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Temporomandibular Disorders: Effectsof Occlusion, Orthodontic Treatment,and Orthognathic SurgeryJEFFREY C. POSNICK, DMD, MD

Incidence of Temporomandibular Disorders

in the General Population and the BasicTreatment Approach

Mandibular Range of Motion

Review of Occlusal Factors and Associationwith Temporomandibular Disorders

Occlusal Conditions More FrequentlyAssociated with TemporomandibularDisorders

Orthodontic Treatment and Its Effects onTemporomandibular Disorders

Association of Jaw Deformities, Orthognathic

Surgery, and Temporomandibular Disorders Brief Overview of Okesons Thinking About

Temporomandibular Disorders and theEffects of Occlusion

Personal Thoughts About the Role of OpenJoint Procedures for TemporomandibularDisorders

Conclusions

average of 55% demonstrates at least one clinical sign.*Schiffman and colleagues completed a cross-sectional epi-demiologic study that indicated that, at any given time,between 40% and 75% of individuals who were notcurrently seeking treatment had at least one sign of MD,and about one third of individuals reported at least onesymptom of MD.296Mongini and colleagues documenteda prevalence of MD symptoms in children and teenagersof 12% and 20%, respectively.210Wanman and colleaguesshowed an incidence of joint noise in young adults in theirlate teens to be as high as 17.5% over a 2-year period. 345

MDs remain a frequent cause of visits to primary carephysicians, otolaryngologists, internists, and pediatricians.Despite the high incidence of MDs, their natural historysuggests that, in up to 40% of patients, symptoms resolvespontaneously.296

MD includes various signs and symptoms of the tem-poromandibular joint (MJ), the masticatory muscles, andrelated structures (Figs. 9-1 through 9-8). Tese may includea spectrum of referred head and neck pain; joint noise (e.g.,popping, clicking, crepitus); reduced or altered mandibularrange of movement as a result of muscle spasm or discdisplacement; condylar head erosion; and direct pain onpalpation of either the MJ or the masticatory muscles. Te

signs and symptoms associated with MDs can also lead tomisdiagnosis.16,112,171,216,342

A wide variety of often contradictory conservativetreatment modalities (i.e., non-invasive or potentiallyIncidence of Temporomandibular

Disorders in the General Populationand the Basic Treatment Approach

Te prevalence of temporomandibular disorders (MDs) inthe general population as reported in the literature varieswidely. It is estimated that an average of 32% of the popula-tion reports at least one symptom of MD, whereas an

*References 22, 24, 39, 40, 50, 80, 81, 83, 94, 95, 116-118, 120, 122, 126, 139, 147, 148, 151, 161, 170, 173, 175-177, 181, 183, 190-195,199, 207, 214, 218, 220-221, 223, 244, 251, 252, 262, 264, 270, 277, 300, 301, 319, 326, 343, 345, 348

Text continued on p. 269


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2CHAPTER 9 Temporomandibular Disorders: Effects of Occlusion, Orthodontic Treatment, and Orthognathic Surgery

Figure 9-1A,Intraoral frontal view of dentition juxtaposed with the underlying alveolar bone. B,Intraoral lateral view of dentition juxtaposedwith the underlying alveolar bone. From Okeson JP: Management of temporomandibular disorders and occlusion,St. Louis, 2012, Elsevier,

p 3, Figures 1-1, Aand B,1-3, and 1-4.

A1

A2

B1

B2

Figure 9-2Lateral view of the craniofacial skeleton. From Okeson JP: Managementof temporomandibular disorders and occlusion,St. Louis, 2012, Elsevier, p 4, Figure 1-5.

Parietal

bone

Occipital

bone

MandibleZygomatic bone

Maxilla

Nasal bone

Sphenoid

bone

Temporal

bone

Frontal bone


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266 SECTION 1 Basic Principles and Concepts

Figure 9-3Bony structures (components) of the temporomandibular joint. MF,Mandibular fossa; AE,articular eminence;STF,squamotympanic fissure. From Okeson JP: Management of temporomandibular disorders and occlusion,St. Louis, 2012,

Elsevier, p 4, Figure 1-12.

MF

AE

AE

AE

MF

STF

Figure 9-4 Anterior cross-sectional view of the articular disc, the fossa, and the condyle.A,Illustration. B,Cadaver speci-men. The disc adapts to the morphology of the fossa and the condyle. LP,Lateral pole; MP,medial pole. From Okeson JP:

Management of temporomandibular disorders and occlusion,St. Louis, 2012, Elsevier, p 8, Figure 1-14.

DISC

MPLP

BA

LP

MP

DISC


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Figure 9-5A,Lateral view illustrations and B,cadaver specimen views of normal movement of the condyle and disc during vertical mouthopening. As the disc moves out of the fossa, it rotates posteriorly on the condyle. First, rotational movement occurs (predominantly in the lower

joint space). After that, translation takes place (predominantly in the superior joint space) as mouth opening continues.A from Okeson JP:Management of temporomandibular disorders and occlusion,St. Louis, 2012, Elsevier, p 17, Figure 1-30. Bcourtesy Terry Tanaka, MD, San

Diego, Calif.

A

B


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Figure 9-6 Illustrations of the normal functional movement of the condyle and disc during the full range of opening and closing. Thedisc is rotated posteriorly on the condyle as the condyle is translated anteriorly out of the fossa. The closing movement is the exact

opposite of the opening movement. From Okeson JP: Management of temporomandibular disorders and occlusion,St. Louis, 2012,

Elsevier, p 19, Figure 1-31.

1

5

28

37

46


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Figure 9-7 Illustration of rotational movement of the mandible. Thismovement occurs with the condyles in the terminal hinge position. This

pretranslation opening will occur until the anterior teeth are approxi-

mately 20 to 25 mm apart. From Okeson JP: Management of tem-

poromandibular disorders and occlusion, St. Louis, 2012, Elsevier,

p 64, Figure 4-7.

Figure 9-8 The second stage of movement during mouth openingis illustrated. Note that the condyle is translated down the articular

eminence as the mouth rotates open to its maximum limit. From

Okeson JP: Management of temporomandibular disorders and occlu-

sion,St. Louis, 2012, Elsevier, p 64, Figure 4-8.

reversible) have been recommended to alleviate thesymptoms of MD and to prevent recurrence.*Enthusiasmby clinicians for the direct surgical alteration of the struc-tures that comprise the MJ to treat MD have waxedand waned over the past half century.60,71,141,143,200,222,241,344Occlusal factors (i.e., degrees of malocclusion) areoften claimed to be associated with MD. Although it issometimes stated that orthodontic treatment increases the

prevalence of MD, it is also claimed that orthodonticmaneuvers (for at least some types of malocclusion)may reduce the signs and symptoms of MD. Studiesdocument that the correction of a baseline jaw defor-mity with malocclusion through orthodontics andorthognathic surgery improves the presenting MD in themajority of the treated patients, whereas a minority getworse.6,29,31,67,102,131,152,232,236,347,349,356,359 Tis is described ingreater detail later in this chapter.

