Inglés (pdf)
Articulo en XML
Referencias del artículo
Traducción automática
Enviar articulo por email
Citado por SciELO 
Similares en
SciELO 
Permalink
INTRODUCTION
Dentin hypersensitivity (DH) is characterized by rapid, acute pain arising from exposed dental tubules in response to thermal, tactile, chemical, and osmotic stimuli1. According to the hydrodynamic theory, physical stimuli promote the movement of fluids within dentin tubules, contracting and expanding odontoblastic processes and stimulating nerve fibers present in the dentin-pulp interface2. DH affects patients’ oral health and quality of life, and is one of their main complaints1. The etiology of DH is multifactorial and often associated with non-carious cervical lesions (NCCL)1,3, whose prevalence is about 11.5%, regardless of the etiology. Molars and premolars are the teeth most frequently affected by NCCL, with incidence and severity increasing with patient age4. The depth and morphology of lesions contribute to high DH levels, and are affected by gastric disease and acidic beverage intake3.
Dental erosion is one of main factors involved in DH. It results from the loss of surface tooth tissue due to the action of acids from intrinsic or extrinsic sources5,6. Acids from intrinsic sources affect the palatal surface of anterior teeth and the occlusal surface of posterior teeth, whereas those from extrinsic sources affect the vestibular and cervical surfaces of anterior teeth6. The action of acids and proteases changes to dissolve minerals, glycoproteins and other components responsible for occluding dentinal tubules7. Reduced salivary flow, either due to medication use or xerostomia, makes it difficult to restore the oral pH and, consequently, contributes to the erosive process3.
Desensitizing and anti-erosive toothpastes are indicated for treating DH8,9. However, their beneficial effects are limited, with results ranging from no action to almost complete desensitization and erosion inhibition, depending on the type. High-quality studies are therefore needed2.
Different components have been added to toothpastes with the aim of increasing the resistance of the dental substrate to erosive processes and/or dentin tubule obliteration2,10,11. Dentifrices containing polyvalent metal ions, such as stannous ions, have effectively reduced the erosion process by depositing ions on eroded tissue, thereby preventing contact with acids2,10,12,13,14. Conversely, abrasive compounds are also often added to dentifrices to improve their cleaning potential15, which may influence the exposure of dentin tubules after erosion-abrasion cycles, increasing permeability and roughness, which have been associated with the development ofDH16,14. Although some studies have evaluated dentifrice action on eroded dentin17,18, there are few studies that have simultaneously evaluated roughness, permeability, and tubular obliteration with the use of sodium fluoride- and stannous fluoride-based dentifrices. The aim of this study was therefore to evaluate eroded dentin properties after erosive-abrasive challenge using three different commercial dentifrices. The hypothesis was that there are no differences between dentifrices in protecting against erosive-abrasive cycles regarding roughness, tubular obliteration, and dentin permeability.
MATERIALS AND METHODS
The project was approved by the Ethics Committee on the Use of Animals of Ara^atuba School of Dentistry (#00414-2018).
Experimental design
The following factors were assessed: (1) two kinds of bovine dentin (sound and eroded); and (2) three dentifrices - fluoride free (without fluoride - WF-negative control - Curaprox Enzycal Zero rybol AG Neuhausen as Rheinfall. Switzerland); with sodium fluoride (NaF - positive control, 1450 ppm NaF Colgate Total 12, Colgate Palmolive, Sao Bernardo do Campo, SP, Brazil); and with stannous fluoride (SnF2, 1100 ppm F as SnF2 Crest Pro-Health, P&G, Cincinnati, Ohio, USA). Table 1 shows the composition and characteristics of each dentifrice. Response variables were surface roughness, dentinal tubule occlusion assessed using scanning electron microscopy (SEM), and dentin permeability. Figures 1 and 2 shows flowcharts of the experiments.
