Isothermal Anneal Effect on Microcrack Density around Leucite Particles in Dental Porcelain

Abstract

Because of the large differential in thermal expansion coefficient between leucite and the surrounding glass matrix, microcracks form around the leucite crystallites during the manufacture of dental porcelain frits. These microcracks decouple leucite from the surrounding glass matrix and affect the bulk thermal expansion of the porcelain frit (Binns, 1983). The purpose of this study was to determine if the microcrack density in a dental porcelain decreased as a result of isothermal heat treatment. Ten specimens of a commercial dental porcelain that had previously exhibited an increase in thermal expansion as a function of isothermal heat treatment were prepared and divided into two groups. The experimental group was heated to 750°C and held for 16 minutes at that temperature. The control group received no anneal. The mean microcrack densities were determined by quantitative stereology to be 575 cm²/cm³ ± 75 cm²/cm³ (mean ± SEM) for the control group (no anneal) and 231 cm²/cm³ ± 25 cm2/cm3 for the experimental group (16-minute anneal at 750'C). The specimens annealed at 750°C had a significantly lower microcrack density (p < 0.001) than those that received no anneal. A model was developed to estimate the effect of microcracking on thermal expansion of the porcelain, and a 6% increase in the coefficient of thermal expansion of the porcelain was predicted from this model as a result of this decrease in microcrack density.

Keywords

Ceramics Dental Materials Dental Porcelain Leucite Microcracking.

Get full access to this article

View all access options for this article.

References

Barreiro MM , Riesgo O. , Vicente EE (1989). Phase identification in dental porcelains for ceramo-metallic restorations. Dent Mater 5:51-57.

Binns D. (1983). The chemical and physical properties of dental porcelain. In: Dental ceramics: Proceedings of the First International Symposium. McLean JW, editor. Chicago, IL: Quintessence Publishing Co., Inc., pp. 41-82.

Burk B. , Burnett AP , inventors (1978). The JM Ney Company, assignee. Leucite-containing porcelains and method of making same. US Patent 4,101,330. Jul 18.

Case ED ( 1984). The effect of microcracking upon the Poisson's ratio for brittle materials. J Mater Sci 12:3702-3712.

Cleveland JJ , Brandt RC (1978). Grain size/microcracking relations for pseudobrookite oxides. J Am Ceram Soc 61:478-481.

Davidge RW , Green TJ (1968). The strength of two-phase ceramic/glass materials . J Mater Sci 3:629-634.

Dorsch P. (1981). Stresses in metal-ceramic systems as a function of thermal history. Ceramic Forum International/Ber Dt Keram Ges 58:1-7.

Dorsch P. (1982). Thermal compatibility of materials for porcelain-fused-to-metal (PFM) restorations. Ceramic Forum International/Ber Dt Keram Ges 59:1-5.

Fairhurst CW , Anusavice KJ , Hashinger DT , Ringle RD , Twiggs SW (1980). Thermal expansion of dental alloys and porcelains . J Biomed Mater Res 14:435-446.

10.

Hahn C. , Teuchert K. (1980). Importance of the glass ceramic system K2O-Al2O3-SiO2 in dental porcelain. Ber Dt Keram Ges 57:208-214.

11.

Hall FP ( 1930). The influence of chemical composition on the physical properties of glass. J Am Ceram Soc 13:182-199.

12.

Hoshikawa T. , Agaki S. (1972). Formation of leucite and thermal expansion in SiO2-Al2O3-K2O-Na2O glasses. Yogyo-Kyokai-Shi 80:42-48.

13.

Kase HR , Tesk JA , Case ED ( 1985). Elastic constants of two dental porcelains. J Mater Sci 20:524-531.

14.

Kerner EH (1956). Elastic and thermoelastic properties of composite media. Proc Phys Soc (Lond) B69:808-813.

15.

Kingery WD , Bowen HK , Uhlmann DR (1976). Introduction to ceramics. 2nd ed. New York: John Wiley & Sons, pp. 583-644.

16.

Kuszik JA , Brandt RC (1973). Influence of grain-size on effects of thermal expansion anisotropy in MgTi2O5. J Am Ceram Soc 56:420-423.

17.

Lindsley DH (1966). P-T projection for part of the system kalsilitesilica . Carnegie Inst Washington Yearbook 65:244-247.

18.

Mackert JR Jr (1988). Effects of thermally induced changes on porcelain-metal compatibility. In: Perspectives in dental ceramics. Proceedings of the Fourth International Symposium on Ceramics . Preston JD, editor. Chicago: Quintessence Publishing Co., pp. 53-64.

19.

Mackert JR Jr , Evans AL (1991a). Effect of cooling rate on leucite volume fraction in dental porcelain. J Dent Res 70:137-139.

20.

Mackert JR Jr , Evans AL (1991b). Quantitative x-ray diffraction determination of leucite thermal instability in dental porcelain. J Am Ceram Soc 74:450-453.

21.

Mackert JR Jr. , Evan AL ( 1992). Multiple firing effect on leucite content of dental porcelains and correlation with thermal expansion (abstract). J Dent Res 71: 238

22.

Mackert JR Jr , Butts MB , Beaudreau GM , Fairhurst CW , Beauchamp RH (1985). Ultrathinning dental porcelain for transmitted light microscopy. J Dent Res 64:1170-1175.

23.

Mackert JR Jr , Butts MB , Fairhurst CW (1986). The effect of the leucite transformation on dental porcelain expansion. Dent Mater 2:32-36.

24.

Manning WR , Hunter O. Jr (1973). Anomalous elastic behavior of polycrystalline Nb2O5. J Am Ceram Soc 56:602-603.

25.

Morey GW (1954). The properties of glass. New York: Reinhold, pp. 271-273.

26.

Prasad A. , Day GP , Tobey RG (1988). A new dimension for evaluation of porcelain-alloy compatibility. In: Perspectives in dental ceramics. Proceedings of the 4th International Symposium on Ceramics. Preston JD, editor. Chicago: Quintessence Publ. Co., Inc., pp. 65-74.

27.

Rekhson SM , Mazurin OV (1977). Stress relaxation in glass and glass-to-metal seals. Glass Technol 18:7-14.

28.

Selsing J. (1961). Internal stresses in ceramics. J Am Ceram Soc 44:419.

29.

Smith JV , Brown WL (1988). Feldspar minerals. Vol. 1. 2nd ed. Berlin: Springer-Verlag, pp. 450-460.

30.

Twiggs SW , Mackert JR JR , Hashinger DT , Fairhurst CW (1987). The effect of heat treatment on the thermal compatibility of dental porcelain (abstract). J Dent Res 66(Spec Iss):294.

31.

Underwood EE (1970). Quantitative stereology. Reading, MA: Addison-Wesley Publishing Co., pp. 38-40.

32.

Vergano PJ , Hill DC , Uhlmann DR (1967). Thermal expansion of feldspar glasses. J Am Ceram Soc 50:59-60.

33.

Weinstein M. , Katz S. , Weinstein AB , inventors (1962). Permadent Manufacturing Corporation, assignee. Fused Porcelain-to-Metal Teeth. US Patent 3,052,982. Sep 11.

34.

Yamamoto M. (1985). Metal-Ceramics. Chicago: Quintessence Publishing Co., pp. 156-202.