Potential applications of certain nickel-titanium (nitinol) alloys.

The mechanical behavior ("shape memory") associated with martensitic solid-state transformation in nearly equiatomic Ni-Ti alloy (55-Nitinol) has been studied. Potential dental and medical applications for 55-Nitinol (55% Ni, 1.5% Co, balance Ti, by weight) and for 60-Nitinol (60% Ni, by weight) have been suggested.

Extrusion of rheometry of fluid materials.

A capillary extrusion rheometer was developed and tested using Newtonian oils of known viscosity and seven endodontic sealers. The described apparatus and technique appear appropriate for comparative assessment of the rheological characteristics of a variety of fluid dental materials.

Apparent viscosities of setting elastomers.

The flow behavior of five elastomeric impression materials was determined by extrusion viscometry. Initial viscosity ranged from 400 to 5,100 poise at a shear rate of 2.2 reciprocal seconds. All of the elastomers showed initial non-Newtonian behavior and increased viscosity with time.

Observations on the elastic behavior of a synthetic orthodontic elastomer.

The study focused on changes in elasticity that accompany water storage of a synthetic orthodontic elastomer. We plotted loading and unloading curves to permit the direct measurement of instantaneous elastic recovery (IER) and permanent set (PS) and the calculation of delayed recovery (DR). We obtained baseline data by testing dry as received material. Comparable tests were performed on material that had been stored in water at 37 degrees C for one, seven, 14, 42, and 70 days. Gas chromatography-mass spectrometry was used for analysis of organic substances leached from the elastomer by water. A two-way ANOVA revealed that extension distance and water storage duration affected load requirement, IER, PS, and DR. The presence of leachable organic substances in 14-, 42-, and 70-day storage water was evidence of time-dependent matrix decomposition. Findings from tests of elastic performance and analysis of specimen storage water indicate that exposure of the elastomer to water leads first to weakening of noncovalent forces and subsequently to degradation.

Apparent cytotoxicity of base metal casting alloys.

The cytotoxic potentials of three Ni-Cr based alloys and an Fe-Cr based alloy were assessed. In tissue culture, casting of all four test materials and powders of the Fe-Cr based material did not elicit adverse cellular changes. However, cultures containing Ni-Cr powders showed prominent zones of lysis and cell alteration. The cytotoxic potential of products obtained from the surfaces of casting alloys may offer an expedient means for estimation of long-term clinical toxicity.

Short-term stress-relaxation behavior of nonmetallic restoratives.

The rheological behavior of five nonmetallic dental materials was studied. Short-term stress relaxation was found to be strongly dependent on time and temperature. Relaxation behavior of the test materials conformed well to simple mathematical models.

Properties of two nickel-chromium crown-and-bridge alloys for porcelain veneering.

Composition, microstructure, mechanical properties, and alloy-porcelain bond strength of two proprietary nickel-chromium-based crown-and-bridge alloys were studied. The materials exhibited compositional as well as microstructural differences. Wiron-S was significantly stronger and harder than Microbond-NP. Microbond-NP yielded alloy-porcelain bond strength values comparable to those of precious alloy-porce-lain combinations.

Further studies on gold alloys used in fabrication of porcelain-fused-to-metal restorations.

Composition, microstructure, castability, mechanical properties, and heat treatment characteristics of two gold-palladium-silver-based alloys were studied. The materials exhibited compositional as well as microstructural differences. Clinically acceptable castings could not be obtained when manufacturers' recommended casting temperatures were used. Ultimate tensile strength, yield strength, modulus of elasticity, and Brinell hardness values for the alloys were comparable. The elastic limit of Cameo, however, was significantly higher than that of vivo-star. Maximum rehardening of annealed castings occurred on reheat treatment at temperatures between 1,200 and 1,300 F. As-cast specimens, however, were not heat hardenable. The sequence of heat treatments used in the application of porcelain reduced slightly the hardness of both alloys. Hardness of the metal substructures was not increased by return of porcelain-coated specimens to a 1,250 F oven for final heat treatment.

Characterization of airborne particles from irreversible hydrocolloids.

