The Evolution of Jaw Kinematic Analysis: From Early Observations to Latest Technologies

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Understanding jaw kinematics has significant implications for understanding and diagnosing oral health conditions as well as improving rehabilitation strategies. Despite technological advancements, challenges such as cost and clinical feasibility hinder widespread adoption. Integrating jaw movement analysis into routine practice requires simplified, affordable tools with real-time data processing. Future innovations, including artificial intelligence and wearable devices, hold promise for enhancing patient care by enabling objective, accessible, and personalized assessments of mastication and jaw function.

Abstract

The analysis of jaw kinematics is a valued approach to study the complex process of mastication. This review aims to provide a historically structured overview of methods used in jaw kinematic analysis, outlining their progression from early techniques to current technologies, and emphasizing key advances, limitations, and future directions. To address this aim, relevant literature was identified through targeted searches in academic databases, and key studies were used to trace earlier foundational work, allowing a historically oriented analysis of the field. The evolution of jaw kinematic methods reflects a progressive shift from subjective and indirect observations toward increasingly objective, dynamic, and three-dimensional assessments of mandibular movement. Despite substantial technological advances, many approaches remain limited by their complexity, cost, equipment size and lack of portability, and reliance on controlled laboratory environments, as well as constraints on natural movement. Nonetheless, these methods have contributed to clinically relevant insights into mandibular biomechanics and oral care, including the evaluation of different clinical conditions and treatment outcomes. Emerging technologies, including the development of more portable systems and improved motion tracking, together with artificial intelligence offer the potential of simplifying data acquisition under more natural conditions and its analysis enabling broader research and clinical use.

1. Introduction

Kinematics, derived from the Greek word “kinetos”, which means to move or displace [1], is a branch of physics and a subset of mechanics that focuses on describing the motion of bodies without considering the forces that cause this motion [2]. It describes the spatial positions of bodies, their velocities (the rate at which they move in a specific direction), and their accelerations (the rate at which their velocities change) [3]. In simpler terms, kinematics deals with how objects move but not why they move in a particular way.

The study of movement relies heavily on kinematic models that provide mathematical frameworks to describe the motion of objects and facilitate the analysis of these movements [4]. For a body moving on a straight path, a set of positions and corresponding times would constitute a suitable scheme or model for describing the motion trajectory along a single dimension. When the motion involves a curved path, a more complex description of position is needed, requiring two- or three-dimensional models [3]. In such cases, motion can be analyzed using six degrees of freedom, categorized as translations (up/down, left/right, forward/backward) and rotations (pitch, yaw, and roll) [5].

Kinematic models are essential for studying complex movements that involve translations and rotations. One specific area where kinematic models have shown great promise is in the analysis of jaw movement. Jaw motion during chewing should be assessed with at least three degrees of freedom, focusing on translations, as these are critical for understanding jaw movement dynamics. The six degrees of freedom (three translational and three rotational) provide a comprehensive framework for tracking jaw motion in multiple dimensions. Understanding the complex motion of the jaw helps clinicians detect abnormalities in movement patterns, aiding in more accurate diagnoses and more effective treatment planning. This review aims to provide a historically structured overview of methods used in jaw kinematic analysis (Table 1), outlining the progression from early techniques to current technologies, highlighting advances and limitations as well as the potential role of emerging technologies in the field. To address this aim, relevant literature on jaw kinematics was identified through targeted searches in academic databases, and key articles were used as a starting point to trace earlier foundational studies. This process allowed the identification of seminal work and the evolution of concepts over time, consistent with a historically oriented review.

Table 1. Timeline of Kinematic Analysis and Jaw Movement Studies.

Ancient observations	300 BC	Aristotle: Earliest recorded observations of human movement.
17th Century	1680	Borelli: First scientific gait analysis using mechanical principles.
19th Century	1830–40s	Weber brothers: Quantitative analysis of gait using tools like the chronograph and diopter.
	1878	Muybridge: First photographic capture of motion, proving all hooves of a trotting horse leave the ground.
	1895	X-rays: Opened new possibilities for studying internal movement (Forssell).
Early 20th Century	1889	Luce used reflective markers to trace jaw movements with early photography.
	1900	Hesse made intraoral tracings of jaw movement with a lead pencil.
	1926	Munzesheimer employed multiple cameras for capturing mandibular movements.
Mid 20th Century	1940s	Kurth used stroboscopic photography for capturing high-speed jaw movements.
	1960s	Early electronic systems introduced (mandibulograph, Case Gnathic Replicator, Case Western Reserve University, Cleveland, OH, USA) with six degrees of freedom.
	1975	Jankelson introduced magnetic tracking for jaw kinematics with the Mandibular Kinesiograph.
Late 20th Century	1980s	Early optoelectronic systems (e.g., Karlsson) introduced to track jaw movements using light-emitting diodes (LEDs).
	1990s	Improvements in optoelectronic systems (MacReflex, OKAS-3D, Qualisays, Gothenburg, Sweden) with higher precision and reduced invasiveness.
Early 21st Century	2000s	Systems like Optotrak (Northern Digital Inc., Waterloo, ON, Canada) and Vicon (Vicon, Oxford, UK) became the gold standard for tracking jaw movement with high accuracy and minimal noise. Modern Magnetic Systems: (Kinesiograph (Myotronics Research Inc., Seattle, WA, USA), Sirognathograph (Siemens AG, Bensheim, Hesse, Germany)) provide detailed jaw movement tracking with six degrees of freedom.

