The habitual chewing side syndrome

Background. Temporomandibular joint (TMJ) disorders (TMD) are defined as a subgroup of craniofacial pain problems that involve the masticatory musculature, the temporomandibular joints (TMJs), and associated structures. Pain and/or limited mouth opening are the main symptoms. The prevalence of treatment need for TMD in adults was estimated to be 15.6%. The cause of TMD remains unknown; however, TMJ overloads are a recognized factor. Aims. The main goal of this work is to assess an association between functional, dynamic and anatomical characteristics of the masticatory system in patients suffering TMD-pain condition and in healthy groups. With this in mind, our team conducted a series of studies to explain this situation, using strictly the scientific method. Method. The masticatory function of 21 completely dentate participants with chronic temporomandibular disorders (all but one with unilateral symptoms) was assessed by observing them eat almonds, inspecting the lateral horizontal movement of the jaw, with kinesiography, and by means of interview. The condylar path in the sagittal plane and the lateral anterior guidance angles with respect to the Frankfort horizontal plane in the frontal plane were measured on both sides in each individual. Results. Sixteen of 20 participants with unilateral symptoms chewed on the affected side; the concordance (Fisher’s exact test, P = .003) and the concordance-symmetry level (Kappa coefficient k = 0.689; 95% confidence interval [CI], 0.38 to 0.99; P=.002) were significant. The mean condylar path angle was steeper (53.47(10.88) degrees versus 46.16(7.25) degrees; P = .001), and the mean lateral anterior guidance angle was flatter (41.63(13.35) degrees versus 48.32(9.53) degrees P = .036) on the symptomatic side. Study power: with a sample size of 19, and assuming a two-sided test at the 0.05 level, the study had power of 0.8 to detect a value of Kappa of 0.6 or larger when testing the null hypothesis that Kappa = 0. Interpretation. The results of this study support the use of a new term based on etiology, ‘‘habitual chewing side syndrome’’, instead of the nonspecific symptom-based ‘‘temporomandibular joint disorders’’; this denomination is characterized in adults by a steeper condylar path, flatter lateral anterior guidance, and habitual chewing on the symptomatic side. Additionally, because muscular activity is responsible for TMJ-loads, muscular coactivation was assessed using surface electromyography (sEMG); although limited, sEMG could inform about some subclinical condition and about the type of muscular co-activation and their asymmetry in TMD patients, that could be of interest to elucidate the physiology of this conditionand showing moderate discriminatory capacity between TMD or healthy subjects. Lastly, this study evaluated incisal forces and muscular coactivation simultaneously. It is suggested that mean incisal forces promote equilibrated muscular coactivation; however, submaximal incisal effective forces required the activation mainly of masseter muscles; due that masseter muscles are responsibles for TMJ-loads, this study allow infer TMJ loads increases during submaximal incisal bitting; probably this task should be avoided in TMD patients. Funding. This study was financed with a grant PI11/02507 from the Institute of Health Carlos III of the Ministry of Science and Innovation of the Government of Spain. It was completed with the equipment granted by the General Directorate of Universities and Research; Department of Education and University. Xunta de Galicia. Official Journal No. 143 Galicia, July 22, 1996. And the Department of Innovation, Industry and Commerce. Xunta de Galicia, April 30, 2004. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Temporomandibular disorders: the habitual chewing side syndrome

Background:Temporomandibular disorders are the most common cause of chronic orofacial pain, but, except where theyoccur subsequent to trauma, their cause remains unknown. This cross-sectional study assessed chewing function (habitualchewing side) and the differences of the chewing side and condylar path and lateral anterior guidance angles in participantswith chronic unilateral temporomandibular disorder. This is the preliminary report of a randomized trial that aimed to testthe effect of a new occlusal adjustment therapy.Methods:The masticatory function of 21 randomly selected completely dentate participants with chronic temporoman-dibular disorders (all but one with unilateral symptoms) was assessed by observing them eat almonds, inspecting the lateralhorizontal movement of the jaw, with kinesiography, and by means of interview. The condylar path in the sagittal plane andthe lateral anterior guidance angles with respect to the Frankfort horizontal plane in the frontal plane were measured onboth sides in each individual.Results:Sixteen of 20 participants with unilateral symptoms chewed on the affected side; the concordance (Fisher’s exacttest, P = .003) and the concordance-symmetry level (Kappa coefficientk= 0.689; 95% confidence interval [CI], 0.38 to 0.99;P = .002) were significant. The mean condylar path angle was steeper (53.47(10.88) degrees versus 46.16(7.25) degrees;P = .001), and the mean lateral anterior guidance angle was flatter (41.63(13.35) degrees versus 48.32(9.53) degrees P = .036)on the symptomatic side.Discussion:The results of this study support the use of a new term based on etiology, ‘‘habitual chewing side syndrome’’,instead of the nonspecific symptom-based ‘‘temporomandibular joint disorders’’; this denomination is characterized inadults by a steeper condylar path, flatter lateral anterior guidance, and habitual chewing on the symptomatic sideThis study was financed with a grant PI11/02507 from the Institute of Health Carlos III of the Ministry of Science and Innovation of the Government of Spain. It was completed with the equipment granted by the General Directorate of Universities and Research; Department of Education and University. Xunta de Galicia. Official Journal No. 143 Galicia, July 22, 1996. And the Department of Innovation, Industry and Commerce. Xunta de Galicia, April 30, 2004S

Asymmetry of dental or joint anatomy or impaired chewing function contribute to chronic temporomandibular joint disorders

Introduction: The etiologies of most chronic temporomandibular joint disorders are unknown. However, an association between habitual chewing on a particular side and chronic temporomandibular joint disorders has been reported. The aim of this study was to investigate the differences between sides (affected vs unaffected) of biodynamic factors (including lateral dental guidance determined by dental anatomy) or condylar path angles (determined by temporomandibular joint morphology) and chewing function (physiological alternate chewing vs single habitual chewing side). The study scope was to investigate possible etiological factors to improve the understanding of temporomandibular joint disorders. The null hypothesis was that no difference would be found between sides that are or are not affected by chronic temporomandibular joint disorders in chewing function or in levels of dental or temporomandibular joint remodeling. Methods: This cross-sectional, double-blind study involved 24 adults with substantial, chronic, unilateral symptoms diagnosed as temporomandibular joint disorders. Chewing function, temporomandibular joint remodeling (using axiography) and dental anatomy (lateral guidance angles using kinesiography) were assessed. Results: Habitual chewing on one particular side was observed in 17 of 24 participants; significantly more (n = 15) chewed on the affected side than on the unaffected side (P = 0.002 in a two-tailed Fisher’s exact test; risk estimate = 4.5; 95% CI 1.326–15.277). The condylar path (CP) angle was steeper on the affected side than on the unaffected side (mean (standard deviation) = 50.52° (9.98°) versus 45.50° (7.98°); P = 0.002 in a two-tailed t-test). The lateral guidance (LG) angles were flatter on the affected side in all 24 participants. Conclusion: Our results suggest that habitual chewing on one side may be associated with increasing condylar path, with flattening lateral guidance angles, and also with chronic temporomandibular joint disorder on the habitual chewing sideThis study was supported by the Carlos III Institute of Health (Ministry of Science and Innovation of the Government of Spain and the European Development Fund, ‘Una manera de hacer Europa’) (grant no. PI11/02507). The design, management, analysis, and reporting of the study are entirely independent of the Carlos III Institute of HealthS