Does an Incremental Filling Technique Reduce Polymerization Shrinkage Stresses?

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.

Challenges to the clinical placement and evaluation of adhesively-bonded, cervical composite restorations

“…Moreover, mathematical analysis of the stresses generated by polymerization suggested that there are problems associated with incremental filling techniques, such as higher tensile stress concentrations at the restoration-enamel interface than those found with single-increment fillings [65].…”

Polymerization shrinkage stress of composite resins and resin cements – What do we need to know?

“…10,41 A popular approach is to restore a cavity in oblique increments to avoid bonding to opposite walls. This technique has been suggested to result in less cuspal flexure compared to a single increment based on tests carried out with aluminum blocks.…”

“…Actually, placing composite in oblique increments causes stresses that can be even higher than would be obtained with a single increment fill (bulk filling). 8,9,41 It is important to emphasize that regardless of the shrinkage stress, proper polymerization throughout a conventional composite depth is difficult to obtain when the material is light cured in a single increment. 8 Reducing the conversion of composite would likely result in reduced stress due to lower volumetric shrinkage, but comes at the expense of the material properties.…”

A Posterior Composite Case Utilizing the Incremental and Stratified Layering Technique

“…The preparation was refined and modified for composite restorations where there were rounded internal line angles, and a beveled cavosurface was employed to expose the maximum amount of enamel rods for bond strength. 2 A combination of the incremental [3][4][5][6][7][8][9][10][11][12] and stratified layering technique 5 was used to fill the tooth. In the incremental technique, each layer was placed in a wedge formation no more than 2-mm thick.…”