Mandibular Range of Motion

Te expected normal mandibular range of motion andinter-incisor mouth opening is discussed periodically in theliterature.9,70,93,115,146,179,197,234,235,249,308,309,311-313,315,316,318 Evena 6-year-old child can often open the mouth to a maximum40 mm or more. Measurements of maximum verticalmouth opening with and without discomfort are considereduseful parameters of MJ health. A restricted mouthopening is considered by many to be a distance of less than40 mm. Only 1.2% of young adults open their mouths lessthan 40 mm. However, 15% of the healthy elderly popula-tion open their mouths less than 40 mm. Any lateral orprotrusive movement of less than 8 mm is considered

restricted, although the significance of this measurement isunclear.

Review of Occlusal Factorsand Association withTemporomandibular Disorders

Clinicians from a spectrum of medical and dental specialtiesoften consider malocclusion to be the major etiologicfactor of MD.An assumed strong association betweenMD and the malpositioning of the teeth serves as onereason why the diagnosis and treatment of MD is gener-

ally considered within the purview of dentistry. Many ofthe therapeutic options for the treatment of MD arebased on the idea of normalizing or neutralizing the

*References 10, 13, 20, 30, 53, 65, 72, 82, 91, 97, 113, 119, 142, 204-206, 213, 219, 238, 266, 297, 324, 328, 336, 338, 339, 360References 1, 4, 5, 8, 11, 12, 14, 15, 17, 21, 23, 26-28, 37, 38, 41, 43,44, 51, 56-58, 63, 64, 78, 79, 85-88, 92, 99-101, 106, 114, 125, 129,130, 132, 133, 136, 140, 149, 153, 162, 163, 178, 186, 188, 196, 198, 201, 202, 208-210, 215, 217, 233, 239, 242, 243, 246, 248, 250, 254-261, 263, 265, 269, 278, 280, 283-287, 298, 299, 302-307, 310, 314,317, 321, 327, 333, 337, 341, 346, 351, 357


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occlusion.135,355 Common treatment approaches to do soinclude the reversible use of an occlusal appliance or defini-tive techniques such as occlusal adjustment (equilibration),restorative dentistry, orthodontics, and orthognathicsurgery. Concurrently, it is also true that either the onset ofMD or the worsening of current symptoms is frequentlyblamed on any one of the previously mentioned treatmentregimens.

Te dental literature contains clinical studies and reportsthat claim there are causal relationships between occlusalfactors and the symptoms and signs associated with MD.Egermark-Eriksson and colleagues examined 402 childrenand reported an association between signs and symptomsof MD, specific malocclusions (i.e., Class II, Class III,anterior crossbite, and anterior open bite), and occlusalsupra-contacts.87Brandt studied 1342 children and founda correlation between MD and degrees of overbite (deepand open) and overjet.33Nilner examined 749 teenagers andyoung adults and reported an association with centric rela-tion (CR)centric occlusion (CO) discrepancies (i.e., slides),balancing-side contact slides, and symptoms and signs ofMD.220Confusion in the literature arises as independentresearch studies have drawn contrary conclusions. DeBo-ever and colleagues examined 135 individuals with signsand symptoms of MD and found no specific associationswith malocclusion.59Gunn and colleagues similarly foundno association between MD and occlusion in 151 migrantchildren that they studied.121 Dworkin and colleaguesexamined 592 individuals within a specific health mainte-nance organization and found no association between MDsigns and symptoms and specific occlusions.80

In their review article, Seligman and Pullinger pointedout that the majority of existing clinical research (up to

that point in time) did not support a clear relationshipbetween occlusion and MD symptoms.302 Tey furtherclarified that the majority of published research reliedon symptom-based data rather than discrete disease classi-fications. Seligman pointed out that symptoms like jointsounds (e.g., popping, clicking, crepitus) and pain (e.g., inthe MJ region and the masticatory system) lack specific-ity.303In addition, most published studies did not differen-tiate between MD diagnostic categories (e.g., discdisplacement, myalgia, MJ osteoarthritis). Most publishedstudies also suffered from a lack of or an inadequate controlgroup. Seligman and colleagues attempted to avoid theseshortcomings by completing a multifactorial analysis of the

risks and relative odds of an individual having a MD as afunction of 1 of 11 common occlusal features.259,304Teylooked for correlations between each of these 11 specificocclusal factors (Box 9-1) and 1 of 6 MJ diagnostic catego-ries (Box 9-2), including asymptomatic normal controlswithout MD.259

Te asymptomatic control subjects (N =147) were con-sidered the reference standard because they were withoutcurrent symptoms or signs of MD and because they hadno history of MD. Occlusal findings in the symptomaticgroup showed wide variations, including the following:

*Data from Pullinger AG, Seligman DA, Gornbein JA: A multiple logistic

regression analysis of the risk and relative odds of temporomandibulardisorders as a function of common occlusal features.J Dent Res

72:968979, 1993.

BOX9-1

Occlusal Features and Factors to Consider

in TMD*

1. Anterior open bite

2. Maxillary lingual posterior crossbite

3. Retruded centric positioninter-contact position slide

length

4. Retruded centric positioninter-contact position slide

asymmetry

5. Unilateral retruded centric position contact

6. Overbite

7. Overjet

8. Dental midline discrepancy

9. Number of missing posterior teeth

10. First molar relationships (i.e., the greater of the

mesiodistal maxillary discrepancies at the first molar

location)

11. Right versus left first molar position asymmetry

*Data from Pullinger AG, Seligman DA, Gornbein JA: A multiple logistic

regression analysis of the risk and relative odds of temporomandibular

disorders as a function of common occlusal features.J Dent Res

72:968979, 1993.

