# Reverse Guided Bone Regeneration (R-GBR) Digital Workflow for Atrophic Jaws Rehabilitation
## 2 Materials and Methods  
Two male patients were referred for a fixed prosthetic rehabilitation of their edentulous areas. The general health condition of both subjects did not contraindicate oral surgical procedures. The clinical intra-oral exam of the first patient showed a left posterior mandible without premolars and molars, lost more than ten years before due to an untreated severe periodontal disease (Figure 1). Figure 1: The pre-operative clinical situation of the first patient. Vestibular (**A**) and occlusal (**B**) point of view. The dedentulous lacuna of the second patient corresponded to the upper right pre- molars, canine and incisor area, including the left first incisor, lost for trauma and dental caries and temporarily rehabilitated with a removable residual teeth-supported prosthetic device. The mandibular arch, lacking the first molars, did not present other dental diseases (Figure 2). After taking a cone-beam CT ([PERSON], Cefla, Imola, Italy), patients underwent scanning of the mouth with an intra-oral scanner (IOS) (iTero Element 2, Align Technology, CA, USA). The DICOM data relative to the bone status were coupled with the standard tessellation language (STL) files relative to the soft tissue characteristics. A virtual wax-up for the correct position of the dental crowns was performed according to the occlusal demands with the opposite dental arch; the crowns were subsequently superimposed to the bone and mucosa representation to identify the discrepancies between the prosthetic and anatomical issues. A simulation of the correct soft tissue final profile was set up, configuring the dimensions and shape of the papillae, and the implants were virtually positioned. The prediction of the bone reconstruction to provide the fixtures with sufficient support came after. The membrane was designed according to the hard tissue volume, position planned and the location of fixation screws. In the first case, it was planned to seat two standard implants in the second pre-molar and second molar location, sustaining a five-crown screw-retained fixed bridge. Implant placement in the canine position was considered after extracting the correspondent mobile tooth. This prosthetic solution entailed a vertical and horizontal bone regeneration of about 8 and 11 mm, respectively, in the molar zone and about 10 mm of thickness in correspondence to the second pre-molar location showing a knife-edge bone ridge (Figures 3 and 4). Figure 2: The pre-operative clinical situation of the second patient. Vestibular (**A**) and occlusal (**B**) point of view. The second case showed a vertical and horizontal bone deficit, with a residual bone ridge defining an extended fenestration. The digital wax-up for the correct crown position, the soft tissue ideal profile and the consequent implant locations guided the bone volume assessment and the relative mesh dimensions and shape (Figure 5). Figure 4: Virtual planning of the first case (phase 2). Ideal choice of the fixtures position and dimensions (**A**); simulation of the bone volume regeneration according to the final result prediction (**B**) and titanium membrane design (**C**,**D**). Figure 3: Virtual planning of the first case (phase 1). Bone defect after segmentation from pre-operative CBCT data (**A**); matching with the pre-operative soft tissue profile from the intra-oral scanning (**B**); superimposition of the digital wax-up and set up of the final ideal gingival architecture (**C**); virtual positioning of the fixtures (**D**). Three standard implants were planned to be seated in the second premolar, right lateral and left central incisors location, supporting a six-crown screw-retained fixed bridge with a required bone reconstruction of about 4 mm and 8 mm in height and width, respectively. The virtual mesh/membrane, saved in STL format, was 3D-printed using digital machine laser sintering (DMLS) without macropores and a few fissures in correspondence to its coronal portion. The same oral surgeon performed the surgical procedures in a dental office under local anesthesia.