Toshio Takatsu

Relationship between surface area for adhesion and tensile bond strength--evaluation of a micro-tensile bond test.

OBJECTIVES The purpose of this study was to test the null hypothesis that there is no relationship between the bonded surface area of dentin and the tensile strength of adhesive materials. METHODS The enamel was removed from the occlusal surface of extracted human third molars, and the entire flat surface was covered with resin composite bonded to the dentin to form a flat resin composite crown. Twenty-four hours later, the bonded specimens were sectioned parallel to the long axis of the tooth into 10-20 thin sections whose upper part was composed of resin composite with the lower half being dentin. These small sections were trimmed using a high speed diamond bur into an hourglass shape with the narrowest portion at the bonded interface. Surface area was varied by altering the specimen thickness and width. Tensile bond strength was measured using custom-made grips in a universal testing machine. RESULTS Tensile bond strength was inversely related to bonded surface area. At surface areas below 0.4 mm2, the tensile bond strengths were about 55 MPa for Clearfil Liner Bond 2 (Kuraray Co., Ltd.), 38 MPa for Scotchbond MP (3M Dental Products), and 20 MPa for Vitremer (3M Dental Products). At these small surface areas all of the bond failures were adhesive in nature. SIGNIFICANCE This new method permits measurement of high bond strengths without cohesive failure of dentin. It also permits multiple measurements to be made within a single tooth.

Tensile Properties of Resin-infiltrated Demineralized Human Dentin

The ability of adhesive resins to restore the physical properties of demineralized dentin has not been well-documented. The unfilled resins that are used for adhesion have relatively low moduli of elasticity and limited ability to increase dentin stiffness, although they may increase the ultimate tensile strength of dentin. This study tested the hypothesis that resin infiltration of demineralized dentin can restore its tensile properties to those of mineralized dentin. Small (ca. 0.5 mm thick x 0.5 mm wide) specimens of demineralized human dentin were infiltrated with one of five different dentin bonding resins over many hours, to determine how these resins altered the tensile properties of dentin. Tensile stress and strain were measured in these and control (mineralized and demineralized) specimens until their ultimate failure. The results indicate that some adhesive resins, after infiltrating demineralized dentin, can restore and even exceed the ultimate tensile strength of mineralized dentin. These resins increased the modulus of elasticity of resin-infiltrated dentin to values equal to or greater than those of the resins but far below those of mineralized dentin. Although the conditions in this experiment were far removed from the manufacturers recommendations or clinical practice, the results support the potential of resin infiltration for reinforcing dentin.

The influence of age and depth of dentin on bonding

OBJECTIVES The purpose of this study was to investigate what influence the two variables of dentin depth and age may have on the tensile bond strengths of three bonding systems. METHODS Dentin discs prepared from human molars were divided into young and old, superficial and deep surfaces. Three bonding systems, Scotchbond Multi-purpose (3M Dental Products), Superbond D-liner (Sun Medical Co.), and Liner Bond II (Kuraray Co.) were the materials tested for tensile bond strength. In addition, the structural variation of the resin-impregnated, or hybrid, layer was compared among the two variables and three bonding systems. RESULTS Tensile bond strengths exceeding 10 MPa were obtained for all materials. After ANOVA, an effect on tensile bond strength could be attributed to dentin age or depth for only Superbond D-liner used on deep-young dentin as compared with old-superficial dentin. All other group comparisons failed to show any variation between dentin depth or age. However, specimens bonded to deeper dentin showed slightly lower strengths. SEM observations showed thicker resin-impregnated layers for Scotchbond MP and Superbond D-liner compared with Liner Bond II. Liner Bond II exhibited a thinner and more diffuse resin-impregnated layer, believed to be due to the different dentin conditioning method. SIGNIFICANCE Dentin age or depth may not show as great an influence on bond strengths with the newer type of bonding systems. The resin-impregnated layer quality, rather than thickness, is believed to be the most important factor for obtaining high tensile bond strengths.

Shear and tensile bond testing for resin cement evaluation

OBJECTIVES The aim of this study was to compare the tensile and shear bond strengths of one experimental and four commercially available resin cements following the ISO document TR 110405 for bond measurement. METHODS Tensile and shear bond tests were performed using bovine enamel and dentin as the tooth substrate with each of the resin cements. Resin composite rods were cemented to the prepared tooth surfaces. The bond strengths were obtained 24 h after cementation, and mode of failure was classified after fracture of the bonds, both visually and by SEM observation. RESULTS Significant differences existed between the two bond test methods for all materials with enamel and three of the five cements when bonded to dentin. The shear test results were always the higher of the two test methods. Mode of fracture varied little for the visual classification, but the morphology from SEM observations showed considerable differences. SIGNIFICANCE Although there are deficiencies in the current test methods these may be outweighed by substrate variables. A test model should be designed to determine which stresses, tensile or shear, are the greatest for different types of restorations. With this information, the type of test selected could provide appropriate information before clinical trials are commenced.

