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.
Comparative Evaluation of the Dimensional Accuracy of Different Putty-Wash Techniques Using Additional Silicon Impression Material In Vitro Study
Purpose: The aim of the present study was to evaluate and compare the dimensional accuracy of stone models made by addition silicone impression material using three putty- wash impression techniques: one step putty wash (dual viscosity), two step and modified two step putty wash technique. Material and Methods: A stainless steel master model was constructed simulating a three-unit fixed prosthesis. Fifteen impressions were make of this master model with each impression technique. The first technique, one step dual viscosity was made with putty in the tray and light body on brass dies and impression was make. The second technique, two step putty/wash, the first step using putty on the tray with acrylic spacer on the dies and impression was make then followed by loading wash material on the dies and reseating the first impression in the second step. The third technique, modified two step made using putty/light body as in the first technique then a hole was made at the edge of two abutments in the polymerized impression, then light body was loaded into the tray and over the model and the tray is reseated. Total of forty five impressions were obtained and casts poured using type IV stone. The accuracy of these casts measured using a travelling microscope. Three dimensions diameter, height, and interabutment distances measurements were obtained and statistical analysis was done using paired T-test, One way ANOVA, and Least Significant Difference (LSD) tests. Result: Showed that a significantly larger dimensions of the resultant stone casts of all techniques in comparison to the master model (P
In vitro study of the number of surface defects in monophase and two-phase addition silicone impressions.
STATEMENT OF PROBLEM
Monophase addition-cured silicone impression materials in stock trays are considered to be alternatives to two-phase systems used with custom trays.


PURPOSE
This study compared the number of surface defects in addition-cured silicone impressions recorded with monophase materials in stock trays and two-phase impressions in custom trays.


METHODS
The number of voids visible on the surface of impressions recorded in vitro were counted. Two monophase impression materials. (President Monobody system 75, Bayer Cutter) in stock trays were compared with impressions recorded with two-phase addition silicone materials (President Plus light-body/regular-body and Zhermack Elite light-body/medium-body) in custom trays. A total of 200 automixed impressions, 50 with each material, were recorded of 50 dentoform molar teeth prepared for full veneer crowns. Impressions were examined for surface voids anywhere on the prepared part of the tooth by a trained examiner.


RESULTS
Mean number of voids observed for the monophase impressions were 3.0 +/- 2.2 for President Monobody system and 3.4 +/- 2.0 for Bayer Cutter system. Mean number of voids for the two-phase materials were 0.8 +/- 1.0 for President Plus, and 1.0 +/- 1.1 for Zhermack Elite. No significant differences were observed for number of voids between the monophase materials or between the two-phase systems (ANOVA and Neuman-Keuls p > 0.05). However, both two-phase materials in custom trays had significantly fewer surface voids than the two-monophase materials (ANOVA and Neuman-Keuls, p < 0.001) used in stock trays.


CONCLUSION
Monophase addition-cured impression materials in stock trays carries an increased risk of void formation on the surface of the impression when compared with two-phase addition silicone materials in custom trays.