Relative flexural strength of dental restorative ceramics.

The relative flexural strengths of ten brands of dental restorative ceramics were evaluated by a three-point bending test. The materials consisted of three low-fusing and one high-fusing feldspathic porcelains and six reinforced dental restorative ceramics which are currently in clinical use. The reinforced ceramic materials investigated utilized a number of different strengthening processes, including alumina and ceramic fiber reinforcement and controlled crystallization. The results of the investigation indicate that significant differences exist among the measured breaking strengths of the various materials. The processes of controlled crystallization and alumina reinforcement appear to be adequate means of improving the bending strength of restorative dental ceramics.

Altered corrosion resistance from casting to stainless steel posts.

Heat treatment during the burnout procedure may cause corrosion of the stainless steel post. This study was undertaken to determine whether alteration of the corrosion resistance of stainless steel posts occurs as a result of various simulated burnout procedures. Stainless steel posts were divided into five groups of five posts: group 1, control; 2, gypsum-bonded investment, bench cooled; 3, gypsum-bonded investment, quenched; 4, phosphate-bonded investment, bench cooled; and 5, phosphate-bonded investment, quenched. The posts were placed in individual containers of Ringer's solution and observed at 30, 180, and 600 days. Scanning electron microscopy, energy dispersive x-ray spectroscopy, optical emission spectroscopy, and optical microscopy were used to evaluate the posts qualitatively and quantitatively. Investment and heat treatment altered the metallic structure of stainless steel posts. Prefabricated posts submitted to simulated burnout procedures had a noticeable reduction in corrosion resistance. Direct casting to stainless steel posts is contraindicated.

[Use of Cotrel-Dubousset material in C1 C2 instabilities]. / Utilisation du matériel de Cotrel Dubousset dans les instabilités C1 C2.

The authors report their experience with the C.D. material for the atlantoaxial displacement. Four cases are presented. The characteristics and advantages of this material are discussed, and compared with the other methods of fixation specially the Knodt-Chirossel.