CONVENTIONAL IMPRESSION VS INTRAORAL SCANNER FOR CAD/CAM PARTIAL RESTORATIONS

Abstract

Purpose. The purpose of this study was to compare the effectiveness of the digital workflow in producing indirect milled restorations starting from a conventional impression technique and from an intraoral digital scanner. In our study we evaluated the accuracy of indirect partial restorations made of zirconia and lithium disilicate, with the two impression techniques. Material and methods. Three first permanent molars with regular anatomy, on which MOD cavities for indirect restorations have been prepared, have been selected for the experimental models. For each experimental model, four impressions have been taken with the conventional technique, poured with hard plaster and scanned in a dental laboratory, and four impressions have been taken with the digital intraoral scanner. From each digital file two SLA epoxy resin models were 3D printed and two indirect restorations, one out of lithium disilicate and one out of zirconia, for a total of 48 models and 48 restorations. Each restoration was tried on the corresponding SLA model and then seated in the master cavity on the original tooth. Each seated restoration was photographed on a stand for repeatability in order to measure and compare gaps at the cervical margin between restoration and tooth. All datas were recorded and undergone statistical analysis. Results. For lithium disilicate restorations a mean marginal gap of 114.12 ± 88.82 μm has been detected for samples obtained with a conventional impression technique and of 33.55 ± 42.83 μm for samples obtained with a digital impression technique. For zirconia restorations a mean marginal gap of 182.58 ± 76.56 μm has been detected for samples obtained with a conventional technique and of 114.52 ± 46.86 μm for samples obtained with a digital technique. Conclusions. Within these experimental conditions, the digital impression technique produced better restorations in terms of marginal adaptation than the conventional impression technique. Moreover, for both techniques has been observed a substantial difference in the marginal adaptation of the two compared materials, with a better performance of lithium disilicate than zirconia. A fully digital workflow, with the limitations of an in vitro simulation, appears to increase the degree of reliability of CAD/CAM workflows.