Accuracy of Digital Workflows in Capturing the Emergence Profile for Crowns

Objectives: Capturing a region of unprepared tooth beyond the crown margin is considered good clinical practice to enable correct emergence profile and long-term periodontal health. The aim of this project was to investigate three digital methods for capturing the apical unprepared portion of the tooth surface for full contour crown fabrication
Methods: Unrestored permanent human teeth were scanned to create 3D printed versions imbedded into 3D printed bone and gingiva model (n=5). The upper first premolar was prepared by an experienced clinician for lithium di-silicate crown 1.00 mm finish line and 1.5 mm buccal, lingual and occlusal reduction. Models were then allocated to one of the following impression techniques: (A) Digital impressions using IOS Primescan (Dentsply) with no retraction cord, (B) Digital impressions using IOS Primescan with retraction cord in-situ and (C) Sectional impression with retraction cord in-situ followed by impression scanning using the pre-release M1 prototype impression scanner (Mimetrik Solutions). Standardised cross-sectional views of the digital scans produced from each technique were generated using Paraview (Kitware). The depth of the sulcus captured at the mesial and distal points (in mm) were measured, reflecting the amount of tooth structure captured beyond the prepared margin
Results: Data showed that the greatest mean sulcus depth was captured when sectional impressions were scanned with Mimetrik scanner (1.61 mm, SD 0.20) followed by IOS with cord group (0.65 mm, SD 0.13). In contrast, minimal sulcus depth was captured in the IOS without cord group (-0.004-0.004 mm, SD 0.01)
Conclusions: The use of retraction cord when utilising digital impression taking methods for crown fabrication is essential to accurately record the apical uncut portion of the crown margins and to fabricate restorations with favourable contours. Scanned sectional impressions were found to capture greater sulcus depth when compared to IOS digital impressions