Nano-hydroxyapatite Toothpaste Research Articles

Effect of Nano-hydroxyapatite Toothpaste on Microhardness of Primary Teeth Enamel in Comparison with Two other Toothpastes “An in Vitro Study”

Effect of Nano-hydroxyapatite Toothpaste on Microhardness of Primary Teeth Enamel in Comparison with Two other Toothpastes “An in Vitro Study”

Effect of a Nano-hydroxyapatite Toothpaste on Enamel Erosive Lesions of Third Molars Induced by Exposure to Orange Juice.

This study aimed to assess the effect of a nano-hydroxyapatite (nano-HA) toothpaste on erosive enamel lesions of third molars induced by exposure to orange juice. In this in vitro, experimental study, the microhardness of 24 sound-extracted third molars was measured by a Vickers tester. The teeth were then randomly assigned to three groups (n = 8) of nano-HA toothpaste (Pharmed), 1.23% sodium fluoride gel, and artificial saliva. The teeth were exposed to orange juice for 5 min daily for 7 days and were then exposed to nano-HA toothpaste, fluoride gel, or artificial saliva (depending on their group allocation) for 10 min a day. The microhardness of the teeth was measured again after 7 days. Data were analyzed using paired t-test, analysis of variance, and Bonferroni test (alpha = 0.05). Within-group comparisons showed a significant reduction in microhardness of the teeth after the intervention in artificial saliva (P = 0.000), and fluoride gel (P = 0.002) groups. However, no significant reduction occurred in the microhardness of the nano-HA group, compared with the baseline (P = 0.132). Between-group comparisons revealed no significant difference in the microhardness of the three groups at baseline (P > 0.05). However, after the intervention, the microhardness of the nano-HA group was significantly higher than that of other groups (P < 0.05). However, the difference in secondary microhardness between fluoride gel and artificial saliva groups was not significant (P = 1.00). Pharmed toothpaste containing nano-HA has optimal efficacy for remineralization of enamel erosive lesions induced by exposure to orange juice.

In vitro comparative SEM analysis of nano-hydroxyapatite toothpaste and diode laser: evaluation of efficacy of dentinal tubular occlusion

ENWEndNote BIBJabRef, Mendeley RISPapers, Reference Manager, RefWorks, Zotero AMA Shamel M, El Banna S. In vitro comparative SEM analysis of nano-hydroxyapatite toothpaste and diode laser: evaluation of efficacy of dentinal tubular occlusion. Journal of Stomatology. 2022;75(1):1-6. doi:10.5114/jos.2022.114033. APA Shamel, M., & El Banna, S. (2022). In vitro comparative SEM analysis of nano-hydroxyapatite toothpaste and diode laser: evaluation of efficacy of dentinal tubular occlusion. Journal of Stomatology, 75(1), 1-6. https://doi.org/10.5114/jos.2022.114033 Chicago Shamel, Mohamed, and Sara El Banna. 2022. "In vitro comparative SEM analysis of nano-hydroxyapatite toothpaste and diode laser: evaluation of efficacy of dentinal tubular occlusion". Journal of Stomatology 75 (1): 1-6. doi:10.5114/jos.2022.114033. Harvard Shamel, M., and El Banna, S. (2022). In vitro comparative SEM analysis of nano-hydroxyapatite toothpaste and diode laser: evaluation of efficacy of dentinal tubular occlusion. Journal of Stomatology, 75(1), pp.1-6. https://doi.org/10.5114/jos.2022.114033 MLA Shamel, Mohamed et al. "In vitro comparative SEM analysis of nano-hydroxyapatite toothpaste and diode laser: evaluation of efficacy of dentinal tubular occlusion." Journal of Stomatology, vol. 75, no. 1, 2022, pp. 1-6. doi:10.5114/jos.2022.114033. Vancouver Shamel M, El Banna S. In vitro comparative SEM analysis of nano-hydroxyapatite toothpaste and diode laser: evaluation of efficacy of dentinal tubular occlusion. Journal of Stomatology. 2022;75(1):1-6. doi:10.5114/jos.2022.114033.

