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STATEMENT OF PROBLEM: The clinical efficacy of selective laser melting (SLM) for fabricating removable partial dentures (RPDs) is not well established. PURPOSE: The purpose of this clinical study was to compare the performance of SLM-fabricated frameworks with that of those fabricated via traditional lost wax casting. MATERIAL AND METHODS: A double-blind, randomized, crossover design was used to compare cobalt-chromium partial denture frameworks (n=29) fabricated by using SLM or traditional methods. The time taken for adjustments and the clinical fit and stability of the adjusted frameworks were appraised. The accuracy of the frameworks was assessed by measuring the space between the occlusal rest seat and the corresponding rest seat. Statistical comparisons between the 2 frameworks were carried out by using a linear mixed-effect model for repeated measurements (α=.05). RESULTS: Frameworks fabricated by using both SLM and traditional techniques had an acceptable fit based on subjective clinical evaluation. The overall mean ±standard deviation space between the occlusal rest and rest seat for SLM frameworks (273.7 ±44.5 µm) was comparable with that of traditional frameworks (242.2 ±44.5 µm). The clinical fit adjustment time, 7.76 ±6.43 minutes for SLM and 5.49 ±6.39 minutes for traditionally fabricated frameworks, was statistically similar (P=.067). CONCLUSIONS: Dentures fabricated via SLM and traditional techniques had comparable accuracy of fit and clinical fitting time.

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PURPOSE: To study the effect of implant analog system, print orientation, and analog holder radial offset on 3D linear and absolute angular distortions of implant analogs in 3D printed resin models. MATERIALS AND METHODS: A sectional master model simulating a 2-implant, 3-unit fixed prosthesis in a partially edentulous jaw was fabricated. Three implant analog systems for 3D printed resin models-Straumann (ST), Core3DCentres (CD) and Medentika (MD)-were tested. The corresponding scan bodies were secured onto the implants and scanned using an intraoral scanner. Models were obtained with a Digital Light Processing printer. Each implant analog system had 2 print orientations (transverse [X] and perpendicular [Y] to the printer door) and 2 analog holder radial offsets (0.04 mm and 0.06 mm), for a total of 60 models. The physical positions of the implants in the master model and the analogs in the printed resin models were directly measured with a Coordinate Measuring Machine (CMM). 3D linear distortion (ΔR) and absolute angular distortion (Absdθ) defined the 3D accuracy of the analogs in the printed models. Univariate ANOVA was used to analyse data followed by post hoc tests (Tukey HSD, α = 0.05). RESULTS: Mean ΔR for ST (-155.7 ± 60.6 µm), CD (124.9 ± 65.0 µm) and MD (-92.9 ± 48.0 µm) were significantly different (p < 0.01). Mean Absdθ was not significantly different between ST (0.57 ± 0.48°) and CD (0.41 ± 0.27°), but both were significantly different from MD (2.11 ± 1.14°) (p < 0.01). Print orientation had a significant effect on ΔR only but no discernible trend could be found. Analog holder radial offset had no significant effect on ΔR and Absdθ. CONCLUSIONS: Implant analog system had a significant effect on ΔR and Absdθ. Compared to the master model, CD produced greater mean interanalog distances, while ST and MD produced smaller mean interanalog distances. MD exhibited the greatest mean angular distortion which was significantly greater than ST and CD.

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PURPOSE: Prior studies have defined the accuracy of intraoral scanner (IOS) systems but the accuracy of the digital static interocclusal registration function of these systems has not been reported. This study compared the three-dimensional (3D) accuracy of the digital static interocclusal registration of 3 IOS systems using the buccal bite scan function. MATERIALS AND METHODS: Three IOS systems compared were 3MTM True Definition Scanner (TDS), TRIOS Color (TRC), and CEREC AC with CEREC Omnicam (CER). Using each scanner, 7 scans (n = 7) of the mounted and articulated SLA master models were obtained. The measurement targets (SiN reference spheres and implant abutment analogs) were in the opposing models at the right (R), central (C), and left (L) regions; abutments #26 and #36, respectively. A coordinate measuring machine with metrology software compared the physical and virtual targets to derive the global 3D linear distortion between the centroids of the respective target reference spheres and abutment analogs (dRR , dRC , dRL , and dRM ) and 2D distances between the pierce points of the abutment analogs (dXM , dYM , dZM ), with 3 measurement repetitions for each scan. RESULTS: Mean 3D distortion ranged from -471.9 to 31.7 µm for dRR , -579.0 to -87.0 µm for dRC , -381.5 to 69.4 µm for dRL , and -184.9 to -23.1 µm for dRM . Mean 2D distortion ranged from -225.9 to 0.8 µm for dXM , -130.6 to -126.1 µm for dYM , and -34.3 to 26.3 µm for dZM . Significant differences were found for interarch distortions across the three systems. For dRR and dRL , all three test groups were significantly different, whereas for dRC , the TDS was significantly different from the TRC and CER. For 2D distortion, significant differences were found for dXM only. CONCLUSIONS: Interarch and global interocclusal distortions for the three IOS systems were significantly different. TRC performed overall the best and TDS was the worst. The interarch (dRR , dRC , dRL ) and interocclusal (dXM ) distortions observed will affect the magnitude of occlusal contacts of restorations clinically. The final restoration may be either hyperoccluded or infraoccluded, requiring compensations during the CAD design stage or clinical adjustments at issue.

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