辅助固位形对低矮磨牙全冠修复体固位力和边缘适合性的影响

Effect of auxiliary resistance forms on the resistance and marginal fitness of complete crowns for short molar preparations

目的研究不同聚合度的沟固位形和洞固位形对低矮磨牙全冠修复体固位力和边缘适合性的影响。方法选取70颗Nissin树脂牙,在研磨仪上预备成聚合度为20°、龈高度为2.5 mm的预备体。选择10颗作为对照组,不制备辅助固位形;另设2个实验组,每组30颗,分别制备沟固位形和洞固位形。沟固位形组又分3个小组,每组10颗,分别在近远中邻面中央制备外展度数为0°、6°和20°的沟固位形;洞固位形组同样分3个小组,每组10颗,分别在面中央预备出外展度数为0°、6°和20°的洞固位形。常规制作金属全冠,体视显微镜下在4个轴面的牙颈部中点处测量冠黏固前后边缘间隙的大小。将黏固全冠的树脂牙牙长轴与水平面呈45°固定于特制底座上,采用万能试验机静态加载记录全冠脱离预备体时的力值。采用SAS 9.2软件进行分析。结果 0°沟固位形组、0°洞固位形组和6°洞固位形组的固位力明显大于对照组,差异有统计学意义(P<0.05);全冠黏固后,除20°沟固位形组外的边缘浮起量与对照组无明显差异外,其余实验组均明显大于对照组(P<0.05)。结论外展度数较小的辅助固位形可增加全冠固位力,但是辅助固位形不利于冠的就位,降低了全冠的边缘适合性;在固位力足够的情况下应尽量避免使用辅助固位形。

Objective To evaluate the effect of different auxiliary resistance forms on the resistance and marginal fitness of complete crowns for short molar preparations. Methods A total of 70 Nissin resin teeth were prepared with 20° total occlusal convergence, 2.5 mm of occlusocervical height, and a shallow finish line on a milling machine. The milled preparations were then randomly assigned to 7 groups of 10. The first group was used as the control group. A total of 30 dies were modified by preparing interproximal grooves with angles of 0°, 6°, and 20° centered on the mesial and distal surfaces of the dies. The rest of the teeth were prepared with occlusal holes in the center of the occlusal surface milled with the same burs to form 0°, 6°, and 20° holes. Cobalt-chromium copings were fabricated for all specimens. The marginal gap of specific points on the axial surface was measured before and after cementation. The resistance of each specimen was evaluated by applying an external force at an angle of 45° to the long axis of the die by using a universal testing machine in a lingual tO buccal direction. The maximum force applied before crown dislodgement was measured. Data were analyzed using the SAS 9.2 software. Results The results showed that the 0° groove, 0° hole, and 6° hole were effective in improving the resistance of the complete crowns （P〈0.05）. The 0° groove, 6° groove, 0° hole, 6° hole, and 20° hole had significant difference with the control group in terms of marginal discrepancies （P〈0.05）. Conclusion Auxiliary resistance forms with less degree indicate greater resistance force but worse marginal fitness. In clinical practice, if the resistance of a preparation is enough, the auxiliary resistance forms should be avoided from being used.