2. Early History of Kinematics

2.1. Early Observations of Human Motion

Interest in human movement dates to ancient times. One of the earliest recorded observations comes from Aristotle, who described around 300 BC that “if a man were to walk on the ground alongside a wall with a reed dipped in ink attached to his head, the line traced by the reed would not be straight but zig-zag, because it goes lower when he bends and higher when he stands upright and raises himself” [6] (p. 511). Early observations of motion lacked quantitative rigor and precision but laid the groundwork for future studies of motion.

2.2. 17th to 19th Century Developments

The 17th century marked a turning point in the study of human motion, as more scientific approaches were introduced. Borelli described that humans do not walk in a perfectly straight line [7]. His gait analysis was conducted using two reference poles positioned one in front of the other. He observed that when he walked toward the two poles, the second pole did not hide the first pole, which indicated he made slight deviations from a straight path, consistently correcting his course. This subtle zigzagging, he noted, was due to natural imbalances in the body and the constant adjustments made to maintain balance and direction, demonstrating that a perfectly straight gait is unnatural. His approach used mechanical principles to explain body movement. In the 1830s/1840s, the Weber brothers used tools like the chronograph and measuring tape to quantify aspects of human gait such as step length and cadence [8]. They also used a diopter, an optical instrument and precursor to the telescope, to measure pelvic tilt at different phases of movement. Additionally, they encased bones in plaster blocks, sawed them into segments to make imprints on paper, followed by illustrations depicting figures in running and springing positions [8,9]. These early studies were instrumental in laying the foundation for later advancements in motion analysis, marking a transition from simple visual observation to more structured, quantitative approaches and highlighting the need for objective measurement. However, these approaches relied on indirect methods and observer-dependent interpretations. Nonetheless, they introduced key principles such as measurement, movement segmentation, and biomechanical interpretation, which later informed the analysis of more specific functional systems, including mandibular movement.

3. Technological Advancements in Motion Studies

Early devices, though useful for basic measurements, could not provide the detail necessary to analyze complex human movements. The development of photography in the 19th century marked a turning point in motion analysis, offering a new level of precision.

3.1. Early Use of Photography for Analyzing Motion

Drawings can be regarded as the initial step in documenting motion, although the invention of photography in 1822 marked a significant advancement. Photography allowed capturing certain positions with single plates initially. In the late 19th century, Muybridge [10], a landscape photographer, developed a system using a series of cameras with high shutter speeds, which allowed for the sequential capture of motion. His groundbreaking work included a series of images depicting a horse in trot, proving with an image that there is a moment during a gallop when none of the horse’s hooves touch the ground [8,11].

Around the same time, Marey, a physiologist, studied, among other things, normal and pathological walking. He was the first to set up a biomechanical laboratory equipped with different measuring instruments, some of which he invented. Marey developed chronophotography, a method that offered significant potential for movement analysis by determining the direction and speed of body landmarks [8]. This technique involved intermittent exposure of a fixed photosensitive plate, controlled by a clock mechanism, to capture successive positions of moving objects. A rotating disk with one or more apertures positioned in front of the camera lens enabled the intermittent exposure of sequential photographs. Despite its significance, this method had limitations, including a low frame rate and the inability to capture depth information. Additionally, the equipment required subjects to remain in constrained setups, inhibiting natural movement. Image analysis was still largely manual, making it prone to errors.

