25years). The clinical dysfunction index outcomewas lower in those experiencing orthodontictreatment than those who had not.

As mentioned earlier, a trend toward decreasedprevalence of TMD signs and symptoms in treatedpatients also was noted by Sadowsky and Poison"and Dahl and coworkers." The signs and symp-toms of TMD in the previously treated orthodon-tic patients were seldom severe enough to say thatthese patients suffered from TMD (even if theyhad signs and symptoms).

Summary

In this paper, we have attempted to review the cur-rent literature regarding the interaction of mor-phologic and functional occlusal factors relative toTMD, We have cited the articles of Seligman andPullinger'-" as comprehensive reviews of the litera-ture on this subject. Of particular importance isthe méthodologie weakness of previously pub-lished studies, particularly with regard to the sam-ple groups studied, the criteria used for evaluation,and the method of analysis employed.

The multiple factor analysis of Pullinger and col-leagues" has indicated that there is a relatively lowassociation of occlusai factors in characterizingTMD, This association, however, is not zero, andseveral occlusal features characterized the diagnos-tic groups:

1, Skeletal anterior open bite2, Overjets greater than 6 to 7 mm3, RCP/ICP slides greater than 4 mm4, Un!lateral lingual crossbite5, Five or more missing posterior teeth

The f!rst three factors often are associated withTMJ arthropathies and may be the result of anosseous or ligamentous change within the tem-poromandibular articulation. Overall, Seligman"estimates that the total contribution of occlusalfactors ro the multifactorial characterization ofTMD patients is about 10% to 20%, with otherfactors, both pronounced and subtle, interacting

Journal of Orofacial Pain 8 5

McNamara et al

and providing the remaining 80% to 90% of thedifferences between patients and healthy subjects.

The second part of this paper reviewed the currentliterature regarding the relationship of orthodontictreatment to TMD, Although this subject became afocus of conversation within the dental and legalcommunities in the late 1980s, little substantiveresearch on this topic was available until recently.

The findings of current research on this subjectcan be summarized as follows:

1. Signs and symptoms of TMD occur in healthyindividuals.

2. Signs and symptoms of TMD increase withage, particularly during adolescence. Thus,TMD that originates during treatment maynot be related to the treatment.

3. Orthodontic treatment performed duringadolescence generally does not increase ordecrease the odds of developing TMD laterin life.

4. The extraction of teeth as part of an ortho-dontic treatment plan does not increase therisk of TMD.

5. There is no elevated risk for TMD associatedwith any particular type of orthodonticmechanics,

6. Although a stable occlusion is a reasonableorthodontic treatment goal, not achieving aspecific gnathologic ideal occlusion does notresult in TMD signs and symptoms.

7. No method of TMJ disorder prevention hasbeen demonstrated.

8. When more severe TMD signs and symptomsare present, simple treatments can alleviatethem in most patients.

Thus, according to the existing literature, therelationship of TMD to occlusion and orthodontictreatment is minor. The important question thatstill remains in dentistry is how this minor contri-bution can be identified within the population ofTMD patients. Future research should be directedtoward developing a more complete understandingof these occlusal factors so that reliable criteria canbe developed to assist the dental practitioner indeciding when dental therapy plays a role in themanagement of TM disorders. Reliable criterialikely would spare many TMD patients significantdental therapies and related health costs. Untilsuch criteria are developed, the dental professionshould be encouraged to manage TMD symptomswith reversible therapies, only considering perma-nent alterations of the occlusion in parients withvery unique circumstances.

Acknowledgments

The authors thank Dr Gary Carter and Ms Kim Huner for theirhelp in preparing the extensive bibliography for this paper.They also thatik Drs Lysle E. Johnston, Jr, Christian S. Stohler,GLinnar E. Carlsson, and J.H.M. Dibbets l̂ or their criticalreviews of this manuscript.

