Chapter 5.1: Physicochemical Interactions between Enamel and Oral Fluids.

Despite all the current knowledge in cariology, research is still being carried out nowadays trying to make dental enamel resistant to dental caries. Since enamel is mainly composed by a mineral, efforts have been put together to make it more resistant to acids produced by dental biofilm when exposed to dietary sugars. Fluoride was once thought to be a micronutrient that impacted caries resistance when incorporated in the tooth mineral, but we now know that the complex interactions at the mineral surface are most important. Every slightly soluble mineral, and enamel is no exception, has a behavior that is determined by the environment where it is located, and in the case of the dental crown, saliva and biofilm fluid play an important role. Enamel can keep in balance or lose its minerals, but it can gain them back. These processes, equilibrium, and loss or gain follow Le Chatelier's principle, and physicochemically, they are known as saturating, undersaturating, and supersaturating conditions, respectively. Saliva, and even the biofilm fluid, is supersaturated with calcium (Ca2+) and phosphate (PO43-) in relation to enamel solubility, and thus the natural tendency of enamel is to gain mineral, conferring saliva with a remineralizing property. However, the decrease in pH and the presence of free fluoride ion (F-) will determine what will happen to the enamel. While lowering the pH of the medium is an imbalance factor, fluoride at micromolar concentration reduces the acid impact. This chapter provides an updated, evidence-based understanding of the interactions between enamel and oral fluids.

The potential of conventional and bulk-fill bioactive composites to inhibit the development of caries lesions around restorations.

PURPOSE: To determine caries inhibition potential of conventional and bulk-fill bioactive composites around restorations. METHODS: Enamel and dentin blocks were prepared using a diamond saw under water irrigation, finished (SiC, 600- and 800-grit) and polished (SiC 1,200, final polish= 0.2 µm). Blocks were then selected through enamel surface microhardness, and enamel and dentin standard cavities were restored (n=10/group) with conventional bioactive composite (Beautifil II, BTF), bulk-fill bioactive composite (Activa BioACTIVE, ACT), glass-ionomer cement (Ionofil Plus, ION), conventional composite (GrandioSO, GSO), and bulk-fill composite (Admira Fusion X-TRA, ADM). Afterwards, the blocks were subjected to pH cycling: 4 hours in demineralization and 20 hours in remineralization solutions for 7 days, before being cut in the middle. One half was used to calculate the carious lesion area (ΔS) using values obtained by cross-sectional microhardness (CSMH) testing. The other half was submitted to polarized light microscopy (PLM) and scanning electron microscopy (SEM). The % of internal gap formation (GAP) of restorations' replicas were analyzed under SEM. Data were analyzed by ANOVA and Tukey test (α= 5%). RESULTS: In terms of CSMH, ION group exhibited the lowest ΔS values, with no significant difference to ADM. The composites BTF and ACT were similar to each other (P< 0.05) and to their negative controls (GSO and ADM), respectively. ION showed lower caries formation under PLM, whereas the GSO group presented a greater demineralized area. ION presented the highest % of internal GAP formation. Bioactive composites (BTF and ACT) were similar to their corresponding conventional ones (GSO and ADM) in terms of GAP formation. CLINICAL SIGNIFICANCE: The glass-ionomer cement was more effective in inhibiting the formation of caries lesions around restorations. Because of the glass-ionomer cement's limited application in high load-bearing areas, the conventional bioactive composite would be a promising clinical choice.

Effect of high-fluoride dentifrice and bracket bonding composite material on enamel demineralization in situ.

