Does an Incremental Filling Technique Reduce Polymerization Shrinkage Stresses?

TLDR

Polymerization of restorative composites causes volumetric contraction that transfers stress to bonded tooth walls, leading to inward deformation that reduces cavity size, and while incremental filling may aid densification and cure, its benefit for shrinkage stress remains uncertain. The study investigates whether incremental filling techniques reduce the stress effect of composite shrinkage on the tooth. Numerical simulations of stress fields for various incremental filling strategies were performed. Simulations show that incremental filling actually increases tooth deformation and results in a higher‑stressed tooth‑composite structure, and that measuring intercuspal distance or simplifying shrinkage stress is inadequate to capture the effect, making it hard to prove that incrementalization reduces shrinkage stress.

Abstract

It is widely accepted that volumetric contraction and solidification during the polymerization process of restorative composites in combination with bonding to the hard tissue result in stress transfer and inward deformation of the cavity walls of the restored tooth. Deformation of the walls decreases the size of the cavity during the filling process. This fact has a profound influence on the assumption-raised and discussed in this paper-that an incremental filling technique reduces the 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-incremental filling techniques increase the deformation of the restored tooth. The increase is caused by the incremental deformation of the preparation, which effectively decreases the total amount of composite needed to fill the cavity. This leads to a higher-stressed tooth-composite structure. The study also shows that the assessment of intercuspal distance measurements as well as simplifications based on generalization of the shrinkage stress state cannot be sufficient to characterize the effect of polymerization shrinkage in a tooth-restoration complex. Incremental filling methods may need to be retained for reasons such as densification, adaptation, thoroughness of cure, and bond formation. However, it is very difficult to prove that incrementalization needs to be retained because of the abatement of shrinkage effects.