During 1895–1897, researchers Braune and Fischer took movement analysis a step further by studying subjects wearing suits strapped with light-emitting tubes [12]. They used a system that ensured accurate timing of light flashes while the subjects walked in the dark, capturing the images with a pair of cameras. Calculations were performed using the points measured on the images. The researchers then manually determined the joint centers and meticulously plotted the results by hand, a task that undoubtedly required countless hours of painstaking work. This effort marks them as pioneers in the first three-dimensional analysis of gait. Together, these photographic approaches represented a major advance over earlier observational methods because they allowed movement to be recorded, reviewed, and analyzed in a more objective and systematic way. However, important limitations continued, particularly the dependence on manual processing, restricted recording conditions, and the limited ability to represent movement in its full complexity. These methods introduced visual documentation and sequential analysis as key principles that later became central to more advanced motion-analysis techniques.

3.2. The Use of X-Rays in Motion Studies

In 1895, the introduction of X-rays opened new possibilities for studying internal movements that were invisible to the naked eye. A few years later, Forssell studied movements of the hand and wrist, taking radiographs in different positions [13]. Subsequently, systems were developed to capture radiographs in sequence; one of these was the “Roentgen cinematograph”. This system used strong drying boxes, each holding a film between two intensifiers, which moved forward using a sliding mechanism. While the patient leaned against a lead shield with an opening, the boxes dropped into a case protected from X-rays. The X-ray tube was positioned behind the patient, and a lead disk with two openings rotated in front of the tube, exposing the film at the right moments. An electric motor powered the whole system, allowing it to take up to four images per second [14].

The introduction of X-ray-based methods marked a key advance by enabling the visualization of internal structures during movement, allowing a clearer understanding of the relationship between observed motion and the joint mechanisms underlying it. However, these techniques were technically demanding, had limited acquisition rates, and faced practical constraints that restricted their broader use. Nevertheless, they represented an important step toward a more integrated analysis of movement and its anatomical basis.

4. Development of Jaw Movement Analysis Techniques

As with other parts of the body, interest in jaw position and movement has been long-standing. The study of jaw movement, particularly during mastication, has benefited from technological advancements over the years.

4.1. Graphic Registration and Early Methods in Jaw Movement Analysis

Early jaw movement studies utilized graphic registration methods. These methods often required markers attached to the teeth, with jaw motion recorded on different materials. While these methods provided initial insights into jaw movement, they were limited in accuracy and disrupted natural movement.

In 1896, Walker remarked that “authorities are quite unanimous in describing the movements of the mandible” as if everything was already known [15] (p. 34). This author commented that the movements of the mandible, as well as of the condyles and ramus, can be seen and felt in thin individuals. Although simple observation provides valuable information without interrupting natural movements, it does not provide precise registration of these movements. To improve accuracy, albeit at the cost of less natural movements, methods using indicators or markers have been used. These attachments are used in graphic methods, where the jaw movement is marked on materials such as paper, cardboard, or other materials via attachments to the teeth. Walker, for example, used a graphite point to trace the movement of the condyle on a sheet of stiff paper held against the side of the face, with the edge parallel to the facial line, mentioning that this method was more efficient than the photographic techniques of the time [16]. He also designed a facial clinometer, which measured angles and the direction of the condyle path, and quantified the distance of one condylar movement in relation to the other during mastication in millimeters [16].

In 1900, Hesse made intraoral tracings during excursive movements [17], covering the upper teeth with a layer of hard rubber and securing a point of a lead pencil in the space of a missing lower molar. He additionally implemented a spring mechanism so that the pencil was lifted when the lower jaw was depressed to allow continuous tracing during jaw separation. In 1908, Bennet used a sort of face bow attached to the teeth with two lamps, one at the condyle and one at the chin. The movements of these lamps, in a sagittal or frontal direction, were magnified by a lens and projected onto a wall, where the positions were recorded [18]. The history of graphic registration includes a wide array of “articulators” with early models dating back to the 19th century, which have evolved into numerous models and variations over time [19]. While graphic registration provided early insights into jaw movement, these methods lacked the precision required for more detailed analysis.

These approaches represented early attempts to apply motion analysis methods, originally developed for whole-body movement, to the study of mandibular function. Their primary aim was descriptive, focusing on documenting and characterizing jaw motion rather than clinical application. While graphic registration provided early insights into jaw movement, these methods lacked the precision required for more detailed analysis, partly due to their reliance on intraoral or extraoral attachments and their potential interference with natural motion.