OBJECTIVE: This in situ study evaluated the effect of high-fluoride dentifrice (5000 µg F-/g) and fluoride-containing bonding composite resin on enamel demineralization adjacent to orthodontic brackets. METHODS: Ten volunteers wore palatal appliances containing bovine enamel blocks with metallic brackets bonded with fluoride-free or fluoride-containing composite resin. During three phases of 14 days each, three dentifrices with different fluoride concentrations (0, 1100, and 5000 µg F-/g) were tested. The cariogenic challenge consisted of 20% sucrose solution dripped 8x/day onto the dental blocks. At the end of each phase, biofilm formed was collected for fluoride analysis. Cross section hardness was performed in enamel blocks, and the lesion area was calculated. Data were analyzed by two-way ANOVA followed by Tukey post hoc test (α = 5%). RESULTS: The only signicant factor for all the variables under study was the dentifrice. Smaller lesion area and higher fluoride concentration on biofilm were found in 5000 µg F-/g group, irrespective of bonding composite resin (p < 0.001). Neither bracket-bonding composite resin nor the interaction between the factors was statistically significant (p > 0.05) for all the variables. CONCLUSION: High-fluoride dentifrice is effective in reducing demineralization on enamel adjacent to orthodontic brackets, while the fluoride-containing bonding composite resin does not influence it. CLINICAL SIGNIFICANCE: Since high-fluoride dentifrice was able to reduce demineralization adjacent to brackets, it can be an option to caries management in orthodontics patients.

Color change, diffusion of hydrogen peroxide, and enamel morphology after in-office bleaching with violet light or nonthermal atmospheric plasma: An in vitro study.

OBJECTIVE: The aim is to evaluate the effect of violet light (VL) and nonthermal atmospheric plasma (NTAP) combined with or without 35% hydrogen peroxide (HP) and 37% carbamide peroxide (CP). METHODS: Bovine crowns were divided into (n = 10) VL, VL/HP, VL/CP, NTAP, NTAP/HP, NTAP/CP, HP, CP, and C (control) groups. Color and whiteness change (CIELAB-Δ Eab, CIEDE2000-Δ E00 , whiteness index-ΔWID ), color parameters (ΔL, Δa, and Δb), and intrapulpal concentration (µL/mL) of HP were assessed by spectrophotometry. Scanning electron microscopy evaluated the morphology of enamel surface. Data were analyzed by two-way analysis of variance and Tukey (Δ Eab , ΔE00 , ΔWID , ΔL, and µL/mL) and Kruskal-Wallis and Mann-Whitney tests (Δ a and Δ b, α = 5%). RESULTS: VL increased ΔEab and ΔWID of CP (P < .05). VL and NTAP alone resulted in perceptible color and whiteness change, but lower than those in the gel-treated groups (P < .05). Activation modes increased ΔL compared with that of C, but only VL enhanced Δb when applied alone or combined with CP. VL and NTAP did not increase HP diffusion (P > .05) or cause alterations in enamel morphology. However, HP and CP promoted topographical changes. CONCLUSION: VL and NTAP changed color to a lesser extent than bleaching gels. VL produced supplementary effectiveness only for CP (ΔEab and ΔWID ), without increasing HP diffusion or changing enamel morphology. CLINICAL SIGNIFICANCE: Although violet LED light and nonthermal atmospheric plasma (NTAP) promoted in vitro perceptible bleaching without compromising enamel morphology, bleaching gels (hydrogen peroxide and carbamide peroxide) were more effective than VL or NTAP. VL or NTAP did not increase intrapulpal diffusion of peroxide.

Penetration of Filled and Unfilled Resin Sealants on Different Enamel Substrates.

PURPOSE: To evaluate the penetration ratio of filled and unfilled resin-based sealants on different enamel substrates and pit and fissure morphologies. METHODS: Forty-eight occlusal enamel blocks obtained from impacted human third molars were randomly divided (n equals eight) according to enamel substrates (sound; caries-like lesion; caries-like lesion plus topical fluoride application) and sealant material (FluroShield; Helioseal Clear Chroma). Sealants were applied on the enamel surface. The specimens were stored in 100 percent humidity for 24 hours at 37 degrees Celsius, sectioned in a buccal-lingual direction (at approximately 50 µm), and examined to determine the sealant penetration ratio (b x 100/a; a equals total fissure length and b equals sealant penetration length) and pit and fissure morphology (V-, U-, or Y-shaped). Statistical analysis was performed using Friedman and Kruskal-Wallis tests (P<0.05). RESULTS: Enamel substrate and sealant material did not affect the sealant penetration ratio, with no interactions between these factors. Moreover, the morphology significantly affected the sealant penetration, with the "Y"-shaped fissures presenting the lowest sealant penetration ratio compared to "U-"shaped (P=0.0001) and "V-" shaped fissures (P=0.0018). CONCLUSIONS: Pit and fissure morphology was a critical factor on sealant's penetration capacity; however, enamel substrate and sealant type did not affect sealant's penetration ratio.

