Learning Curve Exists in CAD, But Does it Matter?

Abstract

Objectives: This study aimed to compare single crown restorations designed by experienced dental technician and by dental students using Computer-Aided Design (CAD) software. Methods: Digital datasets of models were obtained and 3D-printed (n=12). Teeth #45 on these models were prepared and scanned again. For each model, crown designs were done by an experienced technician (group TD), and by two dental students after 3-hour standard training of the same technician (group AD), respectively, with CAD software (Zfx Manager 2.0). The original tooth morphology and crown designs were superimposed (Geomagic Control 14.0), and occlusal morphological parameters, including average positive and negative profile discrepancy, standard deviations (SD), estimated root mean square (RMSestimate), volume discrepancy, volume/area profile discrepancy, and cusp angle, were analyzed. Fracture resistance was determined using compressive load-to-fracture test (Instron E3000, crosshead speed 0.5mm/min) on monolithic lithium disilicate crowns (IPS e.max CAD) that were milled, sintered, and adhesively luted to the 3D-printed dies. The failure mode was recorded and examined under microscopy, while representative samples were examined using SEM. Paired t-test, repeated measurements of ANOVA, Fisher’s exact test, and Pearson’s correlation were used in statistical analysis (α=0.05). Results: For profile and volume discrepancy parameters, no significant differences were found between crowns designed by the dental technician and students except average positive profile discrepancy (p<0.05). Both group TD and AD had significantly higher cusp angles than the original teeth (p<0.05). No significant difference was found in load capacity values, while group TD has a significantly higher percentage of bulk fracture (p<0.05). Conclusions: With the aid of CAD software, no significant discrepancies in occlusal morphology exist between technician- and student-designed crowns except average positive profile discrepancy and cusp angle. Furthermore, both groups can achieve clinically acceptable fracture resistance.