DOES AN INCREMENTAL FILLING TECHNIQUE REDUCE POLYMERIZATION SHRINKAGESTRESSES

It is widely accepted that volumetric contraction and solidification d uring the polymerization process of restorative composites in combinat ion with bonding to the hard tissue result in stress transfer and inwa rd deformation of the cavity walls of the restored tooth. Deformation of the walls decreases the size of the cavity during the filling proce ss. This fact has a profound influence on the assumption-raised and di scussed in this paper-that an incremental filling technique reduces th e stress effect of composite shrinkage on the tooth. Developing stress fields for different incremental filling techniques are simulated in a numerical analysis. The analysis shows that, in a restoration with a well-established bond to the tooth-as is generally desired-incrementa l filling techniques increase the deformation of the restored tooth. T he increase is caused by the incremental deformation of the preparatio n, which effectively decreases the total amount of composite needed to fill the cavity. This leads to a higher-stressed tooth-composite stru cture. The study also shows that the assessment of intercuspal distanc e measurements as well as simplifications based on generalization of t he shrinkage stress state cannot be sufficient to characterize the eff ect of polymerization shrinkage in a tooth-restoration complex. Increm ental filling methods may need to be retained for reasons such as dens ification, adaptation, thoroughness of cure, and bond formation. Howev er, it is very difficult to prove that incrementalization needs to be retained because of the abatement of shrinkage effects.