Accuracy of milled models fabricated from optical impressions (iTero system).

Objective: This in-vitro study evaluates the accuracy of a milled polyurethane die system (“Digital Die”) generated from optical impressions (iTero-CADENT), compared to conventional stone dies generated from elastomeric impressions (“Conventional Die”).

Method: Four typodont teeth (Maxillary central incisor #9, Maxillary second molar #15, Mandibular premolar #21 & Mandibular first molar #30) were prepared for PFM crowns with chamfer margins. These ‘Master dies’ were impressed with light and heavy bodied polyvinyl-siloxane impression material (Aquasil Ultra® -Dentsply) and cast in scannable stone (Diamond Die - Hi-Tec Dental) to produce 24 individual ‘reference’ dies. These were divided into 2 groups of 12. One ‘reference’ group of stone dies was re-impressed with PVS to produce 12 corresponding stone models (Die Keen™ Heraeus Kulzer). The other ‘reference’ group was subjected to optical scans with the iTero scanner to produce 12 corresponding iTero polyurethane models with removable dies. The resulting dies from both groups were used to fabricate individual full coverage metal copings (Rex 4 Alloy™, Pentron) using conventional wax-up technique and casting. Each cast coping was placed on its corresponding ‘reference’ die. All copings were measured for marginal fit at 8 different locations around the margin under an optical stereomicroscope at 100x magnification. Results were analyzed using the t-test.

Result: Mean marginal gaps were 19.3 +/- 10.4μm for the “Conventional Die” group and 21.2 +/-9.9μm for the “Digital Dies” (iTero).

Conclusion: Both systems produced cast copings with marginal fit well within accepted clinical standards. There was no significant difference (P=0.2) between the die system accuracies, validating the theory that the iTero digital dies generated from optical impressions are as accurate as conventional dies.