Rehabilitation of fully edentulous patients with implant-supported fixed or removable restorations is regarded as the optimal treatment for fulfilling the patients' functional and aesthetic requirements^1,2). The introduction of cone beam computed tomography (CBCT) and 3D imaging instruments has substantially facilitated implant treatment planning. These tools facilitate the virtual planning of 3D implant positions and the fabrication of a computer-based surgical guide³⁾. Computer-guided surgery should be considered for patients requiring implant placement in cases of complete or partial edentulism to optimize functional and aesthetic outcomes with a higher accuracy⁴⁾.

Computer-assisted implant surgery typically involves the fabrication of a radiopaque scan appliance⁵⁾ or scan appliance with added radiopaque markers⁶⁾. Then, a double scan protocol is employed for prosthetic driven planning of edentulous patients. First, the patient is scanned while wearing the scan appliance using CBCT, and the scan appliance itself is scanned using CBCT. Then, Digital Imaging and Communications in Medicine (DICOM) files are imported and registered on implant planning software to facilitate the fabrication of the surgical guide^4-6). This conventional technique is widely used and has been demonstrated to be effective if the existing denture is properly aligned with the mucosa and corresponds to the optimal future tooth position⁶⁾. However, Scan appliance fabrication makes the superimposition more complex and may introduce errors through CBCT artifacts which make accurate image interpretation problematic^5,7).

The introduction of intraoral scanners has revolutionized the digital dentistry. They provide more convenient treatment plans for the patient and the clinician with high accuracy and less time⁸⁾. Despite the challenges that may present around the direct digital scanning of edentulous arch, their yielded results recently are comparable to the conventional impression^9,10).

In the presented case here, surgical guide for implant placement in totally edentulous maxilla was fabricated without the need for scan appliance or auxiliary tools. In addition, full digital workflow was employed for prosthetic driven implant placement.

A 58-year-old woman presented with completely edentulous maxilla. The patient was seeking a minimally invasive surgical procedure. So that, the treatment plan was to restore the maxillary arch with implant-supported fixed complete denture by using computer-guided flapless surgery.

The patient underwent a single CBCT scan procedure using cone beam computed tomography (CBCT) (Plan-meca promax; Palnmeca, Helsinki, Finland). The scan was performed with the patient’s edentulous upper arch with no appliances. This scan was performed after placing a suitable sized cheek retractor and making sure that the soft tissue was displaced away from the ridge as possible. The patient was then instructed to bite firmly on a pair of cotton rolls placed between the gingiva of the upper arch and the opposing arch. The volume of interest was centralized in the CBCT scanner. Careful thresholding was performed according to the grey scale value of reconstruction of the soft tissue which defined the transition between the target material and the surrounding background (Fig. 1).

Figure 1. Soft tissue filter ranging to obtain an optimum 3D reconstruction approximating the dimensions of the maxillary ridge.

Another scan was performed for the edentulous maxillary ridge including the palatal area and the opposing mandibular arch using an intraoral scanner (Trios 3; 3shape, Copenhagen, Denmark) (Fig. 2). Registration between the CBCT scan and the intraoral scan of the patient maxillary edentulous arch was made, first by point-to-po-int registration followed by automatic voxel-based surface registration by the software (Real guide ver. 5; 3DIEMME, Como, Italy). Clear landmarks were selected such as the frenum, midline area or any clear landmark in the soft tissue (Fig. 3).

Figure 2. Intraoral scan of the edentulous maxillary ridge.

Figure 3. (A, B) Digital waxing up

A trial denture base was designed on CAD software (3shape dental systems; 3shape, Copenhagen, Denmark) and fitted in the patient mouse. Then, a wax rim was added over it with some metal markers on the facial side of the wax rim for easier scanning and registration. Inter-maxillary relation was then recorded in centric relation. The bite blocks were scanned while the patient is occluding in the centric relation. After then, a full scan of the bite block in the patient mouth was obtained by using the intra-oral scanner. The two scans of the bite block were superimposed over each other by using the added metal markers. Then, both scans were superimposed over the scan of the edentulous maxillary arch.

Digital smile design was carried out with the DSD software (NemoSmile Design 3D; Nemotec, Madrid Spain) (Fig. 4A, B). Then, a trial teeth setting is performed to fabricate an esthetic prototype. The esthetic prototype was fitted in the patient mouth to take the patient approval (Fig. 5). Occlusal adjustments were then performed by using (T-Scan; Tekscan, Norwood, MA). After fitting of the prototype, it was fully scanned by using intraoral scanner, and superimposed over the scan of the edentulous arch. Then, the scan of the prototype was imported relevant to the registration position of the intraoral scan of the edentulous maxilla on the implant planning software (Fig. 6).

