Strontium and Caries: A Long and Complicated Relationship

Investigations into the role of strontium (Sr) in caries prevention have attracted great interest in the research community in the past, with their peak in the 1970–80s. To this date, no clear indication of the relative importance of Sr in caries prevention has been provided. A vast number of animal caries, epidemiological and mechanistic studies have been conducted. Although there is much discrepancy, the majority of studies suggest that Sr exhibits some cariostatic properties, predominantly in the presence of fluoride. An optimum Sr concentration of 5–10 ppm in drinking water has been proposed as a direct result of several epidemiological caries studies. Despite these results, no direct link can be established between Sr and caries prevention as, to date, no relevant, randomized controlled trials have been reported. The extrapolation of potential cariostatic properties of Sr from epidemiological studies is difficult due to the co-presence of several other trace elements in the water of the study areas, with many of these elements being attributed cariostatic properties in their own right. Furthermore, the role of caries risk factors was not taken into consideration. There is a clear need for further research, especially on the mineral phases in the dental hard tissues, plaque and plaque fluid associated with Sr as these may give rise to a better understanding of this subject matter. Based on the current data, the cariostatic properties of Sr, or at least those proposed by some authors, cannot be supported

Fluoride dose-response of human and bovine enamel caries lesions under remineralizing conditions

Purpose: To investigate the relative fluoride dose-response of human and bovine enamel caries lesions under remineralizing conditions and utilizing an established pH cycling model. Methods: Early caries-like lesions were formed in human and bovine enamel, characterized using Vickers surface microhardness (VHN) and assigned to five dentifrice treatment groups: 0/250/1100 ppm fluoride as sodium fluoride (F as NaF) formulation 1; 1100 ppm F as NaF formulation 2; 1000 ppm F as monofluorophosphate (MFP) formulation 3. The daily pH cycling regimen comprised: 4xl-minute dentifrice slurry treatments; lx4-hour acid challenge and intermittent remineralization in a l:l-mixture of pooled human/ artificial saliva. After 20 days, VHN of specimens were measured again and changes from lesion baseline calculated (REM). Subsequently, enamel fluoride uptake (EFU) was determined using the microdrill technique and specimens were demineralized again to determine their acid resistance (DEM). Data were analyzed using two-way ANOVA (factors: enamel, dentifrice). Results: Both enamel type and dentifrice as well as their interaction affected REM and DEM. EFU was only affected by dentifrice. Human and bovine enamel showed a good fluoride dose-response for REM and correlated well. However, bovine enamel showed more remineralization than human enamel. There were good correlations between dentifrice-F concentration vs. REM and EFU, and between REM vs. EFU, regardless of enamel type

Effectiveness and Mechanisms of Action of Whitening Dentifrices on Enamel Extrinsic Stains

poster abstractWhitening dentifrices utilize different approaches for stain removal and/or prevention, including the use of abrasive, oxidizing and chemical cleaning agents. The objectives of this in vitro study were: 1. to compare the whitening effect of commercial whitening and non-whitening dentifrices; 2. to verify the mechanism of action of whitening dentifrices by contrasting two experimental models: chemical (toothpaste exposure only) and chemo-mechanical (toothpaste exposure with tooth brushing abrasion). Two hundred fifty six bovine enamel specimens (10x10mm) were prepared and partially stained. They were assigned to 8 groups: 6 whitening dentifrices, 1 non-whitening reference dentifrice and deionized water (control); and further divided in 2 subgroups (n=16) according to the experimental models: chemical or chemo-mechanical. Specimens were daily exposed to dentifrice slurries 2x/day for 1min and brushed or not, according to each model. In between dentifrice treatments, specimens were exposed to the staining solution for 5h. This protocol was repeated for 5 consecutive days and enamel color changes (Delta E) were measured by spectrophotometry, after each day. The abrasivity of the toothpastes was determined using standard test (ISO 11609). Significantly higher Delta E values (whitening effect) were observed for all groups (p0.05). Whitening dentifrices can be effective preventing/removing enamel surface staining, when associated to tooth brushing abrasion. This seemed to be modulated mainly by the abrasive level of the tested toothpastes, with no action attributed to the chemical agents

In situ anticaries efficacy of dentifrices with different formulations – A pooled analysis of results from three randomized clinical trials

