Minoru Nishiyama

A Comparison of the Tensile Bond Strengths of Composite Resins to Longitudinal and Transverse Sections of Enamel Prisms in Human Teeth

The tensile bond strengths of composite resins to transverse and longitudinal sections of enamel prisms etched with phosphoric acid were examined. The tensile bond strengths were 18-19 MPa to the transverse and 10-11 MPa to the longitudinal sections and thus were influenced by the nature of the enamel crystal planes. These facts suggest that composite resin restorations will have a longer life span if the enamel walls are given marginal forms to produce transverse rather than longitudinal sections of enamel prisms.

Evaluation of different bonded investments for dental titanium casting

The properties of several different investments were investigated including phosphate bonded, magnesia bonded, and alumina cement investments.Measurements included the setting expansion, thermal expansion, and compressive strength of investments, as well as the tensile strength, elongation, Vickers hardness (VHN) and surface roughness of titanium castings. For phosphate bonded investment, the setting expansion after being mixed with its own mixing solution was 2.10%, which was larger than the other investments; the thermal expansion was −0.25% at 200 ^∘C, the compressive strength 14 and 5 MPa after heating. For titanium cast in phosphate bonded investment, the hardness on its top surface was 655 Hv, the tensile strength was 379 MPa, the elongation was 19.4%, and the surface roughness was 2.29 μ m. Athough the thermal expansion of phosphate bonded investment is small, the setting expansion is large enough to compensate for the shrinkage of titanium castings. As its thermal expansion at T ≥ 600∘C was constant and its heating-cooling cycle was almost reversible, these two properties can reduce the thermal shock and thus avoid cracking of the investment.

Bond Strength to Dentin Subjected to Temporary Cementation of Resin Based Luting Agents

目的: リン酸を表面処理剤とするレジン系装着材料の仮着した象牙質に対する接着強さの影響を明らかにするために, 比較検討を行った.方法: HY-Bond Temporary Cement Hard (以下HYB), Freegenol Temporary Pack (以下FTP) およびNeodyne T (以下NDT) の3種類の仮着材で, レジンプレートを牛歯象牙質に仮着した.Variolink II (以下V2) およびRely X ARC (以下RX) を用いて, IPS Empressを接着して勢断接着試験用試料を作製した.仮着を行っていないものをコントロール (以下CON) とした.仮着した象牙質およびIPS Empressに対する表面処理は, 製造者指示に従って行った.試料を37℃ で24時間精製水中保管後, 勇断接着強さを測定した.結果: V2の接着強さは, CON (11.4MPa, a, b), HYB (12.7MPa, a), FTP (7.6MPa, b, c) およびNDT (5.9MPa, c) であった.CONと比較してNDTが有意に (P<0.05) 低い値を示したが, HYBおよびFTPでは有意差が認められなかった.一方, RXの接着強さは, CON (21.7 MPa, d), HYB (11.3MPa, e), FTP (6.0MPa, f) およびNDT (11.2MPa, e) であった.CONと比較してすべての仮着材で有意に低い値を示した.最も低い値を示したFTPでは, CONの27.5%であった.同一文字は多重比較において危険率5%で有意差がないことを示す.結論: V2とRXは, 接着強さが低下した仮着材がそれぞれで異なったことから, リン酸処理を行うレジン系装着材料の接着強さは, 組合せによって影響が異なることが明らかとなった.

A Study on Repair Restoration with High Filler Containing Indirect Composites-Surface Treatment for Light Cured Type Resins-

目的: 光重合タイプの高フィラー型硬質レジンの補修時における有効な表面処理方法を知ることを目的とした.方法: ArtglassおよびGradia (エナメル色ペーストAEおよびGE, デンチン色ペーストADおよびGD) を用い, 製造者指示に従い重合した被着体 (2×2×12.5mm) に, 処理なし (NT), シラン処理 (S), ボンディング処理 (B), シラン処理とボンディング処理を併用 (SB) の4条件で表面処理を行った.追加築盛は, 直接法および間接法のそれぞれで, 製造者指示の補修用レジンを用いて曲げ接着試験用試験体 (2×2×25mm) を重合して作製した.試験体は, 37℃ で24時間水中保管後に3点曲げ試験を行い, 曲げ接着強さを得た.結果: 被着体AEは直接法ではSB>S>B>NT, 間接法ではSB≧S>B>NTの順で, 被着体ADは直接法および間接法の両者で, SB>S>B>NTの順で有意に大きな曲げ接着強さを示した.一方, 被着体GEは, 直接法ではSB>B≧S>NT, 間接法ではSB≧S≧B>NTの順で, 被着体GDは, 直接法ではSB≧B>S>NT, 間接法ではSB≧B≧S>NTの順で有意に大きな曲げ接着強さを示した.結論: 最適な表面処理は, AEが直接法でSB, 間接法でSBおよびS, ADが直接法および間接法の両者でSB, GEが直接法ではSB, GDがSBおよびB, GEおよびGDともに間接法ではS, BおよびSBであった.

A Study on Thermal Properties of All Ceramic Restorations. All Ceramics.

