[Effect of different light curing distances on degree of conversion of multiple coating of two adhesive systems]

ABSTRACT

Degree of conversion [DC] is one of the most considerable factors in polymerization of composite resin. Cytotoxicity and physico mechanical properties of dentin bonding agents [DBA] are greatly depend on the DC. The aim of this in vitro study was to evaluate the DC of two totals etch dentin adhesives in different layers and different distances of light tip during curing. Two kinds of dentin adhesive systems were selected including optibond solo plus, filled and single bond, unfilled. The dentin adhesives were applied on polyethylene sheets [5x5 cm]. Each group of dentin adhesives was divided into two groups [n=15] based on the number of coating layer [one and four layers]. Each group was divided into three groups based on the distance of light tip during curing. [1, 3 and 6 mm] [n=5]. Each specimen underwent light curing for 20 seconds. The samples were analyzed with FTIR [Fourier Transform Infrared Spectroscopy] for the amount of double bonds [C=C] and [C=O] before and after curing. The DC was calculated and the data were analyzed by three way ANOVA pair wise comparison [alpha=0.05]. Mean amount of DC for optibond solo plus [71.6% +/- 1.4%] was higher than single bond [56% +/- 1.5%]. There was no significant difference in DC using one layer and four layers and also 1 mm and 3 mm distances of light tip and adhesives but 6 mm distant showed a significantly lower mean amount of DC than 1 mm and 3 mm distances. This in vitro study showed that the degree of conversion in dentin adhesives was related to the composition of these materials. Six mm distance of light lip could decrease the DC while 4 layers of DBA were similar to that one of 1 mm