Avaliação da resistência ao cisalhamento e do grau de conversão de resinas compostas utilizadas para confecção de attachments ortodônticos com diferentes protocolos de fotopolimerização

Abstract

Introduction: Fracture or fall of attachments can cause delaysin orthodontic treatment, causing loss of effectiveness of planned movement and/or tracking of the aligner. Objective: To evaluate the shear bond strength and degree of conversion of resins used to manufacture orthodontic attachments subjected to different photopolymerization protocols. Methodology: The study sample consisted of 120 bovine lower incisors embedded in acrylic resin and used as a base for making rectangular attachments measuring 03 mm in length, 1.5 mm in width and 1 mm in height. The sample was divided equally into 03 groups corresponding to the resins Opallis Flow®, GrandioSO Heavy Flow® and Supreme Flowable Restorative®. These groups were subdivided into 04 groups (n=10) according to the polymerization time: 03 seconds (3.200 mW/cm2), 06 seconds (3.200 mW/cm2), 20 seconds (1.000 mW/cm2) and 40 seconds (1.000 mW/cm2). After installing the attachments, the specimens were subjected to shear testing in a universal testing machine (Oswaldo Filizola, São Paulo, Brazil), model AME5k, using a 5kN load cell until fracture occurred. For the conversion degree (GC) test, 60 composite resin specimens were prepared in the shape of rectangular attachments with the same dimensions as the shear test, divided into 03 groups (n=20) according to the aforementioned resins and subdivided into 04 groups (n=05) in relation to the polymerization times studied. The GC was analyzed after 24h of polymerization of the specimens using FT-IR infrared spectroscopy analysis (Perkin Elmer, Waltham, Massachusetts, USA). The data were statistically analyzed using two-way ANOVA and Tukey's post-test. Results: there was a statistical difference for the resin factor (p<.001) and polymerization time (p<.001) with interaction between the factors (p<.001) in relation to shear bond strength. Regarding the degree of conversion, there was a statistical difference for the resin factor (p=.024) and polymerization time (p=.020) with no interaction between the factors. Conclusion: The nanoparticle resin (Supreme Flowable Restorative®) and the longer polymerization time (20 and 40 seconds) showed better mechanical performance in the shear bond strength test and a higher degree of conversion.