The use of a new calcium mesoporous silica nanoparticle versus calcium and/or fluoride products in reducing the progression of dental erosion

Abstract Objective There is increasingly common the consumption more times a day of foods and acidic drinks in the diet of the population. The present study aimed to evaluate and compare the effects of a calcium mesoporous silica nanoparticle single application of other calcium and/or fluoride products in reducing the progression of dental erosion. Methodology Half of the eroded area was covered of 60 blocks of enamel, after which the block was submitted to the following treatments: (Ca2+-MSN), casein phosphopeptide–amorphous calcium phosphate (CPP-ACP); CPP-ACP/F-(900 ppm F−); titanium tetrafluoride (TiF4 1%) (positive control); sodium fluoride (NaF 1.36%) (positive control); and Milli-Q® water (negative control) before being submitted to a second erosive challenge. A surface analysis was performed via a three-dimensional (3D) noncontact optical profilometry to assess the volumetric roughness (Sa) and tooth structure loss (TSL) and and through scanning electron microscopy (MEV). An analysis of variance (ANOVA) and Tukey’s test were performed. Results Regarding Sa, all experimental groups exhibited less roughness than the control (p<0.05). The TSL analysis revealed that the Ca2+-MSN and NaF groups were similar (p>0.05) and more effective in minimizing tooth loss compared with the other groups (p<0.05). Conclusions The Ca2+-MSN and NaF treatments were superior compared with the others and the negative control.


Introduction
Teeth can be exposed to acidic compounds during normal daily activities, especially during the consumption of soft drinks and juices, while taking medications with an acidic composition, or after being subjected to intrinsic acids such as esophageal reflux, these compounds can cause an irreversible and progressive loss of tooth enamel. 1,2 As a result, many clinical consequences arise, including tooth sensitivity or the loss of dental structure around the restorations, which can lead to a gap that may eventually progress to dentin exposure. 3 For these reasons, products exist to help minimize the evolution of existing erosion lesions. Fluorides are the adjuncts most commonly used to prevent further enamel structure loss, as they form a protective layer of calcium fluoride (CaF 2 ) over the enamel surface. 3 This CaF 2 layer serves as a mineral reservoir on the enamel surface and, in cases of demineralization, it is the first to be dissolved. 4 Other fluoride products such as titanium tetrafluoride (TiF 4 ) act by forming a titanium oxide film that prevents erosion. 5,6 In addition, researchers have explored the use of calcium-based products such as CPP-casein phosphopeptide, and ACP-amorphous calcium phosphate paste; and CPP-ACP/F − in the remineralization of dental enamel.
CPP provides calcium and phosphate at the enamel surface and which acts in the demineralizationremineralization process. 7,8 Amorphous calcium phosphate, when placed in an acidified pH solution, separates from the CPP, leaving the phosphate and calcium ions to interact with the dental enamel, helping to prevent mineral loss. 9 Mesoporous silica has great research relevance in the area of health, and with wide application in the field of biomaterials, since it has a great capacity to incorporate molecules within its numerous pores present in its structure and release them in a sustained manner. 10 Positive results have previously been found following use of a novel calcium mesoporous silica nanoparticle (Ca 2+ -MSN) to prevent dental caries (unpublished data). In this formulation, silica is present as a mesoporous nanocomposite with high adsorption and is thus able to incorporate gradual-release compounds. Mesoporous silica is a nanocomposite that is capable of incorporating several compounds for its gradual release. In the case of our study, calcium was incorporated as the objective was to release calcium gradually. However, other compounds such as NaF, TiF 4 (unpublished data), substances for medical use are also used. 11 In addition, the nanocomposite silica has a high surface area since it has a large amount of hexagonal-shaped pores, which increases the loading of substances inside; 11 and adequate thermal stability, that is, mesoporous silica can resist changes in temperature, without however changing its initial composition. 12 Its application has been studied as a means to carry compounds and promote their slow release on an applied surface, 13 which could interfere with mineral loss kinetics.
Therefore, based on the prior established benefits of the novel calcium mesoporous silica material in caries prevention and treatment, since calcium can minimize mineral loss whether in the process of caries or tooth erosion, so, the present study aimed to evaluate and compare the effects of a single application of this compound to those of other calcium and/or fluoride products, specifically in regard to reducing the progression of dental erosion.

Methodology
This in vitro study evaluated the effects of a single application of Ca 2+ -MSN in reducing the progression of dental erosion and compared the findings to other calcium and/or fluoride products. The choice of 10 blocks per group was made after performing a sample calculation to detect a significant 50% difference in mean mineral loss in each treatment group as compared with the negative control group while considering a statistical power of 80%, a unilateral test, and a significance level of 5%. 14 The BioEstat  (6) Milli-Q ® water (Millipore Corp., Burlington, MA, USA) as a negative control. Subsequently, the blocks were one again exposed to in vitro erosive challenges and the topography of each block was analyzed via threedimensional (3D) noncontact optical profilometry and scanning electronic microscopy (SEM).

