Retentive strength of dental composite to metal surfaces.

Retentive strength of the metal-composite interface was studied with tensile tests for 10-mm and 4-mm diameter specimens. In both series nonperforated and perforated metal surfaces with various numbers of holes were used. The specimens were tested after 1 day of storage in air and after thermocycling in water at 7 degrees C and 60 degrees C, respectively. The nonperforated specimens had the highest retentive strength values for both small and large specimens. The retentive strength decreased with increasing number of perforations and for nonperforated specimens with large retentive area. Thermocycling reduced the tensile force required to break the specimens by 4% to 50%. The fracture surface was mostly located close to the metal surface, indicating that this is the zone of stress concentration. With increasing length of the bond edge a reduction of the retentive strength was observed.

A binary dental gold-cobalt alloy of eutectic composition.

A new dental gold alloy was investigated for the casting of prosthetic restorations. The binary alloy is composed of 10 weight-percent Co and 90 wt% Au. Studies of the structure of the alloy revealed a rod-eutectic structure with Co rods in Au matrix. By special heat treatment (solution treatment and precipitation treatment) the hardness was increased up to 280 Hv. The hardening effect caused by Co atom groups in the Au matrix was studied by transmission microscopy. Casting experiments were performed using conventional dental casting procedures. Metallographic studies revealed no Co rods in the surface layer of the castings after the heat treatment.

Absorption of gas in dental gold alloys during melting.

The absorption of gas during heating and melting of pure gold and of two dental gold alloys was studied by gas chromatography. The metals were melted by two methods, i.e. gas-torch and electric heating. The specimens were analysed regarding the content of hydrogen, oxygen and nitrogen. The amount of nitrogen was not measurable in all specimens. Oxygen gas occurred with rather high values in the two dental gold alloys. The hydrogen content was often larger than the solubility limit. It is proposed that hydrogen often gives pore precipitation. It is also proposed that special caution must be taken during melting to reduce the hydrogen content in the melt before casting. D-alloy (palladium) demonstrated high H and O values on gas-torch heating.

The cytotoxic effect of denture base polymers.

The cytotoxic potential of autopolymerized pour and dough type resins and heat cured resins was studied by in vitro cell culture techniques. Human epithelial cells (NCTC 2544) were grown in Eagle's minimal essential medium on the surface of the polymer disks. The cell multiplication on the surface of the specimens was measured. One heat cured resin and one pour type resin demonstrated a slight cytotoxic effect. The other polymers gave a moderate cytotoxic effect. The study did not indicate any difference in the cytotoxicity of the polymers when manufactured by alternate processing methods.

Roentgenological detection of casting defects in cobalt-chromium alloy frameworks.

A method for non-destructive X-ray investigation of casting defects in cobalt-chromium prosthetic frameworks has been developed and tested. The attenuation properties of a cobalt-chromium alloy were studied. A dental X-ray machine with a tube voltage working at 70 kVp and a focus-film distance of 45-50 cm on dental ultraspeed film made it possible to detect defects representing 10% or less of the thickness of cobalt-chromium details with dimensions between 0.6 and 3.0 mm. The frequency and site of internal defects in sixty-six frameworks were investigated. Of the sixty-six frameworks only two were without roentgenologically visible defects. In the other sixty-four frameworks 294 pores or cracks were recorded. The defects were mostly situated in the saddles. Porosities occurred in 53% of the saddlebar regions. The results confirmed the need for a non-destructive routine test of prosthetic frameworks.

Microstructure of the solder-casting zone in bridges of dental gold alloys.

The composition and structure were studied in the cast and in the solder of bridges which had failed clinically. Both materials were gold alloys but with different contents of Pt, Ag and Zn. The metallographic investigation revealed defects mostly in the solder, situated in the subsurface layer. SEM studied of the fracture surface revealed large porosites and a structure of dense parallel lines--striations--, indicating that the material had failed from fatigue. The materials in the fractured bridges were identified by micro-probe measurements. It was stated that cast material and solder material used together, were of different composition.

Influence of stone mixing agents, impression materials and lubricants on surface hardness and dimension of a dental stone die material.

The influence of different stone mixing agents, impression materials and lubrication methods on the surface hardness of a stone die material has been evaluated. For one impression material the dimensional effect of the mixing agents and lubrication on the dies was also studied. The stone die material was mixed with water or a gypsum hardener and allowed to set on surfaces of glass, agar-agar, polyether, polysulfide and silicone impression materials. The lubrication methods for the stone were mineral oil, water soluble lubricant and mineral oil followed by water soluble lubricant. The surface hardness was measured according to the Brinell test. The Brinell test was chosen after a comparative study of the Brinell, Vickers and Knoop hardness test methods. The results showed that gypsum hardener was preferable to distilled water. The impression materials appear to have influence on the surface hardness of stone. The effect differed on water mixed and hardener mixed stone which emphasizes the importance of the mixing agent. All lubrication decreased the surface hardness of stone. With hardener mixed stone the combination of mineral oil followed by water soluble lubricant seemed preferable. Neither the gypsum hardener nor the lubrication influenced the dimension of the stone die material.

Denture stomatitis. A clinical, electron-microscopic, microradiographic and light-microscopic study.

The present study includes a reexamination of 10 patients who, two years ago received complete upper and lower denture treatment to eliminate an existing denture stomatitis. Clinical healing of the denture stomatitis was obtained only in one patient, whereas the remaining nine patients wtill displayed an obvious denture stomatitis. Biopsies were taken from the palatal mucosa and examined histologically, microradiographically, and by electron microscopy. The results of these examination indicated that, in denture stomatitis there is a reduced thickness of the epithelium, an absence of a stratum corneum, a markedly widened intercellular space, especially in the stratum basale, and an intense infiltration of inflammatory cells, plasma cells and lymphocytes in the connective tissue, as well as in the epithelium. These changes are characteristic features of an inflammatory process, and similar to the changes which occur, for example, in chronic, marginal gingivitis. The composition of the inflammatory infiltrate suggested that, in denture stomatitis, immunological phenomena influence the pattern of the tissue reaction.

Denture stomatitis. A histological and microradiographic study of the alveolar mucosa.

The alveolar mucosa in the upper jaw from 12 patients suffering from severe denture stomatitis was examined histologically and microradiographically using ultrasoft X-rays. Pathological changes of the epithelial cell layers were observed in all cases. In 10 of the 12 cases examined no keratinization was found. A reduction in the number of epithelial cell layers was commonly observed. In most cases the connective tissue showed signs of moderate to severe inflammation. The inflammatory reaction and the degenerative changes of the tissue were presumably due to a combined effect of microorganisms and mechanical trauma.