Features in subjects with the frontal occlusal plane inclined toward the contralateral side of the mandibular deviation

Biomechanical analysis of stress distribution changes in the maxillomandibular complex following surgical correction for facial asymmetry with reverse occlusal cant: A pilot finite element study

The effect of surgical correction for facial asymmetry on stress distributions remains unclear, particularly in cases where the occlusal cant inclines toward the side opposite to the mandibular deviation (reverse occlusal cant). This pilot study aimed to investigate the biomechanical effects of surgical correction for reverse occlusal cant using finite element (FE) analysis. FE model of the maxillomandibular complex with a reverse occlusal cant inclined at 3-degree to the Frankfort horizontal plane was constructed. Surgical simulations using Le Fort I osteotomy and bilateral sagittal split ramus osteotomy were performed for cant corrections ranging from 0- to 5-degree in 1-degree increments. Stress analysis under masticatory loading was conducted, and von Mises stress distribution around the temporomandibular joint (TMJ) and occlusal surfaces was compared across models. Cant correction from 0- to 3-degree revealed a decreasing trend in stress around the TMJ, while from 3- to 5-degree resulted in an increasing trend. Conversely, stress on the occlusal surface showed an opposite pattern, with both increases and decreases inversely related to TMJ stress. The 3-degree correction model demonstrated the lowest stress and minimal left-right stress imbalance around the TMJ, while exhibiting the highest stress and the largest distribution area on the occlusal surface. These findings suggest that surgical cant correction significantly alters stress distribution around the TMJ and occlusal surfaces in patients with skeletal asymmetry and reverse occlusal cant.

Analysis of the Relationship Between Unilateral Posterior Crossbite and Alterations in the Eruptive Trajectory of Maxillary Canines, the Occlusal Plane, and the Inclination of the Labial Commissure

OBJECTIVES

The aim was to establish whether there is a relationship between the presence of unilateral posterior crossbite (u-PCB) and the mesio-distal inclination of permanent upper canines, the angulation of the occlusal plane, or the labial commissure inclination in children.

METHODS

A cross-sectional association study was conducted. Panoramic radiography was used to measure the inclination of the canines and the occlusal plane, and frontal rest photography was used to measure the inclination of the labial commissure. The measurements were performed with tpsDig264 software version 2.25, 2016, Ecology & Evolution, SUNY), and the data obtained were analyzed with SPSS 22.0 software, using ANOVA and Kruskal-Wallis tests for the statistical analysis.

RESULTS

A total of 106 patients with u-PCB and 41 patients in the control group were studied. No statistically significant differences were observed in the inclination of the right and left canines in patients with u-PCB compared to patients in the control group. There is a relationship between the presence of u-PCB and the inclination of the occlusal plane. No statistically significant differences were observed in the inclination of the labial commissure in patients with u-PCB compared to patients in the control group.

CONCLUSIONS

There is no relationship between the presence of u-PCB and the alteration in the eruptive trajectory of the permanent upper canines or in the inclination of the labial commissure. However, a relationship between the presence of u-PCB and altered occlusal plane inclination was found.

Correlation Between Facial Asymmetry and Maxillary Sinus Size or Volume Using Dental Cone-Beam Computed Tomography Images

Objectives This study investigated correlations between facial asymmetry and left-right differences in maxillary sinus size and volume, as well as their relationships with skeletal morphology. Methods The participants were 154 Japanese adults (56 men, 98 women) aged 18 to 38 years (mean age, 24.1 ± 5.3 years). Cone-beam computed tomography (CBCT) images were analyzed using InVivo™ 6 software (Anatomage, Inc., San Jose, CA, USA). Facial asymmetry was assessed at six landmarks: orbitale, condylion, and gonion (all bilateral); anterior nasal spine; deepest point in bony concavity (B point); and menton (at midline). Maxillary sinus height, width, length, and volume were measured. Participants were classified into skeletal classes (I, II, III) and vertical growth patterns (horizontal, average, vertical). Spearman's rank correlation coefficient was used to assess the relationships of these six facial asymmetry landmarks with differences in maxillary sinus linear measurements and volume. Results The facial asymmetry index was positively correlated with maxillary sinus length in the condylion region and height in the gonion region. As left-sided facial deviation increased, the right maxillary sinus became larger; conversely, as right-sided facial deviation increased, the left maxillary sinus became larger. Thus, the maxillary sinus on the nondeviated side tends to be larger. Vertical facial growth patterns showed greater maxillary sinus height and volume in the vertical growth group than in the average growth group. Conclusions Asymmetry in specific facial regions may be associated with region-specific variations in maxillary sinus morphology, and vertical skeletal patterns may influence maxillary sinus development. These findings offer insights into the relationship between facial asymmetry and maxillary sinus structure.

