Causal Relationship between Occlusal Factors and Temporomandibular Disorders
Consistency of association
De Laat et al. investigated the correlation between occlusal parameters and symptoms of TMJ dysfunction and reported that the occlusal relationship could not possibly have a causal role in TMJ dysfunction . Furthermore, Egermark-Eriksson et al. reported that an attempt to analyze the longitudinal relationship between occlusal interference and the signs and symptoms of mandibular dysfunction did not reveal any strong correlations . Although asymmetric RCP-ICP slides were more prevalent in women with reduced disk displacement and large RCP-ICP slides, it was not clear whether these associations were etiologic or because of other secondary causes . Two recent studies by the same authors (Torii and Chiwata, 2007, 2010) reported the relationship between occlusal discrepancy (HOP and BOPO)and TMD symptoms [10,11].
A causal factor is responsible for the occurrence of symptoms. It is apparent that occlusal discrepancies did exist before the appearance of symptoms in the pilot study conducted by Torii and Chiwata . However, it is unclear whether the interferences in RCP or RCP-ICP existed before or after the appearance of the symptoms [4,5].Coherence of association
What does RCP mean physiologically? Why does the elimination of interferences in RCP or RCP-ICP relieve TMD symptoms? The answer to these questions have not yet been obtained. In infants, TMJ and jaw muscle function before tooth eruption, enabling the teeth to erupt and occlude in an optimal position . Weak jaw muscles affect tooth eruption leading to malocclusion and occlusal discrepancies between HOP and BPOP. Changes in the structure of TMJ or jaw muscles may be attributed to disturbances in teeth eruption, leading malposition. Thus, the pathological changes observed in TMJ and the jaw muscles appear because of the additional task of having to adapt to the malposition of the teeth within the mandible.
This is an interventional experiment; as previously mentioned, the elimination of occlusal interferences in RCP and RCP-ICP did not relieve TMD symptoms. In the contrast, the elimination of occlusal discrepancies between HOP and BPOP ameliorated TMD symptoms .
The etiology of TMD is considered to be multifactorial, and occlusal factors are currently not included among the causal factors of this disorder. However, the occlusal discrepancy between HOP and BPOP appears to play a causal role , thereby warranting the requirement for further studies to explore this aspect.
The author declares that he has no competing interests.
Department of Prosthodontics, School of Life Dentistry, Nippon Dental University, Japan
6.Torii K, Chiwata I. Relationship between habitual occlusal position and flat bite plane-induced occlusal position in volunteers with and without temporomandibular joint sounds. Cranio. 2005, 23(1):16-21.
7.De Laat A, Van Steenberghe D, Lesaffre E. Occlusal relationships and temporomandibular joint dysfunction. Part II: Correlations between occlusal and articular parameters and symptoms of TMJ dysfunction by means of stepwise logistic regression. J Prosthet Dent. 1986, 55(1):116-121.
8.Egermark-Eriksson I, Carlsson GE, Magnusson T. A long-term epidemiological study of the relationship between occlusal factors and mandibular dysfunction in children adolescents. J Dent Res. 1987, 66(1):67-71.