The role of desensitizing and anti-erosive dentifrices on dentin hypersensitivity and dentin wear has been widely explored due to the high incidence and prevalence of the disease. According to our results, some dentifrices promoted less surface loss compared to control, implying that some components of the formulas tested demonstrated protective effects against erosive wear in dentin. These findings led us to reject the first null hypothesis. Regarding tubular occlusion, changes occurred in the dentin surfaces of some groups, with differences compared to the control group brushed with distilled water. In addition, even though the three groups had ODT values that were the same as at baseline, this led to the rejection of our second null hypothesis.
Only a weak negative correlation was found between SL and ODT (ρ = 0.07; p > 0.05), which may be related to the different active ingredients to which the specimens were subjected. First, it was hypothesized that a toothpaste that would promote less surface loss would produce greater tubular occlusion, but given the weak, positive, and non-significant correlation between these two variables, this was not observed. This result and the non-significant correlations observed between ODT, SL, and pH values led us to accept our third null hypothesis.
Although different results have been shown between surface loss and tubular occlusion promoted by dentifrices, the use of all tested desensitizing and anti-erosive products can be indicated and considered safe for the use by patients with risk of developing erosive wear, as the changes they caused in dentin were not greater than those observed in brushing with distilled water. Our results showed that dentifrices claiming to have an anti-erosive properties did not differ from those claiming to be desensitizers, which is in agreement with a previous investigation showing that desensitizing and anti-erosive promoted less dentin surface loss at different levels [11]. It could be suggested that the differences in formulations between these products are minimal, perhaps limited only to their active ingredients or fluoride formulations.
Different levels of SL and ODT were observed among the groups. Most of the desensitizing toothpastes act via tubule occlusion due to the nature of the deposits formed by the active ingredients on the tooth surface. On the other hand, the abrasives used in regular toothpastes can also have occlusion effects via deposition at the entrances of the tubules [12]. The EDS analysis showed that calcium and phosphorus were present in all groups, which may explain the tubule occlusion that occurred with the toothpastes without active ingredients, regardless of the functions claimed. These EDS data were in accordance with our previous study on calcium in toothpastes [13]. The distilled water in the negative control did not contain any abrasives that would occlude tubules, which could explain the lack of differences observed before and after cycling in the negative control group. Although Bianco Pro clinical and Elmex Sensitive groups did not show differences in regard to their initial experimental times, the tricalcium phosphate (TCP) contained in both toothpastes was expected to provide calcium and phosphate for tubular occlusion to occur; however, these ingredients did not withstand the acid challenge. The first toothpaste claimed to be anti-erosive, which may be suitable for enamel, but the second toothpaste claimed to be desensitizing via Pro-Argin technology with arginine bicarbonate, and yet it was not strong enough to resist the intensive acidic and abrasive challenges. To date, there are no studies in the literature about Bianco oral care; thus, its mechanism of action should be further investigated. So, this study could serve as a reference for future studies. Regarding to SL, the abrasive wear was measured profillometrically. Comparing Elmex Sensitive versus Colgate Total 12 the results revealed a similar low values for both products [14]. Another study showed that Elmex Sensitive and Elmex Erosion showed no significant difference from artificial saliva (negative control), similar to our SL data.
A previous study showed that the viscosity of Sensodyne Repair & Protect (SRP) could be an important issue for better tubular occlusion [13]. It could explain our ODT data from SRP. The negative control was similar to almost all toothpaste groups; it only differed from the SRP group, probably due to the active ingredient: calcium sodium phosphosilicate (CSP). CSP is an agent that releases calcium and phosphate ions in an aqueous medium and forms a layer of carbonated hydroxyapatite; this is relevant in the erosion process that reduces demineralization and increases mineral deposition [15], and our EDS graphs confirms these elements present on the dentin surface. According to our previous in vitro and in situ studies, SRP showed more tubular occlusion in both studies [10, 13, 16]. The previous studies were performed using different abrasive and erosive models, but the Novamin technology employed by SRP was resistant in different situations, showing SEM with tubular occlusion. However, in terms of profilometry, previous studies showed no statistical differences from the negative control. We should have in mind that these studies were done with different concentrations of citric acid and the erosive challenge may have been different, resulting in another level of surface loss, and the deposits on the dentin tubule could be removed by a stronger acid challenge. The present study used 0.3% citric acid, and perhaps this lower concentration was able to promote a low level of erosive tooth wear. Thus, the mineral content of the toothpastes may have helped and improved the ion exchange capacity of the tooth with the environment, protecting the tooth against erosive tooth wear.