This study was conducted to investigate the thermal properties (thermal diffusivity, specific thermal capacity and thermal conductivity) of all ceramic restorative materials. Measurement of thermal properties of IPS Empress®, DiCOR® and adhesive resin cement Variolink II were performed by the Xenon flash method. The results obtained were as follows. Thermal diffusivity (×10-2cm2s-1) was 0.372-0.423 for IPS Empress®, 0.614 for DiCOR® and 0.191-0.193 for Variolink. Specific thermal capacity (Jg-1K-1) ranged from 0.695 to 0.872 for IPS Empress®, 1.119 for DiCOR® and 0.733-4.114 for Variolink. Thermal conductivity (Wm-1K-1) was 0.644-0.770 for IPS Empress®, 1.721 for DiCOR® and 0.297-0.475 for Variolink. Thermal conductivity of IPS Empress® was found to be less than that of human enamel, while that of DiCOR® was greater than that of human enamel. Thermal conductivity of Variolink was smaller than those of human enamel and dentin.The above results indicated that IPS Empress® had greater thermal insulation capability than human enamel and dentin and that DiCOR® had less.

A Study on Tensile Bond Strength of Silicone-rubber Soft Relining Material: Denture Relinig to Various Denture Base Materials.

The tensile bond strength (TBS) to denture base materials of silicone-rubber soft relining materials (DRS: Denture Relining Soft type, GC) immersed in water at 37°C from 1 day to 8 weeks was investigated. Four denture base metals (18 K-Au alloy, Ag-Pd-Au alloy, Co-Cr alloy and Pure Ti) and two denture base resins (polycarbonate resin and polysulfon resin) were used. The TBS of DRS was 1.39-2.05 MPa to denture base metals and 1.59-1.81 MPa to denture base resin after 1-dayimmersion, and 1.59-2.75 MPa and 1.47-2.33 MPa respectively after 8-week immersion. These values were significantly superior to those of two ordinary silicone-rubber relining materials.

A Study on the Fine Particle Glass Ionomer Cements for Luting. Setting Characteristics and Disintegration Rate.

For improvement of film thickness of final cementation, 2 brands (Shofu HY-BOND GLASS-IONOMER CX and GC Fuji-I) of Glass Ionomer Cement were milled and the experimental fine particlepowder was produced. Ohmae et al. reported the retention, total film thickness, and physical properties in aprevious study. In this study, the setting characteristics of these experimental cements, specific surface areaof particle, and disintegration rate were investigated. The results were as follows: Peak time of reaction ofexperimental cements using a differential scanning calorimeter were shorter than normal GICs. The startingpoint of dissappearance of fluidity of experimental cements using a thermomechanical analyzer were shorteras the perticle size became smaller. The specific surface area of experimental particle increased as theparticle size became smaller. The disintegration rate of experimental cements increased compared to normal GICs.

A Study of Toothbrush Abrasion on Adhesive Resin Cement. Filler Contents of the Routing Cement.

Although there have been reports on the abrasion of resin cements, cement film thickness was hardly considered.Takamisawa evaluated the influence of the cement film thickness on the abrasion of non-filler type resin cement, and concluded that there was a close relationship between number of times and depth of abrasion. The rate of increase of the wear depth was affected by the cement film thickness.Since most resin cements contained microfiller, Variolink (Vivadent) was examined and it was IPSEmpress (Vivadent) cem kit.Newly-designed appliances to prescribe 3 cement film thicknesses were used, namely 50, 100, and 200 μm, and the abrasion for each thickness in toothbrush abrasion test was observed.Continuous measurements were made of the sectional profile, wear depth, and surface roughness by scanning laser microscope.In SEM observation, the abrasion surface showed different aspects between non-filler and microfiller types.While there was a close relationship between number of times and depth of abrasion as in the case of non-filler type, the amount of increase of the wear depth varied with the cement film thickness.Test results indicated that the cement film thickness had influence on the abrasion of resin cement, and resistance of abrasion was influenced by filler type and resin matrix.

A Study on the Retention Force of Crowns. Influence to the Changes in the Powder Particle Size Distribution of Glass Ionomer Luting Cement on the Retention Force of Crowns.

When cementing a crown, the amount of final seating is affected by the film thickness of the dental cement. To decrease the film thickness of glass ionomer cement (GIC), a GIC powder (Shofu Hybond Glass ionomer CX) was milled and three experimental fine particle powders were produced. The purpose of this study was to investigate the physical properties of fine particle GICs (ISO-9917, compressive strength, setting time, film thickness) and retention force of the crown cemented. The powder was milled with Centrifugal Fluidized Milling Machine (CF-160 Ube Kousan Co.) to produce the particle size (CX-01: maximum particle size:∅6μm, CX-02: 8μm, CX-03: 12μm). The results were as follows: In specimen containing a large amount of fine particles (CX-01), the best seating of a crown was accomplished (total film thickness: 8.0μm), though both compressive strength and film thickness was reduced to some extent. On the other hand, there was no significant difference between the retention force of normal GIC and fine particle cement (CX-01, 02, 03). The setting time of CX-01, 02, 03 was slightly longer than that of normal GIC.

Influence of Changes in the Powder Particle Size Distribution on the Physical Properties of Luting Agents. Mainly on Influence of Pretreatments of Abutment Tooth before Final Cementation.

Our department has been researching the influences of changes in particle size distribution on the physical properties of luting agents. It is said that luting agents are largely affected by contact with water. In the present study, changes in the physical properties after contact with water at the time of cementation were determined in several types of glass-ionomer cement for Luting (Gcement), which differed in particle size distribution, by using an ivory or agar jig. The physical properties of G cement were also examined after pretreatment of the abutment tooth with a surfacetreatment agent and a temporary cement inside the ivory jig.As a result, the greater the content of fine particles was, the greater the compressive strenght, tensile strength and scratch hardness of G cement tended to be. G cement containing high proportions of fine particles was not likely to be affected by water. Pretreatment suchas temporary cementation or surface-treatment prior to cementation for crown or bridge formation was found to be effective for preventing deterioration of the physical properties of G cement.