Comparison of Accuracy Between a Conventional and Two Digital Intraoral Impression Techniques

Aims: The objective of this study was to compare the precision and trueness of full-arch impressions using either a conventional polyvinylsiloxane (PVS) material or 2 intraoral optical scanners. Methods: Full arch impressions were obtained of a reference model using addition silicone impression material (Aquasil Ultra; Dentsply Caulk, Delaware, USA) and two optical scanners (Trios, 3Shape, Copenhagen, Denmark and CEREC Omnicam, Sirona, Wals, Austria). Surface matching software (Geomagic® Control™, 3D Systems©, Rock Hill, SC, USA) was used to superimpose the scans within groups in order to determine the mean deviations (μm) between the scans. The overall mean precision and trueness for each group was calculated and compared statistically using one-way analysis of variance with post-hoc Bonferroni (trueness) and GamesHowell (precision) tests (IBM© SPSS® ver 24, IBM UK Ltd, Portsmouth, England). Qualitative analysis was also carried out from three-dimensional maps of differences between scans. Results: Mean and standard deviations (SD) of precision for conventional, Trios and Omnicam groups were 21.7 (±5.4), 49.9 (±18.3), and 36.5 (±11.12), respectively. Mean and standard deviations (SD) for trueness were 24.3 (±5.7), 87.1 (±7.9), and 80.3 (±12.1) respectively. The conventional impression showed statistically significant improved mean precision (P<.006) and mean trueness (P<.001) compared to both digital impression procedures. There were no statistically significant differences in precision (P=0.153) or trueness (P=0.757) between the digital impressions. The qualitative analysis revealed local deviations along the palatal surfaces of the molars and incisal edges of the anterior teeth in the order of <100μm. Conclusion: Conventional full-arch PVS impressions exhibited improved mean accuracy compared to 2 direct optical scanners. No significant differences were found between the two digital impression methods

Comparison of Fit Between Zirconia and Metal Copings Fabricated Conventionally or Using Different CAD/CAM Technique

This study was designed to assess the fit of cobalt chromium copings fabricated using direct metal laser sintering and to compare with copings fabricated from nickel chromium (traditional casting) and zirconia (milled from partially sintered blanks). For both cobalt chromium and zirconia groups, impressions were generated using direct or indirect digitization. There were 5 experimental groups of 12 copings fabricated for a prepared maxillary right molar. The intimacy of fit (measured at the margin, axial wall and occlusal) was assessed using a replica method technique. The results showed that zirconia copings produced using direct digitization had significantly smaller marginal, axial and occlusal measurements compared to other groups (p⟨0.05). Nevertheless, all groups had a mean marginal gap within accepted clinical values. Though there was a decrease in the intimacy of fit from the margin to axial wall to the occlusal surface. It can be concluded that the fit of zirconia copings fabricated using direct digitization was significantly better than the other groups. However, it can be expected that further enhancement and refinement of additive technology such as direct metal laser sintering will offer clinicians a viable alternative to nickel chromium analogue production methods in the future

The Accuracy of Digital Implant Impressions when Using and Varying the Material and Diameter of the Dental Implant Scan Bodies

The effects of using and varying the material and diameter of implant scan bodies (ISBs) on the level of accuracy of digital implant impressions is unclear. The purpose of this study was to investigate these effects on the level of accuracy of scans made by an extraoral scanner (EOS) and intraoral scanner (IOS). A stone cast with two sets of ISBs was used. ISBs were made of titanium (TI) or polyether ether ketone (PEEK). Each set consisted of two narrow diameter (ND) and two regular diameter (RD) ISBs. Sixtysix scans were performed and imported into an inspection and metrology software to conduct the three-dimensional (3D) comparisons (N=140) and obtain root mean square (RMS) values. RMS values were analyzed with descriptive and inferential non-parametric statistics (α=.05). The use of ISBs did not improve the overall EOS and IOS scans accuracies. Also, varying the ISBs' diameter and material influenced the EOS and IOS accuracies. For the EOS, the precision in descending order was as follows RD TI, ND TI, RD PEEK, ND PEEK. In contrast, for the IOS an inverse relationship was noted. Finally, precision assessment should always be performed for any reference scanner under the proposed test conditions