Jaw Position Research Articles

Clinical decision of centric relation.

Centric relation (CR) was used in the complete dentures for edentulous jaws firstly. Then, CR was gradually applied in the clinical diagnosis and treatment of dentate jaws. Regarding the application of CR in dentate jaws, there are many doubts about its rationality. For instance, should CR be the core of diagnosis and treatment of temporomandibular disorders? Should CR be used as the jaw position of establishing occlusion in occlusal reconstruction? Should CR serve as the target jaw position in orthodontic treatment? Meanwhile, varieties of CR clinical applications are objective. According to the existing evidence, this paper summarizes the applicable conditions of several main clinical situations with little controversy. We preliminarily put forward the decision tree for the clinical application of CR, which can be used as a reference in clinical practice.

Prevalence of Malocclusion among School aged Children and Adolescents in Kabul, Afghanistan

One of the major public health concerns is the prevalence of malocclusion among school-aged children. Malaligned teeth and incorrect jaw posture are referred to as malocclusion, and they can cause a number of functional and cosmetic problems. The aim of this study was to investigate the prevalence of malocclusion in school-aged children and adolescents in Kabul, Afghanistan. This descriptive cross-sectional study was conducted at the Faculty of Dentistry, Kabul University of Medical Sciences “Abu Ali Ibn Sina” (KUMS). The data were collected from High schools in Kabul, Afghanistan during 2019 and 2020. A sample of 479 children and adolescents, 236 females (49.3%) and 243 males (50.7%) 8-18 years old (mean age 14.16±2.8) were randomly selected from four high schools of different districts of Kabul city. We used the angle classification for sagittal plane malocclusion; open bite and deep bite for vertical plane malocclusions; cross bites for transverse plane malocclusion; midline diastema, spacing and crowding show the tooth material and arch length discrepancies. This study demonstrated that only 41 (8.6%) of subjects had normal occlusion while 92.4% of subjects had different types of malocclusions. Class I malocclusion was found in 275 subjects ( (57.4%, class II Division 1 in 63 subjects (13.1%), Class II Division 2 in 64 subjects (13.4%), Class III malocclusion in 36 subjects (7.5%), moreover, crowding in 183 (38.2%), spacing in 79 (16.5%), midline diastema in 54 (11.3%), crossbite in 77 subjects (16.1%), open bite in 23 subjects (4.8%) and deep overbite in 44 subjects (9.2%) were found. According to Angle’s classification of malocclusion class I malocclusion was the most prevalent malocclusion and class III was the least prevalent malocclusion in school-aged children and adolescents in Kabul city.

Correlation of Clivus Length and Angle with Chronological Age, Gender, Sagittal Growth Pattern of the Jaws, and Skeletal Maturation Using Lateral Cephalometry.

Determination of remaining growth potential of patients is the most important factor in orthodontic treatment. This study aimed to assess the correlation of clivus length and angle with age, gender, sagittal growth pattern of the jaws, and skeletal maturation using lateral cephalometry. This cross-sectional study was conducted on 390 lateral cephalograms (Vatech, paX-i3D Green, South Korea) of patients aged 6 to 25 years. The patients were assigned to three groups of skeletal class I, II, III (n=130) with equal gender distribution. The clivus length and angle, Welcher angle, maxillary and mandibular effective length, sella turcica to Nasion (SN), and the angles between SN and point A (SNA), between SN and point B (SNB), and between NA and NB (ANB )were measured. Correlations of variables with age and gender, and cervical vertebral maturation stage (CVMS) were analyzed using the Pearson and Spearman's correlation tests, independent t-test, and one-way ANOVA at 0.05 level of significance. Clivus length had a significant correlation with SNA (r= 0.103, p= 0.042), SNB (r= 0.108, p= 0.033), maxillary (r= 0.547, p< 0.001) and mandibular (r= 0.589, p< 0.001) effective lengths, SN length (r= 0.586, p< 0.001), and CVMS (r= 0.697, p< 0.001). Clivus angle had a significant correlation with SNA (r= 0.105, p= 0.039), SNB (r= 0.155, p= 0.002), maxillary (r= 0.507, p< 0.001) and mandibular (r= 0.596, p= 0.001) effective lengths, SN length (r= 0.566, p< 0.001), and CVMS (r= 0.699, p< 0.001). The mean clivus length (p= 0.006) and angle (p= 0.002) were significantly higher in males, and had a significant correlation with age (r= 0.636 and r= 0.718, p< 0.001). The mean clivus length and angle were not significantly different in class I, II, III (p> 0.05). All parameters were greater in males, and increased with age (except Welcher angle). Clivus length and angle had significant correlations with position of both jaws but not with sagittal relationship.

