Dynamic Navigation for Dental Implant Placement

To increase the accuracy of dental implant placement and reduce the complications, a range of navigation techniques based on imaging studies have been developed. Preoperative imaging and special 3D implant planning software can be used to plan the exact position of the dental implant^1,2.

The aim of implant surgery navigation is to accomplish a more anatomically precise placement of the dental implant to achieve the most ideal position, to reduce the risk of possible iatrogenic complications (nerve, vascular, bone, and sinus injuries). The navigated surgery decreases the invasiveness of the intervention (flapless surgery), which can lead to fewer complaints and faster recovery. The accurate implant placement is based on prior prosthetic planning (it is possible to perform the operation on the basis of a preoperative tooth installation) and the optimal implant positioning can help avoid bone grafting.

Nowadays, there are two types of computer-assisted implant (CAI) surgical placement navigation systems-static and dynamic navigation systems. Static navigation is a controlled implant placement method using a preplanned and prefabricated surgical template. Dynamic navigation is a preplanned computer-guided implant surgical placement method without a surgical template using optical control. The control procedure uses point cloud-based image registration to merge the virtual images with the real environment by applying 3D image overlay³.

DCAI systems make possible real-time, objectified instrument control within a GPS-like framework. Typically, they use optical tracking to detect and track the position of (optical) reference markers placed over the patient and the surgical instruments, and provide continuous visual feedback on the implant surgical placement process^1,2.

The movement and position of the surgical instrument during surgery can be monitored live on a three-dimensional image on a monitor. During the procedure, the camera system allows continuous monitoring and comparison of the position of the patient's jawbone and the position of the surgical instrument.

There are two types of dynamic navigation systems: one is the passive system, in which case the registration devices (reference bases) reflect light emitted from the light source back to the stereo cameras; the other is the active system, where the registration devices emit light which is followed by stereo cameras^4,5.

The next level of dynamic navigation systems uses servo motors to guide the surgeon's hand with tactile stimuli so that the device with robotic arms can determine the surgeon's movements or even replace them completely in the distant future^4,5,6,7.

Informed consent was obtained from every patient before surgery. After the interventions anonymized retrospective data was used in this study.

1. Steps in the traditional workflow of dynamic navigation systems using labeled clip calibration method (only for use on jawbone with teeth):

1. Attach a radiopaque fixation clip to the teeth of the jawbone where the treatment is to be performed (maxilla/mandible) using a thermoplastic material.
2. Make a CBCT examination of the patient with a labeled clip in the mouth (CBCT, FOV 8 cm x 11 cm, 12 mA, 95 kV).
3. Plan the position of the implant according to the prosthetic architecture with the appropriate software.
4. Calibrate the device (each step can be activated on display with the Play symbol).
   1. Register the handpiece.
      1. Calibrate handpiece chuck.
      2. Calibrate the rotating marker-disc inserted into the handpiece.
      3. Assemble the arm between the patient tracker and the labeled clip, and calibrate it.
5. Check calibration by holding the tip of the measured drill to the surface of the labeled clip (Figure 1).
   1. Fix the labeled clip holding the optical marker (tracker) on the teeth of the upper or lower jaw (on which jaw the implant placement occurs). Ensure to insert the clip in the same position registered on the preoperative CBCT.
   2. Calibrate the labeled clip by touching the metal spheres of the clip with the pivot of the probe.
6. Perform the navigated implant placement in local anesthesia, injecting 2 mL of articain (80 mg/2 mL articain/ampoule).
   1. Measure the drill length (touching the drill to the go plate) (Figure 2).
   2. Check the real-time visual accuracy before drilling (touching the drill to any tooth surface and checking that it is in the same position on the monitor and the mouth).
   3. Determine the entry point of drilling. Explore the operation site without the flap.
   4. Drill the bone with dynamic navigation control (Figure 3, Figure 4, and Figure 5) .
   5. Measure the implant length (touching the implant to the go plate).
   6. Place the implant with the handpiece wearing the tracker controlled by the dynamic navigation system.
   7. Close the wound with 5.0 monofilament, nonabsorbable polypropylene suture, or fix the prefabricated prosthetic work.
7. Acquire control radiologic imaging (CBCT, FOV 8 cm x 11 cm, 12 mA, 95 kV).

