Sadao Wakumoto

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.

Vibrational Analysis by Raman Spectroscopy of the Interface Between Dental Adhesive Resin and Dentin

The Raman microprobe technique was applied for analysis of the molecular components at the adhesive interface between 4-META/MMA-TBB resin and dentin. The Raman spectra showed that the 4-META molecules in monomer solution were mostly hydrolyzed into 4-MET molecules, which were then co-polymerized with MMA molecules to form resin and resin-reinforced dentin layers. On the basis of line analysis by the Raman microprobe, resin molecules were estimated to penetrate 6 μm into the dentin from the interface. Raman intensity studies indicated that the concentration of 4-MET molecular units in the resin-reinforced dentin was more than four times the concentration in the original monomer solution. This demonstrated the excellent infiltration ability of 4-MET monomer into dentin substrate in situ.

Effect of water sorption and thermal stress on cavity adaptation of dental composites.

The effect of water sorption of composite and thermal stress on the marginal adaptation to the dentin cavity wall was evaluated by measurement of the gap width between composite fillings and the dentin cavity wall. The wall of a cylindrical dentin cavity prepared in the proximal surface of extracted human molars was cleaned with neutralized 0.5 M EDTA and pre-treated with one of three experimental dentin primers [35% hydroxyethyl methacrylate (HEMA), 35% HEMA containing 5% glutaraldehyde, and 35% glyceryl methacrylate]. A light-activated composite (Silux, 3M Co., St. Paul, MN) was used to fill the cavity after application of a bonding agent (Clearfil New Bond, Kuraray Co., Osaka, Japan). The marginal gap width was measured after the specimens were immersed in water and thermal-cycled. The initial contraction gap of the tested bonding systems was closed completely by the water sorption of the composite for six hours, and such a marginal adaptation was not interrupted by 60 thermal cycles between 10 and 45 degrees C. Among the dentin primers tested, only the 35% aqueous solution of glyceryl methacrylate mediated gap-free fillings in all specimens.

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.

Bonding Efficacy of Erythritol Methacrylate Solutions as Dentin Primers

The bonding efficacy of aqueous solutions of two kinds of erythritol methacrylates as dentin primers was examined by measurement of the polymerization contraction gap of a light-activated resin composite in a cylindrical dentin cavity and the tensile bond strength of the composite to the flat dentin surface. The dentin surface was cleaned with neutralized 0.5 mol/L EDTA and pre-treated with a meso-erythritol or penta-erythritol methacrylate solution, followed by application of a commercial dentin bonding agent (Clearfil New Bond) and a resin composite. Among the tested primers, a 40% meso-erythritol methacrylate solution was shown to be the most effective because, in contrast to the other primers, contraction gap formation by the composite was prevented in all tested specimens.

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.

A delayed hypersensitivity reaction to dentine primer in the guinea-pig.

OBJECTIVE This study was undertaken to examine the possibility of a delayed hypersensitivity reaction or contact dermatitis occurring in the guinea-pig in response to methacrylate derivatives used as experimental dentine primers. METHODS The dentine primers 2-HEMA, GM, MA and MMA were tested in a guinea-pig maximization test. RESULTS All the dentine primers tested produced positive delayed hypersensitivity reactions in the guinea-pig. MMA produced the most severe reaction. CONCLUSION It is concluded that in the clinical situation, clinicians and other members of the dental team should be aware of the need for careful handling of the dentine primers tested.

The efficacy of dentine adhesive to sclerotic dentine

OBJECTIVE To evaluate the effect of a dentine bonding system to sclerotic dentine in comparison with normal dentine. METHODS The efficacy of the dentine bonding system to sclerotic dentine was examined by measuring wall-to-wall polymerization contraction gap width. The dentine cavity wall was pretreated with an experimental dentine bonding system with and without a dentine primer. The dentine primer was glyceryl mono-methacrylate (Blemmer GLM, NOF Corp., Tokyo, Japan) (GM), which contained esterified methacrylate with a polyvalent alcohol, which is similar to 2-HEMA. The structure of sclerotic dentine and the changes to that structure caused by etching were observed using a scanning electron microscope (SEM). RESULTS With GM priming, complete marginal integrity was obtained regardless of the type of dentine. Without GM priming, complete marginal integrity was obtained in half of the specimens of the sclerotic dentine, and was not obtained in any of the specimens of normal dentine. In the SEM study, the structure of sclerotic dentine was considered to be viable for adhesion. However, this was not the case when etched with phosphoric acid. CONCLUSION It was concluded that sclerotic dentine had a clear advantage over normal dentine with regard to the adaptation of resin composites. Therefore the structure of sclerotic dentine possesses a naturally derived structure to which a primer may attach. Sclerotic dentine is part of the bodys natural defenses and should be preserved. It should not be exposed to acid etching which would damage its structure.