Improved Cantilever-Beam Based Instrument for Evaluating the Polymerization Stresses

Measuring polymerization stress (PS) due to material shrinkage continues to be challenging due to large variability introduced by sample geometry and cure conditions, but also the instrument itself. Objectives: To modify the ADA tensometer, a cantilever-beam based instrument, and improve its sensitivity for evaluating the development of shrinkage stresses during dental composite polymerization. Methods: Analytical and finite element analyses were performed on a cantilever-beam based tensometer to determine the optimized beam configuration to achieve maximum sensitivity. Based on these calculations, a new instrument was constructed. A calibration procedure was developed, and results from validation experiments were compared to results obtained using a previous instrument configuration. Results: PS results for a commercial dental composite determined using the optimized tensometer design give the correct trend in PS as a function of beam length or specimen height, whereas the previous tensometer configuration cannot differentiate stresses generated for the same experiments. Conclusions: This work demonstrates the importance of beam dimensions and relative rigidity of components on the accuracy of PS measurement via a cantilever-beam based tensometer. The guidelines for designing a tensometer that satisfies the necessary accuracy requirements are provided, and the easy-to-conduct calibration procedure is desirable for frequent recalibration of the tensometer. This instrument can discern smaller differences generated by various composites. Support: NIDCR/NIST Interagency Agreement Y1-DE-7005-01.