Dimensional Accuracy of Stone Casts Made from Silicone-Based Impression Materials and Three Impression Techniques

Abstract

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.

Dimensional accuracy of different impression techniques of partially edentulous mandibular arch

“…The monophase technique was performed using acrylic resin trays (Vipi Flash, VIPI, Pirassununga, São Paulo, Brazil) with internal relief (2 mm) 7 . Initially, an adhesive layer (Universal Adhesive, Heraeus Kulzer GmBH, Hanau, Hesse, Germany) was applied to each acrylic resin tray and allowed to dry for five minutes 7 .…”

“…Initially, an adhesive layer (Universal Adhesive, Heraeus Kulzer GmBH, Hanau, Hesse, Germany) was applied to each acrylic resin tray and allowed to dry for five minutes 7 . The elastomeric impression material (type III) was placed on the internal surface of the acrylic resin tray.…”

“…Several studies showing differences in dimensional accuracy between the impression techniques are found in literature [8][9][10][11][12][13][14][15] . Conversely, other studies show similar outcomes between different impression techniques 7,[16][17] or only small differences within a specific group of elastomeric impression materials 18 . Therefore, there is conflicting evidence on impression techniques.…”

“…These impression materials are hydrophilic and present adequate properties, such as good tear strength and quick elastic recovery, along with excellent accuracy and dimensional stability [5][6] . The different viscosities allow them to be used in three impression techniques: 1-step putty/light-body, 2-step putty/lightbody, and monophase [6][7][8] . Several factors affect the dimensional accuracy of elastomeric impression material molds, such as the type of impression material used and its adhesion to the tray, viscosity, hydrophilicity, thickness, by-product formation, the time spent during cast pouring, incomplete elastic recovery, and polymerization/thermal shrinkage [7][8] .…”

“…The different viscosities allow them to be used in three impression techniques: 1-step putty/light-body, 2-step putty/lightbody, and monophase [6][7][8] . Several factors affect the dimensional accuracy of elastomeric impression material molds, such as the type of impression material used and its adhesion to the tray, viscosity, hydrophilicity, thickness, by-product formation, the time spent during cast pouring, incomplete elastic recovery, and polymerization/thermal shrinkage [7][8] . Several studies showing differences in dimensional accuracy between the impression techniques are found in literature [8][9][10][11][12][13][14][15] .…”