2. Steps in the dynamic navigation systems using the tracer calibration method (not labeled method):

1. Perform CBCT of the patient (without clip in the mouth).
2. Plan the position of the implant according to the prosthetic architecture with the appropriate software.
3. Calibrate the device as detailed in step 1.4.
4. Calibrate the system without a labeled clip (not labeled method).
   1. Transfer the plan of the implant surgical placement into the software of the used navigation system. Select the workspace on the 3D CT image of the navigation software.
   2. Fix the tracker on the teeth (with an unlabelled clip) or in case of an edentulous jaw with a special tracker-holding arm.
   3. Select the typical anatomical points (teeth or bone surface) on a 3D CT image of the navigation system (minimum three points).
   4. Identify the selected anatomical points in the mouth by touching them with a probe tool. (Figure 6).
   5. Perform refinement procedure on three to four areas by drawing on the surface of the anatomical structure with a probe.
5. Place the implant with navigation in local anesthesia, injecting 2 mL of articain (80 mg/2 mL articain/ampoule).
   1. Measure the drill length (touching the drill to the go plate).
   2. Check the real-time visual accuracy before drilling (touching the drill to any tooth surface and checking that it is in the same position on the monitor and in the mouth).
   3. Determine the drilling point. Explore the operation site without the flap.
   4. Drill the bone with dynamic navigation control.
   5. Measure the implant length (touching the implant to the go plate).
   6. Place the implant with the handpiece wearing the tracker controlled by the dynamic navigation control system.
   7. Close the wound with 5.0 monofilament, nonabsorbable polypropylene suture or fix the prefabricated prosthetic work.
6. Make control radiologic imaging (CBCT, FOV 8 cm x 11 cm, 12 mA, 95 kV).

To use DCAIS correctly, the system must be calibrated. There are several calibration methods that can affect the accuracy of the implant placement. This study aimed to assess the potential impact of different calibration methods on the accuracy of DCAIS.

Based on the interventions performed so far, the use of DCAIS allows a high-precision implant placement. In our early studies, we compared 41 clip calibrated dynamic navigated implant placements with 17 tracer calibrated dynamic navigated implant placements.

According to our early data (Table 1, Table 2, Table 3, Figure 7, Figure 8, Figure 9, and Figure 10), when using the two calibration methods, the results showed that there is no significant correlation between the platform and angular deviation in buccolingual (BL) and mesiodistal (MD) directions. Comparing the planned and final position of the implants, the calibration with a clip proved more accurate compared to one made with a tracer, but the difference is not significant (Table 1, Table 2, Table 3, Figure 7, Figure 8, Figure 9, and Figure 10). Based on previously published data by Block et al., implant placement with a dynamic navigation system allows high-precision implant placement¹. The accuracy of the intervention can be improved by training⁸.

Figure 1: Calibration with clip. Calibration by holding the tip of the measured drill to the surface of the labeled clip. Please click here to view a larger version of this figure.

Figure 2: Drill calibration. Measuring the drill length by touching the drill to the go plate. Please click here to view a larger version of this figure.

Figure 3: Drilling process in the mouth. Drilling the bone under dynamic navigation control. Please click here to view a larger version of this figure.

Figure 4: Real-time live view of the drilling process on the monitor. Real-time control view of bone drilling. Please click here to view a larger version of this figure.

Figure 5: Real-time live view of the drilling process on the monitor. Real-time control view of bone drilling. Please click here to view a larger version of this figure.

Figure 6: Calibration with tracer. Identifying the selected anatomical points in the mouth by touching them with a probe tool. Please click here to view a larger version of this figure.

Figure 7: Mean deviation of the measured values (difference between the planned and final position of the implants) using the two different calibration methods. Global Platform deviation (mm): spatial distance between the center of the implant platform of planned and placed implants. Platform B/L deviation (mm): spatial distance between the center of the implant platform of planned and placed implants in buccolingual dimensions. Platform M/D deviation (mm): spatial distance between the center of the implant platform of planned and placed implants in mesiodistal dimensions. Platform depth deviation (mm): spatial distance between the center of the implant platform of planned and placed implants in depth dimensions. Platform non-depth deviation (mm): the resultant of the Platform B/L and M/D deviations. Apical non-depth deviation (mm): the resultant of the apical B/L and M/D deviations. Global Apical deviation (mm): spatial distance between the center of the implant apex of planned and placed implants. Apical B/L deviation (mm): spatial distance between the center of the implant apex of planned and placed implants in buccolingual dimensions. Apical M/D deviation (mm): spatial distance between the center of the implant apex of planned and placed implants in mesiodistal dimensions.Apical depth deviation (mm): spatial distance between the center of the implant apex of planned and placed implants in depth dimensions. Please click here to view a larger version of this figure.