BOX9-2

Temporomandibular Joint Diagnostic Categories

to Consider in TMD*

1. Disc displacement with reduction (N =81)

2. Disc displacement without reduction (N =48)

3. Temporomandibular joint osteoarthrosis with disc

displacement history (N =75)4. Primary osteoarthrosis (N =85)

5. Myalgia only (N =124)

6. Asymptomatic normals (N =147)

Overjets ranging from 1 to +6 mm Overbites ranging from 2 to +10 mm

Midline discrepancies of up to 5 mm Anteroposterior molar relationships from 6 to +6 mm Molar asymmetries of 0 to 6 mm CRCO slides of up to 2 mm

Tere were also a wide variety of crossbites, asymmetricalslides, posterior contacts, and severe attrition facets in thecontrol group. Interestingly, no anterior open bites werefound in the control group.

Te authors concluded that what have been traditionallyconsidered malocclusions cannot be used to define or


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Overjet (>6 to 7 mm)

In the patients that were studied, an overjet of more than4 mm was more likely to be associated with osteoarthritis.Only when the overjet was more than 6 mm was there anassociation with disc displacement. Te occurrence of aprogressive overjet in adults would be suggestive of activecondylysis. It was not stated in what percentage of those

individuals with significant overjet (i.e., >6 to 7 mm) theocclusal feature was part of a developmental jaw deformityrather than occurring secondarily only after condylysis witha loss of condylar height.

Centric RelationCentric Occlusion Slides

Limited occlusal slides (i.e., 1 mm) were common in allpatient groups, including the normal controls. CRCOslides of more than 2 mm were only found in the patientswith MDs. Pullinger found that larger slides were fre-quently associated with osteoarthritis of the condylar head.He questioned the advisability of the clinicians automaticattempt to relieve the occlusal slides in all individualswhether by irreversible (e.g., occlusal equilibration, ortho-dontics, surgery, restorative dentistry) or reversible (e.g.,occlusal splints) meansbecause the observed slide may beeither adaptive or inconsequential.260

predict either individuals with MD or those who are orwill become asymptomatic. No single occlusal factor wasable to differentiate a MD patient from a healthy subject.Te authors did identify four specific occlusal features thatoccurred mainly in individuals who were symptomatic withMD (see diagnostic categories 1 through 5) and that wererarely found in those who were asymptomatic for MD (seediagnostic category 6). Te occlusal features that primarily

occurred in individuals with symptomatic MD includedthe following:

1. Te presence of a skeletal anterior open bite2. CR-CO slides of more than 2 mm3. Overjets of more than 4 mm4. Five or more missing and unreplaced posterior teeth

Pullinger and colleagues concluded that occlusioncannot be considered the most important factor in the defi-nition of MD but that specific occlusal factors do makebiologic contributions to MD and thus cannot beignored.254-261 In most individuals, they observed that thehuman biologic system will adapt to a variety of malocclu-sions in an attempt to achieve MJ stability. Te authorssurmised that some occlusal features will place greateradaptive demands on the individuals biologic system thanothers. Although most individuals are able to compensatefor their occlusal disharmony without problems, adaptationfor others may lead to a greater risk for MD. On thebasis of this data, the authors stressed the importance offive occlusal conditions, which in isolation or combinationare more likely to reach the threshold that exceeds adapta-tion for an individual and therefore results in MJ dysfunc-tion. Te high-risk malocclusions are discussed later in

this chapter.

Occlusal Conditions MoreFrequently Associated withTemporomandibular Disorders

Anterior Open Bite

Research by Pullinger and colleagues showed a strongrelationship between osteoarthritis of the condylar headwith a loss of condylar height and an anterior open-bitemalocclusion.254-261 Interestingly, anterior open bite was

not commonly associated with disc displacement disorderswith or without reduction. Myalgia (i.e., masticatory musclediscomfort) was also a frequent symptom among patientswith an anterior open bite. It is not stated in what percent-age of individuals the anterior open-bite malocclusionoccurred only secondarily as a result of osteoarthritisfollowed by a loss of condylar height with clockwiserotation of the mandible. Terefore, it is unclear what per-centage of the examined individuals with anterioropen bites had these finding as part of a developmentaljaw deformity.

NOTE: The studies by Pullinger and colleagues

seem to confirm that the occlusal features of anterior

open bites; overjets of more than 6 mm; and CRCO

slides of more than 2 mm are frequently seen in

conjunction with osteoarthritis (i.e., loss of condylar

height) and less commonly seen with disc displacementdisease. Unfortunately, it is not clearly stated which came

first: a developmental deformity with malocclusion and

then osteoarthritis or condylysis with the loss of

posterior facial height that results in a secondary jaw

deformity with malocclusion.

Unilateral Maxillary (Lingual) Crossbite

Te occlusal feature of unilateral maxillary crossbite occursin about 10% of the adult population, and it is frequentlyfound in association with MJ disc displacement with orwithout disc reduction. Approximately 25% of the patients

with non-reducing disc displacements were found to haveunilateral maxillary lingual crossbites. Tis indicated toPullinger and colleagues that disc displacement may be abiologic adaptive response of the individual to a unilateralmaxillary lingual crossbite.260 Te investigators theorizedthat these individuals may later be prone to osteoarthritis.Tey suggested that the orthodontic treatment of a unilat-eral crossbite discovered during childhood should be con-sidered as a preventative measure to reduce the adaptivedemands on the masticatory system. Tey did not come tothe same conclusion for the correction of a longstanding


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of) the osteoarthritic changes. Interestingly, when openbites are observed in children, they are rarely associatedwith MJ symptoms. In the pediatric population, themajority of observed open bites represent a developmentaljaw deformity rather than a result of osteoarthritis. Never-theless, it is recommended that, when either a child or anadult is found to have an anterior open bite, radiographicanalysis of the condylar head should be undertaken to check

for osteoarthritic changes.

Orthodontic Treatment and Its Effectson Temporomandibular Disorders

Review of the Literature

Te relationships among malocclusion, orthodontic treat-ment to improve the occlusion, and the effects on MD isdiscussed frequently in the literature.*A spectrum of orth-odontic treatment philosophies has been championed byindividual practitioners on the basis of presumed effects onMD. Te longitudinal nature of orthodontic treatment,which is often carried out over several years, means that achanging MD history would also be expected in a controlgroup that is not simultaneously undergoing orthodontictreatment. Terefore, the occurrence of joint noise (e.g.,popping, clicking) or myalgia (i.e., masticatory muscle dis-comfort) during orthodontic treatment may either be theresult of the treatment or consistent with the natural historyof the untreated individual.

Sadowsky and colleagues reported on 75 adult studypatients who had undergone orthodontic treatment withfull appliances during adolescence at least 10 years earlier.290Te treated group was compared with a group of 75 similar

adults with untreated malocclusions. Te authors also wenton to increase both their control and subject groups and toreport these additional findings several years later.291In thetwo sequenced studies, respectively, 15% to 21% of thetreated subjects presented with one or more signs of MD(e.g., joint noise), and 29% to 42% had at least one or moresymptoms of MD. Tere were no statistically significantdifferences between the treated and untreated (control)groups.

