ORIGINAL ARTICLE
Vanara Florêncio Passos&Andréa Araújo de Vasconcellos&
José Heriberto Pinheiro Pequeno&Lidiany Karla Azevedo Rodrigues& Sérgio Lima Santiago
Received: 29 May 2013 / Accepted: 10 February 2014 / Published online: 28 February 2014
#Springer-Verlag Berlin Heidelberg 2014
Abstract
ObjectivesThis study assessed the effect of three commercial dentifrices with different fluoride-containing compounds in controlling the progression of dentin loss using an in vitro erosion-abrasion model.
Materials and methodsDentin specimens were randomized into four groups (n=10): control (no F), Elmex (1,400 ppm AmF), Meridol (1,400 ppm AmF/SnF2), and Crest Pro-Health (1,100 ppm SnF2). The dentin specimens were submitted to cycles of demineralization (HCl 0.01 M for 60 s), remineralization (artificial saliva for 60 min), and immersion in 1:3w/wof dentifrice/artificial saliva, followed by tooth-brushing (150 tooth-brushing strokes). The cycle was repeated three times daily for 5 days. Surface loss was quantified by stylus profilometry. Data were submitted to one-way ANOVA and Tukey’s tests (p<0.05).
ResultsWear (μm ± SD) was control 4.1±1.2, Elmex 3.7±
1.5, Meridol 1.3±0.4, and Crest Pro-Health 2.1±0.7. There-fore, all products (except Elmex) produced statistically signif-icantly less mineral loss (p<0.05) when compared with the control.
Conclusion None of the dentifrices avoided the erosive-abrasive process; however, SnF2-containing dentifrices were effective in statistically significantly reducing dentin loss. Clinical relevanceScientific literature shows evidence that fluoride can strengthen dental tissue against erosive acid dam-age. However, the beneficial effect of different fluorides pres-ent in commercial dpres-entifrices is questionable. Thus, a
determination of an effective fluoride dentifrice may be ben-eficial in the reduction of the erosive process in patients with gastric disorders.
Keywords Abrasion . Dentifrice . Dentin erosion . Hydrochloric acid . Fluoride
Introduction
Patients who suffer from eating disorders, such as recurrent vomiting, regurgitation, or gastroesophageal reflux [1,2], are at a higher risk for erosion due to chronic oral contact of hydrochloric acid, which is produced by the stomach. These patients require a prolonged medical treatment until ending the contact of stomach acid with teeth [3]. According to Ranjitkar et al. [3], the success of medical intervention is variable, and adequate treatment is difficult to manage. There-fore, in addition to eliminating the cause, the use of products that inhibits the harmful action of endogenous acid should be beneficial.
One approach in preventive strategies of erosion includes the application of topical fluorides in the form of dentifrices, varnishes, gels, and solutions, as soon as possible and in a form that can be applied by the patients themselves. This beneficial effect may be associated with the formation of mainly CaF2-like products or by forming a physical barrier, which could protect the tissue against acid attack [4–6]. In addition to common fluoride compounds, such as NaF, new preparations that include AmF and polyvalent metal cations (stannous) have recently been studied for preventing erosion [7–16]. Ganss et al. [9] found an almost complete inhibition of erosive enamel loss when using AmF/SnF2and SnF2 solu-tions, while AmF showed no effect. However, the mecha-nisms of action on enamel are different for dentin due to its complex histological structure [6]. The erosive process on V. F. Passos
:
A. A. de Vasconcellos:
J. H. P. Pequeno:
L. K. A. Rodrigues
:
S. L. Santiago (*)Faculty of Pharmacy, Dentistry and Nursing, Federal University of Ceará, Fortaleza, CE, Brazil
e-mail: sergiosantiago@yahoo.com
V. F. Passos
University of Fortaleza, Fortaleza, CE, Brazil DOI 10.1007/s00784-014-1213-6
dentin causes the exposure of the organic matrix, which acts as a diffusion barrier, consequently assuming a buffering capac-ity sufficient to retard further demineralization [17].
