[Effect of premolars scissor bite on the sagittal position of mandible].

Purpose: To study the effect of adolescent premolar scissor bite on the sagittal position of mandible and provide proper reference for correct orthodontic diagnosis and right time to treatment. METHODS： One hundred adolescents (54 females, 46 males) with scissor bite of premolars(70 were unilateral,30 were bilateral) were selected as experimental group between 2004 to 2017 from the Department of Orthodontics, Stomatological Hospital of China Medical University. Among them, 54 females served as female group, 46 males served as male group; 30 were bilateral and 70 were unilateral. Lateral cephalograms were recorded before treatment. 16 sagittal hard tissue variables on maxilla and mandible were measured cephalometrically by Winceph 9.0 software, and the cephalometric data were analyzed statistically by using SPSS 21.0 software package.

Results: Compared with normal occlusion, Beta angle, SNB, SND, ANB, AB-Plane angle, APDI, convexity angle, facial angle, Wits, Co-Po showed statistically significant difference in both unilateral group and bilateral group (P<0.05). In addition, Go-Pog showed statistically significant difference between normal occlusion and unilateral group(P<0.05).

Conclusions: Adolescents with premolar scissor bite restricts the sagittal position of mandible and tend to have skeletal Ⅱ sagittal jaw relationship. Scissor bite affects the growth of mandible and makes mandibular body length and mandibular length less than normal. More attention should be paid to scissor bite as early as possible to decrease the harmful effects on growth of mandible and sagittal jaw relationship.