Attending physician, Second Clinical Division, Peking University Hospital of Stomatology, Beijing, PR China.
Resident, Center of Digital Dentistry, Faculty of Prosthodontics, Peking University School and Hospital of Stomatology & National Engineering Laboratory for Digital and Material Technology of Stomatology & Research Center of Engineering and Technology for Digital Dentistry of Ministry of Health, Beijing, PR China.
J Prosthet Dent. 2018 Oct;120(4):525-529. doi: 10.1016/j.prosdent.2017.10.014. Epub 2018 Apr 5.
Marginal discrepancy is key to evaluating the accuracy of fixed dental prostheses. An improved method of evaluating marginal discrepancy is needed.
The purpose of this in vitro study was to evaluate the absolute marginal discrepancy of ceramic crowns fabricated using conventional and digital methods with a digital method for the quantitative evaluation of absolute marginal discrepancy. The novel method was based on 3-dimensional scanning, iterative closest point registration techniques, and reverse engineering theory.
Six standard tooth preparations for the right maxillary central incisor, right maxillary second premolar, right maxillary second molar, left mandibular lateral incisor, left mandibular first premolar, and left mandibular first molar were selected. Ten conventional ceramic crowns and 10 CEREC crowns were fabricated for each tooth preparation. A dental cast scanner was used to obtain 3-dimensional data of the preparations and ceramic crowns, and the data were compared with the "virtual seating" iterative closest point technique. Reverse engineering software used edge sharpening and other functional modules to extract the margins of the preparations and crowns. Finally, quantitative evaluation of the absolute marginal discrepancy of the ceramic crowns was obtained from the 2-dimensional cross-sectional straight-line distance between points on the margin of the ceramic crowns and the standard preparations based on the circumferential function module along the long axis.
The absolute marginal discrepancy of the ceramic crowns fabricated using conventional methods was 115 ±15.2 μm, and 110 ±14.3 μm for those fabricated using the digital technique was. ANOVA showed no statistical difference between the 2 methods or among ceramic crowns for different teeth (P>.05).
The digital quantitative evaluation method for the absolute marginal discrepancy of ceramic crowns was established. The evaluations determined that the absolute marginal discrepancies were within a clinically acceptable range. This method is acceptable for the digital evaluation of the accuracy of complete crowns.
边缘不吻合是评估固定义齿修复体准确性的关键。需要一种改进的方法来评估边缘不吻合度。
本体外研究的目的是使用数字方法评估常规和数字方法制作的陶瓷冠的绝对边缘不吻合度，并采用基于三维扫描、迭代最近点配准技术和逆向工程理论的数字方法对绝对边缘不吻合度进行定量评估。
选择 6 个上颌右中切牙、上颌右第二前磨牙、上颌右第二磨牙、下颌左侧切牙、下颌左第一前磨牙和下颌左第一磨牙的标准牙体预备体。为每个牙体预备体制作 10 个常规陶瓷冠和 10 个 CEREC 冠。使用牙科铸体扫描仪获取预备体和陶瓷冠的三维数据，并使用“虚拟就位”迭代最近点技术对数据进行比较。逆向工程软件使用边缘锐化和其他功能模块提取预备体和冠的边缘。最后，基于沿长轴的圆周功能模块，从陶瓷冠边缘的点与标准预备体之间的二维横截面直线距离，获得陶瓷冠的绝对边缘不吻合的定量评估。
常规方法制作的陶瓷冠的绝对边缘不吻合度为 115 ±15.2 μm，数字方法制作的陶瓷冠的绝对边缘不吻合度为 110 ±14.3 μm。方差分析显示，两种方法之间或不同牙齿的陶瓷冠之间均无统计学差异（P＞.05）。
建立了陶瓷冠绝对边缘不吻合度的数字定量评估方法。评估结果表明，绝对边缘不吻合度在临床可接受范围内。该方法可用于全冠精度的数字化评估。
