In the investigation of the cytotoxicity of dental restorative and luting materials in vitro, use of a dentin substitute which exhibits properties similar to those of dentin is essential. In the present experiment, the permeability of various potential dentin substitutes to eugenol from zinc oxide eugenol cement was determined using ultraviolet spectroscopy and compared with the permeability of dentin slices and powder. The mean amount of eugenol that permeated dentin slices was 20 μg/ml. However, this amount showed large variations, while variations in dentin powder, purified collagen and agar gel were smaller. Further studies on the properties of dentin and kinds of dental materials are needed for clarification of in vitro investigation of dentin permeability. We discuss the search for alternatives to the biological substance, which has many shortcomings associated with its use.

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Bonding of light-cured bonding agent containing 2-methacryloyloxyethyl hydrogen maleate (2 MEM) to dentin treated with various etchants (37% phosphoric acid, 1 M lactic acid, 0.5 M EDTA・2 Na and 10-3 solution) was investigated. When the dentin was treated with 1 M lactic acid, 0.5 M EDTA・2 Na and 10-3 solutions, the thickness of the acid-proof dentin layer at the interface between the resin and etched dentin was about 1 μm, but when the dentin was treated with 37% phosphoric acid solution, the thickness of the layer was about 3 μm. There was no significant difference in bond strength to etched dentin under any of these conditions. The bond strength did not decrease with time regardless of type of etchant.

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Although handpieces are used in various dental practices, no simple and reliable sterilization process for them has been established.The final solution to this problem is to develop disposable instruments, but this is a difficult task due to their precise inner structure.We report the development of air turbine handpieces using plastic journal bearings with hydrodynamic lubrication for the realization of disposable dental handpieces.Their rotational properties were investigated to examine their clinical usefulness.The speed achieved with the handpiece using plastic bearings was about 85% of that using ball bearings under the freerunning condition and 80% in stopping torque.The handpiece was applied to the preparation of extracted human teeth and it was found to have cutting ability satisfactory for clinical usage.

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This study investigated the pre-treatment of metals for obtaining firm adhesion between the adhesive resin, Panavia EX, and the dental alloys.The effects of the pre-treatment by the metal primer containing 0.5% 10-Methacryloyloxydecanethiol(MDT)on the adhesive strength of the adhesive resin to various pure metals and four types of dental alloys(gold alloy, 12% Au-Ag-Pd alloy, 78% Pd alloy and Ni-Cr alloy)were examined.The surface of pure metals, on which such a metal primer was used, was analyzed by ESCA.Stable adhesive strength, such as 280〜350kgf/cm², was obtained when the adhesive primer was applied to the #600 polished surface of Au, Ag and Pd.Especially the adhesion to Au and Ag was found to be stable and durable during the thermal cycling test.ESCA analysis revealed the chemical bond between MDT and pure metals(Au and Ag)after the surface of pure metals was washed by acetone following this adhesive primer.Favorable adhesive strength, such as 450〜500kgf/cm², was obtained even after 24 hours of immersion in 37℃ water, when the surface of the dental alloys(gold alloy, 12% Au-Ag-Pd alloy and 78% Pd alloy)was pretreated with this adhesive primer.However, during the durability test, the adhesive strength to the 78% Pd alloy decreased to about 35〜40% of early strength.With the gold alloy and 12% Au-Ag-Pd alloy, more than 80〜95% of early strength was maintained.

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The chemical composition of the surface film formed on dental alloys by surface treatments was determined using x-ray photoelectron spectroscopy(XPS), to understand the interfacephenomena between the alloys and 4-META/MMA-TBBO resin.Three Ni-Cr alloys(one basic and two commercial alloys)were anodically oxidized in 70% H₃PO₄ or a commercial electrolyte for surface treatment, and then the film formed on the alloy was analyzed.XPS findings revealed that appreciable amounts of PO₄^3- were contained in the film.Also, the concentration of chromium in the surface film formed on the alloys with the treatment was larger than in that formed without the treatment.Furthermore, silicon, which was added in a small amount to the commercial alloys, was an important element for the formation of the film.

