Complete arch digital implant scan accuracy with screw-retained or snap-on scan bodies: A comparative in vitro study

Statement of problem: Different scan body types have been reported to influence intraoral scanning accuracy. Stiff implant connections allow the use of snap-on scan bodies. However, data on the influence of scan body retention type are lacking. Purpose: The purpose of this in vitro study was to assess and compare the accuracy of complete arch digital scanning with that of screw-retained or snap-on scan bodies. Material and methods: An edentulous mandibular master model with 4 conical connection analogs was digitized with an extraoral optical scanner to achieve a reference file. Seventy-six test scans were obtained with an intraoral scanner: 38 using screw-retained and 38 using snap-on scan bodies. The resulting 76 test files were aligned to the reference file with a best fit algorithm. Linear (ΔX, ΔY and ΔZ- axis), and angular deviations (ΔANGLE) were evaluated for each implant position (n=304). Three-dimensional (3D) deviation was calculated for each position according to the Euclidean distance (ΔEUC). Descriptive analysis and multivariable analysis were stratified considering scan body type and implant position (α=.05). Results: Considering ΔEUC, scan body type showed no significant difference (P=.097), while implant position was statistically significant (P<.001), with the left second premolar as the most critical and the right lateral incisor the most accurate. Considering ΔANGLE, the snap-on scan bodies were significantly better (P=.033). The implant position also resulted in statistically significant differences (P<.001) with the left second premolar being the most critical and the right lateral incisor as the most accurate. Conclusions: Snap-on scan bodies showed comparable 3D and higher angular accuracy compared with screw-retained scan bodies. Tilted posterior implants were the least accurate and resulted in more critical positions, especially the most distal position to be recorded.