The physical properties of a Micro titane^® K-file(MT)made of titanium alloy(Ti-6Al-4V)were compared with those of a conventional K-file made of stainless steel(MN and ZP).Resistance to torsional fracture, angular deflection and resistance to bending were examined according to the ISO standard 3630.The shape of the of tip the new files and fractured surface after the torsional fracture test were observed with a scanning electron microscope.In addition, the cutting area of the transparent curved root canal model treated by each K-file was calculated by a digital image analyzer.K-files No.15 to 40 in size were used.The tip of MT had a obtuse angle compared with that of MN or ZP.The resistance to the torsional fracture and bending was smaller in MT than in MN or ZP.Angular deflection in MN and ZP was proportional to file size, but obtained a definite value in MT.MT broke at right angles to the longitudinal axis after the torsional fracture test and it's surface was flat.The cutting area in MT was significantly smaller than that in MN or ZP.These findings suggested that MT was adapted to stricuture and curved root canal for flexibility.

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The amounts of monomers eluted from experimental light-activated composite resins based on TEGDMA and two types of urethane dimethacrylates were measured by HPLC.Seven different types of filler systems were employed to examine the effect of filler particle size on the monomer elution.For all of the composite resins, the amount of eluted monomers significantly increased with the increase in the depth from the exposed surface.The amount of eluted monomers significantly increased with the decrease in the filler particle size ranging from 1.6 to 18.8μm.These findings indicated that the curing of the composite resins was affected by the difference in refractive indices between filler particle and resin matrices.

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The effects of surfactants dissolved in MMA, Triton X-100, Span 85 and Tween 20, on the bonding of MMA-TBB resins to extracted bovine dentin conditioned with 10-3 were studied.Triton X-100 could promote the impregnation of the monomer, and the bond strength increased to 15MPa and the hybrid layer was identified by SEM and TEM examination.Generally creation of a hybrid layer is essential to bond resins to dentin, but an exception was found in Span 85 and Tween 20/MMA-TBB resins.The surfactants were accumulated at the adhesive interface during their diffusion and lower tensile bond strength and adhesive failure were observed.However, the hybrid layer was sandwiched by the cured resin and the intact dentin.

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The properties of synthesized phosphazene oligomers(polyphosphazene linear monomers)mixed with cyclophosphazene monomer and polymerized with a light curing apparatus were examined.〓NP(EMA)₂〓_n were synthesized by replacing 2 of chlorine(Cl)of polydichlorophosphazene〓NPCl₂〓_nsynthesized by ring opening polymerization of hexachlorocyclotriphosphazene(P₃N₃Cl₆)with 2-hydroxyethyl methacrylate[HO(CH₂)₂OOC(CH₃)C=CH₂](HEMA)and〓NP(TF)₁(EMA)₁〓_n monomer were synthesized by replacing 1 of chlorine with HEMA and trifluoroethanol[HOCH₂CF₃].The molecular weight of the synthesized oligomers was 6, 500〜8, 000.When two kinds of 10〜30wt% synthesized oligomers were mixed with cyclophosphazene monomer P₄N₄[OCH₂CF₃]₂[O(CH₂)₂OOC(CH₃)C=CH₂]₆(4PN(TF)₂(EMA)₆)and light cured, in the case of 20wt% mixture, mechanical properties were preferable.

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Recent dental resin adhesives have very high bond strength to non-caries-affected tooth.However, in most cases in general practice, the adhesives are used on caries-affected dentin.The effects on bond strength of various factors, such as the hardness, inorganic components(Ca, Mg, P)determined by X-ray micro-analysis, dyeing degree determined by caries detector, and artificial caries determined by culturing of Streptococcus Mutans on the tooth were examined.Although no relationship could be obtained in the statistical analysis as the bond strength for individual teeth was widely different, there was a strong relationship between the bond strength and the distance from enamel-dentin junction, or inorganic components especially Mg.Concerning the influences of bond strength in the various mechanical properties of the tooth, the strength of the whole tooth substrate was much stronger than the surface hardness.However, the relationship with the colour difference by caries detector was not clear, and no change was detected with the artificial caries because the surface condition differed from the natural caries.