Anti-caries evaluation of a nano-hydroxyapatite dental lotion for use after toothbrushing: An in situ study

ObjectivesThe aim of this randomized, double-blind, two-arm crossover in situ study was to investigate whether nano-hydroxyapatite (nanoHAP) dental lotion (Apagard Deep Care) applied immediately after tooth-brushing with nanoHAP toothpaste (Apagard M-plus) enhances the remineralization promotion and the demineralization inhibition efficacies of nanoHAP toothpastes. Methods64 sound enamel blocks and 64 blocks bearing artificially-produced initial caries were produced from human permanent molar teeth. During each treatment period, lasting 14 days per arm, two blocks, one sound and one lesion-bearing, were exposed to either 5% nanoHAP-containing or placebo dental lotion after tooth-brushing with 5% nanoHAP toothpaste, via an intra-oral appliance worn by 30 adults in each of the study groups. Baseline and post-test mineral loss were quantified using transverse microradiography (TMR). One-sided t-test of one group mean was used for intragroup comparison, while two-sided t-test of two independent means was used to compare the two dental lotions. ResultsPairwise comparison (baseline vs. post-test) indicated significant (p<.001) remineralization by nanoHAP toothpaste in both groups. However, when compared against each other, there was a significantly (p<.001) greater percentage of remineralization with nanoHAP lotion [58.4(±1.8)%] than with placebo lotion [37.7(±2.2)%]. TMR examination showed absolute demineralization inhibition in sound enamel blocks exposed to either lotions. ConclusionsToothpaste containing 5% nanoHAP effectively remineralized initial caries and inhibited demineralization of healthy enamel; however, the application of a dental lotion containing 5% nanoHAP after brushing resulted in superior remineralization compared to a placebo lotion. Clinical SignificanceDental lotion containing 5% nanohydroxyapatite used immediately after toothbrushing with 5% nanohydroxyapatite toothpaste can serve as an adjunct to enhance the clinical benefits of the toothpaste.

The in situ potential of synthetic nano-hydroxyapatite for tooth enamel repair

This study was designed to evaluate whether nano-hydroxyapatite toothpastes with or without fluoride would be more advantageous than a fluoride toothpaste in the repair of eroded enamel in situ. Twenty-one subjects participated in this single-blind, randomized, cross-over design study with three 7-day treatment phases. In each phase, the subjects wearing a palatal appliance containing five sterilized enamel specimens used either one of the two test regimens (1% nano-hydroxyapatite toothpaste and 2.25% nano-hydroxyapatite/1450 parts per million (ppm) fluoride toothpaste) or one control (1400 ppm fluoride toothpaste). Enamel specimens were extraorally demineralized (4 × 5 min/day) and were intraorally treated with the toothpastes (2 × 2 min/day). The nano-hydroxyapatite toothpaste groups exhibited significantly higher surface microhardness than did the standard fluoride toothpaste group (p &lt; 0.05). Enamel surface hardness was increased only by nano-hydroxyapatite toothpastes after in situ treatment compared with the baseline (p &lt; 0.05). Morphological analysis demonstrated an apatite-type crystal deposition on the eroded enamel surface produced by nano-hydroxyapatite toothpastes, while fluoride toothpaste failed to show any significant surface deposition. Chemical analysis showed a higher content of calcium and phosphorus in the enamel surface treated with nano-hydroxyapatite toothpastes compared with that in the control one (p &lt; 0.05). It is concluded that home use of nano-hydroxyapatite containing toothpastes may have a protective effect against erosion at the enamel surface.

Remineralization Potential of Nanohydroxyapatite Toothpaste Compared with Tricalcium Phosphate and Fluoride Toothpaste on Artificial Carious Lesions.

