[Micro powder retention for retaining acrylic resin veneers. 1. Application of pressure sensitive adhesive]

Powder retentions are widely used in clinical for retaining acrylic resin facing of veneered crown. These retentions show relatively high bond strength and easy manipulation compared with the traditional retention devices of bar, hole, bead, loop and etc. However, the particle size of powders commercially available are above 250 microns and reduced the thickness of facing resin. Thereupon, smaller diameter of powder were trially applied, however, microparticles were submerged under adhesive and undercut effective for retaining resin was lost. In this research, a new powder retention system adopted pressure sensitive adhesive was studied. The trial adhesive includes volatile solvent like as the traditional adhesives. However, the solvent vapors rapidly and the adhesive applied onto the wax pattern showed pressure sensitivity. Six different sizes of spherical powder were used and the smallest and largest particle size were 90-110 microns and 230-250 microns respectively. New powder retention system applied sensitive adhesive exhibited excellent bond strength to photo polimerized composite facing resin and denture base resin. The powder of 110-130 microns diameter showed shear bond strength values of above 200 kgf/cm2 after 30,000 thermocycles.