To the best of the current authors’ knowledge, no studies exist that have examined the in vitro effect of AmF or SnF2 -containing dentifrices on dentin after erosion caused by hydro-chloric acid. Although amine fluoride has been used to stabilize Sn in aqueous formulations [18], some authors have reported effective antierosive results to AmF on enamel [13,20]. Addi-tionally, it seems relevant to study the interplay of amine and/or stannous fluoride in the preventive measures against tissue loss caused by combined erosive-abrasive challenge on dentin.
Consequently, this study was designed to investigate the effect of three commercial dentifrices that contain AmF, SnF2, or AmF/SnF2with respect to its protective effect on dentin loss using an erosive-abrasive model. These dentifrices were com-pared with a nonfluoride dentifrice. The null hypothesis tested was that there is no difference among the protective effects of the tested dentifrices on the dentinal erosion/abrasion.
Materials and methods
Ethical aspects
The protocol (no. 131/2009) was approved by the local ethics committee. The extracted human teeth were collected after receiving the patient’s informed consent. The collected third molars were stored in a 0.01 % (w/v) thymol solution at 4 °C and were used within 1 month after extraction.
Dentin sample preparation
Root dentin slabs (4×4×2 mm) were obtained from freshly extracted and caries-free third molars. The dentin slabs were obtained using a water-cooled low-speed diamond disk mounted in a sectioning machine (IsoMetTMlow-speed saw; Buehler, Lake Bluff, IL, USA). Subsequently, the slabs were embedded in self-polymerized acrylic resin cylinders (Arotec S.A. Ind. e Com., Cotia, SP, Brazil) with the external surface of the substrates exposed to facilitate handling. The slabs were ground flat with wet 320-, 600-, and 1,200-grit silicon carbide paper (Extec, Enfield, CT, USA) and polished with a 1-μm
diamond paste (Extec, Enfield, CT, USA). After each grinding and polishing procedure, the specimens were sonicated for 2 min (Ultra Cleaner 1400, Unique, Indaiatuba, SP, Brazil) in deionized distilled water, and polished surfaces that were free of visual defects or cracks were selected.
An initial surface hardness (SH) test was performed with five indentations in the center of the slab with a Knoop diamond under a 25-g load for 5 s (FM7 AMRS; Future Tech., Tokyo, Japan) to select 40 slabs. The slabs, which presented microhardness values ranging from 52 to 64 kg/mm2, were randomly assigned into four groups (Table1) according to a computer-generated randomization list (n=10). The pH values of the experimental dentifrices were obtained using slurry containing 1:3 w/wof dentifrice/artificial saliva, and all the toothpastes presented silica as an abrasive.
In order to maintain reference surfaces for lesion depth determination, a layer of an acid-resistant varnish with a dark color (Colorama, CEIL Coml. Exp. Ind. Ltd., São Paulo, Brazil) was applied on one half of the surface of each slab.
Erosion-abrasion cycling model
Demineralization was performed by immersing each slab in 3 mL of hydrochloric acid (HCl 0.01 M, pH 1.96) for 60 s. Subsequently, each sample was remineralized in 5 mL of artificial saliva (1.45 mM Ca, 5.4 mM PO4, 0.1 M Tris buffer, 2.2 g/L porcine gastric mucin, pH 7.0) under constant agitation for 60 min. The slabs were then immersed in 3 mL of 1:3w/w of dentifrice/artificial saliva for 60 s. Next, the specimens were positioned in a brushing machine (MSEt—1,500 W; Marcelo Nucci ME, São Carlos, SP, Brazil) and brushed with 150 strokes (37 °C). The load of toothbrushes (Colgate Professional Extra Clean, Colgate Palmolive Industrial Ltda., São Bernardo do Campo, SP, Brazil) applied on the surface of the specimens was approximately 200 g. During this procedure, the specimens were plated for suspensions of dentifrice and artificial saliva (1:3;w/w), according to each group. After each cycle, which was composed of demineralization, remineralization, and tooth-brushing, the specimens were again rinsed in deionized distilled water. All solutions were used at room temperature. The de-scribed cycle was repeated three times daily for 5 days at room temperature, as shown in Fig. 1. After the daily cycles, the samples were stored overnight in artificial saliva at 37 °C.
