Photoelastic Analysis Of Composite Shrinkage Stress Photoactivated By Different Methods

Objective: The aim of this study was to evaluate the polymerization shrinkage stress of composites photoactivated by different modulated methods.

Method: Sixty discs of photoelastic resin (Araldite GY 279/Aradur 2963) were prepared with cylindrical cavities (6mm diameter, 2mm height) in the center of each disc. The side walls of cavities of photoelastic resin were roughened and prepared with adhesive system. Filtek LS (3M/ESPE) and Filtek Z350 (3M/ESPE) were inserted in bulk and photoactivated with quartz-tungsten-halogen lamp XL2500 (3M/ESPE), using the following method (n=10): continuous (C) - 600 mW/cm² for 40 s; continuous with low irradiance (CL) - 150 mW/cm² for 160 s; soft-start (SS) with 150 mW/cm² for 5 s + 600 mW/cm² for 39 s; and pulse-delay (PD) - 150 mW/cm² for 5 s + 3 minutes in dark room + 600 mW/cm² for 39 s modes. The stress generated by polymerization shrinkage was analyzed immediately after the photoactivation using a plane polariscope. Quantitative analysis of stress was done using UTHSCSA Image Tool software. Data were submitted to two-way ANOVA and Tukey’s test (α=0.05).

Result: Filtek Z350 (5.1 MPa) showed shrinkage stress significantly higher than Filtek LS (3.8 MPa). C (4.1 MPa) and SS (4.4 MPa) methods showed significantly higher shrinkage stress than CL (3.3 MPa) and PD (3.5 MPa) methods for Filtek LS, and SS showed the highest shrinkage stress (5.5 MPa) for Filtek Z350.

Conclusion: Low shrink resin composite Filtek LS showed the lowest shrinkage stress while soft-start showed the highest stress among the photoactivation methods.