The use of a dynamic real-time jaw tracking device and cone beam computed tomography simulation
Abstract
Background:
The aim was to introduce and preliminarily evaluate a new software application, SICAT Function, which can directly combine and merge three-dimensional cone beam computed tomography (CBCT) and electronic SICAT jaw motion tracking (JMT) data.
Methods:
A detailed description of the methods and dynamic clinical simulation of mandibular movements of a patient are demonstrated. Functional jaw movements on 3 days were recorded by JMT tracking system. The simulation was performed by merging CBCT and JMT data in the software SICAT Function suite. The condylar position simulated by SICAT Function suite was compared with real condyle position showed by a CBCT of the patient.
Results:
The incisor ranges of functional movements were displayed by JMT tracking system. The visualization of patient-specific mandibular movement including the translation of the condyles was displayed after data merge. The recordings of mandibular movements of the patient were similar on 3 different days. The condylar position simulated by SICAT was coincident with real condyle position by CBCT data with the same amount of mouth opening.
Conclusions:
The SICAT Function software is a system capable of measuring and visualizing patient-specific jaw movement relative to the patient-specific anatomy of the jaw. Further studies are needed to validate its accuracy and its potential for future use.
INTRODUCTION
The masticatory system is an important part of the craniofacial complex. The temporomandibular joints (TMJs), together with the dentition, the masticatory muscles, the vascular and nervous systems supplying these tissues, constitute the major components of any healthy stomatological system. Jaw recording of the system has been done by gnathologists for the understanding of the normal function of the stomatognathic system and also for the diagnosis and treatment of diseases of TMJs such as temporomandibular disorders (TMDs). This system has been analyzed for many years, but the methods used record statistic points or single positions of the mandible (e.g., protrusion, excursion, etc.). The masticatory system is, however, dynamic, and the main component lies in the mandible. The mandibular movement executed by TMJ is a motor functional movement that reflects the command of all these components and is critical not only for an oral-related function such as food taking and speech but also for the systematic, mental, and physical functions of the body.[1]
Various devices have been developed to record and analysis the mandibular movement for more than a century.[2] There are methods using mechanical devices with graphical methods involving marking needles, recording styli and pantographs, and almost all these methods have the disadvantage of causing interference with jaw movements.[3] Photographic techniques required complicated manual transference to produce tracings of jaw movements and thus result in the inherent possibility of introduced error.[2] Roentgenographic methods with radiation exposure have been used in the past but may not be allowed by ethical review committees for experimental purposes in the modern day due to the patient safety concerns.[3] Two systems of magnetometry, the mandibular kinesiograph,[4] and the Sirognathograph,[5] which depend on the changes in the magnetic flux occurring when a small bar magnet moves relative to a sensor, have been used to measure mandibular movements in three dimensions for a long time. These devices are found not to interfere with the mandible movements. Optoelectronic tracking systems obtain mandibular movements using cameras to tracking the spatial position of light-emitting diodes.[6] They also have an advantage of less disturbing to individual chewing pattern.[7]
These methods alone however do not include the TMJs and the surrounding anatomical structures. Furthermore, precise measurements are not taken into consideration. Three-dimensional (3D) TMJ morphology is made up of hard and soft tissue structures. These structures have been reconstructed by spiral and helical computed tomography (CT) and magnetic resonance imaging (MRI). Datasets have been merged with 3D TMJ reconstruction by CT and electromagnetic tracking device[8] or optoelectric measuring systems,[6] and ultrafast MRI and jaw movement recordings by optoelectric measuring systems[9] in few previous studies. The main disadvantage of MRI imaging is that the patient is lying supine on the scan bed, which might alter the mandibular movement. Furthermore, the MRI imaging is not clear at detail visualization of bony anatomy.[6] The disadvantage of CT image used before is the radiation exposure. Furthermore, the visualization of patient-specific jaw movement and chewing pattern has not been clearly presented before.
The purpose of this study was to introduce and preliminarily evaluate a new software application, SICAT Function (SICAT, Bonn, Germany), which can directly combine and merge 3D cone beam CT (CBCT) and electronic jaw motion tracking (JMT) data. CBCT, which offers a 3D image of facial and dental structures, has been widely used in the dental field.[10,11] The SICAT JMT+ system is an electronic recording system that is based on 3D ultrasound measurements. The ultrasound-based system converts the propagation times of multiple acoustic signals into spatial information, which therefore could record the lower jaw movements of the patient in all degrees of freedom. A detailed description of the methods and dynamic clinical simulation of mandibular movement of a patient is performed and demonstrated.