Vocal tract dynamics shape the formant structure of conditioned vocalizations in a harbor seal.

Formants, or resonance frequencies of the upper vocal tract, are an essential part of acoustic communication. Articulatory gestures-such as jaw, tongue, lip, and soft palate movements-shape formant structure in human vocalizations, but little is known about how nonhuman mammals use those gestures to modify formant frequencies. Here, we report a case study with an adult male harbor seal trained to produce an arbitrary vocalization composed of multiple repetitions of the sound wa. We analyzed jaw movements frame-by-frame and matched them to the tracked formant modulation in the corresponding vocalizations. We found that the jaw opening angle was strongly correlated with the first (F1) and, to a lesser degree, with the second formant (F2). F2 variation was better explained by the jaw angle opening when the seal was lying on his back rather than on the belly, which might derive from soft tissue displacement due to gravity. These results show that harbor seals share some common articulatory traits with humans, where the F1 depends more on the jaw position than F2. We propose further in vivo investigations of seals to further test the role of the tongue on formant modulation in mammalian sound production.

Impact of delivery variations on 3D dose distributions for volumetric modulated arc therapy plans of various complexity.

Delivery variations during radiotherapy can cause discrepancies between planned and delivered dose distribution. These variations could arise from random and systematic offsets in certain machine parameters or systematic offsets related to the calibration process of the treatment unit. The aim of this study was to present a novel simulation-based methodology to evaluate realistic delivery variations in three dimensions (3D). Additionally, we investigated the dosimetric impact of delivery variations for volumetric modulated arc therapy (VMAT) plans for different treatment sites and complexities. Twelve VMAT plans for different treatment sites (prostate-, head & neck-, lung-, and gynecological cancer) were selected. The clinical plan used for the treatment of each patient was reoptimized to create one plan with reduced complexity (i.e., simple plan) and one of higher complexity (i.e., complex plan). This resulted in a total of 36 plans. Delivery variations were simulated by randomly introducing offsets in multi-leaf collimator position, jaw position, gantry angle and collimator angle simultaneously. Twenty simulations were carried out for each of the 36 plans, yielding 720 simulated deliveries. To explore the impact of individual offsets, additional simulations were conducted for each type of offset separately. A 3D dose calculation was performed for each simulation using the same calculation engine as for the clinical plan. Two standard deviations (2SD) of dose were determined for every voxel for 3D-spatial evaluations. The dose variation in certain DVH metrics, that is, D2% and D98% for the clinical target volume and five different DVH metrics for selected organs at risk, was calculated for the twenty simulated deliveries of each plan. For comparison, the effect of delivery variations was assessed by conducting measurements with the Delta4 phantom. The volume of voxels with 2SD above 1% of the prescribed dose was consistently larger for the complex plans in comparison to their corresponding simple and clinical plans. 2SDs larger than 1% were in many cases, found to accumulate outside the planning target volume. For complex plans, regions with 2SDs larger than 1% were detected also inside the high dose region, exhibiting, on average, a size six times larger volume, than those observed in simple plans. Similar results were found for all treatment sites. Variation in the selected DVH metrics for the simulated deliveries was generally largest for the complex plans with few exceptions. When comparing the 2SD distribution of the measurements with the 2SD distribution from the simulations, the spatial information showed deviations outside the PTV in both simulations and measurements. However, the measured values were, on average, 35% higher for the prostate plans and 10% higher for the head & neck plans compared to the simulated values. The presented methodology effectively quantified and localized dose deviations due to delivery offsets. The 3D analysis provided information that was undetectable using the analysis based on DVH metrics. Dosimetric uncertainties due to delivery variations were prominent at the edge of the high-dose region irrespective of treatment site and plan complexity. Dosimetric uncertainties inside the high-dose region was more profound for plans of higher complexity.

