This study set out to compare the three-dimensional (3D) trueness of crowns produced from three types of lithium disilicate blocks. The working model was digitized, and single crowns (maxillary left second molar) were designed using computer-aided design (CAD) software. To produce a crown design model (CDM), a crown design file was extracted from the CAD software. In addition, using the CDM file and a milling machine (N = 20), three types of lithium disilicate blocks (e.max CAD, HASS Rosetta, and VITA Suprinity) were processed. To produce a crown scan model (CSM), the inner surface of each fabricated crown was digitized using a touch-probe scanner. In addition, using 3D inspection software, the CDM was partitioned (into marginal, axis, angular, and occlusal regions), the CDM and CSM were overlapped, and a 3D analysis was conducted. A Kruskal–Wallis test (α = 0.05) was conducted with all-segmented teeth with the root mean square (RMS), and they were analyzed using the Mann–Whitney U-test and the Bonferroni correction method as a post hoc test. There was a significant difference in the trueness of the crowns according to the type of lithium disilicate block (p < 0.001). The overall RMS value was at a maximum for e.max (42.9 ± 4.4 µm), followed by HASS (30.1 ± 9.0 µm) and then VITA (27.3 ± 7.9 µm). However, there was no significant difference between HASS and VITA (p = 0.541). There were significant differences in all regions inside the crown (p < 0.001). There was a significantly high trueness in the angular region inside the crown (p < 0.001). A correction could thus be applied in the CAD process, considering the differences in the trueness by the type of lithium disilicate block. In addition, to attain a crown with an excellent fit, it is necessary to provide a larger setting space for the angular region during the CAD process.
Purpose A clinical study to evaluate the intraoral adjustment of crowns fabricated using different scanners. Materials and Methods A total of 15 patients requiring single ceramic crowns were recruited. Impressions were made according to four protocols: a conventional approach and using three intraoral scanners (IOSs) (CS3600 (Carestream Dental, Atlanta, GA), i500 (Medit, Seoul, Republic of Korea), and EZIS PO (DDS, Seoul, Republic of Korea)). Four crowns per patient were fabricated using lithium disilicate ceramic. An experienced dentist performed the internal adjustment in the oral cavity. Three‐dimensional analysis was conducted using an inspection software program (Geomagic Control X; 3D Systems, Rock Hill, SC). Statistical analysis was conducted using one‐way analysis of variance and Tukey's honest significance difference tests (α = 0.05). Results A significant difference was observed in the intraoral adjustment among the conventional approach and the three IOSs (F = 213.7, p < 0.001). Crowns fabricated by conventional impressions (20.1 ± 1.4 µm) displayed better three‐dimensional conformity before and after intraoral adjustment than IOS groups (29.6 ± 4.3 µm) (p < 0.001). Conclusions Crowns fabricated using conventional impressions required fewer intraoral adjustments of the intaglio surface than those fabricated using IOSs.
pISSN 0301-2875, eISSN 2005-3789 203 서론 과거 대부분의 보철물은 수작업으로 제작되었기 때문에, 작업 과정에서의 오차가 빈번하였다. 또한 개인의 기술 수준에 따라 서도 완성된 보철물의 결과는 일관성이 있지 않았다. 1 하지만 이 러한 문제들을 해결하기 위해, 1980년대 Duret과 Preston 2 은 치 과용 computer-aided design and computer-aided manufacturing (CAD/CAM) 시스템이라는 새로운 대안을 제시하였다. 3 따라서 오늘날의 치과용 CAD/CAM 시스템은 비용, 인력 그 리고 시간절약 등을 보완할 수 있으며 3차원 가상 모형으로 전환 하기 위한 필수적인 요소로 자리잡고 있다. 1 치과용 CAD/CAM 시스템은 다음과 같이 세가지 요소로 구성 되었다. 1) 환자의 구 강 내 데이터 수집; 2) 디자인 소프트웨어를 이용한 보철물 디자 인; 3) 공정 장비를 이용한 제조 4 그리고 환자의 구강 내 데이터 수집은 스캐너를 통해 얻을 수 있다. 치과용 스캐너의 종류로는 구강 내를 직접 스캔하는 구강 내 스캐너(Intra-oral scanner)와 Purpose:The purpose of this study was to verify the effect of the abutment superimposition process on the final virtual model in the scanning process of single and 3-units bridge model using a dental model scanner. Materials and methods: A gypsum model for single and 3-unit bridges was manufactured for evaluating. And working casts with removable dies were made using Pindex system. A dental model scanner (3Shape E1 scanner) was used to obtain CAD reference model (CRM) and CAD test model (CTM). The CRM was scanned without removing after dividing the abutments in the working cast. Then, CTM was scanned with separated from the divided abutments and superimposed on the CRM (n=20). Finally, three-dimensional analysis software (Geomagic control X) was used to analyze the root mean square (RMS) and Mann-Whitney U test was used for statistical analysis (α=.05). Results: The RMS mean abutment for single full crown preparation was 10.93 µm and the RMS average abutment for 3 unit bridge preparation was 6.9 µm. The RMS mean of the two groups showed statistically significant differences (P<.001). In addition, errors of positive and negative of two groups averaged 9.83 µm, -6.79 µm and 3-units bridge abutment 6.22 µm, -3.3 µm, respectively. The mean values of the errors of positive and negative of two groups were all statistically significantly lower in 3-unit bridge abutments (P<.001). Conclusion: Although the number of abutments increased during the scan process of the working cast with removable dies, the error due to the superimposition of abutments did not increase. There was also a significantly higher error in single abutments, but within the range of clinically acceptable scan accuracy. (J Korean Acad Prosthodont 2019;57:203-10)
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