Surface Roughness and Color Stability of 3D-Printed Denture Base Materials after Simulated Brushing and Thermocycling.

Three-dimensional (3D) printing is increasingly used to fabricate denture base materials. However, information on the effect of simulated brushing and thermocycling on the surface roughness and color stability of 3D-printed denture base materials is lacking. The aim of this study was to evaluate the effect of brushing and thermocycling on the surface roughness and color stability of 3D-printed denture base materials and to compare with those of milled and heat-polymerized denture base resins. Disk-shaped specimens (Ø 10 mm × 2 mm) were prepared from 4 different denture base resins (NextDent Denture 3D+ (ND); Denturetec (SC); Polident d.o.o (PD); Promolux (CNV)) (n = 10). Surface roughness (Ra) values were measured before and after polishing with a profilometer. Initial color coordinates were measured by using a spectrophotometer after polishing. Specimens were then consecutively subjected to simulated brushing (10,000 cycles), thermocycling (10,000 cycles), and brushing (10,000 cycles) again. Ra and color coordinates were measured after each interval. Color differences (ΔE00) between each interval were calculated and these values were further evaluated considering previously reported perceptibility (1.72 units) and acceptability (4.08 units) thresholds. Data were analyzed with Friedman, Kruskal-Wallis, and Mann-Whitney U tests (α = 0.05). Ra (p ≥ 0.051) and ΔE00 (p ≥ 0.061) values among different time intervals within each material were similar. Within each time interval, significant differences in Ra (p ≤ 0.002) and ΔE00 values (p ≤ 0.001) were observed among materials. Polishing, brushing, and thermocycling resulted in acceptable surface roughness for all materials that were either similar to or below 0.2 µm. Color of ND printed resin was affected by brushing and thermocycling. All materials had acceptable color stability when reported thresholds are considered.

Effect of printing layer thickness on the trueness of 3-unit interim fixed partial dentures.

STATEMENT OF PROBLEM: Three-dimensional printing has facilitated the fabrication processes in dentistry. However, knowledge on the effect of layer thickness on the trueness of 3D-printed fixed partial dentures (FPDs) is lacking. PURPOSE: The purpose of this in vitro study was to compare the effect of printing layer thickness on the trueness of 3-unit interim FPDs fabricated by using additive manufacturing with that of those fabricated by subtractive manufacturing. MATERIAL AND METHODS: The right first premolar and first molar teeth of a dentate mandibular model were prepared for a 3-unit restoration and then digitized by using an intraoral scanner. A 3-unit interim FPD was designed to fabricate 40 restorations by using either the additive (NextDent C&B MFH) with layer thicknesses of 20 µm (n=10), 50 µm (n=10), and 100 µm (n=10) or subtractive manufacturing technique (Upcera) (milled, n=10). After fabrication, the interim FPDs were digitized by using the same intraoral scanner and were superimposed over the design data by using a 3D analysis software program. Root mean square (RMS) was used to analyze the trueness of the restorations at 4 different surfaces (external, intaglio, marginal area, and intaglio occlusal) and as a complete unit (overall). Data were analyzed with the Kruskal-Wallis and Wilcoxon tests with Bonferroni correction (α=.05). RESULTS: The 100-µm-layer thickness interim FPDs showed the greatest overall (P≤.015), external (P≤.021), and intaglio occlusal (P≤.021) deviations, whereas the milled interim FPDs showed the lowest (P=.001). No significant differences were found among the test groups for marginal RMS (P≥.108). The differences between the 50-µm-layer thickness and 100-µm-layer thickness interim FPDs for the intaglio surface deviations (P=.064) and between the 20-µm-layer thickness and 50-µm-layer thickness interim FPDs for each surface tested were not statistically significant (P≥.108). CONCLUSIONS: The printing layer thickness had a significant effect on the trueness of the additively manufactured interim FPDs. However, subtractively manufactured interim FPDs presented higher trueness than those additively manufactured, regardless of the printing layer thickness.