A 3D-CBCT Volumetric Analysis of Cervical Vertebrae Angulation and Airway Dimensions

Aim: To evaluate the relationship between airway dimensions and cervical vertebrae angulations in dental patients using three-dimensional cone beam computed tomography (3D-CBCT) technology. Materials and Methods: Pre-treatment CBCT scans and cephalometric radiographs were measured for 59 patients (mean age 22±2.3yrs.) using the Dolphin3D software system (version 11.7; Dolphin Imaging &amp; Management Solutions, Chatworth, CA) to record airway dimensions and cervical vertebral angulations. All CBCT images were acquired using the same standard protocol for collection using the iCAT CBCT Unit (Imaging Sciences International, Hatfield, PA): 13cm field of view, 0.4mm voxel size, 8.9sec scan time. Intraclass Correlations (ICC) were performed on duplicate measurements of 10 CBCT scans after a two-week interval to assess reliability. P-value and Pearson correlation coefficients were used to statistically assess the relationship between vertebral angulations and airway dimensions. Results: ICC values from the reliability assessment were &gt;0.90. Pearson correlation coefficients were categorized based on confidence level as follows: high (&gt;0.75 or &lt;-0.75), moderate (0.5 to 0.74 or -0.5 to -0.74), or weak (0.3 to 0.49 or -0.3 to -0.49). No high/moderate correlations were observed. Weak correlations (p&lt;0.05) were observed between the nasopharyngeal volume and the soft tissue thickness at CV1(-0.47) and CV2(-0.34). A weak correlation was observed between the nasal cavity volume and S-N (+0.41) as well as ANS-PNS(+0.38). A weak correlation was observed between the total airway volume and the soft tissue thickness at CV2(-0.34). Conclusion: The soft tissue thickness of the posterior wall of the airway at the level of cervical vertebrae-2 appears to have a weak, negative correlation with several upper airway parameters and total airway volume. Soft tissue thickness of the posterior pharyngeal wall is crucial for dental clinicians to analyze prior to some procedures such as orthognathic surgery and orthodontic treatment that involve growth modification and jaw positioning, as it may have an association with decreased airway volume. Clinical Significance: The relationship between cervical vertebrae angulation, airway, and craniofacial morphology is a complex aspect of human anatomy. In dentistry, it is crucial that clinicians recognize the vital role cervical vertebrae angulation and airway interact in relation to craniofacial morphology. Knowledge of these interconnections will significantly inform treatment planning for multiple oral health conditions such as malocclusions, jaw discrepancies, and temporomandibular joint disorders.

The influence of oral breathing type on the formation of occlusion in students of general educational institutions of the Ministry of Defense of Russian Federation

BACKGROUND: Among students of general education organizations of the Ministry of Defense of Russian Federation, respiratory diseases is the leading cause of general somatic morbidity and amount to 1543.5‰. When examining students, pathology of the upper respiratory tract is often diagnosed, such as partial or complete obstruction of the nasopharynx and/or oropharynx. Against this background, the formation of the oral type of breathing occurs, which affects the state of general somatic health and growth and development of the facial skeleton. AIM: To evaluate the influence of oral breathing on the dentoalveolar and gnathic parameters of the maxillofacial region in students of educational institutions of the Ministry of Defense of Russian Federation. MATERIALS AND METHODS: This study examined two groups of students aged 13–15 years from the St. Petersburg Cadet Military Corps named after Prince Alexander Nevsky: group 1, 30 cadets with oral breathing, and group 2 (control), 30 cadets with nasal breathing. All patients underwent an examination of the oral cavity, a photo protocol, scanning of the dentition, and cone-beam computed tomography of the skull bones and first cervical vertebrae in natural occlusion with a resolution of 17×15. The data were checked for normal distribution of features. The article presents arithmetic averages and their errors (M±m). RESULTS: All the examined group 1 students with oral breathing were diagnosed with distal bite in combination with other dental anomalies: combined anomalies in the form of distal bite and disocclusion in the frontal region (56.7%); close position of the anterior group of teeth (93.3%); and unilateral (30.0%) and bilateral (13.3%) cross occlusion due to narrowing of the upper and lower jaws. In most cases, the group 1 students were diagnosed with a gnathic form of dentoalveolar anomaly (ANB parameter, 6.6±2.4°; Beta parameter, 24.7±3.1°) against the background of retroposition of the lower jaw (SNB parameter, 75.4±2.8°) and a decrease in the length of the lower jaw (Co–Gn parameter, 106.0±2.8 mm). All the group 2 (control) students had a neutral occlusion with a normal position of the upper jaw (SNA parameter, 81.4±2.1°) and a normal position of the lower jaw (SNB parameter, 79.8±1.6°) and the first skeletal class (ANB parameter, 2.3±1.1°; Beta parameter, 30.1±2.5°). CONCLUSION: Oral breathing is accompanied by the development of disto-occlusion with the formation of a vertical gap in combination with cross occlusion in the lateral sections and close position of the anterior group of teeth against the background of a narrowing of the upper and lower jaws. Prompt diagnosis of upper respiratory tract pathology prevents the development of dentoalveolar and gnathic disorders of the maxillofacial area. To treat patients with oral breathing, a simultaneous approach is required with the involvement of a full-time otolaryngologist at the medical center.