Sample preparation
Sixty enamel blocks measuring 6×6×2 mm were cut using an Isomet low-speed saw cutting machine

Treatments and erosive challenge
The enamel blocks (n=60) were randomly assigned into six groups (n=10 each) according to the proposed surface treatment. Half of each block was covered with an acid-resistant varnish (untreated area) ( Figure   1D) and the other half (i.e., the eroded area) was submitted to the first erosive challenge for three days, three times daily, for five minutes ( Figure 1E

Results
The negative control blocks presented higher mean values of Sa in comparison with the difference between the eroded and treated areas of the experimental blocks (p<0.05). Furthermore, the studied products were able to reduce the mean difference of Sa between the eroded and treated areas as compared with the positive control (p<0.05), without statistical differences (p>0.05) ( Table 1).
Based on the findings of TSL difference between the eroded and treated areas, the Ca 2+ -MSN and NaF treatments were found to be similar in terms of effect (p>0.05) and thus more successfully reduced erosion progression than did CPP-ACP, CPP-ACP/F − , or TiF 4 . These latter treatments yielded results similar to those of the negative control (p<0.05) ( Table 1).
When the SEM images ( Figure 2) were reviewed, the groups that best inhibited the progression of enamel loss (i.e., those that showed the smallest step between the eroded and treated areas) were the novel Ca 2+ -MSN and NaF groups. The control group presented the largest step and a visible degree of surface loss. The color scale of the 3D profilometry images confirmed that steps had formed between the eroded and treated areas in each product group ( Figure 3).

Discussion
The present study aims to compare the effects of a novel Ca 2+ -MSN and other commonly used products on dental erosion. In present study, the novel Ca   Table 1-Mean ± standard deviation of differences in volumetric roughness (S) and TSL (trated-eroded área) of enamel after application for each product and erosive challenge To our knowledge, this is the first study to incorporate calcium into a novel mesoporous silica nanoparticle applied to act as a limiting factor in the progression of dental erosion. The positive results obtained herein in regard to reducing the loss of tooth structure in comparison with other products may possibly be due to the fact that the porous structure of the silica encapsulates the to-be-released compounds, acting as a stabilizer and increasing the reaction by gradually releasing the compounds, thus creating chemical stability. 20,21 Ca 2+ -MSN showed results as positive as NaF, which is a product considered the gold standard in the use of remineralization. As a result, Ca 2+ -MSN can be considered an important product to be incorporated into future in vivo studies, since it has benefits and positive results as seen in the present study. It is a product with high substantivity, containing many pores that allows a greater incorporation of several substances (in the case of our study calcium was chosen), to be a compound that has a synthesis using a simple process (providing a good cost /benefit), to be a biocompatible product in humans and in addition ,for having a great benefit for its chemical stability capacity, 22,23 keeping its properties stable even in the oral cavity that undergoes changes in temperature and pH.

Mean (SD) Mean (SD)
When analyzing the fluoride compounds, positive results were obtained regarding the use of NaF, which can possibly be explained by the fact that fluoride decreases the solubilization of dental enamel (hydroxyapatite) through the formation of CaF 2 , leading to establishment of a barrier that is the first to be diluted after an erosive challenge. However, in the present study, TiF 4 was not as effective as NaF in reducing the progression of enamel erosion.
Nevertheless, we can speculate that TiF 4 may still be able to prevent dental erosion. 24 The use of a new calcium mesoporous silica nanoparticle versus calcium and/or fluoride products in reducing the progression of dental erosion According to Reynolds 31 (2009) andRose 32 (2000), this is due the compound CPP-ACP includes a technology that adheres to the plaque, providing a reserve of calcium and phosphate. However, no benefits were identified as existing for either CPP-ACP and CPP-ACP/ F − regarding preventing dental plaque by creating a reservoir of phosphate and calcium ions in the present study, and neither compound presented a similar efficacy against tooth erosion as compared with Ca 2+ -MSN and NaF. In addition, the flow addition product had a concentration of 900 ppm of F-, which may have been the differential factor, since the CPP-ACP/F-showed more erosion, compared to the positive controls that had 6,153-and 6,135-ppm concentrations of F-, respectively.
In addition, the lesser effectiveness in our study, of CPP-ACP and CPP-ACP/F− products, when compared to the use of more used products such as NaF for example, may have been due to the chosen time of application, studies that chose application times that varied between 3 to 5 minutes, showed better results when compared to our study, for example. [33][34][35] Conclusions Based on the results of the present study, the