Is Incisor Compensation Related to Skeletal Discrepancies in Skeletal Class III? A Retrospective Cephalometric Study.

This study investigated compensation in skeletal Class III subjects to compare various severities of abnormal jaws. A retrospective analysis of 137 skeletal Class III cephalograms (63 males and 74 females) was conducted, with cephalometric assessments determining skeletal and dental values. The results were compared with Class I cephalograms. Incisor compensation was examined by pairing normal jaws with varied abnormal jaws, classified by severity using one standard deviation (SD). Statistical analyses included Kruskal-Wallis tests, Bonferroni tests, Spearman's correlations, and multiple linear regression. Four skeletal Class III groups were identified: OMx+PMd, RMx+OMd, OMx+OMd, and PMx+PMd (P = prognathic; O = orthognathic; R = retrognathic; Mx = maxilla; Md = mandible.). The upper central incisor (U1) showed proclination, and the lower central incisor (L1) showed retroclination across all groups except for U1 in PMx+PMd and L1 in OMx+OMd, which exhibited normal inclination. U1 exhibited limited compensation even with progressive maxillary retrognathism, while L1 showed limited compensation after one SD of mandibular prognathism. Maxilla (SNA) and jaw discrepancy (ANB) were inversely related to the U1 degree, whereas only jaw discrepancy (ANB) was positively related to the L1 degree. U1 in PMx+PMd and L1 in OMx+OMd showed no incisor compensation. U1 had limited compensation even with progressive maxillary retrognathism while L1 showed limited compensation after one SD mandibular prognathism.

Effect of the application of digital technology-assisted optimization in the process of adjusting jaw position.

OBJECTIVES: The aim of this study was to demonstrate a novel jaw position adjustment technique derived from digital twins and evaluate the application effect of digital technology-assisted optimization in the process of adjusting jaw position on patients with temporomandibular disorders (TMD). METHODS: A total of 74 patients with TMD who attended the Department of Temporomandibular Joint, West China Hospital of Stomatology, Si-chuan University, between June 2022 and May 2023 were selected. The patient's initial computed tomography (CT) and bilateral temporomandibular joint data obtained by magnetic resonance imaging (MRI) were collected. The 148 joints were divided into the normal disc-condyle relationship (N) group, disc displacement with reduction (DDWR) group, and disc displacement without reduction (DDWoR) group. Assisted by digital technology, the patient's CT data were reconstructed, and a personalized reference plane was established to adjust the jaw position. A three-point bite guiding splint was designed by the adjusted occlusal space and then fabricated by 3D printing technology. It was worn by the patients and then reviewed by MRI. Before and after the adjustment of jaw position, the amount and direction of condyle and disc displacement and the angle between condyle and disc were measured as the evaluation indexes of the effect of the adjustment. The correlation with condylar displacement was evaluated. RESULTS: In the N group, the disc moved backward and downward along the X and Z axes by (-0.60±0.62) and (0.51±0.71) mm, respectively. In the DDWR group, the disc moved backward and upward along the X and Z axes by (-1.33±1.38) and (-0.09±1.31) mm, respectively. In the DDWoR group, the disc moved forward and downward along the X and Z axes by (0.49±1.76) and (1.35±1.76) mm, respectively. The angle between the condyle and the disc decreased after adjustment of the jaw position in all three groups. All patients showed improvement in symptoms after adjustment. CONCLUSIONS: Digital technology-assisted jaw position adjustment can simplify the process, reduce the sensitivity of the technique, and improve patients' disc-condyle structure and symptoms. Therefore, its application in the treatment of patients with TMD is of great clinical significance.

Comparison of the accuracy of different types of bite recordings - an in vitro study.

OBJECTIVES: Reconstruction of a three-dimensional jaw position determined by a bite recording is an important aspect of prosthetic therapy. Different materials are used for this purpose. In the dental technical workflow, recordings are used to mount a lower jaw cast in a patient-like spatial position relative to the upper jaw cast. We evaluated the accuracy of positioning under the influence of different jaw positions and materials. MATERIALS AND METHODS: In an experimental setup, comprising an articulator, a pair of metal casts, and an optoelectronic measurement system, the spatial position of the incisal point and two condylar points were measured. To evaluate the accuracy of repeated repositioning of casts in the technical workflow, 324 measurements were taken from 108 recordings, consisting of silicone bite-stops made of addition curing silicone with 95 shore hardness, acrylic wafers, and wax recordings. The recordings were obtained in four jaw relations differing in vertical and protrusive components. RESULTS: Of the three materials/material combinations examined, silicone showed the most consistent results across all measurements, followed by the acrylic wafer system, and then wax recordings. Generally, recordings with smaller gaps between the jaws and no protrusive components showed greater deviations compared to jaw positions with greater protrusion and higher vertical dimensions. CONCLUSIONS AND CLINICAL RELEVANCE: To achieve reliable model mounting with high accuracy, recordings should include the use of a frontal jig and four small recording platelets made of silicone, especially if only a slight elevation of the vertical dimension is needed.

