New Definition for Relating Occlusion to Temporomandibular Joint Conditions (PDF)

THE CLASSICS New definition for relating occlusion to varying conditions of the temporomandibular joint: Conditions of the temporomandibular joint orthodontists need to know Gye Hyeong Lee,a Jae Hyun Park,b Sang Mi Lee,c and Danal Moond Yeosu, Seoul,...

THE CLASSICS New definition for relating occlusion to varying conditions of the temporomandibular joint: Conditions of the temporomandibular joint orthodontists need to know Gye Hyeong Lee,a Jae Hyun Park,b Sang Mi Lee,c and Danal Moond Yeosu, Seoul, Goyang, and Gwangju, South Korea Dawson defined the position and condition of these as adapted centric postures in his article. Proper con- dylar position and stability of the temporomandibular joint are essential for successful orthodontic treat- ment. Centric relation is a necessary concept in reaching ideally aligned condyle-disc assemblies. Well- adapted temporomandibular joints allow function with comfort and stable positioning, even despite pos- sible deformations of the condyle. The study of Dawson’s work may prompt a broader perspective on orthodontic diagnosis and treatment. (Am J Orthod Dentofacial Orthop Clin Companion 2021;1:181-6) Gye Hyeong Lee Jae Hyun Park Sang Mi Lee Danal Moon a d Roth Orthodontic Society, and Department of Orthodontics, Department of Orthodontics, School of Dentistry, Chonnam School of Dentistry, Chonnam National University, Gwangju National University, Gwangju and Catholic University, Seoul, and Kyung Hee University, Seoul, South Korea; Private practice, South Korea; Private practice, Gwangju, South Korea. Yeosu, South Korea. All authors have completed and submitted the ICMJE Form for b Postgraduate Orthodontic Program, Arizona School of Den- Disclosure of Potential Conflicts of Interest, and none were tistry & Oral Health, A.T. Still University, Mesa, Ariz; Graduate reported. School of Dentistry, Kyung Hee University, Seoul, South Korea. Address correspondence to: Jae Hyun Park, Postgraduate c Graduate School of Dentistry, Chonnam National University, Orthodontic Program, Arizona School of Dentistry & Oral Gwangju and Catholic University, Seoul, South Korea; Private Health, A.T. Still University, 5835 E Still Circle, Mesa, AZ practice, Goyang, South Korea. 85206; e-mail, [email protected] October 2021, Vol 1, Issue 3 181 Lee et al. The Classics assemblies with intracapsular deformation and structural change. Dawson suggested a new term, adapted centric posture, to define the identical condition commonly referred to today as mandibular stabilization.10-12 CENTRIC RELATION Dawson9 described the requisite position of the man- dibular condyle in terms of muscular physiology and neu- rology. During jaw closure of intact TMJs, the condyle-disc assemblies are pulled up onto the articular eminence by a triad of strong elevator muscles (Fig 1). The complete release of the lateral pterygoid muscles, which generally contract at mouth opening, is essential during jaw closure https://www.thejpd.org/article/S0022-3913(05)80315- to ensure a coordinated neuromuscular function.13 With 4/fulltext the contraction of elevator muscles and the inferior lateral pterygoid muscle release, the condyles can slide up to the O rthodontic treatment is a kind of oral rehabilitation process that deals with natural teeth. The goals of orthodontic treatment, namely proper occlusal functions, facial esthetics, dental esthetics, and periodon- tal and temporomandibular joint (TMJ) health, are coinci- apex of force positions.14 According to Dawson,9 the coor- dinated neuromuscular state is when the condyle-disc assembly is stopped against the buttressed bone at the height of concavity in the medial third of each fossa (Fig 2). He emphasized that all the force vectors induced in dent with the goals of general dental treatment. The excursive movements and CR keep the condyles loading functional treatment goal of orthodontic treatment against the eminence (Fig 3). So, it can be said that the CR revolves around mutually protected occlusion with even of intact condyle-disc assemblies is the most superior occlusal contacts on closure and anterior guidance for position against the eminence. immediate posterior disclusion in an eccentric movement. In his article, Dawson9 mentions some confusion sur- In particular, the stability of the TMJ is a fundamental prin- rounding the concept of the “most retruded” position in ciple of occlusion. A stable condylar position should be identifying the CR. Pushing the jaw back to find the seated the starting point of occlusal treatment as it has a signifi- condylar position might come from a lack of understanding cant influence on overjet, overbite, and posttreatment sta- about the coordinated masticatory system and anatomic bility.1-3 Although the relationship between condylar structure of the TMJs. Unfortunately, pushing the jaw pos- position and temporomandibular joint disorders (TMD) is teriorly toward the “most retruded” position is still not still very controversial, orthodontists need to have a good uncommon. He clarified that the condyles should not be idea of the appropriate condylar position for accurate forced away from the eminence. Rather, the position