Akihiro Fujishima

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.

Comparison of four modes of fracture toughness testing for dental composites

OBJECTIVES Investigators have reported on the measurement of fracture toughness (K(lc)) of dental composites using a variety of testing methods. However, fracture toughness has been shown to be dependent upon several variables, including crack-tip sharpness and specimen geometry. This study was designed to compare the fracture toughness values obtained for two experimental and three commercial posterior composites, using four popular testing methods. METHODS The four methods for testing fracture toughness included single-edge notched, compact tension, short rod with chevron notch and double torsion. The results were compared by ANOVA and Tukeys multiple comparison test (p < or = 0.05). RESULTS The values obtained from the short rod test were significantly higher than those from the three other tests. Evaluation of the load-deflection curves and fracture surfaces suggested that the data for this test may not have been valid because a stable crack growth region could not be identified. In general, the fracture toughness results obtained from the double torsion test were lower than values obtained from the single-edge notched and compact tension methods. The double torsion test was the most difficult to conduct, resulting in only a 50% success rate. SIGNIFICANCE The double torsion test, though possibly the most technique-sensitive of the four fracture toughness methods evaluated provides the most information about crack initiation and propagation and may be most indicative of the true fracture toughness of dental composites.

In vitro inhibition of caries around a resin composite restoration containing antibacterial filler.

Class V cavities were prepared and restored with resin composite containing antibacterial filler powder (Apacider-AW, Ap-AW) using experimental restorations. The restored teeth were incubated in vitro with the cariogenic bacteria Streptococcus mutans IFO 13955. Ground sections were then prepared and examined using macrophotography. Lesions of the outer and inner wall were noted, and the depths of which the lesions penetrated were measured. We found that, in restorations containing 1-5 wt% Ap-AW, caries penetrated the marginal area, while in restorations containing 10 wt% Ap-AW the margin remained free of caries out to a distance of about 1.1 and 1.8 mm on the occlusal and gingival sides, respectively.

The mechanical properties of dental thermoplastic materials in a simulated intraoral environment

Abstract The present study assessed the mechanical properties of dental thermoplastic materials in a simulated intraoral environment. Eight dental thermoplastic products – EVA (Bioplast), PE (Copyplast), PETG (Duran), PP (Hardcast), PC (Imprelon“S”), A+ (Essix A+), C+ (Essix C+), and PUR (Invisalign) – were examined using the following tests: (1) 2-week water absorption test, (2) thickness-change tests with thermoforming and water absorption, (3) tensile tests under room temperature (23 °C) and in a simulated intraoral environment (37 °C). The results were as follows: (1) water absorption increased with time and ranking was (from highest to lowest): PUR, PETG, A+, PC, EVA, PP, C+, and PE. (2) The changes in thickness ranged from 74.9 to 92.6% in comparison with the specimens before thermoforming. Linear expansion with water absorption ranged from 100.3 to 119.9%. (3) The elastic moduli of PC, PETG, and A+ in the simulated intraoral environment showed significant increases in original sheets; in contrast PP, C+, PE, and EVA were significantly reduced. No significant changes were observed in PUR. Tensile yield stress of the specimens in the simulated intraoral environment decreased in comparison with original sheets. The present result suggests that the mechanical properties of dental thermoplastic materials varied due to environmental factors. Moreover, behavior change is influenced by molecular structure and orientation. The application of thermoplastic materials for orthodontic tooth movement requires a sufficient understanding of the material characteristics, optimal material selection, and design.

