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INTRODUCTION

Although osseo-integration of dental implants is predictable¹, thorough pre-operative planning is a prerequisite for a successful treatment outcome.²Anatomic limitations as well as prosthetic considerations encourage the surgeon to obtain a very precise positioning of the implants. Historically, standard radiographic imaging techniques (intra-oral and panoramic) were available for investigation of potential implant sites. Throughout the years, spiral tomography and computed tomography (CT) were often used as a diagnostic tool.³ These techniques provide a 2-dimensional cross section image of the desired implant location and enables a detailed bucco-lingual view of the dimensions of the jawbone. Nowadays, it is well known that 3-dimensional CT scan based pictures allow a more reliable treatment planning than when only 2-dimensional data are available.⁴ Transforming the CT scan images into a 3D virtual image can be achieved using computer software packages,⁵ allowing for a 3D viewing using Computer Aided Design (CAD) technology. For years, stereolithographic guided surgery seemed to be the golden standard in computer guided implant surgery. The technique has been well developed over the last years and several scientific reports have been published regarding accuracy, complications, survival and success⁶. Real-time navigation seems to be a valuable alternative to stereolithographic (static) guided surgery as it offers the clinician some advantages compared to the former technique. Using real-time (dynamic) navigation one can avoid the fabrication of a stereolithographic template resulting in a less expensive treatment. As navigation is considered as a dynamic guided surgery system, changes to the treatment planning (location and size of the implants, number of the implants, flap or flapless…) can be easily made intra-operatively.

CASE PRESENTATIONS

The first patient treated was a 59 year-old female consulting the dental office for replacement of two premolars in the maxilla, in locations 15 and 24 (Fig. 1, Fig. 2, Fig. 3). Patient was in good general condition and was a nonsmoker. Intraoral examination revealed numerous amalgam fillings and some metal-porcelain crowns (Fig. 4). Teeth 15 and 24 had to be extracted previously due to cariogenic process. Periodontal screening showed no signs of pathology. Treatment involved placement of 2 osseo-integrated implants in the edentulous regions of the maxilla.

The second patient was a 55 year-old male visiting the office to restore a recently extracted lateral incisor (Fig. 5, Fig. 6). He was a non-smoker, in good general health and not suffering from any systemic disease. Intra-oral examination showed several crowns in the maxilla and a residual root fragment in location 15 (Fig. 7, Fig. 8). Patient suffered from moderate periodontal breakdown. This periodontal condition has been present yet stable for several years.

For both of the patients, impressions of the dental arch were taken prior to implant installation using an irreversible hydrocolloid (Cavex CA37, fast set, Cavex Holland BV, Haarlem, The Netherlands) to fabricate a diagnostic cast (Fig. 9). This cast was used as a model for the molding of theNaviStent in order to have a perfect fit. The NaviStent serves as scanning template and is worn by the patient during the scanning procedure and the surgery. (Fig. 10).

Afterwards, the patient was sent to the CBCT and a scan was made with the NaviStent in place.

SURGICAL PROCEDURE

The surgery was performed under local-regional anaesthesia. Appropriate aseptic and sterile conditions prevented post-operative infections. During the operation, the NaviStent was placed over the remaining teeth (Fig. 11). The NaviStent was primarily fixated around the undercuts of the remaining teeth and additionally by application of a denture adhesive (prothese kleefcreme).

The osteotomies were prepared at maximum of 1500 rpm using the Navident navigation system to guide the drilling procedure in real-time by indicating the desired drilling pathway on the computer screen. Prior to the use of each new drill, a calibration process is performed (Fig. 12). No punching of the gingival tissues was performed prior to the preparation of the implant sites.

In the first patient, 2 Xpeed® Anyridge® implants (Megagen, Seoul, South-Korea) were installed. At locus 15; a 10 mm length and a 4 mm wide fixture was inserted whereas at locus 24 a 13 mm length and a 3,5 mm diameter wide implant was installed (Fig. 13, Fig. 14, Fig. 15).

