[Invitro comparison between the effects of two tooth bleaching agents on surface micro hardness of microhybrid composite]

ABSTRACT

Tooth whitening products may have effects on various properties of restorative materials including hardness. This study investigated the effects of two at-home bleaching agents [Kimia 16%, Opalescence PF 15%] on hardness of a microhybrid composite. Thirty cylindrical-shaped specimens of microhybrid composite Z250 [3M, Dental Products, USA] with 5mm diameter and 2mm height were prepared and divided into three treatment groups comprising a control and two different bleaching groups. Control specimens were stored in distilled water for two weeks. Specimens of bleaching groups were exposed to the bleaching agents [Kimia 16% the first bleaching group and opalescence 15% for the second group] 1 hour daily for 2 weeks. After treatment, the hardness of specimens was tested using Vickers-test Instrument under 300 gr load for 15 seconds. The data were analyzed using One-way ANOVA and Tukey tests [alph=0.05]. The mean composite microhardness for control, Kimia and Opalescence groups were 97.93 +/- 4.59, 95.56 +/- 2.75 and 86.57 +/- 2.59 respectively. It was observed that the bleaching materials softened the composite Z250. However, ANOVA showed the difference between Kimia group and control group was not significant [P=0.280]]. Hardness of Opalescence group was significantly lower than the two other groups [P=0.000]. Regarding the decreased microhardness of microhybrid composite, Kimia 16% at-home bleaching agent is more desirable than Opalescence PF 15%