4.2. Early Use of Photography and Cinematography in Jaw Movement Analysis

The introduction of photography significantly improved the ability to capture jaw movement. In the late 19th century, Luce was already using photographs as a method to study jaw movement [20]. By attaching a small, reflective silver bead to a wooden dowel held between the lower central teeth, Luce was able to capture the bead’s path in bright sunlight. A side profile of the subject was photographed while their jaw moved, and the reflected light from the bead traced a continuous line on the photographic plate. In the initial stages of his research, Luce began by using a single bead. Subsequently, he incorporated bright beads into the framework and securely attached them to the incisors, opposite to the condyle, angle, and symphysis. He used the photographs to analyze tracing of different jaw movements, demonstrating through frontal images that jaw movements during opening and closing do not follow straight lines [20]. Based on his studies, Luce mentioned errors in the descriptions of jaw movement, referencing works dating back to 1735 [20].

As photography techniques evolved, researchers began incorporating more sophisticated methods such as chronophotography. Marey, who had previously studied other body movements such as gait, proceeded to also study jaw movement. He used his chronophotography equipment and a photographic gun, in which the film advanced automatically in front of the lens, stopping during each exposure, and advancing again with a jerk [8]. Instead of beads, Marey used a metallic bar over the lower and posterior edge of the mandible. A head support ensured that the only movements registered were those of the mandible, and a black fabric velour was placed between the markers and the face to create a dark field. The subject wore a headpiece with a ruler to measure the extent of the movements. Subjects were instructed to decompose a chewing movement into four or five steps. During those stops, the camera’s shutter remained open for half a second [21]. Although initially only one camera was used, Munzesheimer has been referenced as using more than one camera in 1926 [18].

Klatsky studied the influence of the physical properties of foods on the jaw movements during mastication with cinefluorography [22]. He used a camera operating at a speed of 16 frames per second, capturing a total of 80 frames over a period of 5 s, which he considered enough as a recording. The moving images were taken from the display on a fluoroscopic screen [22].

In the 1930s, Hildebrand undertook thoroughly studying mandibular movement for his PhD thesis. He mentioned that movement could be analyzed in two fundamental ways: by registering different positions and subsequently compiling a path of movement from those positions, or by registering the entire path during movement. He took advantage of methods available at the time, such as “Roentgen kymography”, “Roentgenfluoroscopy”, photography, and “kinematography”, and invested resources to refine some of these methods. Hildebrand assumed that: (1) by using a stationary plate and an indicator illuminated at regular intervals he could only register a single cycle, as multiple cycles would be superimposed; (2) the use of two cameras would complicate calculations unless they were synchronized, which presented technical challenges; and (3) since he could not have access to a stereoscope camera, he began using a mirror positioned at a 45-degree angle in combination with the “kinematograph”. He considered that with this setup, a single image could render the position in three dimensions and register both space-path and space-speed. Although he claimed that limiting head movement during recordings was advantageous, this approach, in reality, is not convenient. By integrating information obtained through different methods, Hildebrand described that mastication can be divided into several stages [18].

In the 1940s, Kurth used stroboscopic photographs to capture mandibular movements, mentioning that the use of this light source allowed the “stopping” of movement and the recording of its direction on a photographic plate with 25 images per second. This frame rate was enough to provide a clear representation of mandibular movement across three spatial planes. A steel pin was positioned between the two mandibular central incisors as a marker, and the face was blackened to reduce reflections. Despite using this photographic method, Kurth placed greater emphasis on graphic tracings made using a facebow with styluses that produced tracings on wax-coated glass plates. To better represent incisor movement during a glide and a masticatory stroke, he created wire models [23].

Ahlgren analyzed different aspects of mandibular movement in 9- to 16-year-old children with different occlusions [24]. He refers using the same cinematographic method used by Hildebrand: an 8 mm movie film recorded at a speed of 24 frames per second and a camera with a shutter speed of 1/250 s. To enhance accuracy, Ahlgren used a head positioner and a mirror system to record jaw movements in the frontal and sagittal planes. Orthodontic bands with soldered extraoral metal balls were placed on the upper incisors to serve as a reference point and on the lower incisors as the indicator of mandibular movements. For the analysis, the film was projected onto an angled mirror, and frames were traced on transparent graph paper with a 2× enlargement. This method enabled the study of both qualitative and quantitative parameters, such as distance and speed. Based on the tracings of 35 children, Ahlgren classified seven different chewing patterns [24].

Taken together, photographic and cinematographic approaches represented a substantial advance over graphic registration by capturing mandibular movement as a dynamic sequence. Importantly, these methods reflected an emerging recognition of the need to analyze the three-dimensional nature of jaw movement, leading to the use of mirrors and multiple perspectives to approximate spatial information. They also made early efforts to identify differences in movement patterns between individuals. However, these approaches depended on markers, head-positioning devices, and labor-intensive frame-by-frame analysis, which limited their precision and practicality. Nonetheless, they were instrumental in advancing toward a more spatially informed understanding of mandibular kinematics.

