Logistic regression analysis on correlation of occlusion asymmetry and temporomandibular disorders

Abstract Background: The association between occlusion and temporomandibular disorders (TMDs) remains obscure. The present purpose was to explore the asymmetrical occlusion feature(s) potentially linked to the temporomandibular disorders. Methods : One hundred and forty-eight female cases with a chief complaint of malocclusion, 84 had not (Group-ORD1) and 64 had signs of TMDs (Group-ORD2), and additional 84 female cases with a chief complain of TMDs problems and a history of orthodontic therapy were included (Group-TMD). The following six occlusion variables, measured on plaster study casts, wererecorded as 1 for asymmetry and 0 for symmetry: (i) the mesial-distal relationship of the first molar (F1) and canine (F2); (ii) overjet and overbite relationship of anterior (F3) and posterior teeth (F4); (iii) tooth/teeth missing (F5); and (iv) the weight of the asymmetrical occluding pair (F6). F6 was the ratio of the number of occluding pairs in symmetrical relation to the number of tooth pairs. If the ratio was greater than 60%, F6 would be recorded as 0, otherwise it would be recorded as 1. Binary stepwise logistic regression method was used for data analyses. Results : For Group-ORD2 versus Group-ORD1, the F6 variable was entered in the simple logistic regression model. The F6 variable and the interactions of F1 and F2 (F1*F2) and of F1, F2 and F6 (F1*F2*F6) entered the multivariable logistic regression model (all OR > 2.68). For Group-TMD versus Group-ORD1, the variables and interactions were F1, F5, and F6 (all OR > 2.39), F4 (OR = 0.28), F5*F6, F1*F2*F6, F1*F5*F6, F1*F2*F5*F6 (all OR > 2.78), and F2*F4, F3*F5, and F2*F4*F6 (all OR < 0.13). For Group-TMD versus Group-ORD2, the variables and interactions were F5, F5*F6, F1*F5*F6 (all OR > 4.03), and F4, F4*F6 and F2*F4*F6 (all OR < 0.21) (all P < 0.05). Of the 84 patients in Group-TMD, 39 had one or more missing teeth due to tooth extraction during orthodontic treatment, and 25 of those 39 patients had asymmetric teeth extraction. Conclusions : Patients with sagittal asymmetry, asymmetrical missing teeth or asymmetrical weight of contact have a higher risk of having TMDs problems which effects could be enhanced by horizontal asymmetry.