Statement of Problem: The quantity of remaining unreacted double bonds may be a significant factor pertaining to the mechanical, physical and chemical properties of restorative resins. Insufficient polymerisation within the hybrid layer may cause significant differences in the quality of this layer, and act as a reservoir for monomer release thus increasing cytotoxic potential.

Purpose: The aim of this study was to measure the degree of conversion of three generations of 3M dentin bonding agents and an experimental dentin bonding agent

Materials and Methods: The quantity was determined from the transmission IR-spectrum of the materials before and after polymerization. ScotchBond MP plus adhesive, SingleBond, Prompt L-Pop, and an experimental dentin bonding were used to measure degree of conversion. Six repetitions of each bonding were investigated. Time of light curing was 120s. Kruskal-Wallis and Mann-whitney test were used to compare groups with P<0.05 as the limit of significance.

Results: The results showed a significant difference between groups (P<0.01). A trend of increasing in Singlebond conversion obtained in comparison with ScotchBond MP plus adhesive, Prompt L-Pop and experimental dentin bonding. The degree of conversion was not statistically significant among the other dentin bondings. No significant difference was found between conversion of the experimental dentin bonding and ScotchBond MP plus adhesive (P=1.00) with P<0.05 as the limit of significance.

Conclusion: Dentin bonding technology continues to evolve toward simpler systems. However, Prompt L-Pop as a self-etching adhesive does not show the trend of increasing the degree of conversion. However, the performance of these simpler systems must be further investigated.