One of its disadvantages is the low dimensional stability due to syneresis and imbibition. Alginate is an irreversible hydrocolloid and is one of the most commonly used materials in dental medicine due to its easy handling, low cost and good tolerance by patients. Nonetheless, going digital is still very expensive, and clinicians continue to use impression materials, such as alginate. The dimensional stability of the impression materials is the key to an accurate reproduction of the oral cavity. It is crucial that they accurately copy the topography, and for that purpose the impression material must be precise and stable. Impressions are the negative of the structures of the oral cavity, both of the teeth to be rehabilitated as well as the adjacent structures. Taking impressions is an important step in oral rehabilitation procedures such as crowns, fixed partial dentures or removable prostheses and their performance may dictate part of the success of treatments. This material can be stored for a week without the risk of clinically significant dimensional changes. No significant shrinkage of the silicone under investigation was found over time. A statistical analysis via a one-way repeated measures ANOVA was performed. The dimensional stability was calculated according to the formula specified in ISO (International Organization for Standardization) 4823:2000. The measurements were performed by laser interferometry, according to the Michelson technique. 10 samples were obtained from this silicone with an automatic mixing machine (Pentamix 2, 3M ESPE™, Seefeld, Germany) according to International Organization for Standardization (ISO) 4823:2000 and stored in the IPQ (Portuguese Institute for Quality) for one week. The purpose of this study is to evaluate the dimensional changes of a first impression type VPS (Vinyl Polysiloxane) (Imprint™ 4 Preliminary Penta™ Super Quick, 3M ESPE™, St Paul, MN, USA). Oral rehabilitation success depends upon the accuracy and dimensional stability of the impressions.
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