Abstract
Crown preparation and cementation are two critical parameters for the success of a prosthetic treatment. Marginal fit is important because a large marginal opening allows plaque and oral liquids to penetrate, resulting in micro-leakage, caries and periodontal disease. The purpose of this study is evaluating and comparing the marginal fit of Cr-Ni metallic crowns using three different wax-up techniques made on molars, extracted because of orthodontic reasons. The freshly extracted teeth were kept in artificial saliva to reduce penetration of microorganisms and simulating oral environment. In vitro cementation with Ketac Cem was carried out after disinfection and drying. Samples were maintained for 24 h at 37oC in distilled water and then gold plated. The marginal gap was analyzed using scanning technique with an electronic microscope in several points for every surface of each tooth. Data were statistically analyzed. Measuring the internal fit requires sectioning of specimens and allows obtaining a small number of samples (1-2 per specimen) which means a limited number of measurements per specimen. Another problem consists in the reduced size of the samples after sectioning. The scanning technique enhances measurements of the marginal gap without sectioning and provides an objective evaluation of preparation and cementation techniques. Key words: scanning electron microscopy, marginal gap, crowns