Real-Time Dynamic Navigation System for the Precise Quad-Zygomatic Implant Placement in a Patient with a Severely Atrophic Maxilla

Summary

Here, we present a protocol to achieve precise quad-zygomatic implant placement in patients with severely atrophic maxilla using a real-time dynamic navigation system.

Abstract

Zygomatic implants (ZIs) are an ideal way to address cases of a severely atrophic edentulous maxilla and maxilla defects because they replace extensive bone augmentation and shorten the treatment cycle. However, there are risks associated with the placement of ZIs, such as penetration of the orbital cavity or infra-temporal fossa. Furthermore, the placement of multiple ZIs makes this surgery risky and more difficult to perform. Potential intraoperative complications are extremely dangerous and may cause irreparable losses. Here, we describe a practical, feasible, and reproducible protocol for a real-time surgical navigation system for precisely placing quad-zygomatic implants in the severely atrophic maxilla of patients with residual bone that does not meet the requirements of conventional implants. Hundreds of patients have received ZIs at our department based on this protocol. The clinical outcomes have been satisfactory, the intraoperative and postoperative complications have been low, and the accuracy indicated by infusion of the designed image and postoperative three-dimensional image has been high. This method should be utilized during the entire surgical procedure to ensure ZI placement safety.

Introduction

In the 1990s, Branemark introduced an alternative technique for bone grafting, the zygomatic implant (ZI), which has also been called the zygomaticus fixture¹. It was initially used for the treatment of trauma victims and patients with tumor resection where there was a defect in the maxillary structure. After maxillectomy, many patients retained anchorage only in the body of the zygoma or in the frontal extension of the zygomatic bone^1,2,3.

More recently, the ZI technique has been widely used in edentulous and dentate patients with a severely resorbed maxilla. The main indication for ZI implants is an atrophic maxilla. The use of four ZIs in an immediate loading system (fixed prosthodontics) is practical for surgeons with broad clinical experience, and it appears to represent an excellent alternative method to bone graft techniques^2,4. However, there are risks when placing ZIs, either by freehand or using a surgical template for guidance. Risks include inaccurate placement within the alveolus, penetration of the orbital cavity or infra-temporal fossa, and inappropriate placement within the zygomatic prominence⁵. The placement of multiple ZIs makes this surgery risky and difficult to perform. Hence, improving the precision of ZI placement is critical to its clinical use and safety.

The real-time surgical navigation system provides a different approach. It provides real-time and completely visualized trajectories through the analysis of preoperative and intraoperative computed tomography images. With the real-time navigation system, both precision and safety have been improved with sophisticated surgery and treatment^5,6. A practical, feasible, and reproducible protocol was developed using the real-time surgical navigation system to precisely place ZIs in the severely atrophic maxilla^5,7,8,9,10. With this protocol, we have treated hundreds of patients with satisfactory clinical outcomes^5,6,7,8,9,10. Here, we present the protocol with the detailed information on the treatment procedure.

Protocol

All of the clinical protocols were approved by the Medical Ethics Review Committee of the Shanghai Ninth People's Hospital, Shanghai Jiao Tong University, School of Medicine (SH9H-2020-T29-3).

