Different protocols to produce artificial dentine carious lesions in vitro and in situ: hardness and mineral content correlation.

This study compared dentine demineralization induced by in vitro and in situ models, and correlated dentine surface hardness (SH), cross-sectional hardness (CSH) and mineral content by transverse microradiography (TMR). Bovine dentine specimens (n = 15/group) were demineralized in vitro with the following: MC gel (6% carboxymethylcellulose gel and 0.1 M lactic acid, pH 5.0, 14 days); buffer I (0.05 M acetic acid solution with calcium, phosphate and fluoride, pH 4.5, 7 days); buffer II (0.05 M acetic acid solution with calcium and phosphate, pH 5.0, 7 days), and TEMDP (0.05 M lactic acid with calcium, phosphate and tetraethyl methyl diphosphonate, pH 5.0, 7 days). In an in situ study, 11 volunteers wore palatal appliances containing 2 bovine dentine specimens, protected with a plastic mesh to allow biofilm development. The volunteers dripped a 20% sucrose solution on each specimen 4 times a day for 14 days. In vitro and in situ lesions were analyzed using TMR and statistically compared by ANOVA. TMR and CSH/SH were submitted to regression and correlation analysis (p < 0.05). The in situ model produced a deep lesion with a high R value, but with a thin surface layer. Regarding the in vitro models, MC gel produced only a shallow lesion, while buffers I and II as well as TEMDP induced a pronounced subsurface lesion with deep demineralization. The relationship between CSH and TMR was weak and not linear. The artificial dentine carious lesions induced by the different models differed significantly, which in turn might influence further de- and remineralization processes. Hardness analysis should not be interpreted with respect to dentine mineral loss.

Comparison of cross-sectional hardness and transverse microradiography of artificial carious enamel lesions induced by different demineralising solutions and gels.

The aims of this study were: (1) to correlate surface (SH) and cross-sectional hardness (CSH) with microradiographic parameters of artificial enamel lesions; (2) to compare lesions prepared by different protocols. Fifty bovine enamel specimens were allocated by stratified randomisation according to their initial SH values to five groups and lesions produced by different methods: MC gel (methylcellulose gel/lactic acid, pH 4.6, 14 days); PA gel (polyacrylic acid/lactic acid/hydroxyapatite, pH 4.8, 16 h); MHDP (undersaturated lactate buffer/methyl diphosphonate, pH 5.0, 6 days); buffer (undersaturated acetate buffer/fluoride, pH 5.0, 16 h), and pH cycling (7 days). SH of the lesions (SH(1)) was measured. The specimens were longitudinally sectioned and transverse microradiography (TMR) and CSH measured at 10- to 220-microm depth from the surface. Overall, there was a medium correlation but non-linear and variable relationship between mineral content and radicalCSH. radicalSH(1) was weakly to moderately correlated with surface layer properties, weakly correlated with lesion depth but uncorrelated with integrated mineral loss. MHDP lesions showed the highest subsurface mineral loss, followed by pH cycling, buffer, PA gel and MC gel lesions. The conclusions were: (1) CSH, as an alternative to TMR, does not estimate mineral content very accurately, but gives information about mechanical properties of lesions; (2) SH should not be used to analyse lesions; (3) artificial caries lesions produced by the protocols differ, especially considering the method of analysis.

Effect of a 4% titanium tetrafluoride (TiF4) varnish on demineralisation and remineralisation of bovine enamel in vitro.

