Journal of Dental Research, Vol 73, 1444-1449, Copyright © 1994 by International & American Associations for Dental Research Online Journals
Effect of grinding and fluoride-gel exposure on strength of ion-exchanged porcelain
K. J. Anusavice, B. Hojjatie and T. C. Chang
Department of Dental Biomaterials, University of Florida, Gainesville 32610-0446.
Strengthening of dental porcelain through a diffusion heat treatment at 450
degrees C of a potassium-enriched, ion-exchange surface coating has been
demonstrated in several recent studies. However, little attention has been
focused on the potential strength reduction of these materials when the
treated surfaces are ground or etched under clinically simulated
conditions. The objective of this study was to test the hypothesis that
partial removal of the surface layers of ion-exchanged porcelains by
grinding or exposure to acidulated fluoride gel will significantly reduce
their flexure strength. Nine groups of body porcelain disks were
ion-exchanged at 450 degrees C for 30 min. One of these groups was
subjected to ion exchange and no further surface treatment. Eight specimen
groups were subjected to the following procedures after ion exchange:
grinding to depths of 50 microns, 100 microns, 150 microns, 200 microns,
and 250 microns, and exposure to acidulated fluoride for 30 min, 60 min,
and 300 min. A tenth group (FC) was fired at 960 degrees C and fast-cooled
in air, but the disks were not subjected to the ion-exchange treatment.
Surface stress was calculated from measured values of cracks induced in the
treated surfaces. Fluoride exposure for up to 60 min resulted in a
significant decrease in surface compression (P < or = 0.05), although
this treatment had no effect on strength. Grinding to a depth of from 100
microns to 250 microns caused a significant decrease in strength, while
removal of a 50-microns layer caused no significant change (P > 0.05).