1. Patient selection

1. The patient inclusion criteria were as follows (Table 1).
   1. Ensure that the patient presents a completely edentulous maxilla or partially edentulous maxilla with few extremely loose teeth (Figure 1A-G).
   2. Ensure that the patient has severe atrophy of the maxilla and insufficient bone volume for conventional implant placement in the anterior and/or posterior maxilla.
   3. Ensure that the patient is aged within 18-80 years and does not have systemic disease.
   4. Ensure that the patient has undergone cone beam computed tomography (CBCT) with analyzed DICOM data⁹.
      NOTE: The preoperative CBCT is obtained using a commercial instrument with the following scanning parameters: 7.1 mA, 96 kV, 0.4 mm voxel size, field of view of 23 cm (D) x 26 cm (H), and scan time of 18 s.
      1. Using a planning software, confirm that the maxillary posterior bone height ranges from 1 to 3 mm in the premolar and molar regions (Cawood and Howell Class VI)¹¹ (Table 2).
      2. Ensure that the measured anterior maxilla has an insufficient width to place regular implants of at least 3.75 mm diameter without additional bone grafting or insufficient height to allow the placement of implants shorter than 10 mm even with a titled approach^7,12,13 (Figure 1G1-G6).
         NOTE: The bone thickness for placing the apex of the ZI should at least be 5.75 mm¹⁴ (Fig. 2A - B) (Table 1).
2. The patient exclusion criteria were as follows (Table 1).
   1. Sufficient bone for conventional implant treatment.
   2. Narrow residual bone for which buccal bone graft is considered more appropriate.
   3. Untreated maxillary sinusitis or a maxillary sinus cyst.
   4. Local or systemic contraindications for oral surgery and implant placement.
   5. For edentulous patients, the maxillary residual bone volume does not meet the standard of classes V or VI of the Cawood Howell classification¹¹.

2. Mini-screw implantation

1. Administer local anesthesia to anesthetize the patient's maxilla, bilateral maxillary tuberosity, midline palatine suture, and both sides of the anterior nasal spine.
2. Implant seven to eight mini-screws (diameter: 1.0 mm, length: 9.0 mm, square cavity: 1.0 mm) in the remaining maxilla under local anesthesia to act as registration points before trajectories planning in the bilateral tubera maxillae, midline palatine suture, and nasospinale.
3. Select the bilateral maxillary tuberosity, midline palatine suture, and both sides of the anterior nasal spine as the bone anchorage areas for fiducials (Figure 3A-C).
   NOTE: To increase the navigation accuracy, the mini-screws should be evenly and dispersedly placed in the indicated area.

3. Preoperative CBCT scanning for planning

1. Perform CBCT using the following scanning parameters: 7.1 mA, 96 kV, 0.4 mm voxel size, field of view 23 cm (D) x 26 cm (H), and scan time of 18 s.

4. Setting registration points

1. Import CBCT data into the presurgical planning software through the DVD drive.
2. Mark all mini-screws as registration points for intraoperative imaging registration (Figure 3D).
   1. Mark the points on the central surface of the titanium mini-screws; this has to be set in a certain sequence.
      NOTE: After the registration points are set, ensure that the intraoral coronal entrance points of the ZI are at or near the alveolar crest with the reference to the zygomatic anatomy-guided approach proposed by Carlos Aparicio¹⁵. The anterior ZI should be at the level of the lateral incisor/canine region and the posterior ZI in the second premolar/the first molar region. The apex of the mesial implant should be placed above that of the distal implant. According to the previous research, the posterosuperior region and the center of the zygoma were the ideal places for the apex of the mesial implant and the apex of the distal implant¹⁶. The length could only be chosen in the range of 30.0 to 52.5 mm. Cylindroid trajectories can be planned as the drilling path (Figure 3E-K).

5. Planning for quad-ZI surgery

NOTE: This protocol requires the navigation system.

