Atsufumi Manabe

Cooperation of Phosphate Monomer and Silica Modification on Zirconia

Ceramic restorations with resin-based adhesive systems have been the focus of recent attention in clinical dentistry. Yttrium-oxide-partially-stabilized zirconia (YPSZ) ceramics have optimized physical properties and exhibit favorable fracture toughness, though their bonding properties are problematic. Although functional phosphate monomers and silica-coating by tribochemical modification were expected to improve the bonding properties between YPSZ ceramics and resin-based adhesives, these two methods remain controversial. This study evaluated the efficiency of silica-coating by tribochemical modification of YPSZ ceramics. The application of phosphate monomer and a silane coupling agent on silica-coated YPSZ was also investigated. The silica-coating of YPSZ ceramics by tribochemical modification was not efficient, given the higher mechanical toughness of the densely sintered ceramics. Stable shear bond strength was achieved on silica-coated YPSZ ceramics with the cooperative interaction of phosphate monomer and silane coupling.

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.

Investigation of self-etching dentin primers

In order to simplify the dentin bonding procedures by combining the dentin cleansing and dentin primer steps, we investigated the efficacy of the four acidic monomers--monomethacryloxyethyl succinate (MES), dimethacryloxyethyl phosphate (DMEP), tertiary butylacrylamide sulfonic acid (TBAS), and 4-methacryloxyethyl trimellitic anhydride (4-META), diluted in 35% hydroxyethyl methacrylate (HEMA) solution--by measuring the maximum contraction gap of the visible-light-curing composite (Silux 3M, St. Paul, MN, USA) in the cylindrical dentin cavity mediated by the bonding agent (Clearfil New Bond, Kuraray Co., Osaka, Japan). More than five of the ten specimens which were pre-treated with an aqueous mixture of 35% HEMA and four functional monomers at the concentrations of 0.1 M, 0.2 M, and 0.3 M showed a complete marginal adaptation, and this result was the same as in the control group in which the cavities were cleansed and pre-treated with 0.5 M EDTA and 35% HEMA, respectively. Moreover, the procedures were simpler. Therefore, these four monomers are considered to be effective as self-etching primers.

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.

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.

Micro-structural integrity of dental enamel subjected to two tooth whitening regimes

Colour modification of tooth enamel has proven successful, but it is unclear how various bleaching applications affect micro-structural integrity of the whitened enamel. To investigate the internal structural integrity of human intact tooth enamel with the application of two commonly used whitening regimes (in-office power bleaching with 35% hydrogen peroxide and home bleaching with 10% carbamide peroxide), evaluations were performed on teeth of identical colour classification. After the bleaching applications, the enamel mineral density was quantified and visualised with micro-computed tomography. The micro-structural differences between the whitened tooth enamel samples were distinctive, though the colour parameter changes within the samples were equivalent. Home bleaching achieved colour modification by demineralisation, whereas in-office bleaching depended on redistribution of the minerals after treatment and subsequent enhanced mineralisation.

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.

Dentin surface roughness vs. bond strength of dentin adhesives

The effects of differently prepared dentin surfaces on the bond strength mediated by five dentin adhesive/composite resin systems were investigated: Clearfil new bond/Clearfil Ray, Gluma/Lumifor, Scotchbond/Silux, Scotchbond 2/Valux, and Tenure/Silux. Bonding surfaces were produced either by wet-grinding of human teeth on SiC paper, grits 180, 240, 320, 400, 600, and 4000, respectively, or by cutting them with dental preparation instruments. The surfaces of the dentin were analyzed by a profilometer. Tensile bond strengths (TBS) were determined two min after light activation of the restorative systems. In spite of greatly different effective areas for bonding, ANOVA showed no significant differences on the 5% level between the TBS means of one material system recorded for the different dentin preparations. It was concluded that the dentin roughness produced by preparation has no significant influence on early bond strengths of bonding composite resin systems.

Bonding stability and shelf life of GLUMA

The long-term bonding stability and shelf life of the two dentin-bonding systems--GLUMA combined with Clearfil New Bond and HEMA combined with Clearfil New Bond--were evaluated by measurement of the tensile bond strength and the wall-to-wall polymerization contraction in the cylindrical dentin cavity. The tensile bond strengths of the two bonding systems did not decrease significantly after the specimens were stored in water at room temperature for a maximum period of 24 weeks. Since the bonding efficiency of the two bonding systems was not affected by the storing of these solutions in a refrigerator for a maximum period of 24 weeks, the shelf life of these agents is considered to be longer than 24 weeks.