Evaluation of antimicrobial potential and surface morphology in thin films of titanium nitride and calcium phosphate on orthodontic brackets.

INTRODUCTION: The goal of this research was to experimentally evaluate the surface morphology and adhesion capacity of Streptococcus mutans (U159) on brackets with thin films of titanium nitride (TN) and of titanium nitride doped with calcium phosphate (TNCP). METHODS: Twenty-four metallic brackets were equally allocated to 3 groups (n = 8), according to the type of covering (no covering, TNCP, and TN). The coatings were deposited by cathodic cage (TNCP and TN groups) and were evaluated by scanning electron microscopy and energy dispersive x-ray spectrometry. The biofilm formation of S. mutans on the surface of brackets was determined by crystal violet assay and subsequent optical density quantification. RESULTS: There was homogeneity on the surface morphology of the tie wing area in all groups, whereas the TNCP group has presented particles in the slot. After 24 hours, a biofilm of S. mutans was formed in all the observed groups. The optical density obtained in all 3 groups was similar (no covering, 0.347 ± 0.042; TNCP, 0.238 ± 0.055; TN, 0.226 ± 0.057), with no statistically relevant difference (P = 0.06). CONCLUSIONS: The thin film of TNCP has altered the surface of the bracket's slot, whereas the coatings of TN and TNCP have not altered the superficial morphology of the tie wings. The presence of coatings have not influenced the formation of the S. mutans biofilm on the surface of metallic brackets.

Effect of oxalate desensitizer on the durability of resin-bonded interfaces.

Potassium oxalate desensitizers were previously shown to effectively reduce the immediate permeability of resin-bonded dentin. The current study evaluated whether the effect of the combined application of oxalate with etch-and-rinse adhesives interferes with the durability of resin-dentin bonds when using etch-and-rinse adhesives. The bond strength of resin-bonded dentin specimens composed of two-step or three-step etch-and-rinse adhesives (Single Bond, One-Step and Scotchbond Multi-Purpose, respectively) was tested immediately (24 hours) and after 12 months of water storage. The adhesives were used either according to the manufacturers' instructions (control groups) or after treating acid-etched dentin with a potassium oxalate gel (BisBlock, BISCO, Inc). The treatment of dentin with potassium oxalate was shown to negatively affect the baseline bond strength of resin-bonded dentin specimens, regardless of the adhesive used (p < 0.05). After storage, the bond strength of the resin-bonded interfaces was significantly reduced for all the tested groups (p < 0.001). Nevertheless, the rate of decreasing bond strength was significantly lower for oxalate-treated specimens than for the controls (p < 0.05).

Permeability of Dental Adhesives - A SEM Assessment.

OBJECTIVES: To morphologically evaluate the permeability of different commercial dental adhesives using scanning electron microscopy. METHODS: SEVEN ADHESIVE SYSTEMS WERE EVALUATED: one three-step system (Scotchbond Multi-Purpose - MP); one two-step self-etching primer system (Clearfil SE Bond - SE); three two-step etch-and-rinse systems (Single Bond 2 - SB; Excite - EX; One-Step - OS); and two single-step self-etching adhesives (Adper Prompt - AP; One-Up Bond F - OU). The mixture of primer and bond agents of the Clearfil SE Bond system (SE-PB) was also tested. The adhesives were poured into a brass mold (5.8 mm x 0.8 mm) and light-cured for 80 s at 650 mW/cm2. After a 24 h desiccation process, the specimens were immersed in a 50% ammoniac silver nitrate solution for tracer permeation. Afterwards, they were sectioned in ultra-fine slices, carbon-coated, and analyzed under backscattered electrons in a scanning electron microscopy. RESULTS: MP and SE showed slight and superficial tracer permeation. In EX, SB, and OS, permeation extended beyond the inner superficies of the specimens. SE-PB did not mix well, and most of the tracer was precipitated into the primer agent. In AP and OU, "water-trees" were observed all over the specimens. CONCLUSIONS: Different materials showed distinct permeability in aqueous solution. The extent of tracer permeation varied according to the composition of each material and it was more evident in the more hydrophilic and solvated ones.

Effects of ethanol addition on the water sorption/solubility and percent conversion of comonomers in model dental adhesives.

OBJECTIVES: This study evaluated the kinetics of water uptake and percent conversion in neat versus ethanol-solvated resins that were formulated to be used as dental bonding agents. METHODS: Five methacrylate-based resins of known and increasing hydrophilicities (R1, R2, R3, R4 and R5) were used as reference materials. Resins were evaluated as neat bonding agents (100% resin) or they were solvated with absolute ethanol (95% resin/5% ethanol or 85% resin/15% ethanol). Specimens were prepared by dispensing the uncured resin into a circular mold (5.8 mm x 0.8 mm). Photo-activation was performed for 80s. The water sorption/diffusion/solubility was gravimetrically evaluated, while the degree of conversion (DC) was calculated by Fourier-transform infrared spectroscopy. RESULTS: Water sorption increased with the hydrophilicity of the resin blends. In general, the solvated resins exhibited significantly higher water sorption, solubility and water diffusion coefficients when compared to their corresponding neat versions (p<0.05). The only exception was resin R1, the least hydrophilic resin, in which neat and solvated versions exhibited similar water sorption (p>0.05). Addition of ethanol increased the DC of all resins tested, especially of the least hydrophilic, R1 and R2 (p<0.05). Despite the increased DC of ethanol-solvated methacrylate-based resins, it occurs at the expense of an increase in their water sorption/diffusion and solubility values. SIGNIFICANCE: Negative effects of residual ethanol on water sorption/solubility appeared to be greater as the hydrophilicity of the resin blends increased. That is, the use of less hydrophilic resins in dental adhesives may create more reliable and durable bonds to dentin.