6. Surgical procedure

1. Lay the patient on the operating table in the supine position after general anesthesia.
   NOTE: It is best to situate the patient in this position before he or she is placed under general anesthesia. Otherwise, it is difficult to switch the position.
2. Fixed skull reference: Rigidly secure the skull reference base to the calvaria with a single self-tapping titanium screw of 1.5 x 6 mm. Secure the reference array to the base and assemble with three marked reflective spheres (Figure 4A-C). Place the navigation system camera in the 1 o'clock position to monitor the skull reference.
3. Registration: Specifically set the navigation system to the individual patient using a positioning probe with a tailor-made reflective ball to contact the outer surface of the mini-screws one after another. Then, display the available sagittal, coronal, axial, and 3D reconstruction images on the navigation screen (Figure 4D-E).
   NOTE: After the registration procedure, check every fiducial marker for precision. The result is acceptable if the error is mostly <1.0 mm. Otherwise, the registration procedure should be repeated until the error becomes acceptable.
4. Standardization: Standardize the drilling before using it in the surgery. Use a calibration block with holes of different diameters to standardize the drill: diameter 2.5 mm (round bur), 2.9 mm (pilot drill), and 3.5 mm (expending drill). The drills should be straightly attached to the bottom of the block by the surgeon, and then the assistant needs to adjust the interface into the calibration module. The equipment will produce a sound once the process is complete.
5. Gingiva flap opening: Determine the extent of the incision with the guidance of surgical navigation. Lift the full thickness flap to allow an adequate view for exposing the planned implant sites.
   NOTE: The range of the periosteal elevation should contain the alveolar crest, lateral wall of the maxilla, and the inferior border of the zygomatic bone.
6. Entrance point marking: First, find the entry point with the help of the navigation probe. Then, use the zygoma handpiece to fix the entry points. Next, find the entry of the zygomatic bone with the probe. Use the zygoma handpiece to prepare the entry point of the zygomatic bone (Figure 4F-G).
   NOTE: Ensure that both the operator and the assistants pay attention to the real surgical area to prevent errors made by the navigation system.
7. Initial preparation: Perform the drilling procedure ensuring that it follows the trajectories from the entry to the exit point as planned. Use the 2.9 mm drill first to prepare the path from the entry point, which was located using the navigation probe, to the entry of the zygomatic bone. Prepare the mesial one first, followed by the distal one.
   NOTE: Check each step with the navigation probe to confirm that the path is correct according to the designed preoperative plan (Figure 4H-I).
8. Widen the implant bed: Use the handpiece to extend the path from the entrance of the zygomatic bone to the terminal point designed at the surface of the zygomatic bone.
   NOTE: Ask the assistant to put a hand on the surface of the lateral orbital wall to ensure its safety. Ensure that the surgeon pays attention to the navigation screen rather than the surgical area.
9. Readings and measurements: Enlarge the trajectory with an expanding drill having a 3.5 mm diameter. Use the measuring bar and navigation probe to check the direction and position of the trajectory. Identify the length of the implant using the measuring tool (Figure 4B).
   NOTE: If the depth does not meet the requirement of the planned length, it is better to prepare it to the set depth.
10. Implantation: Implant the ZIs using a specific manual tool.
11. Suturing: After ZI implantation, use the navigation probe to verify correct positioning. Place multi-unit abutments and healing caps on the implants and suture the incision with polypropylene 4-0 suture. The hairline incision should also be sutured after the reference frame is removed.

7. Postoperative medication

1. Administer the patient a 5-day prescription of antibiotics, analgesics, and mouthwash solution (chlorhexidine 0.12%).

8. Immediate restoration

1. Perform immediate restoration in the patient within 72 h (Figure 5C-G).

9. Image integration

1. Obtain postoperative CBCT scanning images and a panoramic radiograph to evaluate the ZI position within 72 h after surgery (Figure 5A-B). Export the postoperative data to the planning software to superimpose the image of the post-operative CBCT and the preoperative surgical plan comparing the location of the entrance point, end point, and angular deviation (Figure 5H-I, Table 4).

Results

The enrolled patient was a 60-year-old woman without any systematic diseases (Figure 1A-D, F). After CBCT scanning, the alveolar ridge in the anterior maxilla was less than 2.9 mm, while the residual bone height in the posterior maxilla region was less than 2.4 mm (Figure 1E, G and Table 1). The width and thickness of the zygomatic bone were approximately 22.4-23.6 mm and 6.1-8.0 mm (

Discussion

Reconstructive rehabilitation of the atrophic maxilla using grafts is difficult because it requires good surgical technique, coverage of high-quality soft tissue over the graft, a significant amount of patient cooperation, and patients with health favorable for the finial restoration^17,18. The placement of dental implants for reconstruction in patients with maxillary atrophy represents a significant clinical challenge. The pattern of facial bone resorption is ass...