Objectives Data generated from three similar in situ caries crossover studies presented the opportunity to conduct a pooled analysis to investigate how dentifrice formulations with different fluoride salts and combinations at concentrations of 1400–1450 ppm F, different abrasive systems and in some cases, carbomer (Carb), affect enamel caries lesion remineralization and fluoridation. Methods Subjects continuously wore modified partial dentures holding two gauze-covered partially-demineralized human enamel specimens for 14 days and brushed 2×/day with their assigned dentifrice: Study 1: sodium fluoride (NaF)/Carb/silica, NaF/silica, NaF + monofluorophosphate (MFP)/chalk; Study 2: NaF/Carb/silica, NaF + MFP/dical, amine fluoride (AmF)/silica; Study 3: NaF/Carb/silica, NaF + stannous fluoride (SnF2)/silica/hexametaphosphate (HMP). All studies included Placebo (0 ppm F) and/or dose-response controls (675 ppm F as NaF [675F-NaF]) ±Carb. Specimens were evaluated for percentage surface microhardness recovery (SMHR) and enamel fluoride uptake (EFU). Results All 1400–1450 ppm F dentifrices except NaF + SnF2/silica/HMP provided significantly greater lesion remineralization than Placebo (p < 0.0001): differences in SMHR ranged from 17.46% (NaF + MFP/dical) to 26.66% (AmF/silica). For EFU (back-transformed log EFU), all 1400–1450 ppm F dentifrices gave significant fluoride uptake compared to Placebo (p < 0.0001): increases in EFU ranged from 4.95 μg F/cm2 (NaF + SnF2/silica/HMP) to 16.32 μg F/cm2 (NaF/carb/silica). Dentifrices containing NaF or AmF as sole fluoride source provided the greatest remineralization and fluoridation; Carb addition did not alter fluoride efficacy; some excipients appeared to interfere with the cariostatic action of fluoride. Treatments were generally well-tolerated with ≤4 treatment-related adverse events per study. Conclusion Commercially available fluoride dentifrices varied greatly in their ability to remineralize and fluoridate early caries lesions. Clinical significance Fluoride dentifrices are the most impactful anticaries modality worldwide. While clinical caries trials have not consistently shown the superiority of one formulation over another, these findings using a sensitive in situ caries model indicated that dentifrices containing NaF or AmF as the sole fluoride source provided the greatest remineralization and fluoridation benefits

In vitro caries lesion rehardening and enamel fluoride uptake from fluoride varnishes as a function of application mode

PURPOSE: To study the laboratory predicted anticaries efficacy of five commercially available fluoride varnishes (FV) by determining their ability to reharden and to deliver fluoride to an early caries lesion when applied directly or in close vicinity to the lesion (halo effect). METHODS: Early caries lesions were created in 80 polished bovine enamel specimens. Specimens were allocated to five FV groups (n = 16) based on Knoop surface microhardness (KHN) after lesion creation. All tested FV claimed to contain 5% sodium fluoride and were: CavityShield, Enamel Pro, MI Varnish, Prevident and Vanish. FV were applied (10 +/- 2 mg per lesion) to eight specimens per FV group (direct application); the remaining eight specimens received no FV but were later exposed to fluoride released from specimens which received a FV treatment (indirect application). Specimens were paired again and placed into containers (one per FV). Artificial saliva was added and containers placed into an incubator (27 hours at 37 degrees C). Subsequently, FV was carefully removed using chloroform. Specimens were exposed to fresh artificial saliva again (67 hours at 37 degrees C). KHN was measured and differences to baseline values calculated. Enamel fluoride uptake (EFU) was determined using the acid etch technique. Data were analyzed using two-way ANOVA. RESULTS: The two-way ANOVA highlighted significant interactions between FV vs. application mode, for both deltaKHN and EFU (P < 0.001). All FV were able to reharden and deliver fluoride to caries lesions, but to different degrees. Furthermore, considerable differences were found for both variables between FV when applied either directly or in close vicinity to the lesion: MI Varnish and Enamel Pro exhibited greater fluoride efficacy when applied in vicinity rather than directly to the lesion, whereas CavityShield and Vanish did not differ. Prevident exhibited a higher EFU when applied directly, but little difference in rehardening

