Effect of Time and Photoactivated Face on Bond Strength of Brackets and on Degree of Monomer Conversion

Abstract Objective was to evaluate the effect of different photoactivation protocols of a high-power photo activator on the shear bond strength (SBS) between metal brackets and dental enamel and on the degree of conversion (DC) of an orthodontic resin. Material and Methods 40 bovine incisor crowns were randomly assigned to 4 groups (n = 10). The brackets were bonded with Transbond XT® resin using 4 protocols according to the “photoactivation protocol” factor which was subdivided into: photoactivated faces and photoactivation time. All the samples were stored for 4 months (water,37ºC) and then subjected to a SBS test (100KgF,1mm/min). 40 resin discs were made to evaluate the monomer degree of conversion. Data from the SBS and DC were assessed by One-way ANOVA and Tukey’s test (5%). Bond failures were analyzed according to the Adhesive Remnant Index (ARI) and evaluated by the Kruskal-Wallis test (5%). Results One protocol showed a clinically acceptable SBS value. There was a statistically significant difference (p = 0.008) in the One-way ANOVA result for SBS values, but the protocols showed statistically similar results (p ≥ 0.05–Tukey’s tests) concerning the photoactivated faces and photoactivation time factors individually. There was no statistically significant difference (p ≥ 0.05) in the One-way ANOVA result for DC values. Conclusion The SBS and DC values will vary depending on the protocol applied and 6 seconds-centered activation seems to be the most suitable for clinical practice. Clinical Relevance: It is possible to maintain the bracket fixation quality with the use of a high-power LED photo activator associated with a shorter photoactivation time.