Comparison of Loup versus Microscope Enhanced CAD-CAM Crown Preparations:  A Micro-CT analysis of Marginal Gaps

Emily C. Alper

Alper, Emily C.1, Isleem, Wael F.2, Atlas, Alan M.1, Setzer, Frank F.1
1University of Pennsylvania School of Dental Medicine, Department of Endodontics
2University of Pennsylvania School of Dental Medicine, Department of Periodontics


Chair-side manufactured CAD-CAM crowns provide clinicians with the ability to restore endodontically treated teeth almost immediately. Long-term success depends on a good marginal fit of the restoration to prevent coronal leakage. Variables for a successful fit in CAD-CAM dentistry include preparation, scanning, milling, crown design, and cementation. While failure in any of these steps may result in poor marginal fit, evidence showed that a successful crown preparation may be the most important step for success. Compared to traditional means of crown preparation utilizing naked eyes or loupes (LOUP), dental operating microscopes (DOM) provide much higher magnification and more direct illumination. Aim of this study was to compare marginal fits of CAD-CAM crowns after preparation with loupes and subsequent preparation refinement with loupes or a DOM. Our null hypothesis was that there was no significant difference in marginal gap between loupes and DOM preparations.


18 mounted extracted molars received initial crown preparations with coarse modified shoulder diamonds using loupes up to 3.0x magnification. Teeth were then randomly divided in 2 groups and refined for additional two minutes with fine diamonds with either loupes (LOUP) or a microscope up to 10x magnification (DOM). The prepared teeth were then scanned with an optical scanner (CEREC Omnicam, Dentsply Sirona, York, PA), Zirconia reinforced lithium silicate crowns manufactured with a milling machine (CEREC MCXL 4 axis; Dentsply), and cemented with a resin cement (Calibra Universal; Dentsply). All teeth were scanned with a micro-CT system (vivaCT-40; Scanco Medical, Bassersdorf, Switzerland) at 21µm nominal voxel size. Resulting DICOM images were imported into ITK-Snap (free software). Marginal and absolute gaps were measured at 24 consistent circumferential points per tooth. Absolute gaps were labeled and the total volume calculated. Paired and unpaired t-tests were used for statistical analysis.


The mean marginal gap was 145.0+/-259.6µm for LOUP and 35.6+/-11.1µm for DOM, which was statistically significant (p=0.0001). Mean gap volume for LOUP was 0.975+/-0.811mm3 and 0.250+/-0.450mm3 for DOM, also statistically significantly different (p=0.0420). There was no significant difference for marginal versus absolute gaps for either LOUP or DOM.


The null hypothesis was rejected. Crowns prepared with microscopes versus loupes resulted in a more precise marginal fit. Implementation of a DOM may allow for better crown adaptations, reducing the risk of coronal leakage. Quality of the marginal fit of chair-side milled crowns may allow utilization in a one-day endodontic treatment - immediate restoration concept.