Midline Symmetry Research Articles

Convolutional Neural Networks and Geometric Moments to Identify the Bilateral Symmetric Midplane in Facial Skeletons from CT Scans.

Simple SummaryThe bilateral symmetry midplane of the facial skeleton plays a critical role in reconstructive craniofacial surgery. By accurately locating the midplane, surgeons can use the undeformed side of the face as a template for the malformed side. However, the location of the midline is still a subjective procedure, despite its importance. This study aimed to present a 3D technique for automatically calculating the craniofacial symmetry midline of the facial skeleton from CT scans using deep learning techniques. A total of 195 skull images were evaluated and were found to be reliable and provided good accuracy in symmetric images.In reconstructive craniofacial surgery, the bilateral symmetry of the midplane of the facial skeleton plays an important role in surgical planning. Surgeons can take advantage of the intact side of the face as a template for the malformed side by accurately locating the midplane to assist in the preparation of the surgical procedure. However, despite its importance, the location of the midline is still a subjective procedure. The aim of this study was to present a 3D technique using a convolutional neural network and geometric moments to automatically calculate the craniofacial midline symmetry of the facial skeleton from CT scans. To perform this task, a total of 195 skull images were assessed to validate the proposed technique. In the symmetry planes, the technique was found to be reliable and provided good accuracy. However, further investigations to improve the results of asymmetric images may be carried out.

Implementation of a self-consistent slab model of bilayer structure in the SasView suite.

Slab models are simple and useful structural descriptions which have long been used to describe lyotropic lamellar phases, such as lipid bilayers. Typically, slab models assume a midline symmetry and break a bilayer structure into three pieces, a central solvent-free core and two symmetric outer layers composed of the soluble portion of the amphiphile and associated solvent. This breakdown matches reasonably well to the distribution of neutron scattering length density and therefore is a convenient and common approach for the treatment of small-angle scattering data. Here, an implementation of this model within the SasView software suite is reported. The implementation is intended to provide physical consistency through the area per amphiphile molecule and number of solvent molecules included within the solvent-exposed outer layer. The proper use of this model requires knowledge of (or good estimates for) the amphiphile and solvent molecule volume and atomic composition, ultimately providing a self-consistent data treatment with only two free parameters: the lateral area per amphiphile molecule and the number of solvent molecules included in the outer region per amphiphile molecule. The use of this code is demonstrated in the fitting of standard lipid bilayer data sets, obtaining structural parameters consistent with prior literature and illustrating the typical and ideal cases of fitting for neutron scattering data obtained using single or multiple contrast conditions. While demonstrated here for lipid bilayers, this model is intended for general application to block copolymers, surfactants, and other lyotropic lamellar phase structures for which a slab model is able to reasonably estimate the neutron scattering length density/electron-density profile of inner and outer layers of the lamellae.

Clinical study of concealed penis correction surgery based on principle of midline symmetry

To investigate the effectiveness of concealed penis correction surgery based on the principle of midline symmetry. Between January 2016 and September 2018, 18 children with concealed penis were treated with correction surgery based on the principle of midline symmetry. All children were 3-12 years old, with an average age of 8.3 years. Physical examination showed that the penis was short; the penis body could not be exposed or be exposed too limited; the corpus cavernosum developed well. The pressure dressing was removed at 3 days after operation and the urethral tube was removed. The color of the glans, the swelling and congestion of penis and scrotum, and the blood supple of the prepuce flap were observed. The operation time ranged from 47 to 54 minutes, with an average of 50 minutes. All children were followed up 3 months after operation. There was no hemorrhage and necrosis of the glans and no infection or ischemic necrosis of the flap. All patients had different degree of prepuce edema at 3 days after operation, 5 patients still had prepuce edema at 2 weeks, and the prepuce edema in all patients subsided at 3 months. All penises were exposed well after midline symmetric anastomosis with no bulky prepuce and scrotum. The correction surgery based on the principle of midline symmetry can be used to correct the appearance of the concealed penis effectively.

Outcomes of conventional versus virtual surgical planning of orthognathic surgery using surgery-first approach for class III asymmetry.

