Annette Wiegand

Insights into preventive measures for dental erosion

Dental erosion is defined as the loss of tooth substance by acid exposure not involving bacteria. The etiology of erosion is related to different behavioral, biological and chemical factors. Based on an overview of the current literature, this paper presents a summary of the preventive strategies relevant for patients suffering from dental erosion. Behavioral factors, such as special drinking habits, unhealthy lifestyle factors or occupational acid exposure, might modify the extent of dental erosion. Thus, preventive strategies have to include measures to reduce the frequency and duration of acid exposure as well as adequate oral hygiene measures, as it is known that eroded surfaces are more susceptible to abrasion. Biological factors, such as saliva or acquired pellicle, act protectively against erosive demineralization. Therefore, the production of saliva should be enhanced, especially in patients with hyposalivation or xerostomia. With regard to chemical factors, the modification of acidic solutions with ions, especially calcium, was shown to reduce the demineralization, but the efficacy depends on the other chemical factors, such as the type of acid. To enhance the remineralization of eroded surfaces and to prevent further progression of dental wear, high-concentrated fluoride applications are recommended. Currently, little information is available about the efficacy of other preventive strategies, such as calcium and laser application, as well as the use of matrix metalloproteinase inhibitors. Further studies considering these factors are required. In conclusion, preventive strategies for patients suffering from erosion are mainly obtained from in vitro and in situ studies and include dietary counseling, stimulation of salivary flow, optimization of fluoride regimens, modification of erosive beverages and adequate oral hygiene measures.

Fluoride in dental erosion.

Dental erosion develops through chronic exposure to extrinsic/intrinsic acids with a low pH. Enamel erosion is characterized by a centripetal dissolution leaving a small demineralized zone behind. In contrast, erosive demineralization in dentin is more complex as the acid-induced mineral dissolution leads to the exposure of collagenous organic matrix, which hampers ion diffusion and, thus, reduces further progression of the lesion. Topical fluoridation inducing the formation of a protective layer on dental hard tissue, which is composed of CaF(2) (in case of conventional fluorides like amine fluoride or sodium fluoride) or of metal-rich surface precipitates (in case of titanium tetrafluoride or tin-containing fluoride products), appears to be most effective on enamel. In dentin, the preventive effect of fluorides is highly dependent on the presence of the organic matrix. In situ studies have shown a higher protective potential of fluoride in enamel compared to dentin, probably as the organic matrix is affected by enzymatical and chemical degradation as well as by abrasive influences in the clinical situation. There is convincing evidence that fluoride, in general, can strengthen teeth against erosive acid damage, and high-concentration fluoride agents and/or frequent applications are considered potentially effective approaches in preventing dental erosion. The use of tin-containing fluoride products might provide the best approach for effective prevention of dental erosion. Further properly designed in situ or clinical studies are recommended in order to better understand the relative differences in performance of the various fluoride agents and formulations.

Influence of study design on the impact of bleaching agents on dental enamel microhardness: A review

OBJECTIVE Numerous studies investigated the impact of bleaching procedures on enamel microhardness. The outcomes of these studies reveal inconsistencies regarding the fact whether a microhardness reduction due to bleaching occurs or not. Aim of the present review was to summarize the existing literature of external bleaching therapies, which used microhardness tests for evaluation of possible effects on enamel and to weigh up different parameters of the study designs with respect to the outcome of these studies. METHODS The data from original scientific full papers listed in PubMed or ISI Web of Science (search term: enamel and (bleaching or peroxide) and (hardness or microhardness or Knoop or Vickers)) and received by additional hand-search meeting the inclusion criteria were included in the review. Influences of different parameters on the outcome of the bleaching treatments were analyzed with the Fishers-exact-test. RESULTS A total of 55 studies were identified with 166 hardness measurements conducted directly after bleaching and 69 measurements performed after a post-treatment episode. Directly after bleaching, 84 (51%) treatments showed microhardness reduction compared to baseline, whereas 82 (49%) did not yield microhardness reduction. After the post-treatment episode, 20 (29%) treatments showed hardness reduction and 49 (71%) did not. A significant higher number of bleaching treatments resulting in enamel microhardness reduction were observed, when artificial instead of human saliva was used for storage of the enamel samples in the intervals between the bleaching applications and when no fluoridation measures were applied during or after the bleaching phase. SIGNIFICANCE The review shows that in those studies, which simulated the intraoral conditions as closely as possible, the risk of enamel microhardness decrease due to bleaching treatments seems to be reduced. Nevertheless more in situ- and in vivo-studies are needed to verify this observation.

