Effect of erosive challenges on deciduous teeth undergoing restorative procedures with different adhesive protocols - an in vitro study

ABSTRACT Objective To evaluate the effect of erosive challenges on the tooth- restoration interface of deciduous teeth treated with different adhesive protocols. Material and Methods Deciduous molars were cut mesiodistally, then embedded, abraded and polished (n=80). Samples were randomly divided according to the adhesive system used into: G1 (Adper Single Bond2®, etch-and-rinse), G2 (Universal Single Bond®, self-etching), G3 (OptibondFL®, etch-and-rinse with Fluoride) and G4 (BondForce®, self-etching with Fluoride). After standardized cavity preparation (2 mm diameter x 2 mm depth), adhesive systems were applied and samples were restored (composite resin Z350®). Half of the samples were exposed to erosive/abrasive cycles (n = 10, each adhesive group), and the other half (control group; n = 10) remained immersed in artificial saliva. For microleakage analysis, samples were submersed in methylene blue and analyzed at 40x magnifications. Cross-sectional microhardness (CSMH) was carried out (50 g/5 s) at 25 μm, 50 μm, and 100 μm from the eroded surface and at 25 μm, 75 μm, and 125 μm from the enamel bond interface. Results Regarding microleakage, 7.5% of the samples showed no dye infiltration, 30% showed dye infiltration only at the enamel interface, and 62.5% showed dye infiltration through the dentin-enamel junction, with no difference between groups (p≥0.05). No significant difference was observed in CSMH at different depths (two-way ANOVA, p≥0.05). Conclusions We did not observe significant changes in microleakage or CSMH after erosive/abrasive challenges in deciduous teeth treated with different adhesive protocols (etch-and-rinse and self-etching adhesives, with and without fluoride).


Introduction
Erosive tooth wear (ETW) is a chemical-mechanical process that leads to the cumulative loss of hard dental tissue without the involvement of bacteria 4 .
Enamel dissolution occurs both at the enamel/acid interface, as well as within a thin, softened, and partly demineralized layer of enamel, leading to mineral loss, and consequently to tooth substance loss 27 .
Tooth structure loss can cause tooth sensitivity, esthetics impairment, and loss of occlusal vertical dimension, leading to the indication of restorative treatment 29 . On the other hand, when exposing teeth with previous restorations to erosive and abrasive challenges, this can interfere in their durability 29 .
Despite ETW being an emerging theme in recent studies, there are aspects that still need to be better explored, especially regarding the adhesive systems properties, restorative materials, and their application in deciduous teeth. The effect of erosive and abrasive challenges on enamel-restoration interfaces has not been deeply investigated up until now.
To obtain an adequate margin seal, it is necessary to apply adhesive systems under ideal conditions, thus ensuring the best restoration function without any breakdown between the tooth and the restoration 6,19,28 . Any failure at the bond interface can lead to microleakage, characterized by the infiltration of bacteria, fluids, chemical substances or ions between the tooth and the restorative material, as well as margin discoloration and even pulp inflammation 19,28 .
Erosive tooth wear lesions in restored teeth are known by margin degradation and restorations rising above the level of the adjacent tooth surface.. This process starts at enamel and can develop until dentin exposure (rounding of cusps and grooves) 4 .
It is possible to assume the bonding success not only depends on adhesive proprieties, but on a combination of important aspects of the tooth substrate and the adhesive system 19 15 . Fluoride has been added to different dental materials to protect dental tissues. Some studies have investigated the effect of adhesive systems with fluoride on the inhibition of secondary caries, using pH cycling models to simulate demineralization and remineralization processes 13,14,22,23 . These studies showed the resistance of the tooth-restoration interface to acid increased when fluoride was present in the adhesive systems. A similar effect might be observed using erosive/abrasive cycles, but up until now, no study has tested this hypothesis in deciduous teeth.
Considering this knowledge gap, the hypothesis of this study was that the effect of erosive challenge on the enamel-restoration interface of deciduous teeth would be different from the selected adhesive protocols (etch-and-rinse and self-etching adhesives, with and without fluoride). The purpose was to evaluate the effect of erosive challenge on the enamelrestoration interface of deciduous teeth treated with different adhesive protocols using cross-sectional microhardness and microleakage.

Experimental design
The sample size measurement was based on Azevedo, et al. 3  n=10) remained immersed in artificial saliva 17 during the experimental phase. In the experimental phase, the samples were stored in relative humidity at 4°C. At the end of the experimental phase, the group samples under test were exposed to 20 erosion cycles and 5 abrasion cycles. The tested variables were mineral loss (measured using CSMH) and marginal microleakage, which was measured by dye penetration degree.

Sample preparation
In this study, sound deciduous molars were randomly selected from a group of extracted teeth

Statistical analysis
The normality of data distributions were evaluated using the Kolmogorof-Smirnov test. Considering data presented a non-normal distribution, non-parametric tests were used. Microleakage data were analyzed using the Kruskal-Wallis test and using CSMH between adhesive systems. The control and test groups were analyzed using two-way ANOVA non-parametric test.

Results
Regarding microleakage, 7.5% of the samples showed no dye infiltration, 30% showed dye infiltration only at the enamel surface, and 62.5% showed dye infiltration with amelo-dentin junction. We observed no significant difference in microleakage in groups when using the Kruskal-Wallis test (p≥0.05; Table 1).
We observed no significant differences in CSMH between the control and test groups at different depths, neither between different adhesive systems (two-way ANOVA, p≥0.05; Table 2).

Discussion
Erosive tooth wear (ETW), considered an emerging problem in oral health, have been increasingly prevalent among adults, adolescents and children 29 .  In our study, we exposed the samples to 20 erosion cycles and 5 abrasion cycles, leading to initial erosive tooth wear, which was not significantly different in the The microhardness values of dentin at 50 µm were similar between one self-etching adhesive system with fluoride and a conventional glass ionomer cement 14 . On the other hand, the same authors investigated different restorative techniques exposed to a cariogenic challenge in an in situ study, and have not found differences between adhesive systems with or without fluoride, and the group restored with conventional glass ionomer cement showed higher CSMH values 13 .
Several studies comparing toothpastes with and without fluoride in erosion-abrasion models showed The short term evaluation could be another limitation of the study. It could be expected that, after a longterm evaluation with more erosion/abrasion cycles and measurements of nanohardness closer than 25 µm from the enamel bond margin, some differences could be observed among the adhesive systems tested in this study. The evaluation of surface loss with profilometry analysis could provide additional information on the effect of erosive tooth wear on deciduous teeth restored with different adhesive systems.
The authors state that erosive tooth wear (ETW) is a condition of growing importance even in primary dentition, requiring preventive to restorative interventions. The selection of the most adequate adhesive system to restore deciduous teeth exposed to ETW is an important step in ensuring the success of restorative treatments.

Conclusion
Therefore, based on the results of this in vitro study, the addition of fluoride to adhesive systems did not interfere in the investigated outcomes (microleakage and CSMH). The different adhesives protocols (etchand-rinse or self-etching) did not show any difference on enamel bonding interface evaluation after erosive/ abrasive challenges.