Fluoride uptake and acid resistance of enamel irradiated with Er : YAG laser

This study evaluated the resistance to demineralization and fluoride incorporation of enamel irradiated with Er:YAG. A total of 110 bovine teeth were selected and divided into eight groups: unlased, 37% phosphoric acid, and samples irradiated with the Er:YAG laser at several fluences (31.84 J/cm(2), 25.47 J/cm(2), 19.10 J/cm(2), 2.08 J/cm(2), 1.8 J/cm(2), and 0.9 J/cm(2)). The application of acidulated phosphate fluoride was performed after treatments. All samples were immersed in 2 ml of 2.0 M acetic-acetate acid solution at pH 4.5 for 8 h, and fluoride, calcium, and phosphorus ions dissolved were analyzed by atomic absorption spectrometry and spectrophotometry. The phosphoric acid and 31.84 J/cm(2) groups presented the lowest dissolution of calcium and phosphorus ions. Higher fluoride incorporation was observed on 1.8 J/cm(2) and 0.9 J/cm(2) groups. Based on these results, Er:YAG laser was able to decrease acid dissolution and increase fluoride uptake and can be a promissory alternative for preventive dentistry.

Fluoride uptake by plaque from water and from dentifrice

It has been suggested that fluoride retention in plaque is limited by available binding sites. We determined the effects of fluoridated or placebo dentifrices on plaque and salivary fluoride concentrations [F]s in communities with different water fluoride concentrations (0.04, 0.85, 3.5 ppm). After one week of dentifrice use, samples were collected 1.0 and 12 hrs after the last use of dentifrices. After the use of fluoridated dentifrice, plaque fluoride concentrations were higher at both times, except at 12 hrs in the 3.5-ppm community. Plaque concentrations at 1.0 hr after the use of fluoridated dentifrice increased almost constantly (6.5 mmol/kg), but then decreased approximately 50% at 12 hrs in each community. Unlike previous studies, the present findings suggest that the use of fluoridated dentifrice is likely to increase plaque fluoride concentrations significantly for up to 12 hrs in areas where the water contains fluoride close to 1.0 ppm. As previously reported, plaque fluoride concentrations were directly related to calcium concentrations.

Effect of application time of APF and NaF gels on microhardness and fluoride uptake of in vitro enamel caries

Purpose : To evaluate the effect of time of fluoride application gel, acidulated or neutral, on in vitro enamel resistance to demineralization and fluoride uptake. Materials and Methods: One hundred and ninety-two human enamel blocks were used in this study and 144 were treated with fluoride gel, acidulated or neutral, for I or 4 minutes. Ninety-six blocks treated with fluoride and 24 control blocks were submitted to a high cariogenic challenge. After the pH-cycling, enamel demineralization was assessed by surface and cross-sectional microhardness. Fluoride in the enamel blocks was also determined after removing an enamel layer by etching acid. Results: Acidulated fluoride gel formed more fluoride in enamel than neutral gel (P < 0.05), and it was also more efficient in reducing the demineralization of the enamel blocks submitted to a cariogenic challenge than the neutral one (P < 0.05). It was found that the time of application was significant in terms of fluoride uptake, but it did not render the enamel more resistant to dernineralization.

Fluoride uptake and acid resistance of enamel irradiated with Er : YAG laser

This study evaluated the resistance to demineralization and fluoride incorporation of enamel irradiated with Er:YAG. A total of 110 bovine teeth were selected and divided into eight groups: unlased, 37% phosphoric acid, and samples irradiated with the Er:YAG laser at several fluences (31.84 J/cm(2), 25.47 J/cm(2), 19.10 J/cm(2), 2.08 J/cm(2), 1.8 J/cm(2), and 0.9 J/cm(2)). The application of acidulated phosphate fluoride was performed after treatments. All samples were immersed in 2 ml of 2.0 M acetic-acetate acid solution at pH 4.5 for 8 h, and fluoride, calcium, and phosphorus ions dissolved were analyzed by atomic absorption spectrometry and spectrophotometry. The phosphoric acid and 31.84 J/cm(2) groups presented the lowest dissolution of calcium and phosphorus ions. Higher fluoride incorporation was observed on 1.8 J/cm(2) and 0.9 J/cm(2) groups. Based on these results, Er:YAG laser was able to decrease acid dissolution and increase fluoride uptake and can be a promissory alternative for preventive dentistry.

