The effect of silver nanoparticles in addition to sodium fluoride on remineralization of artificial root dentin caries.

BACKGROUND: Silver nanoparticle was developed to overcome the drawback of silver diamine fluoride. However, evidence is limited, especially in root caries. The aim of this study was to evaluate the remineralization effect of silver nanoparticles on root caries. MATERIALS AND METHODS: Fifty-five root human dentin slices size 5 × 5 mm2 from patients aged over 60 years old were immersed in demineralized solution to create artificial caries. Specimens were allocated into five groups according to the remineralizing agents: silver diamine fluoride (SDF), silver nanoparticles solution (AgNPs), silver nanoparticle solution followed by sodium fluoride varnish (AgNPs+NaF), sodium fluoride varnish (NaF), and tap water. After 8 days of pH-cycling challenge, the microhardness test, lesion depth evaluation, dentin surface morphology, and elemental analysis were performed. Data was analysed using F-test One-way ANOVA followed by Tukey's post hoc test and paired T-test. RESULTS: All test groups demonstrated a significantly higher microhardness value and lower lesion depth compared with the control group. AgNPs+NaF and NaF-treated groups showed lower efficacy than SDF. Crystal precipitation was presented in all groups composed of silver. CONCLUSION: Addition of fluoride varnish did not benefit for silver nanoparticles in preventing further demineralization. SDF provides the highest effectiveness in elderly root carious dentin.

Change in surface hardness of enamel by a cola drink and a CPP-ACP paste.

OBJECTIVES: This in vitro study used surface microhardness to evaluate whether a paste containing casein phosphopeptide amorphous calcium phosphate (CPP-ACP) can reharden tooth enamel softened by a cola drink, and how different saliva-substitute solutions affect the enamel hardness. METHODS: Twenty-four bovine incisors, each tooth consisting of treatment and control halves, were immersed in a cola drink (Coke) for 8 min, then placed under a 0.4 mL/min drip with various saliva-substitute solutions. The saliva-substitute solutions were: saliva-like solution (SLS) with 1 ppm fluoride, SLS without fluoride, and Biotene mouthwash. CPP-ACP paste was applied to the treatment halves for 3 min at 0, 8, 24, and 36 h. Knoop microhardness measurements were performed at baseline, after the cola drink immersion, and after 24 and 48 h contact with saliva-substitute solution. RESULTS: Enamel hardness significantly decreased after immersion in cola drink (ANOVA, p<0.05). After contact with saliva-like solutions for 48 h, those treated with CPP-ACP paste were significantly harder than those untreated regardless of the presence of 1 ppm fluoride in the saliva-like solution (ANOVA, p<0.05). Biotene mouthwash significantly softened the enamel surface (ANOVA, p<0.05). Two-way ANOVA showed significant effects of the CPP-ACP paste application and types of saliva-substitute solutions on the changes in surface hardness of the softened enamel at a significance level of 0.05. CONCLUSION: The application of CPP-ACP paste with continuous replenishment of saliva-like solution for 48 h significantly hardened enamel softened by a cola drink. Biotene mouthwash softened enamel surface after 48 h contact.

Shear bond strength of dual-cured and self-cured resin composites to dentin using different bonding agents and techniques.

This study determined the effects of bonding agents on the shear bond strength of dual- and self-cured resin composites to dentin. Two light-cured dentin bonding agents (Excite and One-Step) and a dual-cured bonding agent (Excite DSC) were compared. Light activation of the bonding agents prior to placement of the resin composites was also evaluated. This in vitro study was performed on 120 extracted non-carious human third molars. The occlusal part of the crowns was removed to expose a flat dentin surface. The teeth were then randomly divided into three major groups for Excite, One-Step and Excite DSC as bonding agents. The specimens in each adhesive group were divided into four subgroups: with and without light activation of the bonding agent and with dual-cured (Luxacore Dualcure, DMG, Hamburg, Germany) or light-cured resin (Luxacore, DMG, Hamburg, Germany) composites. After placing the restorations, the specimens were kept in water at 37 degrees C for 24 hours before being tested for shear bond strength on an Instron universal testing machine at a crosshead speed of 0.5 mm/minute. The results showed that the shear bond strength of dual-cured resin composite to dentin was significantly higher than that of self-cured resin composite (p = 0.017). Light activation of the bonding agents prior to applying the resin composites led to a significantly higher shear bond strength of the resin composites to dentin, compared to no light activation (p < 0.05).

Determination of elastic modulus of dentin by small spherical diamond indenters.

A nano-indentation test was applied to determine elastic modulus (E) and hardness (H) of dentin. Three spherical indenters with nominal radii of 20, 5 and 1 microns were used and load/partial-unload cycles were repeated. Each cycle provided E and contact pressure or Meyer's hardness. The plot of contact pressure versus penetration depth was converted into a normalized indentation stress-strain relationship, which was used to select the optimum maximum indentation force for each indenter. The results were compared with those determined by the conventional triangular pyramidal (Berkovich) indenter technique. The comparable E value, irrespective of radius, was 19.5-20.9 GPa and the 1 micron indenter was able to provide E values of peritubular (28.0 GPa) and intertubular dentin (14.9 GPa). The H values generated with the Berkovich indentation technique were comparable to those determined by the spherical indenter technique at indentation strains of 0.9 and 0.5 for the 1 and 5 microns indenters.

A comparison of the mechanical properties of three glass-ionomer cements.

A comparison was made on the mechanical properties of three glass-ionomer cements, one of which was of experimental fiber-reinforcing and auto-curing type. Two others were proprietary auto-curing and light-activating cements. Biaxial flexure test was conducted on disc samples. Three-point bending test was also carried out on bar samples to determine modulus of elasticity and strength. All samples were kept at 37 degrees C and 100% RH for 24 h before testing under ambient conditions. A prolonged fracture process was observed in the experimental cement, demonstrating the effect of fiber incorporation in stabilizing the fracture process. The proprietary cements failed in a brittle manner. Comparison of the mechanical properties identified three characteristics. These were a high Weibull modulus resulting from the stabilization in fracture process, a modulus of elasticity value comparable to that of dentin, and a high biaxial flexure strength close to that of a dental resin composite.