5. Electronic Systems in Jaw Kinematics Analysis

Despite the progress made with mechanical and photographic methods, these approaches had inherent limitations in precision and ease of use. Technological advancements and increased accessibility of computers in the 1960s and 1970s facilitated the development of more efficient motion capture systems, which brought a new level of accuracy, efficiency and accessibility in jaw kinematics analysis, although the early electronic systems were hindered by slow data processing speeds. The development of electromechanical and photoelectric systems allowed for more precise, non-invasive tracking of rigid body motions. These systems enabled the monitoring of three-dimensional jaw movements using six degrees of freedom.

5.1. Early Electronic Systems in Jaw Kinematics Analysis

In 1962, Beck and Morrison introduced a system based on the principle that the motion of a rigid body can be described by the simultaneous positions of three reciprocating points, which are not on the same straight line and that are contained in three mutually perpendicular planes. This system consisted of two servomechanisms. The first mechanism included a transducer and a recorder. The head position was stabilized using a framework attached to the upper teeth and served as the reference for the movements. An extraoral transducer was attached to three irregularly positioned points of the mandible. The movement of the three points was mechanically transmitted to six rotary transmitters within the transducer. The output from each transmitter was fed to one of six recording pen motors. The path of each point was recorded in ink by two tracings since two transmitters were attached to each point. The second servomechanism sent the information from the patient to the duplicator, which contained the patient’s dental cast, enabling the observation of movements and contacts [25].

A few years later, Messerman developed the Case Gnathic Replicator: a system that consisted of two external face-bows securely attached to the patient’s upper and lower teeth, along with six incremental photo-optical transducers. The outputs were recorded on a multichannel tape recorder, producing data in a digital format suitable for computer analysis. This system is reported to allow a comprehensive recording of the six degrees of freedom of the mandible, without a restrained head position [26]. Like the Beck and Morrison system, the system was called a replicator because it functioned by duplicating the movements of the patient’s dental casts. This system was used in studies in children aged 4 to 17 to compare their chewing patterns with those of adults [27].

In the early 1960s, an electromechanical device known as the “mandibulograph” was developed [28]. This instrument was initially designed to measure the position of a single point on the mandible in three dimensions. It functioned using three electrical translational transducers that recorded the displacement of a rod connected through a flexible coupling to the lower incisors [28]. Posteriorly, three rotational transducers (potentiometers) were included to measure mandibular rotation, providing a three-dimensional representation of jaw movements, including chewing. This system required control of baseline drift through the use of both lateral and postero-anterior x-rays, at least two appointments, laboratory work, and head stabilization with a plaster headcap [28].

Gillings and Graham deemed that the mechanical linkage between the frameworks attached to the jaw and the recording devices interfered with normal function [29]. They therefore designed a photoelectric mandibulograph to study different aspects of three-dimensional mandibular movement. This system used a mandibular rod with a light attached to the labial surfaces of the lower incisors and a lightweight headframe with photocells. As the mandible moved, the light’s position relative to the photocells changed, modifying the electrical outputs. These changes in output activated a pen to trace lines on a moving recording paper. The system used three sets of photocells: one for open–close, another for left–right, and a third for anterior–posterior jaw point movements, producing life-size continuous three-channel paper tracings (vertical, lateral, and anteroposterior). An advantage of this equipment was that it did not require restriction of head movement during chewing, and jaw cycle movements could be observed directly on an oscilloscope, which were photographed to verify the data from the tracings [29,30].

Refined systems devised at that time can be broadly categorized into optical and magnetic systems. Optoelectronic tracking systems use the optical spectrum to track position and orientation, offering high accuracy and robustness to environmental conditions [31]. In contrast, electromagnetic tracking systems use an electromagnetic field to track the pose of electromagnetic sensors, providing fast and accurate tracking without line-of-sight constraints.

In the 1970s, advancements in superconducting magnetic gradiometer technology led to the application of superconducting gradiometers in magnetic tracking [32]. This progress facilitated the development of magnetic systems to study chewing cycle kinematics [33]. Magnetic systems use an array of sensing elements that detect changes in the direction and strength of fields emitted by a magnet as its distance changes. Additional magnetometers are needed to detect and cancel the effect of the Earth’s magnetic field. The data output from these systems provides information on the three-dimensional position of the mandible, which can subsequently be analyzed or replayed using computer software [33,34]. When compared to a computer-controlled electronic measuring system, the mandibular kinesiograph demonstrated reliable accuracy and linearity in tracking mandibular movements, confirming the validity of the mandibular kinesiograph recordings as accurate representations of mandibular movements at the incisor point [34].