Table 1 Dentifrice product information and pH values obtained of slurry (dentifrice/artificial saliva)
Trade name Fluoride pH RDA Manufacturer
Control No F 7.33 70 Manufactured
Elmex 1,400 ppm AmF 5.86 100 Gaba International, Münchenstein, Switzerland Meridol 1,400 ppm AmF/SnF2 6.00 100 Gaba International, Münchenstein, Switzerland
Crest Pro-Health Enamel Shield 1,100 ppm SnF2 5.64 144 Crest, Procter and Gamble, Cincinnati, OH, USA
Tissue loss measurements
After the experimental period, the nail varnish was carefully removed using acetone and a scalpel blade without touching the dentinal surfaces. The specimens were allowed to dry for 10 min before analysis in order to reduce the possible interference caused by the shrink-age of the organic content. Dentinal wear was deter-mined in relation to the reference surfaces, using a profilometer (Hommel Tester T1000, Hommelwerke GmbH, Germany). The wear assessments were standard-ized with parameters of Lm = 1.5 mm and Lc = 0.25 mm, with Lm = extension considered, and Lc = cutoff. The de-vice presented an accuracy of 0.01 μm. The radius of
the diamond stylus was 5 μm, and the measurements
were made at a constant speed of 0.15 mm/s under a force of 0.8 mN. Five random readings were performed on each slab, at intervals of 100 μm. These profilometric
traces were taken by moving the stylus from the refer-ence to the exposed surfaces. The differrefer-ences deter-mined the surface wear. For each sample, a mean was calculated from the values obtained from the five traces.
Statistical analysis
Mean and standard deviation (SD) values of wear per group were calculated. Statistical procedures were per-formed using the Statistical Package for the Social Sci-ences (SPSS 17.0) for Windows. A Kolmogorov-Smirnov test was applied to all groups to test for the normal distribution of errors. Because the values were normally distributed across all of the groups, ANOVA and Tukey’s post hoc tests were used for comparative purposes. The level of significance was set at 5 %.
Results
Mean dentinal loss for all experimental groups is presented in Fig.2. After 5 days of erosion and abrasion cycles, tissue loss was the highest in the control group, and all products (except Elmex) significantly reduced mineral loss, on the order of 37– 67 % (p<0.05 when compared with the control). However, Meridol and Crest Pro-Health were statistically similar to each other. There were no significant differences between the con-trol group and Elmex (p=0.948).
Discussion
The current study evaluated the effect of three commercial dentifrices containing AmF, SnF2, or AmF/SnF2on the reduc-tion of dentin erosion using an erosive-abrasive model. The design of the present study allows for the simulation of the effect that hydrochloric acid (simulating gastric acid) may have in combination with toothbrushing on dentin. During the cy-cling regime, the brushing model followed an erosive-abrasive methodology [21] that was performed three times each day of the experiment. This approach is justified by the population studies that indicate a frequency of toothbrushing of more than two times a day [22], with similar data observed in a Brazilian population [23]. Nevertheless, the acquired pellicle was not formed, once it might act as a diffusion barrier, reducing acid exposure. Thus, salivary pellicle presents preventive effects against further erosive challenges [24]. Therefore, this pellicle may hamper the identification of the real effects of different types of fluorides, since the most severe erosion will be required for a correct analysis of the preventive action of the agents used. To quantify the main findings of the current study, the methodology to measure dentin wear was stylus profilometry, Fig. 1 Twenty-four-hour cycle
which is a widely applied method for the analysis of tooth erosive/abrasive wear [25]. The preventive approach applied in the current study was the use of a fluoride dentifrice, considering that they are used daily and can be easily accessed by the general population, as an alternative for reducing erosion [26]. However, the level of wear can be modulated not only by fluoride but also by the abrasiveness of the dentifrice [27]. The dentifrice abrasivity is determined by a radiotracer method, which pro-vides a value of relative dentin abrasivity (RDA) that starts at 0 and is open-ended. In this present study, the dentifrices tested presented values of RDA raging from 70 to 144, which may be considered dentifrices of medium abrasivity; however, there is no consensus about a classification of dentifrices with respect to this aspect. Furthermore, few studies have been shown that toothbrushing abrasion is related to the abrasivity of dentifrices for eroded dentin. Hara et al. [27] and Wiegand et al. [28], evaluating the impact of dentifrice abrasivity on abrasion of eroded dentin, showed that dentin loss increases with the RDA value of the dentifrice. Other experiments confirm additive and synergistic effects to the development of erosive-abrasive le-sions on dentin by erosive challenge combined with brushing with dentifrice [26,29]. Therefore, this might explain the reason of the numerically higher loss values for Crest dentifrice than Meridol, in spite of both contain the same fluoride.
