Mackert J Rodway, Sheen Geoffrey W, Williams Amalia L, Russell Carl M, Ergle Janet W
Section of Dental Materials, Department of Oral Rehabilitation, Medical College of Georgia School of Dentistry, Augusta 30912-1260, USA.
Int J Prosthodont. 2003 Nov-Dec;16(6):647-52.
This research determined whether there is a measurable effect of local geometry factors on leucite content of dental porcelain in fixed partial dentures (FPD).
Four-unit FPD frameworks (n = 36) were fabricated using a nickel-chromium alloy (Rexillium III). Body porcelain (Crystar, shade A2) was applied in one increment and subjected to two simulated body firings, followed by a simulated glaze firing to achieve a thickness of 1.5 to 2.0 mm. The completed FPD specimens were randomly assigned to three groups of 12 specimens each: (1) simulated post-soldering, (2) multiple firing, and (3) control. The FPDs from each test group were sectioned into individual units: canine retainer, premolar pontic, molar pontic, and molar retainer. The porcelain was removed from each unit, and the leucite content was measured via quantitative x-ray diffraction.
Porcelain cracking indicated that the soldering simulation had successfully reproduced conditions in the dental laboratory that result in porcelain cracking during soldering. The leucite content was not significantly different between the retainer and pontic units for either the soldering simulation or control FPDs, although the canine retainer units did have a slightly lower leucite content than the pooled values of the other units. Comparison of the pooled data for the three groups indicated statistically significant differences among the leucite contents.
Compared to the control, the simulated post-soldering procedure produced a significant increase in leucite, and the multiple firing group exhibited a significant decrease in leucite. Increases in leucite weight fraction during post-soldering operations-and the larger thermally induced stresses that accompany these leucite increases-are responsible for the cracking that occurs.
本研究确定局部几何因素对固定局部义齿（FPD）中牙科烤瓷材料白榴石含量是否存在可测量的影响。
采用镍铬合金（Rexillium III）制作四单位FPD支架（n = 36）。一次性涂抹体瓷（Crystar，A2色），进行两次模拟体焙烧，随后进行模拟釉面焙烧，以达到1.5至2.0毫米的厚度。将完成的FPD标本随机分为三组，每组12个标本：（1）模拟焊接后，（2）多次焙烧，（3）对照。将每个测试组的FPD切割成单个单位：犬牙固位体、前磨牙桥体、磨牙桥体和磨牙固位体。从每个单位中去除烤瓷材料，并通过定量X射线衍射测量白榴石含量。
烤瓷材料出现裂纹表明焊接模拟成功再现了牙科实验室中导致焊接过程中烤瓷材料出现裂纹的条件。对于焊接模拟或对照FPD，固位体和桥体单位之间的白榴石含量没有显著差异，尽管犬牙固位体单位的白榴石含量略低于其他单位的汇总值。三组汇总数据的比较表明，白榴石含量之间存在统计学上的显著差异。
与对照组相比，模拟焊接后程序使白榴石显著增加，多次焙烧组白榴石显著减少。焊接后操作过程中白榴石重量分数的增加以及伴随这些白榴石增加而产生的更大热诱导应力是导致出现裂纹的原因。