To determine if patient outcome variables differ between conventional and virtual surgical planning of orthognathic surgery for class III asymmetry. This retrospective case-control study examined 95 patients with class III asymmetry who had been consecutively treated with at least a Le Fort I osteotomy and a bilateral sagittal split osteotomy with a surgery-first approach. Two groups were examined: 51 patients treated with conventional surgical planning and 44 with virtual surgical planning. After treatment, quantitative assessment was determined with measurements of midline symmetry, contour symmetry, and overall facial symmetry using standardized frontal photographs. Subject assessments were analyzed with questionnaires regarding self-perception of overall appearance, satisfaction with appearance, and quality of life. Conventional and virtual surgical planning resulted in significant improvements in outcomes for all patients. However, facial midline and overall facial symmetry were significantly greater for the virtual compared with the conventional group. There were no significant differences in subjective measures of appearance, satisfaction with appearance, and quality of life for patients treated with conventional or virtual surgical planning; measures were high for both groups. Conventional and virtual surgical planning of surgery-first bimaxillary orthognathic surgery resulted in quantitative and qualitative improvements in facial symmetry. Although patient satisfaction was similar for both approaches, virtual surgical planning was superior to conventional surgical planning for the improvement of midline and overall asymmetry. Improvements with virtual surgical planning in facial midline, facial contour, and overall facial symmetry are as good as or better than conventional surgical planning.

Test of a relationship between spatial working memory and perception of symmetry axes in children 3 to 6 years of age

ABSTRACTChildren’s memory responses to a target location in a homogenous space change from being biased toward the midline of the space to being biased away. According to Dynamic Field Theory (DFT), improvement in the perception of the midline symmetry axis contributes to this transition. Simulations of DFT using a 3-year-old parameter setting showed that memory biases at intermediate target locations were related to the perception of midline. Empirical results indicated that better perception of midline was associated with greater memory biases away at the 20° and 40° targets in 3-year-olds, and greater biases away at 60º in 4- to 6-year-olds. Findings support the DFT in that perception of midline is associated with memory biases.

Smile Aesthetics among Late Adolescents: Perspective of Adolescents, General Dentists and Orthodontists

Introduction: An adolescent’s personal experiences, peer influences and social environment can affect their preference towards smile aesthetics and have influence apart from the opinion of their orthodontists. Aim: To evaluate and compare the preferences regarding smile arc, gingival display, midline symmetry, shape and size of incisor teeth, buccal corridor space and smile index of adolescent subjects between late adolescents, general dentists and orthodontists. Materials and Methods: A total of 52 orthodontists, 111 general dentists and 275 adolescents (156 females, 119 males) had participated in this cross-sectional study from 1st September 2019 to 31st January 2020. Each participant was shown a photo album consisting of 5 sets of photographs of male and female adolescent subjects and was asked to rate them on 7 selected variables. The data obtained was subjected to comparison between the groups using Chi-square test. Results: While assessing smile of the female subject, other than the incisal edge position, the intergroup comparisons of gingival display (p=0.0001), midline symmetry (p=0.0001), shape of incisor teeth (p-value=0.0001), buccal corridor space (p=0.001), ratio of central: lateral incisor (p=0.016) and smile index (p=0.0001) were statistically significant. While assessing smile of the male subject, the intergroup comparisons of incisal edge position (p=0.0001), gingival display (p=0.001), midline symmetry (p=0.007), shape of incisor teeth (p-value=0.0001), buccal corridor space (p=0.0001), ratio of central: lateral incisor (p=0.0001) and smile index (p=0.0001) were statistically significant. Orthodontists’ accepted gingival display of 0-2 mm, midline deviation up to 2 mm and buccal corridor space of upto 5 mm and upto 25% increase in smile index in both genders. Conclusion: The Orthodontists and dentists have more similarities than differences in comparison to adolescents with respect to the smile preferences of adolescent subjects.

Long-term outcomes of bimaxillary surgery for treatment of asymmetric skeletal class III deformity using surgery-first approach.

Although several studies have reported the advantages of the surgery-first approach for orthognathic correction of Class III deformity, there are few reports of the success of this approach for patients with facial asymmetry. Therefore, the purpose of this study was to evaluate the outcome of bimaxillary surgery for asymmetric skeletal Class III deformity using a surgery-first approach. Sixty-five patients who consecutively underwent at least a combined Le Fort I and a bilateral sagittal split osteotomy for asymmetric skeletal Class III deformity were identified in the authors' patient database. Standardized frontal photographs were used to measure the change in midface, intercommissural line, chin from midface, and chin deviation angles as well as upper, middle, and lower contour deviation angles. The facial midline symmetry index, facial contour symmetry index, and overall facial symmetry index were also calculated. Self-reported questionnaires regarding overall appearance and satisfaction with facial areas were administered at least 1year post-surgery. Forty-six patients had genioplasty. There was a statistically significant improvement in the deviation angles measured and the facial midline, facial contour, and overall facial symmetry index. Self-reported questionnaires, completed at least 1year post-surgery, showed that patient satisfaction was high. These findings demonstrate that the surgical-orthodontic treatment with surgery-first approach can successfully maintain or improve facial symmetry. The surgery-first approach for improving facial asymmetry using the guidelines described for setups of the models is a feasible alternative to the classic orthodontic-first approach for bimaxillary orthognathic surgery.

