Consani Rafael Leonardo Xediek, Domitti Saide Sarckis, Consani Simonides
Department of Prosthodontics, Piracicaba Dental School, Campinas State University, São Paulo, Brazil.
J Prosthet Dent. 2002 Sep;88(3):285-9. doi: 10.1067/mpr.2002.128447.
The pressure of final closure may be released when the flask is removed from the mechanical or pneumatic press and placed in the spring clamp. This release in pressure may result in dimensional changes that distort the denture base.
The purpose of this study was to investigate differences between the dimensional stability of standardized simulated denture bases processed by traditional moist heat-polymerization and those processed by use of a new tension system.
A metal master die was fabricated to simulate an edentulous maxillary arch without irregularities in the alveolar ridge walls. A silicone mold of this metallic die was prepared, and 40 stone casts were formed from the mold with type III dental stone. The casts were randomly assigned to 4 test groups (A-D) of 10 specimens each. A uniform denture base pattern was made on each stone cast with a 1.5-mm thickness of base-plate wax, measured with a caliper. The patterns were invested for traditional hot water processing. A polymethyl methacrylate dough was prepared and packed for processing. The flasks in groups A and B were closed with the traditional pressure technique and placed in spring clamps after final closure. The flasks in groups C and D were pressed between the metallic plates of the new tension system after the final closure. The group A and C flasks were immediately immersed in the water processing unit at room temperature (25 degrees +/- 2 degrees C). The unit was programmed to raise the temperature to 74 degrees C over 1 hour, and then maintained the temperature at 74 degrees C for 8 hours. The group B and D flasks were bench stored at room temperature (25 degrees +/- 2 degrees C) for 6 hours and were then subjected to the same moist heat polymerization conditions as groups A and C. All processed dentures were bench cooled for 3 hours. After recovery from the flasks, the base-cast sets were transversally sectioned into 3 parts (corresponding to 3 zones): (1) distal of the canines, (2) mesial of the first molars, and (3) mesial of the posterior palate). These areas had been previously established and standardized by use of a pattern denture in the sawing device to determine the sections in each base-cast set. Base-cast gaps were measured at 5 predetermined points on each section with an optical micrometer that had a tolerance of 0.001 mm. Collected data were analyzed with analysis of variance and Tukey's test.
Denture bases processed with the new tension system exhibited significantly better base adaptation than those processed with traditional acrylic resin packing. Immediately after polymerization (Groups A and C), mean dimensional change values were 0.213 +/- 0.055 mm for the traditional packing technique and 0.173 +/- 0.050 mm for new tension system. After delayed polymerization (Groups B and D), the values were 0.216 +/- 0.074 mm for the traditional packing technique and 0.164 +/- 0.032 mm for new tension system. With both techniques, dimensional changes in the posterior palatal zone were greater (conventional = 0.286 +/- 0.038 mm; new system = 0.214 +/- 0.024 mm) than those elsewhere on the base-cast set.
Within the limitations of this study, the new tension packing system was associated with decreased dimensional changes in the simulated maxillary denture bases processed with heat-polymerization.
当烧瓶从机械或气动压力机中取出并放入弹簧夹中时，最终闭合的压力可能会释放。这种压力释放可能会导致尺寸变化，从而使义齿基托变形。
本研究的目的是调查通过传统湿热聚合处理的标准化模拟义齿基托与使用新张力系统处理的义齿基托在尺寸稳定性上的差异。
制作一个金属主模型，以模拟无牙槽嵴壁不规则的无牙上颌弓。制备该金属模型的硅橡胶模具，并用III型牙科石膏从模具中制作40个石膏模型。将模型随机分为4个测试组（A - D），每组10个样本。用卡尺测量，在每个石膏模型上制作一个厚度为1.5毫米的均匀义齿基托蜡型。将蜡型包埋以进行传统的热水处理。制备聚甲基丙烯酸甲酯面团并进行充填处理。A组和B组的烧瓶采用传统压力技术闭合，最终闭合后放入弹簧夹中。C组和D组的烧瓶在最终闭合后在新张力系统的金属板之间加压。A组和C组的烧瓶立即在室温（25摄氏度±2摄氏度）下浸入水处理单元。该单元程序设定为在1小时内将温度升至74摄氏度，然后在74摄氏度下保持8小时。B组和D组的烧瓶在室温（25摄氏度±2摄氏度）下放置6小时，然后进行与A组和C组相同的湿热聚合条件处理。所有处理后的义齿在工作台上冷却3小时。从烧瓶中取出后，将基托 - 模型组合横向切成3部分（对应于3个区域）：（1）犬齿远中，（2）第一磨牙近中，（3）后腭近中）。这些区域先前已通过在锯切装置中使用模型义齿确定并标准化，以确定每个基托 - 模型组合中的切片。使用精度为0.001毫米的光学显微镜在每个切片的5个预定点测量基托 - 模型间隙。收集的数据采用方差分析和Tukey检验进行分析。
使用新张力系统处理的义齿基托比使用传统丙烯酸树脂充填处理的义齿基托表现出明显更好的基托适应性。聚合后立即（A组和C组），传统充填技术的平均尺寸变化值为0.213±0.055毫米，新张力系统为0.173±0.050毫米。延迟聚合后（B组和D组），传统充填技术的值为0.216±0.074毫米，新张力系统为0.164±0.032毫米。两种技术中，后腭区域的尺寸变化（传统方法 = 0.286±0.038毫米；新系统 = 0.214±0.024毫米）均大于基托 - 模型组合其他部位的尺寸变化。
在本研究的局限性内，新的张力充填系统与热聚合处理的模拟上颌义齿基托尺寸变化的减少有关。