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A new binder, using Al(H₂PO₄)₃ has been developed for application to dental investments.The heating characteristics on the set materials of Al₂O₃・5H₂O-Al(H₂PO₄)₃ were examined.Two types of Al(H₂PO₄)₃, powder and liquid were used and synthetic amorphous Al₂O₃・5H₂O was selected as a reactor on the basis of previous investigations.When the set binders were heated, berlinite(quartz form of AlPO₄)or cristalphite(cristobalite form of AlPO₄)was produced at the initial stage of heating and Al₂O₃ was produced in the same samples at high temperatures.The amount of AlPO₄ produced was affected by the molar ratio Al₂O₃/P₂O₅ of the binder and showed the maximum value at the molar ratio Al₂O₃/P₂O₅=1.When Al(H₂PO₄)₃ powder was used, the set binders expanded during heating by both the α-β transformation of berlinite or cristalphite and the reconstructive transformation of berlinite form to cristalphite form.The maximum expansion reached 7%(1, 100℃).When using Al(H₂PO₄)₃ liquid, all of the set binders contracted during heating.The sufficient compressive strength(13-13.5MPa)of set binders after heating at 1, 000℃ was obtained by addition of MgO(50wt%)to Al₂O₃・5H₂O(50wt%).

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Ordinarily the metal parts of prosthetic devices are soldered by the investment method.However, this procedure is relatively complex and time consuming.Since a laser is capable of concentrating high light energy on a small spot, we considered the possibility of using a laser for joining the precise and minute parts of prosthetic devices.We carried out basic welding experiments using a normal pulse, Nd:YAG laser processing apparatus to weld titanium, which is being used frequently in dentistry.Laser-welding of titanium must be carried out in an argon atmosphere. Further studies are required to determine the optimum way to create an argon atmosphere and to determine the optimum irradiation power.When titanium was irradiated in an atmosphere of ordinary air, cracks appeared in the metal surface, welds crack, and the mechanical properties of the metal were debilitated.Greater tensile strength, yield strength and elongation of titanium were generally observed for increase in laser irradiation power.Even in an argon atmosphere, the intensity of the laser irradiation must be at least 21 J/P to maintain the tensile strength and yield strength of the original metal.Differences in the laser irradiation atmosphere significantly affected the elongation of titanium.

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The CAD system was developed to produce a crown prosthesis.Three molars of 5 to 7 with the 6 molar to be abutted to produce a crown prosthesis were measured, and the data of the 6 molar for data base was adopted.They were adjusted including the proximal contact by the program"ABCR-Y".It was carried out by examining the size, position and rotational angles of crown relative to the abutment by the CG image from the three directions x, y and z.The data for crown and margin of abutment were connected by extending the crown edge smoothly by using the third order B-Spline function.In the 4 array data of mesial and distal end of crown, no crossing points with the margin line were observed by the extension.Since, the crown data were transferred so that the y axis became perpendicular to the CRT surface, and the mouse manual data were input and they were connected smoothly by the Spline curves.Thus, by the present CAD procedure, the edge data for the crown data base were connected with the margin of abutment smoothly.Further improvements will be made to obtain an occlusal condition with an antagonistic tooth.

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A fracture mechanics approach, using fracture toughness(K_IC)failure criterion, is the most appropriate method for brittle materials such as posterior composite resins.Recently, one of us developed a new method for determination of the K_IC value using a specimen in the shape of a ring.In this study, we discussed the advantages of the ring specimen and measured the K_IC value of three commercial posterior composite resins(Clearfil photo posterior, P-50 and Occlusin).It is easy to introduce a fatigue-precrack in the ring specimen used in this study and to control the crack length with a fatigue testing machine.The ring specimen demonstrates a constant stress intensity factor over a significant range 0.58≦(a+Ri)/Ro≦0.76, so that the exact measurement of the crack length is unnecessary.The K_IC values of OCC(1.87±0.07MPam^1/2)showed significantly higher values than CPP(1.52±0.03MPam^1/2)and P-50(0.88±0.05MPam^1/2).The average coefficient of variance was 2.7%.In conclusion, the ring specimen is a reliable, accurate and reproducible means of measuring the K_IC value.

