Laszlo B. De Simon

Characterization of Osseous Tissues by Thermogravimetric and Physical Techniques

Changes in osseous tissue after injury were studied in monkeys with the use of thermogravimetric analysis (TGA) and mechanical strength measurements. An exponential relationship was found to exist between strength and weight loss for repair tissues 3 to 8 weeks old. The quantitative techniques investigated seem promising for the improved characterization of mineralized tissue.

Extrusion 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.

Surface characteristics of alginate impressions

Abstract The effects of storage conditions on the surface characteristics of three irreversible hydrocolloids were studied. Downward inversion of impressions markedly slowed surface changes in air. Counter-replicated detail was relatively stable in dilute aqueous solutions of potassium sulfate, potassium chloride, and sucrose. Rapid surface deterioration occurred in aqueous solutions of zinc or calcium sulfates and in ~99 per cent ethyl alcohol.

Effect of ultrasonic instrumentation on the retention of simulated cast crowns

The effect of ultrasonic instrumentation on the retention of cemented cast restorations was studied. Forces required to dislodge castings from specimen assemblies subjected to ultrasonic vibrations did not differ significantly from those required to cause failure of noninstrumented specimens. The results indicate that clinical application of the ultrasonic device would not affect adversely the retention of properly cemented and well fitting cast restorations.

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.

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.

Stress relaxation of interim restoratives

Stress relaxation of four temporary restoratives was studied. In the vicinity of ambient mouth temperature, the relaxation characteristics of an unmodified zinc oxide-eugenol cement were more favorable than those of IRM and Cavit. The plastic behavior of gutta-percha temporary stopping precluded assessment of its relaxation at temperatures in excess of 22 degrees C.

Further Studies of Resin-Modified Temporary Restorative Materials

Composition and physical properties of a polycarbonate resin-reinforced zinc oxide-eugenol cement and of a formulation based on zinc oxide, eugenol and o-ethoxybenzoic acid (EBA) were determined. Both materials were similar in strength, but the polycarbonate-containing material was tougher and showed less solubility and disintegration. Cementing film thicknesses were obtained with the EBA cement.