Introduction Nanohydroxyapatite (nano-HA) has been utilized as an alternative agent for dental enamel remineralization. This study compared remineralization potential of nano-HA toothpaste (NHT), functionalized tricalcium phosphate toothpaste (TCPT), and fluoride toothpaste (FT) on carious lesions. Materials and Methods Sixty extracted human premolars were prepared for artificial carious lesions with synthetic polymer gel. Samples were divided into four groups according to testing agents: NHT, TCPT, FT, and one group with no treatment (NT). Each group was subjected to pH-cycling with the application of toothpaste in slurry form twice a day (2-min each) for 10 days. Surface microhardness was measured before demineralization, after demineralization, and after pH-cycling. Hardness at different periods, percentage of hardness recovery (% HR), and percentage of remineralization potential (%RP) were determined and statistically analyzed with ANOVA and Tukey comparisons (α = 0.05). Polarized light microscopy (PLM) was utilized to assess lesion depth. Results Significant remineralization of carious lesions was observed among different toothpastes compared to NT (p < 0.05). No significant difference in remineralization potential was found among NHT, TCPT, and FT (p > 0.05). No significant difference in % HR and % RP was seen among NHT, TCPT, and FT (p > 0.05). PLM indicated a greater decrease in carious depth upon using NHT compared to TCPT and FT, with minimal increase in depth for NT. Conclusions NHT has comparable capability to TCPT and FT in hardness recovery. However, decrease in carious depth was evidenced with PLM for NHT more than TCPT and FT. Thus, NHT was suggested as a potential remineralization product for treating initial carious lesions. Clinical Significance. The study showed that NHT had the potential to remineralize artificial carious lesion. It was confirmed in potential in the lesion depth reduction and forming a new enamel layer. NHT showed its capability as an alternative for dental caries therapeutic.

Nano hydroxyapatite toothpaste as a treatment for dentine hypersensitivity: A systematic review

Nano hydroxyapatite toothpaste as a treatment for dentine hypersensitivity: A systematic review

Substituted Nano-Hydroxyapatite Toothpastes Reduce Biofilm Formation on Enamel and Resin-Based Composite Surfaces.

Background: Toothpastes containing nano-hydroxyapatite (n-HAp) substituted with metal ions provide calcium and phosphate ions to dental hard tissues, reducing demineralization, and promoting remineralization. Few data are available about the effect of these bioactive compounds on oral microbiota. Methods: This in vitro study evaluated the influence of two commercially-available substituted n-HAp-based toothpastes (α: Zn-carbonate substituted n-HAp; β: F, Mg, Sr-carbonate substituted n-HAp) on early colonization (EC, 12 h) and biofilm formation (BF, 24 h) by oral microbiota. Controls were brushed with distilled water. Artificial oral microcosm and Streptococcus mutans biofilms were developed using human enamel and a resin-based composite (RBC) as adherence surfaces. Two test setups, a shaking multiwell plate and a modified drip-flow reactor (MDFR), were used to simulate clinical conditions during the night (low salivary flow and clearance) and daytime, respectively. Energy-dispersive X-ray spectrometry (EDS) was used to evaluate specimens’ surfaces after toothpaste treatment. Fluoride release from β toothpaste was evaluated. Viable adherent biomass was quantified by MTT assay, and biofilms’ morphology was highlighted using confocal microscopy. Results: EDS showed the presence of remnants from the tested toothpastes on both adherence surfaces. β toothpaste showed significantly lower EC and BF compared to control using the artificial oral microcosm model, while α toothpaste showed lower EC and BF compared to control, but higher EC and BF compared to β toothpaste. The effect shown by β toothpaste was, to a minimal extent, due to fluoride release. Interestingly, this result was seen on both adherence surfaces, meaning that the tested toothpastes significantly influenced EC and BF even on RBC surfaces. Furthermore, the effect of toothpaste treatments was higher after 12 h than 24 h, suggesting that toothbrushing twice a day is more effective than brushing once. Conclusions: The efficacy of these treatments in reducing microbial colonization of RBC surfaces may represent a promising possibility in the prevention of secondary caries.

Evaluation of the effects of Er:YAG laser, Nd:YAG laser, and two different desensitizers on dentin permeability: in vitro study.

The purpose of this in vitro study was to evaluate and compare the efficacy of erbium-doped yttrium aluminum garnet (Er:YAG) laser, neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, PrevDent nano-hydroxyapatite toothpaste plus Repairing Serum Kit (PNH), and NUPRO Sensodyne Prophylaxis Paste with NovaMin (NPP) on dentin permeability reduction. Forty dentin discs obtained from bovine incisors were divided into four study groups: Er:YAG laser-treated (2940nm; 0.2W, 80mJ/pulse, 3Hz); Nd:YAG laser-treated (1064nm; 1W, 10Hz); PNH-treated; and NPP-treated groups. The quantitative changes in permeability of each dentin disc were measured using a computerized fluid filtration method (CFFM) before and after desensitizer treatments. The data were analyzed using the Wilcoxon, paired-samples t, Kruskal-Wallis, and Mann-Whitney U tests. The dentin surfaces and tubules were also morphologically detected by scanning electron microscopy (SEM). In all groups, dentin permeability was significantly reduced after the desensitizer and laser treatments (p < 0.05). Among the groups, we detected a significant difference in only when comparing the Er:YAG laser- and NPP-treated groups (p = 0.034). SEM analysis revealed physical changes in the dentin surface in all groups. This in vitro study shows that all tested desensitizers and laser treatments reduced dentin permeability. Also, surface changes, such as complete or partial occlusion or shrinkage of dentin tubules, were observed in all groups. Although the laser groups performed best, the PNH protocol can be considered as an alternative therapeutic product. In addition, clinical and laboratory studies should be performed for this product, and their efficacy should be assessed by combined therapy with lasers.

