Tracking Tag Stabilization With a Small-Diameter Implant in an Edentulous Mandible to Assist Dynamically Navigated Surgery: A Case Report

Guided implant surgery can be used to assist clinicians placing dental implants with accuracy and precision.¹  This is particularly important when reconstructing anatomically challenging and difficult to access areas. Static guides provide an accurate and efficient technique for placement of dental implants but require the presence of dentition or reliable submucosal bony structure for stabilization for accuracy.²  Fibula free flap reconstructions typically lack these landmarks due to the presence of bulky skin paddles, making static guide anchorage difficult.³  In situations in which static guide use is not reliable, dynamic navigation offers an alternative approach to assist with the placement of implants with similar accuracy.⁴ 

Dynamic guided implant placement on the mandible requires the use of a radiographic fiducial marker to register and orient the cone-beam computerized tomography (CBCT) to the patient. Once the CBCT has been registered to the patient, the fiducial marker is replaced with the patient tag so the computer navigation system can optically track the patient. With the drill-tracking tag and patient tag, the computer can track the position and orientation of the patient and drill using motion-tracking optical assistance in real time during implant placement (Figure 1). Typically, these radiographic fiducial markers and patient-tracking tags are applied to teeth using clips or stents. In edentulous cases, there are several options to complete fiducial marking and incorporate a patient-tracking tag. One such option involves using bone screws as fiducial markers and a bone-anchored patient tag. The bone screws are used to register the mandible to the CBCT using a tracer device. The bone-anchored patient tag allows for tracking of the patient's mandible. The utilization of a bone-anchored patient tag requires a larger incision and reflection of tissue to secure compared with using the small-diameter implant (SDI) to secure the patient tag (Figure 2).

The goal of this report was to describe the use of a temporary dental implant to secure a radiographic fiducial marker and patient-tracking tag to an edentulous mandible for dynamically guided implant placement into a fibula microvascular free flap.

A 73-year-old man with an edentulous mandibular fibula free flap reconstruction secondary to treatment for a stage IVb squamous cell carcinoma of the left tonsil and subsequent osteoradionecrosis presented to the clinic desiring implant reconstruction. His medical history included hypothyroidism controlled with levothyroxine. His initial diagnosis of squamous cell carcinoma at age 60 was treated with resection, neck dissection, chemotherapy, and radiation therapy. Six years later, he was diagnosed with stage II (T2N0M0) squamous cell carcinoma of the tongue that was treated with a hemiglossectomy and radiation therapy with a total dose of 6000 cGY. Five years following his second diagnosis of cancer, he was referred to the Oral and Maxillofacial Surgery Department at Virginia Commonwealth University for suspected osteoradionecrosis. His clinical examination revealed exposed mandibular bone in the right quadrant approximating 1.5 × 0.5 cm and another area in the anterior mandible approximating 1.0 × 0.5 cm. Extraorally, he had a draining fistula in the submental region that was tender to palpation. The CBCT scan revealed osteolytic changes from the right angle to the contralateral body of the mandible with a fracture at the right parasymphyseal region (Figure 3a). The clinical and radiographic findings were consistent with a pathologic fracture (Figure 3b). He was taken to the operating room for resection of his mandibular osteoradionecrosis and reconstruction with a vascularized free fibula flap in 2018.

The treatment plan included placement of 5 Nobel Active NP 3.5- × 11.5-mm dental implants (Nobel Biocare, Kloten, Switzerland) for mandibular implant-retained fixed prosthesis. Verbal and written consents were obtained. Into the midline area, 2% lidocaine with 1:100 000 epinephrine was infiltrated. An SDI, specifically a 2.2- × 12-mm SDI O-Ball implant (OCO Biomedical, Albuquerque, NM, USA), was placed into the midline area of the reconstructed mandible. A radiographic fiducial marker (ClaroNav, Ontario, Canada) was secured to the SDI (Figure 2), and the patient was scanned to obtain a preoperative CBCT scan (i-CAT, Hatfield, Penn) with the radiographic fiducial marker in place.

Immediately after the CBCT, intravenous access was obtained, and the patient was moderately sedated and administered a dose of 900 mg of intravenous clindamycin. The data from the CBCT were loaded into the dynamic guidance system software (Navident–Claronav, Ontario, Canada), where virtual implant placement including appropriate implant size (width and length) and the implant position was planned virtually into the available space to provide support for a prosthesis (Figure 4). Implants were planned in a manner so as to avoid any screws and plates, avoid the lingual and facial plate of the mandible, and to be axially positioned as lingual as possible due to the class III skeletal relationship.

The spatial matching of the patient to the virtual on-screen representation (CBCT image) was registered by using the patients' preoperative CBCT with the radiographic fiducial marker previously secured to the SDI. On the dynamic guidance software, the outline of the radiographic fiducial marker was outlined, which provided the software with the position of the implant relative to the radiographic fiducial marker. At the beginning of surgery, the patient tag was attached to the SDI, which provided the software the real-time spatial position of the patient's mandible (Figure 5A). The patient tag secured on the SDI and the drill-tracking tag on the handpiece were tracked by the stereoscopic camera. Calibration of the handpiece (Biomet 3i LLC, Florida, United States) and each consecutive drill was performed according to the dynamic navigation workflow protocol (Navident - ClaroNav, Ontario, Canada) before use (Figure 5b). Registration and calibration allow for continuous tracking of the jaw during the navigated osteotomy preparation and implant placement and for maintaining the accuracy if the patient moves. The dynamic navigation device was placed in front of the operator with the camera above the operating field. Appropriate positioning of the patient, camera, and the computer had to be ensured to enable easy visualization of the computer screen that displayed real-time feedback of the drill in relation to the planned implant position (Figure 5c). The tracking system array from the camera to the patient and the drill-tracking tags during implant placement accurately located the position of the handpiece in relation to the patient and the scan providing real-time video feedback, which was used to guide the osteotomy and implant placement to the planned location and desired depth and angulation. The dynamic navigation systems allowed the surgeon to fully visualize the osteotomy and implant site on the computer screen during preparation.

