gUIDe TemplaTe IN saNDwICh OsTeOTOmy fOR pOsTeRIOR eDeNTUlOUs maNDIble

Background: The study was conducted to evaluate the accuracy of a novel design computergenerated surgical guide template (SGT) using rapid prototyping to guide the osteotomy cuts in sandwich osteotomy technique according to the pre-planned position to prevent injury to the inferior alveolar nerve. Methods: Eight partially edentulous patients showing atrophy in the posterior mandibular ridge were included. A SGT was designed according to each case using a 3D modeling software to guide the bony osteotomy cuts during the surgical procedure. Preoperative, immediate post-operative and after 4 months CBCT was done for all patients. Dental implants were installed at the grafted sites after 4 months. Results: Linear measurements were taken from the pre and post-operative CBCT. No statistically significant difference was found between the pre and post-operative measurements (P ≤ 0.05). Conclusion: The computer generated SGT provided enhanced visualization, better treatment planning, predictable results and a less technique sensitive procedure. Key wORDs: Atrophied posterior mandible, Sandwich osteotomy technique, Computergenerated surgical guide templates, Rapid prototyping (994) Mohamed Farid Shehab E.D. J. Vol. 62, No. 1 turn over in the mandible 2, 3. An implant-supported prosthesis could be the ideal option. There are many techniques used in attempt to overcome decreased alveolar ridge height and the danger of injuring the inferior alveolar nerve. They include, onlay bone grafts 4, interposition bone gafts 5, nerve repositioning 6, distraction osteogenesis 7, short implants 8 and the use of metallic mesh to form and retain a particulate graft for vertical ridge augmentation 9. Interpositional bone grafts “sandwich-technique” has been used for many years. Several studies showed successful outcomes in vertical height increase ranging from 4-8 mm and minimal graft resorpion after 1 year follow up 5, 10. Other studies found a median vertical gain of about 6-7 mm using the sandwich osteotomy technique 11. However, there are some limitations including limitation of augmentation height because of the soft tissue stretching and the precision required to save the mandibular nerve in the horizontal osteotomy 12, 13. Surgical techniques have been greatly enhanced by the use of computer-aided design/computer-aided manufacturing (CAD/CAM) technology proving to be efficient and highly accurate 14, 15. The computer generated surgical guide templates (SGT) have been used in many applications in the field of oral and maxillofacial surgery like orthognathic surgery 16, 17, jaw reconstruction 18, TMJ reconstruction and implant surgery 19. The percision of the rapid prototyped surgical guide templates in accurate fitting have been evaluated and proven to be dependable and reliable in achieving the predicted treatment plan 20 Schneider et al 2009 reviewed the accuracy of computer-guided templates and found that the survival rate of implants placed with computer-guided templates is comparable to conventionally placed implants ranging from 91% to 100% after follow up of 12–60 months 21. They allow the clinician to safely position the fixtures according to bone volume anatomical structures providing excellent tools for pre-operative implant planning, thus increasing the predictability of esthetic and functional treatment outcomes 22-24. Computer generated Surgical Guide Templates (SGT) are the product of Rapid Prototyping concept which is defined as a digital tool that grows parts on layer by layer basis without machining, molding or casting using additive process technique. There are numerous surgical applications for Rapid Prototyping as: Pre-operative visualization and planning, Pre-forming of fixation components, Manufacture of surgical guides and templates, Simulation of surgical procedure, Evaluation of prosthesis fit, Demonstration to patient and Intra-operative guidance Surgeon training25, 26. The current study was conducted to evaluate the accuracy of a novel design computer-assisted SGT using rapid prototyping techniques to guide the osteotomy cuts in the sandwich osteotomy technique according to the pre-planned position to aid in preventing injury to the inferior alveolar nerve. maTeRIals aND meThODs A total of eight consecutive patients (6 women and 2 men) with mean age of 44.75 years were selected from the Oral and Maxillofacial Surgery Department, Faculty of Oral and Dental Medicine, Cairo University. The study protocol was approved by the Research Ethics Committee in Cairo University, Cairo, Egypt prior to data collection and all participants signed an informed consent agreement. No funding or reimbursement was provided to the research or participants. The following selection criteria were fulfilled: partially edentulous patients with atrophic mandibles in the posterior region, behind the canine region. The starting alveolar bone height above the mandibular canal ranged between 5 and 7 mm and a transverse width of minimum 4 mm as measured CliniCal aCCuraCy of a Computer-generated surgiCal guide template (995) by Cone-Beam Computed Tomography (CBCT) (I-CAT® PreciseTM, manufacturer, I-CAT® technology located in Hatfield, PA). Patients did not have medical or psychological problems that could impede graft or implant success. preoperative surgical planning Pre-operative CBCT (P0) was performed for each patient, then the DICOM files were imported into a 3D modeling software (mimics 15.0, Materialise) where a Virtual surgical guide template (VSGT) was designed according to each case (Figure 1). The inferior margin of the template was located at least 2 mm below the ridge bone and approximately 1.5–2 mm above the mandibular canal. The inferior margin was designed to have sufficient thickness for the resting of piezo-surgery inserts and chisels. The vertical mesial margin was made 2 mm distal to the last tooth and the vertical distal margin was made based on the implant-graft treatment planning. The graft thickness was not less than 2 mm thick. The VSGT was then exported as STL files to 3D printing machine (InVision Si2, 3D Systems, Rock Hill, SC) using rapid prototyping techniques to fabricate the Final SGT (Figure 2).