Larsson and colleagues evaluated 23 individuals whohad undergone orthodontic treatment during adolescenceat least 10 years earlier.172Mild MD was recorded in 8 outof 23 (35%) of the patients, whereas only 1 (4%) had severe

MD. Te authors compared this with published epide-miologic controls and stated that there was no difference inthe incidence of MD in the treated group versus thecontrol group.

Dahl and colleaguesexamined 51 subjects 5 years afterthe completion of orthodontic treatment and comparedthem with an untreated control group.54Te authors found

unilateral posterior crossbite in an adult, because skeletaladaptation would have already occurred. Unfortunately, theinvestigators did not clarify if the crossbites in their studypatients were the result of developmental jaw deformities(e.g., asymmetrical mandibular excess) or simply due to themalpositioning of the teeth. Tey did not specificallycomment on whether orthognathic surgery should becarried out in conjunction with orthodontics (if needed) in

young adults to correct the presenting malocclusion as away to prevent the progression of MD.

Missing Posterior Teeth (5)

Te investigators found that, when five or more posteriorteeth were missing, the incidence of MD increased. Tisincludes MD categories of both osteoarthritis and discdisplacement with or without osteoarthritis. Pullinger andcolleagues further claimed that, when two or four of theposterior teeth (bicuspids) were removed as part of anorthodontic treatment protocol, there was a negligible effecton MD.260 Other studies carried out by Kayser156 andWitter354 have also documented acceptable masticatoryfunction after bicuspid extractions and orthodontic treat-ment without increased signs and symptoms of MD.

*References 2, 3, 19, 34, 35, 42, 45-49, 52, 68, 69, 84, 89, 90, 104, 107-109, 127, 134, 137, 138, 150, 155, 159, 164, 168, 169, 182, 184, 185, 203, 224, 237, 240, 245, 253, 268, 271-276, 279, 281, 282, 288-291, 323, 325, 329-332, 334, 352, 358

NOTE: The multifactorial analysis of occlusal factors

and TMD disease categories carried out by Pullinger and

colleagues showed that, except for the few clearly

defined occlusal features described previously, there was

a low probability of a malocclusion being associated

with TMD. Seligman and colleagues estimated that the

overall contribution of occlusal factors for the defining of

patients with TMD was only in the range of 10% to20%.302The corollary is that 80% to 90% of the causative

factors cannot be explained by patients presenting

malocclusions.

In the Pullinger and Seligman study, it must be assumedthat many of the significant overjets observed in the adultsubjects were secondary deformities after condylar resorp-tion (i.e., condylysis).260Te authors did not present evi-dence to suggest that the presence of significant overbite oroverjet plays a role in the pathophysiology of non-arthriticdisorders of the MJ, and they did not show that it was a

causative factor in the observed osteoarthritis. Tey dobelieve that a combination of unilateral retruded centricposition in the presence of a clinically apparent retrudedcentric positioninter-contact position slide may encourageMJ disc displacement but that unilateral retruded centricposition per se is not associated with MD. Tey foundthat lost molar support (i.e., 4 or 5 posterior teeth) may beassociated with osteoarthrosis. Tey concluded that a dentalmidline discrepancy is not a predictor of MD develop-ment during adulthood. Anterior open bite is frequent inthe presence of condylysis or osteoarthritic changes in theMJ, but it is probably the result of (rather than the cause


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Orthodontic Treatment UndertakenSpecifically to RelieveTemporomandibular Disorders

In everyday dental practice, the establishment of a preferredintra-arch morphologic relationship of the teeth and thenthe achievement of a satisfactory inter-arch relationship ofthe teeth in one jaw to those in the other jaw (i.e., occlu-

sion) serves as the basis of treatment objectives. Accordingto a review of the literature, the establishment of a normalocclusion through orthodontic mechanics or via otherdental means carried out for the purpose of eliminating orpreventing the worsening of MD does not seem war-ranted. Pullinger and Seligman have stated five potentialexceptions to this, which were described previously in thischapter.255-261 McNamara and colleagues also stated thatprudent basic dental treatment objectives will generallyinclude the establishment of the six keys to ideal occlusionas advocated by Andrews, when feasible; the establishmentof a limited CRCO slide (i.e., 6 to 7 mm); the limiting of unilateral maxillary lingualcrossbites in children; and the establishment of a stableposterior occlusion.

Orthodontic Treatment UndertakenSpecifically to PreventTemporomandibular Disorders

Te literature also contains studies that suggest that specificorthodontic maneuvers are effective for the prevention ofMD. Te studies by Magnusson and colleagues187-192andthe study by Egermark and colleagues89suggest preventative

MD advantages related to orthodontic occlusal correc-tions. At 5 and 10 years, these investigators reevaluated agroup of 402 children and adolescents who had originallyundergone a full course of orthodontic treatment. TeHelkimo Index was used to measure clinical signs of MDin the now older age group (i.e., 25 years old). Interest-ingly, the Helkimo Index outcome was lower in those whohad undergone orthodontic treatment as compared with thecontrol group. Te studies by Dahl and colleagues andSadowsky and colleagues also demonstrated a trend(although not a statistically significant one) toward thedecreased prevalence of MD signs and symptoms inorthodontically treated patients.53,290,291Tese studies would

require further confirmation before accepting them as cred-ible indications of a cause-and-effect relationship.

Summary of Effects of Orthodontic Treatmenton Temporomandibular Disorders

McNamara, Seligman, and Okeson summarize their under-standing of the relationship between orthodontic treatmentand MDs as follows203:

1. Signs and symptoms of MD do occur in healthyindividuals.

no statistical differences in MD between the two groups.Te number of subjects in both groups who had at least onemild MD symptom was relatively high (70% in the treatedgroup versus 90% in the untreated group). Mild symptoms(e.g., joint noise), masticatory muscle fatigue, and stiffnessin the lower jaw were frequently observed in both groups.

A study by Smith and Freerexamined 87 individualswho were treated with full orthodontic bracketing during

adolescence.320 Te treatment group (N = 87) was com-pared with an untreated control group (N =28). Four yearsafter treatment ended, MD symptoms were found in 21%of the treated group and 14% of the control group; this wasnot found to be statistically significant. Te one symptomthat was statistically more common in the treatment groupwas a soft click (64% of the treated group versus 36% ofthe untreated group).

