The effect of polymerization protocol on the flexural strength and degree of conversion of an indirect resin composite
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Purpose: SR Nexco Paste is an indirect resin composite indicated for the fabrication of implant-supported, implant-retained restorations. Currently, select few laboratory polymerization devices have been tested and approved for its use, limiting utilization to extra-oral and laboratory settings. The purpose of this study was to investigate the flexural strength and degree of conversion of SR Nexco Paste with newly tested polymerization protocols in an effort to maximize the material's usage in the clinical setting. Materials and Methods: 36 beam-shaped samples were fabricated according to specifications set forth by ISO 4049 to test the flexural strength (FS) of SR Nexco Paste. Four polymerization protocols were followed: Group 1) Bluephase G2 (Ivoclar Vivadent) cured for 1 minute and 40 seconds, Group 2) Bluephase G2 (Ivoclar Vivadent) cured for 3 minutes and 20 seconds, Group 3) Lumamat 100 (Ivoclar Vivadent) cured for 11 minutes, Group 4) Triad 2000 (Dentsply) cured for 5 minutes. To obtain the degree of conversion (DC) 20 disc-shaped samples were fabricated and polymerized following the same four polymerization protocols. Results: The mean flexural strength (mean FS=149.78, SD=11.99) and degree of conversion (mean DC=71.11, SD=5.58) of samples polymerized in Triad 2000 for 5 minutes were significantly higher than all other groups. The mean flexural strength of samples polymerized by Bluephase G2 (mean FS=112.51, SD=12.80) for 1 minute and 40 seconds was significantly lower than other groups. Discussion: Based on the results, all polymerization protocols demonstrated clinically acceptable flexural strength values well above 50 MPa, as set forth by the ISO standard. The additional element of heat generated by the Triad 2000 device may contribute to its superior flexural strength and degree of conversion values. Conclusion: Within the limitations of this study, Bluephase G2 (Ivoclar Vivadent) and Triad 2000 (Dentsply) can achieve satisfactory polymerization comparable to the existing approved devices. While Bluephase G2 can be utilized for the intra-oral polymerization of SR Nexco Paste, the Triad 2000 unit can serve as an alternative in-office device for successful extraoral polymerization.