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The bonding effect of the chelating agent and metallic ion as primer of dental resin cement was examined.The primer was a combined phytic acid and SnF₂ solution(<PYA-SnF₂>primer)that was useful for protection of dental pulp.The effect was evaluated by the shear bond strength of resin cement to sintered hydroxyapatite and bovine dentin.Adhesives used were Panavia EX and Super Bond C&B.The etching agent was phytic acid solution, 40%-phosphoric acid solution and 10%-chitric acid-3%-iron(III)chloride solution, and saturated solution of SnF₂ was used as a source of metallic ion.The treatment with combined phytic and SnF₂ solution improved the bond strength of the adhesion of resin cement to apatite, but it was not clearly for bovine dentin.The application of SnF₂ solution after treatment by<PYF-SnF₂>primer, improved the bond strength and the adhesion.The bond strength was improved by treatment with a higher concentration of phytic acid solution by adhesive of Super Bond to apatite.Bovined dentin was treated for 30 seconds with 3-50% phytic acid solution then with SnF₂ solution applied.The appropriate concentration of phytic acid solution on the bovine dentin was approximately 3%.The difference with the kind of adhesive was small.The duration of the treatment with phytic acid solution or SnF₂ solution had litte effect on the bond strength of resin cement to bovine dentin.The surface of bovine dentin treated with <PYA-SnF₂>primer was the same as that treated with the 10-3 solution, and the<PYA-SnF₂>primer was slightly infringed on hard tissue of tooth.

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Usually, prosthesis are manufactured by the casting technique.To make precise castings, high technical skill and attention are required.Heating of mold is not only required for dewaxing but for many important roles, such as mold strengthening, ensuring air-permeability of mold and preheating for precise casting.To fill these roles, temperature control during the heating process is essential.Although it is known experimentally that the temperature varies with the position in the furnce and the mold temperature varies depending on the arrangement of the molds, no precise study about this problem has been reported.In the present study, the temperature distribution in the furnace without mold and actual mold temperatures placed in the furnce were measured and recorded using a conventional furnace which is usually used in the dental clinic.Experimental data were examined from the view points of temperature changes due to heating and cooling, mold size and arrangement in the furnace.With no molds, less temperature difference was measured between top and bottom of the furnace and also between right side and left side.However, it is observed that much temperature difference exists between door side and deep of the furnace.When the molds were put in the furnace, there was less temperature differences among the molds which were placed crowded together at the center of the furnace than when the molds were placed scatteringly from door side to deep of the furnace.Temperature differences among molds became larger at elevated temperatures due to influence of heat radiation.It is concluded that detailed studies on the relationship between mold temperature changes during heating and results of castings are necessary to build a better casting system for dental materials.

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Retention forces of super-elastic Ti-Ni alloy castclasps were studied, in comparison with other conventional dental alloys, such as cobalt-chromium alloy, gold-silver-palladium alloy and titanium.Retention forces were measured by repeated setting-removal test of the Akers type castclasps with a tooth model.Considering from retentive force-displacement curves, the retentive force of Ti-Ni alloy castclasps showed little change during the 1, 000 cycles of the test, with either the 0.25 and 0.50mm undercut.On the other hand, retention forces of conventional dental alloy clasps decreased obviously with both a 0.25 and 0.50mm undercut with increasing number of setting and removal.Ti-Ni having th super-elastic property could be applied to castclasps with much deeper undercut than other dental alloys conventionally used in designing castclasps in prosthodontics.Futhermore, the super-elastic property could prevent castclasps made of Ti-Ni alloy from being broken.

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The present study was carried out to develop an accurate and quantitative measurement method for in vivo wear of posterior resin composite restoration.The measurement was performed using a newly developed and a precise 3-D digitizer interfaced with a personal computer.A plastic model of an extracted human upper premolar was mounted on the XY coordinate sliding table of the digitizer(CAMM-3 System)and digitized using a needle probe(PZC-100).The model was remounted in several optional positions and digitized.Three distinctive anatomical features, like pits or concavities, were selected for the reference points to superimpose on the above data.The B-spline curved surface interpolation was fitted to the digitized data to search the bottom of these areas, and these were decided as the real reference points.After identification of the real reference points, two data points were superimposed with the coordinate transform to confirm each reference point, and the B-spline curved surface interpolation was fitted.The accuracy of the superimposition was calculated.Also the wear measuring method was applied to fit this newly developed quantitative system using the artificial wear composite restoration on the extracted upper premolar.Consequently, the dimensional accuracy of this system proved satisfactory and the obtained results were very useful to evaluate the wear of the restorations.