Color and translucency of milled polymethyl methacrylate crowns on non-tooth-colored interim abutments with different surface treatments.

STATEMENT OF PROBLEM: The interim rehabilitation of implants has become a necessity, particularly for those placed in the esthetic regions. However, the optical properties of computer-aided design and computer-aided manufacturing (CAD-CAM) polymethyl methacrylate (PMMA) crowns on interim abutments with different surface treatments are unclear. PURPOSE: The purpose of this in vitro study was to investigate the color and translucency of CAD-CAM PMMA crowns when different surface treatments were used on titanium interim abutments. MATERIAL AND METHODS: A maxillary dentate stone cast with a narrow-diameter implant analog at the left lateral incisor site was used. Three titanium interim abutments (blue) were divided into 3 groups according to the surface treatment they received: control (steam cleaning), opaqued (120-µm Al2O3 airborne-particle abrasion and opaque application), and airborne-particle abraded (120-µm Al2O3). Thirty PMMA crowns (A2 shade) were milled (n=10). The color coordinates of the crown-interim abutment pairs and a shade tab (A2) were measured by using a colorimeter. The color differences (ΔE00) between the crowns and the shade tab and the relative translucency parameter (RTP) values of the crowns were calculated by using the CIEDE2000 formula. One-way ANOVA was used to analyze the ΔE00 and RTP values with subsequent Tukey honestly significant difference tests (α=.05). RESULTS: The abutment surface treatment significantly affected the ΔE00 of interim crowns from the shade tab (P<.001), but no significant effect was found on RTP (P=.26). The control group had the highest ΔE00 from the shade tab (P≤.011). No significant difference (P=.14) was found between the opaqued and the ΔE00 of the airborne-particle abraded groups from the shade tab. CONCLUSIONS: The surface treatments of interim abutments affected the color of CAD-CAM PMMA crowns, which differed from that of the shade tab. The color of crowns on opaqued or airborne-particle abraded interim abutments was closer to the color of the shade tab. Abutment surface treatments did not affect the translucency of crown-interim abutment pairs.

Influence of 3D analysis software on measured deviations of CAD-CAM resin crowns from virtual design file: An in-vitro study.

OBJECTIVES: To evaluate a nonmetrology-grade and a metrology-grade 3D analysis software when measuring the deviations of computer-aided-design/ computer-aided-manufacturing (CAD-CAM) fabricated crowns from the virtual design file. MATERIALS AND METHODS: A right first molar on a mandibular dentate model was prepared and scanned with an intraoral scanner, i500 (Medit). A complete coverage crown was designed in standard tessellation language (STL) format and 20 resin crowns were fabricated with CAD-CAM. The crowns were then digitized using the same intraoral scanner (test-scans). Root mean square (RMS) method was used to evaluate the deviations between the test-scans and the design file of the crowns on 3 surfaces (overall, external, and internal) using a metrology-grade, Geomagic Control X (3D Systems) and a nonmetrology-grade, Medit Link (Medit) software. The data were analyzed with Welch two-sample t-tests to compare two software for the non-inferiority of the nonmetrology-grade software with a 50 µm threshold and the potential superiority of the metrology-grade software (α = 0.05). RESULTS: The Welch two-sample t-tests for the non-inferiority analysis showed that the differences between the nonmetrology-grade and the metrology-grade software were below the threshold of 50 µm for each surface tested (p <0.001). The differences between the two-tested software were nonsignificant for each surface analyzed when superiority was considered (p ≥.194). CONCLUSION: The nonmetrology-grade software performed similar to the metrology-grade software when analyzing the deviations of CAD-CAM crowns. Therefore, the nonmetrology-grade 3D analysis software may be considered for the deviation measurements of similar restorations. CLINICAL SIGNIFICANCE: The trueness of crowns after fabrication may affect their fit, and 3D analysis of trueness prior to the delivery appointment with the tested nonmetrology-grade software after fabrication may facilitate potential clinical adjustments and delivery of the crowns.