Some authors have shown that fluoride dentifrices can enhance the resistance of the eroded dental substrate [26,27,
30, 31]. Although not completely avoided erosion, fluoride dentifrices have shown significant reduction in dentin wear [26, 32, 33]. Thus, the data reported in the current study support this protective effect since the hypothesis that there are no differences in the effects between dentifrices tested was rejected, because dentifrices containing fluoride in the forms of SnF2 (Crest Pro-Health Enamel Shield) and AmF/SnF2 (Meridol) reduced tooth wear caused by hydrochloric acid on dentin in vitro.
To the knowledge of the current authors, no study has evaluated the erosion/abrasive effects of AmF-containing
dentifrices on dentin. The application of AmF fluoride may lead to the formation of CaF2products that can protect against acid attack. As the formation of the CaF2layer is enhanced under acidic conditions [34], the amine fluoride dentifrice slurry (pH=5.86) used in this study might be less effective than acidic products. Furthermore, other possible explication to the result might be the application cycle time (60 s) that it was too limited to allow for the formation of CaF2-like layer using an almost neutral dentifrice. In addition, other reason for the lack of effect of this dentifrice might be related to CaF2 -like products not being sufficiently resistant to avoid loss of dental structure after a strong erosive process and brushing with a dentifrice of medium abrasivity. Ganss et al. [35] investigated the stability of CaF2-like layers under erosive conditions on dentin, proving the low acid resistance of the CaF2products. Moreover, Wiegand et al. [36], evaluating the protective effect of AmF solution on dentin unbrushed or brushed and submitted to erosion with hydrochloric acid (60 s), showed that the surface precipitates were affected by brushing, reducing the protective action of AmF products.
The best protective effects in the current study were found when tin fluoride was used, corroborating with other study that assessed dentifrice slurry containing similar fluoride type [27]. The form that tin acts in dentine tissue is currently not well defined. Babcock et al. [37] verified that stannous fluo-ride and hydroxyapatite form four main products, such as Sn2OHPO4, Sn3F3PO4, Ca (SnF3)2, or CaF2 salts. So, it is likely that the current result might be attributed to the fact that, when Sn-products are used, the dentinal surface is covered by a layer containing the reaction products of SnF2and hydroxy-apatite [37], which may obliterate patent dentinal tubules. These precipitated layers are acid-resistant, protecting the underlying hydroxyapatite. In addition, the simple presence of the cited salts may be relevant for protection against ero-sion. Moreover, the interpretation of this result may require some understanding of the complex structure of dentin. The erosive demineralization of dentin causes the exposure of the Fig. 2 Erosive/abrasive dentin
organic matrix, and phosphoproteins that are present in that matrix might attract the stannous ion, which is then retained in this layer and might also accumulate in the underlying miner-alized tissue [33]. Recently, Ganss et al. [38] showed that the demineralized organic dentin matrix is strikingly resistant to mechanical forces, resisting a force of 2 N, which is similar to the brushing force applied in the present study. Therefore, the toothbrushing applied in the current study likely did not remove this protective layer, which has been verified as es-sential for the effectiveness of fluoride dentifrices in reducing dentin loss [14].
Recently, Hara et al. [38] and Comar et al. [33] showed that stannous fluoride present in dentifrice provides a protective benefit against repeated erosive and abrasive challenges, sim-ilar to the result obtained in the current study. According to Ganss et al. [16], the main mechanism of action of SnF2is the uptake of tin in the underlying mineralized tissues, rather than in a surface precipitation. Therefore, tin is retained in the demineralized organic matrix and accumulates in the under-lying mineralized tissues.
Considering all of the current findings, the in vitro exper-imental model suggests that Sn fluoride is an effective protec-tive agent to be incorporated into dentifrices, since both Meridol and Crest Pro-Health, commercial products contain-ing tin, minimized the erosive-abrasive root dentin wear, even when using a strong acid challenge.
Conflict of interest The authors declare that they have no conflict of interest.
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