A Pilot Study Showing Application of Palatal Bone Harvesting Under Dynamic Navigation Guidance in Oral Implantology

Summary

The protocol introduces a novel surgical method for palatal ring bone block harvesting using dynamic navigation guidance, addressing the challenge of insufficient bone volume in typical intraoral grafting areas and offering a viable solution for effective bone augmentation in implant dentistry.

Abstract

In cases of insufficient bone volume in the implant area, bone augmentation surgery is often required to ensure an adequate amount of bone around the implant. In autologous bone grafting procedures, some patients face insufficient bone volume at conventional intraoral bone harvesting sites. Due to the high difficulty associated with completing palatal osteotomies freehand, fewer palatal lateral osteotomies have been reported, and palatal bone blocks are not routinely used in bone augmentation procedures. With the development of digitally guided implant technology, palatal bone harvesting has become feasible. In this paper, we will present a method of obtaining a circumferential bone block of the palate for implant surgical application through dynamic navigation guidance. A total of three patients had undergone this procedure to obtain circumferential palatal bone blocks and completed bone augmentation surgery. The bone augmentation results in the implanted area have been favorable, and there has been some bone recovery at the harvesting site. This is a safe and effective way to obtain intraoral bone blocks.

Introduction

In recent years, with the advancement of implant technology, more and more patients with tooth loss are choosing dental implants for restorative treatment^1,2. One of the keys to implant success is adequate bone volume in the alveolar ridge. Patients often experience varying degrees of alveolar bone resorption after tooth extraction. According to previous studies, the alveolar ridge width decreases by 5-7 mm, and the alveolar ridge height decreases by 2-4.5 mm within 12 months after tooth extraction³. Therefore, bone augmentation is a very important part of oral implantology, which offers the possibility of performing implant surgery in patients with inadequate implant conditions.

Patients with different types of alveolar ridge defects are treated with different bone augmentation techniques, such as distraction osteogenesis⁴, Maxillary Sinus Floor Elevation⁵, Guided Bone Regeneration⁶, Onlay Bone Graft⁷, etc. Autogenous bone block grafting is a common surgical option for patients with substantial loss of alveolar ridge width and height for better support and osteogenesis. Patients with severe bone defects require larger autograft bone blocks. Petrungaro and other scholars have statistically shown that ascending ramus, anterior mandible, and tuberosity, among the intraoral bone retrieval sites, yielded about 5-10 mL, 5 mL, and 2 mL of bone volume, respectively. Extraoral bone retrieval sites, including the posterior iliac crest, anterior iliac crest, tibia, etc., can obtain 20-70 mL of bone volume, but the difficulty and risk of extra-oral bone block retrieval surgery is high⁸.

In some patients, the conventional intraoral bone extraction site is unable to provide the appropriate volume of bone. A 2013 imaging-related study by Qinghua et al. showed that the maxillary palate is a potential osteotomy area in the oral cavity⁹. The palatal bone is predominantly cortical, supplemented by cancellous bone, and bone fragments obtained from this site exhibit good supportive and osteogenic properties. The palate also has a rich blood supply, is covered by keratinized epithelium, and demonstrates a high healing capacity after osteotomy. Because the palate lies in a blind area of the surgical field, and the operating space is constrained by the patient's mouth opening degree, the operational space is adjacent to critical anatomical structures such as the nasal cavity, maxillary sinus, and multiple tooth roots. Consequently, the difficulty of performing a freehand palatal osteotomy is high, which is why palatal osteotomy is seldom reported, and palatal bone blocks have not been widely used in bone augmentation surgeries. The absence of a specific tool for palatal bone extraction further increases the difficulty of the operation.

With the advances in computer-assisted implant surgery (CAIS), maxillary palatal bone extraction became possible. Static guides are difficult to apply to maxillary palatal osteotomies due to resin and guide ring thickness requirements, which require an increased degree of patient mouth opening¹⁰. The emergence of the dynamic CAIS system overcomes the above difficulties. The dynamic CAIS system uses motion-tracking technology to track implant drilling instruments and the patient's jaw position. This achieves real-time tracking of the surgery and feedback on the software to guide the surgery in real time¹¹. Dynamic navigation makes maxillary palatal osteotomies possible by ensuring the accuracy of the osteotomies with low requirements for the patient's mouth opening and allowing for clear visualization of the operation.

Protocol

The study was approved by the Ethics Committee of West China Stomatological Hospital of Sichuan University (No. WCHSIRB-D-2021-209-R1), and all participants volunteered to participate in this clinical trial and signed an informed consent form. All patients were admitted to the Department of Implantology at West China Stomatological Hospital, Sichuan University, China, presenting with dental defects characterized by horizontal or vertical bone defects and expressing a desire for implants.