Comparison of extraction versus non-extraction orthodontic treatment outcomes for borderline cases in the Indian population

Introduction: The purpose of this study was to assess orthodontic treatment outcomes in Indian patients with borderline problems treated with and without extractions. Methods: Records of 25 borderline patients treated at the Orthodontic & Dentofacial Orthopaedics Department M.A. Rangoonwala Dental College, Pune were evaluated retrospectively by 5 associate professors. Each judge evaluated the post-treatment records independently for tooth alignment, overbite, overjet, midline symmetry, lateral occlusion, and facial profile, and rated them on a scale from 1 to 5. Results: The only statistically significant difference between the extraction and non-extraction groups was for facial profile, with the judges preferring the extraction profiles. When profile changes from pretreatment to post-treatment were examined, significant differences in treatment-associated changes between extraction and non-extraction groups were all related to the lower lip and chin. Conclusions: In this sample of Indian borderline orthodontic patients, these clinicians had a statistically significant preference for the facial profiles of the extraction patients, but no statistically significant preferences for tooth alignment, overbite, overjet, midline symmetry, or posterior occlusion. Keyword: Borderline patients, Extraction, Non-extraction, Facial profiles

Hydrogel spacer distribution within the perirectal space in patients undergoing radiotherapy for prostate cancer: Impact of spacer symmetry on rectal dose reduction and the clinical consequences of hydrogel infiltration into the rectal wall

PurposeHydrogel prostate-rectum spacers, biomaterials placed between the prostate and rectum, continue to gain interest as a method to reduce or limit rectal dose during dose escalated prostate cancer radiation therapy. Because the spacer is initially injected into the perirectal space as a liquid, the final distribution can vary. The purpose of this study was to evaluate hydrogel spacer (SpaceOAR system) implantation and distribution from a recent prospective randomized control trial and correlate spacer symmetry with rectal dose reduction as well as rectal wall infiltration (RWI) to acute and late toxicity. Methods and materialsT2-weighted magnetic resonance imaging sets of 149 patients enrolled in a prospective clinical trial who received transperineal spacer injection were assessed for hydrogel spacer midline symmetry and RWI using a semiqualitative scoring system. Symmetry was then correlated to rectal dose reduction using a Student t test (1-tailed, paired), whereas a Fisher exact test was used to correlate RWI with acute and late rectal toxicity. All patients had control treatment plans created before spacer injection. ResultsHydrogel spacer was symmetrically placed at midline for 71 (47.7%) patients at the prostate midgland as well as 1 cm superior and inferior to midgland. The remaining 78 (50.9%) patients had some level of asymmetry, with only 2 (1.3%) having far lateral distribution (ie, >2 cm) of hydrogel spacer. As the hydrogel spacer became more asymmetric, the level of rectal dose reduction relative to their control plans decreased. However, all but the most asymmetrical 1.3% had significant rectal dose reduction (P < .05). Rectal wall hydrogel spacer infiltration was seen in 9 (6.0%) patients. There was no correlation between RWI and procedure-related adverse events or acute/late rectal toxicity. ConclusionsSignificant reduction of rectal dose can still be achieved even in the setting of asymmetric hydrogel spacer placement. RWI does not correlate with patient complications.

Reliability of CBCT in the diagnosis of dental asymmetry.

ObjectiveThe aim of this study was to validate a method used to assess dental asymmetry, in relation to the skeletal midline, by means of CBCT.MethodsTen patients who had CBCT scans taken were randomly selected for this study. Five different observers repeated 10 landmarks (x, y and z variables for each) and 12 linear measurements within 10 days. Measurements were taken in both arches to evaluate symmetry of first molars, canines and dental midline in relation to the skeletal midline. Intraclass correlation coefficient (ICC) was carried out to assess intra- and interobserver reliability for landmarks and distances. Average mean difference was also assessed to check measurement errors between observers.ResultsICC landmarks was ≥ 0.9 for 27 (90%) and 25 (83%) variables for intra- and interobserver, respectively. ICC for distances was ≥ 0.9 for 7 (58%) and 5 (42%), respectively. All ICC landmarks for distances were >0.75 for both intra- and interobserver. The mean difference between observers was ≤ 0.6 mm for all the distances.ConclusionThe method used to assess dental asymmetry by means of CBCT is valid. Measurements of molars, canines and dental midline symmetry with the skeletal midline are reproducible and reliable when taken by means of CBCT and by different operators.

