Pre-heating mitigates composite degradation

Abstract

Dental 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 matrix (2x8 mm) and the composites Durafill VS (Heraeus Kulzer),Z-250(3M/ESPE), and Z-350 (3M/ESPE), cured at 25 degrees C (no pre-heating) or 60 degrees C (pre-heating). Specimens were stored sequentially in the following solutions: 1) water for 7 days (60 degrees C), plus 0.1 N sodium hydroxide (NaOH) for 14 days (60 degrees C); 2) 50% silver nitrate (AgNO3) for 10 days (60 degrees 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 (alpha=5%). Results: Radiopacity levels were as follows: Durafill VS<Z-350<Z-250 (p<0.05). The depth of silver penetration into the composites ranked as follows: Durafill 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 degrees C mitigated the degradation of composites based on analysis of radiopacity and silver penetration depth.