1. Patient information collection

1. Select patients based on the following inclusion criteria: age 18-65 years; good oral hygiene; no systemic disease or well-controlled systemic disease; patients presenting dental defects with horizontal or vertical bone defects and wishing to receive implants; patients were compliant, volunteered to participate in this clinical trial, and signed an informed consent form.
2. Exclude patients based on the following exclusion criteria:patients with a low amount of bone loss in the edentulous area who do not require block bone grafting; patients who do not have sufficient bone in the palatal bone extraction area for palatal bone extraction operation;acute inflammation of neighboring teeth, degree II looseness or greater, or one-walled sub-bone pockets; osteoporosis or history of taking or injecting bisphosphonates; those with poorly controlled systemic diseases; history of head and neck radiation therapy; female patients who are pregnant or breastfeeding are not candidates for implant surgery;those who are unable to cooperate with the follow-up examinations.
3. Collect DICOM data from Cone Beam Computed Tomography (CBCT) scans, imaging in 100 x 100 mm (WXH), with a scan time of 30 s, performed on patients wearing the registration device.
   1. Select the appropriate type of registration device according to the patient's intraoral condition (Figure 1). Secure the registration device to the patient's remaining maxillary teeth using polyether impression material in a position as close to the missing teeth as possible. Perform hand-assisted fixation for 5 min to allow the material to set thoroughly.
   2. Take off the registration device and remove the excess material with a scalpel. Reposition the registration device in the patient's mouth and check for firmness of repositioning. If resetting is not possible or firmness is poor, remove all polyether material and repeat step 1.3.1.
   3. Take CBCT after the registration device is placed on the patient and check its stability. Use cotton balls to elevate the patient's posterior teeth to prevent displacement of the registration device when the patient bites into it during filming. Obtain DICOM data of CBCT scans while the patient is wearing the registration device (Figure 2A).
4. Perform an oral scan of the patient to obtain data from the patient's intraoral model using an oral scanning instrument or alginate modeling (Figure 2B).

2. Designing the dynamic navigation software

1. Create a new patient. Click on Open Case. Import DICOM data and oral scan data into the software.
2. Based on the preliminary design of the patient's implant surgery, create the implant, crown, and abutment tooth position. Place additional implants at the 14^th and 24^th tooth positions to indicate the maxillary palatal bone extraction sites. If the patient's implant design involves the 14^th and 24^th positions, replace the implant, marking palatal bone extraction as necessary.
3. Click Start Design. Click on Cutter to remove parts of the CBCT model that interfere with the design by trimming it. Take care to preserve the high-density radiolucent points of the registration device and essential structures such as the maxillary palate and implant sites.
4. Click on Crown Design on stl to virtually align the missing teeth, paying attention to occlusion and gingival margin position in order to achieve restoration-oriented implant therapy.
5. Click Panorama Curve. Draw a panoramic line at the apex of the maxillary alveolar ridge. Click stl superimposition. The CBCT data is then fitted to the intraoral model data.
   NOTE: The software features AI (Artificial Intelligence) operation for fitting, but manual fitting should be used if AI fitting is unsatisfactory. Manual fitting involves aligning the CBCT model with the hard tissue of the intraoral model's teeth by selecting four identical points, which should be as spread out as possible.
6. Check the fitting results by observing whether the outer contour of the crown on CBCT coincides with the contour line of the intraoral model. If there is a deviation, repeat the manual fitting in step 2.5, replacing the tip as appropriate, until the fitting is successful.
7. Click Implant Design. Perform implant, bone harvesting and bone augmentation surgical designs.
   1. Place virtual implants in the edentulous area and position them on implants or bone block retaining nails as required. Click Fine-tune Implant to make fine adjustment (Figure 3).
   2. Click on positions 14 and 24 in the schematic at the top left of the page to create virtual implants. Ensure the diameter and length of the virtual implant matches the design of the bone extraction.
   3. Drag the virtual implant to the palate, place it and fine-tune it according to the bone retrieval design. Perform a detailed inspection after placement, taking care to avoid damaging adjacent important anatomical structures, and retain at least a 1.5 mm safety distance (Figure 4).
8. Click Set Marker Points. By clicking on the high-resistance radiographic spot in the 3D CBCT model, the software will automatically detect the registration device model for matching.
9. Save and export the project. Import it into the navigation software on the computer connected to the Position Sensor prior to surgery.

3. Dynamic navigation preparation

1. Installation of patient tracker and fixing device
   1. Select the appropriate fixing device according to the placement position, while avoiding the registration device and the surgical area (Figure 5).
   2. Connect the patient tracker to the fixing device using the connection device (Figure 6). Restore the registration device to the patient's mouth, place the fixing device in the patient's mouth, and adjust the movable joints of the connection device to the appropriate position before fixing them. Ensure that the patient tracker is not obscured by intraoperative maneuvers of the operator and that the receiver of the position sensor acquires the relevant information.
   3. After filling the fixing device outside the mouth with composite resin material, fix the patient tracker to the patient's remaining maxillary teeth through the fixing device using the composite resin material (Figure 7). Stabilize the intraoral fixation device for 3-5 min and not release it until the temporary crown material has completely solidified.
   4. Check the security of the patient tracker by lightly touching it. If it is loose, repeat step.
2. Intraoperative registration
   1. Click on the Patient Tracker icon to enter the calibration screen.
   2. Select the corresponding code in the software based on the actual Handpiece Tracker and Patient Tracker version being used for the current procedure.
   3. Adjust the position and angle of the Position Sensor and Handpiece Tracker so that the Position Sensor receives signals from the Handpiece Tracker and Patient Tracker in a stable manner. Then, click Registration.
3. Intraoperative calibration
   1. Click on the Calibration button at the lower right corner to enter the alignment screen.
   2. Confirm the tightness of the registration device after resetting. Replace the drill pin with a short ball drill for Dynamic Navigation. Use a short ball drill to tap the spherical pit of the registration device while the assistant clicks the Calibration button on the software. Repeat 5x-6x by replacing different spherical pits.
   3. Check the accuracy of calibration computed by AI; a tolerance within 0.3 mm is recommended. If the accuracy tolerance is too large, delete the data and repeat step 3.2. After confirming the accuracy, click Start Navigation.