In the second patient, a solitaire Xpeed® Anyridge® implant with a length of 10 mm and a diameter of 3,5 mm was placed at locus 22 (Fig. 16, Fig. 17). An Xpeed® Anyridge® implant consists of a nanolayer of calcium ions incorporated on the sandblasted, large-grit, acid-etched (SLA) implant surface. All the implants were inserted into the maxilla with a maximum insertion torque of 35 Ncm.

As the implant fixtures were also calibrated for use with the navigation system (Fig. 18), their exact position could also be tracked during insertion. This means that both implant preparation drilling and the implant placement process are tracked in real time. Depth of drilling and placement are guided by Navident using on screen visual representation and auditory cues to aid the clinician. Immediately after implantation, cover screws were placed onto the implants and hand torqued (Fig. 19, Fig. 20).

Postoperatively, patient received a prescription for antibiotics (amoxicilline 1000 mg, 2x/d, 4 days), for non-steroidal anti-inflammatory drugs (ibuprofen 600mg, 3x/d) and for a mouthwash (chlorhexidine 0,12%, 2x/d). After 1 week, a post-operative visit was scheduled. No signs of infection or inflammation were present as the healing went on uneventfully (Fig. 21, Fig. 22, Fig. 23).

CONCLUSIONS

In a one week postoperative follow up the patients reported no pain or swelling associated with the dental implant procedure. Further postoperative results are being tracked and reported as part of a qualitative study being done in cooperation with the University of Ghent. The potential of the Navident dynamic navigation system with regard to minimally invasive and accurate implant surgeries will be evaluated during this study.

Case

The following case report describes the treatment of a 65-year-old male with an one-year history of maxillary partial edentulism (Fig. 1). He was discontent with the stability of his prosthesis and expressed that through the unstable prosthesis situation he has lost social self-confidence. In the initial appointment he thus stresses his need for a “fixed solution”.

His medical history did not reveal any specific systemic disease or condition that contraindicates oral surgery. The patient’s soft tissues on the edentulous ridges were healthy and panoramic X-rays showed expanded sinuses at both sides and irregular alveolar ridges. The treatment plan, carried out for a maxillary screw-retained fixed prosthesis, included two implants at the pre-maxillary region and two tilted in the posterior maxilla to avoid a sinus lift surgery.

Stent placement

In order to acquire both anatomical and prosthetic information prior to the surgery, a scan prosthesis was manufactured by duplicating the maxillary denture (Fig. 2). It is important that the scan prosthesis has the same aesthetic and functional information as the complete denture or set-up. Thus, the scan prosthesis was checked for its fit, aesthetics and maxilla mandibular relation (Fig. 3). The scan prosthesis was then used together with a Navident Edentulous Kit for CBCT imaging.

The Navident edentulous protocol consists of a SDI (Small Diameter Implant of 2.2mm or 2.5mm diameter), which is inserted into the alveolar ridge of the arch to be operated, prior to the acquisition of the CT scan. This temporary SDI serves as a mount for the CT marker and for the Jaw Tag used for the registration of the CT scan to the patient and for tracking the patient’s jaw during surgery.

The SDI can be placed either in a vertical position or in a horizontal position in relation to the alveolar crest. A special plastic arm with a proprietary aluminium bracket is then used for the connection of the CT marker and Jaw Tag to the SDI. Two types of arms are available: one for a vertically placed and another for a horizontally placed SDI (Figs. 4a and b). In the presented case, the SDI has been placed vertically to achieve the required stability (Fig. 5).

The CT marker, containing the fiducial marker used for the registration of the CT scan to the patient, was attached to the V-type arm on the fix-plate at one end. At the other end, the assembly was placed over the SDI’s square head and secured to it using a setscrew which was embedded in the aluminium bracket, with this creating a complete “NaviStent” (Fig. 6).

The scan prosthesis was then modified to accommodate the aluminium bracket before it was placed over the maxillary edentulous ridge (Figs. 7 & 8). For accuracy purpose, it is imperative that the scan prosthesis is stable, while at the same time it should not interfere with the NaviStent.

