Tokuji Hasegawa

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 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.

Quantitative microleakage of some dentinal bonding restorative systems

The quantitative microleakage of class V cementum (dentin) cavities restored with six dentinal bonding restorative systems was determined in vitro. Ninety extracted human permanent first and second mandibular and maxillary premolars were used in this study. Class V preparations were made in cementum (dentin) at the root facial surfaces. The preparations were restored with 1) a dentin bonding system containing 2% HEMA and BisGMA and a light-cured microfilled composite; 2) the same materials only substituting META/MMA base and TBB catalyst monomers for the BisGMA sealer; 3) a dentin bonding system containing 35% HEMA with META/MMA base and TBB catalyst, and a light-cured hybrid composite; 5) the same dentin bonding system only substituting the 35% glycerylmethacrylate for the 35% HEMA and using the microfilled composite; and 6) the previously described system with a substitution of 0.5 mol EDTA for the 10% citric acid -3% FeCl3. Fifteen teeth were restored with each procedure. The restorations were finished with 12-bladed carbide burs 15 min after placement, the teeth were stored in saline at 37 degrees C for 24 h, finished with Sof-Lex discs and then thermocycled in 2% methylene blue solution 500 times between 50 degrees C and 8 degrees C with a dwell time of 15 s. Quantitative microleakage was determined by a spectrophotometric dye-recovery method and expressed in microgram/dye/restoration. The data were analyzed by ANOVA, Student-Newman-Keuls and Kruskal-Wallis tests. The quantitative microleakage of the teeth restored with the adhesive systems containing 35% glyceryl methacrylate was significantly reduced. The bonding mechanism of glyceryl methacrylate is not known.

Possibility of Allergic Reaction to Dentin Primer

We studied the allergic reaction of guinea pigs to glyceryl methacrylate (GM), hydroxyethyl methacrylate (HEMA) and meso-erythritol methacrylate (EM), which are used as dentin primers. On the 18th day of the application test, when macroscopic investigation revealed an inflammatory reaction, the methacrylic acid-treated group showed marked eschar formation in comparison with the control group. In each of the dentin primer groups, a slight degree of skin redness was noted, but there were no serious symptoms. On the 25th day, the applications were resumed macroscopic inspection on the 32nd day found eschar in the methacrylic acid group only. Therefore, this experiment with dentin primers suggests a delayed allergic reaction. Local irritability test showed a more severe reaction than the application test. In this test, all experimental dentin primers and methacrylic solution promptly showed inflammation, and the chemical compound, methacrylic acid was a factor in inflammation.

Role of protease maturation lipoprotein in osmoadaptation of Streptococcus mutans.

Osmoadaptation may be an important trait for the pathogenicity of Streptococcus mutans. However, how this organism adapts to changes in osmolality in the oral cavity remains unclear. In this study, we showed that S. mutans utilizes K(+) for osmoadaptation, in which protease maturation lipoprotein (PrtM) plays an important role. Although growth of the wild-type strain was impaired in a hyperosmotic medium [brain heart infusion (BHI) containing 0.3 M NaCl] compared with that in an unmodified BHI, the prtM mutant grew much more poorly in 0.3 M NaCl BHI. Comparison of growth behavior in the hyperosmotic medium supplemented with different osmoprotectants revealed that only the addition of K(+) allowed the bacteria to overcome the impairment of growth caused by the high osmolality. These results suggest that K(+) is an important compatible solute for S. mutans. Moreover, K(+) -associated recovery of growth was not observed for the prtM mutant, indicating that PrtM plays a critical role in the utilization of K(+) . Quantitative reverse-transcriptase polymerase chain reaction analysis showed that prtM was induced by osmotic stress, implying that prtM is an osmoresponsive gene. These findings suggest that K(+) is an important compatible solute for S. mutans, and that the osmoresponsive lipoprotein PrtM is involved in K(+) utilization, contributing to osmoadaptation of S. mutans.

Rapid detection and identification of Streptococcus ratti by a species-specific PCR method

To establish a rapid and species-specific detection and identification method of Streptococcus ratti by polymerase chain reaction, two PCR primer pairs specific to S. ratti were designed on the basis of the nucleotide sequence of the dextranase gene (dex) of S. ratti ATCC19645(T). The primer pairs specifically detected S. ratti, but none of the other mutans streptococci (16 strains of 6 species). The PCR procedure was capable of detecting 1 pg of genomic DNA purified from S. ratti ATCC19645. We developed the Streptococcus mutans-, Streptococcus sobrinus-, Streptococcus downei- and Streptococcus salivarius-specific PCR methods (the dex PCR methods) with the primer pairs specific for a portion of the dex gene of each species. The mixture of these primer pairs including S. ratti (this study) successfully differentiated the five species of mutans streptococci by species-specific amplicons of different lengths. These results suggest that the present PCR method is suitable for the specific detection and identification of S. ratti, and that the mixture of primer pairs for the dex PCR methods is useful for species-specific detection and rapid discrimination of each species in mutans streptococci.