Magne P, Kwon K R, Belser U C, Hodges J S, Douglas W H
School of Dentistry, University of Minnesota, Minneapolis, Minn., USA.
J Prosthet Dent. 1999 Mar;81(3):327-34. doi: 10.1016/s0022-3913(99)70277-5.
Anterior teeth are especially subject to the thermal variations of ingested food and drinks. Postoperative cracks of porcelain laminates are considered a possible consequence of polymerization shrinkage, function, and thermocycling.
This investigation was conducted to define the parameters associated with the development of cracks in porcelain veneers using cyclic thermal fatigue.
Twenty-seven maxillary incisors were restored with porcelain laminate veneers and subjected to thermocycling (5 degrees C to 50 degrees C) for 1000 cycles. Ceramic cracks were reported for 11 of the 27 specimens. Teeth were sectioned and prepared for SEM analysis. Measurements of the ceramic and the luting composite thicknesses were performed for each specimen at different restoration locations (facial, incisal, and proximal).
No significant differences in the ceramic or the luting composite thicknesses were observed between cracked and uncracked specimens. However, significant differences were observed in the ratio of the ceramic and luting composite thicknesses. Most cracked samples exhibited a ratio at the facial location below 3.0 (2.6 +/- 0.35), whereas most noncracked specimens were above this value (3.9 +/- 0.19). Incisal and especially proximal measurements alone were not significantly different between cracked versus uncracked specimens. Ceramic was slightly thinner in the facial aspect than in the proximal aspect, which was also thinner than the incisal aspect. Composite in the facial aspect was thinner in the cervical area than in the incisal third of the tooth.
Significant cyclic temperature changes can induce the development of flaws in porcelain veneers. Control of tooth reduction and the application of die spacers during laboratory procedures undoubtedly represent key elements; a sufficient and even thickness of ceramic combined with a minimal thickness of luting composite will provide the restoration with a favorable configuration with regard to crack propensity, namely, a ceramic and luting composite thickness ratio above 3.
前牙特别容易受到摄入食物和饮料的温度变化影响。瓷贴面术后出现裂纹被认为是聚合收缩、功能和热循环的可能结果。
本研究旨在确定使用循环热疲劳法时，与瓷贴面裂纹形成相关的参数。
用瓷贴面修复27颗上颌切牙，并进行1000次循环的热循环（5摄氏度至50摄氏度）。27个样本中有11个报告出现陶瓷裂纹。将牙齿切片并准备进行扫描电子显微镜分析。在不同修复位置（唇面、切端和邻面）对每个样本的陶瓷和粘结性复合材料厚度进行测量。
在有裂纹和无裂纹的样本之间，未观察到陶瓷或粘结性复合材料厚度有显著差异。然而，在陶瓷和粘结性复合材料厚度的比值上观察到了显著差异。大多数有裂纹的样本在唇面位置的比值低于3.0（2.6±0.35），而大多数无裂纹的样本高于该值（3.9±0.19）。仅切端尤其是邻面的测量结果在有裂纹和无裂纹的样本之间无显著差异。唇面的陶瓷比邻面稍薄，邻面又比切端薄。唇面的复合材料在颈部区域比牙齿切端三分之一处薄。
显著的循环温度变化可导致瓷贴面出现缺陷。在实验室操作过程中控制牙齿预备量和使用代型间隙剂无疑是关键因素；足够且均匀的陶瓷厚度与最小的粘结性复合材料厚度相结合，将为修复体提供关于裂纹倾向的有利结构，即陶瓷与粘结性复合材料厚度比高于3。