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Resumen

Revisión literaria sobre oclusión, tratamiento de ortodon.cia y los desórdenes temporomandibulares

Al realizar una revisióri de la literatura con respecto a la inter-acción de los factores oclusales funcionales y morfológicosrelativos a los desórdenes temporomandibulsres IDTIvl), se haencontrado que hay una asociación relat iva niente baja en cuartoa los factores oclusales al caracterizar el desorden temporo-mandibular La mordida abierta anterior esquelética, las sobre-mordidas horizontales mayores de 6-7 mm, la posición cuspideafetruida/los deslizamientos de la posición intercuspidea mayoresde 4 mm, la mordida cruzada lingual unilateral,y S ó mas dientesposteriores ausentes son las cinco caracteristicas oclusales quehan sido asociadas con grupos de diagnóstico específicos deDTM Los primeros tres factores a menudo están asociadoscon artropatias de la articulación temporomandibular (ATM) ypueden ser el resultado de cambios en los huesos o los liga-mentos dentro de la ATM En cuanto a la relación del trata-miento de ortodoncia con los DTM, la literatura actual indica quela ortodoncia efectuada durante la adolescencia generalmenteno aumenta o disminuye las posibilidades de desarrollar DTMmas tarde. No existe un riesgo elevado de DTM asociados conningún tipo particular de técnica ortodóntica o con protocolos deextracción. Aunque la oclusión estable es un objetivo razonabledel tratamiento de ortodoncia, el hecho de no alcanzar unaoclusión específica, gnatológicamente ideal, no quiere decrr quese van a presentar signos y síntomas tem poro mandibulares Porlo tanto, de acuerda a la literatura actual, la relación de los DTMcon la oclusión y el tratamiento ortodóntico, es mírima. Lossignos y síntomas de tos DTM ocurren en individuos sanos yaumentan con la edad, particularmente durante la adolescencia;por lo tanto, los DTM que se originan durante vanos tipos detratamientos dentales quizás no estén relacionados al trata-miento, pero quizás pueden ser un fenómeno que ocurrenaturalmente.

Zusammenfassung

Okiusion, kieferortfiopádische Behandlung und Myo-arthropathien. Eine Literaturùbersicfit

Eine Übersicht der aktuellen Literatur unter Berücksichtigung derWechselwirkung von morphologischen und funktionellenokklusalen Faktoren bezüglich der Myoarthropathien zeigt einerelativ kleirie Assoziation zwischen okklusalen Faktoren undMyoarthropathien Skelettal antenor offener Biss, Overjetsgrosser als 6-7 mm, eine Abgleitbewegung von RK zu IK vonmehr als 4 mm, unilateraler Kreuzbiss und iünf oder mehrfehlende Seitenzahne stellen die fünf okklusalen [Merkmale dar,welche mit spezifischen diagnostischen Gruppen bei Myo.arthropatliien in Zusammenhang gebracht wurden Die ersterdrei Faktoren sind oft mil Kiefergelenksart h ropa thien assozúertund konnteri das Resultat einer ossären oder íigamentárenVeränderung innerhalb des Gelenks darstellen. Was eineWechselwirkung von kieferorthopädischen Behandlungen undMyoarthropathieri anbelangt, zeigt die aktuelle Literatur keinerhöhtes oder erniedrigtes Risiko des Auftretens einer Myo.arthropathie im Erwachsenenalter, wenn eine kieferortho.pädiEche Behandlung in jugendlichem Alter durchgeführt wird.Es existiert kein erhöhtes Risiko fur das Auftreten einerMyoarthropathre durch irgendeine kieferorthopadrsche Technikoder durch Extraktionen, Obwohl eine stabile Okklusion einvernünftiges kieferorthropadisches Befiandlungsziel darstelt, hatdas Verfehlen einer gnathologisch idealen Okklusion keineMyoadhropathie zur Folge Daher ist m Übereinstimmung mitder existierenden Literatur die Beziehung zwischenMyoarthropathien und Okklusion beziehungsweise kiefer-orthopädischer Behandlung unbedeutend, Zeichen undSymptome einer Myoarthropathie treten bei gesundenIndividuen auf und nehmen mit dem Alter zu, vor allem wahrendder Adoleszenz, Daher sind Myoarthropathien, welche währendverschiedener Arten von zahnarztlicher Behandlung auftreter,nicht gezwungenermasseri mit der Behandlung verbunden, son-dem können ein natürlich auftretendes Phänomen darstellen.


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Occlusion, Orthodontic Treatment, and Temporomandibular … · 2010. 3. 12. · Occlusion, Orthodontic Treatment, and Temporomandibular Disorders: A Review James A, McNamara, Jr,