Comparison Between Radiotracer and Surface Profile Methods for the Determination of Dentifrice

poster abstractIntroduction: ISO11609 states that a surface profile (Sp) method can be used to determine dentifrice abrasivity in relation to dentin (RDA) as an alternative to the traditional radiotracer method (Rt). A comparison between both methods was performed in this study. Methods: Specimens from human root dentin were prepared for each method and randomly assigned to 8 dentifrice/abrasive groups (n=8), which represented a wide abrasivity range. Aqueous dentifrice slurries or abrasive suspensions in a solution containing 0.5% carboxymethylcellulose and 10% glycerin were used to brush specimens in a custom-made V-8 cross-brushing machine. Two independent studies (Sp, Rt) were carried out. For Rt, the specimen preparation, study design, analysis and calculation of the abrasive level (RDA) followed the ISO11609/Annex A guidelines. Similarly for Sp, the ISO11609/Annex B recommendations were followed, except by the number of brushing strokes, which was pre-determined to be 2000 strokes (instead of 10000) in a preliminary test. Data were analyzed using ANOVA and Tukey tests, with significance level set at 5%. The correlation between methods was also investigated. Results: Overall, higher variation and RDA values were observed for the Sp method compared to Rt. While good correlation was found between methods (R2=0.841), group ranking was dissimilar and better statistical differentiation among groups was observed in Rt. Conclusions: The Rt method showed to be a more standardized and robust method compared to Sp for the determination of RDA values of dentifrices/abrasives. Sp needs to be further developed before being considered as an equivalent test method for RDA. The determination of the abrasive levels of toothpastes using standard testing methods is important to guide oral care professionals and patients on the prevention of toothbrushing abrasive wear

Interaction between toothpaste abrasivity and toothbrush filament stiffness on the development of erosiveabrasive lesions in vitro

Objectives To investigate the loss of enamel and dentin surface caused by the interaction between abrasives in toothpaste and toothbrush filament stiffness. Methods The study followed a 2 (high-level or low-level abrasive; silica) × 3 (filament stiffness; soft, medium or hard) × 2 (cycling time; 3 or 5 days) factorial design. Polished bovine enamel and dentin specimens (n = 8 each per group) were subjected to 5 days of erosion/abrasion cycling: erosion (5 minutes, four times daily, 0.3% citric acid, pH 3.75); abrasion (15 seconds, twice daily, 45 strokes each, 150 g load, automated brushing machine); and fluoride treatment [15 seconds with abrasion and 45 seconds without abrasion; 275 p.p.m. fluoride (F−) as sodium fluoride (NaF) in abrasive slurry]. Enamel and dentin specimens were exposed to artificial saliva between erosion and abrasion/F− treatment (1 hour) and at all other times (overnight). Non-contact profilometry was used to determine surface loss (SL) after 3 and 5 days of cycling. Data were analysed using three-way analysis of variance (ANOVA) (factors: abrasive/filament stiffness/time), with separate analyses conducted for enamel and dentin. Results For enamel, only ‘cycling time’ was found to affect SL, with 5 days of cycling resulting in a greater SL than 3 days of cycling. Overall, there was little SL for enamel (range: 0.76–1.85 μm). For dentin (SL range: 1.87–5.91 μm), significantly higher SL was found for 5 days of cycling versus 3 days of cycling, with particularly large differences for hard stiffness/high-level abrasive and medium stiffness/low-level abrasive. For high-level abrasive, after 5 days of cycling hard stiffness resulted in significantly higher SL than did medium stiffness, with no other significant differences according to stiffness. Overall, high-level abrasive resulted in significantly higher SL than did low-level abrasive, with strong effects for all combinations, except medium stiffness after 5 days. Conclusion The interplay between abrasivity and filament stiffness appears to be more relevant for dentin than for enamel

Artificial biofilm thickness and salivary flow effects on fluoride efficacy – A model development study

This laboratory model development study investigated the interaction between artificial biofilm thickness and salivary flow rate on fluoride-mediated prevention of enamel caries lesion formation. This 5-day pH cycling study on sound bovine enamel specimens utilized a continuous flow model and followed a 4 (agarose biofilm thickness-‘no biofilm’/1/2/3mm)×2 (remineralizing solution flow rate-0.05/0.5ml/min)×2 (fluoride-0/383ppm as sodium fluoride) factorial design. Vickers surface microhardness change was the outcome measure. Data were analyzed with three-way ANOVA. The three-way interaction gel thickness×flow rate×fluoride concentration was significant (p=0.0006). 383ppm fluoride caused less softening than 0ppm regardless of gel thickness or flow rate. 0.5ml/min flow rate caused less softening than 0.05ml/min for ‘no biofilm’ and 1mm biofilm thickness regardless of fluoride concentration, for 2 and 3mm with 0ppm F but not for 383ppm F. For 0.05ml/min, softening was reduced as gel thickness increased from ‘no biofilm’-1-2mm, but not from 2-3mm. For 0.5ml/min, ‘no biofilm’ caused more softening than 1, 2, and 3mm, but 1, 2, and 3mm were not different from each other for both 0 and 383ppm F. The present findings suggest that the efficacy of fluoride in preventing enamel demineralization is affected by both biofilm thickness and salivary flow rate, with both thicker biofilms and higher flow rate resulting in less demineralization

