No abstract

This study was conducted to assess the clinical effect of photodynamic therapy (PDT) in the decontamination of the deep dentin of deciduous molars submitted to partial removal of carious tissue. After cavity preparation, dentin samples were taken from the pulp wall of nineteen deciduous molars before and after PDT application. Remaining dentin was treated with 0.01% methylene blue dye followed by irradiation with an InGaAlP diode laser (λ -660 nm; 40 mW; 120 J/cm 2 ; 120 s). Dentin samples were microbiologically assessed for the enumeration of total microorganisms, Lactobacillus spp. and mutans streptococci. There was no significant difference in the number of colony-forming units (CFU) for any of the microorganisms assessed (p > 0.05). Photodynamic therapy, using 0.01% methylene blue dye at a dosimetry of 120 J/cm 2 would not be a viable clinical alternative to reduce bacterial contamination in deep dentin.

Aim: This study evaluated the acidogenicity of human milk by the dental biofilms of children with and without early childhood caries (ECC). Method: Biofilms of 16 children (7 with ECC; 9 caries free) were exposed to human milk or 10% sucrose solution in the crossover design, and the biofilm pH was determined. Results: Breastfeeding did not provoke a decrease in biofilm pH, irrespective of the children's caries status, whereas sucrose decreased the pH for both groups. In addition, higher ΔpH_5min (pH variation occurring at 5 min) was observed in the biofilms of ECC children (p < 0.05). The results suggest that breastfeeding may not contribute to ECC.

Dental biofilm bacteria can bind calcium ions and release them during a pH drop, which could decrease the driving force for dental demineralization (i.e. hydroxyapatite dissolution) occurring at reduced pHs. However, the kinetics of this binding and release is not completely understood. Here we validated a method to evaluate the kinetics of calcium binding and release to/from Streptococcus mutans, and estimated the importance of this reservoir as a source of ions. The kinetics of calcium binding was assessed by measuring the amount of bound calcium in S. mutans Ingbrit 1600 pellets treated with PIPES buffer, pH 7.0, containing 1 or 10 mM Ca; for the release kinetics, bacterial pellets previously treated with 1 mM or 10 mM Ca were exposed to the calcium-free or 1 mM Ca PIPES buffer, pH 7.0, for up to 60 min. Binding and release curves were constructed and parameters of kinetics were calculated. Also, calcium release was assessed by exposing pellets previously treated with calcium to a pH 5.0 buffer for 10 min. Calcium binding to bacteria was concentration-dependent and rapid, with maximum binding reached at 5 min. On the other hand, calcium release was slower, and according to the calculations, would never be complete in the groups pretreated with 10 mM Ca. Decreasing pH from 7.0 to 5.0 caused a release of calcium able to increase the surrounding fluid calcium concentration in 2 mM. The results suggest that dental biofilm bacteria may act as a calcium reservoir, rapidly binding ions from surrounding fluids, releasing them slowly at neutral pH and promptly during a pH drop.

Sucrose is the most cariogenic dietary carbohydrate because it is a substrate for insoluble extracellular polysaccharide (IEPS) production in dental biofilms, which can proportionally decrease bacterial density and, consequently, the number of biofilm calcium (Ca) binding sites. Ca bound to bacterial cell walls can be released into the biofilm fluid during a cariogenic challenge, reducing the driving force for mineral dissolution provoked by the pH drop. Thus, we investigated the effect of an IEPS-rich extracellular matrix on bacterial Ca binding after treatment with Ca solutions. Streptococcus mutans Ingbritt 1600 was cultivated in culture broths supplemented with 1.0% sucrose or 0.5% glucose + 0.5% fructose. The IEPS concentration in bacterial pellets was determined after alkaline extraction. Bacterial pellets were treated with 1 mM or 10 mM Ca ++ solutions at 37°C for 10 to 60 min. Ca binding to bacterial pellets, determined after acid extraction using the Arsenazo III reagent, was fast and concentration dependent. Although the IEPS concentration was approximately ten times higher in bacterial pellets cultivated in sucrose as compared to its monossaccharides, bound Ca concentration after Ca treatment was similar in both conditions. These results suggest that IEPS may not influence the amount of Ca bound to reservoirs of dental biofilms.

It has been suggested that fluoride binding to dental biofilm is enhanced when more bacterial calcium binding sites are available. However, this was only observed at high calcium and fluoride concentrations (i.e., when CaF₂ precipitation may have occurred). We assessed fluoride binding to Streptococcus mutans pellets treated with calcium and fluoride at concentrations allowing CaF₂ precipitation or not. Increasing calcium concentration resulted in a linear increase (p < 0.01) in fluoride concentration only in the pellets in which CaF₂ precipitated. The results suggest that CaF₂ precipitation, rather than bacterially bound fluoride, is responsible for the increase in fluoride binding to dental biofilm with the increase in calcium availability.

Calcium fluoride-like materials ("CaF 2 ") formed on dental surfaces after professional fluoride application are unstable in the oral environment but can be retained longer with a daily NaF mouthrinse. We tested the effect of twice daily 0.05% NaF rinses on the retention of "CaF 2 " formed on enamel and dentine after applying acidulated phosphate fluoride (APF). "CaF 2 " formed on enamel/dentine by APF application significantly decreased after exposure to artificial saliva and the 0.05% NaF rinse was ineffective to avoid this reduction. These findings suggest that the combination of APF and 0.05% NaF is not clinically relevant, either for caries or dental hypersensitivity.

Purpose. To evaluate the mineral ion loss of root dentine after treatment with 2% chlorhexidine solution (CHX) and to compare its yield and flexural strength (fs) after exposure to calcium hydroxide [Ca(OH)2]. Materials and Methods. Dentine bars (DB) were made from 90 roots of bovine incisors and randomized into three groups: GControl: distilled/deionized water (DDW), GNaOCl: 2.5% sodium hypochlorite + 17% EDTA, and GCHX: CHX + DDW. The release of phosphate (PO4) and calcium (Ca) ions was measured by spectrophotometry. The DB were exposed to Ca(OH)2 paste for 0, 30, 90, and 180 days. DB were subjected to the three-point bending test to obtain yield and fs values. The fracture patterns were evaluated (20x). Data were analyzed using Kruskal-Wallis and Dunn's post hoc tests or one- and two-way ANOVA followed by Tukey's post hoc test (α = 0.05). Results. GCHX showed lower PO43− and Ca2+ ionic release than GNaOCl (p < 0.001). For yield and fs, GCHX > GNaOCl in all periods (p < 0.001), except for yield strength values on 90 days (p = 0.791). A larger frequency of vertical fractures was observed in GNaOCl and that of oblique fractures in GCHX (p < 0.05). Conclusions. CHX prevented PO43− and Ca2+ loss and showed a tendency to preserve the yield and fs of root dentine over time following exposure to Ca(OH)2 paste.