Seminars in Orthodontics RSS feed: Current Issue. Each issue provides up-to-date, state-of-the-art information on a single topic in orthodontics. Readers are kept abreast of the latest innovations, research findings, clinical applications and clinical methods. Collection of the issues will provide invaluable reference material for present and future review. http://www.semortho.com/?rss=yesElsevier Inc.en © 2012 Published by Elsevier Inc. All rights reserved. Seminars in Orthodontics1073-8746181March 2012 © 2012 Published by Elsevier Inc. All rights reserved. healthpermissions@elsevier.comhttp://www.semortho.com/article/PIIS1073874611001241/abstract?rss=yesEditorial Board10.1053/S1073-8746(11)00124-1Seminars in Orthodontics 18, 1 (2012)2012-03-01Seminars in Orthodontics2012-03-01181S1073-8746(11)X0005-1iihttp://www.semortho.com/article/PIIS1073874611001265/abstract?rss=yesTable of Contents10.1053/S1073-8746(11)00126-5Seminars in Orthodontics 18, 1 (2012)2012-03-01Seminars in Orthodontics2012-03-01181S1073-8746(11)X0005-1iiiihttp://www.semortho.com/article/PIIS1073874611000958/abstract?rss=yes Truth is a constant variable. We seek it; we find it; our viewpoint changes, and the truth changes to meet it. William J. Mayo Function and dysfunction of the temporomandibular joint is currently one of the most intensely debated subjects in the field of medicine. Asymmetries of structure and function do not share an evidently obvious causal relationship with the development of the disorders of this joint. Furthermore, the symmetry of structure and function does not exclude the possibility of development of the disorders of this joint. This paradox is the subject of inquiry of articles in this issue of Seminars in Orthodontics. Definitive scientific answers to clinical questions related to temporomandibular disorders and their orthodontic implications should be based on the principles of evidence, biology, and translational research. The new emphasis in biomedical research is on interdisciplinary and translational research. Advances in interdisciplinary research will be particularly important in the diagnosis and treatment of temporomandibular disorders in view of new research in the fields of pain neurobiology, muscle biology, genetics, molecular biology, tissue engineering, and biomechanical analysis of forces acting on the temporomandibular joint. These investigations will throw light on interindividual variability in the manifestation of causal effects of apparently similar etiologic factors and develop signature profile of patients susceptible to development of temporomandibular disorders. In view of this, articles on neurobiology of pain, mechanical signal transduction consequences for masticatory muscle, and biomechanics of disk displacements have been included in this issue. Finally, there is the perennial question of what qualifies as evidence, statistical methodology or clinical reality/experience (). Until the time statistical evidence for definitive cause-and-effect relationship of etiologic factors and effectiveness of different treatment protocols are established, individual interpretation prevails. It is the hope that this issue of Seminars in Orthodontics will aid the clinician and academician in their interpretation of function and dysfunction of this apparently indeterminate system and initiate an inquiry on their part to provide answers to the questions that need further investigation.IntroductionRakesh Koul10.1053/j.sodo.2011.09.001Seminars in Orthodontics 18, 1 (2012)2012-03-01Seminars in Orthodontics2012-03-01181S1073-8746(11)X0005-111http://www.semortho.com/article/PIIS107387461100096X/abstract?rss=yes Skeletal muscle can readily respond to physiological demands, causing changes in muscle mass and the fiber properties to meet the functional needs. Muscle adaptation is a coordination of endocrine, metabolic, and mechanical signals resulting in changes at the transcriptional and translational levels. New evidence suggests that the signal transduction pathways that are responsive to mechanical changes diverge in the craniofacial and axial muscles. Two regions where sensors for load exist, the sarcolemma and the contractile apparatus, have many proteins that are poised to convert mechanical perturbations into molecular signals and ultimately into changes in gene expression. Changes in the mechanical signal transduction system might