Preparation of dentin specimens
Ninety bovine incisors from 23 animals aged 24 to 30 months were extracted, cleaned, and stored in distilled water until the beginning of the experiment, for a maximum time of 60 days. Any teeth with clinical evidence of caries, root resorption, cracks, or fractures were excluded from the study. Dental crowns were separated from the roots using an IsoMet 1000 precision cutting saw (Buheles, IL, USA) with diamond disc (4” × 0.12” × 'A”, Buehler, Illinois, USA) under water cooling.
Sixty roots were cut with diamond disc (4” × 0.12” × ½”, Buehler, Illinois, USA) under water cooling to obtain dentin blocks (4 × 4 × 1 mm), and abraded with sandpaper discs of decreasing grit (# 320, # 600, # 800, and #1200) until they were 1 mm thick, and prepared to undergo initial dentin permeability analysis.
The other thirty roots were sectioned transversely into blocks 1 mm thick (8 × 8 mm), which were polished with silicon carbide sandpaper discs of decreasing grit (# 320, # 600, # 800, and # 1200) using a polisher (Aropol E, Arotec, Cotia, SP, Brazil). The final polishing was performed using felt disc and diamond polishing paste (1 pm, Arotec APL4), and surfaces were coated with an acid-resistant varnish (Colorama, Sao Paulo, SP, Brazil), to serve as a reference area (sound dentin).
Initial analysis of dentin permeability
To standardize dentin blocks, the 60 specimens (4 × 4 × 1mm) underwent initial dentin permeability analysis. Specimens were immersed in a 37% phosphoric acid solution (1 ml/block) for 30 seconds, washed twice for 1 minute in deionized water, and dried with absorbent paper to remove the smear layer. Cellular and extracellular contents were removed from inside dentinal tubules by immersing the blocks in a 10% NaOH solution (3 ml/block) for 6 hours, followed by deionized water (3 ml/block) for a further 6 hours19,20.
Each specimen was coupled to a fluid infiltration system (Dentin Permeability, Odeme, Luzerna, SC, Brazil) with 1.9 psi initial water pressure. An air bubble was inserted in the capillary tube, and the pressure was increased to 3 psi, stabilizing the air bubble for 30 seconds. After stabilization, the flow through the block was recorded for 3 minutes by recording the bubble displacement within the capillary tube using a 1 mm-resolution digital caliper. The displacement, expressed in mm, provides the flow rate (Q) - volume of deionized water passing through dentinal tubules -, determined by the following formula: Q = (Vs × D)/(L × T), where Vs is the standard volume of the capillary tube in pl, D the bubble displacement in mm, L the capillary length in mm, and T the time in minutes. The dentin permeability (Lp), expressed in pl.cm2/min.cm H2O, is calculated based on the filtration rate (Q), using the following formula: Lp = Q/(PH × Asup), where PH is the hydrostatic pressure and Asup the exposed dentin surface area16,20. Specimens with initial dentin permeability between 1.5 and 2.5 pl.cm2/min.cm H2O were selected.
Erosion - abrasión process
For the erosion process, thirty blocks (8 × 8 × 1 mm) were coated with an acid-resistant varnish (Colorama, Sao Paulo, SP, Brazil), serving as reference area (sound dentin) prior to the challenge. The other sixty blocks (4 × 4 × 1 mm) underwent the challenge after initial permeability had been determined. The erosion process consisted of treating the specimens using an orbital shaker table (Tecnal TE - 420, Piracicaba, SP, Brazil), while immersed in 0.05 M citric acid solution (Merk Biochemistry, Damstadt, Germany) (pH 3.2 - 2 ml/specimen) for 2 minutes, 4 times per day, with 1-hour intervals between each cycle, for 5 days21. After the first and last erosive cycles of the day, specimens were brushed with the evaluated toothpastes for 15 seconds (1:3 - toothpaste/distilled water - slurry) using an automatic brushing machine, 45 strokes, 2 N force (MSET, Elquip, Sao Carlos, SP, Brazil) perpendicular to the specimen surface (extra-soft Condor, round bristles, Sao Bento do Sul, SC, Brazil) and immersed in slurry for 2 minutes at room temperature21. After each cycle, specimens were rinsed in distilled water for 30 seconds and stored in a remineralizing solution (artificial saliva: 1.5 mmol.l-1 Ca(NO3)24H20; 0.9 mml.l-1 NaH2PO4.2H2O; 150 mmol.l-1 KCl, 0.1 mol.l-1 Tris buffer; pH 7.0) at 37 °C. Specimens were kept in artificial saliva at 37 °C at the end of each experimental day and stored in 100% humidity, with distilled water at 37 °C at the end of the erosive-abrasive protocol until they were analyzed.