Shear bond strength of four commercial bonding systems to cpTi

Abstract Objectives . The purpose of this study was to evaluate the bond strength of veneering composite to commercially pure titanium (cpTi) using several different bonding systems and a post-cure heat treatment. Methods . Four commercial bonding systems (Cesead, Kuraray; New Metacolor, Sun Medical; Silicoater MD, Kulzer; Thermoresin LC II, GC) were evaluated. Bonding was attempted with the opaque resin provided by each bonding system as well as with the New Metacolor opaque resin. New Metacolor resin composite was used for the veneering composite. Half of the specimens were subjected to a post-cure heat treatment at 100°C for 30 min. The shear bond strengths were tested after aging the specimens in water at 37°C for 1 d and also after thermocycling for 16.5 d (20,000 cycles). Results . Strong bonds, exceeding 20 MPa, were achieved with all of the bonding systems with the exception of Thermoresin LC II, which is designed for noble metals. Bond strengths were only increased by the post-cure heat treatment for the New Metacolor system. Thermocycling caused a significant reduction in bond strength for the New Metacolor and the Thermoresin LC II systems. The use of the New Metacolor opaque resin produced increased bonding for the Silicoater MD and the Cesead systems, but the effect was eliminated after thermocycling. Significance . Strong, durable bonds can be achieved between composite and sandblasted cpTi, thus enhancing the usefulness of this metal for esthetic resin-veneered crowns and other fixed prosthetics.

A study on the adsorption structure of an adhesive monomer for precious metals by surface-enhanced Raman scattering spectroscopy

In order to clarify the role of a primer on the adhesion between dental precious metals and resin, surface-enhanced Raman scattering (SERS) technique has been applied to the structural analysis of the adhesive monomer, 6-(N-(4-vinylbenzyl)propylamino)-1,3,5-triazine-2, 4-dithione (VBATDT) adsorbed on colloidal Au surfaces. VBATDT is one of the major components of commercial primers. A mixture of a methanol solution of VBATDT and aqueous Au colloid was illuminated by the 647.1 nm line from a Kr ion laser to obtain the SERS. The most intense peak at 458 cm-1 due to C = S stretching in the Raman spectrum of solid VBATDT disappears completely in the SERS, while all the other peaks due to vinylbenzyl group vibrations remain unchanged. It suggests that some structural change occurs in VBATDT upon adsorption on Au which involves the C = S bonds and that the molecule undergoes thione-thiol-type tautomerization in the adsorption process. The SERS spectrum of a commercial primer containing VBATDT exhibits a similar spectral pattern. The present results lead us to conclude that some specific interactions exist between the sulfur atoms of VBATDT and Au surface to form chemical bond likes, which are effective to improve the bond strength between dental precious metals and resin. The ambivalent properties of the primer, chemical stability in storage and chemical affinity to Au, are also explained by the thione-thiol-type tautomerization of VBATDT on the basis of the spectroscopic evidence.

A study on adsorption structures of methacryloyloxyalkyl dihydrogen phosphates on silver substrates by infrared reflection absorption spectroscopy

10-Methacryloyloxydecyl dihydrogen phosphate (M10P) for use in dentistry has recently been noted as an adhesive monomer contained in a metal primer. Although the treatment of a metal surface with primer before the application of resin is recognized to improve the adhesion between metal and resin, the role of M10P in the adhesion process has not been clarified. In this study, infrared reflection absorption (IRA) spectroscopy was employed to study the adsorption structures of M10P as well as 2-methacryloyloxyethyl dihydrogen phosphate (M2P) on evaporated silver substrates. The IRA spectra of the self-assembled films of those phosphates verified the adsorption of M10P or M2P on silver substrates from the methyl methacrylate solutions (5 x 10(-5) mol/L). The saturation coverages of M10P and M2P were completed after about 50 and 25 min, respectively. Two characteristic bands around 980 and 1080 cm-1 due to the PO(2-)3 stretching vibrations were observed. These results indicate that the phosphate groups of both monomers are adsorbed to silver surfaces in the dissociated form, -PO(2-)3, and form hydrophobic monolayers. The monolayer of M10P was found to be more durable against thermocycling in water than that of M2P by IRA measurements. The roles of M10P in the metal primer are presumably to form such a monolayer with appreciable durability and to promote polymerization with resin monomers.

Preventive effect of tooth fracture by pulsed Nd:YAG laser irradiation with diamine silver fluoride solution.