contribute to unique physiological and pathologic features of masticatory muscle. This review will define the molecular components that form a new set of intrinsic factors that could lead to myogenic temporomandibular joint disorders. Mechanical Signal Transduction: Divergent Communication and the Potential Consequences for Masticatory MuscleElisabeth R. Barton10.1053/j.sodo.2011.09.002Seminars in Orthodontics 18, 1 (2012)2012-03-01Seminars in Orthodontics2012-03-01181S1073-8746(11)X0005-129http://www.semortho.com/article/PIIS1073874611000971/abstract?rss=yes The hyperdivergent facial profile presents the orthodontist, oral surgeon, and restorative dentist with problems that might not be solvable with any one or all of our specialties. This article will review the literature on the possible predisposing and precipitating factors that might contribute to hyperdivergent facial profiles. We will attempt to correlate facial morphology as it might relate to disk displacement (DD) and degenerative joint disease (DJD). Human and animal studies will be reviewed that support these observations. Our hypothesis is that this hyperdivergent facial profile is often associated with bilateral DD and/or DJD. The effect of DD/DJD in animal and human studies and the effect of cartilage degeneration on hard and soft tissues will be reviewed. The presence of catabolic biological markers of joint degeneration (interleukin-1β, interleukin-6, matrix metalloproteinases, tumor necrosis factor-α, C-reactive protein, synovial fluid proteins) and anabolic markers (tissue inhibitors of metalloproteinases, interleukin-4, interleukin-10, interleukin-13) will be discussed. Epidemiologic studies suggest that in patients presenting with temporomandibular joint pain, there is a strong correlation between the disorder and severe mandibular retrognathia in adult women (odds ratio, 6.3). Human cephalometric studies will demonstrate that bilateral DD/DJD is highly correlated with the hyperdivergent facial profile. Follow-up orthognathic surgery studies suggest that correction might be unstable. This review will present a compelling case that the hyperdivergent facial profile is strongly correlated with bilateral DD and/or DJD. Clinicians should be aware of these findings and convey this information to patients presenting for dental treatments. Predisposing and Precipitating Factors in Temporomandibular DisordersRoss H. Tallents, S. Stein, D.J. Macher, R.W. Katzberg, W. Murphy10.1053/j.sodo.2011.09.003Seminars in Orthodontics 18, 1 (2012)2012-03-01Seminars in Orthodontics2012-03-01181S1073-8746(11)X0005-11029http://www.semortho.com/article/PIIS1073874611001034/abstract?rss=yes Patients with facial pain and jaw function problems constitute a large and heterogeneous group. Disk displacement and osteoarthritis are the most common intra-articular abnormalities observed at imaging. As disk displacement is seen rather frequently in asymptomatic volunteers, it is a challenge to explain why disk displacement sometimes is symptomatic and sometimes is not. The present review focuses on abnormalities in the condylar bone marrow and the intra-articular soft tissues accompanying the disk displacement. The findings of temporomandibular joint in asymptomatic volunteers and in temporomandibular disorder (TMD) patients are reviewed. Both bone marrow edema and marrow necrosis are documented at histology and at magnetic resonance imaging (MRI) in TMD patients. Intra-articular soft tissue changes, such as synovitis, are additionally documented at arthroscopy. However, there is a controversy concerning which diagnostic imaging information is essential. Although there is no doubt that disk displacement and osteoarthritis may be accompanied by inflammatory alterations in the bone marrow and the intra-articular soft tissues, it has been difficult to consistently relate a specific imaging manifestation (bone edema, joint effusion, and synovitis) to joint pain. Longitudinal studies are needed to evaluate the importance of MRI abnormalities in the management of TMD patients. Clinical Significance of Changes in the Bone Marrow and Intra-Articular Soft Tissues of the Temporomandibular JointTore Arne Larheim, Tsukasa Sano, Yoritaka Yotsui10.1053/j.sodo.2011.10.006Seminars in Orthodontics 18, 1 (2012)2012-03-01Seminars in Orthodontics2012-03-01181S1073-8746(11)X0005-13043http://www.semortho.com/article/PIIS1073874611000983/abstract?rss=yes