Fluoride varnishes containing calcium glycerophosphate: fluoride uptake and the effect on in vitro enamel erosion

OBJECTIVES Calcium glycerophosphate (CaGP) was added to fluoride varnishes to analyze their preventive effect on initial enamel erosion and fluoride uptake: potassium hydroxide (KOH)-soluble and KOH-insoluble fluoride bound to enamel. MATERIALS AND METHODS This study was carried out in two parts. Part 1: 108 enamel samples were randomly distributed into six varnish groups: base varnish (no active ingredients); Duraphat® (2.26 %NaF); Duofluorid® (5.63 %NaF/CaF2); experimental varnish 1 (1 %CaGP/5.63 %NaF/CaF2); experimental varnish 2 (5 %CaGP/5.63 %NaF/CaF2); and no varnish. Cyclic demineralization (90 s; citric acid, pH = 3.6) and remineralization (4 h) was made once a day, for 3 days. Change in surface microhardness (SMH) was measured. Part 2: 60 enamel samples were cut in half and received no varnish (control) or a layer of varnish: Duraphat®, Duofluorid®, experimental varnishes 1 and 2. Then, KOH-soluble and KOH-insoluble fluoride were analyzed using an electrode. RESULTS After cyclic demineralization, SMH decreased in all samples, but Duraphat® caused less hardness loss. No difference was observed between varnishes containing CaGP and the other varnishes. Similar amounts of KOH-soluble and insoluble fluoride was found in experimental varnish 1 and Duofluorid®, while lower values were found for experimental varnish 2 and Duraphat®. CONCLUSION The addition of CaGP to fluoride varnishes did not increase fluoride bound to enamel and did not enhance their protection against initial enamel erosion. CLINICAL RELEVANCE We observe that the fluoride varnishes containing CaGP do not promote greater amounts of fluoride bound to enamel and that fluoride bound to enamel may not be closely related to erosion prevention.

Sodium fluoride effect on erosion-abrasion under hyposalivatory simulating conditions

Objectives: To investigate the effect of fluoride (0, 275 and 1250 ppm F; NaF) in combination with normal and low salivary flow rates on enamel surface loss and fluoride uptake using an erosion-remineralization-abrasion cycling model. Design: Enamel specimens were randomly assigned to 6 experimental groups (n = 8). Specimens were individually placed in custom made devices, creating a sealed chamber on the enamel surface, connected to a peristaltic pump. Citric acid was injected into the chamber for 2 min followed by artificial saliva at 0.5 (normal flow) or 0.05 (low flow) ml/min, for 60 min. This cycle was repeated 4×/day, for 5 days. Toothbrushing with abrasive suspensions containing fluoride was performed for 2 min (15 s of actual brushing) 2×/day. Surface loss was measured by optical profilometry. KOH-soluble fluoride and enamel fluoride uptake were determined after the cycling phase. Data were analysed by two-way ANOVA. Results: No significant interactions between fluoride concentration and salivary flow were observed for any tested variable. Low caused more surface loss than normal flow rate (p < 0.01). At both flow rates, surface loss for 0 was higher than for 275, which did not differ from 1250 ppm F. KOH-soluble and structurally-bound enamel fluoride uptake were significantly different between fluoride concentrations with 1250 > 275 > 0 ppm F (p < 0.01). Conclusions: Sodium fluoride reduced enamel erosion/abrasion, although no additional protection was provided by the higher concentration. Higher erosion progression was observed in low salivary flow rates. Fluoride was not able to compensate for the differences in surface loss between flow rates. © 2013 Elsevier Ltd. All rights reserved.