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The effect of surface treatment on the structural change of dentinal collagen and the durability of the adhesiveness to resin were examined and its mechanism was considered.From the adhesive strength test, scanning electron microscopy(SEM)and transmission electron microscopy(TEM)for acid-etched dentin, treated with various solutions of 2-hydroxyethyl methacrylate(HEMA), the following results were obtained.The highest adhesive tensile was observed after immersion in water at 37℃ for one day and after 20, 000 thermal cycles following the application of HEMA/water solution.Therefore, we concluded that the collagen layer of the adherent surface changes characteristically.The transformation of the microfibril structures of dentinal collagen fibers was supported by the fact that the resin impregnated layer was thicker than the others.Adhesive tensile strength was not improved when the phosphoric acid etching technique was followed by application of different HEMA solutions(HEMA/ethanol, HEMA/benzene and 100% HEMA).However, tensile strength scarcely decreased after thermal cycling and increased proportionally to the application time.

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Super-elastic Ti-Ni alloy wire, which has excellent spring-back properties, is now used extensively in orthodontics.However, clinical orthodontic techniques require special operations such as shaping of equipment and attachment to an additive by bending and soldering.Therefore, considering the features of the Ti-Ni alloy wire, it is difficult to perform such operations.In respose to these problems, a method applying a crimpable hook, which has been used in orthodontics as an auxiliary, to Ti-Ni alloy wire was invented and has been used effectively.However, it is not clear why the crimp method is so effective for Ti-Ni alloy wire.In this study the relationship between the crimpable hook and Super-elastic Ti-Ni alloy wire was examined using a tensile test, SEM and DSC.The findings suggested that the fixation by Ti-Ni alloy wire and the crimpable hook results from the super-elasticity affected by stress-induced martensitic transformation and reverse transformation.

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Temporomandibular joint(TMJ)disorders accompanied by disk displacements and/or disk perforations have been considered to be the result of excessive TMJ loading.However, the precise values for loads acting on TMJ during mastication have not been measured.In this study, a micro pressure-sensor(3mmφ)composed of biocompatible HAP(hydroxyapatite)-piezoelectric PZT(Lead Zirconate Titanate)laminated ceramics was designed and then fabricated to measure directly the load acting on the local surface area of the condylar head of monkey during mastication.First, the pressure-sensor was calibrated under the cyclic loading conditions.The results of a calibration test showed a linear relationship(r=0.9981)between the integrated output of the sensor and the load up to 19.6N.Subsequently, the pressure-sensors were implanted into the anterior and superior surface of the condylar heads of monkeys, and then the loads acting on the sensors were recorded during the mastication of hard foods.The maximum load of 2.05N, 0.42N, and 0.18N was measured at the maximum opening of mandible, during chewing movement, and during grinding movement, respectively.Assuming that the load was distributed uniformly on the sensor, these maximum loads could be converted into the maximum pressure of 0.29MPa, 0.07MPa, and 0.03MPa, respectively.

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We investgated the spreading area of silver solder Ti at 800℃ or 900℃ using KHF₂-LiF-NaCl-KCl fluxes and tested the joint strength of Ti bonded with resistance brazing.We also observed the surface of a fractured joint by SEM and analyzed a brazed joint with EPMA.When the concentration of NaCl+KCl was 0, 10, 20, 30, 40 and 50%, the spreading areas increased with increasing LiF/KHF₂ and was the maximum at the ratio of 1.5 for 0% NaCl+KCl, 0.43〜0.46 for 10 to 40%, and 0.06〜1.5 for 50%.No significant differences in the joint strengths were obtained with the fluxes of the maximum spreading for any NaCl+KCl composition.The strength was also not significantly different with the LiF/KHF₂ for 30% NaCl+KCl.TiCu and TiCu₂ were found in the solder at the boundary of the joint. Fractures occurred near the boundary of the joints and the fracture surface was brittle. These fluxes had a broad effective range for the Ag solder-brazing of Ti with resistance brazing.

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To improve the bonding of light-cured composite resin to dentin, a new monomer, 2-Acryloyloxyethyl hydrogen maleate(2AEM), was prepared by the addition of maleic anhydride to 2-Hydroxyethyl acrylate, was identified by elemental analysis and IR and NMR spectra.Dentin etched and unetched with 0.5M EDTA solution(EDTA)and 37% phosphoric acid solution were treated with 2AEM, and the bond strengths of light-cured composite resin were measured.Also, the resin-dentin interface, and the dentin surfaces after the shear bond test were observed by SEM.When polished dentin was treated with 2AEM for over 3min, the bond strength of light-cured composite resin was higher than that without treatment, and the acid-proof dentin layer was less than 1μm thick at the resin-dentin interface.When etched dentin was treated with 2AEM for 1min, the bond strength was markedly improved, and the thickness of the acid-proof dentin layers was 1μm for EDTA and 3μm for phosphoric acid.When etched dentin was treated, the specimens after the shear bond tests showed resin and dentin cohesion fractures.

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