The relationship between the perception of axes of symmetry and spatial memory during early childhood

Early in development, there is a transition in spatial working memory (SWM). When remembering a location in a homogeneous space (e.g., in a sandbox), young children are biased toward the midline symmetry axis of the space. Over development, a transition occurs that leads to older children being biased away from midline. The dynamic field theory (DFT) explains this transition in biases as being caused by a change in the precision of neural interaction in SWM and improvements in the perception of midline. According to the DFT, young children perceive midline, but there is a quantitative improvement in the perception of midline over development. In the experiment reported here, children and adults needed to determine on which half of a large monitor a target was located. In support of the DFT, even the youngest children performed above chance at most locations, but performance also improved gradually with age.

Single-Splint Technique in Orthognathic Surgery: Intraoperative Checkpoints to Control Facial Symmetry

Despite the most meticulous preoperative planning and execution, intraoperative soft-tissue response to dentoskeletal changes is often different from those statistically predicted, especially when midline asymmetry is present. A "single-splint" technique for bimaxillary surgery, with intraoperative adjustments and checkpoints, was developed in an attempt to overcome these limitations. The purpose of this study was therefore to determine whether this technique can improve the midline symmetry of facial soft tissues. Forty-five patients who underwent at least a Le Fort I and a bilateral sagittal split osteotomy of the mandible were identified in the authors' patient database. Standardized frontal photographs were used to measure the change in midfacial, intercommissural, chin to midface, and chin to ideal facial midline angles. The facial midline symmetry index, an overall score of facial symmetry, was also calculated. This study demonstrates that there is a statistically significant improvement of the four angles measured and of the facial midline symmetry index. These findings demonstrate that the single-splint technique with its intraoperative checkpoints can successfully maintain or improve facial midline symmetry. Thus, the single-splint technique is a useful alternative to the classic two-splint technique for bimaxillary surgery.

Symmetry, probability, and recognition in face space

The essential midline symmetry of human faces is shown to play a key role in facial coding and recognition. This also has deep and important connections with recent explorations of the organization of primate cortex, as well as human psychophysical experiments. Evidence is presented that the dimension of face recognition space for human faces is dramatically lower than previous estimates. One result of the present development is the construction of a probability distribution in face space that produces an interesting and realistic range of (synthetic) faces. Another is a recognition algorithm that by reasonable criteria is nearly 100% accurate.

Location memory biases reveal the challenges of coordinating visual and kinesthetic reference frames

Five experiments explored the influence of visual and kinesthetic/proprioceptive reference frames on location memory. Experiments 1 and 2 compared visual and kinesthetic reference frames in a memory task using visually-specified locations and a visually-guided response. When the environment was visible, results replicated previous findings of biases away from the midline symmetry axis of the task space, with stability for targets aligned with this axis. When the environment was not visible, results showed some evidence of bias away from a kinesthetically-specified midline (trunk anterior-posterior [a-p] axis), but there was little evidence of stability when targets were aligned with body midline. This lack of stability may reflect the challenges of coordinating visual and kinesthetic information in the absence of an environmental reference frame. Thus, Experiments 3-5 examined kinesthetic guidance of hand movement to kinesthetically-defined targets. Performance in these experiments was generally accurate with no evidence of consistent biases away from the trunk a-p axis. We discuss these results in the context of the challenges of coordinating reference frames within versus between multiple sensori-motor systems.

Innervation of the Joint and Role of Neuropeptides

Rheumatoid arthritis is considered to represent a disease of the synovial membrane, osteoarthritis of the hyaline articular cartilage, and osteoporosis of the bone. It can be questioned to what extent this is true and to what extent these diseases could be considered to be due to extra-articular, extra-skeletal pathology related to the neuroendocrine system. Pain is the main symptom in arthritis. This is related to prostaglandin-mediated sensitization of the primary afferent nociceptive nerves. Accordingly, nonsteroidal anti-inflammatory drugs are used in symptomatic treatment, occasionally together with opioids and tricyclic antidepressants. The midline symmetry and involvement of the richly innervated, small peripheral joints in rheumatoid arthritis have raised speculation about the role of neurogenic inflammation and neuropeptides in its pathogenesis. In contrast to the free nerve endings, the role of the proprioceptive sensors is to provide information of our actual motor performance (the afferent copy of our movements) compared to the efferent motor program, which is activated by our will to move. These include proprioceptors in the skin (e.g., Meissner corpuscles), muscles (annulospiral and flower-spray endings of the muscle spindles), Golgi tendon organs, and Ruffini end organs and Pacinian corpuscles in the superficial and deep layers of the joint capsule. Elderly people may have slow reflexes, lax joints, joint incongruity, and loss of muscle power; obesity, alcohol and medicinal use, and joint pain can be combined with poor/nonexisting capacity for repair and remodeling of the musculoskeletal tissues. Impaired biomechanics contributes to increased joint tenderness, accumulation of minor trauma (secondary osteoarthritis), and falls (osteoporotic fractures). More attention needs to be paid to aging of proprioception, not only to the terminal disease target.