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Effectiveness of several methacrylates dissolved in MMA-TBB resin on the bonding to dentin pretreated with EDTA3-2(NH₄/Fe)was studied.SEM revealed that HEMA and triethyleneglycol monomethacrylate promoted the monomer diffusion into the treated dentin and a higher bond strength was obtained.Tag formation was also encouraged by their addition into MMA.This was identified by microscopic observation of the Fe³⁺ adsorbed onto the cut dentin surface hy staining with taninc acid.

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The GLUMA primer consisting of glutaraldehyde(GA)and hydroxyethyl methacrylate(HEMA)has been reported to be effective to improve the bond strength between dentin and resins.The mechanism of the action of GLUMA or role of GA and HEMA in GLUMA has not been fully explained yet.As part of the study to understand GLUMA, we investigated the bond strength between dentin and MMA-PMMA/TBBO resin and polymerization of MMA with TBBO in the presence of GA or decalcified dentin.When dentin was pretreated with EDTA, the primer containing GA was effective for improving the bonding, but the HEMA primer was practically ineffective.Polymerization of MMA with TBBO in the presence of decalcified dentin revealed that treatment of the dentin with GA promoted the chain transfer reaction and grafting of MMA to the dentin.These findings suggested that grafting of MMA onto dentin collagen modified with GA by the chain transfer mechanism is involved in the strong adhesion of resin to dentin.

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Calcium carbonate(CaCO₃)was applied as a filler for polyaddition-type silicone impression material, and the effect on viscosity, dynamic viscoelasticity and tensile behavior were investigated.The CaCO₃ filler was treated with a titanate coupling agent(Isopropyl triisostearoyl titanate)in n-hexane at 1% concentration, and was mixed to a prepolymer consisting of a hydrogen polydimethylsiloxane and a vinyl polydimethyl-siloxane in 40%, 50% and 60% contents by weight.The viscosity of these silicone compounds and mechanical properties of set materials were measured by a cone and plate viscometer, the dynamic shear test and the tension test, respectively.Viscosity η of the silicone compound blended treated-filler was lower than that of the silicone compound blended untreated-filler.Similarly, titanate surface treatment decreased the storage modulus G' and loss tangent tan δ of set material, but did not affect tensile behavior.This suggests that the material is more soft and flexible, in addition to the fact that the high filling of CaCO₃ results in a lowering of the material cost.The application of a CaCO₃ filler treated with titanate coupling agent could be useful for the development of new silicone impression material.

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The electrochemical behavior of Ti, Pd, Co and TiPd alloys was investigated to obtain the fundamental data for evaluating the corrosion resistance of TiPd-Co alloys.The rest potentialtime curve and anodic polarization of the casting specimen were measured in 0.9% NaCl solution at 37℃.Pd showed the highest positive value of the rest potential and Co showed the lowest negative value.The potential of Ti increased with time and reached a fairly high value of -0.03V after 5 hours.TiPd alloys exhibited a potential between the value of Ti and Pd.In anodic polarization, an abrupt increase in current density at 1.0V was observed for Pd.From 0.0V to 1.2V, Ti showed a constant, small amount of current density attributed to passivity.Co had the poorest corrosion resistance.The trance-passivity potential of the TiPd alloys was 0.55V.This potential of the TiPd alloys allowed to stand at room temperature for several days after polishing was shifted to the noble value by 0.1〜0.15V and the current density decreased.These findings are useful in the evaluation of the corrosion resistance of TiPd-Co new shape memory alloys.

