Assessing two dominant methods of dental composites linear polymerization shrinkage management: macromonomers and prepolymerized fillers

Recently, many dental composites labeled as low shrinkage have been presented. However, corporations obscure either the production procedure or the brand new formula’s impact on mechanical properties, which led us toward choosing two outstanding controlling routes of polymerization shrinkage (specifically designed macromonomers and prepolymerized fillers (P.P.F.)) to compare their actual advantage and disadvantage in terms of mechanical properties. Macromonomers were synthesized by using a magnetic stirrer during two stages, using HEMA, Caprolactone, IPDI, and 1,6-Hexanediol for the whole macromonomer structure. For P.P.F. synthesis, a composite mixture has been prepared in which instead of photo-initiators, benzoyl peroxide and benzophenone were added following by polymerization in an ordinary oven with a temperature of 100 °C. In this study, we found that any formula with great amount of P.P.F. (20% of fillers portion) results in a brittle composite, which was due to both high viscosity and heterogeneity. Furthermore, great percentage of P.P.F. is accompanied by the lowest ceramic filler percentage among the entire groups, and as a result, such formula shows the lowest microhardness (82.8 kg/mm 2 ). On the other hand, adding high percentage of macromonomer (%20 of resin portion) brings about both high polymerization shrinkage (%2.56) and weakened mechanical properties (97.9 MPa for flexural strength) resulting from lower percent of Bis-GMA in comparison with other groups. Our findings proved that only the combination of two methods has the capability to be considered in mass production and what that greatly impresses the polymerization shrinkage is P.P.F. in the entire groups. The other conclusion of this study is that the application of nanofillers is mandatory if it is intended to control shrinkage with two mentioned routes.