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Influence of impression materials and techniques, times and pouring materials on dimensional accuracy of total casts by contact scanner and marginal fit of Y-TZP frameworks


This study will examine the accuracy of total dental casts obtained from different impression techniques, casting times and impression's disinfection, as well as measure the cervical marginal fit of zirconia frameworks on dental preparations for full crown. A master model, with preparations in the teeth 14, 16, 21 and 25, on which Y-TZP frameworks will be made by CAD/CAM technology, will be used. Three impression techniques will be used: (T1) simultaneous and (T2) reline - relief with PVC film and (T3) digital impression - Cerec Conect Omnicam (Sirona). Conventional molds will be subjected to disinfection with sodium hypochlorite 1.0% for 10 min prior to gypsum pouring. For the impression with condensation silicone, casts will be poured after 30 minutes, 3 or 7 days. For the addition silicone, casts will be obtained after 2 hours, 3, 7 or 15 days. For each impression technique / pouring time, 8 impressions will be obtained with stock tray and condensation (Speedex; Coltène / Whaledent Inc.) or addition (Express XT; 3M ESPE) silicone, by a single calibrated operator. The castings will be made with plaster type IV (GC Fuji Rock EP - GC America or Zero Stone - Dentona AG). For the analysis of dimensional accuracy, the casts will be scanned by a contact scanner MDX-40 (Roland, Information Technology Center - CTI, Campinas, SP, Brazil), calibrated at 0.2 mm for each stroke of the contact tip on the scanned surface. The 3D measurements will be compared with those obtained from digital impressions (T3), by digital superposition. For the analysis of cervical marginal fit of the Y-TZP, the frameworks will be passively adapted on the dental preparations in the gypsum casts, and the measurements performed in stereo. The results will be submitted to normality homoscedasticity tests and the most appropriate statistical method will be selected to evaluate the influence of the independent variables of the study, adopting a significance level of 5.0%. (AU)