The evolution of temporomandibular disorders: A shift from experience to evidence.

After over 80 years of much obsession as well as avoidance of the subject of temporomandibular disorders (TMDs), the dental profession is still divided over what they are and how to deal with them. Over this period, nearly every discipline in dentistry has played some role in the development of this field. Unfortunately, a significant amount of this information has been based on personal opinion, experience-based philosophies, or poorly conducted research. Furthermore, each dental specialty has been responsible for contributing to the concepts of the etiology and management of TMDs with their own professional bias; for example, orthodontists describe these problems in orthodontic terms and offer orthodontic treatments or solutions for their patients. As various treatment approaches were found to be effective at least some of the time, this has further led to misinformation and confusion within the profession. Advances in research from diverse fields, including neurophysiology, pain pathophysiology, genetics, endocrinology, behavioral sciences, and psychology, have significantly altered our understanding of TMDs and how they should be managed. The rigid mechanical and dental-based model of the past has been gradually replaced by a biopsychosocial medical model for the diagnosis and treatment of TMDs as well as other acute and chronic pain disorders. This paper discusses the evolution of our understanding of TMDs since they were first described 85 years ago. Contemporary scientific findings and their implications are presented in some detail for clinicians who wish to provide the appropriate management for their orofacial pain patients.

An evidence-based evaluation of the concept of centric relation in the 21st century.

The concept and application of a temporomandibular joint (TMJ) relationship identified as centric relation (CR) has changed significantly over the past century. Originally proposed as a biologically reasonable position where maxillary and mandibular dentures should occlude, it later was applied to the dentate population as well. The term "ideal" was used by the gnathologic dental community as they sought to define the exact details of CR in terms of condyle-fossa relationships. Assessments of patients' occlusion were then made in relation to CR, and discrepancies between the two positions were described as being problematic. Since not all dentists have accepted this concept, the clinical application of CR has become a topic of major dental confusion and controversy. To further complicate things, the formal definitions of CR have continuously changed over the past 40 years. In this paper, the biologic development of occlusal and TMJ relationships is reviewed, followed by a discussion about the validity of applying CR concepts and procedures in contemporary clinical and research settings. Special attention is devoted to the alleged relationships between occlusion, jaw positions, and temporomandibular disorders (TMDs). Current evidence suggests that it is time to stop applying CR concepts to the evaluation and dental treatment of healthy dentate individuals. For patients with TMDs, it is time to apply current concepts of biopsychosocial assessment and management rather than following the 20th century mechanistic models of fixing dental and skeletal malalignments.

Condylar position assessed by magnetic resonance imaging after various bite position registrations.

INTRODUCTION: In this study, we evaluated the reliability and validity of 3 bite registrations in relation to condylar position in the glenoid fossae using magnetic resonance imaging in a symptom-free population. METHODS: Nineteen subjects, 14 men and 5 women (ages, 20-39 years) without temporomandibular disorders were examined. Three bite registrations were taken and evaluated on each subject: centric occlusion, centric relation, and Roth power centric relation. The differences in condyle position among the 3 bite registrations were determined for the left and right condyles: centric occlusion-centric relation, centric occlusion-Roth power centric relation, and centric relation-Roth power centric relation for each plane of space. RESULTS: The results indicated that (1) all measurements collected had large standard deviations and ranges with no statistical significance, and (2) of the 19 subjects and 38 condyles assessed, 33 condyles (87%) were concentric in an anteroposterior plane. In the transverse anatomic plane, all condyles were concentric. CONCLUSIONS: The clinical concept of positioning the condyles in specific positions in the fossae with various bite registrations as a preventive measure for temporomandibular disorders and as a diagnosis and treatment planning tool is not supported by this study.

Orthodontics and temporomandibular disorders: a curriculum proposal for postgraduate programs.

In a previous article, we reported the results of a survey of American and Canadian orthodontic postgraduate programs to determine how the topics of occlusion, temporomandibular joint, and temporomandibular disorders were currently being taught. Based on the finding of considerable diversity among those programs, we decided to write a curriculum proposal for temporomandibular disorders that would be compatible with and satisfy the current curriculum guidelines for postgraduate orthodontic programs. These guidelines arose from a combination of the requirements published by the American Dental Association's Commission on Dental Accreditation and the written guide (July 2010) of the American Board of Orthodontics for the its clinical examination. The proposed curriculum, based on the latest scientific evidence in the temporomandibular disorder field, gives program directors a template for covering these subjects thoroughly. At the same time, they can focus on related orthodontic issues, so that their future graduates will be prepared to deal with patients who either have or later develop temporomandibular disorder problems.

Survey of orthodontic residency programs: teaching about occlusion, temporomandibular joints, and temporomandibular disorders in postgraduate curricula.

INTRODUCTION: Teaching orthodontic postgraduate students about occlusion and the temporomandibular joint is a fundamental component of their education, but faculty members are confronted with disputes and controversies about these topics. The purpose of this study was to ascertain where the orthodontic teaching community currently stands on the topics of occlusion, temporomandibular joint, and temporomandibular disorder. METHODS: A 46-question survey was sent to every orthodontic program director in the United States and Canada (n = 69). Responses were submitted by 46, and the results were tabulated. RESULTS: Three interrelated topics (normal or ideal temporomandibular joint, normal or ideal occlusion, and management of temporomandibular disorder) are being taught in diverse ways in these postgraduate orthodontic programs. CONCLUSIONS: The results of this survey will help us to understand and improve how these topics are being taught at accredited orthodontic programs in the United States and Canada. Perhaps a standardized curriculum can be developed.

Deconstructing evidence in orthodontics: making sense of systematic reviews, randomized clinical trials, and meta-analyses.

Much has been written in support of systematic reviews and the randomized clinical trials and meta-analyses upon which they are based. Clearly, the medical profession (as opposed to the dental profession) has been the leader in publishing the benefits of systematic reviews over the traditional, qualitative narrative reviews. At the same time, the medical profession also appears to be ahead of the dental profession in recognizing the limitations of such reviews. That said, there are a number of inherent problems with systematic reviews, as well as the randomized clinical trials and meta-analyses that back them up. To better facilitate evidence-based decision making, this article discusses the shortcomings of systematic reviews so that practitioners are fully aware of their drawbacks, as well as their benefits.

Implications of the inclination of the mandibular first molars in the extractionist versus expansionist debate.

Some orthodontic expansionists (versus extractionists) hold a notion that in the decision to treat nonextraction, expansion treatment can be predicated and dictated based on the degree of facial-lingual inclination of the mandibular molars (particularly the mandibular first molars). For instance, some modern-day expansionists argue that mandibular first molars with a facial crown lingual inclination of approximately -30 degrees (based on Andrews' measurement) indicate that the mandibular arch, and subsequently the maxillary arch, needs to be developed or expanded to allow for more arch and tongue space. However, this thinking is based on a false premise; the mandibular first molars are normally lingually inclined approximately -30 degrees and not naturally found in an upright facial-lingual position of approximately -12 degrees.