Impact of Saliva and Intraoral Appliances on Erosion Lesion

Objectives: Previous study evaluated palatal and mandibular appliances for the rehardening of initial erosion, however the volunteers reported that mandibular appliance was not comfortable. This pilot in situ study assessed the effect of different times of salivary exposure on the rehardening of softened enamel using different types of intraoral appliances.
Methods: Bovine enamel blocks were subjected in vitro to short-term acidic exposure by immersion in hydrochloric acid 0.01 M (pH 2.3) for 30 s, resulting in initial erosion (surface softening). Then 40 eroded enamel blocks were selected by surface microhardness. The blocks were randomly assigned into 5 volunteers who wore palatal and mandibular appliances each containing 4 eroded enamel. The volunteers used the aplicances during 12 nonconsecutive hours do to different periods of salivary effect (groups: 30 min, 1 h, 2 h and 12 h). For the last evaluated period (group 12 h), the appliances were used at night, during the volunteers' sleep. Surface hardness of enamel blocks were analyzed after erosion and after each period of salivary exposure, enabling percentage of surface hardness recovery calculation (SRH). The data were tested using Repeated Measures ANOVA and Tukey’s test (p <0.05).
Results: The results showed no difference in the degree of enamel remineralization using palatal and mandibular intraoral appliances (p=0,603945). Considering the times of exposure, similar degree of enamel erosion rehardening was observed between 30 minutes and 1 hour. The groups of 2 hours and 12 hours also presented the same rehardening ability, which was higher than groups 30 min and 1 h.
Conclusions: Regardless of the type of device, two hours of salivary exposure seems to be appropriate for partial rehardening of the softened enamel surface layer.