Radiographic guide with radio-opaque markers
The double-scan technique with fiducial marker-based matching (i.e. gutta percha) can also be a possible source of error. If the matching of the radiopaque markers is incorrect, this introduces errors in positioning of the scanned image of the denture in relationship to the dental arch . Pettersson et al.  experienced that automatic superimposing procedure of gutta percha markers found with some software programs sometimes proceeded without notification of errors, often when motion artefacts were present. Thus checking the accuracy of the fusion procedure must be performed with every double-scan procedure to assure optimal interpretation of the digitised information and minimising errors.
4.2.2 Integrated Digital Workflow
Ritter et al.  assessed the accuracy of this newly developed digital workflow on 16 patients through 1792 measurements. All data pairs were matched successfully and mean deviations between CBCT and optical surface scanning data were between 0.03 (±0.33) and 0.14 (±0.18) mm. According to the results of this study, they concluded that registration of 3D surface data and CBCT data works reliably and is sufficiently accurate for implant planning. Therefore the digital integrated workflow using tooth-supported surgical templates, having a higher degree of accuracy when compared to the bone- and mucosa-supported surgical templates, may reduce the 3D discrepancy between the virtual plan and the real-life insertion of the implant [14, 22–24].
The recently introduced 3D software program (NobelClinician, Nobel Biocare, Kloten, Switzerland) automatically overlays the DICOM data from CT/CBCT of the patient with the STL data from the extra-oral (EOS) and/or intraoral (IOS) high-resolution optical surface scanning of the patient anatomy with or without tooth set-up, using a proprietary algorithm process (SmartFusionTM, Nobel Biocare). Therefore the patient’s dentition is scanned and integrated with the craniofacial (hard tissue) model to create a more accurate 3D model of the patient’s hard- and soft-tissue anatomy [25, 26].
Technically, the accuracy of this automatic matching workflow is 1 voxel size below (internal data, Nobel Biocare) manual segmentation workflow, based on pairing at least three points on the surface of the patient CT/CBCT anatomy with the equivalent ones of the patient anatomy achieved by the digital high-resolution optical scanning. An additional benefit to streamline the workflow comes from the use of an intraoral optical scanner to retrieve the surface scanning of the residual dental arch and soft-tissue architecture. The combination of intraoral scanners and cone-beam computerised tomography images, by mutual superimposing and use of planning software, provides an almost complete three-dimensional representation of soft and hard tissues.
4.2.3 The Smiling Scan
4.3 Surgical Workup
Once the planning is completed and approved by the clinician, the digital information is used to produce the surgical template with CAM rapid prototyping (milling or 3D printing) that will be tooth supported in the case of a dentate patient or mucosa supported in case of a fully edentulous patient. Based on three-dimensional imaging and a three-dimensional design, the computer-assisted surgical templates are commonly produced using photopolymerisation techniques after which the metal drill/guide sleeves are bonded by hand into the openings found in the surgical template.
Tooth-supported surgical template : This template rests on occlusal surface teeth in order to provide a rigid support to the template during the implant placement. In the case of a patient with terminal dentition, the strategic teeth kept to support the surgical template will be removed after the implants are placed.
Mucosa-supported surgical template : The surgical template is positioned on top of the mucosa. This is used in fully edentulous patients.
Bone-supported surgical template : The surgical template is placed on the bone after opening an extensive mucoperiosteal flap is elevated.
Special supported, surgical template: The surgical template is attached to (mini) implant or pin implants inserted before or during the actual implant surgery.
The bone-supported surgical guides showed the highest inaccuracy , while a high level of accuracy could be achieved when reference mini-implants were used to support the radiographic template during the computer tomography scan and the final surgical guide, leading to the immediate loading of a prefabricated implant-supported prostheses. However positioning mini-implants prior to the main surgical procedures results too cumbersome, complicated and not easily applicable in daily practice. Tooth-supported guides showed significantly smaller deviations compared with mucosal- and bone-supported guides: 0.87 ± 0.40 mm (coronal deviation), 0.95 ± 0.60 mm (apical deviation) and 2.94° (angular deviation) . However a wider variation of values was reported for sites with only a few teeth remaining. Larger deviation was also found for templates relying on unilateral anchorage (free-ending tooth-supported templates such as Kennedy Class I or II partially dentate patients) due to tilting and bending of the template . The use of a rigid material for fabricating the surgical template or the relining of the templates in order to obtain sufficient stiffness to prevent such tilting should be advocated.