Permanent Magnet Tracking Method Resistant to Background Magnetic Field for Assessing Jaw Movement in Wearable Devices.

There is a large gap between primitive bruxism detectors and sophisticated clinical machines for jaw kinematics evaluation. Large, expensive clinical appliances can precisely record jaw motion, but completely restrain the patient for the duration of the test. Wearable bruxism detectors allow continuously counting and recording bites, but provide no information about jaw movement trajectories. Previously, we developed a permanent magnet and three-axis magnetometer-based method for wearable, intra-oral continuous jaw position registration. In this work, we present an effective solution of the two main drawbacks of the method. Firstly, a two-adjacent-magnetometer approach is able to compensate for background magnetic fields with no reference sensor outside of the system's magnetic field. Secondly, jaw rotational angles were included in the position calculations, by applying trigonometric equations that link the translation of the jaw to its rotation. This way, we were able to use a three-degree-of-freedom (3-DOF) magnetic position determination method to track the positions of the 5-DOF human masticatory system. To validate the method, finite element modeling and a 6-DOF robotic arm (0.01 mm, 0.01°) were used, which showed a 37% decrease in error in the average RMSE = 0.17 mm. The method's potentially can be utilized in small-scale, low-power, wearable intra-oral devices for continuous jaw motion recording.

The impact of a total knee arthroplasty on jaw movements, upper body posture, plantar pressure distribution, and postural control.

Objective: The purpose of this study was to examine the influence of a total knee arthroplasty (TKA) on linked cranial and caudal structures. Methods: Thirty-five (14f/21m) subjects participated in this study: 15 subjects (9f, 6m) pre- and post- TKA and a control group of 20 subjects (5f, 15m). The measurements included: jaw condyle position and movement, back scan, plantar pressure distribution, and body sway. Results: There were no significant differences in electronic position analysis of the jaw; however, the protrusion of the TKA group improved (p = 0.001). The test group had a more anteriorly inclined thoracic spine and a less pronounced lumbar lordosis. Before and after surgery, the body sway in the test group was larger. Conclusion: The TKA affected most prominently the static mechanisms of the postural control and the spine position. The trajectories of the mandible during protrusion also changed slightly.

Can jaw position affect the fine motor activity of the hand during writing?

BACKGROUND: Jaw and neck systems have been shown to be functionally related and changes in either system can modulate gross motor functions, such as posture control. It remains to be seen if any change in jaw position can affect fine motor skills. The objective of this study was to determine the effect of resting, open and clenched jaw positions on various handwriting parameters while standing on firm and unstable surfaces. METHODS: Handwriting samples were collected from 36 healthy male participants (age, 15-35 years) using a digitizer tablet (WACOM Intuos 4) with noninking pen in the resting, open and clenched jaw positions while standing on firm and unstable surfaces. The measured handwriting parameters included duration, vertical size, horizontal size, absolute size, average absolute velocity, and absolute jerk. Recordings and analyses were performed using NeuroScript MovAlyzeR software. RESULTS: All handwriting parameters varied among the resting, open, and clenched jaw positions on both the firm and unstable surfaces. However, based on statistical analyses, there were no significant differences in the handwriting parameters among three jaw positions on both surfaces (p > .05). CONCLUSION: This study revealed that all handwriting parameters varied among the resting, open, and clenched jaw positions on both the firm and unstable surfaces, showing that change in the jaw motor system may potentially affect the fine motor skills. However, on statistical analysis, there was no significant effect of 3 studied jaw positions on fine motor skills as seen on gross motor skills among healthy individuals.

[Method and accuracy of determining the jaw position of repositioning splint with the aid of digital technique].