METHODS
Subject description
A 27-year-old female patient came with a chief complaint of “retroclined upper and lower incisors.” She had a symmetric and maxillofacial structure in the frontal view, and her profile was straight. Intraorally, her molar and canine relationships were Class I on both sides. Her dental midline was coincident with face midline. Cephalometric radiograph and tracing indicated a skeletal Class I relationship and retroclined upper and lower incisors. The patient reported occasionally moderate muscular and TMJ pain during mandibular movements and pain on palpation of bilateral TMJs. The maximal mouth opening was normal (41 mm) with some lateral displacement of the mandible during jaw opening. The sample had little to no functional shift on mandibular closure.
SICAT jaw motion tracking+ tracking system
The SICAT JMT+ system mainly includes a facebow, a lower jaw sensor, a SICAT Fusion Bite tray, a SICAT Fusion Bite adapter, a para-occlusal T-attachment, a SICAT JMT+ basic unit, and SICAT JMT+ application software [Figure 1]. The facebow has a nose pad to help locate the facebow, an upper headband, and a rear headband to secure the position. It contains six ultrasonic microphones to receive the information from four ultrasound transmitters in the lower jaw sensor. Both the receiver and transmitter modules are connected with the evaluation electronics in the SICAT JMT+ basic unit via a connecting cable. The SICAT Fusion Bite tray is a fiducial transfer tray, and it could be connected to the lower jaw sensor by the SICAT Fusion Bite adapter. There are eight radiopaque markers on the tray, which will serve as landmarks for the fusion of CBCT data and JMT. The paraocclusal T-attachment is attached to the lower teeth and move with the mandibular movement to make the recording of movement possible and it could be connected to the lower jaw sensor by the magnetic attachment.
Main components of the SICAT jaw motion tracking+ system
Cone beam computed tomography
The CBCT device (Sirona Galileos, Bensheim, Germany) was used, which acquires the images with a scan time of 14 s, capture the maxilla-mandibular region in a 210° rotation, and has a reported radiation dosage of only 29 µSi to 54 µSi according to the manufacturer. The field of view is a spherical volume of 15 cm. The voxel size is between 0.15 mm and 0.30 mm, and the grayscale is 12 bit. The voxel size of CBCT scans in this study is 0.30 mm. The acquired CBCT data were transferred from the scanner to a work station where 3D images were constructed by GALAXIS 3D software (Sirona Galileos, Bensheim, Germany). The data were saved as DICOM (digital imaging and communication in medicine) format.
Data acquisition
A CBCT scan was originally taken to examine her condylar status for diagnostic and treatment purposes of this patient for her TMDs. Considering her TMD problems, the CBCT was taken with the SICAT Fusion Bite in the mouth during the CBCT scan for tracing her mandibular movement later. To transfer the coordinate system of the jaw tracking device, a SICAT fusion bite [Figure 2] was prepared with the SICAT Fusion Bite tray as follows: (1) silicone impression material was put in both the maxillary and mandibular side of the Fusion Bite reference tray, (2) the patient was asked to bite on the impression material, (3) the bite was taken out of the patient's mouth after the impression was done and was trimmed to remove excess materials. The patient was asked to wear the SICAT Fusion Bite in the mouth during CBCT scan.
Preparation of SICAT Fusion Bite and paraocclusal T-attachment
To prepare the tracking, the paraocclusal T-attachment was shaped according to the lower dental arch. Autopolymerizing composite was applied such as Luxatemp (3M ESPE; Seefeld, Germany) to the bending part of the T-attachment, and adapted to the tooth surfaces or to the study model, and it was left to harden [Figure 2]. Excess material and sharp edges were removed and it was made sure that the upper teeth and the SICAT Fusion Bite are not in touch with the paraocclusal T-attachment to guarantee an undisturbed functional movement of the jaw in the occlusion.