Karlsson developed a camera that registers signals from light-emitting diodes (LEDs) [35]. One LED is attached to the lower incisors, while at least one is placed on the forehead. These LEDs are connected to a control unit via thin titanium wires, operated at a fixed repetition frequency. The LEDs on the forehead serve as a reference for mandibular movements, with cancellation of the head movements by subtraction. The light emitted by each LED focuses onto position-sensitive detectors in the cameras, where the signals are amplified, digitized, and can be recorded using either an analog tape recorder or stored in a computer. Although three cameras can be used, a computer can compute the three-dimensional coordinates of movements using two cameras positioned perpendicularly. This system is mobile, precise, reproducible, and reduces manual labor when the signals are processed by the computer. In another approach, Ow et al. demonstrated that the LED used to register mandibular movements can be placed on the skin [36].

Hamborg and Karlsson made changes to improve this optoelectronic system [37]. In this new version, a reflective marker was placed on the chin, and three markers in an L-shaped configuration were attached to a frame on the forehead. An infrared flashlight, synchronized with the electronic shutter and positioned around the lens, illuminated the field of view, reflecting light back to the camera. The video camera had a detecting system for infrared light. After identifying the different markers used, a video processor dealt with the video speed calculation of marker center coordinates processed by special software. Since a Mac computer was used, this system was called the MacReflex movement monitoring system (Qualisys, Gothenburg, Sweden). Before recording, the system required calibration using a reference structure consisting of six spherical markers with known positions. Two cameras enabled the recording of movements in three dimensions. During recording, a monitor displayed the markers in real-time, allowing for their identification and tracking. This system allowed for the recording of fast movements and offered a straightforward setup. These innovative optoelectronic systems offered several advantages, such as limited influence on normal masticatory function, the ability to measure multiple variables with high precision, no restriction of head movements, and were relatively easy to handle. A comparison of results obtained using mandibular markers on the chin versus the teeth indicated that, while the use of the chin marker is less precise, it is sufficient for studies involving large sample sizes where trends are analyzed [37].

The OKAS-3D system is another optoelectronic jaw motion recording system that operates with six degrees of freedom [38]. It uses a floating circle target tracker and is particularly suitable for recording small bodily movements at a high sampling rate with minimal noise. This system builds on a previous approach that used a single floating circle target tracker. However, that setup was limited to tracking a single point in two dimensions. To address this limitation, a second tracker was incorporated into OKAS-3D, with one tracker positioned for the frontal view and the other for the side view. OKAS-3D captures movement in three dimensions using a system of mutually perpendicular photocells located on lightweight frames attached to the upper and lower teeth [38]. Although it is highly accurate, the OKAS-3D system requires a confined recording space and can restrict natural movement during analysis.

These systems represented a major step forward by enabling more precise and dynamic recording of mandibular motion, with increasing recognition of the need to capture its three-dimensional nature under natural conditions. From this stage onward, head movement was no longer constrained, and intraoral devices were simplified with diverse sensing elements, some applied externally, reducing interference with natural motion. The introduction of computers and dedicated software reduced manual processing and enabled the analysis of multiple variables. These advances facilitated more practical setups and supported emerging clinical applications, including the identification of differences in jaw movement between populations such as children and adults.

5.2. Modern Electronic Systems in Jaw Kinematics Analysis

Building on the foundation laid by early electronic systems, modern technologies in jaw kinematics analysis have achieved unprecedented levels of accuracy and usability. The early 21st century brought about systems with high precision, low latency, and minimal noise, allowing the study of complex movements in fine detail. Multiple markers can now be tracked in free movement conditions. However, these setups remain expensive and require large spaces, making them suitable for research but impractical for routine clinical or practical applications.

The most commonly used magnetic systems are the Kinesiograph (Myotronics Research Inc, Seattle, WA, USA) and the Sirognathograph (Siemens AG, Bensheim, Hesse, Germany)), although others, such as the Jaw Tracker (Bio JT-3D™ BioRESEARCH Associates, Inc., Milwaukee, WI, USA), are also available. In these systems, the magnet is attached to the lower teeth, while the sensors and magnetometers are mounted on different designs of headframes. Despite providing accurate data, some distortion has been reported [39], the system is expensive, and the setup is complex. Furthermore, they require a controlled environment, as the presence of metallic or ferromagnetic sources can affect measurement accuracy [31].

