Fleming G J, Shelton R M, Marquis P M
Biomaterials Unit, School of Dentistry, University of Birmingham, UK.
Dent Mater. 1999 Jan;15(1):62-70. doi: 10.1016/s0109-5641(99)00015-9.
Zinc phosphate cements are supplied in powder/liquid form so that a range of mixing ratios are naturally generated in clinical practice. However, these cements are known to have a deleterious effect on dental ceramics and the impact of variations in cement mixing on the strength of dental porcelain was investigated in the present study.
Vitadur-N core porcelain was fabricated into discs (15 mm diameter and 2 mm thickness), zinc phosphate cements of different mixing ratios were applied to the discs to produce a luting cement thickness and the samples were stored for 24 h prior to testing in a water-bath at 37 +/- 1 degrees C. The mean fracture strength, standard deviation and associated Weibull moduli (m) of the coated porcelain discs were determined as a function of mixing ratio using bi-axial flexure (ball-on-ring) by fracturing sets of 30 specimens coated with cements manipulated at different mixing ratios.
The strength data for the coated porcelain discs showed little variation in magnitude and consistency ranging from 108 +/- 8.3 MPa (m = 14.0 +/- 2.6) at 1.7 g/ml to 112 +/- 8.5 MPa (m = 14.6 +/- 2.7) at 2.6 g/ml and 108 +/- 8.1 MPa (m = 14.4 +/- 2.6) at 3.2 g/ml. However, the plots of survival probability against strength for coated specimens prepared using mixing ratios below that recommended by the manufacturers' for luting purposes (2.6 g/ml), appeared to develop an asymmetry at the lower values of strength.
It was proposed that the increased corrosive acidic environment for cements prepared at mixing ratios below 2.6 g/ml may have extended pre-existing flaws in the porcelain discs thereby possibly producing the asymmetry in the survival distributions.
磷酸锌水门汀以粉/液形式供应，因此在临床实践中会自然产生一系列混合比例。然而，已知这些水门汀对牙科陶瓷有有害影响，本研究调查了水门汀混合变化对牙科瓷强度的影响。
将维他多尔-N核瓷制成圆盘（直径15毫米，厚度2毫米），将不同混合比例的磷酸锌水门汀应用于圆盘以产生粘结水门汀厚度，样品在37±1℃的水浴中测试前储存24小时。使用双轴弯曲（环上球）对30个涂有以不同混合比例调配的水门汀的试样进行断裂，测定涂层瓷盘的平均断裂强度、标准偏差和相关的威布尔模量（m），作为混合比例的函数。
涂层瓷盘的强度数据在大小和一致性上变化不大，在1.7克/毫升时为108±8.3兆帕（m = 14.0±2.6），在2.6克/毫升时为112±8.5兆帕（m = 14.6±2.7），在3.2克/毫升时为108±8.1兆帕（m = 14.4±2.6）。然而，对于使用低于制造商推荐的粘结用途混合比例（2.6克/毫升）制备的涂层试样，强度生存概率图在较低强度值处似乎出现不对称。
有人提出，对于以低于2.6克/毫升的混合比例制备的水门汀，其腐蚀性酸性环境增加可能会扩大瓷盘中预先存在的缺陷，从而可能在生存分布中产生不对称性。