diagnosis and proper occlusal treatment. should be achieved by coordinated muscle function. The In general, the proper condylar position is identified as “retruded” position can be acceptable if coordinated mas- centric relation (CR) because it is the only clinically repro- ticatory muscles achieve it. Considering this point, we ducible, comfortable, and mechanically equilibrial posi- should remember that this literal “retruded” position is tion.4 However, confusion about the proper condylar not very different from the “uppermost” position in the position has existed in academia for many years. Defini- actual anatomy of the condylar fossa. tions about CR in the current glossary of prosthodontic Dawson9 illustrated the specific anatomic structures of terms have been amended multiple times, primarily the condyles constructing a proper CR. He indicated that because of confusion about the position of the condyle- when condyle-disc assemblies are properly seated in CR, disc assembly in the glenoid fossa. The definitions have the medial poles of the condyles should be at the highest transitioned from a retruded posterior position to a supe- point of concavity of each condylar fossa. And the fossa rior position and now to an anterosuperior position.5-8 This walls where the medial poles are in contact should curve conceptual change might have arisen because of a lack of downwards in all directions so that from a correct CR, the histologic and mechanical understanding about TMJs. condyles cannot move forward, backward, or medially Dawson’s9 article “New definition for relating occlusion without moving downward (Fig 4). Dawson stated the CR is to varying conditions of the temporomandibular joint” is the same as the midmost position of the mandible (Fig 5). thought to be the first and most insightful study about the The condyles must move downward from CR as they move proper condylar position. Dawson explained the signifi- medially.13,15 cance of condylar position and desirable conditions of the Numerous electromyographic studies14,16-21 have repor- temporomandibular joints. He dealt with the rationale for ted that occlusal interference to CR disrupts the coordina- positioning intact condyle-disc assemblies and TMJ tion of masticatory muscle function. Any occlusal 182 AJO-DO CLINICAL COMPANION  Lee et al. Fig 3. A, All elevator muscles direct the condyles Fig 1. During normal jaw closure, 3 major masticatory muscles anterosuperiorly in CR. B, In eccentric movement, condyles are determine the position of the TMJ. Contraction of the still kept loaded against the condylar eminence’s posterior mastication muscles in coordinated function pulls condyles up slope. to posterior slopes of the articular eminence. Inferior lateral pterygoid muscles, the antagonist, are relaxed during comfortably and stably. Dawson9 called this condition of uninterrupted closing of the jaw. the condyle-fossa relationship “adapted centric posture.” Adapted centric posture is the relationship of the mandible interference during jaw closure may activate the inferior to the maxilla that is achieved when deformed TMJs have lateral pterygoid muscles to contract, which causes a adapted to the degree where these can comfortably hold deflection of the bone-braced condylar position. This reflection is commonly known as “protective co-contrac- tion” or “muscle splinting.”20,22 Prolonged disruptive occlusal contact could result in chronic myofascial pain because of these uncoordinated muscle activities. In an attempt to verify the accurate CR of condyle-disc assem- blies, Dawson reported that the assemblies require consid- erable precision as even minute deflective occlusal factors can cause the reflective muscles to contract. Therefore, he recommended verification of an accurate CR to determine the relationship between occlusion and properly posi- tioned TMJs. ADAPTED CENTRIC POSTURE Despite deformation, some TMJs can function comfort- ably and with an acceptable degree of stability. Although the condyle-disc assemblies are not well-aligned enough to meet the criteria of CR, some TMJs still function Fig 2. The condyle-disc assemblies are pulled up until the medial poles of the condyles are buttressed against the medial Fig 4. In coordinated muscle function, medial poles of condyle- third of the articular fossa. The buttressed point (red dot) is disc assemblies are braced at the highest point of concavity of established as the apex of forces from contraction of the each condylar fossa in CR. The condyles cannot move elevator muscles and release of the inferior lateral pterygoid anteriorly, posteriorly, or laterally from a seated position muscles. This indicates the most superior position where without moving inferiorly: A, Coronal view; B, Sagittal view; C, medial poles are positioned against bone. Axial view. October 2021, Vol 1, Issue 3 183 Lee et al. example, when chewing food, compressive force is loaded onto a point on a buttress against the condyle.23 With an anterior disc displacement, discomfort may result from compression of the vascular and innervated retrodiscal tis- sue by the condyle. However, the retrodiscal tissue some- times undergoes histologic changes to create fibrous connective tissue, which is called