Distribution of fluoride and calcium in plaque biofilms after the use of conventional and low-fluoride dentifrices

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

CO2 laser-irradiation through topically applied fluoride increases acid resistance of demineralised human enamel in vitro

PURPOSE: To evaluate the effect of CO2 laser treatment through topically applied amine fluoride solution on demineralised enamel. MATERIALS AND METHODS: Sixty extracted human molar crowns were selected and cut longitudinally into half. One half was subjected to a 10-day pH-cycling procedure to create caries-like lesions, whereas the other was left non-demineralised. The following treatments were randomly assigned (one treatment per tooth, on respective non-demineralised and demineralised matched specimens): exposure to a 1% amine fluoride solution for 15 s without irradiation (group I), irradiation for 15 s with a continuous-wave CO2 laser (group II), or laser-treatment for 15 s through the amine fluoride solution applied immediately beforehand (group III). Fluoride uptake (n = 30) and acid resistance (n = 30) were determined after treatment. Enamel surface alterations after laser irradiation were monitored using scanning electron microscopy. RESULTS: In groups I and III, an increased fluoride uptake was detected (p < or = 0.05). Laser irradiation through topical fluoride resulted in an increased acid resistance of sound and demineralised enamel specimens in deeper layers (p < or = 0.05). In addition, less surface alterations were observed in SEM examination of specimens irradiated through the amine fluoride solution compared with counterparts treated with laser only. CONCLUSIONS: CO2 laser light application through an amine fluoride solution may be instrumental in enhancing acid resistance of sound and demineralised enamel.

Rehardening of acid-softened enamel and prevention of enamel softening through CO(2) laser irradiation

Objectives: The aims of the present study were to investigate whether irradiation with a CO(2) laser could prevent surface softening (i) in sound and (ii) in already softened enamel in vitro. Methods: 130 human enamel samples were obtained and polished with silicon carbide papers. They were divided into 10 groups (n = 13) receiving 5 different surface treatments: laser irradiation (L), fluoride (AmF/NaF gel) application (F), laser prior to fluoride (LF), fluoride prior to laser (FL), non-treated control (C); and submitted to 2 different procedures: half of the groups was acid-softened before surface treatment and the other half after. Immersion in 1% citric acid was the acid challenge. Surface microhardness (SMH) was measured at baseline, after softening and after treatment. Additionally, fluoride uptake in the enamel was quantified. The data were statistically analysed by two-way repeated measurements ANOVA and post hoc comparisons at 5% significance level. Results: When softening was performed either before or after laser treatment, the L group presented at the end of the experiments SMH means that were not significantly different from baseline (p = 0.8432, p = 0.4620). Treatment after softening resulted for all laser groups in statistically significant increase in SMH means as compared to values after softening (p < 0.0001). Enamel fluoride uptake was significantly higher for combined laser-fluoride treatment than in control (p < 0.0001). Conclusion: Irradiation of dental enamel with a CO(2) laser at 0.3J/cm(2) (5 mu s, 226 Hz) not only significantly decreased erosive mineral loss (97%) but also rehardened previously softened enamel in vitro. (C) 2011 Elsevier Ltd. All rights reserved.

Effect of erosive pH cycling on different restorative materials and on enamel restored with these materials

This in vitro study evaluated the effect of erosive pH cycling on the percentage of surface micro-hardness change (%SMHC) and wear of different restorative materials and bovine enamel restored with these materials. Eighty enamel specimens were randomly divided into eight groups according to the restorative materials and immersion media used: GI/GV-resin-modifled glass-ionomer, GII/GVI-conventional glass-ionomer, GIII/GVII-resin composite and GIV/GVIII-amalgam. Over a period of seven days, groups GI to GIV were immersed in a cola drink (ERO) for 5 minutes, 3x/day and kept in artificial saliva between erosive cycles. Groups GV to GVIII were immersed in artificial saliva (SAL) throughout the entire experimental period (control). Data were tested for significant differences using ANOVA and Tukey`s tests (p < 0.05). For %SMHC, considering the restorative materials, no significant differences were detected among the materials and immersion media. Mean wear was higher for the resin modified glass ionomer cement when compared to conventional cement, but those materials did not significantly differ from the others. For enamel analyses, erosive pH cycling promoted higher wear and %SMHC compared to saliva. There were no significant differences in wear and %SMHC of enamel around the different restorative materials, regardless of the distance from the restorative material (50, 150 or 300 mu m). In conclusion, there were only subtle differences among the materials, and these differences were not able to protect the surrounding enamel from erosion.