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Previously, an apatite-collagen complex was prepared by the incubation of phosvitin cross-linked collagen for one week in a daily renewed solution of calcium β-glycerophosphate in the presence of alkaline phosphatase.In the present study, such factors affecting precipitation of apatite on the collagen fibrils as solution concentration, amounts of alkaline phosphatase and phosvitin added, and the solution pH were investigated to obtain a better condition to synthe-size the apatite-rich-collagen complex.In solutions of β-glycerophosphate, the activity of alkaline phosphatase was examined over a range of pH values.The optimum pH for hydrolysis by alkaline phosphatase was around 10.0, slightly higher than the pH of the solution(8.50)previously used.Interestingly, phosvitin was found to increase the activity of alkaline phosphatase, resulting in more liberation of the inorganic phosphate.As a result, more apatite was precipitated on the collagen fibrils, although phosvitin has been known to be a strong inhibitor in the formation of apatite.

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A light-cured glazing agent for resin composite restorations has been recently developed.Two types of glazing agents(GA-100 and Bell Feel Brightener)were compared for various properties in the laboratory, such as resultant air-inhibition layer after curing, abrasion resinstance, surface gloss, film thickness created due to the application technics, and dynamic hardness, and also GA-100 was clinically applied and evaluated with time.The width of the air-inhibition layer of GA-100 and Bell Feel Brightener was about 1.0μm and 1.5μm, respectively.In the tooth brushing abrasion test, GA-100 showed relatively high wear resistance as compared with Bell Feel Brightener, The worn surface of GA-100 was smoother than that of Bell Feel Brightener.The film thickness of the GA-100 coating on the resin composite using an accessory brush and light-cured after gentle air blowing was about 8μm.After two applications in the same way, the film thickness became about 10μm, In the specimen kept in vertical position the clinical situation, the resultant thickness was about 5μm.Dynamic hardness of GA-100 was higher than that of Bell Feel Brightener.The clinical findings were as follows.The surface of the GA-100 coating on three kinds of light cured anterior resin restorations preserved its smoothness and gloss even after three month service.GA-100 was found to be applicable to other brands of resin composite.GA-100 was effective as the varnishing agent and also glazing material for glass polyal-kenoate cement restorations.

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The surface texture changes of four kinds of resin composites were compared with that of commercially available acrylic plate, which was used as a control.Roughness and gloss of various polished resin surfaces before and after a toothbrushing test under various abrasive conditions were measured by a profile recorder and a gloss meter.The worn surfaces of the resin composites were observed using a scanning electron microscope.The surface roughness of all resin composites more or less increased after the toothbrushing test.The MFR type resin(Silux Plus)showed the smoothest surface.Also, the surface roughness of the Hybrid type resin(BR-100)was close to that of the MFR type resin, with no significant difference.The abrasive agent comprising toothpaste, glycerine and water had the most severe effect on the surface texture of the resin composites.

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Recently, several dentin bonding systems have been developed and marketed in order to ensure the adhesion of the resin composite to dentin.In the present study, tensile bond strengths of six commercially available bonding systems to the flat bovine dentin surface were determined.The results obtained were in descending order of magnitude as follows:Tenure solution, 75.6kgf/cm²;Scotchbond 2, 66.8kgf/cm²;Clearfil PhotoBond, 60.0kgf/cm²;Gluma, 35.7kgf/cm²;Mirage-Bond, 33.7kgf/cm²;and RestoBond 3, 31.3kgf/cm² Statistically significant differences were found between the mean tensile bond strengths of the first three systems and the others.

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Mechanical properties of unalloyed titanium vary with the content of impurities.The relationship between mechanical properties of titanium castings and the impurities in casting materials was investigated.Five different grades of unalloyed titanium were used as the materials for casting, and a phosphate bonded silica investment was used as the mold material.The mechanical properties of titanium castings were investigated by a tensile test and a micro Vickers hardness test.When titanium materials of lower impurity were used, the titanium castings showed low tensile strength of 300〜400MPa, and large elongation of more than 20%;comparable to type II gold alloys.On the other hand, when materials of high impurity were used, the elongation was decreased, and the tensile strength increased to 500MPa;comparable to type IV gold alloys.The hardness of titanium increased about 57〜68 in Vickers hardness by casting with a phosphate bonded silica investment.This seemed to be caused by the impurities contaminating metal in the melting and casting process.In conclusion, titanium materials should be selected according to the application.

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