H. Chigira

Self-etching dentin primers containing phenyl-P.

The dentin bonding efficacies of two commercial dentin bonding systems and experimental self-etching dentin primers composed of methacryloxyethyl hydrogen phenyl phosphate (Phenyl-P) and either hydroxyethyl methacrylate (HEMA) or glyceryl methacrylate (GM, 2,3-dihydroxypropyl methacrylate) were examined. The wall-to-wall polymerization contraction gap width of a commercial light-activated resin composite in a cylindrical dentin cavity and the tensile bond strength to a flat dentin surface were measured. Changes in dentin hardness were determined by Micro Vickers Hardness measurement, and an SEM observation was performed after priming. Formation of a contraction gap was completely prevented by the application of Phenyl-P diluted in HEMA or GM solution combined with a commercial dentin bonding agent, although gap formation was evident in nearly half of the specimens with both commercial dentin bonding systems. The mean tensile bond strengths of the tested groups varied from 16.3 to 20.7 MPa, and there were no significant differences between groups. Based on the measurement of Micro Vickers Hardness and SEM observation after priming, a slight reduction in dentin hardness was observed. However, this reduction in dentin hardness due to self-etching priming did not significantly correlate with either contraction gap width or tensile bond strength.

Efficacy of various commercial dentin bonding systems

OBJECTIVES The purpose of this study was to test the bonding efficacy of fifteen commercial dentin bonding systems and also to determine the effect of various commercial dentin cleaners on bonding and dentin hardness. METHODS Each commercial bonding system was examined by two methods: 1) measuring the maximum contraction gap of a light-cured composite in a cylindrical dentin cavity; and 2) determine the tensile bond strength to a flat dentin surface. In addition, various commercial dentin cleansers were investigated to determine if dentin hardness was reduced after cleaning. As a control, the dentin surface was cleaned with neutralized EDTA prior to the combined application of an experimental dentin primer, a commercial bonding agent, and a commercial light-cured composite. RESULTS The study demonstrated that complete marginal adaptation was obtained by the experimental dentin bonding system used as the control. However, it was not possible to completely prevent gap formation with the commercial dentin bonding systems tested. A high correlation (R = 0.88) was observed between maximum contraction gap width and reduction of hardness only in the group in which the dentin was rinsed after cleaning. SIGNIFICANCE It is very important to combine optimal dentin cleansers, primers, and bonding agents to compensate for the polymerization contraction stress of the composite. Therefore, it was speculated that the commercial dentin bonding systems tested in this study consisted of unsuitable materials.

Factors affecting tensile bond strength of composite to dentin

Five factors which might affect the tensile bond strength of an experimental dentin bonding system to extracted human dentin were evaluated. Flat dentin surfaces of extracted human teeth were cleaned with 0.5 mol/L EDTA and pretreated with 35% glyceryl methacrylate solution. A commercial light-activated composite was then bonded using a commercial bonding agent. The five evaluated factors were: 1) embedding or not embedding the specimens in an epoxy resin, 2) thickness of the specimens, 3) crosshead speed during measurement, 4) storage time of the specimens, and 5) dentin substrate depth. Measurements were made of the bond strengths that resulted from the effects of these varied factors. These measurements were compared to a control group. Only the specimen thickness significantly affected the measured bond strength, and extremely thin specimens (about 1 mm) showed the lowest bond strength.

Effects of self-etching primers on dentin.

The effects of self-etching dentin primers on the hardness of dentin was evaluated by determination of the Vickers Hardness of both untreated dentin and dentin treated with different primers. Several experimental primers were prepared by dilution of dicarbonates or their esterified salts with different ratios of HEMA to obtain ratios of 5% and 35% by weight. Methacryloxyethyl succinate (MES) and Methacryloxyethyl phthalate (MEP) experimental primers caused less softening of dentin than did maleic acid diluted with HEMA or a commercial dentin primer (Scotchprep, 3M). A high correlation was observed between the pH of a primer and the hardness of dentin treated with the primer. A correlation was also observed between the hardness of treated dentin and the wall-to-wall polymerization contraction of a light-curing microfilled resin (Silux, 3M).