The human lateral pterygoid muscle plays an important role in the control of jaw movements. This review provides an update on some aspects of the normal function of the lateral pterygoid muscle and its response to alterations, including mandibular advancement, occlusal changes, and experimental orofacial pain. Both the upper or superior head (SHLP) and the lower or inferior head (IHLP) of the lateral pterygoid insert predominantly into the neck of the condyle. A number of recent studies have carried out recordings of jaw movement and electromyographic (EMG) activity from the lateral pterygoid muscle, where verification of electrode location has been achieved through computer tomography imaging. From these studies, there is no evidence of background EMG activity within IHLP or SHLP when the jaw is in the clinically determined postural jaw position. There is little evidence for a reciprocal relation in activity between SHLP and IHLP, and both SHLP and IHLP play an important role in contralateral, protrusive, and jaw-opening movements and force generation. There is evidence for independent activation of subcompartments within the lateral pterygoid muscle to allow a range of force vectors to be delivered to the condyle. In terms of the role of the lateral pterygoid muscle in mandibular advancement and occlusal changes, the lack of studies of these issues, where verified recordings have been made from the lateral pterygoid muscle, means that there is no definitive evidence in humans for the “lateral pterygoid hypothesis,” and there is also little reliable information as to the effect of occlusal variables on the activity of the lateral pterygoid muscle. There is also little information on the effect of pain on lateral pterygoid muscle activity, although recent studies demonstrate that the pattern of pain-induced changes in lateral pterygoid muscle EMG activity is not clear-cut but can vary with the task performed and jaw displacement magnitude. The lateral pterygoid muscle is a difficult muscle to access, and only verified recordings from the muscle will yield definitive conclusions. The Lateral Pterygoid Muscle: Function and DysfunctionGreg M. Murray10.1053/j.sodo.2011.10.001Seminars in Orthodontics 18, 1 (2012)2012-03-01Seminars in Orthodontics2012-03-01181S1073-8746(11)X0005-14450http://www.semortho.com/article/PIIS1073874611000995/abstract?rss=yes This article discusses the subject of articulators in orthodontics. It is in 3 parts: the first deals with why articulators are used; the second deals with techniques needed to use the instrumentation; and the third illustrates how they are used in diagnosis. Using articulators, occlusal problems otherwise hidden can be uncovered, especially the cases that involve the vertical dimension. As with any diagnostic instrumentation, the practitioner has to learn how to use the instrument and the limitations imposed by said instrument. Articulators in OrthodonticsTheodore D. Freeland10.1053/j.sodo.2011.10.002Seminars in Orthodontics 18, 1 (2012)2012-03-01Seminars in Orthodontics2012-03-01181S1073-8746(11)X0005-15162http://www.semortho.com/article/PIIS1073874611001009/abstract?rss=yes Persistent pain is the main reason for patient presentation with temporomandibular joint (TMJ) disorders. The pain is thought to result, at least in part, from sensitization of trigeminal sensory neurons that innervate the TMJ region. Sensitized sensory neurons can be hyperexcitable, responding both more readily and more vigorously to peripheral stimuli. At a cellular level, it is the distribution and function of ion channels and receptors that determine neuronal hyperexcitability. Thus, these ion channels and receptors are potential targets for the development of novel therapeutics. In this review, we will explore the role of specific ion channels and receptors that are actively being investigated in preclinical studies, focusing on inflammatory-induced pain of the TMJ, and comment on the therapeutic potential of pharmacological manipulation of these channels and receptors in the treatment of pain associated with TMJ disorders. Neurobiology of Temporomandibular Joint Pain: Therapeutic ImplicationsErnest A. Jennings, Michael C. Williams, Vasiliki Staikopoulos, Jason J. Ivanusic10.1053/j.sodo.2011.10.003Seminars in Orthodontics 18, 1 (2012)2012-03-01Seminars in