The weak negative correlation between pH and ODT (ρ = -0.29) and SL (ρ = -0.07) found in this study corroborated with previous data [17]. The pH of toothpastes is relevant to erosive tooth wear because their active ingredients require specific pH values to exert their desired effects [18]. A lower pH increases the formation of CaF2-like deposits on tooth surfaces and is also important for the mechanism of action of other active ingredients, such as stannous [19]. Accordingly, our results showed that toothpastes with lower pH values showed lower SL, such as Elmex Erosion (pH: 4.9) and Elmex Anti Caries (pH: 5.2). These toothpastes contain stannous chloride and amino fluoride, respectively. Besides stannous, Elmex Erosion contains chitosan, which might interact with collagen by forming cross-links, protecting the dentin against enzymatic degradation. It was shown that the same concentrations of acidic SnF2 and AmF may be more effective than NaF in protecting against erosion [19]. Nevertheless, the toothpastes that presented low SL and significantly differentiated from regular fluoridated toothpaste (Colgate Total 12) had amino in their formulations (Elmex Erosion and Anti-Caries). This result is probably due to other factors and ingredients of the toothpaste. Due to their surfactant properties, the amino fluoride molecules (Olafluor) are released and, when at a slightly acidic pH, form a layer of stable and durable calcium fluoride on the tooth surface. The detergent action of these organic compounds is combined with the action of fluoride, resulting in increased protection from the action of the acid [20]. This layer acts as a reservoir in pH-dependent fluoride. It should be noted that, although this toothpaste had an anti-caries claim, patients with high risks of ETW have pH variations in their oral cavity frequently. Therefore, these toothpastes could be suitable for preventing ETW as well, based on our low SL results. A study showed that the pH of Elmex Erosion (EE) was 4.7 [21], a similar value to what we observed; however, this study’s results showed that a higher pH was associated with a lower SL and that a lower pH was not associated with SL. This relationship between pH and SL could explain the non-significant correlation between these two variables in our results.
Although the SRP toothpaste obtained the best result in terms of ODT, this does not mean that the other toothpastes were ineffective. All toothpastes that showed a difference from the negative control and from baseline may be suitable for patients with DH, since they promoted ODT (EA, CT, EE, BA, SRP, CP, and SRR). Similar to the profilometry results, the groups that differed from the negative control demonstrated interesting results in regard to preventing erosive tooth wear (BP, SRP, EE, and EA). However, the results from the Elmex Anti-Caries and Elmex Erosion groups were remarkable, as ETW was reduced by 40%. In patients with aggressive ETW, this finding is interesting. These data are in accordance with a study that presented 44.8% (EA) and 66.8% (EE) reductions in erosion compared to control under extrinsic conditions and a pH of 2.5 [22]. The same study evaluated the related dentin abrasion (RDA) values of the toothpastes, showing that EA had an RDA value of 57.4 and EE had a value of 18.8. Thus, perhaps the low RDA values could justify the low SL observed.
One explanation for the lower SL and ODT of EE could be that this toothpaste contains chitosan as already mentioned, a cationic polysaccharide, which is assumed to form acid-resistant multilayers has been shown to be effective in reducing ETW [23]. Its lubricating effects might reduce the abrasivity of toothpastes by binding to the silica particles on the tooth surface, thereby protecting the particles under the dentin.
Furthermore, all dentifrices showed P and Ca in the EDS analyses, even the negative control group without toothpaste. This could be explained by the presence of artificial saliva compounds, proving the role of saliva in the ETW process. The use of artificial saliva in our model of study was a limitation because it did not contain proteins and enzymes enabling either salivary pellicle formation on the dentin or promoting the breakdown of MFP to release available fluoride [24]. This further limited the potential protective effects of some dentifrices, which could be present in clinical conditions. Despite this limitation, SRP showed better ODT properties, whereas EA performed better in terms of SL.
A systematic review showed that toothpastes with NaF provided limited protection, with moderate evidence, while Sn/associations exhibited a protective effect with low evidence in regards to enamel erosion and erosive wear [25]. Regarding the active ingredients, another systematic review showed that toothpastes containing potassium, stannous fluoride, strontium, calcium sodium phosphosilicate, arginine, and nano-hydroxyapatite relieve the symptoms of DH, but it did not advise the use of toothpastes containing strontium and amorphous calcium phosphate, and further high-quality studies are needed [26]. In randomized controlled trials, most toothpaste formulations showed evidence of superiority against placebo or fluorides (amine fluoride, sodium monofluorophosphate, or sodium fluoride). Calcium sodium phosphosilicate (found in Sensodyne Repair & Protect) was most beneficial for all three stimuli, with high to moderate certainty. SnF2 alone and potassium combined with SnF2 or hydroxyapatite were beneficial for tactile and air stimulation with high to moderate certainty. Arginine was beneficial for air stimulus, and strontium and potassium were beneficial for tactile stimuli, with moderate certainty [27]. In addition, technologies such as the Pro-argin-containing and Novamin-containing toothpastes were effective for DH reduction; thus, both, according to the authors, can be prescribed to treat DH in adults with equivalent effectiveness up to four weeks [28].
Calcium and phosphate are important for equilibrium in the oral cavity [29]. This is especially true for caries, but not for the erosion process, because remineralization is limited [30]. Moreover, toothpastes with calcium compounds provided no further protection for dentin when compared to fluoridated toothpaste [31]. In the present study, all toothpastes contained Ca per the EDS analysis, and when the formulation had calcium, the toothpastes showed greater SL. The five groups that did not differ from the negative control were Colgate Pro-Relief, which contains arginine and calcium carbonate: both Bianco toothpastes containing tricalcium phosphate (TCP), Elmex Sensitive with arginine bicarbonate and TCP, and Sensodyne Rapid Relief containing pentassodium triphosphate and hydrated silica.
In summary, the present in vitro findings showed greater tubular occlusion was promoted by the 5% Sodium Calcium Phosphosilicate desensitizing dentifrice and better protection against erosive tooth wear by the dentifrice containing Amine Fluoride; however, the other toothpastes that presented a reduction in the number of dentin tubules compared to baseline and less surface loss could be suitable for patients with hypersensitivity dentin or erosive tooth wear, respectively.