High prevalence rates of dental erosion had drawn clinicians’ and researchers’ attention to this problem [10, 13, 25]. The increased consumption of acidic soft drinks and energy drinks especially among adolescents and children established the importance of effective preventive measures [26].
Different fluoride presentations were tested against dental erosion as toothpaste, rinses, gels, and varnishes [3, 18, 20, 27].
The rise of SDF as an effective anti-cariogenic agent, their role in the prevention of mineral loss, and increasing the resistance of dental hard tissues to acids lead us to study their effect on dental erosion [11, 12, 28]. The effectiveness of SDF- KI is less than SDF alone in the prevention of caries progression as KI reduces the number of silver ions that have antimicrobial properties, but this effect is irrelevant to dental erosion due to the absence of bacterial component [29].
To our knowledge, this is the first study to evaluate the effect of SDF-KI in the prevention of dental erosion in primary teeth; we studied its effect versus CPP-ACPF, NaF and SDF alone. We kept the comparisons between fluoride-containing products for the treatment groups as the effect of dental erosion without fluoride is overwhelming [1, 18, 19, 21]. The SDF group was added to compare its effect with and without the addition of KI.
The choice of CPP-ACPF was due to its ability to protect against acidic attacks and its remineralization potential [16]; however, its effect against erosion is still controversial [17, 26]. CPP-ACPF is different from any other fluoride-containing preventive measure in the high availability of calcium and phosphate, so the preventive action of fluoride is aided by the high uptake of calcium and phosphate from the surrounding environment in the presence of CPP-ACPF [30].
As for NaF, it is the most commonly used fluoride salt and it has shown an effective preventive role so we used the 5% NaF varnish for comparison [18, 21, 31].
For those two comparator groups of CPP-ACPF and NaF, varnishes were chosen over other forms of fluoride as it is commonly used with the young age, it offers high fluoride concentrations and a relatively long adherence and fluoride release time to the tooth surface and both factors are required to offer better protection against lower concentrations of erosive acids [3, 21].
Trying to mimic the clinical situation the varnish was applied only once and removed after 24 h as this might occur in the oral cavity by tooth brushing and other mechanical actions, so their chemical rather than their physical protective effect was tested [17, 18].
For the evaluation of dental erosion, several techniques had been used both in vivo and in vitro [18]. As an accurate and reliable technique, surface microhardness has been used frequently to assess dental erosion in vitro [17, 19, 23].
The differences in surface microhardness values between the SDF-KI, NaF and CPP-ACPF groups showed no statistically significant difference. The lowest reduction in surface microhardness was in the SDF group. The control group showed a statistically significant difference in microhardness compared to the treatment groups of SDF and NaF. Similarly, Suresh et al. reported a statistically significant difference in microhardness in favor of SDF compared to the control group [14], also Gokkaya et al. study [12] showed a statistically significant decrease in microhardness of the control group in comparison to the treatment groups of NaF and CPP-ACPF varnishes and showed a nonsignificant difference in surface microhardness reduction between the CPP-ACPF varnish and NaF varnish. While a statistically significant difference in microhardness in favor of CPP-ACPF paste in comparison to fluoride varnish was previously reported in Carvalho et al. study [17].
The lowest decrease in surface microhardness in the SDF group could be attributed to the high fluoride concentration with the synergic effect of high silver ions that can increase surface hardness by forming silver phosphate and insoluble metallic silver salts [12,13,14]. However, there was no statistically significant difference with the SDF-KI on the percent change of surface microhardness despite of the scavenging of silver ions. The privilege of high fluoride concentrations is still present in the professionally applied varnishes as NaF and CPP-ACPF and that explains why there was not a statistically significant difference between the treatment groups. Their effect against the erosive challenge is due to the establishment of the protective layer CaF–like layer on the enamel surface and the formation of fluorapatite crystals [14, 26]. On the other hand, the additional remineralizing effect of calcium and phosphate in the CPP-ACPF was not evident in these results.
The evaluation of dental erosion by calcium and phosphorus loss using spectrophotometry has been considered another efficient and sensitive method [10]. Unsurprisingly, the control group showed the highest results in calcium and phosphorous loss in comparison to the treatment groups with a statistically significant difference.
The results for phosphorous loss showed that the SDF group showed the lowest values although not statistically significant than the other treatment groups, this positive effect of SDF in the prevention of phosphorous loss was recorded in a previous study [10] where 10%SDF group showed a statistically significant difference from 2%NaF solution group with a high acidic challenge of 10%citric acid, while in the milder challenge of 1% citric acid, both agents were effective with no statistically significant difference. One explanation could be the formation of silver phosphate on the enamel surface due to the reaction with silver ions in SDF while the addition of KI in the SDF-KI group affected the silver ions.
As for calcium loss, all treatment groups showed no statistically significant difference between them. Similarly, the comparison between NaF and CPP- ACPF varnishes showed no statistically significant difference before, concerning calcium loss [19], although both groups showed statistically significantly lower values than the negative control group of deionized water. Both agents had a protective effect against dental erosion but with no superiority of one over the other [1, 19].
Measuring surface roughness is an established approach for erosion testing [1, 17], this method provides a very descriptive presentation of the erosion effect, in this study AFM was used to study the topography of the etched and the treated enamel surface, mean Sq of each group was presented as an estimation of the surface roughness and accordingly, the erosive effect of the tested groups.
The AFM results were compatible with the surface microhardness results. They showed that all the tested materials decreased the surface roughness compared to the control group after the erosive challenge.
The surface microhardness and mineral loss results as well as the AFM images showed that those tested fluoride products offered some degree of protection but not complete prevention against dental erosion in accordance with previous studies [10, 13, 19, 21, 32].
Considering that the major concern for the use of SDF is its staining potential so the color changes were assessed in this study. The assessment of color changes by the naked eye is often subjective, so the device-based measurements using the spectrophotometer were chosen as an objective and more precise method [29].
The color change assessment showed no statistical difference between all groups, whereas the highest mean value was recorded in the SDF group expectedly followed by the SDF-KI group. These results were similar to a previous study where SDF-KI caused perceptible staining when used for recurrent caries prevention adjacent to restorations [29].
In the current study, we tried to mimic the intra-oral environment as far as possible; however, some limitations were present, as in the oral cavity erosion never occurs solo, it is usually superimposed by abrasion due to food chewing or tooth brushing. Further studies with larger sample sizes and in vivo settings are required for a better evaluation of the clinical effectiveness of SDF-KI in the prevention of dental erosion and its associated risk of teeth discoloration.
