Comparison of Raters’ Reliability of Two Methods for Measuring Tooth Preparations Undercuts using Professional Computer-Aided Design Software

Abstract

Background: Tooth preparation for fixed dental prostheses requires achieving adequate biological, functional,
and aesthetic requirements. One critical aspect of preparation is avoiding undercuts, which can compromise the
prosthesis’ fit, retention, and resistance. Detection of undercuts is traditionally done visually, but advancements
in computer-aided design (CAD) software provide new methods for assessing undercuts. This study compares
the reliability of two professional CAD software – Fusion 360 and ExoCad – in detecting undercuts in tooth
preparations. Materials and Methods: Seventy-two tooth preparations from 26 dental stone casts were scanned
and digitized into 3D models. Two experienced prosthodontists analyzed undercuts in the 3D models using
Fusion 360 and ExoCad. Interclass correlation coefficient (ICC) values were calculated to evaluate intra- and
inter-rater reliability between the software and operators. Results: The ICC analysis indicated excellent intra
rater reliability for one operator using both software, while the other operator showed poor to fair reliability.
Inter-rater reliability was excellent for ExoCad in some instances but varied significantly across locations and
software. The overall presence of undercuts ranged from 85.3% to 98.7%. Conclusion: Variations in undercut
detection between the software were operator-dependent, highlighting the importance of operator skill in
aligning the insertion path. Future studies should explore multi-unit preparations and unified CAD algorithms
for undercut detection