A randomised clinical evaluation of a fluoride mouthrinse and dentifrice in an in situ caries model

Objectives Fluoride mouthrinses provide advantages for fluoride delivery by maintaining elevated intra-oral fluoride concentrations following fluoride dentifrice use. This in situ caries study investigated potential anti-caries efficacy of a 220 ppm fluoride mouthrinse. Methods This was an analyst-blinded, four-treatment, randomised, crossover study using partially demineralised, gauze-wrapped, human enamel samples mounted in a mandibular partial denture. Participants brushed twice daily for 14 days with either a 1150 ppm fluoride or a fluoride-free placebo dentifrice and either rinsed once daily with the 220 ppm fluoride mouthrinse or not. Following each treatment period, percent surface microhardness recovery (%SMHR) and enamel fluoride uptake (EFU) were assessed. Results Fifty three participants completed the study. Compared with the placebo dentifrice/no rinse treatment, the fluoride-containing regimens demonstrated greater enamel remineralisation (%SMHR) and fluoridation (EFU): fluoride dentifrice/fluoride rinse (%SMHR difference: 21.55 [95% CI: 15.78,27.32]; EFU difference 8.35 [7.21,9.29]); fluoride dentifrice/no rinse: 19.48 [13.81,25.15]; 6.47 [5.35,7.60]; placebo dentifrice/fluoride rinse: 16.76 [11.06,22.45]; 5.87 [4.72,7.00] (all P < .0001). There were no significant differences in%SMHR between fluoride regimens. The fluoride dentifrice/fluoride rinse regimen was associated with higher EFU than the fluoride dentifrice/no rinse (1.88 [0.75,3.01], P = .0013) and placebo dentifrice/fluoride rinse regimens (2.48 [1.34,3.62], P < .0001). Treatments were generally well-tolerated. Conclusions The in situ caries model demonstrated that the fluoride mouthrinse is effective in promoting enamel caries lesion remineralisation and fluoridation whether used following a fluoride or non-fluoride dentifrice. Additive (potential) anti-caries benefits of a fluoride rinse after a fluoride dentifrice were confined to enhancements in lesion fluoridation (EFU). Clinical significance In conjunction with a fluoride dentifrice, fluoride mouthrinses enhance enamel fluoridation, which may be useful in caries prevention

Erosion Remineralization Efficacy of Gel-to-Foam Fluoride Toothpastes in situ: A Randomized Clinical Trial

This single-center, randomized, placebo-controlled, four-treatment, four-period crossover study compared the enamel remineralization effects of low- and medium-abrasivity gel-to-foam toothpastes and a reference toothpaste (all 1,450 ppm fluoride as NaF) versus placebo toothpaste (0 ppm fluoride) using a short-term in situ erosion model. Subjects (n = 56) wearing a palatal appliance holding acid-softened bovine enamel specimens brushed their teeth with the test toothpastes. Thereafter, the specimens were removed for analysis of percent surface microhardness recovery (%SMHR) and percent relative erosion resistance (%RER) at 2, 4, and 8 h. Both low- and medium-abrasivity gel-to-foam fluoride toothpastes and the reference toothpaste provided significantly greater %SMHR than placebo at all assessment time points (all p < 0.05). No statistically significant difference of %SMHR was observed between the fluoride treatment groups at any time point. Similarly, all fluoride products provided significantly superior %RER versus placebo (all p < 0.0001), whereas no significant difference of this parameter was noted between the fluoride treatment groups. Increasing numerical improvements of %SMHR and %RER were observed in all four treatment groups over time (2, 4, and 8 h). The present in situ model is a sensitive tool to investigate intrinsic and fluoride-enhanced rehardening of eroded enamel. All three fluoride toothpastes were more efficacious than placebo, and there were no safety concerns following single dosing in this short-term in situ model