a pseudodisc.24 With this change, blood vessels, and accompanying nerves evacuate the retrodiscal tissue, and the fibrous tissues extending from the original disc allow it to accept loading without discomfort (Fig 6). Dawsons’s concept about the proper state of TMJs was Fig 5. During the contraction of medial pterygoid muscles, confirmed and developed by additional research. Okeson25,26 medial poles are braced against the midmost position of the articular eminence. This midmost position is simultaneously agreed with orthopedic principles associated with mastica- the uppermost position. tory functions. He described the changes of the treatment objective in the management of disc derangement disorders. the firm occlusal load when completely seated at their The long-term studies revealed that the attempts to reposi- most superior position against the articular eminence. He tion (recapture) anteriorly displaced discs using an anterior also explained that adapted centric posture is the midmost positioning appliance are not effective.27-30 Okeson31 explains position; when a disc is displaced, the medial pole of the these results on the basis of histologic properties of the artic- condyle adjusts to the concavity of the fossa and maintains ular disc. Because the shape of the articular disc, composed contact against its medial inclination. of dense fibrous connective tissue, can be altered irreversibly, The adaptive changes in TMJs may result in deforma- recapture of the disc cannot be achieved. He suggested that tions of intracapsular structures. Some pain and dysfunc- clinicians should have treatment goals toward establishing an tion can accompany this adaptive process. Besides, in orthopedically stable relationship with proper masticatory many patients who complain of TMD symptoms, the dis- function. And he concluded there is a need for adaptive comfort is more myogenous than intracapsular, even with fibrotic and avascular retrodiscal tissue.31 Scapino24 and Per- some deformation present in the intracapsular structure. eira et al32,33 also concluded that fibrotic changes in retrodis- Because of this, Dawson9 emphasized the need for accu- cal tissue result in reduced pain. rate evaluations, not just a check to see whether deforma- Therapy using a stabilization splint will cause the TMJs tions are present or not. Each patient should be evaluated to be seated correctly in the most forward and upward to determine whether they have adapted to function with position in the articular fossae with a pseudodisc forma- comfort and stability. tion.32,34 It is not recommended to distract the condyle anteriorly for treatment position with only the use of an anterior repositioning splint (ARS).35 Although the use of PSEUDODISC FORMATION ARS has relieved pain in some patients, it presented lim- Dawson described the changes of deformed TMJ struc- ited efficacy recapturing the anteriorly displaced disc tures to achieve the adapted centric posture. The according to long-term evaluations.27-29 An ARS or flat “pseudo-disc” within deformed TMJs is an adequate alter- splint should be followed by a stabilization splint to native that enables function with comfort and stability. For achieve a stable mandibular position. Dawson’s suggestion Fig 6. TMJ: A, Well-aligned condyle-disc assembly; B, Considering anterior disc displacement, condyle articulating onto vascular, innervated retrodiscal tissue generates pain in loading; C, With pseudodisc formation, the condyle functions on adaptive fibrotic tissue, fabricated to accept loading without discomfort. 184 AJO-DO CLINICAL COMPANION  Lee et al. that the treatment position should be determined on the 9. Dawson PE. New definition for relating occlusion to varying basis of CR or adapted centric posture has significant conditions of the temporomandibular joint. J Prosthet Dent 1995;74:619–27. implications for the correct application of splints.3,16,36-39 Dawson’s detailed description of CR and adapted cen- 10. Mohan B, Sihivahanan D. Occlusion: the gateway to suc- tric posture can be helpful in our daily practice. Most clini- cess. J Interdiscip Dentistry 2012;2:68–77. cians should be aware that an adequate mandibular 11. Dawson PE. Functional occlusion from TMJ to smile design. position is the starting point for all aspects of treatment, St Louis: Mosby; 2007. p. 69–73. including diagnosis and long-term stability of treatment 12. Lee GH, Lee SM, Park JH. The role of mandibular stabilization results. This is an important concept that suggests how the in orthognathic surgery. Semin Orthod 2019;25:188–204. patient’s TMJs should be prepared before starting ortho- 13. Dawson PE. Evaluation, diagnosis and treatment of occlu- dontic diagnosis and treatment. It also indicates the treat- sal problems. p 28, 2nd ed. St Louis: Mosby; 1989. p. 28– 39. ment goals of temporomandibular disorder. Furthermore, the misconception that orthodontic treatment causes TMD 14. Mahan PE, Wilkinson TM, Gibbs CH, Mauderli A, Brannon can be resolved by determining the optimal TMJ position LS. Superior and inferior bellies of the lateral pterygoid muscle EMG activity at basic jaw positions. J Prosthet before orthodontic treatment. 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