COMPUTER-GUIDED IMPLANT PLACEMENT ASSOCIATED WITH COMPUTER-AIDED BONE REGENERATION IN THE TREATMENT OF ATROPHIED PARTIALLY EDENTULOUS ALVEOLAR RIDGES: A PROSPECTIVE PROOF-OF-CONCEPT STUDY

Study background: Recent advances in 3D radiological techniques and virtual planning softwares allow the clinician to visualize simultaneously the anatomy of the patient and the prosthetic wax-up directly within the digital environment. This enables ideal planning of the correct position of dental implants considering at the same time anatomical structures and prosthetic demands. The virtual project is then transferred to the surgical site by means of stents realized on the basis of the virtual project. Implants are finally inserted with a computer-guided approach in the desired positions. So far, this technique has been safely used in anatomical situations presenting an adequate amount of bone so that bone augmentation procedures can be avoided and an adequate implant positioning can be achieved. Aim: The purpose of the present proof-of-concept study was to evaluate the effectiveness of computer-guided implant placement associated to computer-aided guided bone regeneration (GBR) in critical anatomical situations presenting less than ideal quality and quantity of supporting bone to receive dental implants in a prosthetically-driven position. Materials and methods: Healthy non-smoking patients seeking a fixed rehabilitation were enrolled if presenting partial edentulism characterized by atrophic alveolar bone in the posterior sectors of maxilla or mandible. Patients underwent conebeam computed tomography (CBCT) exam and impression of the edentulous space was scanned optically. Data of the two acquisitions were imported and matched within dedicated software. At this point, it was possible to plan the ideal position of the implants in a prosthetically-driven position according to a virtual wax-up. The missing bone was virtually augmented according to the position of the implants and the anatomy of the residual alveolar ridge. The project was transferred to the surgical environment by means of stereolithographic model fitted with the augmented bone and tooth-supported guide. Prior surgery, a dense-expanded-polytetrafluoroethylene (d-e-PTFE) membrane was trimmed and contoured based on the said model. Under local anesthesia on outpatient basis, a full thickness flap was raised and implants were inserted with a computer-aided fully-guided approach. Subsequently, the alveolar ridge was augmented by grafting autogenous bone particles harvested nearby the surgical site with a bone scraper and deproteinized bovine bone mineral (DBBM) granules in a 1:1 ratio. The graft was covered with previously shaped d-e-PTFE membrane fixed with osteosynthesis screws to the underlying bone. A first intention healing was accomplished with horizontal mattresses and single stitches. The duration of the surgery was registered in minutes. Patients were given a questionnaire reporting visual analogue scales (VASs) used to self-register postoperative pain, swelling, bleeding, and perception of the operation during the first post-operative week. Follow-up recalls were scheduled to clinically and radiographically evaluate the post-operative course. Post-operative CBCT scan was acquired to superimpose the position of the implant obtained during the surgical procedure with that planned in the virtual project. The aim was to evaluate the accuracy in terms of linear and angular deviations. To this end, a control group consisting of implants placed with a computer-aided fully-guided approach by means of mucosa-supported screw-retained surgical guides in fully edentulous patients served as reference point. After 6 months from the surgical procedure, the re-entry surgery was carried out to clinically evaluate the quality and quantity of augmented bone. After testing for normality assumption, parametric and non-parametric statistical tests were used to explore the study variables. The significance threshold was set at 0.05. Results: Overall, 11 patients were considered eligible and were consecutively enrolled and treated, of which 5 in the test group (2 males and 3 females), and 6 in the control group (5 males and 1 female). The mean age was 52.2 ± 6.41 years in the test group, and 60.17 ± 12.73 years in the control group (p = 0.238). The mean surgical duration was 92 minutes. No intra- and post-operative complications occurred during the entire study period. Only one patients exhibited a dehiscence of the lingual flap with d-e-PTFE membrane exposure. This was related to an erroneous management of the lingual flap during the surgery, a fact that was not attributable to the experimental procedure itself. Nevertheless, at the re-entry surgery all patients showed complete filling of the bone defect with no clinical and radiological signs of infection or resorption. The newly formed bone-like tissue appeared well vascularized and integrated within the recipient bone. In some cases, implants were completely covered by the regenerated hard tissue. No early losses were observed. In regards to patient-centered outcomes, pain scored exceptionally high with respect to the other variables. The peak was observed at 2 days post-operatively (mean VAS = 64.4 ± 5.17). Swelling peaked the third post-operative day (mean VAS = 56.4 ± 8.14), while the peak of bleeding was registered after 1 day from the surgical procedure (mean VAS = 16.2 ± 2.58). As expected, all variables decreased significantly from their respective peaks up to the seventh post-operative day (p < 0.05). The mean VAS score for the patients’ perception of the operation was 36 ± 8.63, with no significant correlation with the variables analyzed (p > 0.05). A total of 10 and 38 implants in the test and control group respectively were available for the accuracy assessment. No statistically significant differences could be found with respect to linear deviation at coronal and apical points and angular deviation of the long-axis among groups. Mean differences between the two groups were 0.04 ± 0.32 mm; 0.02 ± 0.35; and 0.27° ± 1.71° respectively (p > 0.05). Conclusions: Within the limitations of the present study, computer-guided implant placement and simultaneous computer-aided bone augmentation yielded encouraging results in terms of efficacy and accuracy. No intra- and post-operative complications were observed, therefore the procedure can be considered safe and predictable with respect to surgical and biological aspects at least on a short-term basis. On the other hand, patient-centered outcomes were below the expectations. Further studies are needed to evaluate survival, success, and complication rates of both implants and prostheses on a long-term basis.