Assessing the Efficacy and Stability of Rapid Maxillary Expansion and the Delaire Appliance in Skeletal Class III Malocclusion: A Narrative Review

Background: A Class III skeletal malocclusion is a very complex condition in orthodontics practice, and its solution is often carried out orthopedically. The most used orthopedic devices include rapid maxillary expansion (RME) and the Delaire Appliances to treat not only maxillary deficiency but also to correct the position of the upper jaw. Even if these interventions become sustainable in the short term, their long-term stability remains questionable. Aim: reveal a pretty complicated relationship between orthopaedic and orthodontic surgeries and their influences on the volume of the upper respiratory tract and craniofacial correction. Methods: We searched multiple online databases including; Web of Science, Scopus, Google Scholar, PubMed, and Cochrane Library. We used the following search strategy; "Rapid maxillary expansion" OR RME AND ("sleep apnea" OR "sleep-disordered breathing" OR "sleep-related breathing disorders" OR "sleep apnea-hypopnea syndrome" OR SAHS) AND (children OR pediatric) AND ("orthodontic treatment" OR "orthopaedic treatment" OR "maxillary expansion") AND (oximetry OR polysomnography). Results: RME and the Delaire appliance were seen to be promising in the short term with an outcome of correction of maxillary transverse deficiency and skeletal relationships. Nevertheless, the issue of the long-term stability was spotted, including with regard to growth. But nevertheless both interventions exhibited some really valuable additions in general treatment of skeletal class III malocclusion. Scientific Novelty: This literature review synthesizes and summarizes the current knowledge on the effectiveness and durability of RME and the Delaire splint concerning skeletal class III malocclusion, presenting perspectives on their short-term impact and long-term performance. With its emphasis on poorly understood issues and new research, it greatly assists in updating our knowledge about orthopedic treatments. Conclusion: In a relatively short period of time, the rapid maxillary expansion method as well as the Delaire appliance can produce positive outcomes in terms of correcting the retroposition in cranial base class III malocclusion. Although, long lasting stability issues remain a worry and make the case for continued research and clinical monitoring for achieving better treatment outcomes and evidence-based practices in orthodontics.

Restoration of teeth lacking complete ferrules using cast precious metal alloy post-and-cores and knife-edged crowns: A retrospective clinical study

Statement of problemWhile the presence of a ferrule has been reported to be essential for post-and-core restorations, many extensively damaged teeth lack complete ferrules. The outcome of post-and-core restorations for these teeth remains uncertain. PurposeThe purpose of this retrospective clinical study was to assess the outcome of cast alloy post-and-cores and knife-edged crowns for the restoration of teeth lacking complete ferrules. Material and methodsA total of 106 participants with endodontically treated teeth with 2 or fewer walls with ferrules who had received cast precious metal alloy post-and-cores along with knife-edged crowns between 2013 and 2022 were recalled for a clinical examination. The minimum follow-up time was 5 months after restoration, and restoration failure and the periodontal status difference between restored teeth and reference teeth were determined. Kaplan-Meier analysis was performed to obtain success curves. The influence of age, sex, jaw position, tooth type, and antagonistic dentition upon the success function was analyzed with the log-rank or Breslow test (α=.05). ResultsA total of 100 participants with 130 restorations were studied. The success rate of the restorations was 93.85% in a mean ±standard deviation period of 48.3 ±26.1 months. The estimated 5-year cumulative success probability was 91.61%. No significant effect on the success of restorations was found regarding age, sex, jaw position, tooth type, or antagonistic dentition (P>.05). The main failure types were post debonding, root fracture, and apical periodontitis. No statistical difference in tooth mobility (Z=−1.265, P=.206) was found between the restored and the reference teeth, but the plaque index and calculus index of the restored teeth were significantly lower than of the reference teeth (Z=−7.216, P<.001; Z=−7.044, P<.001). Teeth that had received cast post-and-cores and knife-edged crowns were found to have no significant correlation with periodontal disease (χ²=1.131, P=.288) or bleeding on probing (χ²=3.436, P=.064). ConclusionsThe clinical outcomes for the restoration of teeth with 2 or fewer walls with ferrules using cast precious metal alloy post-and-cores and knife-edged crowns were favorable, exhibiting a high 5-year cumulative success probability and no increased periodontal health risk.

