Dimensional Accuracy Of The Different Impression Materials And Techniques Used In Fixed Prosthodontics

Minu Dhungana (Masters Degree Candidate); Prof. Handong Zhang, MDS; DrYumei Ding, PhD (Tutor), Department of Stomatology, Union Hospital of TongjiMedical College of Huazhong University of Science and Technology, Wuhan,Hubei, ChinaObjective: The objective of this in vitro study was to evaluate and compare thedimensional accuracy of the cast obtained from different impression materials andtechniques commonly used in fixed prosthodontics.Materials and methods: The impressions were made from a metallic master modelmade of stainless steel that simulated a tooth preparation for mandibular molar. Thefollowing impression materials were evaluated: polyvinyl siloxane in1-step dualviscosity technique (group1), polyvinyl siloxane in2-step dual viscosity technique(group2), laminated reversible/irreversible hydrocolloid impression technique (group3) and improved alginate (group4). Dimensional changes (mm) were assessedbetween the master model and the stone model (type IV gypsum) at two referencepoints marked in the mesiodistal and buccolingual surfaces. The measurements of themaster model and stone model were made with digital micrometer (accuracy of0.001mm) Results: The stone dies obtained with all the materials and techniques hadsignificantly larger dimensions as compared to the master model (p<0.05). The lowestto highest deviation from the master model was found to be in group2, group1, group3and highest deviation was shown by group4. One way analysis of variance revealedno significant differences in dies obtained from the different groups of the impression.In comparison with the two mixing techniques for the polyvinyl siloxane material2-step dual viscosity was more accurate than1-step dual viscosity technique.Conclusions: We concluded that all the impression materials and techniques specifiedabove are accurate and can provide satisfactory clinical results when used in thecorrect method.