A standardized method to determine the effect of polymerization shrinkage on the cusp deflection and shrinkage induced built-in stress of class II tooth models

Jean Gabriel Pottier, Andrew Gregg, Wondwosen Aregawi, Ehsan Nasiri, Alex Fok, Yi Liu, Laurent Kreplak, Richard B. Price, Daniel Labrie

Research output: Contribution to journalArticlepeer-review


Objectives: Using standardized aluminum tooth models, this study: 1) measured the deflection along the cusp wall of models with a Class II cavity restored using either bulk filling or horizontal incremental filling techniques, and 2) calculated the cusp deflection and built-in stress within the restored tooth models for both filling techniques using a finite element (FE) model. Methods: Standardized tooth models with Class II cavities 4 mm deep, 4 mm high and 6 mm wide were machined out of aluminum. The models were restored using Filtek Posterior Restorative A2 shade resin-based composite (RBC). Both bulk filling and horizontal incremental filling techniques were used to restore the tooth models. After photocuring for 20 s from a single peak wavelength light-curing unit (LCU) with a radiant exitance of 1.25 W/cm2, the deflection of the cusp wall surface was measured using a profilometer. A FE model was used to predict the cuspal deflection and built-in stress of the restored tooth models. Results: The elastic modulus within the FE model was parameterized using cusp deflection data obtained on a bulk filled tooth model. An agreement was found between the measured and predicted cusp deflection only when considering partial stress relaxation within the first incremental layer for the two-layer incremental filling technique. The calculated built-in stress was significantly reduced within the RBC and along the cavity walls when the cavity was filled incrementally in a horizontal direction compared to when it was bulk filled, resulting in a significantly smaller cusp deflection. Significance: The FE model was first calibrated and then validated using measured cusp deflection data. Partial stress relaxation may play a significant role in the horizontal incremental filling technique. The model can be used to predict where the built-in stress within the tooth model occurs. This study explains why for a given RBC, a horizontal incremental filling and curing technique results in lower built-in stress within the restored tooth and lower cusp deflection compared to the bulk curing technique.

Original languageEnglish (US)
Article number103987
JournalJournal of the Mechanical Behavior of Biomedical Materials
StatePublished - Nov 2020

Bibliographical note

Funding Information:
We would like to thank J. Dahn for the use of his profilometer. We would like to express our gratitude to 3M Oral Care for the donation of the LCU, adhesive, and RBCs and Kuraray Noritake Dental Inc. for the donation of the metal primer used in this study. This work was supported in part by the Department of Physics and Atmospheric Science, Department of Dental Clinical Sciences, Dalhousie University , and the Minnesota Dental Research Center for Biomaterials and Biomechanics .


  • Built-in stress
  • Bulk filling
  • Cuspal deflection
  • Finite element analysis
  • Incremental filling
  • Interfacial stress
  • Resin-based composite
  • Restoration
  • Tooth model

PubMed: MeSH publication types

  • Journal Article
  • Research Support, Non-U.S. Gov't

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