Effect of Thermocycling and Bleaching on Hardness of two Resinous Dental Materials

Abstract

Aim: this in vitro study was conducted to evaluate the effect of thermocycling and bleaching on hardness of two composites. Methods: a total of 20 samples were used in this study divided into 2 groups (n=20) according to type of composite used Bis-GMA based and Bis-GMA free; each group was divided into 2 sucgroups (n=5) bleached and non-bleached and all subgroups were subjected to 
thermocycling then vickers hardness test. Results: The results showed that there were significant differences between all groups and subgroups. The highest mean hardness number (32.44VHN ±1.61) was recorded in the non bleached non thermocycled BIS-GMA based composite. The lowest mean hardness number (16.06 VHN ±0.93) was recorded with the bleached and thermocycled BIS-GMA
free composite. Conclusion: Conjugation of bleaching and thermocycling have marked decreasing effect on surface hardness of dental resin composite. Bis-GMA based composite can resist scratching after bleaching and thermocycling more than Bis-FMA free composite.