Effect of different salivary exposure times on the rehardening of acid-softened enamel

Abstract

This in situ study assessed the effect of different times of salivary exposure on the rehardening of acid-softened enamel. Bovine enamel blocks were subjected in vitro to a short-term acidic exposure by immersion in 0.05 M (pH 2.5) citric acid for 30 s, resulting in surface softening. Then, 40 selected eroded enamel blocks were randomly assigned to 10 volunteers. Intraoral palatal appliances containing 4 enamel blocks were constructed for each volunteer, who wore the appliance for 12 nonconsecutive hours: initial 30 min, followed by an additional 30, and then by an additional 1 hour. For the last additional 10 hours the appliances were used at night, during the volunteers' sleep. Surface hardness was analyzed in the same blocks at baseline, after erosion and after each period of salivary exposure, enabling percentage of surface hardness recovery calculation (%SHR). The data were tested using repeated measures ANOVA and Tukey's test (α = 0.05). Increasing periods of salivary action promoted a progressive increase in the surface hardness (p < 0.001). However a similar degree of enamel rehardening (p = 0.641) was observed between 2 hours (49.9%) and 12 hours (53.3%) of salivary exposure. Two hours of salivary exposure seems to be appropriate for partial rehardening of the softened enamel surface. The use of the intraoral appliance during sleep did not improve the enamel rehardening after erosion.

Impact of a simplified in situ protocol on enamel loss after erosive challenge

“…A possible explanation for this result is the low salivary flow rate during sleep that provided little protective effect against erosion, since all the properties of saliva depend on salivary flow [ 29 ]. In addition, the interplay among enamel, saliva, and erosive acid at the distinct demineralization and remineralization phases should be considered [ 15 , 16 ]. Mendonça et al tested in situ the effect of enamel salivary exposure time prior to an acid challenge on demineralization prevention (initial erosion) [ 15 ].…”

“…On the other hand, keeping the blocks in saliva for a 12-h overnight period did not enhance this protection [ 15 ]. In relation to remineralization, Alencar et al (2016) assessed the effect of different salivary exposure times on the rehardening of acid-softened enamel and found that the use of an intraoral appliance for 10 hours during sleep did not improve the enamel rehardening from the initial erosion lesion [ 16 ]. Although the term remineralization is generally used in dental erosion, the mineral uptake is confined to the surface and near-surface softened layer [ 30 ], differently from what occurs with caries.…”

“…A previous in situ study has shown that a 12-hour overnight use of the intraoral appliance resulted in a similar erosion prevention compared to a 2-hour daytime use [ 15 ]. In addition, the use of an intraoral appliance during sleep did not improve saliva ability to reharden an erosion lesion when compared to a 2-hour daytime use [ 15 , 16 ]. However, no study has clarified the impact of overnight salivary effect on enamel loss, considering both demineralization and remineralization episodes using an in situ experimental erosive cycling model.…”

“…Moreover, a recent study has shown that the protein profile of the acquired pellicle changes according to its location in the dental arches, which might influence the protective ability of the protein film against erosion [ 19 ]. In previous studies involving initial erosive lesions, the location of the intraoral appliance did not interfere in the rehardening potential of saliva on enamel [ 16 ] and its ability to protect against initial erosive demineralization [ 15 ]. However, no information is available considering erosive cycles and advanced erosive lesions.…”

Utilização de pastas contendo fosfopeptídeo de caseína-fosfato de cálcio amorfo com e sem fluoreto na prevenção da erosão dentária: uma revisão da literatura

“…Assim sendo, estudos in situ, são utilizados para contornar as dificuldades de realização de estudos de erosão dentária in vivo 53 , oferecendo ainda a vantagem da padronização dos desafios erosivos, como concentração, volume e duração da exposição ao agente erosivo iguais para todos os grupos de estudo, minimizando a variabilidade 54 , somada a exposição dos espécimes ao ambiente bucal. Na maior parte dos estudos in situ já realizados (quadro 01) a aplicação da pasta de CPP-ACP foi feita depois do desafio erosivo.…”