[Implications of choice of products and impression technique on the thickness of the dento-prosthetic interface of the CAD-CAM crowns].

The purpose of this study is to find out what type of impression material is able to achieve a CAD-CAM (Procera) crown with minimal thickness at the dental-prosthetic interface, taking into account the effect of the oversize replica and dimensional variations of the impression materials over time. The accuracy of the marginal adaptation will therefore depend on the oversize replica of clinical preparation controlled by the constant K. Three different types of impression materials: medium viscosity polyether (Impregum 3M-ESPE, Germany), silicones polyvinyl siloxane A (Putty + Very Light) and (Heavy + Light) (Express 3M-ESPE, Germany), were used for making impressions of fifteen initial prototype maxillary teeth made of nickel chrome. The cast of the impressions were poured with plaster type IV (Zhermack, Italy), on which thirty Procera crowns were fabricated. The thickness of the dental-prosthetic interface was then studied at three levels: 0, 1 and 2 mm. The results show that the impression material has a statistically significant impact on the thickness of the dental-prosthetic interface at all three levels. The most compressive impression technique, Putty + Very Light gave the best results at the three levels pre-cited. The results analyzed under optical microscopy show a statistically significant difference between the three impression material products (p-value < 0.05). The calibration constant K, according to each clinical situation, can therefore lead to optimal dental-prosthetic inter-face.