Rendell and colleaguesexamined 462 individuals (90%adolescents and 10% adults) who were undergoing orth-odontic treatment in a graduate orthodontic dental schoolclinic.267With the use of a modified Helkimo Index, only11 of the patients presented with MD signs or symptomsbefore treatment. Of the other 451 patients, during the18-month study, none developed MD signs or symptoms.For those with preexisting MD signs or symptoms (N =11), there was no consistent change in the level of pain ordysfunction reported during treatment.

Kremenak and colleagues reported pretreatment andposttreatment MD examination data from 109 patientswho were treated with full orthodontics.166,167Te HelkimoIndex scores were also compared. No statistically significantdifferences were noted between the subjects pretreatmentand posttreatment scores. Ninety percent of the patientshad Helkimo Index scores that either remained the same or

improved, and 10% of the treated patients had scores thatworsened. Te authors concluded that the orthodontictreatment provided to their patients was not an importantetiologic factor for the development of MD.

Hirata and colleaguesexamined 102 individuals beforeand after orthodontic treatment for signs and symptoms ofMD.128 Tey compared their treatment group with 41untreated controls who were matched for age. Te incidenceof MD for the treatment and control groups was notstatistically significantly different.

Studies have also been carried out to evaluate specificorthodontic treatment maneuvers and their relationship toMD symptoms and signs. Te studied orthodontic

maneuvers include the type of orthodontic mechanics used;extraction versus non-extraction therapy; orthodontic treat-ment and posterior condylar displacement; and orthodontictreatment focused on classic gnathologic principles.

NOTE: In the studies that were reviewed, no

consistent benefits or causative factors of TMD were

identified on the basis of any specific orthodontic

treatment maneuvers carried out in the treatment group

as compared with controls.


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signs and symptoms have been examined in clinical studiesfor the past several decades.*Te quality of the research andtherefore the value of the conclusions vary. Tere are justthree longitudinal prospective controlled clinical trialstudies that have been carried out to assess the effects oforthognathic surgery on MD: the studies by Onizawa andcolleagues,232 Panula and colleagues,236 and Dervis andcolleagues.67

Te study by Onizawa and colleaguessought to evalu-ate changes in the symptoms of MD after orthognathicsurgery.232 MJ symptoms in preoperative orthognathicpatients (N = 30) were compared with those of healthycontrol volunteers (N =30). Changes in MD symptomswere evaluated in both groups at 3- and 6-month postopera-tive intervals. Te authors found no significant differencesin the incidence of MJ sounds, deviation of mouthopening, or tenderness on direct palpation of the MJand masticatory muscles between patients who were sched-uled to undergo orthognathic surgery and control volun-teers. Te treatment group did not report MJ symptomssignificantly more often than the control subjects. At boththe 3- and 6-month postoperative intervals, half or more ofthe treatment group showed no change in MJ sounds,deviation of mouth opening, or tenderness on palpation ofthe MJ or masticatory muscles. At each evaluation timeframe, some individuals in both the control group and thestudy group exhibited improvement in MJ symptoms,whereas others showed a change for the worse. Findings ofpostoperative MJ sounds were observed to be associatedwith a reduction of mandibular mobility (i.e., mouthopening). Te authors concluded that MD symptomsdid not always show improvement after surgical correctionand that, for some patients, the symptoms changed for

the worse.Panula and colleaguescarried out research to study theeffects of orthognathic surgery on MJ dysfunction.236Tey completed a prospective follow-up study to examinethe influence of orthognathic procedures for the correctionof dentofacial deformities on signs and symptoms of MJdysfunction. Sixty consecutive patients with dentofacialdeformities were examined preoperatively and then twiceafter orthognathic surgery. Te Helkimo Anamnestic andDysfunction Indices were also given as a questionnaire, andthe results were used as part of the determination. Teprevalence of headache was also assessed. Te averagefollow-up was 4 years after the initial preoperative examina-

tion. A group (N =20) with a similar type and grade ofdentofacial deformity who elected not to undergo surgicalcorrection or any other occlusal therapy served as the controlgroup. Te majority of the treatment group (73%) wasfound to have signs and symptoms of MJ dysfunction orMD during the preoperative examination. At the final

2. Signs and symptoms of MD increase with age, particu-larly during adolescence.

3. Orthodontic treatment performed during adolescencegenerally does not increase or decrease the odds of devel-oping MD later in life.

4. Te extraction of teeth as part of an orthodontic treat-ment plan does not increase the risk of MD.

5. Tere is no elevated risk for MD associated with

any particular type of conventional orthodonticmechanics.

6. Although a stable occlusion is a reasonable orthodontictreatment goal, the inability to achieve a specific gnatho-logic ideal occlusion does not result in MD signs orsymptoms.

7. No specific method of MD prevention has been dem-onstrated to be effective.

8. When more severe MD signs and symptoms arepresent, simple forms of treatment can alleviate them inmost patients.

*References 6, 7, 25, 32, 33, 36, 55, 61, 62, 66, 67, 96, 98, 103, 105,110, 111, 123, 124, 131, 144, 145, 154, 157, 158, 160, 174, 180, 187, 189, 211, 225, 226, 232, 236, 247, 292-295, 322, 335, 340, 347, 349, 350, 353, 356, 359

NOTE: McNamara, Seligman, and Okeson suggestthat until reliable criteria are developed for the

treatment of TMD, the dental and medical professions

should be encouraged to manage presenting TMJ

symptoms with reversible therapies and to only consider

permanent alterations in the occlusion (for the specific

purpose of treating or preventing TMD) in patients with

very unique circumstances. This is in agreement with the

National Institure of Health conference guidelines which

states that reversible therapies should be used in the

primary treatment of TMD219

A summary of evidence-based systematic reviews ofMDs was carried out by Rinchuse and McMinn.283Teirsystematic review resulted in the following conclusions:

1. Occlusion, which was once considered the primary andsole cause of MD, now at best is recognized as havinga secondary role in causing it.

2. Conventional orthodontic treatment that improves theocclusion does not cause MD.

3. Te use of occlusal adjustments in orthodontic patientshas no evidence-based support for the treatment ofMD.

4. Tere is evidence-based support for the use of occlusal

splints and biofeedback for the treatment of MD.

Association of Jaw Deformities,Orthognathic Surgery, andTemporomandibular Disorders

Review of the Literature

Te association of a jaw deformity with malocclusion andthe effects of orthodontic and surgical correction on MD


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3. Despite the trend for diminished signs and symptoms ofMD after orthognathic surgery and orthodontics, indi-viduals did not always show improvement; for some, thesymptoms changed for the worse.