Analysis of the correlation between peri-implant probing depth and radiographic bone level

Objective: To evaluate the correlation between peri-implant probing depth (PPD) and radiographic bone level (rBL) in implants with peri-implantitis. Methods: From January 2019 to December 2022, 24 patients with 30 implants who suffered from peri-implantitis at the Department of Periodontology, Peking University School and Hospital of Stomatology were included in the present research. SPSS 26.0 software was used to simple random sampling select 30 healthy implants from which with electronic examination records in Department of Periodontology, Peking University School and Hospital of Stomatology from January 2007 to June 2023 as the control group. On the premise of retaining the implant prosthesis, PPD (distance between pocket bottom and peri-implant soft tissue margin) was examined using a Williams periodontal probe with a light force (about 0.2 N), and a total of 4 sites were recorded for each implant. Periapical radiography and cone beam CT were applied to measure the rBL (distance between the reference point at the neck of the implant and the apical point of the bone defect) and the width of the bone defect (DW), and the type of the bone defect was recorded. The correlation and consistency between the diagnosis of PPD and rBL were analyzed. Results: PPD was significantly correlated with rBL in a total of 60 implants in 180 sites (r=0.64, P<0.001). The chi-square test showed an 8.15-fold increase in the detection rate of PD≥6 mm at sites with rBL≥1 mm (P<0.001). Multivariate logistic regression analysis showed that rBL was still statistically associated with PPD after adjustment for jaw position and examination position of implants. Take rBL <1 mm as reference, the odds ratios (OR) of 1 mm≤rBL<2 mm, 2 mm≤rBL<3 mm and rBL≥3 mm group with PPD were 6.23 (P=0.014), 2.77 (P=0.183) and 10.87 (P=0.001), respectively. Conclusions: There is a positive correlation between PPD and rBL in implants with peri-implantitis. PPD can be used as a clinical examination index to assist in estimating the level of peri-implant bone under the premise of retaining the prosthesis.

A feasibility study to predict 3D dose delivery accuracy for IMRT using DenseNet with log files.

This study aims to explore the feasibility of DenseNet in the establishment of a three-dimensional (3D) gamma prediction model of IMRT based on the actual parameters recorded in the log files during delivery. A total of 55 IMRT plans (including 367 fields) were randomly selected. The gamma analysis was performed using gamma criteria of 3% /3 mm (Dose Difference/Distance to Agreement), 3% /2 mm, 2% /3 mm, and 2% /2 mm with a 10% dose threshold. In addition, the log files that recorded the gantry angle, monitor units (MU), multi-leaf collimator (MLC), and jaws position during delivery were collected. These log files were then converted to MU-weighted fluence maps as the input of DenseNet, gamma passing rates (GPRs) under four different gamma criteria as the output, and mean square errors (MSEs) as the loss function of this model. Under different gamma criteria, the accuracy of a 3D GPR prediction model decreased with the implementation of stricter gamma criteria. In the test set, the mean absolute error (MAE) of the prediction model under the gamma criteria of 3% /3 mm, 2% /3 mm, 3% /2 mm, and 2% /2 mm was 1.41, 1.44, 3.29, and 3.54, respectively; the root mean square error (RMSE) was 1.91, 1.85, 4.27, and 4.40, respectively; the Sr was 0.487, 0.554, 0.573, and 0.506, respectively. There was a correlation between predicted and measured GPRs (P < 0.01). Additionally, there was no significant difference in the accuracy between the validation set and the test set. The accuracy in the high GPR group was high, and the MAE in the high GPR group was smaller than that in the low GPR group under four different gamma criteria. In this study, a 3D GPR prediction model of patient-specific QA using DenseNet was established based on log files. As an auxiliary tool for 3D dose verification in IMRT, this model is expected to improve the accuracy and efficiency of dose validation.