These magnetic systems have been widely used in various studies and continue to be used in updated versions [40,41,42]. For instance, the K7-1 Kinesiograph measures jaw movements with an accuracy of 0.1 mm, and the sensor array weighs 113 g [42]. The Sirognatograph was used in studies involving children four or older, with primary dentition and a unilateral crossbite [43]. Recent research has focused on the development of smaller and intraoral magnetic wearable devices [44]. Morikawa et al. introduced a mouthpiece-type portable device capable of measuring six degrees of freedom, where the magnet is placed on a mouthpiece affixed to the upper molar, and the magnetic and orientation sensors are attached to a mouthpiece on the lower molar [44].

The Optotrak system (Northern Digital Inc., Waterloo, ON, Canada) captures three-dimensional measurements and tracks motion with six degrees of freedom in real time. It uses active optical technology to measure the position and orientation of up to hundreds of markers within a pre-calibrated 20 m³ measurement volume. The system records data as three-dimensional points rather than two-dimensional images, which helps reduce the likelihood of errors or biases. The accuracy of the model available at the start of the 21st century, at two meters, was 0.1 mm in the x and y dimensions and 0.15 mm in the z dimension. The Optotrak Certus optical tracking system enhances performance by automatically and individually tracking each marker with an accuracy of 0.1 mm and resolution of 0.01 mm, independent of sampling rate, and with minimal latency and noise [45]. The Optotrack system has been used to study within-subject variability in chewing cycle kinematics and to investigate the association of chewing cycle kinematics with masticatory performance [46,47].

Vicon (Vicon, Oxford, UK), another optoelectronic system, is considered the gold standard for motion capture systems due to its high accuracy and low error rates [48,49]. The system uses a combination of cameras and passive markers, accompanied by software for data analysis. Originally designed for gait analysis, Vicon is now applied across several fields. A review reported that in 23 studies related directly or indirectly to the dental field, it has been predominantly used in the study of: speech properties like pronunciation, dento-oro-facial level changes that influence posture and body movement, and facial muscle analysis. Only two studies focused on mandibular dynamics during chewing, and another two on mandibular kinematics in laterality and protrusion movements [49]. The youngest subjects in the reviewed studies in which Vicon was used were three years old, but in these cases, the system was not used for analyzing mandibular dynamics, only speech [49]. The implementation of this technology is constrained by its cost and the space requirements for setup.

In addition to the insights gained from studying masticatory movements with these systems, such as the effects of bolus size and hardness [46], both optoelectronic and magnetic jaw-tracking systems have proven valuable in research across several oral conditions. In the orthodontic field, these systems have been particularly useful for understanding, as well as contributing to the diagnosis and treatment, of specific malocclusions. One study reported that adult patients with a deep bite exhibit cycles with a reduced vertical excursion and velocity, but increased posterior excursion compared to controls [50]. Similarly, a study in pre-adolescents with deep bite found an increase in the lateral component of the closing stroke following functional therapy [51]. In children with a unilateral posterior crossbite, rapid palatal expansion did not modify the abnormal cycle shape, although some aspects of masticatory kinematics did respond to orthodontic intervention [52]. In contrast, functional appliances have been shown to reduce the percentage of abnormal chewing patterns (reverse sequence chewing cycles) [53].

Regarding conditions requiring orthognathic surgery, Youssef et al. reported no significant differences in chewing cycle duration or mandibular excursions in patients after four types of surgical procedures [54]. Combined orthodontic and orthognathic treatment in patients with skeletal Class III malocclusion improved their mandibular chewing movement with the greatest changes observed in the horizontal plane and a marked reduction in mandibular deviation during mouth opening [55]. In the context of unilateral condylar process fractures, a study found that these patients had changes with greater excursion toward the balancing side during the opening phase, with more apparent changes when chewing on the opposite side of the fracture that persisted two years after treatment [56].

6. Animal Studies in Jaw Kinematics

Researchers have also been interested in studying different aspects of masticatory function in animals. Areas of focus include: ontogeny [57]; neural cortical control [58]; tongue movement coordination [59]; chewing behavior with different types of food [60,61]; differences in movement during different phases [62]; the impact of pathology [63]; and differences before and after dental treatment [64].

Studies on the movement of anatomical structures during chewing or eating have been conducted in animals such as lizards [62], rodents [57], rabbits [65,66], primates [58,61], horses [60,63,64], and pigs [59,61]. All these studies offer valuable insights into understanding masticatory function from a broader, comparative perspective. By studying how different species use their jaws during various tasks, researchers can explore evolutionary adaptations in jaw structure and function, as well as differences across species.

