Abstract
Background Dental cusp angulation provides valuable insights into chewing efficiency and prosthesis
safety. Artificial intelligence-enabled computing of cusp angles has potential important
value, but there is currently no reliable digital measurement method as a cornerstone.
Objectives To establish a digital method for measuring cusp angles and investigate inter-rater
and intra-rater reliabilities.
Methods Two cusp angles (angles α and β) of the first molar were measured on 21 plaster casts
using a goniometer and on their corresponding digital models using PicPick software
after scanning with a CEREC Bluecam three-dimensional (3D) intraoral scanner. Means ± standard
deviations, as well as intraclass correlation coefficients (ICCs) and Pearson's correlation
coefficients (PCCs) were calculated, and repeated measures analysis of variance was
performed. The Bland–Altman method was used to calculate the difference and mean degree
values of two measurement methods from both examiners, and the Bland–Altman diagram
was drawn using MedCalc software.
Results When the examiner was experienced, angle α was 139.19° ± 13.86°, angle β was 19.25° ± 6.86°,
and a very strong positive correlation between the two methods was found (r > 0.9; p < 0.001). No significant difference between the two methods was found using the repeated
measures analysis of variance (p > 0.05). The Bland–Altman diagram showed that the two methods were highly consistent.
For inter-rater assessments, the ICC and PCC values of the cusp angulation using the
digital method were all higher than the corresponding values measured on traditional
casts. For intra-rater assessments, the ICC values of cusp angulation using the digital
method were higher than the corresponding values measured on traditional plaster casts
for both examiners. However, repeated measurements of the angle β of the inter-examiners
revealed significant differences (p < 0.05) for both methods.
Conclusions Cusp angulation using 3D digital models is a clinical option and appears to improve
the reliability of cusp angulation compared with measuring plaster casts using a goniometer.
This variability was still evident when measuring small cusp angles using the digital
model for inexperienced examiners.
Keywords reliability - dental cusp angulation - 3D digital models - cracked tooth
