The Journal of Adhesive Dentistry, 01/2003

The objectives of this investigation were to analyze the adhesive interactions between type 1 collagen and two hydrophilic monomer primers (ligands) for dentin bonding through computer modeling and a novel immunochemical binding assay method. The hydrophilic monomers studied included 2-hydroxyethyl methacrylate (HEMA) and 2-acryloyloxyethyl phosphate (PA). For computer modeling studies, a triple helical model structure of collagen fibril extracted from a public domain Protein Data Bank was used. The ligand conformations were modeled and optimized by Sybyl, and their interactions with the triple helical collagen structure in a solvent environment of water were simulated by AutoDock software. The effect of ligand binding to subsequent monoclonal antibody binding was also studied using an immunochemical binding assay method developed by us. The computer simulation results and binding assay results were analyzed for relationships pertinent to collagen-ligand interaction in bonding of dentin primers to demineralized dentin. Computer docking results indicate that ligand binding to collagen is favored to occur at cavity sites on the collagen molecular surfaces, where steric and electrostatic effects may play a critical role in mediating van der Waals and Coulombic interactions between ligand and receptor molecules. Prior ligand exposure of collagen reduces subsequent antibody binding during in vitro experiments. Differences in antibody binding were observed both as a function of ligand type and its concentration. Both steric complementarity and electrostatic complementarity conditions were observed in the docking site selection. Under conditions of ligand binding, antibody binding is diminished as a function of ligand structure and its concentration. The results suggest that approaches combining computer modeling and in vitro binding assay methods are powerful tools in evaluating dentinal adhesion at the atomic and/or molecular level.

The purpose of this study was to evaluate the effects of concentration and pH of silver nitrate solution on nanoleakage in occlusal flat surfaces bonded with three dentin bonding systems. The dentin bonding systems used in this study were Single Bond, PermaQuik, and Prompt L-Pop. Flat occlusal dentin surfaces from extracted human molars were bonded with one of the dentin bonding systems. The teeth from each subgroup (n = 4) were placed in one of the following silver nitrate solutions: 50% w/v, 25% w/v, 10% w/v, and 2% w/v (pH 3.4, 4.2, 4.4, and 4.9, resp), and 50% w/v buffered to pH 6 in total darkness for 24 h, rinsed in running water for 5 min, immersed in photodeveloping solution for 24 h, and exposed to light for 8 h. Specimens were sectioned, mounted on stubs, carbon coated and observed in a Field Emission SEM using backscattered electron mode. FE-SEM images showed that samples from different concentrations of silver nitrate solution had leakage patterns similar to that of samples from 50% w/v for all dentin bonding systems. The concentrations and pH values of silver nitrate solutions did not affect leakage patterns in any of the systems. A lower concentration of silver nitrate solution may be used in a nanoleakage study, although the present results need to be replicated to determine an ideal concentration.

To determine if adverse chemical interaction and adhesive permeability are both responsible for the incompatibility between a single-step, self-etching adhesive and chemically-cured or dual-cured composites. Bonding was performed with Xeno CF Bond (Dentsply-Sankin), on either hydrated (H) or dehydrated (DH) human dentin. For microtensile bond strength evaluation, a dual-cured hybrid composite (Bis-Core) was activated using: (1) the light-cured (L) mode (base syringe only), (2) delayed light activation (DL) (base syringe left on top of cured adhesive in the dark for 20 min before activation), and 3) the chemically-cured (C) mode (base and catalyst syringes in the dark). A chemical co-initiator (B; BondLink) was also applied to the cured adhesive before coupling with the composite in chemically-cured mode. This resulted in seven experimental groups: (1) L-H (control); (2) DL-H; (3) DL-DH; (4) C-H; (5) C-DH; (6) C-B-H; and (7) C-B-DH. For transmission electron microscopy, the dual-cured composite in the seven groups was replaced with a light-cured microfilled composite (Metafil CX) and an experimental chemically-cured microfilled composite of the same composition. Specimens were immersed in ammoniacal silver nitrate for 24 h. After reduction of the diamine silver ions to silver, undemineralized and unstained sections were examined for nanoleakage within the resin-dentin interfaces of the seven groups. For the light-cured modes, bond strengths fell substantially in DL-H but not in DL-DH. For the chemically-cured modes, bond strengths were lowest in C-H and only increased slightly in C-DH. The use of a chemical co-initiator with the adhesive further improved the bond strength in C-B-H. Only C-B-DH was not significantly different from the control light-cured mode L-H. Two abnormal modes of silver deposition were observed in resin-dentin interfaces. A continuous layer of silver was observed when the chemically-cured composite was applied to the cured adhesive in the absence of the chemical co-initiator (C-H; C-DH). Silver-impregnated water blisters were identified when the chemically-cured composite was coupled to bonded hydrated dentin (C-H; C-B-H). Similar water blisters were seen in DL-H in which adverse chemical interaction should not occur. Adverse chemical interaction between catalytic components of chemically-cured composite and the tested single-step, self-etching adhesive was the major cause of reductions in bond strength, while adhesive permeability was a minor cause of bond strength reduction. The combination of these two factors accounts for the substantial reduction in bond strength when chemically-cured or dual-cured composites were coupled to bonded hydrated dentin.