Figure 8: Standard deviation of the measured values. The difference between the planned and final position of the implants using the two different calibration methods. Please click here to view a larger version of this figure.

Figure 9: Standard error of mean deviation of the measured values. The difference between the planned and final position of the implants using the two different calibration methods. Please click here to view a larger version of this figure.

Figure 10: Analysis of the measured values. The difference between the planned and final position of the implants using the two different calibration methods. Please click here to view a larger version of this figure.

Table 1: Mean deviation of the measured values. The difference between the planned and final position of the implants using the two different calibration methods.

Table 2: Standard deviation of the measured values. The difference between the planned and final position of the implants using the two different calibration methods.

Table 3: Standard error of mean deviation of the measured values. The difference between the planned and final position of the implants using the two different calibration methods.

Table 4: Advantages and disadvantages of dynamic navigated implant systems.

In the labeled clip-used dynamic navigation implant placement system, the traditional workflow is done by clip calibration. There are three radiopaque metal spheres on the surface of the clip, which are clearly visible on the CBCT scan. In the case of the tracer calibration method, these metal spheres containing clips are neither necessary for the CBCT scanning nor system calibration. In cases with existing teeth, both the labeled and unlabelled clips can be used (two different calibration methods). The clip is attached to the teeth with thermoplastic material. In toothless cases, only the tracer method without a clip can be used for calibration. The clip fixed on teeth or a special holding arm fixed on the jawbone holds the optical reference base during the navigated implant surgical placement³ (Table 4).

To ensure accurate registration, the clip should be fixed in exactly the same position relative to the jawbone during implant placement. A loosely or inaccurately fixed clip can lead to navigation errors and irreversible deviation from the planned implant position. The disadvantages of using the clip calibration method are the need for clip preparation itself, adequate training of personnel, inhibited imaging in closed occlusion due to the clip(the bite planning is limited), and difficult dynamic navigation⁹ as a result the placement of the clip being too close to the surgical site during implant placement, causing overlap between the clip and the optical reference base on the handpiece.

In the case of navigated implant surgical placement performed with unlabeled clip, contrary to the radio-opaque clip, anatomical formations (e.g., tooth, bone) or other structures (e.g., crown) are used for calibration. In contrast to the known shape of a fixed clip, reference structures are made visible for navigation by a surface touch scan with a device called a tracer. The tracer is a pointed, pen-like device with an optical tracking base. The tracer is used to identify three to six points or even entire surfaces, which are clearly visible on the image thanks to the tracker. This provides a registration mapping between the created image and the physical surface of the patient's candidate structure. This surface detecting method is used in case of toothlessness as well.

The accuracy of the dynamic navigation system is similar to the one reported for static navigation systems. We have achieved the same result in the two calibration methods within the dynamic navigation.

With DCAIS, there is less need for exploring large bone surfaces; therefore, incisions can be reduced, and decreased mucosal flap formation can be achieved. In the case of the dynamic method, it is possible to modify the surgical plan or deviate from the plan in real-time. The dynamic implant placement system operates with shorter surgical instrumentation; therefore, it can be used in second molar regions and in the case of patients having a limited opening of the mouth. There is no need for specific drill equipment or surgical instruments for dynamic navigation systems. Monitoring the surgery on display allows for an ergonomic body position of the specialist, so the surgeon is able to achieve ideal posture^1,8,10.

By using the tracer calibration of dynamic navigation, we can achieve the same accuracy and avoid the need for clip preparation. The accuracy of the methods depends on the doctor, and adequate training is essential. The method needs very precise planning, and more accurate implant positioning and prosthetic results are expected.

The method allows for immediate implant loading (in case of strong primary stability), as the prosthesis can be prepared in advance based on the design. If the surgical procedure is accurate, the prosthesis fits the position of the implant. The main obstacles to using DCAIS are its (currently) high cost and time-consuming learning process.