Bond strength of the metal post to the intra-radicular deep dentin is of extremely importance to the success of the post and core build-up.However, decreases in bond strength in deep dentin have been widely reported.We tested the shear bond strength of 4 commercialized adhesive resin cement systems to bovine radicular deep dentin and to coronary superficial dentin.Moreover, we examined the effect of a conditioning method(NC pre-conditioning)on the radicular deep dentin by measuring the shear bond strength and analyzing the resin-dentin interfacial zone by scanning electron microscopy(SEM).These was a decrease in the adhesive properties of all the commercialized resin cements used in deep dentin, prepared according to the manufacturer's instructions, when compared to superficial dentin.On the other hand, the NC pre-conditioning method produced a significant increase in shear bond strength, especially in the radicular deep dentin.Furthermore, there was almost no decrease in the adhesive strength due to thermocycling.We concluded that NC pre-conditioning is effective to obtain good adhesion to radicular deep dentin.

View full abstract

The effectiveness of miniaturized dumbbell-shaped bonded bovine dentin specimens to measure their tensile bond strength was studied.The 4-META/MMA-TBB resin bonded to bovine dentin conditioned with 10-3 for 10, 30 and 60 s, were sectioned and trimmed to the dumbbell specimen with a cross-section of 3.0×2.0 mm at the adhesive interface.The tensil bond strength was 20.5, 16.2, and 12.7MPa, respectively.Fractures due to tensile stress occurred in the remaining demineralized dentin in all three groups.These findings were quite different from those obtained by the conventional bonding test.In conclusion, dumbbell specimens are useful to evaluate bonding quality of resin to dentin in a short period.

View full abstract

Recently the titanium alloys have been designed for use in dentistry. Although the Ti-6Al-4V alloy has been brought into the market as a dental casting alloy, problems remain in the biocompatibility of vanadium and in the mechanical properties as well as the castability. The Ti-6Al-7Nb alloy was developed as a biomedical alloy by replacing vanadium in the Ti-6Al-4V alloy with niobium.Previously, we found that the Ti-6Al-7Nb alloy had suitable properties as a material for dental casting through a casting test and mechanical test. In this study, a long-term dipping test was carried out using the cast specimens made of titanium, Ti-6Al-4V and Ti-6Al-7Nb alloys in 1.0% lactic acid in order to evaluate their corrosion resistance in a physiological atmosphere. The amount of titanium ion released from Ti-6Al-7Nb alloy was less than that from the Ti-6Al-4V alloy and comparable to that from titanium.

View full abstract

The effects of aging on tensile strength of bovine dentin were examined.Teeth of cows between aged 1.5 and 6 years old were classified into 4 groups according to dental age.The tensile test was performed using dumbbell-shaped dentin specimens prepared from these teeth and fracture surfaces were observed using SEM. The gradients obtained from the stress-deformation curve were not significantly different with the group.The tensile strength decreased slightly with aging, but not significantly. In Weibull analysis, the scale parameter remained constant but the Weibull moduli, (11.4, 10.2, 9.6, 6.3), decreased with aging. Fractographic analysis revealed no remarked difference among fracture surfaces with the group, except increasing plugged dentinal tubules with aging.

View full abstract

We examined the effects of extracts and filtrates on cell viability after gyration of six types of spherical restorative materials on a titanium plate.The extracts obtained with titanium coupled with Type 3 gold alloy, gold-silver-palladium alloy, titanium and composite resin did not affect the cell viability, while the extracts obtained with titanium coupled with cobalt-chromium alloy or nickel-chromium alloy suppressed the cell viability with increased specimen weight, or gyration speed, or extraction period.The extracts and filtrates had similar effects on cell viability.Cell viability decreased by the extraction in serum-containing MEM.The present method of obtaining extracts from restorative materials coupled with titanium might be an approach to express in vitro cytotoxicity of dental materials which are occluded with others in the mouth.

View full abstract

Studies of titanium casting have been carried out for several years.However, titanium casting has many problems which may cause external and internal defects.Currently there appeared new casting machines and casting molds for titanium casting.Thus, many titanium casting systems have been developed, and eventually casting systems have flooded to the market, so that it has become difficult to choose optimal method among the different types available.This is considered one of the major obstacles for popularization of titanium castings.The purpose of this study is to evaluate the different casting methods under various casting temperatures on the titanium castability.The castability of each casting methods showed significant coefficient of correlation during castability and mold temperature(p<0.01).The mold temperature was one of the major factors influencing to casting condition in each casting method.And the influence of mold temperature for castability showed different tendency in each casting method.Mold temperature was less affective to the optimal casting force, when it was estimated in optimal range.

View full abstract

We examined conditions for sandblast treatment to both CP titanium(CP Ti)and cobaltchrome alloy(Co-Cr)used as a control, to fabricate a veneered titanium crown using a non-mechanical retention bead method.Three average particle sizes of alumina(50, 110 and 250μm)were used at a pressure of 0.25〜0.45 MPa for 5〜30 seconds to examine the changes of surface texture on CP Ti and Co-Cr.Weight loss of cp Ti by sandblasting treatment increased with the increase of treatment time linearly, but there was little effect from particle size.Weight loss of Co-Cr was greater than that of CP Ti, but volume loss of Co-Cr was almost equal from that of CP Ti.Alumina particles were clearly observed on the sandblasted surface by backscattered electron(BSE)image, and the area percentage of alumina detected on the picture analysis from BSE image was 54〜61% when treated for 10 seconds at 0.45 MPa.EPMA showed the amount of alumina was 33〜45 wt% on CP Ti and 22〜42 wt% on Co-Cr, respectively.Alumina content on the specimen was larger when treated with 50μm alumina particle than 250μm, but was not affected by treating time and pressure.The decreases in pressure from 0.45 to 0.25 MPa decreased the deformation of the CP Ti plate significantly, but did not decrease the surface roughness.Those results suggested that lower pressure and shorter treatment time were suitable for sandblasting titanium compared to those needed for other dental alloys.Furthermore, we need information on both the bonding of metal and the alumina surface to clarify bonding to alumina sandblasted metals.

View full abstract

We examined bonding strengths of commercial veneering resin bonding systems to CP titanium after sandblasting using three different sizes of alumina particles(50μm, 110μm and 250μm).We also examined bonding properties of those systems to sintered alumina plate, since we previously noted that the sandblasted surface of titanium was severely contaminated by alumina particles.Sandblasting with 250μm alumina particles showed the highest bonding strength, and bonding strength increased with increase in the size of alumina particles.However, there were no significant differences in strength between 110μm and 250μm, or between polished surface and 50μm.Bonding strength for sintered alumina was significantly lower than that of titanium for NMC and CSD systems which showed excellent bonding for titanium.Therefore, the existence of alumina on the titanium surface by sandblasting was not useful for improving bonding properties on the sandblasted surface of CP titanium.

View full abstract

Phosphoric acid modifies peptides in demineralized dentin which collapse easily during the drying process.The collapsed demineralized dentin does not permit monomer impregnation and makes preparation of hybridized dentin difficult.Methacrylates with hydrophilic and hydrophobic groups, 2-hydroxy-3-phenoxypropyl methacrylate(HPPM), 4-methacryloyloxyethyl trimellitic acid(4-MET)and 2-methacryloyloxyethyl phenyl hydrogen phosphate(Phenyl-P), dissolved in 30% HEMA primer could restore the permeability of shrunken demineralized dentin which enhanced hybrid layer formation.As a result, hybridized dentin was prepared in a shorter period when such a HEMA primer dissolved a methacrylate with hydrophilic and hydrophobic groups was applied on the shrunken demineralized dentin.

View full abstract