Shrinkage stresses associated with incremental composite filling techniques.

It is commonly accepted that stresses associated with polymerization shrinkage of composite restoratives can be reduced by utilization of an incremental filling procedure. A recent report using finite element analysis on a simple box preparation has shown that such a procedure actually produces higher stresses. The purpose of this investigation was to visualize the stresses generated by composite resin placed into photoelastic models of two surface preparations using different incremental techniques. Primary molar preparations were cast life-sized in a photoelastic material. Cavity walls were cleansed, primed and coated with unfilled resin. Incremental filling techniques of a hybrid composite resin were gingivo-occlusal, oblique, and facio-lingual. Comparisons were made with the bulk placement technique. The stresses developed within the model teeth were observed in the field of a circular polariscope under magnification. Generally few differences in shrinkage-induced stresses, were observed between the incremental filling techniques tested. The lowest shrinkage stresses were generated by the bulk placement technique.