不同边缘设计的髓腔固位冠修复下颌前磨牙的应力分析

Influence of different designs of marginal preparation on stress distribution in the mandibular premolar restored with endocrown

目的采用三维有限元方法,研究髓腔固位冠修复下颌第一前磨牙牙体缺损时,不同边缘设计对牙体组织和修复体所受应力的影响。方法建立4种边缘设计形式(平面对接式边缘、直角肩台、135°肩台、凹面形边缘)的下颌第一前磨牙髓腔固位冠修复模型。加载点为牙齿长轴与牙合面交点,方向为与牙齿长轴平行、与牙齿长轴成45°,力量大小为100N。计算分析4种边缘设计形式的髓腔固位冠修复后牙体组织和修复体颈部的应力分布情况及最大Von Mises应力值。结果(1)沿牙齿长轴方向加载,应力集中出现在修复体和牙齿颈部的舌侧边缘,平面对接式边缘和直角肩台的颈部应力分布要比135°肩台和凹面形边缘的应力分布均匀;(2)施加与牙齿长轴成45°的载荷,应力主要集中在颊侧边缘,平面对接式边缘较其他3种边缘形式的应力分布要更为均匀,牙齿和修复体的最大应力值均明显高于与牙齿长轴平行加载情况下的应力值;(3)无论施加与牙齿长轴平行还是与牙齿长轴成45°的载荷,平面对接式边缘的牙齿和修复体颈部的应力值均最小,修复体颈部的应力值要大于牙齿颈部的应力值;(4)平面对接式边缘牙釉质的应力水平高于牙本质。结论从基牙和修复体受力情况来讲,髓腔固位冠修复采用平面对接式边缘和直角肩台优于其他边缘设计。

Objective To evaluate the effect of different designs of marginal preparation on stress distribution in the mandibular premolar restored with endocrown using three- dimensional finite element method. Methods Four models with different designs of marginal preparation, including the flat margin, 90° shoulder, 135° shoulder and chamfer shoulder, were established to imitate mandibular first premolar restored with endocrown. A load of 100 N was applied to the intersection of the long axis and the occlusal surface, either parallel or with an angle of 45° to the long axis of the tooth. The maximum values of Von Mises stress and the stress distribution around the cervical region of the abutment and the endocrown with different designs of marginal preparation were analyzed. Results The load parallel to the long axis of the tooth caused obvious stress concentration in the lingual portions of both the cervical region of the tooth tissue and the restoration. The stress distribution characteristics on the cervical region of the models with a flat margin and a 90° shoulder were more uniform than those in the models with a 135° shoulder and chamfer shoulder. Loading at 45° to the long axis caused stress concentration mainly on the buccal portion of the cervical region, and the model with a flat margin showed the most favorable stress distribution patterns with a greater maximum Von Mises stress under this circumstance than that with a parallel loading. Irrespective of the loading direction, the stress value was the lowest in the flat margin model, where the stress value in the cervical region of the endocrown was greater than that in the counterpart of the tooth tissue. The stress level on the enamel was higher than that on the dentin nearby in the flat margin model. Conclusion From the stress distribution point of view, endocrowns with flat margin followed by a 90° shoulder are recommended.