Orthodontic treatment for prominent lower front teeth (Class III malocclusion) in children.

Orthodontic treatment for prominent lower front teeth (Class III malocclusion) in children.

Fully digital workflow of occlusal reconstruction treatment in a patient with congenital dentition defects.

Occlusal reconstruction is a critical intervention for patients with dental hard tissue defects, temporomandibular joint (TMJ) disorders, and jaw position abnormalities. Clinical efficiency and outcomes of these procedures have improved with advances in digital technologies. This case report aims to illustrate a comprehensive digital workflow for occlusal reconstruction in a patient with congenital dentition defects, emphasizing the application of digital technologies to enhance treatment outcomes. A 28-year-old woman with previously installed porcelain-fused-to-metal bridge restorations presented with a fractured prosthesis and TMJ symptoms. A multidisciplinary approach was adopted involving the use of digital facebow, intraoral scanners, digital smile design, and CAD/CAM technologies. The process included the extraction of defective restorations, temporary restorations to refine jaw position, and final permanent restorations. The digital workflow facilitated precise diagnostics and treatment, culminating in the successful installation of permanent restorations. Regular follow-ups at one- and three-months post-treatment confirmed stable occlusal function and high patient satisfaction. This case report showcases the potential of multiple digital technologies to streamline complex dental treatments and achieve high-quality results. The integration of digital technologies in occlusal reconstruction treatments offers significant benefits in terms of precision, patient comfort, and esthetic outcomes.

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

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). 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. 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. 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.

Long-term stability of jaw reconstruction with microvascular bone flaps: A prospective longitudinal study

ObjectivesMicrovascular bone flap jaw reconstruction has achieved satisfactory clinical outcomes. However, little is known about the long-term stability of the reconstructed jaw. This prospective longitudinal study aimed to investigate the long-term stability of jaw reconstruction and factors that were associated with it. MethodsPatients with successful computer-assisted osseous free-flap jaw reconstruction in the Department of Oral and Maxillofacial Surgery, Queen Mary Hospital, Hong Kong were recruited for this prospective longitudinal study. The three-dimensional jaw models at the pre-operative plan, post-operative 1-month, and 2 years were aligned and compared. ResultsA total of 69 patients were recruited, among which 48 patients were available for the long-term analysis. Compared to 1-month after surgery, further deviation from the pre-operative plan was observed at post-operative 2 years. Lack of accuracy in surgery, segmental mandible resection especially with the involvement of mandible angles, and post-operative radiation therapy were identified as the significant factors affecting the positional stability of the reconstructed jaw (p < 0.05). Stable reconstruction was observed in the subgroup analysis of patients without post-operative radiation therapy. ConclusionUp to the best of our knowledge, this is the first prospective longitudinal study reporting the long-term stability of jaw reconstruction and its affecting factors. Our data demonstrated that the reconstructed jaw position lacked stability over the postoperative period. How to improve long-term stability of reconstructed jaw thus optimize the functional outcomes warrants further studies.

Influence of oral motor tasks on postural muscle activity during dynamic reactive balance.

Jaw clenching improves dynamic reactive balance on an oscillating platform during forward acceleration and is associated with decreased mean sway speed of different body regions. It is suggested that jaw clenching as a concurrent muscle activity facilitates human motor excitability, increasing the neural drive to distal muscles. The underlying mechanism behind this phenomenon was studied based on leg and trunk muscle activity (iEMG) and co-contraction ratio (CCR). Forty-eight physically active and healthy adults were assigned to three groups, performing three oral motor tasks (jaw clenching, tongue pressing against the palate or habitual lower jaw position) during a dynamic one-legged stance reactive balance task on an oscillating platform. The iEMG and CCR of posture-relevant muscles and muscle pairs were analysed during platform forward acceleration. Tongue pressing caused an adjustment of co-contraction patterns of distal muscle groups based on changes in biomechanical coupling between the head and trunk during static balancing at the beginning of the experiment. Neither iEMG nor CCR measurement helped detect a general neuromuscular effect of jaw clenching on the dynamic reactive balance. The findings might indicate the existence of robust fixed patterns of rapid postural responses during the important initial phases of balance recovery.