Reducing dentine hypersensitivity with nano-hydroxyapatite toothpaste: a double-blind randomized controlled trial.

The present randomized double-blind clinical trial aimed to compare the efficacy in reducing dentin hypersensitivity of a dentifrice formulation containing nano-hydroxyapatite with a fluoride dentifrice and a placebo. One hundred and five subjects were recruited to participate in the study. A computer-generated random table with blocking to one of the three study treatments was used in order to have 35 subjects per group: (1) nano-hydroxyapatite 2% gel toothpaste fluoride free; (2) fluoride gel toothpaste; (3) placebo. Groups 1, 2, and 3 were instructed to treat their teeth for 10min twice a day with the provided toothpaste gel. The participant's dentin hypersensitivity was evaluated at baseline and after 2 and 4weeks using airblast and tactile tests. In addition, a subjective evaluation using a visual analogue scale was used. Significant lower values of cold air sensitivity and tactile sensitivity (p<0.05) were found for the test group at 2weeks and 4weeks. In addition, statistically significant (p<0.05) lower values of sensitivity were reported for group 1 compared to those for groups 2 and 3 at 2 and 4weeks, respectively. The VAS scores were significantly lower (p<0.05) in the test group at 2 and 4weeks compared to those at baseline and in the control groups. The application of nano-hydroxyapatite in gel toothpaste fluoride free is an effective desensitizing agent providing relief from symptoms after 2 and 4weeks.

Effect of nano-hydroxyapatite toothpaste on microhardness ofartificial carious lesions created on extracted teeth.

Background. Many types of toothpastes contain substances that can remineralize initial enamel caries. This study aimed to assess the effect of nano-hydroxyapatite (NHA) on microhardness of artificially created carious lesions.Methods. In this in vitro study, NHA was prepared using sol-gel technique and added to the toothpaste with 7% concentration. A total of 80 extracted sound teeth were collected. The crowns were polished using 500-grit abrasive paper. The specimens were randomly coded from 1 to 80. Number 1 to 40 were assigned to group A and numbers 41 to 80 to group B. The microhardness was measured using HVS-1000 Vickers microhardness tester. The specimens were demineralized using 37% phosphoric acid for 3 minutes in order to create artificial carious lesions and then were rinsed with water, air-sprayed for 3 minutes and dried. Microhardness was measured again. Next, the specimens were brushed for 15 days, twice daily, for 15 seconds. After 15 days, microhardness was measured again. Toothpaste A contained NHA and fluoride and toothpaste B contained fluoride alone. Data were analyzed using SPSS 16, with one-sample Kolmogorov-Smirnov test and ANOVA at a significance level of P<0.05.Results. The microhardness of specimens significantly decreased following acid exposure (P<0.01) but increased again in both groups after exposure to toothpastes. The increase in microhardness was significantly greater in group A (P<0.01).Conclusion. The toothpaste containing NHA was more effective than the toothpaste without NHA for the purpose of remineralization.

Comparative Evaluation of Effect of Nano-hydroxyapatite and 8% Arginine Containing Toothpastes in Managing Dentin Hypersensitivity: Double Blind Randomized Clinical Trial.