4. After orthognathic surgery and orthodontic treatment,a decrease in masticatory muscle tenderness was fre-quent. A decrease in joint tenderness on palpation wasalso a common occurrence.

5. In one of the three studies reviewed, a decrease inmaximum mouth opening was observed, but this wasnot found to be of clinical importance.

Tere are other less rigorous reports and studies that canbe found in the literature that also analyze the effects oforthodontics and orthognathic surgery carried out for thecorrection of dentofacial deformities on MD, includingthe following:

Karabouta and colleaguesreviewed 280 individuals withdifferent patterns of mandibular deformities (e.g., progna-thism, retrognathia, open bite, asymmetry) who underwentorthognathic surgery that included sagittal split ramus oste-otomies of the mandible. Before surgery, the patients werefound to present subjective or objective MJ dysfunctionsymptoms with an incidence of 41%.154After surgery, theincidence of such symptoms in the same patients wasreduced to 11%. Individuals with no preoperative MJdysfunction symptoms developed such symptoms with anincidence of 4% after surgery.

White and colleagues set out to review the prevalenceof MD in patients with dentofacial deformities who wereundergoing orthognathic surgery.349Preoperatively, 49% oftheir study group presented with MD. After orthognathic

surgery, in the symptomatic patients, 89% had improvedtemporomandibular function, 3% were unchanged, and8% developed increased symptoms. Of the preoperativeasymptomatic patients, 8% developed MD after surgery.In the study group, MD was significantly greater inpatients with Class II skeletal deformities as compared withthose with Class III tendencies. Overall, temporomandibu-lar function generally improved in both treatment groups(i.e., Class II and Class III) after successful surgery.Hori and colleagues reported three individual (non-consecutive) cases in which there was a worsening of preex-isting MJ dysfunction after sagittal split ramus osteotomyof the mandible and 6 weeks of intermaxillary fixation.131

All three of their patients initially presented specificallyseeking treatment of malocclusion for the relief of MD.All three patients had active MD before and after theirorthognathic procedures.

Aghabeigi and colleaguesstudied the effect of orthogna-thic surgery on the MJ of patients who presented with ananterior open bite.6Tis was a retrospective survey study ofpatients (N =83) who presented with an anterior open bitewho then underwent orthognathic surgery. Te preopera-tive prevalence of head and neck pain was 32%, MJ dys-function was found in 40% of patients, and limited mouth

postsurgery examination (i.e., 4 years after surgery), theprevalence of MD had been reduced to 60%. Tere wasalso a dramatic improvement in the prevalence of headache,which was initially experienced by 63% of patients andreduced to 25% of patients at the final visit. Te authorsconcluded that signs and symptoms of MD, includingpain (headache) levels, could be reduced with orthognathictreatment. Te risk of an orthognathic patient experiencing

new MD was extremely low. No association could beshown between MD and any specific type or magnitudeof dentofacial deformity.

A study was conducted by Dervis and colleagueswiththe objective of looking at the long-term prevalence ofMD in individuals with a dentofacial deformity who thenunderwent orthognathic surgery as compared with a controlgroup.67Signs and symptoms of MD in both the dento-facial deformity patients and the control group were evalu-ated before surgery, 1 week after release of intermaxillaryfixation, and 1 and 2 years after surgery with the use of theHelkimo Anamnestic and Dysfunction Indices. At both theinitial preoperative examination and the final examination(i.e., 2 years after surgery), signs and symptoms of MD inthe patients who were undergoing orthognathic surgerywere compared with those of healthy control subjects. Telengths of condylar pathways during opening and withlateral and protrusive movements were also evaluated withthe use of axiography. A statistically significant reduction ofMD symptoms and signs 2 years after surgery as com-pared with before surgery was found. Interestingly, at theinitial examination, the patients with dentofacial deformi-ties who were scheduled to undergo orthognathic surgerydid not report MD signs and symptoms with a greaterfrequency than other healthy control subjects. At the final

examination (i.e., 2 years after surgery), greater improve-ments in MD symptoms in the patients who had under-gone orthognathic surgery were found as compared withhealthy control subjects. Te authors also found a statisti-cally significant decrease in masticatory muscle tendernessafter surgery. Te authors concluded that the functionalstatus of the MJ can be improved with orthognathicsurgery. Tere was no clear association between MDsymptoms and a specific type or pattern of dentofacialdeformity.

When comparing and contrasting the three publishedlongitudinal prospective controlled studies that were con-ducted to determine the effects of orthognathic procedures

on MD symptoms and signs (i.e., Onizawa and col-leagues,232 Panula and colleagues,236 and Dervis and col-leagues67), several observations can be made:

1. Patients with dentofacial deformities who were sched-uled to undergo orthognathic surgery were not found tohave significant differences in their MD signs andsymptoms as compared with patients in the controlgroups.

2. After orthognathic surgery and orthodontics, signs andsymptoms related to MD were frequently improved.


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have a high probability of the significant worsening of MJdysfunction after surgery. Tis reported high incidence ofMD and condylar resorption after orthognathic surgery iscontrary to all other studies reported in the literature.Borstlap and colleagues reported about a consecutiveseries of individuals who were scheduled to undergo sagittalsplit ramus osteotomies for both Class II mandibular ret-rognathism and Class III mandibular prognathism.31

Patients were reviewed preoperatively, immediately postop-eratively, and at 3, 6, and 24 months postoperatively. Anysigns and symptoms of MD were documented, includingclicking, preauricular pain, maximum mouth opening, pro-trusive movements, and lateral excursions. Te authorsdocumented that 56% of the patients with preexistingMD had relief of their signs and symptoms. Interestingly,22% of individuals without preexisting MD went on todevelop clinical signs or symptoms after surgery.Bock and colleaguesstudied the importance of temporo-mandibular function as a factor in the achievement ofpatient satisfaction after orthognathic surgery.29Te authorsorthognathic surgery patients (N =102) were examined atan average of 47 months after surgery. Te average age oftheir patients was 24 years. A patient satisfaction question-naire and other modalities were reviewed, including theHelkimo Index, clinical findings, nerve function parame-ters, and the incidence of intraoperative and postoperativecomplications. Te results of their study showed that 91%of patients were satisfied or very satisfied with their overallorthognathic results. Answers to the questionnaires revealedthat only 79% of patients would undergo treatment again(i.e., 21% of the patients would not). Statistically significantdifferences were found in the Helkimo Index and in thepain reported both in the MJs and with jaw movements

between the satisfied and dissatisfied postoperative patients.Te authors surmised that the 21% of patients who wouldnot undergo treatment again were more likely to have agreater degree of MD and limitations with regard to man-dibular range of movement. Statistically significant differ-ences were found between those who were satisfied andthose who were dissatisfied with surgery on the basis of theirHelkimo Indices. Tose with pain on palpation in the MJregion and those with pain experienced during motion ofthe mandible were more likely to be overall dissatisfied withthe treatment. Te persistence of postoperative symptomsof MD, including pain, was the single most importantcorrelation with low patient satisfaction.