CT scan

The following CBCT imaging protocol for Navident dynamic navigation was applied during CT imaging. Before the scanning procedures, both the modified scanning prosthesis and the NaviStent had been placed into the patient’s upper jaw (Figs. 9 & 10). A CT marker was then connected to the NaviStent. A scout view had been acquired prior to the actual scan to verify the presence of the CT marker in the CT scan. In order to allow for accurate registration, at least three corners of the fiducial marker must be present in the scan. In order to maintain a high level of accuracy during navigation, it is mandatory that the slice thickness must not exceed a maximum of 0.4mm. In this case, the slice thickness had been set to 0.3mm. Afterwards, the scan was exported in DICOM format, then imported into Navident.

Osteotomy planning

When the CT scan is imported into Navident, a proprietary algorithm detects the fiducial’s image in the scan, then registers it with a mathematical model of the fiducial that is stored in the computer memory. This enables Navident to map the Jaw Tag, which is the tag mounted onto the patient, to the CT image during navigation.

For this case, Ankylos dental implants had been selected. The implants with a diameter of 3.5mm and a length of 11mm were planned on the locations 15, 12, 22 and 25 using the Navident planning software (Fig. 11). The following parameters were considered when osteotomies were planned:

1. Alveolar ridges, though they had a sufficient bone height, were narrowing at the crestal 1/3. Without waiving or compromising the restorative information, the implant locations were planned to be deeper where at least 2mm of buccal plate thickness could be achieved.
2. Straight implants were placed at 12 and 22 and tilted ones at 15 and 25.
3. Angulated distal implants were planned 1mm mesially to the sinus wall.
4. The angle of distal abutments was planned to be 30 degrees to the occlusal plane to have the retaining screws access holes placed in the denture’s occlusal aspect since screw-retained abutments have 30-degree joints.
5. The plane of the implant collars was planned to be parallel to the occlusal plane.

Case Report

The patient was 57 year old healthy female that was referred to our clinic to replace the missing maxillary second premolar at the 2.5(13) site with a dental implant. The Navident workflow consists of four main sequential steps: stent fabrication, CT(computer tomography) scan with the stent and affixed CT marker in the patient’s mouth, digitally planning the implant surgery in the Navident software, and lastly completing the live guided implant surgery. One of the biggest advantages of the Navident system is that these four sequential steps can all be completed in one appointment provided the clinic has an available CBCT scanner.

The NaviStent functions as a retainer onto which the CT marker is affixed to while the patient undergoes her CBCT scan. The NaviStent is a custom single use retainer made of a thermoplastic material called Naviplast than can be heated in hot water and molded to the patient’s dentition. The stent was trimmed and the planned implant site was cut open to expose the ridge. The CT marker was then fixed to the stent by way of a thumb screw. The NaviStent with the attached CT Marker was placed into the patient’s mouth. The stent was checked for stability in the patient’s mouth. A CBCT scan was completed for the entire maxillary arch being sure to include the arm of the CT marker which contains the aluminum fiducial.

The CBCT scan was then imported into the Navident software. The Navident software automatically registers the fiducial and asks you to inspect the registration to ensure there is no malalignment. Our implant position is prosthetically determined, so our first step was to place a virtual crown at the 2.5 (13) site. The vertical height of bone from the ridge to the sinus floor was measured using the software measuring tool and found to be 7.4mm (Fig 2).

Our treatment plan involved placing a Straumann Bone Level Tapered SLActive Roxolid 4.1mm x 10mm implant as a single stage flapless approach with an internal sinus elevation. Taking advantage of the freedom of the Navident system, we were able to plan our surgery to place a Straumann dental implant and complete our internal sinus lift using the HIOSSEN CAS-KIT (Crestal Approach Sinus Kit). To control our drilling depth and use the live navigation to guide us to the sinus, a digital implant was placed in the ideal location with respect to the digital crown. This digital plan would guide us to the sinus floor for the sinus elevation and allow ideal implant placement.

Live Navigation Implant Surgery and Internal Sinus Elevation.