Differential outcomes of jaw bone position after surgical-orthodontic treatment in three types of skeletal Class III asymmetry patients

BACKGROUND/PURPOSE

Facial asymmetry is common in Class III patients requiring orthognathic surgery. This study aimed to analyze jaw bone position after surgical-orthodontic treatment in three types of skeletal Class III asymmetry patients.

METHODS

The retrospective study included 30 Class III patients who underwent surgical-orthodontic treatment comprising LeFort I osteotomy and bilateral sagittal split osteotomy (BSSO) without genioplasty. Cone-beam computed tomography (CBCT) images obtained before surgery (T1) and after post-surgical orthodontic treatment (T2) were superimposed with voxel-based registration. Patients were classified into three groups based on T1 CBCT scans. Groups 1 and 2 exhibited menton and ramus deviated to the same side. Menton deviation was larger than ramus width asymmetry in group 1, while the reverse was true for group 2. Group 3 had menton deviation contralateral to the side with greater ramus width.

RESULTS

Menton deviation after treatment was improved in all groups. Ramus width asymmetry and coronal ramus angle difference decreased in groups 1 and 2. Neither improvement nor deterioration of ramus width asymmetry was noted for group 3. Comparing to groups 1 and 2, group 3 had greater roll and yaw rotations of distal segment, more upward pitch of proximal segment on chin deviation side, and largest inward yaw as well as backward translation of proximal segment on non-deviation side.

CONCLUSION

The positional changes of osteotomy segments differed among three types of mandibular asymmetry. Special attention should be given to the atypical mandibular asymmetry with mandibular body and ramus deviating to opposite directions during surgical correction of jaw deflection.

Selected muscle tone and asymmetry of the occlusal plane in case of intracapsular temporomandibular joint disorder

Objective: To discover the extent of the connection between occlusal plane asymmetry and the rest tone of the four muscle groups of the orofacial region with temporomandibular joint pathology.Methods: Eighty-seven subjects were divided into two groups. The following methods were applied: clinical examination, roentgenological examination, and electromyography. Data were evaluated and statistically analyzed.Results: The variability of occlusal plane inclination in relation to the porion plane was 0-4.6º.The tonus of masseter muscle was higher in the experimental group: 1.45 mV more than in the control group: 1.23 mV (p < 0.05).Conclusion: Asymmetry of the occlusal plane inclination was found for nearly all subjects in both groups. It can be compensated for by adaptation mechanisms and does not cause temporomandibular joint disorders. Undertaken research shows the existence of a proven correlation between TMJ disorders and the resting tonus of the masseter muscle.

Occlusal function and electromyographic activity of masticatory muscles in skeletal Class III patients with different patterns of mandibular asymmetry

BACKGROUND

Although jaw asymmetry is commonly seen in skeletal Class III patients, its correlation with occlusal function and masticatory muscle activity has not been fully elucidated.

OBJECTIVES

The purpose of this study was to investigate the occlusal function and masticatory muscle activity in skeletal Class III patients with various patterns of mandibular asymmetry.

METHODS

Forty-two patients and 10 normal participants were examined. The patients were categorised into three groups. Groups 1 and 2 exhibited menton and ramus deviation to the same side. Menton deviation was larger than ramus deviation in Group 1, whereas Group 2 showed the inverse relation. Group 3 patients showed menton and ramus deviation in opposite directions. Occlusal contact area (OCA), relative bite force (RBF), and temporalis anterior (TA) and masseter muscle (MM) activity at maximum clenching were measured using T-Scan Novus system and Bio-EMG-III. Statistical analysis was performed using the t-test, one-way analysis of variance with Bonferroni correction and Spearman correlation (α = .05).

RESULTS

Compared with normal participants, the patients had smaller OCA and greater asymmetry in the distribution of masticatory muscle activity. Greater ramus deviation was associated with smaller OCA in Group 1 but with larger OCA in Group 3. In Group 1, greater menton deviation was related to stronger TA activity on the non-deviation side. In Group 2, greater ramus deviation was related to stronger MM activity on the deviation side.

