Evidence of a Critical Leucite Particle Size for Microcracking in Dental Porcelains

Abstract

The leucite particles in dental porcelains are often partially encircled by microcracks that are the result of the thermal expansion mismatch between leucite and the surrounding glass matrix. Although the magnitude of the stress at the particle-matrix interface is independent of the particle size (Selsing, 1961), Davidge and Green (1968) showed experimentally that there is a critical particle size below which microcracking is absent. The critical particle size is explained by a Griffith-type energy balance criterion: Below the critical size, the stress magnitude may be sufficient to cause cracking, but there is insufficient strain energy for the creation of the new surfaces of the microcrack. The purpose of the present study was to determine whether the mean leucite particle size of a dental porcelain influences the degree of microcracking in the porcelain. Microcrack density, leucite particle surface area per unit volume, and leucite mean volume-surface diameter, D _3,2, were determined by quantitative stereology on 10 specimens each of 6 dental porcelains and Component No. 1 of the Weinstein et al. patent (US Patent 3,052,982, 1962). The fraction of leucite particles with microcracks around them, f_mc, was estimated for each porcelain from the microcrack density and the leucite surface area. Using the equations of Selsing (1961) and Davidge and Green (1968), we calculated the critical particle diameter, D_c , for leucite to be 4 μm. The porcelains were partitioned according to whether their mean leucite particle diameters, D _3,2, fell above or below D _c, and their values of f_mc were analyzed by a permutation test with random re-sampling. The porcelains with mean leucite particle diameters below D _c had a significantly lower fraction of cracked particles compared with the porcelains with mean leucite particle diameters above D_c (p < 0.05). This study provides evidence that microcracking in dental porcelain can be minimized by a reduction of the mean leucite particle diameter to less than 4 μm.

Keywords

ceramics dental porcelain leucite,x-ray diffraction microcracking scanning electron microscopy mechanical stress dental materials

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References

Binns DB (1962). Some physical properties of two-phase crystal-glass solids. In: Science of ceramics. Vol. 1. Stewart GH , editor. London: Academic Press, pp. 315-334.

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). Leucite-containing porcelains and method of making same. US patent 4,101,330, July 18.

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

Denry IL , Crimaldi AJ , Rosenstiel SF (1995). Fracture toughness, Vickers hardness, and elastic modulus of crystalline leucite (abstract). J Dent Res 74:38.

Denry IL , Mackert JR Jr , Holloway JA , Rosenstiel SF (1996). Effect of cubic leucite stabilization on the flexural strength of feldspathic dental porcelain. J Dent Res 75:1928-1935.

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.

Goldstein JI , Newbury DE , Echlin P. , Joy DC , Romig AD Jr , Lyman CE , et al. (1992). Scanning electron microscopy and x-ray microanalysis. 2nd ed. New York : Plenum Press, pp. 69-147.

Good P. ( 1994). Permutation tests: a practical guide to resampling methods for testing hypotheses. New York: Springer-Verlag, pp. 29-30.

10.

Heinrich Kfj (1981). Electron beam x-ray microanalysis. New York: Van Nostrand Reinhold Company, pp. 467-514.

11.

Hermansson L. , Carlsson R. (1978). On the crystallization of the glassy phase in whitewares. Trans J Br Ceram Soc 77:32-35.

12.

Hilliard JE (1967). The calculation of the mean caliper diameter of a body for use in the analysis of the number of particles per unit volume . In: Stereology. Elias H , editor. New York: Springer-Verlag , pp. 211-215.

13.

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

14.

Khajotia SS , Mackert JR Jr , Twiggs SW , Russell CM , Williams AL (1999). Elimination, via high-rate laser dilatometry, of structural relaxation during thermal expansion measurement of dental porcelain . Dent Mater 15:390-396.

15.

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

16.

Mackert JR Jr , Williams AL (1996). Microcracks in dental porcelain and their behavior during multiple firing. J Dent Res 75:1484-1490.

17.

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

18.

Mackert JR Jr , Rueggeberg FA , Lockwood PE , Thompson WO (1994). Isothermal anneal effect on microcrack density around leucite particles in dental porcelain. J Dent Res 73:1221-1227.

19.

Mackert JR Jr , Twiggs SW , Evans-Williams AL (1995). Isothermal anneal effect on leucite content in dental porcelains. J Dent Res 74:1259-1265.

20.

Manly Bfj (1991). Randomization and Monte Carlo methods in biology . London: Chapman and Hall, pp. 49-52.

21.

Robinson Vne (1974). The construction and uses of an efficient backscattered electron detector for scanning electron microscopy. J Phys E Sci Instr 7:650-652.

22.

Ruoff AL (1973). Materials science. Englewood Cliffs, NJ: Prentice-Hall, Inc., p. 27.

23.

Russ JC ( 1986). Practical stereology. New York : Plenum Press, pp. 53-72.

24.

Sahagian DL , Proussevitch AA (1998). 3D particle size distributions from 2D observations: stereology for natural applications. J Volcanol Geotherm Res 84:173-196.

25.

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

26.

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

27.

Twiggs SW , Hashinger DT , Fairhurst CW (1990). Viscosities of porcelains formulated from the Weinstein patent. JAm Ceram Soc 73:446-449.

28.

Underwood EE (1970). Quantitative stereology. Reading, MA: Addison-Wesley Publishing Co., pp. 38-40, 103-105, 141-143.

29.

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

30.

Walsh JB (1965). The effect of cracks in rocks on Poisson's ratio . J Geophys Res 70:5249-5257.

31.

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