4. Palatal bone extraction and alveolar ridge bone grafting under Dynamic Navigation guidance

NOTE: In the following operations, each time the operator changes the drilling needle, the assistant must select the appropriate type of drilling needle in the software. The operator is advised to verify this by placing the tip of the drill pin on the cusp of the crown of the neighboring tooth and observing whether the position shown on the navigation software corresponds to reality (Figure 8).

1. After local anesthesia is completed, use a pioneer drill under Dynamic Navigation guidance to locate the bone extraction site. Use a 2 mm diameter twist drill for guided cavity preparation. According to the preoperative design of the diameter of the bone extraction, use the corresponding guided osteotomy ring drill to extract the bone.
2. Take the soft tissue above the ringbone block and place it in saline for later use.
3. Prepare the central hole of the ringbone block according to the surgical design. For example, for patients requiring bone ring surgery have the center of the bone block reamed incrementally based on the size of the implant being used.
4. Carefully remove the ringbone block using a minimally invasive dental elevator. Place the ringbone block in situ on the palate or in saline for later use (Figure 9).
5. Complete the bone grafting procedure according to the surgical design (Figure 10).

5. Treatment of palatal wounds

1. Place silver-containing gelatin sponges in the holes of the palatal fossa to assist in hemostasis. Use surgical sutures (Monofilament polypropylene suture 5-0 ) to secure the soft tissue to the palatal incision.
2. Apply compression with a gauze ball to stop bleeding. Take an alginate impression as soon as possible after the operation and make a pressure-membrane retainer-type palatal shield for the patient on the same day.
3. Instruct patients to perform 24 h postoperative wear and only remove the palatal guard for cleaning after each meal. Palate guards should be worn for 30 days.
4. After surgery, perform a maxillary CBCT scan. Follow-up appointments are made 1 week, 2 weeks, and 1 month after surgery. Remove stitches 2 weeks after surgery.
5. Postoperatively, instruct patients to take amoxicillin capsules (0.25 g, 3x a day) for 7 days. If allergic to penicillin, give azithromycin (0.25 g, 1x a day), and diclofenac sodium extended-release capsules (Intaquan 0.1 g, 2x a day) to relieve postoperative pain as necessary. Additionally, ask patients to use 0.12% cotrimoxazole rinse solutions for gargles (10 mL, 2x- 3x a day) for 1 month postoperatively. Remove sutures 2 weeks after the operation and conduct oral hygiene counseling.

Results

Between May 2021 and May 2022, three patients were included in the West China Hospital of Stomatology at Sichuan University to complete palatal osteotomies. Obtained ring bone blocks of palatal origin were used for autologous bone ring grafting and implanted during simultaneous implant surgery. All patients received 3.3 mm Straumann implants. All patients successfully integrated the grafted bone block, the implant osseointegration was well established, the restorations were good, and the patients were satisfied with thei...

Discussion

Block bone grafting is commonly used clinically to enhance bone volume in areas with bone defects. Grafted bone blocks can be categorized into three types based on their source: allogeneic, xenogeneic, and autogenous bone blocks. Allogeneic bone blocks are easier to obtain and relatively inexpensive, but their effectiveness in vertical bone augmentation is limited¹². Allogeneic bone can yield better osteogenic results but is more costly and carries risks such as rejection reactions and ethical con...

Materials

Name	Company	Catalog Number	Comments
3D Bone Graft Set	Zepf	47.500.31
3-matic software	Materialise	13
3Shape software	3Shape	1.7.27.6
Bio-Gide	Geistlich
Bio-Oss	Geistlich
Carestream 360 oral scanner	OneX	FN-11
CBCT scanner Morita 3D Accuitom	Morita	1620
Dcarer dynamic navigation	Dcarer
Dental implant dynamic navigation sys-tem software	Dcarer	3.0.7.2432
Dental tines	Zepf	17.008.01
Drufomat scan	DREVE	DV3300
GraphPad Prism 9	GraphPad	9
Mimics software	Materialise	21
PROLENE Monofilament polypropylene suture 5-0	Johnson & Johnson	W8310
Straumann Dental Implant System	Straumann	021.3312
Straumann Surgical Toolbox	Straumann	040.165
Temporary crown and bridge material automix system	Coltene	170152-202
Thermo-forming foils and plates	DREVE	20172636510