Five Nobel Active NP 3.5- × 11.5-mm implants (Nobel Biocare) were placed with the patient under local anesthesia using minimal flap elevation to protect the vascular supply to the transplanted fibula. Every drill was calibrated according to the protocol before being used. Navigated placement was used for every drill in the preparation sequence to place all implants. Four of the five implants achieved good primary stability, with an insertion torque of 40 Ncm acquired (Figure 6b). Multi-unit abutments (Plus Conical Connection NP 3.5 mm, Nobel Biocare) were placed and covered with comfort caps. Following implant placement, a postoperative CBCT scan (i-CAT) was taken to verify the actual position of the implant (Figure 6c).

The preoperative CBCT with planned implant positions and the second CBCT taken after implant placement were superimposed. Accuracy was assessed by comparing the positions of the virtually planned to the actually placed implants and calculating the deviations (Figure 7). Pre- and postoperative CBCT scans were taken using the same settings, and superimpositions were performed aligning the reproducible anatomical landmarks on both CBCT scans. Superimposition and accuracy assessments were performed by the first author (D.T.). Four deviations between planned and placed implant positions were calculated digitally using EvaluNav software (ClaroNav, Ontario, Canada).

• Entry deviation (lateral 2D): horizontal distance between the planned and actual drilling point, lateral deviation of the cervical part of implant

• Apical vertical deviation (V): height deviation between the apex of the planned and placed implant position

• Apical 3D deviation: deviation between the apexes of the planned and placed implant taking into account entry, apical vertical, and angular deviation

• Angle deviation: deviation of the long axis of the placed implant according to the planned position

Five implants were placed with guidance by dynamic navigation. Insertion torque and primary stability were favorable for 4 implants, whereas 1 implant did not achieve integration and had to be removed at the postoperative appointment (Figure 8a). The authors believe primary stability was not achieved on the fifth implant due to overpreparation of the site. The fibula bone quality was dense and had a narrow window, and an implant would have too high of an insertion torque and, after preparing the site again, would no longer have primary stability. In future cases, tapping the site before implant placement could potentially alleviate this problem.

Four types of deviations between the planned (marked in yellow) and the actual implant position (marked in red) were assessed on superimposed CBCT scans (Figure 7). Placed implants aligned well with planned implant positions reflected in the following average deviation values: (1) the entry (2D) deviation was 1.3 mm, (2) the apex (3D) deviation was 1.8 mm, (3) the apex (V) deviation was 0.8 mm, and (4) the angular deviation was 3.1°. These values are similar, within 1 standard deviation, to previous studies examining the accuracy of dynamically guided implant placement⁵  (Table 1; Figure 7).

The patient was released to a prosthodontist 6 months after surgery for prosthetic rehabilitation of his mandibular dentition using conventional prosthodontic techniques (Figure 8). The final prosthesis consisting of maxillary complete denture and mandibular hybrid was fabricated using a ceramic-reinforced polyether ether ketone framework (Bredent, Chesterfield, UK). Placement of implants with dynamic navigation into the reconstructed mandible aimed to restore the patient's function and esthetics (Figure 9) and to protect the integrity of the reconstructed mandible by first virtually placing implants in suitable positions and accurately executing the virtual plan clinically by dynamic navigation.

Free flap and osseointegrated implants provide the means to predictably restore large complex defects and oral function following tumor resection.⁶  Virtual planning of implants allows the surgeon to avoid compromising the transplanted bone graft by virtually placing implants, avoid hitting the reconstruction plate and fixation hardware, and engage the reconstructed mandible bicortically to provide implant stability. Dynamically navigated implant placement also enabled minimally invasive incisions and flaps for placement of implants, minimizing the compromise of vascular supply to the transferred fibula. This technique is particularly helpful when executing a flapless technique through a bulky skin paddle, where blindly, and repeatedly, locating osteotomies for the insertion of drills and implants is often very difficult. Navigation provides very favorable execution of the virtual treatment plan with real-time visual feedback during the procedure.

Implant placement with the assistance of dynamic navigation is more accurate than free-hand placement and at least as accurate as static guided surgery.^1,7  This can offer an advantage, especially in demanding anatomical conditions.⁷  Some dynamic navigation systems are highly accurate,⁸  enabling exact realization of the preoperative plan with increased efficiency.⁹  Advantages offered by dynamic navigation systems include positional real-time feedback on the computer screen and accuracy control of the implant placement throughout the procedure. The use of dynamic navigation in this case included additional advantages of minimally invasive flap access for the implant osteotomy, protection of anatomic and reconstructed structures, and reliable guidance and access in a patient with limited mouth opening and challenging anatomy. Moreover, dynamic navigation encourages high accuracy and fewer complications, resulting in a more predictable prosthetic rehabilitation.^6,10 

A downside to a dynamic navigation system mostly involves the cost of the equipment and the operator's learning curve. The limitation of this publication is that it describes a single case, and the observations cannot be generalized. To further validate this novel technique and determine its accuracy and precision, a larger sample of cases is needed in future studies.