Adhesion of Denture Characterizing Composites to Heat-Cured, CAD/CAM and 3D Printed Denture Base Resins.

PURPOSE: To measure the adhesion of the denture characterizing composite to heat-cured, CAD/CAM and 3D printed denture base resins. METHODS AND MATERIALS: Two different denture characterizing composites with different viscosities (SR Nexco; high viscosity (SR) and Kulzer Cre-active; low viscosity (K)) and three denture base resins (Heat cure, CAD-milled and 3D printed) were investigated. 60 beams (25 × 4 × 3 mm) were fabricated for each denture base resin; 30 were bonded to SR and 30 to K to form a beam 50 × 4 × 3 mm. These were further divided (n = 10/group) to simulate the effects of 0, 6, and 12 months intraorally via thermocycling. The beams were subjected to a 4-point bend test using the chevron-notched beam method. Fracture toughness K1C (MPa ·m1/2 ) and flexural bond strength (MPa) were calculated. All specimens were analyzed for the mode of failure under the light microscope and selected specimens under scanning electron microscope. Results were statistically analyzed using ANOVA (SPSS Ver 25). RESULTS: The mean K1C was highest for the SR composite bonded to the heat-cured denture resin group (0.28 ± 0.11), followed by CAD/CAM (0.18 ± 0.04) and 3D printed groups (0.23 ± 0.16). Differences were not statistically significant (p = 0.268). Within each group, aging showed no statistical significance between the mean K1C and flexural bond strength (p = 0.209). The mean K1C for the K composites bonded to the three different denture bases were significantly lower compared to the SR group (p < 0.001). The mean K1C for the heat-cured denture resin group was (0.21 ± 0.1), followed by CAD/CAM (0.13 ± 0.04) and 3D printed groups (0.03 ± 0.02). Within each of the K group, aging showed a statistical significance for both the mean K1C and flexural bond strength (p = 0.002). CONCLUSION: The high viscosity SR showed significantly higher K1C and flexural bond strength to the lower viscosity K when bonded to heat-cured, CAD-milled and 3D printed denture base resins. Heat-cured denture base resins produced the highest K1C and flexural bond strength when bonded to two different types of characterizing composites.

Evaluation of surface roughness, hardness and elastic modulus of nanoparticle containing light-polymerized denture glaze materials.

STATEMENT OF PROBLEM: The surface hardness and roughness of different glaze materials for denture base acrylic resins have not been well reported. PURPOSE: The purpose of the study was to measure the surfaces hardness, elastic modulus and surface roughness of 5 different light-polymerized glaze materials for poly methyl methacrylate (PMMA) denture base materials. MATERIAL AND METHODS: A total of 210 PMMA resin specimens (10 × 5 × 2 mm) were prepared (30 per group); control group was untreated, group 1 was surface treated with conventional pumice and high shine paste; group 2 to 6 specimens were glaze coated with different commercially available denture glaze materials. 20 specimens out of 30 underwent thermocycling to simulate 6 months and 12 months in vivo. Nanoindentation was performed to measure the surface hardness and elastic modulus. Surface roughness was quantitatively analysed using surface metrology software and qualitatively analysed under scanning electron microscope (SEM). Collected data was statistically analysed using SPSS version 24. RESULTS: The mean surface hardness of tested specimens ranged from 0.33 ±0.09 GPa to 0.68 ±0.10 GPa. Specimens coated with Optiglaze produced statistically higher surface hardness compared to other groups (P< 0.01). Aging of 6 months and 12 months was found to have no statistical significance for all groups' surface hardness values. For elastic modulus, specimens coated with Nanovarnish produced statistically higher values compared to other groups (P= 0.03). Thermocycling showed no influence on the elastic modulus of specimens. The mean surface roughness of all groups ranged from 0.16 ±0.01 to 0.30 ±0.02 µm with no statistical significance between groups (P= 0.67). However, under SEM analysis, surfaces showed increased roughness over time. CONCLUSIONS: Statistically significant differences in surface hardness and elastic modulus were found among the different types of surface coated denture acrylic resins. Silica-nanoparticle containing surface coatings produced the highest surface hardness and elastic modulus, however there was no statistical significance found in aging for 6 and 12 months. Contrary to expectations, the surface roughness did not have a significant increase in all groups over time, despite changes observed under SEM. CLINICAL IMPLICATIONS: This study will contribute to our understanding of surface glazed PMMA acrylic resin denture materials and how it improves the surface strength. This research can help dental clinicians and technicians select the most effective polishing and coating material for the dentures.