OBJECTIVE: To establish the workflow of determining the jaw position of repositioning splint with the aid of digital technique, and to evaluate the accuracy of this workflow and compare the accuracy of raising different vertical dimensions in vitro. METHODS: A volunteer was recruited. The data of full-arch scans, cone beam computed tomography (CBCT) image and ultrasonic jaw motion tracking of the volunteer were acquired. The full-arch scans were merged with the CBCT image, which were then matched to the jaw motion tracking reference system. The jaw position of repositioning splint was determined when the anterior teeth opening was 3 mm and the condyle was in centric relation of the fossa in the sagittal plane. A digital repositioning splint was designed in the software based on virtual articulator and fabricated with additive manufacturing technique. After the splint was tried in, another CBCT image was taken and a qualitative analysis was conducted to compare the position of condyle between these two CBCT images. In the in vitro study, standard dental plaster casts with resin ball markers attached to the base were mounted onto a fully adjustable articulator in the intercuspal position. The dental casts were scanned by an extraoral scanner to establish digital models. The ultrasonic jaw motion tracking device was used to obtain simulated jaw movements on the articulator, which was repeated for three times. The digital models and data of jaw movements were merged in one coordination with the aid of bite forks. The jaw position of repositioning splint was determined by adjusting data of jaw movements, each of which was used to determine three vertical jaw positions 4 mm, 5 mm, and 6 mm with the horizontal jaw position of protrusion 2 mm. The virtual articulators with differently adjusted jaw movements were applied in designing repositioning splints, and the final repositioning splints and virtual jaw relationships were exported in STL format. Then the repositioning splints were fabricated with additive manufacturing technique and tried in plaster casts on the mechanical articulator, which were scanned and the jaw relationships on the mechanical articulator were exported later. The virtual jaw relationships and scanned jaw relationships were registered according to lower models and displacement of upper models was calculated. Ball markers were fit to acquire the coordinates of centers and absolute difference values of centers along three coordinating axes X, Y, and Z were calculated. One-way analysis of variance was conducted using SPSS 18.0 software to compare deviations of the three different vertical jaw relationships in two-side test and the significance level was 0.05. RESULTS: With the aid of multi-source data fusion and individualized jaw motion, the clinical workflow of determining jaw position of repositioning splint was preliminarily established. The designed jaw position was realized on the right and the condyle was more inferior than the designed position on the left. Both displacement of the upper models and absolute difference values of centers showed no significant differences (P>0.05) in different vertical jaw dimensions. The displacement of the upper models was (0.25±0.04) mm. The absolute difference values of centers along the three coordinating axes X, Y, and Z were respectively (0.08±0.01) mm, (0.30±0.02) mm, and (0.21±0.04) mm. CONCLUSION: A novel method of determining the jaw position of repositioning splint with the aid of digital technique is established. It is proved to be feasible by try-in after multi-data fusion, computer-aided design and computer-aided manufacturing. As is shown in vitro, it is accurate to apply this method in adjusting jaw position. Further clinical trial will be designed to evaluate its clinical effect.

Influence of different jaw positions on dynamic balance using Y-balance test.

BACKGROUND: Jaw sensory-motor system has been shown to affect static balance of the body. It would be interesting to know whether it can influence dynamic balance as well. The objective of this study is to examine the influence of different jaw positions on dynamic balance using the Y-balance test. METHODS: Eighty healthy male participants aged 20-35 years were invited to participate in this study. Dynamic balance was measured by the Y-balance test in three directions (anterior, posteromedial, and posterolateral) for each leg separately in three jaw positions: resting jaw (control), open-jaw, and clenched jaw. RESULTS: There were no significant differences in reach distances between the different jaw positions except in the posterolateral direction. In comparison with resting jaw position, reach distance was significantly higher in open-jaw position for the right leg and in clenched and open-jaw positions for the left leg in the posterolateral direction. CONCLUSIONS: Although various studies have shown direct or indirect influence of jaw sensory-motor system on static postural control, results of this study point to limited relation with dynamic postural control among healthy subjects. However, it supports the potential of the jaw sensory-motor system to affect motor control during functional tasks in patients with postural instability or similar disorders.

Effect of jaw functional status on neck muscle endurance.

OBJECTIVE: To investigate the effect of resting jaw and maximum voluntary clenching on neck flexor and extensor muscle endurance. DESIGN: Neck flexor and extensor endurance was measured in a college health clinic in 85 male college students in two test positions: resting jaw (control) and maximum voluntary clenching. RESULTS: Mean neck flexor muscle endurance values during resting jaw and maximum voluntary clenching were 70.06 SD 28.24, and 60.03 SD 16.5, seconds respectively. Mean neck extensor muscle endurance values during resting jaw and maximum voluntary clenching were 105.54 SD 29.9, and 98.32 SD 24.54, respectively. Both values were significantly lower while maximum voluntary clenching as compared to resting jaw position (p < 0.05). CONCLUSION: Modification of jaw position can affect neck muscle endurance. Results of this study further supports sensory-motor relation between jaw and neck region.

