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Denture bases machined from prepolymerized materials have become popular. However, information on the effect of simulated brushing and coffee thermocycling (CTC) on their surface roughness and stainability is lacking. The purpose of this in vitro study was to compare the effect of simulated brushing and CTC on the surface roughness (R a) and stainability of computer-aided design and computer-aided manufacturing (CAD-CAM) denture base materials and a heat-polymerized denture base material. Forty disk-shaped specimens were prepared from 3 CAD-CAM denture base resins (AvaDent, AV; Merz M-PM, M-PM; and Polident d.o.o, Poli) and a heat-polymerized polymethylmethacrylate resin (Promolux, CV) (n=10). R a values of the specimens were measured by using a noncontact profilometer after conventional polishing. The color coordinates were also measured over a gray background with a spectrophotometer. Specimens were then consecutively subjected to simulated brushing for 20 000 cycles, CTC for 5000 cycles, and another 10 000 brushing cycles. R a and color coordinates were measured after each interval. Color differences (ΔE 00) were calculated by using the CIEDE2000 formula, and the data were analyzed by using 2-way analysis of variance and Tukey honestly significant difference tests (α=0.05). The time interval had a significant effect on R a (P <.001) as brushing cycles resulted in higher values than those at baseline and after CTC (P <.001). However, the differences between brushing cycles (P =.143) and between the baseline and after CTC (P =.994) were not significant. The interaction between the material type and time interval was significant for ΔE 00 (P =.016). The only significant difference in ΔE 00 values was observed between M-PM and CV after all treatments were completed (P =.029). Brushing increased the R a of all materials when compared with the baseline. All materials showed similar stainability throughout the brushing and CTC processes. However, M-PM CAD-CAM denture base resin underwent a greater color change after all treatments were completed than conventional denture base resin. All color changes can be considered clinically small, considering reported perceptibility and acceptability thresholds. [ABSTRACT FROM AUTHOR]

Purpose To evaluate the effect of glass fiber/filler particles proportion on flexural strength and diametral tensile strength of an experimental fiber-reinforced composite. Methods Four experimental groups ( N = 10) were created using an experimental short fiber-reinforced composite, having as a factor under study the glass fiber (F) and filler particle (P) proportion: F22.5/P55 with 22.5 wt% of fiber and 55 wt% of filler particles; F25/P52.5 with 25 wt% of fiber and 52.5 wt% of filler particles; F27.5/P50 with 27.5 wt% of fiber and 50 wt% of filler particles; F30/P47.5 with 30 wt% of fiber and 47.5 wt% of filler particles. The experimental composite was made up by a methacrylate-based resin (50% Bis-GMA and 50% TEGDMA). Specimens were prepared for Flexural Strength (FS) (25 mm × 2 mm × 2 mm) and for Diametral Tensile Strength (DTS) (3 × 6 Ø mm) and tested at 0.5 mm/min in a universal testing machine. Results The results (in MPa) showed significance (different superscript letters mean statistical significant difference) for FS ( p < 0.009) and DTS ( p < 0.001) – FS results: F22.5/P55: 217.24 ± 20.64 B ; F25/P52.5: 245.77 ± 26.80 AB ; F27.5/P50: 246.88 ± 32.28 AB ; F30/P47.5: 259.91 ± 26.01 A . DTS results: F22.5/P55: 21.82 ± 4.42 B ; F25/P52.5: 22.00 ± 7.40 B ; F27.5/P50: 18.63 ± 4.41 B ; F30/P47.5: 31.05 ± 2.97 A . In SEM analysis, areas without fiber reinforcement demonstrated to be more prone to the presence of bubbles and crack development. The group F30/P47.5 showed areas with a great quantity of fibers without empty spaces for crack propagation. Conclusion Increasing fiber content results in higher flexural and diametral tensile strength of an experimental composite reinforced with glass fibers. [ABSTRACT FROM AUTHOR]

Additive manufacturing is commonly used for the fabrication of definitive casts with removable dies. However, how the trueness and fit of removable dies are affected by printing layer thickness is lacking. The purpose of this in vitro study was to investigate the trueness and fit of additively manufactured removable dies printed in different layer thicknesses. A mandibular cast with a prepared right first molar tooth was digitized (CEREC Primescan), and its standard tessellation language (STL) file was imported into a software program (DentalCAD 3.0). A removable die (D-STL) and a hollow cast with (M-STL) or without the die (SM-STL) were designed. D-STL and SM-STL were imported into a nesting software program (Composer), and 45 removable dies in 3 layer thicknesses (100 μm, 50 μm, and 50 to 100 μm) (n=15) and 1 cast (100-μm) were additively manufactured. Each removable die (TD-STLs), the cast with each die (TM-STLs), and the cast without the die (TSM-STL) were digitized by using the same scanner. All STL files were imported into a software program (Medit Link v 2.4.4), and TD-STLs were superimposed over D-STL. The root mean square (RMS) method was used to analyze the trueness of the dies at 2 different areas (crown and root portion) and as a complete unit (overall). Overall RMS values of the cast with and without the die were also calculated after superimposing TM-STLs over M-STL. The fit of the dies in the cast was evaluated by using a triple-scan protocol to measure deviations at 5 different points (point M: most mesial point of the margin; point TM: tip of the mesial cusp; point O: deepest point of the occlusal fossa; point TD: tip of the distal cusp; point D: most distal point of the margin) on the crown portion. One-way ANOVA and Tukey honestly significant difference tests were used to evaluate data (α=.05). The RMS values of removable dies showed significant differences at each area (P ≤.002). The 50- to 100-μm group had higher overall RMS values than the 100-μm group (P =.017). The 100-μm group had the highest RMS values for the crown portion (P ≤.019), while the 50-μm group had the highest RMS values for the root portion (P <.001). The 50-μm group had the lowest RMS values for the crown portion when the die was in the cast (P <.001). Except for point TM (P =.228), significant differences were observed among the test groups at all points (P <.001). The 50-μm group had the lowest distance deviations at points M, TD, and D (P ≤.005), while the 100-μm group had the highest distance deviations at points O and D (P ≤.010). Removable dies fabricated by using a 100-μm or 50- to 100-μm combined layer thickness had trueness that was either similar to or better than that of dies fabricated with a 50-μm layer thickness. When the die was on the cast, the 50-μm layer thickness resulted in the best crown portion trueness. However, because the deviation differences among groups were clinically small, the 100-μm layer thickness can be considered for the efficient fabrication of removable dies when the tested printer and resin are used. [ABSTRACT FROM AUTHOR]