Mechanical properties of titanium connectors.

The tensile mechanical properties of welded titanium joints were studied, and intact titanium was used as controls. Welded joints were fabricated with either a stereographic laser-welding technique or a gas tungsten arc welding technique. The effect of heat treatment following a simulated porcelain application was also investigated. Heat-treated laser welds had significantly lower ultimate tensile strengths. Heat treatment had no effect on the modulus of elasticity or elongation, but generally significantly decreased the yield strength of the titanium specimens. The gas tungsten are welding specimens had significantly higher yield strengths and elastic moduli than the other two groups. The elongation of the control specimens was significantly greater than the elongation of the gas tungsten arc welding specimens, which was in turn significantly higher than that of the laser-welded specimens.

Shear bond strength of composite resin to porcelain.

This study evaluated the effect of porcelain surface treatment on the shear bond strength of composite resin to various porcelains and porcelain combinations. A variety of feldspathic porcelains with low and medium alumina content were tested. Porcelain/composite resin samples were stored in 37 degrees C water, thermocycled 1,000 times, and tested in shear. A 3-minute etching using hydrofluoric acid significantly increased the bond strength of most of the feldspathic porcelains with low and medium alumina content. Silane application to all types of etched porcelain had no significant effect on bond strength.

Effect of post adaptation on fracture resistance of endodontically treated teeth.

This study determined the effect of different post designs and varying amounts of post-to-canal adaptation on the fracture resistance of endodontically treated teeth. Forty freshly extracted maxillary central incisors were endodontically treated. Groups of 10 teeth were prepared according to four experimental designs. Cast post and cores and crowns were waxed, cast, and luted with zinc phosphate cement on a static loading device. The teeth were embedded in acrylic resin and the crowns were loaded on a universal testing machine at 130 degrees to the long axis of the tooth until failure. Maximum adaptation of the residual root structure with a tapered post significantly increases the fracture resistance of endodontically treated teeth, but upon failure renders the tooth nonrestorable. Tapered posts resulted in fractures that were directed more apically and lingually. Parallel-sided posts had a lower frequency of fracture upon failure, involving less tooth structure. Parallel-sided posts surrounded by large amounts of cement had no significant effect on failure loads.

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.

Ferrule design and fracture resistance of endodontically treated teeth.

This study evaluated the fracture resistance of pulpless teeth with various ferrule designs and amounts of coronal tooth structure. One millimeter of coronal tooth structure above the crown margin substantially increased the fracture resistance of endodontically treated teeth, whereas a contrabevel at either the tooth-core junction or the crown margin was ineffective. The thickness of axial tooth structure at the crown margin did not appreciably improve resistance to fracture.

Optimum placement of osseointegrated implants.

A method was described that includes a stent provided by the restorative dentist indicating optimum implant location. The stent, with imbedded metal bearings, is worn by the patient during tomographic radiographic survey. The tomogram provides a more accurate image of the quantity and quality of the osseous structures. The same template may be used as a surgical stent to aid the surgeon in initial bur placement. Through careful planning and systematic control, the predictable placement of osseointegrated implants can be achieved. With cooperative efforts of restorative dentists and surgeons, more than 400 implants have been successfully placed at University of California, Los Angeles, School of Dentistry.