The facebow was positioned stably on the patient's head making sure that the upper headband was on the patient's skull, and the nose pads were not too tight to stretch the skin in the nasion area, and the elastic rear headband was tightened comfortably for the patient. The SICAT Fusion Bite was placed in the mouth and the patient was asked to bite into the impression. The occlusion was checked by examining if the teeth were in the right position of the impression and stability was checked by moving the Fusion Bite [Figure 3a]. The paraocclusal T-attachment was mounted firmly in the patient's mouth using medical acrylic glue such as Histoacryl (B. Braun Melsungen; Melsungen, Germany) [Figure 3b]. The software SICAT JMT was started. First, the SICAT JMT lower jaw sensor was attached to the SICAT FusionBite [Figure 3c]. “Record” was clicked and the software guided the program throughout the calibration sequence. The position relationship between the upper jaw and the head was recorded. The SICAT Fusion Bite was left in mouth and the lower jaw sensor was attached to the paraocclusal T-Attachment and then “record” was clicked. The original position between the mandible and the head was recorded. The SICAT Fusion Bite was removed. Then, the functional jaw movement such as opening, right and left lateral movement, protrusion, and chewing were recorded. The jaw movements including opening, right and left lateral movement, and protrusion of this participant on day 1 (T1), day 2 (T2), and day 3 (T3) were recorded.
Device on the patient's head. (a) The SICAT Fusion Bite in mouth. (b) The paraocclusal T-attachment attached to the lower arch in mouth. (c) The facebow was stably positioned on patient's head. The lower jaw sensor was attached to the SICAT Fusion Bite. Later, the lower jaw sensor would be attached to the paraocclusal T-attachment
Data fusion
The CBCT data and JMT files were loaded in the software SICAT Function suite. Axial slices were scrolled through until at least one spherical radiopaque marker was shown, marker was marked, and it was repeated until three spherical markers were marked [Figure 4a]. All eight radiopaque markers were automatically found after three radiopaque markers on the Fusion Bite tray were identified, and the tray was located [Figure 4b]. Then, the CBCT and JMT data was automatically merged.
Merge of cone beam computed tomography and jaw moving tracking data and segmentation of the mandible. (a) Scroll through the axial slices until at least one spherical radiopaque markers is shown, mark the marker, and repeat until three spherical markers are marked. (b) All of the eight radiopaque markers were automatically found after three radiopaque markers on the Fusion Bite tray were identified, and the tray was located. (c) Segmentation of the mandible
Segmentation of mandible
Segmentation of the mandible could be performed semi-automatically in the software. When the approximate position of the mandible was indicated by drawing marks on the radiographic sectional slices, the software calculated the data, and presented a 3D image of the cropped mandibular segment on the screen [Figure 4c]. The blue color was used to represent the mandible and the green color for the fossa. The procedures for dynamic real-time jaw tracking and CBCT simulation are summarized in Figure 5.
The procedures for dynamic real-time jaw tracking and cone beam computed tomography simulation
RESULTS
Recording of mandibular movement by SICAT jaw motion tracking+
Mandibular movements, including opening, right/left lateralization, and protrusion were recorded. The incisor ranges of these movements were automatically displayed, and results are summarized in Table 1. The movements were observed in dynamic mode and from different angles. The tracings of opening, right lateral movement, left lateral movement, and protrusion in selected planes are presented in Figures Figures66–9. It can be seen from images and recording radios that the mandible shifted to the right when opening and protrusion. The movements of the left and right lateralization were not symmetrical. From the results of the 3 continuous days, the mandibular movements of the patient were similar on the different days but not exactly the same.
Table 1
The summary of mandibular movements of the patient in 3 continuous days
Tracing images in selected planes by jaw motion tracking during opening
Tracing images in selected planes by jaw motion tracking during protrusion
Tracing images in selected planes by jaw motion tracking during left lateral movement
Tracing images in selected planes by jaw motion tracking during right lateral movement
Merge cone beam computed tomography and jaw motion tracking data in SICAT function suite
The CBCT reconstructed mandible was successfully segmented. In addition, the segmentation of the glenoid fossa was also successfully completed. After merging the CBCT and JMT data, the visualization of patient-specific movement of the mandible including the translation of the condyles was displayed. In the dynamic mode, the movement path of any selected point on the condyle and the mandible body such as interincisal point movement of the lower mandibular teeth were depicted on the simulation. Selected simulation images of the movement are presented in Figures Figures1010–12. Based on the anatomical information provided by CBCT data and movement information by the JTM data, we could observe the movement of the condyle in the patient's fossa.
