Precision post - crown preparation and stabilization: a new approach

Objectives: To compare the resistance to transverse forces of two types of crown post that occasionally loosened in clinical practice though their resistance to axial forces has been found to be good. A post stabilizer was designed to obviate this problem. It is tubular with a flange that is seated on the root face. Its diameter fits accurately over the post and its outer surface fits precisely into a cavity. This cavity was cut by two trephines that were guided by the cemented post. It is by virtue of the precision fit of the stabilizer round the post and into the root that the post was to be stabilized. Methods: Roots, into which 20 threaded, parallel 316 stainless steel posts and 20 roughened parallel stainless steel posts had been cemented to a depth of 7mm, were placed concentrically into specimen holders. These were secured by precision chucks to the Woehler fatigue machine. The specimens were kept wet throughout the experiment in which rotating bending moments were applied to the posts with and without the post stabilizer. The range of loads applied, were in the clinical range. Results: Under the heaviest loads posts fractured after twenty seconds when normally cemented with a resin based cement. Under the same load, applied 2800 times per minute, identical posts with a post stabilizer, continued to run for extended periods from 90 to 180 minutes. A large spread of results is expected in these experiments though the application of the post stabilizer is shown to improve resistance to transverse forces by statistically highly significant amounts. Conclusions: It has been shown that a post stabilizer enables axially highly resistant posts that still loosen in clinical practice, to survive transverse loads comparable to those applied in mastication, by a very large factor.