• Dimensional Stability of CAD/CAM Patterns: A Longitudinal Study

      Byun, Shane S.; Masri, Radi, 1975- (2020)
      The goal of this study was to investigate the accuracy, over time, of computer-aided design and computer-aided manufactured (CAD/CAM) dental patterns in two different materials (resin and wax) using two different fabrication methods (subtractive and additive manufacturing). The intaglio surface of the patterns (n=48/time period) were evaluated at five predetermined time periods (zero minutes, 20 minutes, 24 hours, one week, and two weeks) relative to fabrication time. Intaglio surface scans of the generated samples were aligned with the Best Fit alignment to the design file (.stl) and compared with 3D Compare on Geomagic Control X to obtain the deviations as a root mean square (RMS). Trueness of the patterns were compared at all time points using three-way Analysis of Variance (ANOVA) (=.05). Accuracy of dental patterns deteriorated over time. When materials were considered, wax had better dimensional stability than resin. When fabrication method was considered, milled patterns had better dimensional stability than printed patterns. Time, material type, fabrication method, and all their interactions, showed a significant effect, however, the differences were very small (ranging from <1 m to 20 m). Thus, both resin and wax CAD/CAM patterns fabricated by additive and subtractive manufacturing can be used to produce dental restorations with acceptable accuracy.
    • Surface Roughness of Zirconia Produced by Additive and Subtractive Manufacturing

      Triana, Frank James; Masri, Radi, 1975- (2021)
      Purpose – The purpose of this in vitro study was to compare surface roughness of full contour zirconia restorations produced by additive and subtractive manufacturing Materials and Methods – Full contour restorations were designed using 3Shape Dental System. The stl files were exported and utilized to guide production of all specimens. Zirconia samples were manufactured by two methods – additive manufacturing (n=10) and subtractive manufacturing (n=18). A two-step polishing protocol was used following sintering. All specimens were subject to profilometry to measure average Ra values. Ra values for both groups were compared. Statistical analysis was performed using t-test (p=0.05). Results – The average Ra value for zirconia restorations in the subtractive manufacturing group was 0.35 ±0.07µm while average Ra for additive manufacturing groups was 1.06 ±0.49 µm. Differences were statistically significant (p < 0.00001). Conclusions – Zirconia restorations produced by subtractive manufacturing were significantly smoother than those produced by additive manufacturing even after post-sintering polishing.