It was the purpose of the study to investigate the short- and long-term bonding to enamel and dentin of a self-etching, one-step adhesive with and without separate curing of the adhesive. The bond strengths were measured both with a light- and with a self-curing resin composite. Multistep bonding systems served as controls. The bonding systems selected were Prompt L-Pop and, as controls, Solobond M, Solobond Plus, and Optibond FL. The resin composites Rebilda LC and Rebilda were bonded to plane enamel or dentin surfaces following application of the bonding systems used in accordance with the recommendations of the respective manufacturers. With Prompt L-Pop, a separate cure of the adhesive was also investigated. After being stored in water at 37°C for 1 day or 1 year, the bonded specimens were broken in shear. The strength of the bond to enamel of Prompt L-Pop increased with time in water, while the bond strengths of the other systems did not change statistically significantly. There was no difference in bond strengths to dentin measured after 1 day and 1 year in water. The self-curing resin composite did not bond with Prompt L-Pop. Separate curing of Prompt L-Pop had no influence on bond strengths. On the basis of this in vitro study, the self-etching, one-step bonding system Prompt L-Pop, although less efficient than the three-step system Optibond FL, would seem to be a viable option compared to multistep systems, except when there is a need to mediate a bond to self-curing resin composite.

To evaluate dentin bond durability using current dentin adhesive resin bonding approaches over a 15-month period of water storage. Forty-four extracted human molars were polished with 600-grit SiC papers exposing occlusal dentin, and randomly distributed into four adhesive groups: total-etch 3-step (TE3) (Scotchbond Multi-Purpose, 3M ESPE), total-etch 2-step (TE2) (Single Bond, 3M ESPE), self-etch 2-step (SE2) (Clearfil SE Bond, Kuraray), and a self-etch 1-step (SE1) (Prompt L-Pop, 3M ESPE). A resin composite crown was incrementally formed and light cured to approximately 6 mm in height. Microtensile specimens were fabricated and stored in distilled water containing 0.5% chloramine T and tensile tested at 1 mm/min after 1, 6, and 15 months. The debond pathway was recorded as either involving the substrate or joint using scanning electron microscopy. SAS software was used to compute Weibull parameters and distributions, Log-rank and Wilcoxon tests were used for comparison of survival curves over time for each adhesive system and between adhesive systems. The TE2 was significantly weaker than TE3 and SE2 after 1 and 6 months of storage, but all three systems were equivalent after 15 months of storage. The SE1 system could not be tested due to 58 of 65 specimens failing during specimen preparation. Failure modes were observed to be dependent upon adhesive system, with only the total-etch 2-step system demonstrating an increasing involvement in the adhesive joint over time. Although differences in bond strength were observed across adhesive systems up to 6 months of storage, no differences were noted at 15 months. This may represent common degradative mechanisms.