A retrospective study of occlusal reconstruction in patients with old jaw fractures and dentition defects

PurposeThis study evaluated the methods and clinical effects of multidisciplinary collaborative treatment for occlusal reconstruction in patients with old jaw fractures and dentition defects. MethodsPatients with old jaw fractures and dentition defects who underwent occlusal reconstruction at the Third Affiliated Hospital of Air Force Military Medical University from January 2018 to December 2022 were enrolled. Clinical treatment was classified into 3 phases. In phase I, techniques such as orthognathic surgery, microsurgery, and distraction osteogenesis were employed to reconstruct the correct 3-dimensional (3D) jaw position relationship. In phase II, bone augmentation and soft tissue management techniques were utilized to address insufficient alveolar bone mass and poor gingival soft tissue conditions. In phase III, implant-supported overdentures or fixed dentures were used for occlusal reconstruction. A summary of treatment methods, clinical efficacy evaluation, comparative analysis of imageological examinations, and satisfaction questionnaire survey were utilized to evaluate the therapeutic efficacy in patients with traumatic old jaw fractures and dentition defects. All data are summarized using the arithmetic mean ± standard deviation and compared using independent sample t-tests. ResultsIn 15 patients with old jaw fractures and dentition defects (an average age of 32 years, ranging from 18 to 53 years), there were 7 cases of malocclusion of single maxillary fracture, 6 of malocclusion of single mandible fracture, and 2 of malocclusion of both maxillary and mandible fractures. There were 5 patients with single maxillary dentition defects, 2 with single mandibular dentition defects, and 8 with both maxillary and mandibular dentition defects. To reconstruct the correct 3D jaw positional relationship, 5 patients underwent Le Fort I osteotomy of the maxilla, 3 underwent bilateral sagittal split ramus osteotomy of the mandible, 4 underwent open reduction and internal fixation for old jaw fractures, 3 underwent temporomandibular joint surgery, and 4 underwent distraction osteogenesis. All patients underwent jawbone augmentation, of whom 4 patients underwent a free composite vascularized bone flap (26.66%) and the remaining patients underwent local alveolar bone augmentation. Free gingival graft and connective tissue graft were the main methods for soft tissue augmentation (73.33%).The 15 patients received 81 implants, of whom 11 patients received implant-supported fixed dentures and 4 received implant-supported removable dentures. The survival rate of all implants was 93.82%. The final imageological examination of 15 patients confirmed that the malocclusion was corrected, and the clinical treatment ultimately achieved occlusal function reconstruction. The patient satisfaction questionnaire survey showed that they were satisfied with the efficacy, phonetics, aesthetics, and comfort after treatment. ConclusionOcclusal reconstruction of old jaw fractures and dentition defects requires a phased sequential comprehensive treatment, consisting of 3D spatial jaw correction, alveolar bone augmentation and soft tissue augmentation, and implant-supported occlusal reconstruction, achieving satisfactory clinical therapeutic efficacy.

Evaluation of mandibular motion in adolescents with skeletal class II division 1 malocclusion during mandibular advancement using clear functional aligners: a prospective study

BackgroundThis study aimed to evaluate the characteristics of mandibular protrusive condylar trajectory in adolescents with skeletal Class II Division 1 malocclusion and the changes of condylar trajectory during mandibular advancement (MA) treatment using clear functional aligners.MethodsThis prospective study consisted of a cross-sectional study and a longitudinal study. In cross-sectional study, sixty-one adolescents were divided into two groups: Class I (n = 30) and Class II Division 1 (n = 31). The condylar trajectory was measured and compared using the Mann–Whitney U test. The longitudinal study was the MA treatment group using clear functional aligner and consisted of 16 participants from Class II Division 1group. The condylar trajectory was collected at three-time points: pre-treatment (T1), during MA treatment at approximately 3 months (T2, 105.6 days average), and at the end of MA treatment (T3, 237.6 days average). The changes at T1, T2, and T3, as well as the symmetry between the left and right condyles across all groups, were examined using the Wilcoxon paired test.ResultsA greater increase in the anteroposterior displacement and space displacement during protrusive movements was observed in the Class II Division 1 group compared with that in the Class I group, with a large difference being observed in the left and right condylar movements. The condylar anteroposterior displacement and space displacement decreased significantly at T2 and increased significantly at T3; however, no significant difference was observed between T1 and T3. A significant difference was observed between the condylar movement on the left and right sides at T1; however, no significant difference was observed at T2 and T3.ConclusionsAdolescents with Class II Division 1 malocclusion had higher protrusive capacity than those with Class I. Moreover, their left and right condylar motion was more asymmetric. The range of condyle motion decreased first and then increased during MA therapy, and the left and right condyle movement became more symmetrical, which may be the adaptive response of neuromuscular function to the changes in jaw position.

