利用锥形束CT对下颌磨牙根分叉病变区骨嵴形态的观察

目的：利用锥形束计算机体层摄影术（cone beam computed tomography, CBCT）观察下颌磨牙Ⅱ度和Ⅲ度根分叉病变区（furcation involvement, FI）近远中向的骨嵴形态和骨袋分布情况，并提出对骨嵴形态的分类方法。方法： 在既存的CBCT资料中，选取存在根分叉区水平向骨缺损的下颌磨牙进行观察,共纳入81颗下颌磨牙，共计117处Ⅱ度或Ⅲ度根分叉病变。依据邻面牙槽嵴顶连线与根分叉顶下方的牙槽嵴的位置关系，将根分叉区近、远中向的骨嵴形态分为凹陷型、水平型和凸出型，其中凹陷型又按照邻面牙槽嵴顶的连线与根分叉顶的位置关系，分为亚型1（牙槽嵴顶连线位于根分叉顶冠方或同一水平）与亚型2（牙槽嵴顶连线位于根分叉顶的根方）， 统计各类型出现的比例，在CBCT的矢状面图像中观察骨袋的分布情况。结果： 在117处Ⅱ度和Ⅲ度FI中，水平型骨嵴形态出现的比例最高（64.10%）， 凸出型出现的比例最低(6.84%)， 凹陷型亚型1和亚型2出现的比例分别为13.68%和15.38%。有利于成骨的凹陷型亚型1的骨嵴形态，在Ⅱ度FI中出现的比例为8.96%，在Ⅲ度FI中为 20.00%；117处病损中，有31处合并骨下袋，其中29处骨下袋位于牙齿邻面，其余2处位于根分叉区,骨下袋出现的频率在凹陷型亚型1中最高。结论： 利用CBCT观察下颌磨牙根分叉区近、远中向的骨嵴形态并进行分类，有利于制定正确的治疗方案，也可用于分析骨嵴形态与再生性治疗成骨效果间的关系。

Observation of bone morphology in furcation defects of mandibular molars using cone beam computed tomography

Objective:To observe mesial-distal bone morphology in classes Ⅱ and Ⅲ furcation involvements (FI) of mandibular molars using cone beam computed tomography (CBCT),to develop a classification system of mesial-distal bone morphology of furcation defects and to observe the intrabony defects on CBCT images.Methods:Based on the existing CBCT data,the mandibular molars with horizontal bone defects in furcation area were observed.One hundred and seventeen sites of 81 mandibular molars with class Ⅱ or class Ⅲ FIclassified on CBCT images were included.The classification system of mesial-distal bone morphology of furcation defects was developed.According to the location of the line drawn from mesial to distal alveolar bone crest (AC-line) of the tooth and bone level under furcation fornix,the bone morphology was classified into three types,including concave type,flat type and protruding type.The concave type was divided into two subtypes according to the location of AC-line and furcation fornix (Fx),which were subtype 1 (AC-line coronal or equal to Fx) and subtype 2 (AC-line apical to Fx).The frequency of each type was calculated and analyzed.The intrabony defects was observed on sagittal CBCT images.Results:In the 117 sites with FI,the flat type appeared with the highest rate (64.10％) and the protruding type appeared with the lowest rate (6.84％).The rates of subtype 1 and subtype 2 of concave type were 13.68％ and 15.38％,respectively.The rate of subtype1 which was supposed to be beneficial for bone regeneration was 8.96％ in class Ⅱ FI and 20.00％ in class Ⅲ FI.Thirtyone intrabony defects were found among the 117 FI,29 of which appeared in proximal aspect of the tooth and the left 2 appeared in furcation area.The highest frequency of the intrabony defects was found in subtype 1 of concave type.Conclusion:The classification of mesial-distal bone morphology on CBCT images may be helpful for clinicians to make accurate treatment plan before surgery and could be used in future studies to understand the influence of bone morphology on regenerative therapy for furcation defects.