Department of Restorative Dentistry, Federal University of Paraíba (UFPB), João Pessoa, Brazil.
J Prosthodont. 2012 Feb;21(2):94-100. doi: 10.1111/j.1532-849X.2011.00793.x. Epub 2011 Nov 2.
The aim of this study was to evaluate the marginal discrepancy (MD) and internal discrepancy (ID) of ceramic crowns manufactured by a CAD/CAM system, having different finish lines. The hypotheses tested were that the finish line type would not influence the MD or ID of the crowns, and ID would not change in different regions.
Three aluminum master dies (height: 5.5 mm, Ø: 7.5 mm, conicity: 6°) with different finish lines (TC: tilted chamfer; LC: large chamfer; RS: rounded shoulder) were manufactured. Ten impressions were made from each master die using a modified parallelometer. Impressions were poured in type IV dental stone, and 30 ceramic crowns (IPS Empress CAD, Ivoclar) were subsequently milled. The crowns were fixed on their respective metallic die using a metallic fixation device. The distance between the external edges of the crown to the edge of the cervical preparation was performed at 50 points on the respective metallic die (MD analysis). With the replica technique, the ID values of each crown were further evaluated at 12 points equidistant to each other in three regions: radius (R), axial (A), and occlusal (Occl). The measurements were performed using an optical microscope (250×). The data (μm) were analyzed using ANOVA and Tukey's test (5%).
The RS group (28.24 ± 11.42 μm) showed significantly lower MD values (p= 0.001) than those of TC (99.92 ± 18.32 μm) and LC (64.71 ± 25.64 μm) groups, both of which also differed statistically from one another. The ID results demonstrated significantly lower values in the LC group (183.01 ± 62.82 μm) (p= 0.0014) than those of TC (216.26 ± 83.23 μm) and RS (219.12 ± 87.24 μm) groups. ID results of TC and RS were not significantly different. Additionally, the ID results showed significant differences among the regions (p= 0.0001). The null hypotheses were rejected.
The RS finish line produced MD values significantly lower than tilted and large chamfer, but large chamfer presented the lowest internal discrepancy values. Independent of the finish line type, internal discrepancy was the lowest in the axial region followed by radius and occlusal regions.
本研究旨在评估不同边缘线设计的 CAD/CAM 全瓷冠的边缘间隙（MD）和内部间隙（ID）。本研究的假设是，不同的边缘线类型不会影响冠的 MD 或 ID，并且 ID 在不同区域不会发生变化。
制作了三个具有不同边缘线（TC：倾斜肩台；LC：大斜面肩台；RS：圆钝肩台）的铝制标准牙（高度：5.5mm，Ø：7.5mm，锥度：6°）。每个标准牙用改良的平行仪制取 10 个印模。将印模灌制在 IV 型牙科石膏中，然后铣削 30 个全瓷冠（IPS Empress CAD，义获嘉）。使用金属固定装置将冠固定在相应的金属模具上。在每个金属模具上的 50 个点上测量冠的外边缘到颈缘预备体边缘的距离（MD 分析）。通过复制技术，在三个区域（半径 R、轴向 A 和咬合 Occl）的 12 个等距点处进一步评估每个冠的 ID 值。使用光学显微镜（250×）进行测量。使用方差分析和 Tukey 检验（5%）对数据（μm）进行分析。
RS 组（28.24 ± 11.42μm）的 MD 值明显低于 TC 组（99.92 ± 18.32μm）和 LC 组（64.71 ± 25.64μm）（p=0.001），后两者之间也存在统计学差异。ID 结果显示 LC 组（183.01 ± 62.82μm）（p=0.0014）明显低于 TC 组（216.26 ± 83.23μm）和 RS 组（219.12 ± 87.24μm）。TC 组和 RS 组的 ID 结果无显著差异。此外，ID 结果在区域之间存在显著差异（p=0.0001）。零假设被拒绝。
RS 边缘线产生的 MD 值明显低于倾斜肩台和大斜面肩台，但大斜面肩台的内部间隙值最低。无论边缘线类型如何，轴向区域的内部间隙最低，其次是半径区域和咬合区域。
