Three-dimensional positional accuracy of intraoral and laboratory implant scan bodies

Statement of problem: In the implant digital workflow, scan bodies provide the 3D position of digital implants in the virtual dental arch. However, limited evidence is available on scan body accuracy, selection, and usage.

Purpose: The purpose of this in vitro study was to evaluate the 3D positional accuracy of 4 intraoral and 6 laboratory scan body systems to the implants and laboratory replicas of an implant system under various torque magnitudes.

Material and methods: Ten test groups comprising 4 intraoral (I): Medentika L-Series (MS), Straumann CARES Mono (SM), Core 3D (CO), Straumann RC (SS); and 6 laboratory (L): Nobel Procera Pos Locator (NP), Sirona InPost (SR), Amann Girrbach (AG), Straumann CARES Mono (SM), Core 3D (CO), Straumann RC (SS) scan bodies were derived from 7 scan body systems. Of these, 3 systems (SM, CO, SS) are used for both intraoral and laboratory applications. The scan bodies were tested on Straumann Bone Level Regular CrossFit implants or laboratory replicas. Eight test groups allowed for the variation of torque application (5, 10, and 15 Ncm), while 2 test groups (NP, SR) were hand positioned only. Prefabricated metal abutments (ME) for both implants and laboratory replicas served as controls. A coordinate measuring machine measured four 3D positional accuracy variables: vertical linear distortion (d_z), 2D tolerance displacement (d_r), global linear distortion (d_R), and scan body height discrepancy (ΔH) (n=10). The data were analyzed with 2-way analysis of variance tests and post hoc analysis with Tukey tests (α=.05).

Results: For both intraoral and laboratory test groups, 2-way ANOVA found that the system had a significant effect on all distortion variables (P<.001), while torque magnitude had a significant effect only on d_z and ΔH (P<.001). Overall, mean d_z ranged from 5 ±12 μm for L-AG at 15 Ncm to 23 ±14 μm for L-AG at 5 Ncm. Mean d_r ranged from 5 ±4 μm for I-SM at 15 Ncm to 73 ±41 μm for L-SS at 10 Ncm, and mean d_R ranged from 11 ±6 μm for I-SM at 10 Ncm to 74 ±41 μm for L-SS at 10 Ncm. Mean ΔH ranged from -5 ±10 μm for I-SM at 15 Ncm to 23 ±14 μm for L-AG at 5 Ncm. Among intraoral test groups, for d_z and ΔH, all the test groups except for I-SM at 15 Ncm and I-MS at 10 and 15 Ncm were significantly more positive than the control (P<.001). For d_r, I-SS at 5, 10, and 15 Ncm was significantly different from the control (P<.001). For d_R, only I-SS at 5 Ncm was significantly different from the control (P<.001). Among laboratory test groups, for d_z and ΔH, L-AG at 5 Ncm and L-CO at 15 Ncm were significantly more positive than the control (P<.001). For d_r, L-SS at 10 and 15 Ncm were significantly different from the control (P<.001). For d_R, only L-SS at 10 Ncm was significantly different from the control (P<.001). Intraoral and laboratory systems show comparable 3D positional accuracy.

Conclusions: Overall, I-SS and L-SS were the least accurate. The system tested had a significant effect on 3D positional accuracy, while torque magnitude had no consistent effect across all systems.