Physical-mechanical Properties of Orthodontic Resins with Different Photoinitiators

Objectives: The objective of the study was to evaluate the physical-mechanical properties of orthodontic resins with different photoinitiators photocured using a poly-wave LED unit.

Methods: A commercial resin Transbond XT (TXT), and 3 experimental resins with different photoinitiators: phenylpropadione + DMAEMA (PPD), camphorquinone + DMAEMA (CQ) or bisacilphosphinic oxide (BAPO) were used. The resins were photoactivated with Valo Ortho unit, either directly or through ceramic brackets. The degree of conversion (DC), hardness (KHN) and softening rate (SR) after immersion in 100% ethanol (n=10) were evaluated. The data were submitted to ANOVA 2-way and Tukey's test (α=0.05).
Results: The resin containing BAPO showed significantly higher DC (76.42%) compared to TXT (40.80%) and higher hardness (53.32 KHN) compared to other resins. The resin containing PPD showed significantly lower hardness (25.38 KHN). The TXT resin showed significantly lower softening rate (40.02%) than the resin containing PPD (49.18%). The other resins did not differ statistically from other materials (CQ-42.24%, BAPO-43.10%). Resins that were directly photoactivated presented better physical-mechanical properties (DC, KHN, and SR).
Conclusions: It can be concluded that the type of photoinitiator and the condition of photoactivation affected significantly the physical-mechanical properties of the evaluated materials. The resin containing BAPO and the direct photoactivation showed better performance compared to the other materials and condition of photoactivation evaluated.