Department of Restorative Dentistry, University at Buffalo School of Dental Medicine, Buffalo, NY.
University at Buffalo School of Dental Medicine, Buffalo, NY.
J Prosthodont. 2020 Mar;29(3):219-225. doi: 10.1111/jopr.13016. Epub 2019 Jan 17.
Modification of intercuspal angulation (ICA) influences the amount of tooth structure removal, which may impact the retention and resistance form of the preparation. This study evaluated the impact of ICA on the marginal gap of CAD/CAM crowns and the influence that tooth structure removal, caused by variation of ICA, has on the resistance and retention form of the preparation.
Sixty ivorine molars were manufactured with various ICAs (100°, 110°, 120°, 140°, 160°, and 180°; 10 per group). The preparations were digitized using an intraoral scanner, and the crowns were designed using a design software. The designed crowns were then manufactured from lithium disilicate using a 3-axis milling machine, with the "detailed mode" selected for the manufacturing. The marginal gap of each crown was evaluated using a stereomicroscope at 20× magnification. Then, the marginal integrity and the resistance form of the preparation were assessed by tactile-visual evaluation, and they were given a categorical score. Crowns were then secured on their associated preparations using a temporary luting agent, and retention force was measured on a universal testing machine under tension with a 0.5 mm/min crosshead speed. Wilcoxon test followed by post-hoc tests (α = 0.05) were used to evaluate the impact of the ICA on the marginal gap and the retention form of the preparation. Fisher's exact test followed by post-hoc tests (α = 0.05) were used to assess the impact of the occlusal preparation design on the marginal integrity and the resistance form of the preparation.
The marginal gap was significantly larger for ICA-180 preparations (72 μm), compared to the other groups (ICA-180 vs ICA-100, ICA-110, ICA-120, and ICA-160 p = 0.0001; ICA-180 vs. ICA-140 p = 0.0017). None of the crowns for ICA-180 preparations had clinically acceptable resistance form. Preparations with ICAs of 100°, 110°, and 120° had a significantly higher value of retention than the other groups (ICA-100 vs. ICA-120 p = 0.0119; ICA-100 vs. ICA-140, ICA-160, and ICA-180 p < 0.0001; ICA-110 vs. ICA-140, ICA-160, and ICA-180 p = 0.0001; ICA-120 vs. ICA-180 p = 0.0017).
Crowns fabricated for preparations with various ICAs had clinically acceptable marginal adaptation. Variation in ICA impacts the loss of tooth structure. This loss of tooth structure may influence the resistance and retention form of the preparation.
调整正中牙合（Intercuspal Angulation，ICA）会影响牙体组织的去除量，这可能会影响修复体的固位和抗力形。本研究旨在评估 ICA 对 CAD/CAM 全冠边缘间隙的影响，以及因 ICA 变化而导致的牙体组织磨除对修复体抗力形和固位形的影响。
使用不同的 ICA（100°、110°、120°、140°、160°和 180°；每组 10 个）制作 60 个象牙磨牙。使用口内扫描仪对预备体进行数字化，使用设计软件设计牙冠。然后使用三轴铣床从锂硅玻璃陶瓷中制造牙冠，选择“详细模式”进行制造。使用立体显微镜在 20×放大倍数下评估每个牙冠的边缘间隙。然后，通过触觉-视觉评估评估边缘完整性和预备体的抗力形，并进行分类评分。然后使用临时粘固剂将牙冠固定在相应的预备体上，在万能试验机上以 0.5mm/min 的十字头速度进行张力测试，测量固位力。采用 Wilcoxon 检验和后续检验（α=0.05）评估 ICA 对边缘间隙和预备体固位形的影响。采用 Fisher 确切概率法和后续检验（α=0.05）评估牙合面预备设计对边缘完整性和预备体抗力形的影响。
ICA-180 预备体的边缘间隙明显大于其他组（72μm）（ICA-180 与 ICA-100、ICA-110、ICA-120 和 ICA-160 相比，p=0.0001；ICA-180 与 ICA-140 相比，p=0.0017）。ICA-180 预备体的牙冠没有一个具有临床可接受的抗力形。ICA 为 100°、110°和 120°的预备体的固位力明显高于其他组（ICA-100 与 ICA-120 相比，p=0.0119；ICA-100 与 ICA-140、ICA-160 和 ICA-180 相比，p<0.0001；ICA-110 与 ICA-140、ICA-160 和 ICA-180 相比，p=0.0001；ICA-120 与 ICA-180 相比，p=0.0017）。
用不同 ICA 制作的牙冠具有临床可接受的边缘适应性。ICA 的变化会影响牙体组织的丧失。这种牙体组织的丧失可能会影响修复体的抗力形和固位形。