The patient was seated for the implant surgery. Local anesthetic was given. The single use JawTag was fixated to the NaviStent with the provided thumb screw. The tag adapter was mounted onto the surgical handpiece and fastened in place according to the company’s instructions. The single use DrillTag was attached to the tag adapter on the surgical handpiece. The NaviStent was placed into the patient’s mouth with the JawTag visible for the Navident camera to detect. Once the CT markers are visible by the camera, they become visible on the side panel on the monitor. The next step was to calibrate the drill axis by placing the handpiece head onto the calibration peg present on top of the JawTag. The handpiece was then rotated back and forth around the peg to register and calibrate the drill axis. The system then prompts us to calibrate the drill. The initial precision point drill was then placed onto the handpiece and calibrated by placing the drill tip into the dimple present at the center of the target on the JawTag (Fig 3). Once the drill tip was calibrated, it then became visible on the monitor against the CT image when it is placed into the surgical field. Our next step was to verify the drill tip position. This was done easily by placing the tip of the bur on a landmark in the jaw to verify accuracy of its positioning. In our case the tip of the drill was verified by placing it on the cusp tip of the neighboring tooth 2.4 (13). The drill was then brought to the surgical site (Fig 4) and the navigated drilling screen comes up which shows a Target view and cross sectional views of the CT images with the drill image visualized in its real-time position (Fig 5). The target and cross sectional views allow you to position the drill into the ideal digitally planned implant position based on the live view of the drill over the CT images.

The drilling process was started with a precision drill to punch a dimple into the bone and give us a soft tissue bleeding point. The bleeding point was then used as a marker to remove a 4mm diameter of crestal gingiva with a tissue punch. The Straumann pilot drill was then calibrated and verified on the handpiece. The 2.2 mm pilot drill was then used to drill at 800rpm to about 7mm into the osteotomy using the live navigation to guide us into the digitally planned position. The second 2.8mm drill in the Straumann Bone Level Tapered implant protocol was calibrated, verified and live navigated to the desired position at a depth of 7mm into the osteotomy.

The drills were now switched to the Hiossen CAS-KIT drills to allow removal of the cortical bone at the floor of the sinus without damaging the Schneiderian membrane. The CAS-Drill tip has an inverse conical shape that forms conical bone chip as it drills to allow it to safely elevate the sinus membrane without perforating it. The bone particles formed when drilling discharge upwards producing a membrane auto-lift function. The Hiossen CAS 3.3mm drill was used with an 8mm stopper as a back up to prevent us from forcefully pushing too deep into the sinus. The CAS drill was calibrated and verified and then live navigated to access the sinus membrane.

Once the membrane was exposed through the osteotomy, it was elevated using hydraulic pressure with the CAS-Kit Membrane Lifter and sterile saline. Cortical allograft chips were then gentled pushed into the void created from the membrane elevation. The jaw stent was removed and the implant was placed through the osteotomy with direct vision. The Straumann Bone Level Tapered 4.1mm x 10mm implant was placed with 50Ncm of primary stability. A healing abutment was then hand torqued in place (Fig 6). A post-operative peri-apical radiograph (Fig 7) was taken to assess the implant placement. The implant can also be live navigated into place, however it needs to be calibrated by touching the tip of the implant over the JawTag dimple, and due to the risk of contamination we chose to place it with direct vision. The company recommends placing a sterile piece of nylon over the dimple when calibrating the implant to keep the conditions of the implant sterile.

Due to the flapless live guided Navident protocol, we were able to release the patient, with no sutures required and minimal trauma to the site. The patient was prescribed anti-inflammatory analgesics and placed on a 7 day antiobiotic course. Her healing was uneventful with minimal discomfort to the area.

Conclusion

Computer guided placement of dental implants is significantly more accurate than free hand surgery. In areas of complex anatomy, computer guided navigational surgery is superior to conventional implant surgery when it comes to preventing iatrogenic injuries. This technology can contribute to considerable improvement in quality and accuracy of dental implant placement. The live real-time view of the exact position of the drill minimizes the potential risk of damage to critical anatomic structures. The optical tracking system seems to be more accurate and have more flexibility during surgery but does require more training to develop hand eye coordination for using the system. However once mastered, this new system can improve on accuracy of surgery, reduce surgeon anxiety, improve patient confidence, and work as a powerful marketing tool for your practice.