OBJECTIVES: This in vitro study assessed the effect of a 4% TiF4 varnish on demineralisation and remineralisation of sound enamel and artificial carious enamel lesions, respectively. METHODS: Bovine sound and carious enamel (n=110) were randomly allocated to each type of varnish: Duraphat-D (NaF, 2.26%F, pH 4.5, Colgate-Brazil, n=30), Duofluorid-F (NaF, 2.71%F, pH 8.0, FGM-Brazil, n=30), TiF4-T (2.45%F, pH 1.0, FGM-Brazil, n=30) and no-fluoride-P (FGM-Brazil, pH 5.0, n=20). For the formation of artificial enamel caries, half of the blocks were immersed in 32 mL buffer acetate solution (16 h), whereas the other half was maintained sound. The varnishes were applied onto the enamel surfaces. Thus, the samples were subjected to pH cycles (37 degrees C) for 7 days. The response variables tested were surface and cross-sectional hardness. Data were tested using Kruskal-Wallis test (p<0.05). RESULTS: All F varnishes significantly reduced demineralisation and increased remineralisation in comparison to placebo. The TiF4 did not significantly reduce the surface enamel softening when compared with the other F varnishes, but it decreased the loss of subsurface hardness to the same extent. In enamel blocks with previous artificial carious lesions, the TiF4 significantly improved the rehardening compared to the other varnishes up to 30 microm depth. CONCLUSIONS: The TiF4 varnish was able to decrease the demineralisation and increase the remineralisation of previously sound and carious enamel, respectively. It was equally effective compared to NaF varnishes on reducing the demineralisation at subsurface, but it was more effective on improving the remineralisation at surface and subsurface.

Response of carious enamel to TiF4 varnish treatment under diverse cariogenic activities in situ.

OBJECTIVE: To compare the effect of TiF4 and NaF varnishes on demineralized bovine enamel under different cariogenic activities in situ. METHODS: Twenty subjects participated of this in situ study with 3 crossover phases (14days each), in which they wore palatal appliances containing demineralized bovine enamel samples (8 samples/appliance for phase) treated with TiF4, NaF (all with 2.45% F) or placebo varnish. The samples were subjected to different cariogenic conditions (1. absence of biofilm accumulation and sucrose exposure; 2. presence of biofilm and absence of sucrose exposure; 3. presence of biofilm and 20% sucrose exposure 4×/day; 4. presence of biofilm and 20% sucrose exposure 8×/day). All were exposed to fluoride dentifrice (2×/day). The mineral content and lesion depth were evaluated using transverse microradiography (TMR) and the data were subjected to RM two-way ANOVA/Bonferroni tests (p<0.05). RESULTS: TiF4 varnish significantly increased the remineralization of artificial carious lesions compared to placebo, regardless of the cariogenic activity. On the other hand, the remineralizing effect of NaF varnish was dependent on the cariogenic activity. For NaF, remineralization happened only in conditions 1 and 3 compared to placebo varnish (p<0.0001). NaF was unable to prevent further demineralization under biofilm accumulation and sucrose exposure 8×/day (condition 4). In the absence of fluoride treatment, demineralization happened in all conditions, except in the condition 1. CONCLUSION: Therefore, 4% TiF4 varnish was the only treatment able to improve enamel remineralization regardless of the cariogenic activity, while NaF varnish failed in preventing further demineralization under high cariogenic activity in situ. CLINICAL SIGNIFICANCE: 4% TiF4 varnish showed better remineralizing effect compared to NaF varnish, which was seen regardless of the cariogenic activity. This is a promising finding to support the indication of TiF4 in the clinic.

Effect of experimental mouthrinses containing the combination of NaF and TiF4 on enamel erosive wear in vitro.

OBJECTIVE: This study analysed the anti-erosive effect of experimental solutions containing TiF4 and NaF. METHODS: Bovine enamel samples (n=15) were treated with: (1) commercial solution with SnCl2/NaF (Erosion Protection(®)); (2) experimental solution with 0.0815% TiF4; (3) 0.105% NaF; (4) 0.042% NaF + 0.049% TiF4; (5) 0.063% NaF + 0.036% TiF4 or (6) control. The samples were submitted to pH cycles and daily fluoride applications for seven days. The enamel wear was measured using a contact profilometer and analysed by ANOVA (p < 0.05). RESULTS: The best anti-erosive effect was found for experimental solution with 0.0815% TiF4 (99% reduction in enamel wear), followed by SnCl2/NaF (78%) and 0.049% TiF4 + 0.042% NaF solution (41%). CONCLUSIONS: The experimental solution containing a specific combination of TiF4 + NaF has the ability to partially reduce enamel erosion.