Patient-specific visualization of mandibular opening movement. (a) condyle pathway; (b) incisor pathway
Patient-specific visualization of mandibular protusion. Condyle pathway (the first and the second columns) and incisor pathway (the third and the fourth columns)
Patient-specific visualization of mandibular lateral movement. (a) Lateral left; (b) lateral right
The precision of the simulated condylar position
According to the simulation of condylar movement presented by the SICAT Function Suite, the extensive displacement of the condyle during opening was noticed. It raised a question that whether the positions of the condyle stimulated by the SICAT Function according to the CBCT data and the JMT data are correct. While the patient had pain in her left joint and was treated in the Prosthodontic Department, another CBCT was obtained to record her condyle status with mouth open after the muscle deprogramming treatment. We loaded the second CBCT data into the SICAT Function Suite, segmented the mandible and fossa, and the condyle position was therefore showed. We compared the simulated condylar position by SICAT Function with the real condyle position in the second CBCT. When the mouth opening distances were the same, the condylar positions were coincident with each other [Figure 13], which indicated that the predicting and the presentation of condylar movement by SICAT Function suite were accurate and reliable.
The same condylar positions were demonstrated between simulated condylar position by SICAT Function suite with similar mouth opening distances and condylar position in the second cone beam computed tomography
DISCUSSION
Real-time recording of mandibular movements
Jaw tracking devices and methods in the past have greatly improved the understanding of masticatory system and mandibular movements. However, more sophisticated technology has made it easier, but methods are still needed for accurate evaluation and extensive exploration of the normal and pathological functions of TMJs. This article demonstrated the use of SICAT Function software (SICAT, Bonn, Germany) and how it creates dynamic real-time JMT data with individual imaging data and provides visualization of true mandibular movements.
The ranges of the movements are easily obtained and are instantaneously presented after the recording. In addition, the simulation images and the entire tracking data of the movements of the mandible are clearly presented. The recordings over 3 sequential days showed that this method may have high repeatability. Although the data is not exactly the same, the possible reason for this might be that the patient has TMD problems, and the movement is not stable. Further studies are needed to validate its accuracy.
The introduction of cone beam computed tomography and SICAT jaw motion tracking+ system
Compared with conventional CT, CBCT has the advantages of lower radiation dose, improved image accuracy, shorter scanning time, and less image artifacts.[12] It will therefore reduce the radiation exposure to the greatest extent. In many dental hospitals and clinics, CBCT has become a routine examination before orthodontic treatment. Although the previous study has used 3D CT to reconstruct maxillofacial skeletal 3D images and to achieve patient-specific mandibular movement analysis,[6] the use of CBCT has not been reported yet.
The SICAT JMT+ system consists of an arc-shaped upper jaw sensor consisting of six ultrasonic receiver microphones on the head bow and an arc-shaped lower jaw sensor with four transmitter modules. During the recording, the ultrasonic transmitters on the lower jaw sensor continuously emit impulses, and the system measures the operating time between the transmitters and receiver microphones; then, calculates the absolute room coordinates of the markers using a triangulation method, and thus converts the propagation times of multiple acoustic signals into spatial information. The system records mandible positions relative to the head at rest and during movements, so head position and head movement have no clinical impact on the results.[13] It then will be much more convenient and accurate when it is used for clinical and research purposes. Besides, the simple components and free movement of the lower jaw sensor in SICAT JMT+ system enable it to measure all the mandibular movements including chewing in all degrees of freedom.
The position of condyle during movement
The condylar movement is more difficult to be observed because of the anatomy of the TMJ. Relying on the CBCT reconstructed condyle, and the JMT recorded data, the condylar displacements during different mandibular movements were clearly demonstrated by the software. After comparing with condylar position in the second CBCT, the result indicated that the condyle position was precisely predicated at rest and during movements by the SICAT Function software. This provides a visualization of the condyle in the joint fossa without taking additional CBCT records.
Future directions
The SICAT Function software provides measurement and visualization of mandibular movement. Furthermore, it provides a way to predict the position of condyle without extra radioactive exposure when the tooth is in specific occlusion. Further studies can verify the repeatability of SICAT Function software and use the system to study the movement of healthy and diseased TMJs, to diagnose patients with jaw deformities and to help the treatment of TMJ problems. Furthermore, the SICAT Function software will benefit the understanding and evaluation of occlusion in dentistry.
CONCLUSIONS
The SICAT Function software is a system capable of measuring and visualizing patient-specific jaw movement relative to the patient-specific anatomy of the jaw. Further studies are needed to validate its accuracy and its potential for future use.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
REFERENCES
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4979326/