The aim of this study was to assess the tensile bond strength of a resin-modified glass-ionomer cement (a: Fuji II LC) and three traditional glass-ionomer cements (b: Ketac-fil; c: Ketac Molar; d: Fuji IX) to caries-affected dentin. Forty human permanent molars with occlusal caries in dentin were selected, embedded in polyester resin, and ground until the carious dentin was exposed. Infected dentin was removed with curettes according to the atraumatic restorative technique (ART), and the tooth surface was smoothed with SiC paper. A bonding site, limited to 3 mm in diameter, was treated with polyacrylic acid for 10 s. After surface treatment, an inverted glass-ionomer cone was prepared for each specimen, using a split bisected Teflon matrix. The cones were immediately protected with a thin layer of nail varnish or bonding agent. Specimens were stored in distilled water at 37oC for 24 h, and then bond strength to failure was tested. The mean (SD) bond strengths in MPa were: a: 8.33 (2.35); b: 2.46 (1.60); c: 0.83 (1.18), and d: 1.45 (1.70). The data were analyzed using ANOVA and Tukey statistical tests. Fuji II LC, a resin-modified glass-ionomer cement, showed higher bond strength values and was statistically superior to the other groups, containing traditional glass ionomer cements (p 0.05). Findings showed that the traditional glass-ionomer cements tested in this study had lower mean bond strength values to caries-affected dentin than did the resin-modified glass-ionomer cement.

The objective of this in vitro study was to evaluate the microleakage in ceramic inlays using different resin cements with margins in enamel and cementum/dentin interfaces. Standard Class II MOD inlay cavities were prepared in 32 noncarious human premolars. The cavities were randomly divided into 4 groups (n = 8): Control group: cavities were treated with Single Bond and incrementally filled with a composite resin (P60); Enforce group: feldspathic ceramic inlays were luted using Prime & Bond 2.1 and Enforce; RelyX group: inlays were cemented with Single Bond and RelyX ARC; Resin Cement group: ceramic inlays were bonded using Single Bond and Resin Cement. Ceramic inlays were previously treated with 10% hydrofluoric acid for 2 min, followed by silane application. After 7 days of storage in distilled water, teeth were submitted to thermocycling. After applying nail varnish, specimens were immersed in 2% aqueous solution of methylene blue for 8 h. After washing, teeth were cut into three sections through the restorations, and the leakage was assessed using a standardized score. Data were submitted to statistical analysis using nonparametric tests (Mann-Whitney and Kruskal-Wallis). Dye leakage at margins in enamel was statistically lower (p 0.01) than at cementum/dentin interfaces. RelyX ARC performed better (p 0.05) than resin cement (enamel) and composite restorations (cementum/dentin). No other statistical differences were observed. Both the material and the substrate interface influenced microleakage of the ceramic inlays.

The purpose of this study was to photoelastically evaluate contraction stresses associated with various resin composite build-up procedures for pulpless molars. Photoelastic models of endodontically treated mandibular molars were fabricated to simulate a preparation for a full-cast crown. The model configuration included three lateral walls, but no post space. The buildups were made with dual-curing resin composite using the following procedures: 1) bulk dual cure, 2) bulk chemical cure, 3) horizontal two increments, dual cure, and 4) indirect. Five specimens were fabricated for each condition. The stresses developed in the models were recorded photographically in the field of a circular polariscope. The build-up procedures tested generated widely different stress distributions and intensities. The highest stresses were seen with the bulk dual-cure method. The slower polymerization chemical-cure group developed distributions similar to the bulk dual-cure group with a significantly lower fringe order. The two horizontal increments dual-cure techniques developed an individual group of fringes for each layer. Compared with the bulk dual-cure group, stresses around the occlusal margin were reduced by incrementalization, while fringes were more closely spaced at the line angles with a slightly lower fringe order. The indirect method demonstrated the lowest stress which extended over the smallest area. Contraction stress in resin composite buildups varied significantly depending upon the procedures of fabrication. The bulk dual-cure method developed the most severe contraction stresses, while the indirect technique resulted in significantly lower contraction stresses than the other techniques tested.