Microhardness of Resin Luting Cement , Influence of Light Curing Units

Objectives: The objective of this study was to verify the microhardness of the resin luting cement Rely-X (3M), comparing light-curing units, intermediary restorative materials and elapsed time after curing. Methods: The specimens with 4mm diameter and 1mm height were fabricated using a metallic mould with a circular opening. The cement was inserted in the circular opening of the mould, then a chip of ceromer (M1) or feldspathic porcelain (M2) (8mm diameter and 1,5mm height), and a mylar strip was set between the cement and the curing light. The photoactivation was done by a halogen based light-curing unit (U1 – Ultralux) and a light emitting diode light-curing unit (U2 – Freelight LED). Analysis of Vickers microhardness were performed in 5 elapsed times after curing with 4 tests per specimen : T1- 5 min.; T2- 10 min.; T3- 15 min.; T4 – 1 hour.Due to the crossing of the number of variables that had been studied, the overall sampling was defined in 40 samples, divided in 4 groups: G1-U1xM1; G2-U1xM2; G3- U2xM1; G4- U2xM2. Results: The analysis of the variance of three factors (light curing uit, material and time) showed that only the factor time was significant (p<0,001). The means and the standards deviations from the results are described as follow: G1T1- 27,2 (3,42); G1T2- 29,5 (3,06); G1T3- 32,0 (2,96); G1T4- 34,8 (3,87); G2T1- 27,7 (2,77); G2T2- 30,1 (2,95); G2T3- 32,1 (3,46); G2T4- 35,5 (3,56); G3T1- 26,5 (2,22); G3T2- 31,5 (2,48); G3T3- 31,0 (1,93); G3T4- 34,8 (2,62); G4T1- 27,3 (2,01); G4T2- 29,8 (1,68); G4T3- 31,7 (1,26); G4T4- 34,2 (2,17). Conclusions: We concluded that only the factor time was significant to increase the hardness of the resin luting cement studied in this research.