Is the red fluorescence of dental plaque related to its cariogenicity?

It has been speculated that the red fluorescence emitted by dental plaque could be related to its cariogenicity. To test this hypothesis, we designed this crossover in situ study, with two experimental phases of 14 days each. Seventeen volunteers, wearing a palatal appliance with bovine enamel blocks, were instructed to drip a 20% sucrose solution (experimental group) or purified water (control group) onto the enamel blocks eight times daily. The specimens were removed after 4, 7, 10, and 14 days, and the red fluorescence of dental plaque formed on the enamel blocks was assessed using a quantitative light-induced fluorescence device. After the plaque removal, surface and cross-sectional microhardness tests were performed to assess the mineral loss. The comparisons were made by a multilevel linear regression analysis. We observed a significant increase in the red fluorescence of the dental plaque after longer periods of formation, but this trend was verified in both groups. The mineral loss assessed by the microhardness techniques, contrariwise, showed a significant increase only in the experimental group. In conclusion, the red fluorescence emitted by the dental plaque indicates a mature biofilm, but this fact is not necessarily associated with its cariogenicity.

Inhibition of enamel mineral loss by fissure sealant: an in situ study.

OBJECTIVES: This study evaluated the effect of fluoride and non-fluoride sealants on hardness decrease (HD) and marginal adaptation (MA) on enamel substrates after cariogenic challenge. METHODS: Occlusal enamel blocks, from human third molars, were randomly divided into six groups (n=12), according to occlusal fissures condition (S - sound; C - caries-like lesion; CF - caries-like lesion+topical fluoride) and sealants (F - FluroShield; H - Helioseal Clear Chroma). Lesion depths were 79.3±33.9 and 61.3±23.9 for C and CF groups, respectively. Sealants were placed on occlusal surface and stored at 100% humidity (37°C; 24h/d). HD was measured by cross-sectional microhardness analysis at the sealant margin distances: -1 (under sealant), 0 (sealant margin), 1, 2 (outer sealant). Sealant MA was observed by polarized light microscopy and scored according to: 0 - failure (no sealant MA or total sealant loss); 1 - success (sealant MA present). MA and HD were analysed by ANOVA-R and mixed model analysis, respectively. RESULTS: For HD (ΔS), F values (6900.5±3686.6) were significantly lower than H values (8534.6±5375.3) regardless of enamel substrates and sealant margin distances. Significant differences were observed among sealant margin distances: -1 (5934.0±3282.6)<0 (8701.5±6175.7)=1 (8473.2±4299.4)=2 (7761.5±4035.1), regardless of sealant and substrate. MA was similar for all groups (p≥0.05). CONCLUSION: MA was not affected by sealant type or substrate condition, whereas enamel HD was favourably impacted by fluoride in the sealant. In addition, sealants were more effective as a physical barrier than as its chemical potency in reducing enamel HD. CLINICAL SIGNIFICANCE: Sealing with a fluoride material is a recommended procedure to prevent caries of occlusal permanent molars in high-caries-risk patients, even though those exhibiting white spot lesions, since the enamel hardness decrease when fluoride sealant was used in vitro.

Influence of different enamel substrates on microtensile bond strength of sealants after cariogenic challenge.

PURPOSE: To evaluate the microtensile bond strength (µTBS) of resin sealer on enamel substrates after cariogenic challenge. MATERIALS AND METHODS: Enamel blocks were obtained from human third molars and randomly divided into 6 groups (n = 10) according to enamel substrates (S: sound, CL: caries-like lesion, or CLTF: caries-like lesion + topical fluoride application) and sealant material (F: FluroShield, or H: Helioseal Clear Chroma). Sealants were placed on enamel surfaces, stored in 100% humidity (24 h, 37°C), and longitudinally sectioned into hourglass shapes. According to the groups, pH cycling was applied and the µTBS test was performed. The fracture patterns were assessed by SEM. RESULTS: Regarding substrates, the highest µTBS values in MPa were observed for CLTF enamel (26.0 ± 7.6), followed by S (22.0 ± 7.4) and CL (15.5 ± 4.9). A significant interaction was found between material and pH cycling (p = 0.0395). F (23.9 ± 7.6) showed higher µTBS values than H (18.3 ± 7.5) when submitted to pH cycling. The majority of samples presented mixed failure. CONCLUSIONS: Enamel substrate significantly affected µTBS, with the highest values for remineralized caries-like enamel lesions. Furthermore, µTBS values were dependent on both materials and pH cycling.