Analysis of surface roughness
Surface roughness was analyzed on the 8 * 8 * 1 blocks. Each specimen presented half sound and half eroded dentin - both analyzed after cycling (Surftest SJ 401 Rugosimeter - Mitutoyo, Mitutoyo American Corporation, Aurora, Illinois, USA) according to the Ra roughness pattern, which is the arithmetic mean between peaks and valleys. The cut-off used to maximize surface undulation filtering was 0.25 mm. Three equidistant readings were made on each surface and averaged22.
Analysis of dentinal tubule obliteration
Three specimens (8 × 8 × 1 mm) per group were fixed in gold-covered metal stubs (SCD 050, Balzers) and subjected to scanning electron microscopy (EVO HD LS-15, Carl Zeiss do Brasil Ltda, SP, Brazil), at 15 kV and x2000 magnification. The number of obliterated tubules was calculated for both sound and eroded surfaces in the same specimen, starting at the center of the sample and following northwest and southeast directions. A representative image of the specimen was used for quantitative analysis of dentinal tubules using the ImageJ software (National Institutes of Health, Betseda, MD, USA). Total number of tubules was determined by counting all the tubules present in the image (Fig. 3A), and the percentage of unblocked tubules was calculated23-24.
Final analysis of dentin permeability
The final analysis of dentin permeability was performed after the erosive-abrasive cycles, as described above.
Statistical analysis
Surface roughness, tubular obliteration, and dentin permeability showed normal distribution (Shapiro-Wilk test) and homogeneity (Cochran test). Data on bovine dentin (sound and eroded) and dentifrices were submitted to two-way repeated measures ANOVA, followed by Tukey’s post-hoc test. Statistical analysis was performed using the SigmaPlot 12.0 software (System Software, San Jose, CA, USA), with 5 % significance level.
RESULTS
Figure 4 presents the results of the surface roughness analysis (Ra). The WF toothpaste showed the lowest roughness after the erosive-abrasive cycles (p=0.001), with values significantly different from those recorded for the fluoride toothpastes, which were statistically similar to each other (p=0.735). After the erosive-abrasive cycles, all the tested toothpastes promoted a significant increase in dentin surface roughness (p<0.001).
Fig. 4 Surface roughness analysis (Ra μm) of dentin blocks according to the treatment group and the specimen area (sound and eroded). Different letters (uppercase between groups and lowercase intragroup) indicate statistically significant differences (p<0.05). WF: toothpaste without fluoride. NaF: toothpaste with sodium fluoride. SnF2: toothpaste with stannous fluoride.
Figures 3 and 5 show the results of the analysis of dentin tubule obliteration using scanning electron microscopy (SEM). No difference was found between toothpastes for sound dentin (p>0.05); however, the WF group had a significantly greater number of unblocked dentin tubules (84%) after the erosive-abrasive cycles compared to the NaF (49.2%) and SnF2 (61.4%) groups (p<0.001), which were statistically similar (p=0.201). All groups presented a significantly increased number of unblocked tubules after the erosion-abrasion cycles (p<0.05). Figure 3 shows an alteration in specimen surface induced by the action of citric acid. In the group comparison, WF presented the greatest number of open dentinal tubules and SnF2 presented some granules deposited on the surface.
