Background: The integration of the current technology of CBCT and 3D CAD/CAM technology has great potential in the field of orthodontics, which is not yet fully investigated. The purpose of this article is to evaluate the accuracy of 3D printed retainers in comparison to vacuum formed retainers. Methods: Alginate impressions were taken for ten patients who have a CBCT scan. A 3D printed retainer and vacuum formed retainer were fabricated. Linear measurements were measured by two assessors using digital caliper. Every measurement on the 3D printed retainer was compared to the corresponding measurement on the thermoformed retainer. The linear measurements were Inter-canine width, Inter-premolar width (first and second premolars), Inter-molar width, Canine-midline length (both sides) and Canine-molar length (both sides). Intra-observer, and inter-observer reliability measurements were done. Results: Results showed excellent intra-observer reliability for the thermoformed retainer and the 3D printed retainer. Inter-observer measurements showed strong agreement between the measurements of the two assessors, for both retainers. The comparison of the thermoformed retainer to the 3D printed retainer showed high statistical agreement, except for the canine-molar on the right side, but with no clinical significance,