Application of a barometer for assessment of oral functions: Donders space.

We developed a barometer applicable to a small space, to assess oral and pharyngeal functions. Negative oral pressure during rest and pressure changes during swallowing were measured in a space between the palate and tongue (STP). Twenty volunteers were asked to sit in a chair in a relaxed upright position. A sensor was placed on the posterior midline of hard palate. Recording commenced just before subjects closed their lips and continued. Subjects were asked to swallow saliva and keep the apposition. Finally, subjects were asked to open their mouth. Recordings were performed five times, and 5 s of continuous data in each phase was averaged. To verify the reliability of the system, the same procedure was accomplished with twin sensors. When the jaw and lips were closed, the pressure slightly decreased from atmospheric pressure (-0·17 ± 0·24-kPa). After swallowing, the pressure in STP showed more negative value (-0·50 ± 0·59-kPa). There is a significant difference between the values in open condition and after swallowing (P < 0·001) and between values after swallowing and final open condition (P < 0·05). Twin sensor showed almost the same trajectories of pressure changes for all the recordings. Obtained negative pressure might generate about 0·71-N of force and would be enough to keep the tongue in the palatal fossa at rest. The system detected large negative/positive pressure changes during swallowing. We conclude this system may be a tool to evaluate oral functions.

Effect of head and jaw position on respiratory-related motion of the genioglossus.

Head and jaw position influence upper airway patency and electromyographic (EMG) activity of the main upper airway dilator muscle, the genioglossus. However, it is not known whether changes in genioglossus EMG activity translate into altered muscle movement during respiration. The aim of this study was to determine the influence of head and jaw position on dilatory motion of the genioglossus in healthy adult men during quiet breathing by measuring the displacement of the posterior tongue in six positions--neutral, head extension, head rotation, head flexion, mouth opening, and mandibular advancement. Respiratory-related motion of the genioglossus was imaged with spatial modulation of magnetization (SPAMM) in 12 awake male participants. Tissue displacement was quantified with harmonic phase (HARP) analysis. The genioglossus moved anteriorly beginning immediately before or during inspiration, and there was greater movement in the oropharynx than in the velopharynx in all positions. Anterior displacements of the oropharyngeal tongue varied between neutral head position (0.81 ± 0.41 mm), head flexion (0.62 ± 0.45 mm), extension (0.39 ± 0.19 mm), axial rotation (0.39 ± 0.2 mm), mouth open (1.24 ± 0.72 mm), and mandibular advancement (1.08 ± 0.65 mm). Anteroposterior displacement increased in the mouth-open position and decreased in the rotated position relative to cross-sectional area (CSA) (P = 0.002 and 0.02, respectively), but CSA did not independently predict anteroposterior movement overall (P = 0.057). The findings of this study suggest that head position influences airway dilation during inspiration and may contribute to variation in airway patency in different head positions.

The impact of a total hip replacement on jaw position, upper body posture and body sway.

OBJECTIVES: The purpose of this study was to examine whether, and to what extent, a total hip replacement can influence the position and the movement of the jaw, the upper body posture and body sway. METHODS: Twenty test subjects (6 females, 14 males) participated in this study pre- and post-total hip replacement, in addition to a healthy control group of 20 subjects (5 females, 15 males). The measurements were conducted by means of an ultrasound system to measure jaw condyle position and movement of the lower jaw, a three-dimensional back scan to analyze upper back posture, and a static and dynamic force plate to measure body sway. For statistical analysis the Wilcoxon-Matched-Pairs-Test or Man-Whitney-U-Test, including a Bonferroni-Holm correction, respectively, was used. RESULTS: After surgery, the mean values of the left and right jaw condyles of the test group moved posterior, and the left condyle position was located more caudally. There were no significant differences concerning the jaw position between the two groups. There was little change in upper body posture in both groups. The test group had a more anteriorly inclined thoracic spine and a less pronounced lumbar lordosis. During static body sway measurements, increased fluctuations in the test group after surgery could be seen. CONCLUSION: Differences between both groups in the pre- and post-surgical condition could be detected. These differences were more prominent when the measured body segments were more distally located with respect to the hip region.