Orthodontics2012-03-01181S1073-8746(11)X0005-16372http://www.semortho.com/article/PIIS1073874611001010/abstract?rss=yes Differently enabled functional movements of the mandible and different types of maxillomandibular and occlusal relations may share a cause-and-effect relationship with the disorders affecting the temporomandibular joint (TMJ). The purpose of this article is to draw inferences with orthodontic implications for the TMJ from an overview of adverse factors for growth and biomechanics of the TMJ, dentofacial characteristics associated with temporomandibular disorders, and mechanism of action of orthodontic interventions affecting the TMJ. Inferences drawn include the importance of history taking, functional evaluation and the need for radiological evaluation of TMJ condyle and disk, and position and function during procedures that are expected to interfere with TMJ homeostasis, for example, surgical craniofacial corrective procedures, functional therapy, and occlusal reconstructive procedures. Extremes of form (eg, excessive overjet and overbite, open bite and deep bite, skeletal hyperdivergence and hypodivergence) and differently enabled mandibular functions resulting in overloading of TMJs are all potential factors in the etiology of its disorders, thus enhancing the need for its evaluation before, during, and after treatment; a reciprocal relationship exists between growth and biomechanics of the TMJ, dentofacial characteristics and articular afflictions, occlusion and TMJ, and mandibular movements and TMJ. These interrelated, interdependent, and/or coexistent factors have a bearing on the diagnosis and treatment of the disorders of the TMJ. Orthodontic therapy should be directed to achieve a structural balance to facilitate physiologic adaptation and rehabilitation. Because the movements of the mandible are not restricted by the joint structure per se, other operative templates, for example, neuromuscular and psychological, apart from the structural template, contribute significantly to its complex functions and pathology. There is a need to find optimum values of structure and function of the masticatory system and develop mechanisms that can record and reproduce highly accurate geometric models of a subject's TMJ and teeth combined with recordings of chewing trajectories and 3-dimensional TMJ movements to obtain subject-specific models of masticatory system by either improving upon conventional mechanical articulators or by application of virtual-reality techniques for the development of virtual articulators for diagnosis and treatment of the disorders of masticatory system. Orthodontic Implications of Growth and Differently Enabled Mandibular Movements for the Temporomandibular JointRakesh Koul10.1053/j.sodo.2011.10.004Seminars in Orthodontics 18, 1 (2012)2012-03-01Seminars in Orthodontics2012-03-01181S1073-8746(11)X0005-17391http://www.semortho.com/article/PIIS1073874611001022/abstract?rss=yes The etiology of temporomandibular joint (TMJ) disorders, including osteoarthritis, is largely unexplained. TMJ disk integrity is crucial, as its failure appears to precede degeneration of the joint. During mandibular function, the TMJ disk undergoes displacements and deformations, generating strains and stresses. Dynamic stereometry, a combination of imaging and jaw tracking, yields a noninvasive, 3-dimensional, and dynamic representation of the relationship between the articular surfaces of the human TMJ. The aim of this study was to refine this method to depict also movement and deformation of the TMJ disk during jaw opening/closing. Data collected in 4 asymptomatic subjects (2 male and 2 female subjects, aged between 24 and 32 years) indicated large disk displacements and deformations that can load TMJ soft tissues during opening and closing of the jaw. Such displacements and deformations can trigger disk damage during dysfunctional loading and/or compromised state of TMJ tissues. These displacements and deformations can also be used for numerical joint modeling. Movements of the Temporomandibular Joint DiskLuigi M. Gallo10.1053/j.sodo.2011.10.005Seminars in Orthodontics 18, 1 (2012)2012-03-01Seminars in Orthodontics2012-03-01181S1073-8746(11)X0005-19298http://www.semortho.com/article/PIIS1073874611001289/abstract?rss=yesFuture Issues10.1053/S1073-8746(11)00128-9Seminars in Orthodontics 18, 1 (2012)2012-03-01Seminars in Orthodontics2012-03-01181S1073-8746(11)X0005-1II