Tensile bond strengths of dual-cured cements between a glass-ceramic and enamel.

STATEMENT OF THE PROBLEM: Dual-cured cements have been used with castable ceramic restorations, but the tensile bond strengths of these materials have not been thoroughly researched. PURPOSE OF THE STUDY: This study compared the tensile bond strengths between Dicor castable ceramics and enamel of four dual-cure cements: Twinlook, Optec Dual-Cure Luting Cement, Clearfil CR Inlay, and Dual Cement. MATERIAL AND METHODS: Truncated cones made of Dicor castable ceramics were cemented to enamel of freshly extracted anterior teeth with these four cements. Before testing, all specimens were immersed in water at 37 degrees C for 24 hours, and thermocycled 1000 times in 5 degrees C and 55 degrees C water, with a dwell time of 30 seconds each. Tensile force was used to separate each specimen with the Instron universal testing machine. RESULTS: Clearfil CR Inlay cement exhibited the highest mean tensile bond strength (18.4 MPa), followed by Dual (18.3 MPa), Twinlook (15.2 MPa), and Optec Dual-Cure luting (14.9 MPa) cements. One-way analysis of variance did not reveal any significant differences (p = 0.05) among groups. A majority of the fracture was adhesive at the ceramic and cement interface. CONCLUSION: All four dual-cured cements formed strong bonds between enamel and Dicor cement, ranging from 14.90 MPa to 18.35 MPa, and there was no statistically significant difference.

Hardness and stress-corrosion of rubber dam clamps.

Rubber dam clamps fracture infrequently during use. There are no American National Standards Institute or International Standards Organization standards for their manufacture. The purpose of this study was to measure the hardness of the clamps and test their resistance to a stress-corrosion test. Upper molar, lower molar, and premolar clamps were obtained from two manufacturers (A, B). The Rockwell C hardness at four sites on the bow of each clamp was then determined. Fresh clamps were placed on blocks corresponding to the average buccal-lingual dimension of the tooth on which they would be used. These blocks were then submerged in room temperature 5.25% sodium hypochlorite for 20 min and then allowed to air dry for 30 min. This was repeated 10 times. Rockwell C hardness values ranged from C30 to 38, with the clamps of manufacturer B being significantly harder. None of the clamps from manufacturer B cracked or corroded. When a third batch received from manufacturer A was tested in the same manner, none of the clamps fractured or corroded either.

Tensile and tear properties of dental dam.

The tensile and tear properties of highly extensible latex are sensitive to specimen shape. Three specimen shapes (ASTM D412 Die C dumbbell tensile specimen, rectangular tensile specimen with 1.74 mm hole, and ASTM D624 Die C tear specimen) were evaluated for proposed ANSI/ADA specification #90 for dental dams. Fresh and aged dental dams from two manufacturers (Aseptico and Hygenic) in three weights (thin, medium, and heavy) and from two other manufacturers (Ivory and Ivoclar) in one weight (medium) were tested. Means and standard deviations of 10 specimens for tensile strength (MPa), elongation (%), and tear strength (kN/m) are included herein. Data were analyzed by analysis of variance. Means were compared by a Tukey-Kramer interval calculated at the 0.05 significance level. The use of the dumbbell and tear specimens for the evaluation of dental dam should be reconsidered. The rectangular specimen with a hole is recommended for use in the proposed specification because of its sensitivity to condition (fresh versus aged) and manufacturer.

Effects of post-curing on mechanical properties of a composite.

The mechanical properties (diametral tensile strength, compressive strength, modulus of elasticity in compression, Knoop hardness, and Rockwell Superficial indentation and recovery) were measured for one light-cured composite (Herculite XRV) post-cured by five different conditions. The post-curing conditions were: boiling water, CRC-100, D.I.-500, Translux EC Light Box, and Triad 2000 with normal light curing as a control. Post-curing Herculite XRV significantly improved the diametral tensile strength (24-39%), Knoop hardness (8-22%) and Rockwell Superficial recovery (3-6%); decreased Rockwell Superficial indentation (0-19%) but did not affect the compressive strength significantly. Modulus of elasticity was not affected, except by the Translux EC Light Box, which increased the modulus by 33%. Post-curing Herculite XRV with the Triad 2000 and Translux EC Light Box produced the most improved properties. Water at 100 degrees C was the least effective of the post-curing methods.

The effects of sodium fluoride and stannous fluoride on the surface roughness of intraoral magnet systems.

Four types of intraoral magnets used for retention of overdentures and maxillofacial prostheses were exposed in vitro to SnF2 and NaF to determine the effects of fluoride rinses on surface roughness. The surface roughness (Ra) was measured, after simulated 1, 2, and 5 years' clinical exposure to fluoride (31, 62, and 155 hours). The mean change in Ra was calculated for each period of simulated exposure to fluoride for each magnet type. Two-way ANOVA was used to compare mean change in Ra between magnets within fluorides, and between fluorides within magnets. Paired t tests were used to compare mean change in Ra within fluorides within magnets. The mean change in Ra increased for all magnets after simulated 1, 2, and 5 years of exposure to SnF2 and NaF (p less than 0.03). Using the change in Ra as an indicator for corrosion, PdCo encapsulated SmCo5 magnets and their keepers demonstrated the least corrosion with either fluoride.

Respirability, microstructure and filler content of composite dusts.

Dusts were generated from five composites, with two different shades each. Between 54 and 70 mass percent of the dust (60 to 92% of the particles) collected was respirable. The average particle size collected was 3.97 microns by mass (0.9 microns by number of particles). Between 14 and 22% of the dust generated was respirable. Filler content of the respirable dust particles was within 3 mass percent of the amount of filler in each cured composite. Powder x-ray diffraction revealed that respirable dust particles collected from composites reported to contain crystalline silica fillers contain the same crystalline silica. The results indicate that improperly protected dental personnel who are regularly exposed to composite dusts generated during high-speed finishing of composites containing quartz filler may be at risk for developing silicosis. Dental personnel should wear masks specifically designed to filter respirable silica when finishing composite restorations with high-speed instrumentation.