Influence of tissue conditioning materials upon the crystalline structure of dental stone and improved dental stone.

Dental stone and improved dental stone were crystallised in contact with six commercial tissue conditioning materials. Their influence on the crystalline structure of dental stone and improved dental stone were investigated using a scanning electron microscope. Tissue conditioning materials cause horizontal orientation of the crystals of calcium sulphate CaSO4 2H2O dihydrate.

Retentive ability of various denture adhesive materials: an in vitro study.

This in vitro investigation of the retentive ability of various commercially available denture adhesives was performed by measuring the adhesion and cohesion that developed between a glass surface and an acrylic resin disk surface when some liquids, adhesive materials, or both were placed between them. Student's paired t-test, repeated measures, and two-factor design analysis of variance were performed to determine the significance among mean values. The adhesive materials studied exhibited a significantly greater retentive ability than that of saliva, and their retentive ability increased significantly when they were used in combination with artificial saliva. Highly significant differences of the retentive ability among the different brands of denture adhesives were observed.

Comparative study of heat release of various cement base materials during their setting.

An ideal cement base material in order to protect the pulpal tissue from several external irritations (microbial, mechanical, thermal, galvanic and osmotic irritations) must present the following requirements: to attach or bond to the residual dentin, to be biocompatible, to present suitable physicomechanical, antimicrobial and optical properties, to be color stable, easy to use and rapid to set. Thermal phenomena developed during the mixing and setting are a factor influencing the biocompatibility properties of these materials. Cement base materials are used under various types of filling materials (amalgams, composite resins, gold and porcelain inlays) and are placed in contact with the dentin that contains exposed dentinal tubules. The purpose of this study was to investigate the possible exothermic reaction of these materials and to measure the developing temperatures for a time period from their mixing up to the completion of their setting. We studied the following types of cement base materials: a) Zinc oxide eugenol cement, b) Zinc phosphate cement, c) Zinc polycarboxylate cement and d) Glass ionomer cement both light- and self-cured. From the obtained results we observed that ZOE cements developed the lowest temperatures ranging from 32.8 degrees C to 37 degrees C, while Zinc phosphate cements developed the highest temperatures ranging from 44.4 degrees C to 52 degrees C. The other two types of materials Zinc polycarboxylate and Glass ionomer cements developed biocompatible temperatures ranging from 38 degrees C to 40.8 degrees C, which usually do not cause deteriorations and harms to the pulp. We concluded that the ZOE cements presented the best thermal behaviour followed by Zinc polycarboxylate and Glass ionomer cements. Hence, these materials can be safely used without causing any pulpal response.

Dimensional stability and reproduction of surface detail of tissue conditioning materials.

Four commercial tissue conditioners have been assessed in terms of their dimensional stability and ability to reproduce surface detail according to ADA specification #19 for impression materials. Results have been compared with those of a number of elastomeric impression materials. The tissue conditioners performed adequately and as such could be used as impression materials within 24 hours of their application. While they did not compare well with the elastomeric impression materials they comply with the limitations of the ADA specifications. It is suggested that standards specific to these materials should be developed.

Influence of tissue conditioners upon the surface hardness of dental stone and improved dental stone.

The surface hardness of dental stone and improved dental stone was investigated when crystallised in contact with tissue conditioners and compared with that observed when the two types of gypsum are crystallised in contact with impression materials used clinically. Vickers hardness tests were performed 45 minutes, 2 hours and 24 hours after the beginning of stone mixing. The tissue conditioners did not have adverse effects on the surface hardness of gypsum products. On the contrary, they gave casts with excellent surface hardness, as did the elastomeric impression materials.

Dental stone and improved dental stone surface hardness: the effect of the addition of potassium salts.

Changes in dental stone and improved dental stone surface hardness observed when prepared with aqueous solutions of potassium salts (K2SO4, KCl, KF, KBr, KNO4, KMnO4, K2Cr2O7) in concentrations of 0.5-5.0% were investigated. Parallel studies were carried out on dental stone and improved dental stone prepared with distilled water and crystallised in contact with alginate impression material, previously immersed in the above solutions for 2 minutes. Vicker's hardness tests were performed 3 hours and 24 hours after the initial set. The surface hardness of dental stone and improved dental stone is increased significantly by either method. The most effective hardening solution is potassium sulphate in concentrations of 0.5-5.0%. The degree of increase in surface hardness is directly proportional to the concentration of the solutions and proportionately greater at a shorter time (3 hours after the initial set).