Accuracy of milled lithium disilicate crowns fabricated by using CBCT and IOS-based digital models

Abstract

Objectives To evaluate the trueness and precision of digital casts generated from intraoral scanning (IOS) and cone beam computed tomography (CBCT). Also, to assess the marginal integrity of milled lithium disilicate (LD) crowns that were fabricated from the IOS and CBCT digital casts. Materials and methods Tooth preparation for an all-ceramic crown was performed on a segmented cast that was later scanned as a master model. Scans were obtained; 10 conventional polyvinyl siloxane impressions were made that were scanned by using CBCT, 10 digital scans by using IOS, and 10 digital scans by using a desktop scanner. DICOM data of the CBCT were converted to STL files. The reference STL file was segmented and prepared for 3D comparison. The 3D comparison was performed to compare the IOS group and CBCT group to the reference STL files. Trueness was determined by measuring the root mean square (RMS) for each group. The data were analyzed by using paired samples t-test. The digital casts from each group were used to fabricate all-ceramic crowns; 10 crowns from a tabletop scanner (reference) digital model, 10 crowns from the IOS digital model, and 10 crowns from the CBCT digital model. Crowns were milled by using IPS emax CAD. The replica method was used to evaluate the marginal integrity of the milled crowns. The thickness of the cross-section of the replica was measured under scanning electron microscopy (SEM). Descriptive statistics of mean and standard error of trueness and marginal gaps for all groups were recorded and compared by applying paired sample t-test and repeated measures ANOVA test, respectively. All the data were analyzed by using statistical analysis software program SPSS, version 29.0. Results The accuracy of the CBCT group was shown to be statistically significantly different from that of the IOS group, based on the results of the paired sample t-test. Crowns made from digital models created by CBCT exhibited a marginal gap that was substantially higher (P < 0.001) than crowns made by using IOS models. Conclusions Within the limitations of this study, it can be concluded that CBCT generated models are statistically significantly less accurate when compared with a Trios 3 IOS, and when compared with a reference tabletop scanner. Additionally, lithium disilicate all-ceramic crowns fabricated from CBCT models recorded more marginal gap when compared with both the control and IOS groups.