Figure 4. Point-to-point registration between the CBCT scan and the intraoral optical scan of the edentulous maxillary ridge.

Figure 5. The fitted protype was imported to the new registration position of the optical scan of the edentulous maxilla in the CBCT to finalize the prosthetic driven implant planning.

Figure 6. Intraoral scan of the 3D printed prototype.

Six implants were planned to be placed in the positions of maxillary right central incisor, canine, and second premolar, and maxillary left central incisor, canine, and second premolar as well as determining the fixation pins position and direction. Finally, the guide was 3D printed (Form2; Formlabs, Somervillr, MA), cured (Form Cure; Formlabs, Somervillr, MA and finished for surgery.

Implant surgery was performed using Ritter implant system (Ritter implants; Ritter, Biberach, Germany). The surgical guide was inserted in the patient’s mouth and fixed using fixation pins followed by implant osteotomy and implant insertion through the guide. Implant drilling and insertion were then performed using the implant guide and cover screws were then attached to all implants.

An immediate post-operative CBCT was performed after surgery and implant insertion. The postoperative CBCT with post-operative implants position was superimposed to the preoperative CBCT of the patient with the preplanned implants position using special software (Ondemand3d in2guide ver. 1.0; Cybermed, Daejeon, South Korea). Both the preoperative and postoperative implants were marked on the software. Automatic calculation was then performed by the software to record the deviation of the inserted implants from the preplanned implants in the form of 3D angles, linear coronal deviations and linear apical deviations. The outcomes indicated that the mean angular deviation was 4.46°±2.49. The mean coronal and apical deviations were 1.97±0.48 mm and 2.54±0.92 respectively.

In this reported scan protocol, the eradication of the fabrication of the scan apparatus has several advantages. The CBCT can be performed very early in the treatment plan, allowing the clinician to assess the bone volume and vital structures prior to beginning the prosthetic planning process. Our case report demonstrates the possibility of superimposing the prosthetic plan on the edentulous ridge in the final treatment plan. This preliminary screening is beneficial in a variety of clinical scenarios. The lack of bone volume may necessitate extensive grafting procedures, which may not be suitable for some patients. If the implant procedure is deemed unsuitable for the patient, the CBCT scan performed during the initial visit may save the patient and clinician time.

Mucosa is always presented with wet shiny surface, devoid of enough anatomical landmarks. This topography compromises the stitching process and thus complicates the direct scanning¹¹⁾. However, the improvement in the artificial intelligence of scanners’ software allows the direct digital impression of the edentulous arch. Recent studies showed accuracy outcomes comparable with the conventional impression especially in cases of well-developed ridge and enough attached mucosa^9,10). Additionally, to increase the registration accuracy between the CBCT and the optical scans, reliable anatomical landmarks could be used such as incisive papilla or any prominent landmarks on the maxillary ridge¹²⁾.

Despite a high degree of registration accuracy between the optical scan of the edentulous ridge and the CBCT scan in the presented case, this technique resulted in relatively higher implant deviation values when compared with literature. Carosi et al in their systematic review have reported implant linear deviation values of 1.23 mm±0.49 mm at shoulder, and 1.46 mm±0.54 at apex¹³⁾. The implant angular deviation in their review was 3.42º±1.13º. These difference in deviation values can be attributed to the mucosa's compressibility. The guide mobility due to tissue compression has been previously reported as inherent error in the mucosa-supported surgical guide^14,15). However, this intrinsic error may be increased in the presented case because the CBCT and optical imaging of the ridge were performed on at-rest tissues. In contrast, the surgical guide was seated on the ridge with compression. This difference may attribute to slight changes in the implant position or angulation.

Another limitation that should be in consideration is the necessity to well-developed ridge with prominent landmarks such as the incisive papilla or the rugae area. These anatomical features facilitate the registration process. In case of flat or underdeveloped maxillae, it may be unsuitable to use this technique. In the same context, the application of this registration protocol in edentulous mandibular arch may be problematic.

While the traditional scan appliance is still the gold standard for creating surgical guides, there are alternative methods that could be used to get around the problems with radiopaque markers. Soft tissue-based registration and total elimination of the scan appliance can be integrated into prosthetic-driven implant planning, making the process simpler overall. however, this method should be considered cautiously when creating computer-assis-ted surgical guides, as it is linked to relatively higher deviation values.

We hereby state that there is no potential conflict of interest.