Frey and colleagues studied the effects of mandibularadvancement procedures and counterclockwise rotation onsigns and symptoms of MD.102Te study patients werefollowed for a minimum of 2 years after orthognathicsurgery. A series of patients with Angle Class II malocclu-sions (N =127) who were undergoing sagittal split ramusosteotomies with advancement and counterclockwise rota-tion of the mandible were studied to evaluate signs andsymptoms of MD at specific intervals after surgery. Teresults of the study indicate that counterclockwise rotationof the mandible was associated with more masticatory

opening was found in 7%. Te overall prevalence of MJsigns and symptoms was not found to be significantly dif-ferent after orthognathic surgery. In the study group, anabnormal psychological profile was the most significantfactor associated with the presence and persistence of MJpain. Te authors concluded that orthognathic surgery doesnot significantly influence MD in patients with anterioropen bites. Female patientsparticularly those with abnor-

mal psychological profilewere at higher risk for persistentpostoperative MJ pain.

Westermark and colleaguesstudied a consecutive series ofindividuals to understand the effects of orthognathic surgeryon the signs and symptoms of MD.347Te authors sent asurvey questionnaire to a consecutive series of patients (N=1516) who initially presented with dentofacial deformitiesand who then underwent orthognathic surgeries that wereperformed by a group of experienced surgeons at a singleinstitution. Te survey was given at least 2 years aftersurgery. Te questions asked in the survey related to jointpain, chewing pain, joint noise, grinding, daytime head-ache, and morning headache. Preoperatively, 43% of thepatients reported subjective symptoms of MD; postopera-tively, 28% of the patients did. Tis difference suggested anoverall beneficial effect of orthognathic surgery on MDsigns and symptoms. Patients with Class II skeletal deformi-ties did not improve as much as with those with Class IIIskeletal prognathism.

Yamada and colleaguesstudied the incidence of condylarmorphologic change, disc displacement, and signs andsymptoms of MD in individuals set to undergo orthogna-thic surgery.359 Te study showed preoperative condylarmorphologic change (unilateral or bilateral) in 36% of thesubjects and in 24% of each joint. Preoperative disc dis-

placement (unilateral or bilateral) was seen in 41% of thesubjects and in 30% of each joint. Te percentage of con-dylar morphologic change and disc displacement was higherfor individuals with anterior open-bite skeletal Class IIgrowth patterns and lower for patients with skeletal ClassIII deformities.

Wolford and colleagues studied changes in MD afterorthognathic surgery in a series of 25 patients who werescheduled to undergo bimaxillary surgery.356 Tey usedmagnetic resonance imaging and clinical verification ofMJ articular disc displacement. Tis was a retrospectiveevaluation with an average follow up of 2.2 years. Presurgi-cally, 16% of the patients had only MJ pain, 64% had

only MJ sounds, and 20% had both MJ pain and sounds.Postoperatively, 24% of the patients had only MJ pain,16% had only MJ sounds, and 60% had both MJ painand sounds. Tirty-six percent of the patients had MJpain preoperatively; this jumped to 84% after surgery. Inaddition, the authors claimed that 6 out of 25 of theirpatients (24%) developed condylar resorption postopera-tively, thereby explaining the high incidence of observedClass II open-bite malocclusion. Te authors demonstratedthat patients with preexisting MJ dysfunction who undergobimaxillary osteotomies via the techniques that they used


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knee pathology in anticipation of improved function andrelief of pain have varied but are currently without consen-sus. Terefore, a randomized clinical trial that included aplacebo group was designed by Moseley and colleagues toaddress this controversy. o blind the placebo group, asham surgical procedure was designed as part of the study.Te placebo subjects were given a general or regional anes-thetic, and incisions were made; however, the arthroscope

was not inserted into the joint, and no therapeutic proce-dure was carried out. Te results of the study were thatneither treatment group (i.e., lysis and lavage or arthro-plasty) offered improved clinical outcomes as comparedwith the placebo group for osteoarthritis. As a consequenceof this evidence-based study, many orthopedic surgeonshave changed treatment recommendations for theirpatients. In any case, Medicare (i.e., the U.S. governmentmedical insurance plan for the elderly) made a decisionthat it would no longer cover arthroscopy for osteoarthritisof the knee. Restorative dentists, orthodontists, and orthogna-thic surgeons should remain circumspect when advisingpatients regarding irreversible treatment specifically for thepurpose of relieving TMD.

Brief Overview of Okesons ThinkingAbout Temporomandibular Disordersand the Effects of Occlusion

Okeson believes that, during the normal use of the mastica-tory system, either local or systemic events can occur thatmay influence function.165,227-231 Each individual has avaried ability to tolerate these events without any adversehead and neck effects. It is likely that an individuals

tolerance can be influenced by these local or systemicfactors. When an event exceeds the individuals physiologictolerance, the system begins to reveal changes. Each com-ponent of the masticatory system can tolerate a certainamount of change. When functional change exceeds a criti-cal level, alteration of the tissues begins. Te tissue break-down site is generally seen in the structure with the leasttolerance. Terefore, the breakdown site varies from indi-vidual to individual. Tis is influenced by factors such asthe individuals unique maxillofacial morphology, previoushead and neck trauma, and local tissue conditions. Teweakest link in the masticatory system will break first(i.e. masticatory muscles, MJs, supporting structures of

the teeth, the teeth themselves). ypically, the weakest struc-tures in the system are the masticatory muscles; this isevidenced by muscle tenderness and pain during mandibu-lar movements.

