Digital and manual evaluation of tooth preparation geometry of single crowns

This data was collected in a laboratory-based cross-sectional study where 125 dies prepared for single crowns were evaluated manually through direct visual inspection and digitally through assessment of STL dataset of each die using a three-dimension (3D) inspection software (GOM Inspect Suite, 2020). The dies were produced from 83 conventional impressions recorded using an elastomeric impression material, either silicone or polyether.
The parameters of tooth preparation geometry evaluated included the buccal-lingual convergence angles (degrees), the occlusal-cervical height (millimetres), the margin design (shoulder, chamfer or knife-edge) and the presence or absence of auxiliary retentive features. The data was evaluated on the basis of the maxillary and mandibular arches, the number of prepared teeth per arch and the commonly prepared type of teeth, whether anteriors, premolars or molars. From the laboratory prescription form, the type of prescribed crown was also recorded.
The aim of the study was to assess the said parameters using a digital and manual technique, to test the hypothesis that there was no difference in the two assessment techniques. This was motivated by the current trend in digital dentistry and the efficiency and convenience offered by intraoral and laboratory scanners.
The dataset comprises of measurements of the said parameters using the two techniques, which can be summarized into means and standard deviations, medians and interquartile ranges, and frequencies and percentages. Statistical inferences can be made using independent sample t-test to compare continuous variables and chi-square to compare categorical variables derived using the two techniques. Further comparisons of the reliability of the two techniques can be performed using inter-class correlations.
The statistical analysis of this data showed that most prepared teeth in the maxillary arch were anterior teeth while in the mandibular arch, they were molars. Most of the prescribed restorations were all-ceramic crowns and most had shoulder margins all around. Many of the measurements were not ideal based on the recommended guidelines. There was no statistically significant difference between the measurements derived from digital and manual assessment of tooth preparation parameters, but the digital technique recorded greater buccal-lingual convergence angles and shorter occlusal-cervical heights than the manual technique.
The digital technique can enable chairside assessment and modifications prior to sending the work to the laboratory thus minimizing errors and repeat work.