This double blind randomized clinical trial was conducted with the purpose of evaluating the effects of Nano-hydroxyapatite toothpaste as compared to 8% Arginine containing toothpaste in the management of Dentin hypersensitivity (DH). Patients (30 in each group) suffering from DH and eliciting a VAS score higher than 2 in air blast and tactile test were randomly allocated (block randomization) into either a group 1 (arginine toothpaste) or group 2 (nHA toothpaste). The primary outcome evaluated was the reduction of DH as measured by the electrical stimulus reading on the digital pulp tester. Current required for eliciting a VAS score of 2 was recorded before application of dentifrice. 1 cm of toothpaste was then expressed on the tooth surface for two minutes in each group and rinsed off. The electrical stimulus required to elicit a VAS score of 2 was recorded after 5 minutes, 1 week and 4 weeks. The desensitizing paste containing arginine provided a statistically significant reduction in DH and so did the paste containing nHA. Mean increase in amperage value (reduction in DH) was higher for nHA based than the arginine containing dentifrice. This difference was not statistically significant showing that both toothpastes are equally effective. The findings of the present study encourage the use of Nano-hydroxyapatite and arginine containing dentifrice as an effective desensitizing agent providing relief from symptoms 5 minutes after application and after 1 and 4 weeks.

An In-vitro Comparison of Nano Hydroxyapatite, Novamin and Proargin Desensitizing Toothpastes - A SEM Study.

Dentinal Hypersensitivity (DH) is commonly encountered clinical condition in dental practice which affects 8-57% of the adult population presenting for dental treatment, but the treatment of the same remains doubtful. The purpose of this study was to evaluate and compare the effects of three different desensitizing agents (15% nano hydroxyapatite crystals; 5% novamin and 8% proargin) on dentinal permeability and tubule occlusion in-vitro. Scanning Electron Microscope (SEM) was used to evaluate the effect of these commercially available desensitizing toothpastes. A total of 40 disc shaped dentin specimens were dissected from extracted premolars. Dentin discs of 1mm were obtained with the help of diamond discs. Ten specimens were randomly selected and allocated to the evaluation groups A (control group), B (Nano-hydroxyapatite), C (Novamin) and D (Proargin). Each treatment group dentine disc specimen was treated with the respective slurry for two minutes for a period of seven days. Each disc was subjected to a pre- and post-treatment SEM analysis to evaluate the changes occurring in the dentinal tubules. The qualitative analysis showed no occlusion of the dentinal tubules in Group A (control group) and Group B (nano-hydroxyapatite) showed 98.1% tubule occlusion. Group C (Novamin) and D (Proargin) showed 83.1% and 69.1% tubule occlusion respectively. Quantitative analysis showed a statistical significant difference between Group B and D (p< 0.005) and no statistical significant difference between group B and C (p= 0.235). Similarly, there was no significant difference between Group C and D as (p=0.235). It was concluded that all the three desensiting agents were effective in the dentine tubule occlusion. In addition efficacy of nano-hydroxyapatite toothpaste was greater compared to the other desensiting agents.

The ability of a nano hydroxyapatite toothpaste and oral rinse containing fluoride to protect enamel during an acid challenge using 19F solid state NMR spectroscopy

Hydroxyapatite is used as a remineralising additive for toothpastes and is promoted as an alternative to fluoride. Recently nano hydroxyapatite (nHA) toothpastes and an oral rinse have been produced with fluoride. This paper investigates the ability of a nHA toothpaste and oral rinse containing fluoride to convert the hydroxyapatite of enamel to fluoridated apatite under demineralisation conditions using weight loss measurements and 19F Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy to determine the formation of fluoridated apatite. The presence of nHA and fluoride was shown to reduce weight loss of enamel slices during a demineralisation treatment and resulted in the formation of fluoridated apatite.

Effectiveness of nano-hydroxyapatite toothpaste in reducing dentin hypersensitivity: A double-blind randomized controlled trial

The present double-blind randomized clinical trial aimed to compare the efficacy in reducing dentin hypersensitivity of a dentifrice formulation containing nano-hydroxyapatite with a fluoride dentifrice and a placebo. 105 subjects were recruited to participate in the study. A computer-generated random table with blocking to one of the three study treatments was used in order to have 35 subjects per group: 1) nano-hydroxyapatite 15% toothpaste, fluoride-free; 2) fluoride toothpaste; 3) placebo. Groups 1, 2, and 3 were instructed to brush their teeth for 2 minutes twice a day with the provided toothpaste. The participant's dentin hypersensitivity was evaluated at baseline and after 2 and 4 weeks using airblast and tactile tests. In addition, a subjective evaluation using a visual analog scale (VAS) was used. Significantly lower values of cold air sensitivity and tactile sensitivity (P<.001) were found for the test group at 2 weeks and 4 weeks. In addition, statistically significantly (P<.001) lower values of sensitivity were reported for group 1 compared to groups 2 and 3, at 2 and 4 weeks respectively. The VAS scores were significantly lower (P<.001) in the test group at 2 and 4 weeks compared to baseline and to the control groups. The findings of the present study encourage the application of nano-hydroxyapatite in fluoride-free toothpaste as an effective desensitizing agent providing quick relief from symptoms after 2 and 4 weeks.