CONCLUSION

Deviation of the menton and ramus was individually related to OCA and masticatory muscle activity, and this relationship varied according to the pattern of mandibular asymmetry.

The Law of Minimum Vertical Dimension: Evidence for Improvement of Dental Occlusion

The law of minimum vertical dimension (MVD) states that “when the mandible moves to reach the maximum intercuspal position, this always involves bringing the mandible and maxilla as close together as possible.” Therefore, after the first occlusal contact is made, the MIP will be reached through reduction of the vertical dimension. Our objective of this study, through an integrative review of the literature review, was to determine whether ignoring this law is a factor that contributes to malocclusion, temporomandibular joint dysfunction, and recurrences of functional orthodontic and orthopedic treatments.We conducted a search of the literature in five of the main electronic scientific databases. The following medical subject heading terms were used in our search: centric relation, dental occlusion, malocclusion, vertical dimension, and mastication. We cross-referenced the descriptors in the following four groups: centric relation and maximum intercuspation; occlusal plane and malocclusion; neuro-occlusal rehabilitation; and vertical dimension and unilateral chewing. From this, we selected 277 potentially eligible articles. Out of these, 209 were excluded in accordance with the exclusion criteria already described. Thus, 65 studies were included in the qualitative synthesis.The articles were also classified according to their impact factor and degree of recommendation, in conformity with the table of the Oxford Centre for Evidence-Based Medicine. The scientific interest in the scope of the articles was also assessed by using three charts developed according to year and country of publication and the percentage of publication. Unilateral chewing creates a vicious cycle of damage that leads to an ever-increasing masticatory deficiency. Most of the articles chosen for this review confirmed that noncompliance with law of MVD was a predisposing factor in cases of relapse, in functional orthodontic and orthopedic treatments, as well as a causal factor in malocclusion and in functional and morphological TMJ dysfunctions.

Effects of Palatal Expansion with Torque Activation using a Transpalatal Arch: A Preliminary Single-Blind Randomized Clinical Trial

Purpose

The literature regarding the treatment of posterior crossbites using a transpalatal arch (TPA) is scarce. Moreover, there is only one clinical study on the correction of unilateral crossbites using torque activation. This is an important clinical issue; therefore, this study was conducted to show the effects of an active Goshgarian TPA in correcting nonfunctional single-tooth unilateral crossbite.

Methods

The present single-blind, randomized clinical trial examined 60 observations on 30 individuals with nonfunctional single-tooth unilateral crossbites in the first permanent molar area. Patients were randomly divided into two groups of "symmetric expansion" [control] and "expansion + torque activation" using Goshgarian TPAs [experimental]. The palatal arch was expanded at a rate of 2 mm/month, for 2-8 months. The average treatment durations were 157.9 and 117.1 days, respectively, for the control and experimental groups. Dentoskeletal alterations were assessed on dental records, posteroanterior frontal cephalographs, and occlusal radiographs taken before and after treatment. Changes induced by treatments in each group and differences between changes in both groups were analyzed statistically (α = 0.05).

Results

The treatment duration was significantly shorter in the experimental group (P < 0.05). The extent of dental displacement on the crossbite side was significant no matter what treatment was applied (P < 0.001); no between-group difference was detected (P > 0.05). Both treatments tilted the teeth in crossbite (P < 0.001) without any between-group difference (P > 0.05). The noncrossbite molar was displaced in the control group, whereas this did not occur in the experimental group (between-group P < 0.001).

Conclusions

The Goshgarian TPA can be used with torque activation in order to deliver a more effective and faster correction of nonfunctional single-tooth unilateral crossbites with more favorable clinical results.

Comparison of maxillomandibular asymmetries in adult patients presenting different sagittal jaw relationships

OBJECTIVE

The present study aims at using cone beam computed tomography (CBCT) to analyze the maxillomandibular characteristics present in adults with mandibular asymmetries and different sagittal jaw relationships.

METHODS

360 patients were selected and divided into three groups (Class I, Class II, and Class III), with 120 individuals per group. The groups were then subdivided according to the intensity of lateral deviation of the gnathion point, into: 1) relative symmetry, 2) moderate asymmetry, and 3) severe asymmetry. Three planes of reference were established in the CBCT images and several measurements were taken to compare the bilateral skeletal differences between the intensities of asymmetry for the different sagittal jaw relationships.