Design of Erosion/Abrasion Studies - Insights and Rational Concepts

In vitro and in situ studies modelling the wear of dental hard tissues due to erosion and abrasion are characterised by a high variation in study designs and experimental parameters. Based on a summary of the existing protocols, the present review aimed to describe and discuss the parameters which must be carefully considered in erosion-abrasion research, especially when it is intended to simulate clinical conditions. Experimental characteristics and parameters were retrieved from a total of 42 in vitro and 20 in situ studies. The key experimental characteristics included parameters of erosion (duration and pH) and abrasion (duration, kinds of toothbrush and toothpaste, brushing force, and time point) as well as co-factors (e.g. dental hard tissue). The majority of studies used models with alternating erosion/abrasion treatments intended to simulate clinical conditions, while other studies exaggerated clinical conditions intentionally, often using only a single erosion/abrasion treatment. Both in vitro and in situ models shared a high level of standardisation, but several studies showed a trend to severe erosion (e.g. >5 min/cycle) or extensive brushing (e.g. >100 brushing strokes/cycle) at a high frequency and repetition rate. Thus, studies often tend to produce a higher amount of wear than in the clinical situation, especially as modifying biological factors (e.g. the dilution of the erosive solution by saliva and the protective effect of the pellicle) cannot be simulated adequately. With respect to the existing models, it seems advisable to diminish duration and frequency of erosion and abrasion to more realistic clinical conditions when the everyday situation is to be simulated. Experimental parameters must be chosen with care to ensure that the problem is investigated in an appropriate mode at standardised conditions and with adequate measuring systems to allow prediction of clinical outcomes.

Chlorhexidine and green tea extract reduce dentin erosion and abrasion in situ

OBJECTIVES This in situ/ex vivo study aimed to analyse the impact of possible MMP-inhibitors (chlorhexidine and green tea extract) on dentin wear induced by erosion or erosion plus abrasion. METHODS Twelve volunteers took part in this cross-over and double-blind study performed in 4 phases of each 5 days. Bovine dentin samples were worn in palatal appliances and subjected to extraoral erosion (4 times/day, Coca-Cola, 5 min) or erosion plus abrasion (2 times/day, fluoride-free toothpaste and electrical toothbrush, 15s/sample). Immediately after each erosion, the appliances were reinserted in the mouth and the oral cavity was rinsed for 60s with: 250 ppm F solution (SnF(2)/AmF, pH 4.5, Meridol-Gaba, Switzerland), 0.12% chlorhexidine digluconate (0.06% chlorhexidine, pH 6.0, Periogard-Colgate, Brazil), 0.61% green tea extract solution (OM24, 100% Camellia Sinensis leaf extract, catechin concentration: 30+/-3%, pH 7.0, Omnimedica, Switzerland) or deionized water (pH 6.0, control). Dentin loss was assessed by profilometry (microm). The data were analysed by two-way repeated measures ANOVA and Bonferroni post hoc test. RESULTS There was a significant difference between the conditions (EroxEro+Abr, p<0.001) and among the solutions (p<0.001). All solutions (F: 1.42+/-0.34; 1.73+/-0.50, chlorhexidine: 1.15+/-0.26; 1.59+/-0.32, green tea: 1.06+/-0.30; 1.54+/-0.55) significantly reduced the dentin wear when compared to control (2.00+/-0.55; 2.41+/-0.83) for both conditions. There were not significant differences among green tea extract, chlorhexidine and F solutions. CONCLUSIONS Thus, the possible MMP-inhibitors tested in this study seem to be a promising preventive measure to reduce dentin erosion-abrasion, but their mechanism of action needs to be investigated in further studies.