When the MJs are the weakened structures in thesystem, the individual may experience joint tenderness andpain. Te MJ can also produce sounds such as clicking orgrating. When the individual has increased muscle activity(e.g., bruxism, grinding), then the next weakest link is fre-quently either the supporting structures of the teeth (i.e.,the periodontium) or the teeth themselves. Te teeth may

muscle tenderness early after surgery, especially in thosewho were undergoing more than 7 mm of advancement.Te combination of extensive mandibular advancementwith counterclockwise rotation was also associated withincreased MD symptoms early after surgery. Interestingly,all MJ symptoms declined by 2 years after surgery. Teauthors conclude that surgical advancement and counter-clockwise rotation of the mandible (i.e., sagittal split ramus

osteotomy) is associated with a slight increase in masticatorymuscle discomfort during initial recovery. All symptomatol-ogy tended to decline over time, which suggests that theamount of advancement and the amount of mandibularcounterclockwise rotation should not be considered as riskfactors for the long-term development of MD in patientswithout preexisting symptoms.Jung and colleaguesretrospectively evaluated the effects ofbilateral intraoral vertical ramus osteotomies with setbackfor the management of Class III skeletal patterns on symp-toms that are associated with MD.152Patients were evalu-ated preoperatively and at intervals (i.e., 1, 3, 6, 12, 18, and24 months) after surgery for specific parameters, includingmouth opening, clicking, and MJ pain. Te authorsreported that 94% of those with preoperative joint noiseachieved resolution. After surgery, 8% of individuals whowere free of noise before surgery developed joint noise after-ward. On average, mouth opening was 50 mm beforesurgery and 49 mm 6 months after surgery. Joints that werefree of pain before surgery remained so. Tose individualswith preoperative MJ pain remained free of pain at 18months. Te authors concluded that bilateral intraoral ver-tical ramus osteotomy with setback as a method of manag-ing Class III skeletal deformities was also effective for therelief of undesirable MJ symptoms (e.g., joint noise, pain)

without negatively affecting mouth opening.

Additional thoughts Concerning Effectsof Orthodontics and Orthognathic Surgeryon Temporomandibular Disorders

It may not be correct to conclude that orthodontic treat-ment and orthognathic surgery carried out for the correc-tion of a presenting jaw deformity with malocclusion arethe responsible factors for any observed reduction or reso-lution of MD signs and symptoms.18During the decadesthat have passed since McCarty and Farrar first defined thediagnoses of internal derangement of the MJ and then

described a disc repositioning procedure to treat it, qualityresearch to evaluate their recommended treatment has beenscant.200Te experience of orthopedic surgeons with regardto the treatment of derangements of the knee shouldremind us of the need for clinical practice to be based onsound supporting evidence. Moseley and colleagues carriedout a controlled clinical trial of arthroscopic surgery (i.e.,lysis and lavage or arthroplasty) for osteoarthritis of theknee that should give us pause when considering irrevers-ible MD treatment.212Clinician opinions regarding theeffectiveness of lysis and lavage or arthroplasty to manage


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A critical review of the literature suggests that outcomesfor open MJ procedures are often unpredictable and mayresult in further MD.73-77Te success rate for redo openjoint surgery is even less favorable. Among the criteria foran open joint procedure are the following: that the clinicianmust be confident that the source of the pain or dysfunctionis arising from within the joint; that the appropriate use ofconservative measures has failed; that the current symptoms

are intolerable to a patient who is psychosocially stable; andthat a significant long-term success rate for the selectedopen joint procedure in the specific patient can be assured.

Although an intracapsular lavage procedure with orwithout limited debridement and lysis of adhesions torelieve inflammation and improve function may be rela-tively benign in experienced hands, disc repositioning anddiscectomy have generally proven to be of little statisticalvalue as compared with conservative measures. Te techni-cal simplicity of disc repositioning and discectomy proce-dures has lured many clinicians into offering them asstandard options; however, a significant long-term successrate has not been documented.

Te overall approach to MD should aim to avoidfurther harm to the joint and err on the side of appropriateconservative management to relieve symptoms and toachieve or maintain reasonable function for the long term.

Conclusions

It is estimated that an average of 32% of the populationwill report at least one symptom of MD and that anaverage of 55% will demonstrate at least one clinical sign.Historically, clinicians from a spectrum of medical anddental specialties have considered occlusion to be the major

etiologic factor for MD. A review of the literature suggeststhat the overall contribution of occlusal factors to identify-ing patients with MD to only be in the range of 10% to20%. Te corollary is that 80% to 90% of the causativefactors among patients with MD cannot be explained bythose patients occlusions.

Te National Institude of Health conference guidelinesstate that reversible therapies should be used for the primarytreatment of MD. Despite these words of caution, studiesdocument that, for whatever combination of reasons, thecorrection of an individuals developmental jaw deformityand malocclusion through successful orthodontics andorthognathic surgery tends to have a positive effect on pre-

existing MD in the majority of patients, whereas a minor-ity of patients will get worse.

show mobility or wear (e.g., loss of enamel, breakdown ofrestorations, fracture). Emotional stress seems to be a majorinfluence on bruxing activity.

According to Okeson, the occlusal condition can influ-ence MDs by way of two mechanisms. One mechanismrelates to the introduction of acute changes in the occlusalcondition (e.g., recent restorative dentistry with an unevenalteration of the occlusal surfaces). Acute changes can lead

to a muscle co-contraction response that leads to a condi-tion of muscle pain. ypically, in these circumstances, newmuscle engrams are developed, and the patient adapts withlittle consequence. A second mechanism relates to a morelongstanding variation in the occlusal condition. In theseconditions, maximum intercuspation (i.e., centric occlu-sion) results in the instability of the masticatory system(e.g., a CRCO discrepancy). Te orthopedic instability isnot likely to withstand significant compressive loadingforces on the MJs. Dental therapy (i.e., the alteration ofthe occlusion) will only be helpful for the relief of MDswhen it effectively relieves one of these conditions (i.e., themuscle co-contraction response or the orthopedic instabilityaccompanied by loading forces).

Dr. Okeson concludes that, in general, conventionalorthodontic treatment is not an effective method for theprevention of MD. As a corollary, a review of the literaturesuggests that patients who receive conventional orthodontictherapy are at no greater risk for the development of MDthan those who do not. According to Dr. Okesons work,any dental or surgical procedure that produces an occlusalcondition that is not in harmony with a musculoskeletalstable position of the joint canbut does not necessarilypredispose the individual to these problems. Alternatively,dental or surgical procedures that reduce one of these occlu-

sal conditions and restore harmony may improve the mas-ticatory system.

Personal Thoughts About the Role ofOpen Joint Procedures forTemporomandibular Disorders

Unanswered questions remain: What is the appropriatetreatment for an individual with a persistent symptomaticintracapsular MJ disorder that has either not resolvedspontaneously or not responded to conservative therapy? Inthese cases, what are the best studies to use to confirm the

diagnosis and then select the appropriate treatmentintervention?

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