The study of skeletal mechanics of anterior crossbite evaluated with SN length

Abstract

OBJECTIVE: To study the stability of SN (anterior cranial base) length and the ability to evaluate upper lower jaws, and study the inner skeletal structure mechanism. METHODS: Interrelated angles, SN length, maxillary and mandible length were measured, the ratios between SN and maxillary and mandible length were compared with normal standard data, the data between mixed and permanent dentition groups were compared. RESULTS: No significant difference was found on SN length between anterior crossbite patients and normal sample. Significant difference was found between crossbite and normal data on the ratio of SN and maxillary length and mandible length. Based on evaluation of SN length, the crossbite can be divided into three types of skeletal structures including normal maxilla and longer mandible, short maxilla and normal mandible, short maxilla and longer mandible, the longer mandible is a main factor. CONCLUSION: With the advantage of stability, SN can be used to evaluate maxilla and mandible, and decide the skeletal mechanics of crossbite individually and accurately.

目的: 探討前顱底長度的穩定性及其評價上下頜骨骨性結構發育狀況的價值。方法: 采用 83例安氏Ⅲ類前牙反牙合者的頭顱側位定位片 ,對相關角度、前顱底長度、上下頜骨長度及前顱底長度與上下頜骨長度的比例進行測量 ,根據正常標準分析前牙反牙合者在替牙期組和恒牙期組的頜骨發育改變。結果: 前牙反牙合組前顱底長度與正常對照組比較無顯著性差異 ,而其前顱底長度、上下頜骨間的比率與正常組比較有顯著性差異。根據前顱底長度評價上下頜骨發育狀況 ,前牙反牙合可分為上頜正常、下頜過長 ,上頜不足、下頜正常 ,以及上頜不足、下頜過長 3種骨性結構 ,其中下頜過長為主要因素。結論: 前顱底長度穩定 ,用其參考評價上、下頜骨的發育狀況 ,分析反牙合的骨性結構機理 ,具有更個體化、更準確的優點。