Fig. 5 Dentinal tubules occlusion – SEM evaluation: values of open dentinal tubules, as a percentage of sound and eroded dentin. Different letters (uppercase between groups and lowercase intragroup) indicate statistically significant differences (p<0.05). WF: toothpaste without fluoride. NaF: toothpaste with sodium fluoride. SnF2: toothpaste with stannous fluoride.
Figure 6 shows the results of dentin permeability.
Fig. 6 Dentin permeability according to dentifrice (μl.cm2/min. cm H2O). Different letters (uppercase between groups and lowercase intragroup) indicate statistically significant differences (p<0.05). Lp = dentin permeability. WF: toothpaste without fluoride. NaF: toothpaste with sodium fluoride. SnF2: toothpaste with stannous fluoride.
No statistical difference was found between WF and NaF toothpastes (p=0.912, 45% and 40% reduction, respectively), but SnF2 showed a 14% reduction in dentin permeability after erosive-abrasive cycles when compared to the other dentifrices (p<0.001). All three dentifrices decreased dentin permeability after the erosive-abrasive cycles (p<0.001).
DISCUSSION
Since one of the main etiologic factors of dentin hypersensitivity (DH) is erosion5, various studies have analyzed several types of dentifrices with desensitizing and anti-erosive components to evaluate their action on the dentin surface2,8,9,17,18,25-27. In the current study, in order to ascertain whether dentifrice fluoride content affected the results, a toothpaste without fluoride (WF) was selected as a negative control. The toothpaste containing sodium fluoride (NaF) was selected as a positive control based on studies that report its protective capacity on the eroded tooth surface10,18,25,28. The toothpaste containing stannous fluoride (SnF2) was selected because studies indicate that its components may cause superficial obliteration of dentinal tubules2,18,27,29, thus addressing the need to assess tubular obliteration and dentin permeability11,16,24. Surface roughness was analyzed to evaluate the influence of toothpaste abrasiveness on the surface of the eroded and abraded substrates.
Dentifrices contain abrasive particles, mostly silica derivatives, as polishing agents15,30. These materials are added to toothpastes to eliminate bacterial biofilms and reduce other debris accumulation on tooth surfaces, but they may increase dentin wear by increasing toothpaste slurry abrasivity (relative dentin abrasivity or RDA)30,31. The WF toothpaste caused significantly lower roughness than others, probably due to its lower RDA value32. The NaF and SnF2 dentifrices promoted similar roughness and wear on eroded dentin, which may be explained by the amount of silica and the chemical influence of other components present in the NaF-based toothpaste10,30. After simulating toothbrushing abrasion equivalent to two years, Aguiar et al.32found that dentifrices with RDA values similar to those of SnF2-based toothpastes cause roughness similar to that caused by the NaF dentifrice, in agreement with our results32.
Surface roughness was higher in eroded dentin than in sound dentin for all tested toothpastes. Tooth surfaces with values above 0.2 and 0.3 pm (after cycling) increased bacterial adhesion to dentin surface33. The literature reports that toothpastes may increase surface roughness 8-fold32,33. This finding corroborates our results, where roughness increased by 8 to 10 times as specimens underwent both abrasive and erosive action.
In addition to silica, toothpastes with desensitizing or anti-erosive action contain particles capable of obliterating dentinal tubules, which can be achieved either by an occluding layer on top of the dentin or by depositing material inside the tubules25. Scanning electron microscopy (SEM) showed a high percentage of open dentinal tubules after the erosive-abrasive challenge, especially in the WF group, mainly because toothpaste WF does not contain functional agents capable of inducing tubular occlusion or intratubular mineralization25. Studies on SnF2-based toothpastes have reached controversial results, since some found
it to be superior to conventional toothpastes12,13,14,29, whereas others reported similar results between them25,28, as does our study. Some studies reported the presence of SnF2 particles on the substrate surface, obliterating the top of dentinal tubules18,25, but found no particles within tubules when they were analyzed in cross-sections25. According to a study by Joao-Souza et al.34, stannous has no protective effect against dental erosion and abrasion but helps reduce open tubular areas.
