Dynamics of composite polymerization mediates the development of cuspal strain

In the current study, we used electronic speckle pattern interferometry (ESPI) to measure tooth deformation in response to polymerization of five resin composites with a range of polymerization shrinkage. Our hypothesis was that composites with higher polymerization shrinkage should cause more cuspal strain as measured by ESPI.

Standardized MOD cavities were prepared and placed into the ESPI apparatus before the cavities were filled with composites (n=10). The ESPI apparatus was constructed to measure the out-of-plane displacement of the lingual cusps of the teeth during the polymerization of the restorative material. A thermocouple was attached to the specimen to monitor thermal changes throughout the polymerization process.

Experiments with empty preparations demonstrated that the ESPI technique was temporally responsive and sensitive to dimensional changes. However, the correlation between polymerization shrinkage of composite resins and ESPI-measured tooth deformation was not straightforward. In particular, a flowable material did not deform the tooth significantly more that a conventional hybrid. Further, an experimental silorane material (with the lowest axial shrinkage) induced the least tooth deformation.

We concluded that ESPI is a viable method for assessing cuspal strain induced by shrinkage of bonded composite restorations, but that polymerization shrinkage data may overestimate shrinkage-induced tooth deformation. The rate of polymerization shrinkage appeared to mediate the development of cuspal strain.