The paper presents selected methods of assessment of tooth preparation based on the literature, among others, computer software cooperating with scanners, e.g. Preppr, DentSim, PREPassistant, E4D Compare, PrepCheck and Simodont Dental Trainer. During tooth preparation for prosthetic restorations, it is necessary to create sufficient space, which will allow the technician to construct an aesthetic and durable restoration. Hard tissues should be prepared very sparingly, while at the same time providing retention and stabilization as well as marginal integration for future restoration. The anatomy of the occlusal surface should be preserved, and the axial walls reduced to the proper thickness to obtain an optimal degree of convergence angle, which equals 6o. The most common errors in tooth preparation for crowns are inadequate reduction of the occlusal surface, the lack of functional cusp bevel and incorrect finish line width. The occlusal surface is excessively reduced on average by 15%, whereas the width of the finish line on the vestibular surface is about 28% too small. The results of the convergence angle measurement exceed three times the recommended values in the literature, which can adversely affect the retention of restoration.