Mahdiyeh Safaee - Iran polymer and petrochemical Institute, P.O. Box: 14965/115, Tehran, Iran.
Hamid Yeganeh - Iran polymer and petrochemical Institute, P.O. Box: 14965/115, Tehran, Iran.
Mohammad Atai - Iran polymer and petrochemical Institute, P.O. Box: 14965/115, Tehran, Iran.

Methacrylate-based composite restorative materials have several drawbacks. Significant shrinkage, early gelation, and residual unreacted monomers due to low conversion are themost of them (1). Recently, thiol-ene systems have been developed due to their inherent advantages. Step-growthradical polymerization results in reduced volume shrinkage and delayed gelation and finally reductions in shrinkage stress 2,3). In this study, the effect of thiol-methacrylate ratio on theshrinkage strain and polymerization conversion of an experimental dental resin is evaluated