Objective: To evaluate the effects of different edge compensation angles on the fracture strength of multilayer zirconia all-ceramic crowns and traditional uniform zirconia all-ceramic crowns.
Methods: The resin tooth preparation specimen of the mandibular first molar with a knife-edge was fabricated. A 3D digital model of the specimen was obtained by scanning it with a 3D dental model scanner. The 3D digital model was imported into computer aided design (CAD) software, and three 3D digital models of the full crown with the same surface shape are designed with the edge compensation angles of 30°, 45° and 60°, respectively. Then, the designed 3D digital model is imported into computer aided manufacturing (CAM) software. Three kinds of multilayer and homogeneous zirconia all-porcelain crowns with different edge compensation angles were fabricated, 10 each for a total of 60. The fracture load of each crown was measured under the electronic universal testing machine.
Results: Fracture load of multilayer and uniform zirconia all-ceramic crowns, (4 322.86±610.07) N and (5 914.12±596.80) N in the 30° group, (5 264.82±883.76) N and (5 220.83±563.38) N in the 45° group and (4 900.42±345.41) N and (5 050.22±560.24) N in the 60° group, respectively. The fracture load of multi-layer zirconia all-ceramic crowns in the 30° group was significantly lower than that of homogeneous zirconia all-ceramic crowns(P < 0.05); there was no statistical significance in 45° group and 60° group(P>0.05). In the multi-layer zirconia all-ceramic crowns: the fracture load of the 30° group was significantly lower than that of the 45° group (P < 0.05); there was no significant difference between the 30° group and the 60° group, the 45° group and the 60° group (P>0.05).In uniform zirconia full crown group: the 30° group was higher than the 45° group, the 30° group was higher than the 60° group (P < 0.05), and there was no significant difference between the 45° group and the 60° group (P>0.05).
Conclusion: The fracture loads of three kinds of uniform and multilayer zirconia all ceramic crowns with different edge compensation angles can meet the clinical requirements. A smaller edge compensation angle is recommended when using traditional zirconia all-ceramic crowns, while 45° is recommended when using multi-layer zirconia all-ceramic crowns.
目的: 评价不同刃状边缘补偿角度对多层氧化锆全瓷冠和传统均质氧化锆全瓷冠断裂强度的影响。
方法: 制作刃状边缘的下颌第一磨牙树脂牙预备体试件，使用三维牙颌模型扫描仪扫描试件，得到其三维数字模型。将数字模型导入计算机辅助设计(computer aided design, CAD)软件中，设计出牙合面形态相同的三种边缘补偿角度分别为30°、45°、60°的全冠三维数字模型，并将其导入计算机辅助制造(computer aided manufacturing，CAM)软件中，加工出三种不同边缘补偿角度的多层和均质氧化锆全瓷冠各10个，共60个。在电子万能试验机下检测各个牙冠的断裂载荷。
结果: 多层和均质氧化锆全瓷冠的平均断裂载荷，30°组分别为(4 322.86±610.07) N和(5 914.12±596.80) N，45°组分别为(5 264.82±883.76) N和(5 220.83±563.38) N，60°组分别为(4 900.42±345.41) N和(5 050.22±560.24) N，其中30°组中多层氧化锆全瓷冠的断裂载荷明显小于均质氧化锆全瓷冠的断裂载荷(P＜0.05)，45°组和60°组中差异均无统计学意义(P＞0.05)。在多层氧化锆全瓷冠中，30°组氧化锆全瓷冠的断裂载荷明显低于45°组(P＜0.05)，30°组与60°组、45°组与60°组差异无统计学意义(P＞0.05)。在均质氧化锆全瓷冠中，30°组高于45°组，30°组高于60°组(P＜0.05)，45°组与60°组差异无统计学意义(P＞0.05)。
结论: 三种不同边缘补偿角度制作的均质和多层氧化锆全瓷冠的断裂载荷均能满足临床要求，在使用传统氧化锆全瓷冠时推荐使用较小的边缘补偿角度，而在使用多层氧化锆全瓷冠时推荐使用的边缘补偿角度为45°。
Keywords: Edge compensation angle; Fracture strength; Knife-edge; Zirconia all-ceramic crown.