Abstract
BackgroundThe aim of this study was evaluated the eroded enamel rehardening potential using upper palatal and lower buccal removable appliances in different times of salivary exposure (30 min, 1h, 2h, 12h) after a single erosive challenge event.Material and MethodsAfter initial surface hardness evaluation, bovine enamel blocks were eroded in vitro (0.01 M hydrochloric acid, pH 2.3, 30 seconds), selected (n = 160) and randomly assigned to the two appliance designs and twenty volunteers. Four enamel blocks were inserted in each removable appliance. On the in situ phase, the volunteers were instructed to use the upper palatal and lower buccal appliances simultaneously for 12 nonconsecutive hours. After each predetermined period of time of salivary exposure, the enamel blocks were removed from the appliances for immediate evaluation of surface hardness, enabling percentage of surface hardness recovery calculation (%SHR). The data were analyzed using two-way ANOVA and Tukey’s test (α=5%).ResultsThe results showed no difference in the degree of enamel rehardening by the upper palatal or lower buccal appliances (p >0.0001). Regarding the time of use of the appliances, it was demonstrated that 30 minutes (upper = 21.12%, lower = 19.84%) and 1 hour (upper = 35.69%, lower = 30.50%) promoted lower hardness recovery than two hours (upper = 44.65%, lower 40.80%) of salivary exposure (p<0.0001). The use of 12 hours (upper = 49.33%, lower = 49.00%), including the sleeping time of the volunteers did not increase the %SHR.ConclusionsThe location of the appliance does not influence the re-hardening ability of saliva and the use of intraoral appliances for 2 hours seems to be appropriate for partial rehardening of the softened enamel surface. Key words:Tooth erosion, in situ, saliva, tooth remineralization.
Highlights
Saliva is an important biological factor for dental hard tissue health maintenance against dental erosion [1]
On the other hand, when considering only one event of erosive demineralization there was no difference on the enamel hardness using the maxillary and mandibular appliances by volunteers [12] Another result showed no difference for the re-hardening effect after a single erosive demineralization [11], is important to emphasize that in this last study the mandibular appliance was made with soft silicon plate, covering the entire lower arch, presenting a completely different design of the appliance used in the present study
Scanning Electron Microscopy observation in one in vitro study showed an amorshowed that 30 minutes and 1 hour promoted lower hardness recovery than 2 hours of salivary exposure, which is similar to previous study [11]
Summary
Saliva is an important biological factor for dental hard tissue health maintenance against dental erosion [1]. Different designs of intraoral appliances, which carry tooth specimens in the oral cavity, have been used in dental erosion in situ models [9,10] These appliances can be removable or fixed; on the lower or upper arches, with intermittent or continuous use [8]. The period of saliva effect, by the time of appliance use can influence on the re-hardening ability Taking this aspect into a consideration, the aim of this study was to compare the erosive enamel rehardening potential using upper palatal and lower buccal removable-appliances in different times of salivary exposure (30 min, 1h, 2h, 12h), in order to elucidate the mechanism in which there is a difference between the palatal and mandibular appliances in erosion cycling studies. Conclusions: The location of the appliance does not influence the re-hardening ability of saliva and the use of intraoral appliances for 2 hours seems to be appropriate for partial rehardening of the softened enamel surface
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