Proper margin width is one of the key factors determining the correct fabrication of a prosthetic crown. Digital technologies, such as intraoral scanners, are increasingly used to assess parameters of tooth preparation for prosthetic crowns. The study aimed to evaluate the conservativeness of tooth preparation performed by third-year dental students on phantom teeth based on margin width and the utility of an intraoral scanner for its assessment. A total of 432 model teeth (KaVo) prepared for crowns by third-year dental students were tested: 216 maxillary right first molars (tooth 16) with a chamfer, and 216 maxillary right first premolars (tooth 14) with a classical shoulder. Tooth 16 was prepared first, followed by tooth 14 one week later. After each preparation, students were evaluated and received instructor feedback. All teeth were scanned using a 3Shape TRIOS 3 intraoral scanner, finish line widths were measured and compared to ideal crown preparation standards. Continuous variables are presented as medians and interquartile ranges, and categorical variables are presented as counts and percentages. Margin widths were compared using the Mann-Whitney U test (with rank-biserial effect sizes), and categorical classifications were analyzed with the chi-square test. A significance level of p < 0.05 was adopted. Calculations were performed using IBM SPSS Statistics 29 and R software (version 4.4.2). For tooth 16, median chamfer margin widths were: mesial 1.08 mm IQR: 0.80–1.45, distal 1.17 mm IQR: 0.79–1.55, lingual 1.17 mm IQR: 0.87–1.41, and buccal 1.07 mm IQR: 0.86–1.35. Optimal widths were achieved by 22.9% (mesial), 21.9% (distal), 16.7% (lingual), and 15.7% (buccal) of students. For tooth 14, median widths were: mesial 0.67 mm IQR: 0.51–0.93, distal 0.87 mm IQR: 0.63–1.29, lingual 0.80 mm IQR: 0.63–1.06, and buccal 0.78 mm IQR: 0.60–1.01, with optimal widths achieved by 40% (mesial), 32.4% (distal), 41.4% (lingual), and 11.9% (buccal). The study revealed significant variability in finish line width among students and tooth surfaces, with most preparations being excessively wide. An intraoral scanner may be a useful tool for assessing the margin width in prepared phantom teeth.
Bereziewicz et al. (Fri,) studied this question.