Occlusal Contacts In Mandibular Protrusion And Lateral Excursion And Occlusal Contacts In Intercuspal Position Under Different Body Positions In Young Adults With Normal Occlusion

Objective:To study the occlusal contacts in mandibular protrusion and lateral excursion in the young adults with normal occlusion. Another objective was to study the influence of the body positions on the occlusal contacts in intercuspal position.Materials and Methods:(1)162volunteers were recruited from Fujian Medical University (male55, female107, age:18-23, ethnic Han). Occlusions of the volunteers were examined with thin articulating film in protrusion and lateral excursion.(2)135volunteers (27volunteers withdrew) were examined with T-scan Ⅲ digital occlusal analysis system at sitting,45°recline and supine positions respectively about the occlusal contacts in intercuspal position. The relationship between the occlusal contacts and the body position was analyzed with SPSS19.0by chi-square test, Fisher’s exact test and randomized block variance analysis, and counted the constituent ratio and the95%confidence interval.Results:(1) In protrusion,111volunteers had contacts only on their anterior teeth (68.52%),49had contacts both on anterior and posterior teeth (30.25%), and2volunteers had contacts only on posterior teeth (1.23%). In lateral excursion, the majority of volunteers had contacts only at the working side (241cases,74.38%); many people contacted both at the working and non-working sides (75cases,23.15%); a few volunteers only had contacts at the non-working side (8cases,2.47%). Among the volunteers,142of them were bilateral symmetry (87.65%), and 20were bilateral asymmetry (12.35%).(2) At the body positions of sitting,45°recline and supine, no significant difference was found on the contact teeth at the first contact frame (p=0.392) and the teeth with highest bite points at the maximum area (MA) frame (p=0.916). While the number of contact points at MA frame was significantly different (p=0.001). Besides, to the center of force (COF), the majority of the volunteers was different on account of the different body positions (94.81%), and the95%confidence interval was (0.911,0.985).45.68%of the COF at MA frame were located in white ellipse,90.86%in gray ellipse, and among the different body positions, no significant difference was found on the distribution of COF (P=0.867).Conclusions:(1) Within the limitation of the study, in mandibular protrusion, contacts only at anterior teeth were most frequently to be observed; while in mandibular lateral excursion, contacts only at the working-side were the predominance. The majority were bilateral symmetry.(2) The contact teeth at the first contact frame and the teeth with highest bite points at the maximum area frame were nothing to do with the body positions. While the number of contact points and the location of COF were different when the body positions changed, but the distribution of COF was not different among different body positions.(3) Compared to the traditional methods, diagnosing and adjusting the abnormal occlusion with T-scan Ⅲ digital occlusal analysis system were more accurate. The best position for occlusion adjustment was the sitting body position.