Relationship between Upper and Lower Molars during Mastication

Objectives：This study investigated the relationship between upper and lower molars in the early stage of mastication. Materials and Methods： We measured the occlusal contact areas during chewing test foods using the three-dimensional shape measurement system and the six-degreeof- freedom mandibular tracking device. The reference points corresponding to “A” and “B” occlusal contacts were selected from the surface of upper dental cast (UA, UB) and lower dental cast (LA, LB). The distance between reference point UA and LA, UB and LB were calculated (|A|, |B|). For evaluation of relationship between upper and lower molars during chewing gum, the ratios of |A|/|B| (AB ratio) were calculated. First 10 consecutive cycles of chewing gum were divided into two phase, early five strokes group (Ge) and last five strokes group (Gl). Paired t-test for AB ratios of Ge and Gl was performed. Results：Paired t-test showed a significant difference between AB ratios of Ge and that of Gl at 0.5 mm away from the terminal position of masticatory movements (p