Influence of temperature and relative humidity on early bond strengths to dentine

The effect of temperature and relative humidity (RH) on the early tensile bond strengths to bovine dentine of two bonding systems (Liner Bond System, and Scotchbond Multi-purpose), and an experimental system (KB-110) were tested. Two environmental conditions, room temperature (23 degrees C/50% RH) and oral temperature (30 degrees C/80% RH), were used in a controlled temperature and humidity chamber. Bond strengths were recorded immediately after, 10 min and 24 h following light curing. The tensile bond strengths did not vary between the two test conditions, but the mode of fracture was observed to change. The 30 degrees C/80% RH condition exhibited a slightly greater degree of adhesive type failures compared with the 23 degrees C/50% RH group. This was particularly so for the experimental system, indicating that different bonding systems may be more or less sensitive to changes in RH and temperature. Failures occurred partially or totally within the resin composite at the early test times, and it was concluded that the bond strengths of the systems tested tended to exceed the early cohesive strengths of the resin composite.

Comparison of three luting agents

Three types of luting cements were compared for acidity, disintegration, and film thickness. The pH during setting of the two types of polycarboxylate cements exceeded 6 after 5 hours; that of the water-settable polycarboxylate cement was the highest, almost reaching neutral. The zinc phosphate cement reached pH 3.4 after 5 hours and 5.5 after 24 hours. All cements tested showed remarkably greater disintegration in the lactic acid solution than in the distilled water. The disintegration of the water-settable zinc polycarboxylate cement in distilled watter was about half that of the other cements. The disintegration in the lactic acid solution was approximately the same for all cements tested. The film thickness was smallest with the water-settable zinc polycarboxylate cement.

A varnish to prevent etching unrestored enamel

The prognosis of acid-etched enamel was investigated in both laboratory and clinical experiments. Acid etching produced irregularities even on the prismless layer that covers prism enamel. The irregularities produced by etching are not remineralized in vivo but are filled with organic debris. Brushing reduced the depth of the irregularities but did not eliminate them. A protective varnish against acid etching was developed. The varnish also serves as a guide to facilitate removal of excess resin beyond the cavosurface margin.

Structure and Effects of Non-gamma-2 Amalgam:

A non-γ2 amalgam was investigated using optical microscopy, electron probe microanalysis, and a micro hardness test. Its improved mechanical properties seem to be the result of the remarkable hardness of reaction rings. Its decreased marginal fracture seems to be caused by the absence of the corrosion-prone γ 2 phase which may cause extrusion of the margins.

Surface adhesion and retentive force of cements

Z inc phosphate cement has been used as a standard luting agent for cast restorations for many years. The retentive force of the cement measured 13% surface adhesion and 87% interlocking force when analyzed by Fusayama et al.’ with cylindric inlays. Polycarboxylate cement proved to be superior to zinc phosphate cement in adhesion to tooth substances and in pulpal compatibility.’ The technical and chemical properties of this type of cement were improved by the development of a water-settable cement.3 A new type of polycarboxylate cement (HY Bond Carbocement, Shofu Dental Mfg. Co., Kyoto, Japan) was recently developed by adding HY agent, a cariespreventing agent that contains zinc fluoride, strontium fluoride, tannic acid, and other components prescribed by Yamaga.4 When tested by Yamada et a1.,5 the addition of the HY agent did not significantly alter the compressive strength, diametral tensile strength, or film thickness, but it slightly decreased disintegration in lactic acid. The three above-mentioned types of cements (Table I) were compared for surface adhesion to tooth substances and dental casting alloys, as well as retentive force of cemented restorations.

Setting Changes of Amalgam Surfaces Observed by a Scanning Electron Microscopic Motion Picture

The changes of the phases on a setting amalgam surface were observed by a scanning electron microscope and recorded on a videotape. The image reproduced on a TV monitor was converted into a 16-mm motion picture with a low speed movie camera. The movie showed the dynamic process of the change of matrixes and residual alloy particles developing new γ1 and γ2 crystals and voids.