Pre-heating mitigates composite degradation

Abstract

D ental composites cured at high temperatures show improved properties and higher degrees of conversion; however, there is no information available about the effect of pre-heating on material degradation. Objectives: This study evaluated the effect of pre- heating on the degradation of composites, based on the analysis of radiopacity and silver penetration using scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS). Material and Methods: Thirty specimens were fabricated using a metallic matri[ ( [ mm) and the composites Dura¿ll 9S (+eraeus .ul]er), =- ( M/ESPE), and Z-350 (3M/ESPE), cured at 25°C (no pre-heating) or 60°C (pre-heating). Specimens were stored sequentially in the following solutions: 1) water for 7 days (60°C), plus 0.1 N sodium hydroxide (NaOH) for 14 days (60°C); 2) 50% silver nitrate (AgNO 3 ) for 10 days (60°C). Specimens were radiographed at baseline and after each storage time, and the images were evaluated in gray scale. After the storage protocol, samples were analyzed using SEM/EDS to check the depth of silver penetration. Radiopacity and silver penetration data were analyzed using ANOVA and Tukey’s tests (D=5%). Results: Radiopacity levels were as follows: Dura¿ll VS Z-350 Z-250 (p 0.05). The depth of silver penetration into the composites ranked as follows: Dura¿ll VS!Z-350!Z-250 (p 0.05). After storage in water/ NaOH, pre-heated specimens presented higher radiopacity values than non-pre-heated specimens (p<0.05). There was a lower penetration of silver in pre-heated specimens (p<0.05). Conclusions: Pre-heating at 60°C mitigated the degradation of composites based on analysis of radiopacity and silver penetration depth.