Reliability of landmark identification for analysis of the temporomandibular joint in real-time MRI

BackgroundReal-time magnetic resonance imaging (rtMRI) is essential for diagnosing and comprehending temporomandibular joint (TMJ) movements. Current methods for tracking and analysis require manual landmark placement on each acquisition frame. Therefore, our study aimed to assess the inter- and intra-rater reliability of placing cephalometric landmarks in frames from a dynamic real-time TMJ MRI.Material and methodsFour real-time MRIs of the right TMJ were taken during mandibular movement at ten frames per second. Seven dentists identified ten landmarks on two frames (intercuspal position—ICP—and maximum mouth opening—MMO) twice at a two-week interval, yielding 112 tracings. Six typical cephalometric measurements (angles and distances) were derived from these landmarks. The reliabilities of landmarks and measurements were evaluated using distance-based (dbICC), linear mixed effect model intraclass correlation (lmeICC), and standard ICC.ResultsThe average inter-rater reliability for the landmarks stood at 0.92 (dbICC) and 0.93 (lmeICC). The intra-rater reliability scores were 0.97 and 0.98. Over 80% of the landmarks showed an ICC greater than 0.98 (inter-rater) and over 0.99 (intra-rater). The lowest landmark ICC was observed for the orbitale and the oblique ridge of the mandibular ramus. However, the cephalometric angle and distance measurements derived from these landmarks showed only moderate to good reliability, whereas the reliability in the frames with ICP was better than those with MMO. Measurements performed in the ICP frame were more reliable than measurements in the MMO frame.ConclusionWhile dentists reliably localize isolated landmarks in real-time MRIs, the cephalometric measurements derived from them remain inconsistent. The better results in ICP than MMO are probably due to a more familiar jaw position. The higher error rate of the TMJ measurements in MMO could be associated with a lack of training in real-time MRI analysis in dentistry.

Analysis of hardware methods of treatment of patients with temporomandibular joint dysfunction

Objective. To conduct a comparative analysis of effectiveness of treatment of patients with dysfunction of temporomandibular joint (DTMJ) using hardware methods of treatment with occlusive mouthguards of various types. Materials and methods. 99 patients (88 females and 11 males aged 41,2 ± 10,7) with different combinations of revealed and confirmed signs of DTMJ were examined from 2013 to 2023. According to the personal clinical picture, complaints revealed, aetiology and pathogenesis of the disease all the patients of the comparison group and 2 main groups (99 patients) were administered individual complex treatment for DTMJ. The treatment was aimed at the elimination of pain, relief of masticatory muscles spasm, improvement of the extent of opening of mouth, correction of the lower jaw position, occlusive interference elimination and restoration of height of the lower third of the face. While carrying out the hardware treatment, occlusive mouthguards of 3 types were made based on the jaw model of the patients. The models were got from the silicone imprints of the jaw. Results. MR images of temporomandibular joints of the 99 patients showed that ventral dislocation of articular disk occurred most frequently (in 88 patients). Less frequently (4 % of cases) it was combined with dislocation of the disk laterally. Rarely distal dislocation of the articular disk occurred – 1,9 % of cases (2 patients). Study of the results of the appliance of different types of occlusive mouthguards demonstrates the necessity to work out the types of occlusive devices allowing decompression of temporomandibular joint elements, centering lower jaw position and orthodontic elimination of dentofacial abnormalities and deformities which lead to occlusive interference. Conclusions. Analysis of occlusive devices used in the diagnosis and treatment of patients with DTMJ shows that the most effective devices are those that successfully combine elements of splints with a narrower purpose.