RESULTS

When the groups were compared by the intensity of asymmetry, significant differences among patients with relative symmetry and moderate to severe asymmetry were found. This was especially noticed for severe asymmetry, suggesting that the deviation of the chin did not constitute the only morphological alteration for these patients, especially because a series of measurements showed significant bilateral differences. When comparing sagittal jaw relationships, the only significant finding was the vertical positioning of the gonion between Class II and III patients with severe asymmetry.

CONCLUSIONS

When comparing the three sagittal jaw relationships with the same intensity of asymmetry, most maxillofacial aspects were quite similar. The only difference was found for patients with severe asymmetry, as the individuals with Class II showed greater bilateral difference in the vertical positioning of the gonion, when compared to patients with Class III.

Compensatory dentoalveolar supraeruption and occlusal plane cant after botulinum-induced hypotrophy of masticatory closing muscles in juvenile rats

OBJECTIVE

The purpose of this study was to investigate changes in the dentoalveolus and occlusal plane associated with the hypotrophy of unilateral masticatory muscles following botulinum toxin (BTX) treatment in the juvenile period of rats.

DESIGN

We hypothesized that the loss of functional loading of masticatory muscles and occlusal force invites compensatory dentoalveolar supraeruption, accelerating occlusal cant and skeletal asymmetry. In order to confirm this hypothesis, six-week-old male rats (N = 5) were treated with BTX simultaneously at the unilateral masseter, temporalis, and medial pterygoid muscles, with a booster injection after six weeks for the experimental group. The control group (N = 6) had saline injections on both sides at the same sites and on the same schedule.

RESULTS

After 12 weeks, masseter and medial pterygoid muscles on the BTX side showed hypotrophic change. The mandibular structure was asymmetrical, with decreased size and lateral tilting. The maxillary and mandibular molars were supraerupted from the Frankfort plane or mandibular inferior border with lateral tilt. They accompanied downward occlusal plane cant resulting from the supraerupted maxillary and mandibular molars on the BTX side. The dentoalveolar structural changes included diminished alveolar bone density, narrow periodontal ligament space, and disorganized distribution of periodontal collagen fiber.

CONCLUSIONS

Unilateral hypotrophy of masticatory muscles affected the growth, symmetry, and structure of the skeletal jaws and dentoalveolus. Our hypothesis about the dentoalveolar compensation, that muscular hypotrophy was closely integrated with dentoalveolar supraeruption and an inclined occlusal plane, was confirmed.

Diagnosis and Surgical Outcomes of Facial Asymmetry According to the Occlusal Cant and Menton Deviation

PURPOSE

Morphologic differences and surgical outcomes were compared between the ipsilateral type of facial asymmetry, in which the menton deviates to the side of the upward frontal occlusal plane (FOP) cant (FOP_UP), and the contralateral type, in which the menton deviates to the side of the downward FOP cant (FOP_DOWN), by using cone beam computed tomography (CBCT) images.

MATERIALS AND METHODS

This retrospective study included consecutive patients with skeletal Class III malocclusion and facial asymmetry who had undergone bimaxillary orthognathic surgery and serial CBCT before, 1 month after, and 1 year after surgery. CBCT images were reconstructed and analyzed for predictor (group and timing) and outcome (CBCT measurements over time) variables. The data were analyzed using independent t tests and paired t tests.

RESULTS

The contralateral group (n = 12) was selected first; the ipsilateral group (n = 12) was selected by matching age, gender, and degree of FOP cant with those of the contralateral group. Before surgery, in the ipsilateral group, the ramal length was longer on the nondeviated (N-Dev) side than on the deviated (Dev) side (P < .05) whereas the mandibular body length showed no significant difference (P > .05). In the contralateral group, the ramal length was longer on the Dev side (P < .05) whereas the mandibular body length was longer on the N-Dev side (P < .01). One year after surgery, most measurements were corrected symmetrically in both groups (P > .05); however, the hemi-lower facial area remained asymmetrical in the contralateral group (P < .05).

CONCLUSIONS

Differences in ramal lengths in the ipsilateral group and mandibular body lengths in the contralateral group between the Dev and N-Dev sides seemed to be the main cause of facial asymmetry. Although facial asymmetry improved after surgery in both groups, asymmetry in the soft tissue remained in the contralateral group 1 year after surgery.

[Mandibular asymmetry: determination of a reliable skin measurement technique]

INTRODUCTION

Clinical measurements in the frontal view underevaluate chin deviation in mandibular asymmetry. The aim of this descriptive study is to search for a reliable method of measuring deviant chins using a facial X-ray as reference.