OBJECTIVE The purpose of the present study was to evaluate the preventive effect of pulsed Nd:YAG laser irradiation with 38% diamine silver fluoride [Ag(NH3)2F] solution for the fracture of endodontically treated teeth in vitro. BACKGROUND DATA There have been no reports on the preventive effect of tooth fracture using Nd:YAG laser with Ag(NH3)2F solution. MATERIALS AND METHODS Twenty-eight human extracted teeth were used in this study. The teeth were randomly classified into four groups: control group, where tooth surfaces were not submitted to any treatment; group 1, where tooth surfaces were coated with 38% Ag(NH3)2F solution; group 2, where tooth surfaces were coated with Ag(NH3)2F solution and irradiated by pulsed Nd:YAG laser for 2 sec; and group 3, where tooth surfaces were coated with Ag(NH3)2F solution and irradiated by pulsed Nd:YAG laser for 10 sec. After preparation, shear tests were performed and the maximum load for the fracture was measured. Results were analyzed using the Scheffe test, and difference at p < 0.05 was considered significant. RESULTS The failure load for group 2 (mean, 182.5 kg) had the highest mean value and differed significantly from those for the control group (mean, 146.3 kg) and group 1 (mean, 147.1 kg; p < 0.05). The failure loads for groups 1 and 3 (mean, 150.0 kg) did not differ significantly from that for the control group (p > 0.05). CONCLUSION The results show that the application of 38% Ag(NH3)2F solution followed by pulsed Nd:YAG laser irradiation for 2 sec is useful for prevention of tooth fracture at endodontically treated teeth.

Nanoindentation tests to assess polymerization of resin-based luting cement

OBJECTIVE The optimal polymerization of resin-based luting cements plays a critical role in the long-term clinical success of dental prostheses and indirect restorations. This study investigated a mutual action between the conformational changes and mechanical properties of a dimethacrylate resin-based luting cement with and without pre-application of the acidic functional monomer 10-methacryloxydecyl dihydrogen phosphate. METHODS Degree of conversion in the luting cement was measured using conventional infrared spectrophotometry. Mechanical properties of the luting cements were also evaluated by quasi-static and dynamic nanoindentation tests. RESULTS The results of infrared spectrophotometry and nanoindentation testing were proportional in samples without functional monomer pretreatment. When considerable residual monomer remains within the final products, the mechanical properties of the resin-based luting cements could possibly be impaired. Although the apparent degree of conversion increased with a mixture of functional monomer, a reduction in the cross-linking polymer network may have resulted in the highest viscoelastic creep behavior of the luting cement. The time-dependent behaviors found in the nanoindentation tests likely resulted from linear polymerization chains of the functional monomer. SIGNIFICANCE The application of an acidic functional monomer may affect the viscosity of resin-based luting cements. Quasi-static or dynamic nanoindentation is a useful tool for assessing the polymerization qualities of resin composites.

Efficacy of experimental dual-cure resin cement for orthodontic direct bond system

Abstract Chemical-cure resin cement has been widely used for orthodontics. To improve the clinical handling of chemical-cure resin cement, a dual-cure resin cement system composed of methyl methacrylate (MMA), urethane dimethacrylate (UDMA) and light activator was developed. The purpose of this study was to estimate the efficacy of an experimental dual-cure resin cement. A composite bracket was bonded to the teeth with one of eight resin cements: (1) Unifast II (Uni II); (2) Unifast II containing camphor quinone (Uni II-CQ); (3) Transbond XT (TB); (4) Orthomite Superbond (SB); (5) Unifast LC (Uni-LC); (6–8) experimental dual-cure resin cement—Exp1, Exp2 and Exp3, respectively. Shear bond strength (SBS) of all of the bonded brackets was measured after the cementation. The data were statistically divided, the highest cement (Uni-LC), the next group (Exp1, Exp2, Exp3 and SB) and the lowest group (Uni II, Uni II-CQ and TB). The dual-cure resin cement exhibited a bonding efficacy comparable to that of Superbond.