Materials

Name	Company	Catalog Number	Comments
Bistoury scalpel	Hufriedy Group	10-130-05
Branemark system zygoma TiUnite RP 35mm	Nobel Biocare AB	34724	TiUnite implant with overlength to place from the maxilla to the zygoma
Branemark system zygoma TiUnite RP 40mm	Nobel Biocare AB	34735	TiUnite implant with overlength to place from the maxilla to the zygoma
Branemark system zygoma TiUnite RP 42.5mm	Nobel Biocare AB	34736	TiUnite implant with overlength to place from the maxilla to the zygoma
Branemark system zygoma TiUnite RP 45mm	Nobel Biocare AB	34737	TiUnite implant with overlength to place from the maxilla to the zygoma
Branemark system zygoma TiUnite RP 47.5mm	Nobel Biocare AB	34738	TiUnite implant with overlength to place from the maxilla to the zygoma
Branemark system zygoma TiUnite RP 50mm	Nobel Biocare AB	34739	TiUnite implant with overlength to place from the maxilla to the zygoma
Branemark system zygoma TiUnite RP 52.5mm	Nobel Biocare AB	34740	TiUnite implant with overlength to place from the maxilla to the zygoma
CBCT	Planmeca Oy,Helsinki, Finland	Pro Max 3D Max
connection to handpiece	Nobel Biocare AB	29081	the accessories to connect the intrument
Drill guard	Nobel Biocare AB	29162	the accessories to protect the lips and soft tissue during the surgery
Drill guard short	Nobel Biocare AB	29162	the accessories to protect the lips and soft tissue during the surgery
Handpiece zygoma 20:1	Nobel Biocare AB	32615	the basic instrument for implant drill
Instrument adapter array size L	BRAINLAB AG	41801
Instrument adapter array size M	BRAINLAB AG	41798
Instrument calibration matrix	BRAINLAB AG	41874	a special tool for drill to calibration
I-plan automatic image fusion software STL data import/export for I-plan VectorVision2®, (I-plan CMF software)	BRAINLAB AG	inapplicability	the software for navigation surgery planning
Multi-unit abutment 3mm	Nobel Biocare AB	32330	the connection accessory between the implant and the titanium base
Multi-unit abutment 5mm	Nobel Biocare AB	32331	the connection accessory between the implant and the titanium base
Periosteal elevator	Hufriedy Group	PPR3/9A	the instrument for open flap surgery
Pilot drill	Nobel Biocare AB	32630	the drill for the surgery
Pilot drill short	Nobel Biocare AB	32632	the drill for the surgery measuring the depth of the implant holes
Pointer with blunt tip for cranial/ENT	BRAINLAB AG	53106
Reference headband star	BRAINLAB AG	41877
Round bur	Nobel Biocare AB	DIA 578-0	the drill for the surgery
Screwdriver manual	Nobel Biocare AB	29149
Skull reference array	BRAINLAB AG	52122	a special made metal reference for navigation camera to receive the signal
Skull reference base	BRAINLAB AG	52129
Suture vicryl 4-0	Johnson &Johnson, Ethicon	VCP310H
Temporary copping multi-unit titanium (with prosthetic screw)	Nobel Biocare AB	29046	the temporary titanium base to fix the teeth
Titanium mini-screw	CIBEI	MB105-2.0*9	the mini-screw for navigation registration
Twist drill	Nobel Biocare AB	32628	the drill for the surgery
Twist drill short	Nobel Biocare AB	32629	the drill for the surgery
Zygoma depth indicator angled	Nobel Biocare AB	29162
Zygoma depth indicator straight	Nobel Biocare AB	29162	the measurement scale for
Zygoma handle	Nobel Biocare AB	29162	the instrument for zygomatic implant placement