Mackert J R, Twiggs S W, Williams A L
Department of Oral Rehabilitation, School of Dentistry, Medical College of Georgia, Augusta 30912-1260, USA.
J Dent Res. 2000 Aug;79(8):1590-5. doi: 10.1177/00220345000790081101.
Dental porcelains that are designed to be fused to PFM (porcelain-fused-to-metal) alloys are formulated by their manufacturers to be closely matched in thermal expansion to these alloys. The high thermal expansion of the mineral leucite has been exploited to regulate porcelain expansion. Leucite, however, has been observed to convert to the sanidine polymorph of feldspar during certain heat treatments within the normal firing range of dental porcelain. The effects of this conversion on porcelain thermal expansion and porcelain-metal thermal compatibility have been uncertain, due to the paucity of published data on the thermal expansion of sanidine. The purpose of this study was to measure the thermal expansion of sanidine by high-temperature X-ray diffraction over the temperature range in which thermal mismatch stresses can develop in porcelain-fused-to-metal restorations, i.e., from room temperature to 700 degrees C. The lattice parameters a, b, c, and beta were determined from the d-spacings and hkl values of multiple reflections by means of a least-squares iteration. The dependence of each lattice parameter on temperature was determined via analysis of variance, and the coefficient of thermal expansion, alpha, was obtained from this analysis. The lattice parameters of sanidine at room temperature were determined to be: a = 0.8524 +/- 0.0015 nm, b = 1.3020 +/- 0.0004 nm, c = 0.7165 +/- 0.0002 nm, and beta = 116.02 degrees +/- 0.01 degree (mean +/- 95% confidence interval). The linear thermal expansion coefficient, a, over the range from room temperature to 700 degrees C was determined to be 4.1 x 10(-6) K(-1) +/- 0.6 x 10(6) K(-1) (mean +/- 95% confidence interval). Because the coefficient of thermal expansion for sanidine is substantially lower than that of leucite (the effective linear thermal coefficient of thermal expansion of leucite over the range of 25 degrees to 700 degrees C is 28 x 10(-6) K(-1)), the conversion of leucite to sanidine during porcelain heat treatments would produce a detrimental lowering of the porcelain thermal expansion.
设计用于与烤瓷熔附金属（PFM）合金熔合的牙科陶瓷，其制造商在配方中使其热膨胀与这些合金紧密匹配。矿物白榴石的高热膨胀特性已被用于调节陶瓷的膨胀。然而，在牙科陶瓷的正常烧制范围内的某些热处理过程中，已观察到白榴石会转变为长石的透长石多晶型物。由于关于透长石热膨胀的已发表数据很少，这种转变对陶瓷热膨胀和陶瓷 - 金属热相容性的影响尚不确定。本研究的目的是通过高温X射线衍射在烤瓷熔附金属修复体中可能产生热失配应力的温度范围内，即从室温到700摄氏度，测量透长石的热膨胀。通过最小二乘法迭代，从多个反射的d间距和hkl值确定晶格参数a、b、c和β。通过方差分析确定每个晶格参数对温度的依赖性，并从该分析中获得热膨胀系数α。透长石在室温下的晶格参数确定为：a = 0.8524±0.0015纳米，b = 1.3020±0.0004纳米，c = 0.7165±0.0002纳米，β = 116.02度±0.01度（平均值±95%置信区间）。在从室温到700摄氏度的范围内，线性热膨胀系数α确定为4.1×10⁻⁶K⁻¹±0.6×10⁻⁶K⁻¹（平均值±95%置信区间）。因为透长石的热膨胀系数远低于白榴石（白榴石在25摄氏度至700摄氏度范围内的有效线性热膨胀系数为28×10⁻⁶K⁻¹），所以在陶瓷热处理过程中白榴石向透长石的转变会导致陶瓷热膨胀有害降低。
