Dimensional accuracy of stone casts made from silicone-based impression materials and three impression techniques.
The aim of this study was to measure and compare the dimensional accuracy of stone casts of a partially edentulous mandibular arch made by two condensation silicones, two addition silicones and three impression techniques (1-step putty/light-body, 2-step putty/light-body and monophase technique). A partially edentulous standard stainless steel mandibular arch cast was obtained with reference points on the permanent mandibular right and left canines, and permanent mandibular right and left second molars. The anteroposterior distances (between the mandibular left canine and second molar and between the mandibular right canine and second molar) and transverse distances (between the mandibular left and right canines and between the mandibular left and right second molars) of stainless steel cast were measured by a microscope at 30× magnification and 0.5 µm accuracy. All impressions were made with condensation or addition silicones. The 1- and 2-step putty/light-body impressions were accomplished with putty and light-body materials and the monophase impressions with light-body material only. After the impression procedures, accuracy of each material and technique was assessed measuring the stone casts poured (n=5) from the impressions, by the same microscope. The differences between the values of stone cast and stainless steel cast were calculated, presented as percentages and analyzed statistically by two-way ANOVA and the means compared by Tukey's test (α=0.05). All distances measured on stone casts showed altered dimensions with significantly negative linear changes (shrinkage) as compared to those of the stainless steel cast. The stone casts made from the addition silicones were dimensionally more accurate. No differences were found among the impression techniques.
Accuracy of three polyvinyl siloxane putty-wash impression techniques.
STATEMENT OF PROBLEM
There is much discussion in the dental literature concerning the effect of the impression technique on the accuracy of cast restorations.


PURPOSE
This study assessed the accuracy of 3 putty-wash impression techniques using the same impression material (polyvinyl siloxane) in a laboratory model.


MATERIAL AND METHODS
The 3 putty-wash impression techniques used were (1) 1-step (putty and wash impression materials used simultaneously); (2) 2-step with 2-mm relief (putty first as a preliminary impression to create 2-mm wash space with prefabricated copings. In the second step, the wash stage was carried out); and (3) 2-step technique with a polyethylene spacer (plastic spacer used with the putty impression first and then the wash stage). For each technique, 15 impressions were made of a stainless steel master model that contained 3 complete crown abutment preparations, which were used as the positive control. Accuracy was assessed by measuring 6 dimensions (intraabutment and interabutment) on stone dies poured from impressions of the master model.


RESULTS
One-way analysis of variance showed statistically significant differences among the 3 putty-wash impression techniques, for all intraabutment and interabutment measurements (P <.001). Overall discrepancies of the 2-step technique with 2-mm relief putty-wash impression technique were significantly smaller than that in the 1-step and polyethylene putty-wash impression techniques.


CONCLUSION
The polyvinyl siloxane 2-step, 2-mm, relief putty-wash impression technique was the most accurate for fabricating stone dies.
Simulation Analysis of Local Heat Treatment Formability of an Aerospace Aluminum Alloy Frame Parts
Wang Zhijian1,a, Guo Fangyu1,b, Shang Xiaofeng1,c, Song Hongwu2,d, Wang Ling3,e and Wang Jiale1,f 1School of Mechatronics Engineering, Shenyang Aerospace University, Shenyang 110136, China 2Institute of Metal Research, Chinese Academy of Science, Shenyang 110016, China 3Shenyang aircraft industry company, Shenyang 110134, China aWangzhijian1974@sina.com, b1486121506@qq.com, c1009074102@qq.com dhwsong@imr.ac.cn, ew_ling2008@aliyun.com, f1591897439@qq.com