比较口内扫描和模型扫描对数字化牙列模型咬合定量分析的影响

目的：为了更准确地进行上下颌牙列数字化模型的咬合状况定量分析，对分别用口内扫描和模型扫描方法获取的三维数字化模型的咬合接触指标进行定量分析及对比研究。方法：用三维激光扫描仪对具有完整牙列并且咬合正常的健康志愿者5人进行口内扫描，分别获取单侧1个牙位（第一磨牙）、2个牙位（第二前磨牙及第一磨牙）、3个牙位（两个前磨牙及第一磨牙）及其邻牙的上下颌数字化模型，运用专用计算机分析软件进行牙尖交错位时咬合接触状况的三维测量及分析，然后用加成型硅橡胶采取上下颌牙列实物印模并灌制超硬石膏模型，应用专用定位装置将上下颌模型在牙尖交错位对合并固定，用激光扫描仪扫描上下颌模型，形成三维数字化牙列模型。对用口内和模型扫描方法分别获得的数字化模型的下颌第一磨牙进行咬合接触紧密程度（上下颌咬合面平均间距）、咬合接触面积及牙尖斜度等咬合相关指标的定量分析和比较。应用配对t检验方法比较两种扫描方法获得数字化模型的各项指标的统计学差异（α=0.05），重复测量计算牙尖斜度的组内相关系数（intraclass correlation coefficient，ICC）进行一致性检验。结果：口内扫描1~3个牙位时获得的上下颌第一磨牙咬合面平均间距分别比模型扫描的小0.134 mm、0.177 mm和0.207 mm，差异有统计学意义（P<0.5）。两种扫描方法的标准差之差分别为0.02 mm、0.02 mm和0.03 mm，差距较小。口内扫描1~3个牙位时下颌第一磨牙的咬合接触面积分别比模型扫描的大8.65 mm2、10.28 mm2和11.46 mm2，差异有统计学意义（P<0.5）。两种扫描方法的标准差之差为0.43 mm2、1.55 mm2和2.04 mm2，1个牙位扫描后的标准差要明显小于2个牙位和3个牙位时。两种扫描方法进行牙尖斜度测量时，ICC大于0.90，两种方法的牙尖斜度测量值差异无统计学意义（P>0.5）。结论：口内扫描测得的咬合面平均间距小于模型扫描测得的，咬合接触面积大于模型扫描测得的，说明口内扫描反映的咬合接触程度更为紧密。两种扫描方法测量咬合接触面积的标准差之差与测量牙位数量相关，两种方法测量得到的牙尖斜度差异没有统计学意义，说明口内扫描进行牙齿形态学指标测量时与模型扫描无明显差别，有望今后替代模型扫描。

Influence of intraoral scan and dental cast scan on occlusal quantitative analysis of virtual dental model

Objective: To make more accurate occlusal quantitative analysis of three-dimensional (3D) virtual dental models and to compare the occlusal contact obtained by intraoral and dental cast scan. Methods: In this study, 5 subjects were intraoral scanned using laser scanner (3 shapes, Germany) to obtain the 3D virtual models of one tooth (the first molar), two teeth (the second premolar and the first molar),three teeth (the premolars and the first molar) and their opposite teeth, respectively. The silicone impressions were made and dental stone models were poured for each of them. The dental casts were scanned and then they were fixed to the maximum intercuspal position with a special locating jig for a rescanning of occlusal position. The virtual models taken intraorally and obtained with dental cast scan were introduced to a 3D quantitative analysis system, and some criteria regarding to occlusal contact were cal-culated and analyzed. The occlusal criteria were mean values of occlusal clearance space between the upper and lower occlusal surface (clearance),occlusal contact area (area),and cusp inclination (angle) of the mandibular first molar. Paired t tests were used to evaluate differences of occlusal criteria between the virtual models obtained with the intraoral scan and dental cast scan (a =0.05). Results: The mean values of occlusal clearance of one to three teeth obtained by way of intraoral scan were smaller than those obtained by way of cast scan by 0. 134 mm, 0. 177 mm, and 0. 207 mm,respectively. While the occlusal contact areas were greater than the cast scan by 8. 65 mm2,10. 28 mm2,and 11.46 mm2. No statistically significant differences were found between the cusps inclinations obtained with the two scanning methods,and the interclass correlations were high. Conclusion: Occlusal clearance obtained by intraoral scan was less than that by cast scan while the occlusal contact area was greater than the latter, indicating that intraoral occlusal contact was closer. The difference of the standard deviations of occlusal clearance measured by the two methods were small and that of occlusal contact area was influenced by the number of teeth scanned intraorally. There was no statistical difference in cusp inclination between the two methods.