MATERIAL AND METHOD

Seventy patients with mandibular asymmetry who had consulted a maxillofacial surgeon were systematically included. Age, sex, cephalometric characteristics, reasons for patient consultation and type of surgery were collected. Two cephalometric methods were tested with respect to the medial sagittal plane (PSM) to compare the assessment of mandibular asymmetry on soft tissue and by cephalometry.

RESULTS

On average, the patients selected were young (26 years +/- 9), women (75% of cases), presented open bite (average FMA: 28° +/- 8°), a skeletal class III tendency, a left-side shift of the chin (63% of cases). They consulted for both aesthetic and functional reasons (51% of cases) and required bimaxillary surgery (66% of cases). Comparison between the photographic angle (formed by the PSM and the line passing through the nasion and reaching the chin point) and the radiographic angle (formed by the PSM and the line passing through the Crista Galli process and the bony chin point angle) showed no significant difference (p = 0.937) and is thus reliable.

A patient with mandibular deviation and 3 mandibular incisors treated with asymmetrically bent improved superelastic nickel-titanium alloy wires

Skeletal and dental discrepancies cause asymmetric malocclusions in orthodontic patients. It is difficult to achieve adequate functional occlusion and guidance in patients with congenital absence of a mandibular incisor due to the tooth-size discrepancy. Here, we describe the orthodontic treatment of a 22-year-old woman with an asymmetric Angle Class II malocclusion, mandibular deviation to the left, and 3 mandibular incisors. The anterior teeth and maxillary canines were crowded. We used an improved superelastic nickel-titanium alloy wire (Tomy International, Tokyo, Japan) to compensate for the asymmetric mandibular arch and an asymmetrically bent archwire to move the maxillary molars distally. A skeletal anchorage system provided traction for intermaxillary elastics, and extractions were not needed. We alleviated the crowding and created an ideal occlusion with proper overjet, overbite, and anterior guidance with Class I canine and molar relationships. This method of treatment with an asymmetrically bent nickel-titanium alloy wire provided proper Class I occlusion and anterior guidance despite the mandibular deviation to the left and 3 mandibular incisors, without the need for extractions.

Relationship between molar occlusion and masticatory movement in lateral deviation of the mandible

INTRODUCTION

The relationship between molar occlusion and chewing patterns was examined in subjects with laterally deviated mandibles.

METHODS

Twenty-three patients with mandibular deviation from the midline (4 mm or more) and skeletal Class I (0° ≤ANB ≤4°) were divided into 2 groups: normal bite and crossbite. The chewing pattern was classified as normal, reversed, or crossover.

RESULTS

The normal bite group had a normal chewing pattern on the affected side 100% of the time and a reversed chewing pattern on the affected and unaffected sides 0% and 7.2% of the time, respectively. Additionally, the normal bite group showed no evidence of a crossover chewing pattern and also had significantly less axial inclination of the mandibular teeth on the affected side compared with the crossbite group; lingual inclination was also evident. The crossbite group had a normal chewing pattern on the affected and unaffected sides 0% and 55.6% of the time, respectively, and reversed and crossover chewing patterns on the affected side 55.6% and 44.4% of the time, respectively.

CONCLUSIONS

A normal chewing pattern tends to result in lingual axial inclination of the mandibular molars on the affected side, as well as a more consistent chewing pattern.

Prevalence and Associated Factors of Mandibular Asymmetry in an Adult Population

BACKGROUND

This study aimed to estimate the prevalence of mandibular asymmetry and investigate some associated factors.

METHODS

Tomographic images of 952 individuals aged from 18 to 75 years old were analyzed. The investigated outcome was mandibular asymmetry. The explanatory variables included gender, age, absence of posterior teeth, and sagittal jaw relationship of the individuals. Statistical analyses included the chi-squared and the Poisson regression with robust variance.

RESULTS

Mandibular asymmetry was present in 17.4% of the sample (95% confidence interval 15.2-20.0). In the bivariate analysis, there was an association between the variables age and sagittal jaw relationship with mandibular asymmetry (P = 0.026 and P = 0.018, respectively). However, in the adjusted regression model, the association with age was not maintained, occurring only an association between sagittal jaw relationship and mandibular asymmetry (P = 0.045), with significant difference between individuals with skeletal Class II and skeletal Class III (P = 0.013).

CONCLUSION

Mandibular asymmetry was not independently associated with sex, age, or absence of posterior teeth. The only verified independent association was between mandibular asymmetry and sagittal jaw relationship.