Alastair N. Stokes

Impact-fracture energy of human premolar teeth

The fracture strength of contralateral pairs of premolar teeth was determined by an in vitro method wherein impact loads of equal energy were applied to the medial aspects of the buccal cusps. Absorbed energy values quantified the fracture resistance of unprepared teeth and teeth restored with MOD amalgams, MOD amalgam overlays, MOD gold overlays, and full gold crowns. It was established that unprepared lower premolar teeth had a greater resistance to fracture than upper premolar teeth, and lower first premolar teeth were more resistant to fracture than the other premolar teeth; the fracture resistance of premolar teeth restored with MOD amalgams was significantly reduced compared with unprepared control teeth; MOD amalgam overlays in premolar teeth produced fracture resistances not significantly different from those for the unprepared controls; and restoration of premolar teeth with MOD gold overlays and full gold crowns enhanced fracture resistance to a level much greater than that of the unprepared control teeth.

Effect of 6-month water storage on silane-treated resin/porcelain bonds

Abstract Circular mesh brackets were bonded by means of a microfilled composite resin to porcelain discs, pretreated with one of two types of silane primer. Shear bond strength determinations were undertaken after 24 h and 6 months water storage. A prehydrolysed, single-component silane primer gave consistently high bond strengths, but a two-part, operator-activated silane primer was associated with substantially lowered bond strengths after 6 months.

Porous metal coatings for resin-bonding systems

Two porous coating systems produced surfaces 20 to 30 microns thick, capable of engaging the unfilled component of composite during bonding procedures. A technique is suggested whereby the thickness of porous coating may be compensated by die spacing. The film thickness of the cement tested would be unlikely to affect the fit of any such prosthesis. Prostheses constructed in this manner would have the benefits of microretention without the technical problems of electrolytic etching.

A Comparison of Diamond and Tungsten Carbide Burs for Preparing Endodontic Access Cavities through Crowns

Diamond and tungsten carbide burs designed for cutting metal were tested with precious and nonprecious bonding alloys. Standard cavities were prepared and timed. Tungsten carbide burs were most effective in preparing cavities in precious alloy but only a coarse dome-shaped cylindrical diamond bur effectively prepared a succession of five cavities in nonprecious alloy without untoward vibration.

Influence of casting procedure on silver-palladium endodontic posts

Silver-palladium alloys have been endorsed on clinical grounds as substitutes for gold alloys in posts and cores. However, carbon absorption during heating and casting can adversely affect the mechanical properties of silver-palladium alloys. In this study the tensile characteristics of endodontic posts cast in silver-palladium alloy using either a graphite or a ceramic crucible were determined. Graphite crucibles were associated with a significantly lower (2P less than 0.00001) percentage elongation than were ceramic crucibles. The need for a carbon-free casting environment for silver-palladium alloys was confirmed. The configuration of the cylindrical, serrated, vented post used in these tests resulted in mechanical properties lower than those achieved with standard metallurgical test procedures.