4.3.1 Type of Guided Surgery (Fully Guided Placement, Semi-guided/Pilot Drilling and Freehand Implant Placement)
4.3.2 Minimally Invasive Surgical Technique: Flapless vs. with Flap
Surgeons, when operating using freehand technique, commonly elevate mucoperiosteal flaps to better visualise the recipient site. This may become unnecessary when fully guided implant placement is performed since the implant positions are predetermined and surgical guidance is provided intraoperatively by the surgical template. CAD-CAM methods may help clinicians to perform successful implant-based rehabilitation while avoiding elevation of large mucoperiosteal flaps or eliminating them altogether, resulting in less pain and discomfort for the patient [29–32]. Flapless or mini-flap surgical procedures preserve blood circulation in the soft tissues, enhancing the recovery of the soft-tissue architecture . Flapless approach may lead to a more favourable bone resorption pattern  but also enhanced papilla regrowth and hence the aesthetic outcome of single implants .
Avoidance of flap elevation seems to benefit peri-implant mucosal outcome, particularly in terms of maximum preservation of peri-implant papillae and reduced mucosal recession . Furthermore, a flapless approach avoids elevation of the mucoperiosteal flap and keeps the periosteum in contact with the bone and the supraperiosteal plexus intact, hence preserving the osteogenic potential and the blood supply to the underlying bone and/or implant. Flapless surgery in patients with newly grafted bone may also reduce the bone resorption associated with interruption of the periosteal blood supply . Bone denudation causes increased bone loss . Flapless computer-guided surgery may allow implant treatment in medically compromised patients who would be excluded due to the stress related to the length of the surgical intervention and the higher risk of intraoperative and postoperative complications . Another benefit from having implants placed using a fully guided approach is the potential for loading the implants immediately .
4.3.3 Drilling Protocol
Stereolithographic surgical templates are fabricated with hollow metallic cylinders to guide implant placement in the virtually planned position. A surgical occlusion index fabricated in silicone (Exabite II NDS, GC Europe, Haasrode-Leuven, Belgium) enables the accurate seating of the surgical template during the intervention.
The precise fit of the surgical template has to be visually and manually checked before surgery. The surgical occlusal index is helpful for the treatment of both edentulous and dentate patients, particularly when the remaining teeth are not adequately positioned in the residual dental arch to assist in mechanically stabilising the surgical guide. Once the surgical template is positioned the template is stabilised with three to four pre-planned anchor pins for the fully edentulous and at least one anchor pin for the dentate arch.
Implant sites are to be prepared according to the manufacturer’s guidelines. However, in the presence of poor-quality bone, or fresh extraction sockets, alteration of the guidelines may be necessary. The implant sites may have to be underprepared without screw tapping, in order to achieve the required primary mechanical stability especially when planning for the immediate provisionalisation.
Immediate loading of the implants is recommended when the insertion torque is greater than 40 Ncm or an implant stability reads higher than 70 ISQ value. If the insertion torque is less than 35 Ncm or ISQ value is less than 55, the authors prefer to leave the implants submerged for 3 months. The implant insertion torque has to be measured with the manual torque wrench after the surgical template is removed to avoid inaccurate measurements due to possibility of binding of the implant carriers (implant mounts) as they are passed through the template.
The neck of the implants should be placed flush with the bone, with exception of immediate post-extraction implants which are placed approximately 1.5 mm below the most coronal bony peak or in situations where the prosthetic requirements demand for deeper placement. Whenever possible implants are engaged bicortically.
4.4 Prosthetic Protocol
4.4.1 Interim Prostheses
A metal-reinforced, screw-retained, acrylic resin interim restoration without any cantilever for immediate implant loading can be conventionally pre-fabricated in the laboratory, using the stereolithographic surgical templates to generate the preoperative master casts after attaching the implant replicas to the surgical template, or milled from poly-methyl methacrylate blank with a CAD-CAM digital integrated workup (NobelClinician Software, NobelDesign software, Nobel Biocare AG).