NANO-HİDROKSİAPATİTLİ (n-HAp) DİŞ MACUNLARININ MİNE REMİNERALİZASYONU ÜZERİNE ETKİLERİ The Effects of Nano-Hydroxyapatite (n-HAp) Toothpastes on Remineralization of Enamel

The purpose of modern dentistry is the early prevention of tooth decay rather than invasive restorative therapy. In recent years, remineralization of the demineralised enamel without using any restorative treatment becomes more important. Nano-sized particles have similarity to the apatite crystals of tooth enamel in morphology and crystal structure. Recently, some reports have shown that nano-hydroxyapatite has some potential to remineralize of enamel lesions. In this review, the effects of nano-hydroxyapatite toothpastes on remineralization were examined and studies on this subject were explained with details.

Enamel and dentine remineralization by nano-hydroxyapatite toothpastes

ObjectivesThis in vitro study evaluated the effects of nano-hydroxyapatite (n-HAp) toothpastes on remineralization of bovine enamel and dentine subsurface lesions. MethodsSpecimens were demineralized, randomly divided into five groups, and exposed to an aqueous remineralizing solution for two and five weeks (37°C). Brushing procedures were performed with the respective toothpaste/storage solution slurry twice daily (2×5s; total contact time of the slurries 2×120s/d): storage in remineralizing solution only (0); additional brushing with B (20wt% zinc carbonate nano-hydroxyapatite, ZnCO3/n-HAp); BS (24wt% ZnCO3/n-HAp); E (0.14wt% amine fluoride); or A (7wt% pure n-HAp). Differences in mineral loss (ΔΔZ) before and after storage/treatment were microradiographically evaluated. ResultsDentine groups 0, B, BS, and A showed significantly higher ΔΔZ values compared to E (p<0.05; ANOVA). Enamel ΔΔZ values of group A were significantly higher compared to group E (p<0.05), whilst no significant differences of these groups could be observed compared to 0, B, and BS (p>0.05). ConclusionsWith the in vitro conditions chosen, toothpastes containing n-HAp revealed higher remineralizing effects compared to amine fluoride toothpastes with bovine dentine, and comparable trends were obtained for enamel.

Remineralization Potential of New Toothpaste Containing Nano-Hydroxyapatite

Hydroxyapatite is the main component of enamel that gives the tooth a bright white appearance and eliminates the diffused reflection of light by filling up the fine pores of the tooth surface. Accordingly, remineralization of the teeth can be expected to some extent if hydroxyapatite is used to treat an incipient caries lesion (early white spot lesion). In addition, the remineralization effect will be increased if the particle size of hydroxyapatite can be reduced to less than that of the micron-size in existing toothpaste preparations. The aim of this in vitro study was to evaluate the effect of nano-hydroxyapatite toothpaste, which was produced by nano-technology, on the remineralization of human enamel. A tooth specimen, on which artificial incipient caries had been induced, was immersed into two toothpaste slurries for remineralization. One contains nano-sized hydroxyapatite and fluoride, and the other contains nano-sized hydroxyapatite excluding fluoride. In order to evaluate the remineralization effect, the Vickers Hardness Number &amp; SEM image of the enamel surface was evaluated at each step. There were significant differences in VHN values between those obtained before and after the remineralization steps. The results showed that the remineralization effect increased with increasing immersing time (P&lt;0.05). However, there were no significant differences in VHN values between the two groups (P&gt;0.05). SEM also demonstrated differences the in micro surface at each step. In conclusion, a toothpaste containing nano-sized hydroxyapatite has the potential to remineralize an incipient caries lesion. In addition, the addition of fluoride had no synergistic effect on remineralization.