Material Thickness of CAD/CAM Designed and Milled Leucite-Reinforced Glass-Ceramic Crowns

Objectives: The aim of this study was to compare material thickness of digitally designed crowns to milled crowns using different methods of analysis, design modes and areas of evaluation.
Methods: Impressions of mandibular and maxillary arches from 40 dental students were taken. Standardized crown preparations were performed and digitally scanned on the right mandibular first molar of each cast. Three different crowns were designed using design modes provided by the Planmeca Romexis software (n=40): Pre-Op, Library A, and Library C. 120 IPS Empress CAD LT crowns were milled. Thickness (mm) of designed crowns was evaluated by Planmeca and 3 Shape software, and milled crowns by a caliper (Calipretto-CR). Material thickness was evaluated in 4 areas: central fossa (CF), bucco-axial wall (BAW), mesiobuccal (MBC) and distolingual (DLC) cusps. Data was evaluated using three-way ANOVA, Games Howell, and Tukey’s post hoc tests (α=.05).
Results: There was significant statistical difference (p<0.001) among areas of evaluation, crowns designed by Planmeca (1.12±0.75) and milled crowns evaluated by the caliper (1.28±0.61). PreOp presented the highest values of thickness in MBC and DLC, Library A in the MBC and Library C in the DLC. The highest values of thickness were achieved in the BAW for Library C, MBC for PreOp and Library A, and DLC for Libraries A and C. CF was affected by the method of analysis, having higher values of thickness when measured by the caliper.
Conclusions: Material thickness was affected by the design modes in all areas of evaluation, except for CF. Milled crowns had higher material thickness in the CF than designed crowns. DLC presented higher material thickness than other areas of evaluation, regardless the methods of analysis.