Department of Biomedical and Neuromotor Science (DIBINEM), Alma Mater University of Bologna, via S. Vitale 59, 40125 Bologna, Italy.
Division of Fixed Prosthodontics and Biomaterials, University Clinics for Dental Medicine, University of Geneva, Geneva, Switzerland.
J Dent. 2022 Dec;127:104334. doi: 10.1016/j.jdent.2022.104334. Epub 2022 Oct 17.
This in vitro research aimed to quantitatively evaluate the enamel and dentin tissue removal and the residual adhesion surface area (RAS) after different margin designs and locations for indirect partial restorations (IPR).
A human molar was scanned using a Micro-CT and the STL file obtained was used to 3D-print 50 resin-tooth replicas. IPR standardized preparations were performed. The specimens were randomly assigned to 5 groups (n = 10), according to preparation and margin location to the dental equator (DE): 1) Rounded shoulder above the DE (SA); 2) Hollow chamfer above the DE (CA); 3) Butt joint above the DE (BJ); 4) Rounded shoulder below the DE (SB); 5) Chamfer below the DE (CB). Then, the tooth replicas were scanned and each STL file was aligned and superimposed to the original STL model file. Data of enamel and dentin volume removal and RAS were assessed and statistically analyzed (one-way ANOVA and Kruskal-Wallis tests for the two dental substrates respectively). Significance was set at p<0.05.
Differences in dental tissue reductions were related to the margin location. Above the equator, SA, CA, and BJ performed comparably (p>0.05). Below the equator, CB was significantly more conservative in enamel reduction than SB (p<0.05) and showed the highest enamel adhesive surface exposure among the tested preparations (p<0.05).
When the preparation margin is placed above DE, BJ determines a greater exposure of dentin, reducing the adhesive surface in enamel. Below DE, SB seems to be more aggressive in terms of tissue removal compared to CB.
The results of this in vitro study suggest that in teeth requiring partial restoration with the margin below the dental equator, a chamfer preparation would be more conservative than a shoulder preparation. When above the equator, preparations with flat designs would expose more dentine providing a worse substrate for adhesion.
本体外研究旨在定量评估不同边缘设计和位置的间接部分修复体（IPR）对牙釉质和牙本质组织的去除以及残留粘结表面积（RAS）。
使用 Micro-CT 对一颗人磨牙进行扫描，获得的 STL 文件用于 3D 打印 50 个树脂牙复制体。进行 IPR 标准化制备。根据制备和边缘相对于牙赤道（DE）的位置，将标本随机分为 5 组（n=10）：1）DE 上方的圆肩（SA）；2）DE 上方的空心倒角（CA）；3）DE 上方的对接（BJ）；4）DE 下方的圆肩（SB）；5）DE 下方的倒角（CB）。然后，扫描牙复制体，每个 STL 文件与原始 STL 模型文件对齐和叠加。评估并统计分析牙釉质和牙本质体积去除和 RAS 的数据（分别对两种牙本质基质进行单向方差分析和 Kruskal-Wallis 检验）。设 p<0.05 为差异有统计学意义。
牙本质组织减少的差异与边缘位置有关。在赤道上方，SA、CA 和 BJ 的性能相当（p>0.05）。在赤道下方，CB 在牙釉质减少方面比 SB 更为保守（p<0.05），并且在测试的制备体中显示出最高的牙釉质粘结表面暴露（p<0.05）。
当预备边缘位于 DE 上方时，BJ 会导致更多的牙本质暴露，减少牙釉质的粘结表面。在 DE 下方，与 CB 相比，SB 在组织去除方面似乎更为激进。
本体外研究的结果表明，在需要在牙赤道以下进行部分修复的牙齿中，与肩台预备相比，倒角预备更为保守。当位于赤道上方时，具有平面设计的预备体将暴露更多的牙本质，为粘结提供更差的基质。
