Three-dimensionally printed denture base resins modified by nanoglass particles and carbon nanotubes.

STATEMENT OF PROBLEM: Three-dimensionally (3D) printed denture base resins exhibit inferior mechanical properties compared with conventional and milled ones, a problem affecting their long-term clinical use. Improved 3D printed resins are required. PURPOSE: The purpose of this in vitro study was to determine whether a 3D printed denture base resin with nanoglass particles and multiwalled carbon nanotubes (MWCNTs) would exhibit enhanced mechanical properties. MATERIAL AND METHODS: The nanoglass particles and MWCNTs were silane coated and added to the resin to obtain the following groups: Control, resin modified with nanoglass particles with 2 percentages, 0.25 wt%, and 0.5 wt%; resin modified with MWCNTs with 2 percentages, 0.25 wt%, and 0.5 wt%; and a combination group with 0.25 wt% of each filler type. The printed specimens (N=330) were tested before and after thermocycling (600 cycles) for flexural strength (FS) and elastic modulus (n=22) by using a universal testing machine and for impact strength (IS) (n=22) by using a Charpy impact tester. The fractured impact specimens were then evaluated by using scanning electron microscopy (SEM). The surface roughness (Ra) (n=11) was assessed by using a profilometer. For data analysis, the 2-way ANOVA test was used for the analysis of FS, elastic modulus, and IS, and the 3-way ANOVA test was used for Ra with a subsequent Tukey post hoc test. Percentage change was compared among groups by using the Kruskal-Wallis test, followed by the Dunn post hoc test with Bonferroni correction (α=.05). RESULTS: The filler content and thermocycling revealed a significant main interaction effect (P<.001) on FS, elastic modulus, and IS, with the 0.5% nanoglass group displaying the highest percentage decrease after thermocycling. The SEM images of fractured impact specimens revealed a brittle failure in the control and nanoglass groups. In contrast, the groups containing MWCNTs and the combination group displayed intermediate to ductile failure. Moreover, a significant inclusive interaction effect (P<.001) was found between the filler content, thermocycling, and polishing on surface roughness, with the 0.5% nanoglass group revealing the highest percentage increase in Ra of the polished surface after aging. CONCLUSIONS: The addition of nanoglass and MWCNTs led to a significant improvement in the FS, elastic modulus, and IS of the 3D printed resin. The combination group displayed the least percentage change among all groups regarding the FS and IS, displaying intermediate to ductile failure. The control revealed the least percentage change in elastic modulus after thermocycling but with lower peak values compared with all other groups.

Evaluation of physicomechanical properties of milled versus 3D-printed denture base resins: A comparative in vitro study.

STATEMENT OF PROBLEM: Studies comparing the physicomechanical characteristics of denture base resins manufactured by computer-aided design and computer-aided manufacturing (CAD-CAM) milling and 3-dimensional (3D) printing are sparse, resulting in challenges when choosing a fabrication method for complete dentures. PURPOSE: The purpose of this in vitro study was to evaluate and compare the impact strength, flexural strength, and the surface roughness of denture base resins manufactured by CAD-CAM milling and 3D printing before and after thermocycling and polishing. MATERIAL AND METHODS: Evaluation of the physicomechanical properties (n=35) was completed before and after 500 thermocycles. Impact strength (n=14) was measured with a Charpy impact tester and flexural strength (n=14) with the 3-point bend test. Surface roughness (Ra) was evaluated (n=7) with a profilometer before and after thermocycling and polishing and by viewing the surface topography before and after polishing using a scanning electron microscope at ×2000. The Mann-Whitney U test and Wilcoxon sign rank test were used for statistical analysis (α=.05). RESULTS: Milled specimens showed statistically significantly higher impact strength before thermocycling and statistically significantly higher flexural strength before and after thermocycling (P=.004) compared with 3D-printed specimens. The Ra values for the milled group were significantly lower than for the 3D-printed group both before and after thermocycling (P=.006) and after polishing (P=.027). Thermocycling resulted in a statistically significant difference in flexural strength (P=.018) in both groups and in surface roughness in the milled group (P=.048); but no significant effect was found on impact strength (P>.05). Ra values for the 3D-printed group decreased after polishing (P=.048). CONCLUSIONS: Milled specimens had higher flexural and impact strength and lower surface roughness values than 3D-printed specimens. Polishing significantly reduced the surface roughness in 3D-printed specimens but had no significant effect on milled specimens.

Microleakage Evaluation of Composite Restorations Following Papain-Based Chemo-Mechanical Caries Removal in Primary Teeth.

AIM: To evaluate the microleakage of composite restorations following Papain-based chemo-mechanical caries removal compared to the conventional drilling method. The characteristic of the hybrid layer was also studied using scanning electron microscopy. STUDY DESIGN: The sample included thirty freshly extracted and exfoliated primary molars with open proximal carious dentin lesions. Teeth were divided into two equal groups, according to method of caries removal. Following caries removal, cavity preparations were restored with composite resin. After thermocycling, teeth were sealed apically and coated with nail polish except the surface of restorations and the surrounding 1mm. Teeth were immersed in basic fuschin dye solution, then they were sectioned mesiodistally. The extent of dye penetration was detected using a light stereomicroscope. After microleakage test, the resin/dentin interface was examined using scanning electron microscopy. RESULTS: There was no significant difference in the degree of leakage between both groups. In the Papacarie group, longer and numerous resin tags were observed with statistically significant thicker hybrid layer than those following the drilling method. However, there was no significant difference between the diameters of resin tags of both groups. CONCLUSIONS: Papacarie does not adversely affect the microleakage of composite restorations and provides a suitable surface for bonding.