The Effect of an Experimental 4% TiF 4 Varnish Compared to NaF Varnishes and 4% TiF 4 Solution on Dental Erosion in vitro

This in vitro study assessed the effect of an experimental 4% TiF4 varnish compared to commercial NaF and NaF/CaF2 varnishes and 4% TiF4 solution on enamel erosion. For this, 72 bovine enamel specimens were randomly allocated to the following treatments: NaF varnish(2.26% F), NaF/CaF2 varnish (5.63% F), 4% TiF4 varnish (2.45% F), F-free placebo varnish, 4% TiF4 solution (2.45% F) and control (not treated). The varnishes were applied in a thin layer and removed after 6 h. The solution was applied to the enamel surface for 1 min. Then, the specimens were alternately de- and remineralized (6 times/day) in an artificial mouth for 5 days at 37°C. Demineralization was performed with the beverage Sprite (1 min, 3 ml/min) and remineralization with artificial saliva (day: 59 min, 0.5 ml/min; during the night: 0.1 ml/min). The mean daily increment of erosion and the cumulative erosion data were tested using ANOVA and ANCOVA, respectively, followed by Tukey’s test (α = 0.05). The mean daily erosion increments and cumulative erosion (micrometers) were significantly less for the TiF4 varnish (0.30 ± 0.11/0.65 ± 0.75) than for the NaF varnish (0.58 ± 0.11/1.47 ± 1.07) or the NaF/CaF2 varnish (0.62 ± 0.10/1.68 ± 1.17), which in turn showed significantly less erosion than the placebo varnish (0.78 ± 0.12/2.05 ± 1.43), TiF4 solution (0.86 ± 0.11/ 2.05 ± 1.49) and control (0.77 ± 0.16/2.06 ± 1.49). In conclusion, the TiF4 varnish seems to be a promising treatment to reduce enamel loss under mild erosive conditions.

Erosion and abrasion of tooth-colored restorative materials and human enamel

OBJECTIVES The aim of this study was to investigate the effects of erosion and toothbrush abrasion on different restorative materials and human enamel. METHODS Human enamel and 5 kinds of tooth-colored restorative materials were used. The restorative materials included three composite resins (Filtek Silorane, Tetric EvoCeram, and Tetric EvoFlow), a polyacid-modified composite (Dyract Extra), and a conventional glass-ionomer cement (Ketac Fil Plus). For each type of the material, 40 specimens were prepared and embedded in ceramic moulds and divided into four groups (n=10): control group (C), erosion group (E), abrasion group (A), and erosion-abrasion group (EA). The specimens were subjected to six daily erosive attacks (groups E and EA; citric acid, pH 2.3, 1 min) and/or six abrasive attacks (groups A and EA; toothbrush abrasion, 100 strokes, 1 min), while the control specimens (group C) were maintained in artificial saliva. After 10-day treatment, the substance loss and surface changes were determined by surface profilometry and scanning electron microscopy. RESULTS Human enamel presented higher substance loss when compared to restorative materials. Generally, combined erosion-abrasion (EA) caused the highest substance loss, followed by erosion, abrasion, and storage in artificial saliva. Composite resin presented highest durability under erosive and/or abrasive attacks. Enamel and restorative materials showed degradation in groups E and EA through SEM observation. CONCLUSIONS Toothbrush abrasion has a synergistic effect with erosion on substance loss of human enamel, polyacid-modified composite and glass-ionomer cement. The acid- and abrasive-resistance of human enamel was lower compared to restorative materials.

Effect of Different Concentrations of Fluoride in Dentifrices on Dentin Erosion Subjected or Not to Abrasion in situ/ex vivo

