Effect of phosphate group addition on the properties of denture base resins.

STATEMENT OF PROBLEM: Acrylic resins are prone to microbial adherence, especially by Candida albicans. Surface-charged resins alter the ionic interaction between the denture resin and Candida hyphae, and these resins are being developed as a means to reduce microbial colonization on the denture surface. PURPOSE: The purpose of this study was to investigate the physical and mechanical properties of phosphate-containing polymethyl methacrylate resins for their suitability as a denture material. MATERIAL AND METHODS: Using PMMA with cross-linker (Lucitone 199) as a control, 4 experimental groups containing various levels of phosphate with and without cross-linker were generated. The properties examined were impact strength, fracture toughness, wettability (contact angle), and resin bonding ability to denture teeth. Impact strength was tested in the Izod configuration (n=16), and fracture toughness (n=13) was measured using the single-edge notched bend test. Wettability was determined by calculating the contact angle of water on the material surface (n=12), while ISO 1567 was used for bonding ability (n=12). The data were analyzed by 1- and 2-way ANOVA (alpha=.05). RESULTS: A trend of increased hydrophilicity, as indicated by lower contact angle, was observed with increased concentrations of phosphate. With regard to the other properties, no significant differences were found when compared with the control acrylic resin. CONCLUSIONS: No adverse physical effect due to the addition of a phosphate-containing monomer was found in the acrylic denture resins. Additional mechanical and physical properties, biocompatibility, and clinical efficacy studies are needed to confirm the in vivo anti-Candida activity of these novel resins.

Defects in hexed gold prosthetic screws: A metallographic and tensile analysis.

STATEMENT OF PROBLEM: Prosthetic gold screw fracture remains a clinical problem in implant prosthodontics. PURPOSE: This study examined hexed gold prosthetic screws for internal defects and determined the effect of these defects on tensile strength. The microstructure, microhardness, and major constituents of the alloys also were determined. MATERIAL AND METHODS: Four intact hexed gold prosthetic screws, 1 from each of 2 different lots from 2 manufacturers (Implant Innovations and Nobel Biocare), were examined with standard metallographic techniques for defects, microstructure, microhardness, and major alloy constituents. Thirty-six screws, 9 from each of the 2 different lots of both manufacturers, were subjected to tensile testing to determine fracture load values. Analysis of variance and Tukey tests were used to identify differences between manufacturers and lots (P<.05). The fracture sites were examined retrospectively with a scanning electron microscope to identify defects that could have contributed to failure. The mode of fracture was characterized. RESULTS: There were no significant defects in the screws tested, but differences were observed in the microstructure, microhardness, alloy composition, and fracture load values for both manufacturers. Screws from the 2 manufacturers demonstrated distinctly different metallurgical characteristics, which highlighted differences in the manufacturing processes. Fracture load values ranged from 850 +/- 20 N to 1093 +/- 64 N. A significant difference was noted for mean fracture load values for the different lots of Implant Innovations screws (P<.05). Ductile fracture was the mode of failure. CONCLUSION: The results of this study suggest that variability in the physical properties of similar hexed gold prosthetic screws made by different manufacturers, as well as different lots from the same manufacturer, may affect clinical success.