pH-cycling models for in vitro evaluation of the efficacy of fluoridated dentifrices for caries control: strengths and limitations

Despite a plethora of in situ studies and clinical trials evaluating the efficacy of fluoridated dentifrices on caries control, in vitro pH cycling models are still broadly used because they mimic the dynamics of mineral loss and gain involved in caries formation. This paper critically reviews the current literature on existing pH-cycling models for the in vitro evaluation of the efficacy of fluoridated dentifrices for caries control, focusing on their strengths and limitations. A search was undertaken in the MEDLINE electronic journal database using the keywords "pH-cycling", "demineralization", "remineralization", "in vitro", "fluoride", "dentifrice". The primary outcome was the decrease of demineralization or the increase of remineralization as measured by different methods (e. g.: transverse microradiography) or tooth fluoride uptake. Inclusion of studies, data extraction and quality assessment were undertaken independently and in duplicate by two members of the review team. Disagreements were solved by discussion and consensus or by a third party. One hundred and sixteen studies were included, of which 42 addressed specifically the comparison of dentifrices using different pH-cycling models. The other studies included meta-analysis or reviews, data about the effect of different fluoride sources on de-remineralization, different methods for analysis de-remineralization and chemical variables and characteristics of dental hard tissues that might have influence on de-remineralization processes. Generally, the studies presented ability to detect known results established by clinical trials, to demonstrate dose-related responses in the fluoride content of the dentifrices, and to provide repeatability and reproducibility between tests. In order to accomplish these features satisfactorily, it is mandatory to take into account the type of substrate and baseline artificial lesion, as well as the adequate response variables and statistical approaches to be used. This critical review of literature showed that the currently available pH-cycling models are appropriate to detect dose-response and pH-response of fluoride dentifrices, and to evaluate the impact of new active principles on the effect of fluoridated dentifrices, as well as their association with other anti-caries treatments.

Mechanisms of action of fluoridated acidic liquid dentifrices against dental caries

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Mechanism of action of tin-containing fluoride solutions as anti-erosive agents in dentine - an in vitro tin-uptake, tissue loss, and scanning electron microscopy study

Solutions containing tin and fluoride exhibit remarkable anti-erosive properties with tin ions as a major agent. To elucidate its mechanism of action in dentine, the tin uptake on and in the tissue was investigated and related to histological findings and substance loss. Samples were treated twice daily, each treatment lasting for 2 min, with fluoride solutions [pH 4.5; 1,500 parts per million (p.p.m.) F] containing 2,100, 1,400, or 400 p.p.m. Sn as SnCl(2). In experiments 1 and 2, samples were eroded with citric acid (pH 2.3) six times each day, each treatment lasting for 5 min; in experiment 2, the demineralized organic matrix was continuously digested by collagenase; in experiment 3, no erosive challenges were performed. Sample surfaces and cross-sections were investigated using energy dispersive X-ray spectroscopy, scanning electron microscopy, and profilometry. Surface retention of tin was found in almost all treatment groups and was highest in experiment 2. On cross-sections, tin was retained within the organic matrix; in mineralized areas, tin was found mainly within a depth of 10 mum. Test solutions inhibited substance loss significantly; in experiment 2, the effect was dose-dependent. Erosion inhibition seemed to depend mainly on the incorporation of tin in the mineralized dentine when the organic portion was preserved, but on surface precipitation when the organic portion was continuously digested.