Dentin bonding: influence of bonded surface area and crosshead speed on bond strength.

This study investigated the influence of the bonded surface area and the crosshead speed on the dentin bond strengths of self-etch adhesives. Bovine mandibular incisors were mounted in self-curing resin and the facial surfaces were wet ground with #600 silicon carbide (SiC) paper. The dentin surfaces were treated according to the manufacturer's instructions. Adhesives were applied, and the resin composites were condensed into molds (2.4 or 4.0 mm in internal diameter), placed on to the dentin, and then light activated. Ten samples per test group were shear tested at crosshead speeds of 0.1, 0.5, 1.0, 5.0, and 10.0 mm/min. The results showed that higher crosshead speeds were associated with higher dentin bond strengths. This relationship was more significant for specimens with a smaller dentin bonding surface area.

Influence of power density and primer application on polymerization of dual-cured resin cements monitored by ultrasonic measurement.

We used ultrasonic measurements to monitor the influence of power density and primer application on the polymerization reaction of dual-cured resin cements. The ultrasonic equipment comprised a pulser-receiver, transducers, and an oscilloscope. Resin cements were mixed and inserted into a transparent mould, and specimens were placed on the sample stage, onto which the primer, if used, was also applied. Power densities of 0 (no irradiation), 200, or 600 mW cm(-2) were used for curing. The transit time through the cement disk was divided by the specimen thickness to obtain the longitudinal sound velocity. When resin cements were light-irradiated, each curve displayed an initial plateau of approximately 1,500 m s(-1), which rapidly increased to a second plateau of 2,300-2,900 m s(-1). The rate of sound velocity increase was retarded when the cements were light-irradiated at lower power densities, and increased when the primer was applied. The polymerization behaviour of dual-cured resin cements was therefore shown to be affected by the power density of the curing unit and the application of self-etching primer.

Self-etching primer systems: changes in dentin bond strength with time.

The purpose of this study was to investigate the development of shear bond strength of resin composites using self-etching primer systems. Four different types of self-etching primer systems with different combinations of their recommended resin composites were used. Bovine incisors were mounted in self-curing resin and the facial surfaces were wet ground on #600-SiC paper to expose the dentin. The shear bond strengths of ten samples per test group were measured at a crosshead speed of 1.0 mm/min after storage for 5, 10, and 60 min, and 24 h in distilled water at 37 degrees C. One-way ANOVA followed by Dunnett's test (alpha = 0.05) was used to examine the significance of differences between the mean bond strength at 24 h and each of the other storage periods. The dentin bond strengths of all the materials tested increased with prolonged storage time. Such differences in the changes in bond strength might have clinical implications if a restoration is subjected to high stress immediately after it has been placed. It is important to consider the development of dentin bond strength to allow the materials sufficient maturation time prior to functional loading or application of other forms of external stress.

Changes in elastic modulus of adhesive and adhesive-infiltrated dentin during storage in water.

The purpose of this study was to determine the elastic modulus of components at the resin-dentin interface with the use of an ultrasound device. Dentin slabs were obtained from freshly extracted bovine incisors shaped into a rectangular form. After demineralization, the dentin specimens were immersed in adhesives and polymerized. Adhesives were also polymerized and trimmed into the same shape as the dentin slabs. The specimens were then immersed in distilled water at 37 degrees C for up to one year. The ultrasound equipment employed in this study was a Pulser-Receiver, transducers and an oscilloscope. By measuring the longitudinal and shear wave sound velocities, the elastic modulus was determined. When the elastic modulus of adhesive resin-infiltrated demineralized dentin was compared with that of adhesives, slightly but significantly lower values were found for adhesives used in a self-etching primer system. On the other hand, a higher elastic modulus was observed for resin-infiltrated dentin than for an adhesive used in an etch and rinse system. The elastic modulus of the resin-infiltrated dentin prepared with the etch and rinse system was affected by long-term storage in distilled water.

Change in elastic modulus of bovine dentine with exposure to a calcium hydroxide paste.

OBJECTIVE: To determine the effect of calcium hydroxide [Ca(OH)(2)] paste exposure on the elastic modulus of bovine dentine. METHODS: Dentine sections (4 mm x 4 mm x 1 mm) were obtained from freshly extracted bovine incisors and placed in dishes containing a 1-mm deep layer of Ca(OH)(2) paste or physiological saline as a control. An ultrasonic device was used to measure the sonic velocities of the longitudinal and shear waves, and the elastic modulus was calculated. Data were examined by analysis of variance followed by the Tukey H.S.D. test in order to compare different storage times. RESULTS: Exposure to Ca(OH)(2) paste significantly increased the mean elastic modulus of the dentine from 16.3 to 22.1 GPa. By contrast, the elastic modulus of the control dentine, which was exposed to physiological saline, remained constant. CONCLUSION: These results demonstrate that exposure to Ca(OH)(2) paste increases the elastic modulus of dentine, thereby making it more prone to fracture.