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Effect of Cubic Leucite Stabilization on the Flexural Strength of Feldspathic Dental Porcelain

The Ohio State Universiy, College of Dentistry, Section of Restorative, Prosthodontics, and Endodontics, 305 W. 12th Avenue, Columbus, Ohio 43210-1241

J.R. Mackert, Jr

Section of Dental Materials, Department of Oral Rehabilitation, School of Dentistry, Medical College of Georgia, Augusta, Georgia 30912-1260

J.A. Holloway

The Ohio State Universiy, College of Dentistry, Section of Restorative, Prosthodontics, and Endodontics, 305 W. 12th Avenue, Columbus, Ohio 43210-1241

S.F. Rosenstiel

The Ohio State Universiy, College of Dentistry, Section of Restorative, Prosthodontics, and Endodontics, 305 W. 12th Avenue, Columbus, Ohio 43210-1241

Previous studies (Mackert and Evans, 1993) have shown that, when feldspathic dental porcelain is cooled, leucite undergoes a transformation from cubic to tetragonal, associated with a 1.2% volume contraction. This contraction leads to the formation of microcracks in and around the crystals and the development of tangential compressive stresses around the crystals. Our aim was to stabilize increasing amounts of the cubic form of leucite in a leucite-reinforced dental porcelain, evaluate its effect on the flexural strength, and characterize its microstructure. The hypothesis was that in the absence of crystallographic transformation, the contraction of the leucite crystals would be lower, thereby limiting the formation of microcracks and minimizing the development of tangential compressive stresses around the leucite particles. We prepared 8 porcelain compositions by mixing increasing amounts of either leucite (KAlSi ₂O₆) or pollucite (CsAlSi₂O₆) with Optec HSP porcelain (Jeneric/Pentron Inc., Wallingford, CT). Porcelain disks were made from each composition (n = 10 per group). X-ray diffraction analyses showed that the amount of stabilized leucite increased with the amount of pollucite added. The microstructure of the specimens containing tetragonal leucite was characterized by twinned leucite crystals, whereas no twinning was observed in the specimens containing cubic leucite. The evaluation of crack deflection showed that significantly less deflection occurred in the specimens containing cubic leucite. The mean biaxial flexural strength for the group corresponding to 22.2 wt% added pollucite, fired at 1038°C, was significantly lower than that for the control group. The group corresponding to 22.2 wt% added leucite fired at 1150°C exhibited a mean biaxial flexural strength significantly higher than that of all other groups that were not significantly different from the control group. Overall, the stabilization of cubic leucite reduced the flexural strength and the number of crack deflections in leucite-reinforced porcelain. Apparently, the development of tangential compressive stresses around the leucite crystals when cooled is responsible for a significant amount of strengthening of feldspathic dental porcelain.

Key Words: ceramics • dental porcelain • leucite, • x-ray diffraction • Received August 14,1995 • Accepted August 14,1996

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Journal of Dental Research, Vol. 75, No. 12, 1928-1935 (1996)
DOI: 10.1177/00220345960750120301


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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Saved Citations Download to citation manager Request Permissions Request Reprints Add to My Marked Citations Citing Articles Citing Articles via Google Scholar Citing Articles via Scopus Google Scholar Articles by Denry, I.L. Articles by Rosenstiel, S.F. Search for Related Content PubMed PubMed Citation Articles by Denry, I.L. Articles by Rosenstiel, S.F. Social Bookmarking                         What's this?