Influence of Light Source and Erosive Challenge on Composite Microhardness

Objective: The aim of this study was to evaluate the microhardness of resin composites photocured by LED and halogen light sources, before and after an erosive challenge.

Method: 90 cylindrical specimens with 3mm diameter and 2 mm high were prepared with 3 different composites (n= 30): G – Grandio SO (Voco), P – P90 (3M/ESPE) and Z – Z350 XT (3M/ESPE). Each group was divided into 3 subgroups (n = 10) according to the curing unit used: V – Valo (LED -Ultradent - 1000 mW/cm²) for 10s, D- Demi (LED - Kerr - 1500 mW/cm²) for 5s and J – Jetlite 4000 plus (QTA - J. Morita - 600 mW/cm²) for 40s. The Knoop microhardness was measured after 24hr on the top and bottom of each specimen. After that, they were submitted to an erosive challenge with a soft drink (Sprite) for 7 days (3 times a day for 5 minutes) and then the microhardness was measured again. The data were evaluated with 4-way ANOVA and Tukey´s test.

Result: ANOVA showed significant differences for all factors analyzed (p<0.05). The results of Tukey´s test for resin was: G (91.06 ±23.23)a, P (49.48 ±11.26)b and Z (72.08 ±17.37)c. For light source: V (67.47 ±24.11)a, D (70.43 ±22.61)ab and J (74.73 ±26.87)b. For erosion: Before (74.75 ±23.17)a and After (66.99 ±25,64)b. For specimen side: Top (77.33 ± 26.65)a and Bottom (64.41 ±20.74)b. The groups followed by the same letter did not showed statistical differences.

Conclusion: The Composite G showed higher microhardness than other composites. The halogen light source tested resulted in better results than LED sources. The erosive challenge led to softening of the surface for all materials. The top of the specimens were harder than the bottom.