Establishment of in vitro and in situ protocols for dental erosion studies

The aim was to compare artificial saliva formulation with and without mucin (in vitro) with human saliva (in situ) on the inhibition of erosive demineralization (subproject I) and on the rehardening of erosion lesions (subproject II), and analyze the influence of the type of intraoral appliance (mandibular X maxillary) in enamel wear caused by erosive challenges (subproject III). In the subproject I, bovine enamel blocks were selected by initial surface hardness and randomized among the groups: GI - human saliva (n=30), GII - artificial saliva without mucin (n=15), GIII - artificial saliva with mucin (n=15) and GIV - deionized water (n=15). Fifteen volunteers wore palatal appliances for 2 hours (GI). In the GII, GIII and GIV groups, the blocks were immersed to the respective solutions for 2 hours. Subsequently, both in vitro and in situ blocks were subjected to initial erosive challenge in 1% citric acid (pH 3.6) for 4 minutes. Final enamel hardness was measured to determine the protective capacity of saliva tested by percentage of hardness loss. For the subproject II, after blocks selection, they were in vitro eroded and randomly among the groups as in subproject I. For erosion, the enamel blocks were immersed on 1% citric acid (pH 3.6) for 4 minutes. Then, in the GI, 15 volunteers wore palatal appliances for 2 hours. In the other groups the blocks were immersed in artificial saliva with (GIII) and without mucin (GII) and deionized water (GIV) for 2 hours. The minerals precipitation on the enamel was evaluated by the percentage of hardness recovery. On subproject III, after enamel blocks selection by surface hardness, they were randomly divided into 2 groups (n=20): GI - palatine appliance and GII - mandibular appliance. Erosive cycling consists in immersing of both devices in 0.01 M hydrochloric acid (pH 2.3) for 2 minutes, 4X/day during 5 days. The analysis of the wear was measured by profilometry and volunteers answered a questionnaire about the comfort of the devices. In the subprojects I and II, data were analyzed by one-way ANOVA and Tukeys test, and in the subproject III It was applied paired t-test (p <0.05). In subprojects I and II it was observed that all studied saliva promoted enamel rehardening and no difference was found between them (p <0.05). In the demineralization test, the artificial saliva with mucin and human saliva (in situ) provided lower enamel hardness loss, showing no difference between them (p<0.05). In the subproject III, the results showed that the specimens allocated in palatine appliance (GI) presented significantly higher erosive wear when compared to the specimens fixed in mandibular appliance (GII). In addition, all volunteers reported greater comfort in using the palatal device. Considering the palatal device is more comfortable and resulted in higher enamel loss when compared to the mandibular device, it is suggested the use of palatine appliances in in situ protocols who want to mimic a patient at high risk of dental erosion. For in vitro studies, the saliva with mucin might be a good substitute for human saliva.