The Study Of The Effect On The Mandible Position And Development In Teenagers With Premolars Scissor Bite

Objective: To study the effect of adolescents premolar scissor bite on the position and development of mandible and provide proper reference for correct orthodontic diagnosis and right time to treatment.Methods: 100 adolescents(54 females,46 males)with scissor bite of premolars(70 unilateral,30 bilateral)were selected as experimental group between 2010 to 2017 from the Department of Orthodontics,Stomatology Hospital of China Medical University;30 bilateral patients served as bilateral group and 70 unilateral patients served as unilateral group.Among unilateral group,54 cases of unilateral group have one premolar scissor bite and 16 cases have two,25 cases of unilateral group were first premolar scissor bite and 29 cases were second premolar scissor bite.Lateral cephalograms were recorded before treatment.20 related hard tissue variables on maxilla and mandible were measured cephalometrically by Winceph 9.0 software and the cephalometric data in different groups were analyzed statistically by using SPSS 21.0 software package.Results: 1.Compared with normal occlusion,Beta angle,SNB,SND,ANB,AB-Plane angle,N-S-Ar,APDI,convexity angle,facial angle,Wits,SN-Go Gn,Ar-Go,S-Co,Co-Po,The three angle showed statistically significant difference in both unilateral group and bilateral group(P<0.05).Besides,Go-Pog showed statistically significant difference between normal occlusion and unilateral group(P<0.05).2.For the variables study group showed difference with normal value above,the Ar-Go and Co-Po of the unilateral group were significantly shorter than the bilateral group(P<0.05).3.For the variables unilateral group showed difference with normal value above,there was no significant difference in the unilateral group between the first premolar scissor bite and the second premolar scissor bite(P>0.05).4.For the variables unilateral group showed difference with normal value above,there was no significant difference in the unilateral group between one premolar scissor bite and two premolar scissor bite(P>0.05).Conclusion: 1.Premolar scissor bite in teenagers restricts the sagittal position of mandible and tend to have skeletal II sagittal jaw relationship no matter the scissor bite is bilateral or unilateral.2.Premolar scissor bite affects the growth of mandible characterized by mandibular retrusion,bilateral scissor bite makes the mandibular ramus and overall length of mandible small,Unilateral scissor bite makes mandibular body length and mandibular length small,the degree of influence from Unilateral scissor bite is more severe than bileral scissor bite.3.The degree of influence from premolar scissor bite on the mandible is not related to the number or the position of it.