Journal of Dental Research, Vol 72, 1429-1433, Copyright © 1993 by International & American Associations for Dental Research Online Journals
Enhanced chemical strengthening of feldspathic dental porcelain
I. L. Denry, S. F. Rosenstiel, J. A. Holloway and M. S. Niemiec
Ohio State University, College of Dentistry, Columbus 43210.
Previous studies on ion exchange of dental ceramics have shown that the
biaxial flexural strength can be improved by exchanging potassium for
sodium ions at temperatures below the strain point. The rubidium ion is
bigger than the potassium ion and can also be considered as a candidate for
replacing smaller ions, i.e., sodium or potassium, although it has not been
used for dental ceramics. The double-step method uses the exchange of a
small ion for a large ion (Li for Na) above the strain point, and the
further exchange of a large ion for a small ion (K for Li) below the strain
point. The purpose of this study was to compare the effect of
rubidium-for-potassium ion exchange with that of potassium-for-sodium
exchange (Tuf-Coat, G-C International Corp., Japan) on the flexural
strength of a feldspathic dental porcelain and to test the hypothesis that
a double-step ion exchange can lead to greater strengthening than potassium
ion exchange alone. Weight measurements were performed before and after
treatment. Qualitative chemical analyses allowed the rubidium, potassium,
and sodium concentration profiles to be determined along cross-sections of
the specimens. The maximum biaxial stresses were calculated after specimens
were fractured in water on a ball-on-ring fixture at 0.5 mm/min. Relative
to the untreated control group, the flexural strength of the
potassium-exchanged groups was significantly increased, except for those
treated at 400 or 500 degrees C. All the groups treated with RbNO3
exhibited a significant increase in flexural strength, with a maximum for
the group treated at 450 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
