This study investigated the durability, especially the nonwaterdegradable qualities, of experimental lightcured composite resin containing barium-borosilicate glass filler. For this purpose, Bis-GMA, a typical component of base monomer in conventional composite resin, was replaced by Bis-GMA-F which is water-repellent. After over 20, 000 thermal cycles, the composite resin containing Bis-GMA retained only 60∼70% of its initial compressive, diametral tensile, flexural strength and flexural elastic modulus. However, the experimental composite resin containing Bis-GMA-F as a resin matrix showed no loss of compressive, diametral tensile strength or flexural elastic modulus, although flexural strength showed some deterioration. It was considered that the difference between Bis-GMA-F and Bis-GMA, as resin matrix, caused variation in the characteristics of water sorption.

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Composite ceramics dispersed through diamond particles with hydroxyapatite as a matrix were prepared by firing at 1250°C under reduced pressure or normal atmosphere. The fracture toughness and physical properties of sintered composite ceramics were examined to determine methods of strengthening hydroxyapatite ceramics. The diamond crystal in composite ceramics was transformed to graphite by firing and the fracture toughness of hydroxyapatite ceramics increased with diamond addition. At 10wt% diamond, the maximum value for fracture toughness was obtained, and the further addition of diamond particles over 10wt% caused fracture toughness to decrease. Such increases in fracture toughness were considered the result of microcracking which occurred during the transformation from diamond to graphite.

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Enamel and dentin surfaces of bovine teeth were characterized after mechanical and chemical removal of temporary cements. The surfaces were examined by scanning electron microscopy and X-ray microanalysis. Contact angles of distilled water were measured to monitor surface wettability. Mechanical removal with a dental probe did not completely remove all of the temporary cement from both enamel and dentin surfaces. These surfaces usually produced contact angles of distilled water greater than that on polished surfaces. Etching with thirty-seven percent phosphoric acid effectively removed the temporary cement that remained on enamel surfaces after mechanical removal but the etchant was not effective on dentin surfaces. Acid etching aftar mechanical removal of cement significantly decreased the contact angles of distilled water on enamel surfaces but the etchant only slightly improved contact angles of distilled water on dentin surfaces.

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To diminish the effect of water on the adhesive durability of lining cement, an experimental lining cement using a hydrophobic polymer as the cement liquid was studied. The polymers were styrene-butadien-alkyl acrylate copolymer (SBA copolymer) and carboxylated styrene-butadien-alkyl acrylate copolymer (CSBA copolymer) and were used as aqueous emulsions. The cement powder consisted of alkaline silicate and calcium disilicate. The pH values of the immersion water of the cement prepared from emulsion of SBA copolymer (SBA cement) was almost the same as that of calcium hydroxide cement. The compressive and diametral tensile strengths of SBA cement gradually increased over time in water. The bond strengths of cement prepared from the CSBA copolymer emulsion containing five percent carboxyl groups by weight were superior to those of calcium hydroxide cement.

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We bonded a glass ionomer cement (GIC) containing various amounts of incorporated tannin-fluoride preparation (HY agent) to bovine dentin and investigated the effect of the ratio of incorporated preparations and the changes in bond strength over time. HY agent was incorporated into the powder at 0% (HY0), 1.5% (HY1.5), 5.0% (HY5), and 10.0% (HY10) by weight. The shear bond strength and percent of the cohesive failure were measured. Similar tests were performed on samples where diammine silver fluoride was applied to the dentin prior to placing the cement. It was found that the bond strength on the first day was increased by incorporating 1.5% of the HY agent in the GIC. The combined use of diammine silver fluoride increased the bond strength of the GIC.

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Statistical fatigue life for body dental porcelains, cooled in a furnace and in air, was predicted from measurements of post-indentation slow growth of radial cracks in water and in air. Cracks were induced in the surfaces of porcelain discs by a Vickers indenter at an applied load of 9.8N. Crack lengths were measured at various times over a period of 5 months to calculate the stress corrosion susceptibility coefficient, n. Lifetime under service stress was estimated from the measured value of n. The ratios of service stress to fracture strength were calculated as 0.47 and 0.69, respectively, for glassy and feldspathic porcelains which were cooled in a furnace and aged in water. The corresponding ratios for tempered (cooled in air) specimens were 0.58 and 0.67, respectively. These were estimated values when service life exceeds 10 years. The results suggest that the air cooling process can effectively increase the service life of glassy porcelains, but, for feldspathic porcelain it is less effective.

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This study developed a simple method for in vivo evaluation of wear on composite resins and examined the role of filler particles in this process. Experimental light-cured composite resins with two different filler systems were prepared: (1) 81wt% fine quartz filler (Conventional type) and (2) 73wt% organic filler (Microfilled type). The resin monomer consisted of 50wt% Bis-GMA and 50wt% TEGMA. These materials were placed in cylindrical cavities 2mm in diameter located in the OCA (occlusal contact area) or the CFA (contact free area) in Au-Pd crowns, temporarily set in a volunteer's mouth. The crowns were removed at monthly intervals for longitudinal SEM observation. Results showed that the newly developed method was useful for observing the in vivo wear-patterns of composite resins. The two experimental composite resins with different filler systems showed quite different wear-patterns.

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One important mechanical property of core composite resins is fracture toughness, K_IC, which expresses serviceability in the oral cavity, such as the resistance to marginal fracture. K_IC values of eight commercial core composite resins were examined by the single-edge notched-beam (S.E.N.B.) method. Two composites containing about 80wt% Si₃N₄ fillers exhibited both the highest K_IC value of around 2.0MN⋅m^-3/2 and the highest hardness value. The other six composites containing 66 to 86wt% SiO₂-based fillers had K_IC values of around 1.2 to 2.0MN⋅m^-3/2, and there was a tendency toward higher K_IC values as hardness increased. It was speculated that the clinical acceptability of core composite resins could be broadened, if dental clinicians selected composites with higher K_IC values.

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To determine how MDP interacts with liposomes, the chemical shifts of dipalmitoylphosphatidylcholine (DPPC)/MDP and dilauroylphosphatidylethanolamine (DLEA)/cholesterol (CS)/MDP liposomes were studied by NMR spectroscopy using a D₂O buffer solution at pH7.0 as a model for biological membranes. Proton chemical shifts of MDP enhanced shielding in DPPC liposomes together with an increase in the mobility of DPPC. However, MDP signals were not observed in DLEA/CS liposomes due to saturation. It is known that an ionized chemical does not lead to increased permeability of cell membranes composed of a lipid bilayer. However, MDP, which is ionized at pH7.0, had a large interaction with the liposome systems. This appeared to arise from hydrophobic interaction between deca methylene groups of MDP and acyl chains of phos-pholipid.

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