Clinical and radiographic assessments

The surgical guides fitted well and facilitated implant placement. All implants were placed in the native bone. No dehiscences of the implant surface occurred.

Post-operative orthopantomograms (OPT) of patients 1 and 2 are shown in Figs. 6 and 7. In patient 1, six implants were placed (NobelParallel Conical Connection implants, Nobel Biocare Holding AG, Zürich-Flughafen, Switzerland; Length 8.5 mm; diameter 3.25 mm). In patient 2, one implant (Straumann Standard Plus, Institut Straumann AG, Basel, Switzerland; Length 4.0 mm; diameter 4.1 mm) was placed at region 35. For patient 2, after osseointegration, the temporary prosthetic construction with a bracket to erupt the 34 was placed. Eruption of the 34 was already seen after 3 months of orthodontic treatment (Figs. 7 and 8). Figure 9 shows the prosthodontic end result of patient 1.

Assessment of accuracy of implant placement

To assess the accuracy of the implant placement, post-operative CBCTs were made of both patients. 3D models of the postoperative result were obtained and superimposed on the data of the implant planning using a surface based alignment method (iterative closest point algorithm) and the same threshold value as used for the pre-operative scans. To deal with the scattering on the post-operative CBCT images in the implant regions, all implants were virtually matched with cylindrical shapes, positioned on the 2D CT data. These cylinders had the same dimensions as the implants and thus adequately represented the implants. The implant placement accuracy was calculated by comparing the pre- and post-implant placement coordinates of the entry point (shoulder), apex (tip) and angular deviation of the implants. Table 1 shows the accuracy data as Euclidian distances (ED) in millimetres (mm) of the entry point (shoulder) and apex (tip) of the implants as well as the degree of angular deviation of all implants (n = 7). Mean shoulder deviation was 1.41 mm (SD 0.55); mean apical deviation, 1.20 mm (SD 0.54); and mean angular deviation, 5.27° (SD 2.51). Figure 10 shows the actual differences in the planned and actual location of the implants of patient 1.