Low-fluoride toothpaste and deciduous enamel demineralization under biofilm accumulation and sucrose exposure.

Because low-fluoride toothpaste (500 p.p.m. F) has not clearly been shown to be effective for controlling caries in caries-active children, this experimental in situ study was conducted to evaluate whether its effect, when compared with a conventional toothpaste (1,000-1,500 p.p.m. F), would depend on the cariogenic challenge. During four phases of 14 d each, 14 volunteers used 500 or 1,100 p.p.m. F toothpaste and wore palatal appliances containing deciduous enamel slabs, on which biofilm was accumulated and exposed to 20% sucrose solution at frequencies increasing from two to eight times per day. The F concentration was determined in the biofilm formed, and enamel demineralization was assessed by surface hardness loss (% SHL) and integrated area of hardness x lesion depth (DeltaS). The F uptake by enamel was also determined. Fluoride in biofilm fluid and solids was statistically higher when conventional F toothpaste was used. The toothpastes did not differ statistically in terms of % SHL, DeltaS, and F in enamel, but only the conventional F toothpaste significantly reduced caries-lesion progression according to the frequency of sucrose exposure. The findings suggest that the high-F availability in biofilm, resulting from the use of conventional toothpaste compared with low-F toothpaste, may be important for reducing caries-lesion progression in conjunction with a high frequency of sucrose exposure.

Effect of starch on the cariogenic potential of sucrose.

Since in vitro and animal studies suggest that the combination of starch with sucrose may be more cariogenic than sucrose alone, the study assessed in situ the effects of this association applied in vitro on the acidogenicity, biochemical and microbiological composition of dental biofilm, as well as on enamel demineralization. During two phases of 14 d each, fifteen volunteers wore palatal appliances containing blocks of human deciduous enamel, which were extra-orally submitted to four groups of treatments: water (negative control, T1); 2 % starch (T2); 10 % sucrose (T3); and 2 % starch+10 % sucrose (T4). The solutions were dripped onto the blocks eight times per day. The biofilm formed on the blocks was analysed with regard to amylase activity, acidogenicity, and biochemical and microbiological composition. Demineralization was determined on enamel by cross-sectional microhardness. The greatest mineral loss was observed for the association starch+sucrose (P<0.05). Also, this association resulted in the highest lactobacillus count in the biofilm formed (P<0.05). In conclusion, the findings suggest that a small amount of added starch increases the cariogenic potential of sucrose.

In situ study of sucrose exposure, mutans streptococci in dental plaque and dental caries

O objetivo deste estudo foi investigar a relação entre exposição à sacarose, níveis de estreptococos do grupo mutans e cárie dental. Voluntßrios adultos participaram neste estudo cruzado realizado em 4 fases de 28 dias cada. Os voluntários utilizaram dispositivos intra-orais palatinos contendo blocos de esmalte dental humano e gotejaram solução de sacarose 20 por cento sobre os blocos dentais de 0 a 8 vezes/dia. Após cada fase, as unidades formadoras de colônias (UFC) foram determinadas na placa dental e cárie foi avaliada atravéz de microdureza da lesão do esmalte. Freqüência do uso de sacarose não teve efeito estatisticamente significante nos níveis de estreptococos do grupo mutans. Nos testes de microdureza, diferenças significativas (p<0,05) em relação à área de perda mineral somente foram observadas quando a exposição à sacarose foi de 8 vezes/dia. Resultados similares foram obtidos quando a microdureza da lesão de cárie foi avaliada a cada distância da superfície do esmalte.