EFEITO DE DIFERENTES pHs E TEMPOS DE APLICAÇÃO DO ÁCIDO METAFOSFÓRICO 40% NAS PROPRIEDADES ADESIVAS EM ESMALTE E DENTINA

Abstract

This study evaluated the effect of application the different pHs (0.5, 1 and 2) of meta-phosphoric acid 40% (MPA) with ortho-phosphoric acid 37% (OPA) in different application times with three laboratory studies in vitro. For all experiments, the teeth were distributed into 12 experimental conditions according to the combination of independent variables: acid [37% orthophosphoric acid (OPA), 40% metaphosphoric acid (MPA) pH - 0.5, 1 and 2] and application time [7, 15 and 30 seconds]. For experiment 1, the acids were applied on 72 human molars for microtensile bond strength (μTBS), and nanoleakage (NL). After acid conditioning the adhesive system was applied (Ambar) and restoration in composite resin was performed. Then, the teeth were sectioned to obtain specimens and tested immediately. The Etching Pattern (PC) was evaluated after acid application in dentin. For experiment 2, 93 human molars were used. After acid application in dentin, the adhesive system was applied and composite resin restoration was made. They were then sectioned, half sticks were tested immediately and the other half after 6 months of storage in water for μTBS and NL analysis. The analysis of chemical composition was performed by micro-Raman spectrometry. For experiment 3, 60 human molars were distributed according to the similar independent variables as the experiment 1 and 2. The enamel surfaces were stored in water (37 °C / 24 h) and tested for (μSBS). The PC and qualitative analysis composition of chemical enamel by micro-Raman test was evaluated. For the experiment 1 and 3, acid vs time of application the μTBS and NL data were submitted to 2-way ANOVA and Tukey's test (α = 0.05). For the experiment 2, acid vs application time vs storage time the μTBS data and NL were submitted to 3-way ANOVA and Tukey's test (α = 0.05). For experiment 1, MPA pH 0.5 showed μTBS similar to OPA, independent of the application time (p> 0.05) and statistically higher NL was observed for OPA compared with MPA (p <0, 03). For experiment 2, a significant decrease μTBS value was observed only OPA after 6 months (p = 0.001) and higher values of NL were found when compared to MPA (p = 0.003). For the experiment 3, OPA and MPA pH 0.5 produced statistically higher μSBS when compared to MPA pH 1 and 2 independent of the application times (p <0.001). The MPA acid is an alternative agent for the simultaneous conditioning of enamel and dentin, increasing the μTBS, reducing the NL immediate and after 6 months of storage when compared to the conventional ortho-phosphoric acid. The sum of the properties evaluated, MPA pH 0.5 showed high μSBS, showing be promissory.