Effect of thermal cycling and disinfection on colour stability of denture base acrylic resin.

OBJECTIVES: The purpose of this study was to investigate the effect of thermal cycling and disinfection on the colour change of denture base acrylic resin. MATERIALS AND METHODS: Four different brands of acrylic resins were evaluated (Onda Cryl, QC 20, Classico and Lucitone). All brands were divided into four groups (n = 7) determined according to the disinfection procedure (microwave, Efferdent, 4% chlorhexidine or 1% hypochlorite). The treatments were conducted three times a week for 60 days. All specimens were thermal cycled between 5 and 55°C with 30-s dwell times for 1000 cycles before and after disinfection. The specimens' colour was measured with a spectrophotometer using the CIE L*a*b* system. The evaluations were conducted at baseline (B), after first thermal cycling (T1 ), after disinfection (D) and after second thermal cycling (T2 ). Colour differences (ΔE) were calculated between T1 and B (T1 B), D and B (DB), and T2 and B (T2 B) time-points. RESULTS: The samples submitted to disinfection by microwave and Efferdent exhibited the highest values of colour change. There were significant differences on colour change between the time-points, except for the Lucitone acrylic resin. CONCLUSIONS: The thermal cycling and disinfection procedures significantly affected the colour stability of the samples. However, all values obtained for the acrylic resins are within acceptable clinical parameters.

Effect of different disinfectants on the microhardness and roughness of acrylic resins for ocular prosthesis.

BACKGROUND: Ocular prosthesis materials should have specific properties for their indication and durability; therefore, it is important to investigate their physical behaviour when affected by several disinfectants. OBJECTIVES: This study evaluated the influence of different disinfecting solutions on the microhardness and surface roughness of acrylic resins for ocular prosthesis. MATERIALS AND METHODS: Fifty samples simulating ocular prostheses were fabricated with N1 resin and colourless resin and divided (n = 10) according to the disinfectant used: neutral soap, Opti-free, Efferdent, 1% hypochlorite (HYC) and 4% chlorhexidine (CHX). Samples were stored in saline solution at 37°C and disinfected during 120 days. Both microhardness and roughness were investigated before, after 60 days and 120 days of disinfection and storage. Microhardness was measured using a microhardner and the roughness with a roughness device. RESULTS: N1 resin showed lower microhardness when compared with colourless resin (p < 0.05). HYC and CHX groups exhibited the highest change of microhardness and roughness values (p < 0.05). An increase in roughness and reduction in microhardness of ocular acrylic resins were observed after both periods of disinfection and storage (p < 0.05). CONCLUSION: Both disinfection/storage periods affected the microhardness and roughness values of the samples.