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ePaper created 2017-01-25, 09:48:20 | version 1.38.0
23 1_2017 multicenter randomized controlled trials with sample size calculation and multivariate analysis. Implants placed into post-extraction sockets showed lower marginal bone remodeling than implants placed into healed sites did; thus, the null hypothesis that there is no difference be- tween the two protocols in terms of hard-tissue response has to be rejected. In the present study, one out of 160 implants failed over a period of five years, accounting for an overall implant CSR of 99.4%. The major clinical conclusion of this retrospective study is that immediate post-ex- traction placement of implants and immediate provisionalization may be considered an effec- tive and reliable treatment option for patients who would prefer to have a shortened overall treatment time and to be rehabilitated immedi- ately with the aid of computer-assisted tem- plate-guided surgery. Proper patient selection and well-trained operators are necessary to min- imize the risk of implant failure. Immediate im- plant placement and provisionalization in both post-extraction sockets and healed sites are technically demanding procedures, and the sur- gical and prosthetic skills required are superior to those necessary for conventional implant treat- ment. To the best of our knowledge at the time of writing this article, there were no other published studies that evaluated the use of a vari- able-thread tapered-body implant with internal conical connection, in-built platform shifting and a moderately rough oxidized surface in com- bination with computer-assisted template-guid- ed surgery to treat failing dentition in the maxil- la. For this reason, it is difficult to evaluate how the present results fit with other comparable studies. However, there is a randomized con- trolled trial that investigated the same implant design that may provide some comparable data.25 The marginal bone remodeling reported in the present study, measured from implant place- ment until the last follow-up examination, was -0.58 ± 0.98 mm. This value is slightly lower than the data reported in the literature for two-piece implants, for which after the initial bone loss during the first year post-placement, about 0.1– 0.2 mm of crestal bone loss was found at the annual follow-up.26, 27 Pozzi et al. recently pub- lished three-year results of a randomized con- trolled trial, reporting a marginal bone remodel- ing of 0.83 ± 0.27 mm around NobelActive implants placed into healed sites in the posterior mandible.25 One reason for these differences may be that surgeons operating freehand tend to elevate wider flaps to better visualize the area in which the implants are to be placed. With ded- icated template-guided implant placement, wid- Period (years) Surviving implants Failed implants Not followed CSR (%)† 0–1 160 0 0 100.0 1–2 160 0 0 100.0 2–3 160 1 11 99.4 3–4 148 0 48 99.4 4–5 100 0 79 99.4 5 21 – – 99.4 er flaps were in many cases considered unneces- sary, since the surgeons were able to rely on the surgical template.11 Another explanation that may account for the differences in the observed MBL changes is that, in some of the aforemen- tioned studies, all of the implants were placed into healed sites.11,25 In the present study, sta- tistical analysis showed a statistically significant difference (P = 0.026) in mean marginal bone remodeling at the last follow-up between im- plants placed into healed sites (-0.67 ± 0.97 mm) and those placed into post-extraction sites (0.42 ± 0.99 mm). These findings are in accordance with a recent systematic review and meta- anal- ysis on the alterations of the bone dimension after immediate implant placement into ex- traction sockets.28 In the present study, the diag- nostic protocol included the calibration proce- dure of the digital workflow for each patient, according to the manufacturer’s instructions. Scanning physical objects like the radiographic guide requires an optimized workflow, because the data are converted into 3-D models, which are used not only for diagnostic purposes but also for physical production. Since the data are digitized using X-ray technology and since mate- rial properties or densities are visualized through various kinds of gray value shades, the workflow is highly dependent on the gray values assigned to the scanned 3-D data from the DICOM files. More precisely, the workflow is dependent on the actual gray value that defines the radiographic guide’s borders. This gray value assignment to the DICOM files is unfortunately not standard- ized for CBCT scanners (almost every scanner assigns different gray values to different objects and materials), making reliable default values for each scanner model almost impossible. This ulti- mately has implications regarding the produced dimensions of the surgical template, as these di- mensions are defined by the gray value selection representing the borders of the scanned radio- graphic guide. In order to automatically detect and automatically apply the correct settings needed for the software to define the actual expert article _ chirurgia guidata Tab. 1_Life table analysis of all surviving implants.* * According to the last recorded patient follow-up. † Cumulative survival rate. 0–116000100.0 1–216000100.0 2–316011199.4 3–414804899.4 4–510007999.4 521 – – 99.4