Airborne particles of irreversible hydrocolloid powders were monitored and characterized. Ten to fifteen percent of the particles were siliceous fibers with dimensions of less than 3mum in diameter and more than 20mum in length. These dimensions conform closely to the dimensions of the fibrogenic and carcinogenic fibres of asbestos, glass, and aluminum oxide. With almost daily utilization of irreversible hydrocolloid materials in the dental office, the improper handling of the materials could be hazardous to the health of dental personnel. It is recommended that inhalation of aerosols arising from irreversible hydrocolloid powders be avoided.

Clinical examination of the head and neck.

In the head and neck examination portion of the ADA health screening program approximately 6% of the examinees were found to have at least one abnormality. Three patients had lesions that were highly suspected of being malignant. Most of the examinees were unaware of their condition, but a small percentage were aware and had chosen to have no diagnostic or curative procedures initiated. Three patients had manifestations of systemic disease of which they were unaware. A method of doing a head and neck examination was demonstrated to the dentists, and the finding of 6% of the dentists with some abnormality indicates the significance of the head and neck examination.

The effect of etchant and cement age on the adhesion of resin composite to conventional and resin-modified glass-ionomer cements.

The effects of etching with maleic or phosphoric acid on the adhesion of resin composite to resin-modified glass-ionomer cement restorative materials were evaluated through a shear bond test. These effects were determined with both recently set and aged cement. For the three resin-modified materials tested, compared to no etching, the two etchants improved or did not affect the adhesion of resin composite, regardless of the age of the cement. For a chemically cured material, included in the study as a control, the same effects were observed, except that etching of the recently set cement with maleic acid was detrimental to adhesion.

Effects of cements and eugenol on properties of a visible light-cured composite.

An in vitro study evaluated the effects of barrier materials on mechanical properties of a visible light-cured composite restorative. The composite was cured and aged over a widely used cavity liner (Dycal), various cements (Fleck's, Durelon, Vitrabond, ZOE B & T) and free eugenol and tested at seven and 28 days. The properties of interest were tensile stress (strength) at rupture, compressive strain (deformation at rupture), and stress-strain ratio at rupture. The experiment indicated that underlying barrier materials exerted neither a beneficial nor an adverse effect upon the restorative's ability to withstand compressive strain and tensile stress (P < 0.05).

Compressive properties of chemically cured, resin modified glass ionomer luting cements.

This study compared the responses of three proprietary chemically cured hybrid glass ionomer luting cements to compressive loading. These cements bear the trade names Advance, Fuji DUET and Vitremer Luting Cement, and are distributed and sold through ordinary domestic and international channels of dental commerce. The findings are as follows: 1. Advance, and Fuji DUET were stronger and stiffer than Vitremer Luting Cement. On the other hand, Vitremer exhibited the highest toughness. 2. The compressive properties of Advance were not affected significantly by increasing the specimen aging period to 28 days from seven days. 3. Prolonged aging of Fuji DUET and Vitremer specimens in a humid environment elicited significant changes in compressive strength and modulus of elasticity. Whereas the strength and elastic modulus changes for Fuji DUET were negative, the changes experienced by Vitremer were positive. 4. Extending the specimen aging period to 28 days from seven days did not affect significantly the toughness of either Fuji DUET or Vitremer Luting Cement. Relatively low elastic moduli limit the application of the chemically cured hybrid glass ionomers to the cementation of one- to three-unit cast fixed restorations.

Resin composites for foundation restorations.

This study focused on the compressive properties of two core buildup materials, Ti-Core, (EDS, Inc.) and FluoroCore, (L.D. Caulk). Specimens were 0.6 x 1.2 cm cylinders, Prior to testing, the specimens were aged in a moist environment for one, seven, or 28 day(s). The properties of interest were compressive strength, modulus of elasticity and toughness. The data set for each of the three compressive properties was subjected to a separate two-way analysis of variance. Scheffé F-tests were used to compare means. Whereas the effect of material on each of the three properties was significant (p < 0.002), the effects of specimen age (p > 0.400) and material x specimen age (p > 0.350) were not significant. FluoroCore was stronger and tougher than Ti-Core. On the other hand, Ti-Core displayed the highest stiffness, but ruptured brittley. The moderately low strength of Ti-Core, and the insufficient elastic modulus of FluoroCore, avert favorable recommendations pertaining to the construction of foundation restorations.