Bond Strength of Denture Teeth to Heat-Cured, CAD/CAM and 3D Printed Denture Acrylics.

PURPOSE: To establish the fracture toughness (K1C ) and flexural bond strength of commercially available denture teeth to heat cured, CAD/CAM and 3D printed denture-based resins (DBRs). MATERIALS AND METHODS: Three types of DBRs (Heat cure, CAD-milled and 3D printed) and four different types of commercial denture teeth (Unfilled PMMA, double cross-linked PMMA, PMMA with nanofillers and 3D printed resin teeth) were investigated. DBR and epoxy embedded denture teeth (n = 30 per group) specimen beams (25 × 4 × 3 mm) were fabricated. The testing ends of all the specimens were surface treated, bonded and processed according to manufacturer's instructions. Twenty specimens were thermal cycled to simulate the effects of 6 and 12 months intraorally. A 4-point bend test, using the chevron-notched beam method was done and K1C (MPa ·m1/2 ) and flexure bond strength (MPa) were calculated. All specimens were analysed for the mode of failure under the light microscope and selected specimens under scanning electron microscope. Results were statistically analysed using ANOVA (SPSS Ver 24). RESULTS: The mean K1C was the highest for the teeth bonded to the heat-cured DBR group (1.09 ± 0.24), followed by CAD/CAM (0.43 ± 0.05) and 3D printed groups (0.17 ± 0.01). Differences were statistically significant (p < 0.01). Within each group, aging showed statistically significantly lower values but no statistical significance between the mean K1C and flexural bond strength (p = 0.36). The dominant mode of failure was cohesive in the CAD/CAM groups and adhesive in the heat-cured and 3D printed groups. CONCLUSION: Teeth bonded to heat-cured DBRs produced the highest K1C .The bond strength decreased significantly with aging. Teeth bonded to CAD/CAM and 3D printed DBRs showed significantly lower bond strength, with no significant influence of aging.

Real-time pulp temperature change at different tooth sites during fabrication of temporary resin crowns.

AIM: To record the pulp temperature at different tooth sites during fabrication of two different temporary crown systems. METHODOLOGY: Two temporary crown systems were investigated; a conventional direct fabricated and a preformed thermoplastic resin system. Extracted caries-free human teeth (incisor, premolar and molar) were prepared for full coverage ceramic restoration with roots sectioned below the cemento-enamel junction. Thermocouple wires were secured at the surface of crown material, the cut dentine and inside the pulp cavity. Provisional crowns (n = 10/group) from each system were formed prior to placement in a water bath of 37 °C to simulate pulpal temperature. Temperatures were recorded using a K-type thermocouple data logger to collect the mean and peak temperature during crown fabrication. Statistical analysis was carried out on all tested groups and heat flow was calculated. RESULTS: For direct fabricated crowns, the mean rise in pulpal temperature recorded was 0.1 °C with the mean temperature range of 37.3 °C-37.8 °C. For the preformed thermoplastic crowns, the mean rise in pulpal temperature recorded was 37.3 °C-45.1 °C. The increase in temperature was significantly higher (6.5 °C for the incisor group, 7.5 °C for the premolar group, and 6.7 °C for the molar group). For both crown systems, the temperature difference between the three different sites; pulp, crown and tooth surface showed a statistical difference (P < 0.01). CONCLUSIONS: The direct fabrication system showed minimal temperature changes within the teeth, while the preformed thermoplastic fabrication system showed larger temperature change in the teeth.