This in situ/ex vivo study assessed the effect of different concentrations of fluoride in dentifrices on dentin subjected to erosion or to erosion plus abrasion. Ten volunteers took part in this crossover and double-blind study performed in 3 phases (7 days). They wore acrylic palatal appliances containing 4 bovine dentin blocks divided in two rows: erosion and erosion plus abrasion. The blocks were subjected to erosion by immersion ex vivo in a cola drink (60 s, pH 2.6) 4 times daily. During this step, the volunteers brushed their teeth with one of three dentifrices D (5,000 ppm F, NaF, silica); C (1,100 ppm F, NaF, silica) and placebo (22 ppm F, silica). Then, the respective dentifrice slurry (1:3) was dripped on dentin surfaces. While no further treatment was performed in one row, the other row was brushed using an electric toothbrush for 30 s ex vivo. The appliances were replaced in the mouth and the volunteers rinsed with water. Dentin loss was determined by profilometry and analyzed by 2-way ANOVA/Bonferroni test (a = 0.05). Dentin loss after erosive-abrasive wear was significantly greater than after erosion alone. Wear was significantly higher for the placebo than for the D and C dentifrices, which were not significantly different from each other. It can be concluded that the presence of fluoride concentrations around 1,100 ppm in dentifrices is important to reduce dentin wear by erosion and erosion + abrasion, but the protective effect does not increase with fluoride concentration.

Comparison of the Effects of TiF4 and NaF Solutions at pH 1.2 and 3.5 on Enamel Erosion in vitro

This study aimed to analyse and compare the protective effect of buffered (pH 3.5) and native (pH 1.2) TiF4 in comparison with NaF solutions on enamel erosion. Bovine samples were pretreated with 1.50% TiF4 or 2.02% NaF (both 0.48 M F) solutions, each at a pH of 1.2 and 3.5. The control group received no fluoride pretreatment. Twenty samples per group were eroded with HCl (pH 2.6) for 10 × 60 s. Erosion was either investigated by profilometry (n = 10) or by determination of calcium release into the acid (n = 10). Additionally, the elemental surface composition was quantified by X-ray energy-dispersive spectroscopy in fluoridated but not eroded samples (6 samples per group). Scanning electron microscopy was performed prior and after erosion (2 samples per group). Cumulative enamel loss (μm) and calcium release (nmol/mm2) were analysed by repeated-measures ANOVA. The Ti and F surface composition was analysed by one-way ANOVA separately for each element. Only TiF4 at pH 1.2 reduced enamel surface loss significantly. Calcium release was significantly reduced by TiF4 and NaF at pH 1.2, but not by the solutions at pH 3.5. Samples pretreated with TiF4 at pH 1.2 showed a significant increase in Ti, while NaF increased F concentration significantly. Only TiF4 at pH 1.2 induced the formation of a glaze-like layer, which was still present after erosion. Enamel erosion can be significantly reduced by TiF4 at pH 1.2 but not at pH 3.5. TiF4 at pH 1.2 was more effective in protecting against enamel erosion than NaF.

Protective Effect of Different Tetrafluorides on Erosion of Pellicle-Free and Pellicle-Covered Enamel and Dentine

The aim was to analyze the protective effects of titanium, zirconium and hafnium tetrafluorides on erosion of pellicle-free and pellicle-covered enamel and dentine in vitro. Eight groups of 20 specimens each of bovine enamel and bovine dentine were prepared. Half the specimens in each group were immersed in human saliva for 2 h for pellicle formation. Specimens were then left untreated (controls) or were treated for 120 s with TiF4, ZrF4 or HfF4 solutions (0.4 or 1%) or 1.25% AmF/NaF gel. All specimens were eroded by exposure to hydrochloric acid, pH 2.6, for 25 min. Cumulative calcium release into the acid was monitored in consecutive 30-second intervals for 5 min, then at 2-min intervals up to a total erosion time of 25 min using the Arsenazo III procedure. Data were analyzed by ANOVA. 1% TiF4 solution offered the best protective effect, especially in dentine (reduction of calcium loss about 50% at 25 min). 1% ZrF4, 1% HfF4 and 0.4% TiF4 also reduced calcium loss, but to a lesser extent. Long-term effects were limited to dentine, while reduction of enamel erosion (about 25%) was restricted to 1-min erosion. The fluoride gel had a protective effect only in dentine. The efficacy of the tetrafluorides was influenced by the presence of the pellicle layer, in that the protection against dentine erosion by TiF4 and ZrF4 was greater on pellicle-covered specimens. Tetrafluoride solutions, especially 1% TiF4, could decrease dental erosion, but were more effective on dentine than on enamel.