Bonding efficacy and interfacial microstructure between resin and dentine primed with glyceryl methacrylate

OBJECTIVES To evaluate the effect of two experimental primers based on glyceryl methacrylate (GM, 2,3-dihydroxypropyl methacrylate) and 2-hydroxyethyl methacrylate (2-HEMA) on the marginal adaptation of light-cured composite placed into cylindrical dentine cavities and to study the interfacial microstructure. METHODS The bonding efficacy of two experimental dentine primers combined with a dentine cleanser composed of either 0.5 mol l-1 EDTA neutralized to pH 7.4 by sodium hydroxide or 10% citric acid containing 3% ferric chloride (10-3 solution), and a commercial dentine bonding agent containing phosphate ester, were examined by measuring the wall-to-wall polymerization contraction gap of a commercial light-activated resin composite placed into cylindrical dentine cavities. The adhesive interface between the dentine and the dentine adhesive was observed using a transmission electron microscope (TEM). RESULTS The formation of a contraction gap was completely prevented by priming with GM, regardless of the dentine cleanser used. However, in groups primed with 2-HEMA, gap formation was observed in three and four specimens out of 10 in the groups that were cleaned with the EDTA and 10-3 solution, respectively. In samples primed with GM, a high-density layer was observed by TEM at the superficial dentine in the hybrid layer, which may have indicated a high monomer content, whereas no density variations were observed in the hybrid layer in samples primed with 2-HEMA.

Marginal adaptation of nine commercial intermediate resins

The bonding efficacy of nine commercially available intermediate resins was examined by measuring the maximum contraction gap of a light-activated composite in a cylindrical cavity of human dentin. With only one exception, the marginal adaptation of the composite improved significantly when the intermediate resins were combined with an experimental dentin cleaning system of the neutralized 0.5 mol/L EDTA and a dentin primer composed of a 35% aqueous solution of either hydroxyethyl methacrylate (HEMA) or glyceryl methacrylate (GM). Complete marginal adaptation was obtained with four tested materials when dentin was pre-treated with EDTA and GM.

Effects of polyvalent alcohol solutions as dentine primers

OBJECTIVES The purpose of this study was to examine the bonding effect of polyvalent alcohols as dentine primers without a methacrylate group, which may cause contact dermatitis. METHODS The efficacy of polyvalent alcohols as dentine primers was estimated by measuring the wall-to-wall polymerization contraction gap width of a light-activated resin composite filled in a cylindrical dentine cavity in an extracted human tooth. A dentine cavity was cleaned with ethylenediaminetetraacetic acid (EDTA) and primed with an aqueous solution of either ethylene glycol, glycerol, erythritol, xylitol or sorbitol at concentrations of between 25 and 75 wt%. A light-cured resin composite was filled after the application of a commercial dual-cured bonding agent. RESULTS Contraction gap formation was completely prevented only in the group in which the dentine cavity had been primed with an aqueous solution of 62.5% wt% ethylene glycol. Furthermore, in the measurement of a tensile bond strength to a flat dentine surface, high tensile bond strength (17.5 +/- 4.4 MPa) was observed in the group that was primed with 62.5% ethylene glycol solution. CONCLUSION These results suggest that it is not necessary to dissolve methacrylates in a dentine primer when the primer is dried with a blast of compressed air before application of a polymerizable, suitable bonding agent. It is concluded that a dentine primer composed of polyvalent alcohol solutions without a methacrylate group which may cause contact dermatitis, is effective as a dentine primer, affects the dentine surface, and promotes the efficacy of the dentine bonding system.

Adaptation of a resin composite in vivo

OBJECTIVE The adaptation of experimental dentine bonding systems has been evaluated in vivo. METHODS A cylindrical cavity which extended into dentine was prepared in the facial surface of vital teeth that were to be extracted for orthodontic reasons. The preparations were restored with a commercial light-activated resin composite that was mediated by experimental dentine bonding systems. The restored teeth were extracted as soon as possible following polymerization of the composite. The marginal and internal adaptation of the resin composite restoration was observed under a light microscope in both horizontal and longitudinal sections of the teeth immediately after extraction. RESULTS Of the experimental dentine bonding systems investigated, those including a primer of glyceryl methacrylate showed complete adaptation whereas those with primers of 2-HEMA showed a contraction gap in three out of 10 specimens.