Degree of conversion and microhardness of dental composite resin materials

Dental composite resins (CRs) are commonly used materials for the replacement of hard dental tissues. Degree of conversion (DC) of CR measures the amount of the un-polymerized monomers in CR, which can cause adverse biological reactions and weakening of the mechanical properties. In the past, studies have determined the positive correlation of DC values determined by Fourier transform infrared spectroscopy (FT-IR) and microhardness (MH) values. The aim of this study was to establish whether MH can replace FTIR for the determination of DC of contemporary CR. Two nano-hybrid CR: Tetric EvoCeram (TEC; Ivoclar Vivadent, Liechtenstein) and IFS Empress Direct (ED; Ivoclar Vivadent) and one submicron-hybrid CR - Charisma Opal (CO; Heraeus Kulzer, Germany) were tested. DC was determined by using FT-IR (n = 10) and Vickers MH (n = 10) was measured using Leitz Miniload 2 Microhardness Tester (Leitz, Germany). The data were analyzed using ANOVA and Tukey's post hoc test (p < 0.05). CO was the highest polymerized material (62.20%) in comparison to TEC (58.85%) and ED (58.78%). Opposite, ED was significantly hardest material (24.49) when compared to CO (17.81) and TEC (20.05). Since the CO was the material with the highest DC, but also with the lowest MH, it can be concluded that the DC of new CR formulations cannot be estimated through the MH data. (C) 2012 Elsevier B.V. All rights reserved.