Effect of chemical disinfectants on the transverse strength of heat-polymerized acrylic resins submitted to mechanical and chemical polishing

Abstract

Immersion in chemical solutions used for cleansing and disinfecting prostheses can decrease the strength of denture base resins, making them more prone to fracture during use. The purpose of this study was to assess the effect of immersion in different chemical disinfectants for varying time periods on the transverse strength of 3 mechanically or chemically polished heat-polymerized acrylic resins. A total of 630 rectangular specimens (65 x 10 x 3 mm), 210 per resin (Classico, Lucitone 550, and QC-20), were fabricated. One side of each specimen was not polished and the other was either mechanically (n=300) or chemically (n=300) polished, and immersed for 10, 20, 30, 45, or 60 minutes in either 1%, 2.5%, or 5.25% sodium hypochlorite or 2% glutaraldehyde. Mechanically polished (n=15) and chemically polished (n=15) control specimens were immersed only in distilled water. The transverse strength (N/mm 2 ) was tested for failure in a universal testing machine, at a crosshead speed of 5 mm/min. Data were statistically analyzed using 2-way ANOVA and Student t test. Multiple comparisons were performed using Tukey and Scheffe tests (alpha=.05). There was significant difference (P < .01) between types of polishing, with chemical polishing resulting in lower transverse strength. ANOVA identified significant differences (P < .01) in strength between mechanically polished Lucitone 550 and QC-20, and among all 3 chemically polished resins. No significant differences were observed between resins submitted to both types of polishing or between different immersion periods (10 to 60 minutes), disinfectants, or interaction. Lucitone 550 resin presented the greatest transverse strength values with both types of polishing. Among the mechanically and chemically polished specimens, transverse strength was not affected after immersion in the disinfectants for the immersion periods tested (10 to 60 minutes). Chemically polished control and experimental (immersed in all solutions) QC-20 specimens showed significant differences in transverse strength values.