The current study also verified a significant increase in the number of open tubules for both sound and eroded dentin in all groups. This is due to exposure to citric acid. Frequent consumption of citric acid leads to tooth structure loss and smear layer removal16. Using an experimental dentifrice with sodium trimetaphosphate associated with fluoride, Favretto et al.19 found a greater number and larger internal area of open tubules by SEM analysis in placebo groups subjected to erosive challenges, as occurred in the WF group in our study19.
Although SnF2 caused dentin obliteration similar to that of NaF, it promoted a significantly 9higher permeability of eroded dentin compared to the other dentifrices after cycling. This may be due to tissue wear resulting from toothpaste abrasiveness, leading to a loss of substrate thickness and possibly interfering with its desensitizing effect25. According to Arnold et al.25, a dentin thickness of approximately 61.98 pm may be lost after an erosive cycle performed with highly abrasive stannous-based dentifrices, which may contribute to dentin sub-surface analysis. Another study found that a SnF2 dentifrice was unable to reduce dentin permeability, in contrast to the NaF dentifrice and two other toothpastes with desensitizing action (one containing calcium silicate and sodium phosphate, and another with potassium nitrate)17,25. Dentinal obliteration can be dissolved by acids25, and the high concentration of abrasive components in SnF2 dentifrices may favor stannous ion bonding with silica, reducing its anti-erosive action15. A meta-analysis found that SnF2-based toothpaste achieved better outcomes than other compounds within a period of up to 2 weeks. However, it lost effectiveness at the 4 and 8-week follow-up, presenting a rapid desensitizing effect8. Another systematic review found that toothpastes containing SnF2 reduced DH effects after 8 to 15 days of brushing27. The use of artificial saliva and the absence of dental biofilm and salivary film may reduce fluoride retention on surfaces in 5-day in vitro erosive protocols35, which are supposedly more aggressive than an in vivo cycling protocol for the same period.
Although fluoride has beneficial effects in treating caries lesions, its actions on the erosive process are not as noticeable26. In the current study, the NaF-based dentifrice contains 350 ppm more fluoride (F) than SnF2. Despite the reduced action of fluoride in the erosive process, this difference may have influenced the lower permeability found in the SnF2group in relation to NaF. These results contradict those reported in another study that evaluated NaF and SnF2 dentifrices, which found decreased dentin permeability for both18.
The group treated with WF toothpaste showed a greater number of open tubules, but lower permeability in eroded dentin, which may be explained by the deposition of calcium phosphate from saliva and a smear layer on the dentin surface20,36. From the results of a meta-analysis that evaluated 30 randomized clinical trials, it was concluded that conventional fluoride toothpastes showed no significant difference in desensitizing effect when compared to placebo8. According to Joao-Souza et al.34, the abrasion resulting from toothbrushing on demineralized dentin may play a role in tubal occlusion by forming a smear layer on the dentin surface. This accounts for the significantly reduced permeability after the erosive-abrasive challenge for all groups when comparing sound and eroded dentin. According to the literature, reduction in dentin permeability ranges from 5 to 50% after treatment with different anti-erosive dentifrices17,36. In the current study, permeability decreased by 14 to 45%, considering all evaluated toothpastes.
This study has some limitations, such as the fact that it did not identify the composition of the particles in the top of the dentinal tubules. The toothpastes evaluated contain other components besides fluoride compounds, which may influence the results. The current study chose to evaluate commercially available toothpastes in order to represent real-life conditions. Further in situ and in vivo studies evaluating the effectiveness of different toothpastes are needed to verify the influence of human saliva on eroded dentin, seeking to prolong the effects of toothpastes on dentinal tubule occlusion for the treatment of DH.
