Influence of bone loss and inclination of incisor on periradicular stresses due to simulated bite force

Abstract Introduction Adults with sequelae of periodontal disease tend to have bone loss, with consequent flaring of the maxillary incisors. Objective The influence of bone loss and the inclination of the maxillary incisor in the distribution of stresses due to simulated bite forces was studied. Material and method Models in epoxy resin were made in three conditions (without bone loss and with bone loss of 5mm and 8mm). Increases in the labial inclination of the maxillary incisor of 10° and 20° were obtained with a beveled metallic block. Loads of 100N were applied five times in each condition using a universal test machine. The models were observed and filmed with a circular polariscope. Orders of isochromatic fringes (stresses) on the labial, lingual, and apex surfaces were recorded. The agreement of the data was evaluated using the weighted kappa test, and the results were 0.89 and 0.82 for intra- and inter-examiners, respectively. Result The results of the Kruskal–Wallis and SNK tests indicated higher stresses (2.0) with increased labial inclination in the labial surface; higher stresses (2.67) with increased bone loss; higher greater stresses with the association of bone loss and labial-inclination (3.6); and the highest stresses tended to concentrate on the labial surfaces, except in cases of normal inclination and without bone loss (0.45). Conclusion It was concluded that increases in both the labial inclination of the maxillary incisors and bone loss increase periradicular stresses, and the combination of these factors further increases the stresses due to bite forces, with the highest concentration on the labial side.摘要 引言：牙周病后遗症成年患者常出现牙槽骨丧失，进而导致上颌切牙唇向散开。 研究目的：本研究探讨了牙槽骨丧失程度与上颌切牙倾斜度对模拟咬合力所致应力分布的影响。 材料与方法：采用环氧树脂制备三种实验模型，分别为无骨丧失组、骨丧失5mm组及骨丧失8mm组。通过斜面金属块使上颌切牙获得10°和20°的唇向倾斜增量。使用万能试验机在每种条件下施加100N载荷，每组重复加载5次。采用圆偏光镜对模型进行观察并摄像，记录唇面、舌面及根尖面的等色条纹（应力）级数。采用加权Kappa检验评估数据一致性，组内与组间检验结果分别为0.89和0.82。 结果：克鲁斯卡尔-沃利斯（Kruskal–Wallis）检验与SNK检验结果显示：唇面应力随唇向倾斜度增加而升高（2.0）；随骨丧失程度加重应力升高（2.67）；骨丧失与唇向倾斜联合存在时应力进一步升高（3.6）；且除正常倾斜且无骨丧失组（0.45）外，应力多集中于唇面。 结论：本研究证实，上颌切牙唇向倾斜度增加与牙槽骨丧失程度提升均可升高根尖周应力，二者联合作用可进一步加剧咬合力所致应力，且应力最高集中于唇侧区域。