Some of these studies have used methods similar to those in humans, such as attaching markers on the skin [65], or teeth [60], using micro inertial measurement units (IMUs) [67], or several cameras [60,61,64]. However, some researchers have opted for implanting markers [62], or surgically exposing structures [66], and many restrain body movement during experiments [61,65]. These methods are not suitable for use in humans. Other methods also not convenient to use in humans are exposure to ionizing radiation [58,62], or CT scans to undertake what has been called XROMM or X-ray Reconstruction of Moving Morphology [68].

These studies not only deepen our understanding of animal biomechanics but also contribute to human jaw motion research. For instance, findings from animal studies often provide baseline data that inform human applications, especially in areas where experimental methods would be too invasive or impractical in humans.

7. Other Approaches in Jaw Kinematics Analysis

The methods developed for jaw kinematics analysis have significantly contributed to the understanding of mastication and other functional jaw movements, while also highlighting the persistent need for methods that are more accessible, less restrictive, and better suited for broader use. However, high cost, technical complexity, and limited practicality continue to restrict their wider implementation.

Recent advancements in body movement tracking technology have focused on the development of smaller, more flexible, and efficient devices, such as IMUs and micro IMUs [69]. IMUs, along with other sensors such as gyroscopes, accelerometers, and related electronic components, have been integrated into wearable technologies. These are extensively used for computer games, visual effects for film, and other virtual experiences [70], and may also offer useful possibilities for the study of chewing cycle kinematics. This approach may offer a less restrictive alternative for movement tracking than some conventional jaw-tracking systems and may help bridge the gap between accurate laboratory-based systems and more accessible methods for functional assessment. This type of technology has not yet been applied to jaw kinematics analysis, but in the context of mastication, a compact device implemented to monitor chewing frequency was found to be sufficiently reliable, supporting the feasibility of less invasive and more practical approaches for recording chewing-related activity [71].

Artificial intelligence (AI) has emerged with many applications and is expected to be integral to the future. The use of AI facilitates task execution, enables automation of processes, and accelerates the acquisition of results. In this context, AI may be particularly useful when functional assessment generates large amounts of data that would otherwise require labor-intensive manual processing and interpretation. Its application to jaw kinematics remains limited. A scoping review on the use of machine learning in dentistry did not identify studies specifically focused on jaw kinematics analysis [72], suggesting that this remains an underdeveloped area. Recent works in mastication assessment suggest that AI may help reduce manual processing, save time, and expedite data analysis. For example, a proof-of-concept study using a YOLOv8-based model (a deep neural network) achieved recall and sensitivity values above 90% for the detection and segmentation of post-masticated food fragments, supporting the feasibility of automated chewing-function analysis in seconds using a cellphone application [73]. Additionally, a recent review has highlighted the growing use of computer vision systems, wearable sensors, and machine learning algorithms in mastication assessment [74], suggesting a potential role for these approaches in improving functional evaluation, treatment planning, and more personalized assessment of mandibular and masticatory function. These applications, however, still require further validation before broader research and clinical implementation in jaw kinematics analysis.

8. Conclusions

The study of jaw kinematics has evolved significantly over the centuries, transitioning from early, rudimentary observational methods to sophisticated, high-precision technologies. The progression from graphic registration and photographic techniques to modern optoelectronic and magnetic systems has provided increasingly accurate representations of jaw motion, enabling researchers and clinicians to better understand the complexities of mastication, speech and other mandibular functions. The introduction of electronic systems in the mid-20th century represented an important milestone, allowing for the capture and analysis of jaw movements in multiple dimensions with greater precision and the possibility of analyzing more natural movements. This technological evolution was accelerated by the arrival of optoelectronic systems and magnetic trackers, both of which have improved the ability to study jaw kinematics with six degrees of freedom. Although these systems have substantially advanced research and clinical applications, they remain costly and setup is demanding, limiting their accessibility for extensive use.

The incorporation of AI methods in recent years suggests additional possibilities for the future of jaw kinematics analysis. These technologies may support the potential for automated data processing, real-time analysis, and more natural study conditions. Moving forward, research in the study of jaw kinematics will likely focus on refining these technologies to improve accessibility and accuracy while minimizing the invasiveness of the tracking systems. The development of smaller, portable devices, trackers, or markers, as well as wearable technologies or technologies that do not require markers, may enhance the possibilities of the field, allowing for long-term, real-world monitoring of jaw movements. However, these emerging approaches still require further validation before broader research and clinical implementation.

Finally, while significant advancements have been made in the study of jaw kinematics, there remains considerable potential for further innovation. As technology progresses, more comprehensive, accessible, and non-invasive systems may develop, with the potential to improve both diagnostic and treatment capabilities in the field of oral health.