Comparison of extraction versus nonextraction orthodontic treatment outcomes for borderline Chinese patients

The purpose of this study was to compare orthodontic treatment outcomes in Chinese patients with borderline problems treated with and without extractions. Records of 39 borderline patients treated at the Faculty Clinic of the Peking University Orthodontic Department were evaluated retrospectively by 5 associate professors. Sixteen patients had been treated without extractions, and 23 had 4 first or second premolars extracted. Each judge evaluated the posttreatment records independently for tooth alignment, overbite, overjet, midline symmetry, lateral occlusion, and facial profile, and rated them on a scale from 1 to 5. The only statistically significant difference between the extraction and nonextraction groups was for facial profile, with the judges preferring the extraction profiles. Fifteen soft-tissue cephalometric variables were measured to determine the source of the difference, and 6 showed statistically significant differences. When profile changes from pretreatment to posttreatment were examined, significant differences in treatment-associated changes between extraction and nonextraction groups were all related to the lower lip and chin. In this sample of Chinese borderline orthodontic patients, Chinese clinicians had a statistically significant preference for the facial profiles of the extraction patients, but no statistically significant preferences for tooth alignment, overbite, overjet, midline symmetry, or posterior occlusion. Extraction treatment increases the inclination of the chin and reduces protrusion of the lower lip compared with nonextraction treatment, and this might explain the difference.

Mapping Collagen Organization in the Human Cornea: Left and Right Eyes Are Structurally Distinct

Aspects of the biomechanics and surface topography of fellow human corneas are known to exhibit midline symmetry, but the structural basis of these observations is poorly understood. The mechanical performance of the cornea is strongly influenced by the organization of stromal collagen fibrils. The present study was designed to examine and compare the organization of collagen fibrils in the corneal stroma of left and right eyes. Wide-angle x-ray scattering was used to map in detail the orientation and distribution of fibrillar collagen across the cornea, limbus, and adjacent sclera of three normal human eyes, including a fellow pair, and the central 9-mm corneal region of a further four eyes. Fibrillar collagen in the human cornea and limbus is arranged anisotropically, and in a highly specific manner. Left and right corneas are structurally distinct. In general, the mass distribution of preferentially aligned fibrils in the cornea appears to exhibit a degree of midline symmetry between left and right eyes. Structural information, such as that presented herein, will enable a better understanding of corneal biomechanics and shape. Midline symmetry in the distribution of aligned, mechanically reinforcing collagen fibrils between left and right eyes may relate to the biomechanical and topographical enantiomorphism reported in the literature.

The Effects of Asthma on Dental and Facial Deformities

Objective. The purpose of the study was to observe facial and teeth alterations in adult patients with asthma as opposed to a group who suffered from hypertension. Methods. All patients included in this cross-sectional observational study were interviewed to obtain clinical data. Patients also followed an orthodontic assessment using model-facial photographic and gypsum casts to diagnose malocclusion and dentofacial deformities. Asthmatic patients were divided in two groups according to asthma onset under or over 14 years of age. Results. A total of 61 asthmatics and 53 hypertensive patients were evaluated. Dental midline symmetry was significantly lower in asthmatics than in the hypertensive group (p = 0.006), whereas incompetent lip posture and open nasal lip angle were significantly more frequent in the asthmatic group than in the control group (p = 0.007 and 0.016, respectively). Asthmatics had more dental crossbite (p = 0.004), overbite (p = 0.01), overjet (p = 0.01), smaller inter bicuspids distance (p = 0.0009) and inter molar distance (p = 0.0001) than the control group. More crowding than diastems was observed in asthmatic patients. An association between the crossbite (p = 0.02) and maxillary crowding (p = 0.03) was also observed with the earlier age of asthma onset. Conclusion: The findings of this study lead us to note that dentofacial anomalies are related to asthma.

Buckling of moderately thick rectangular composite plates subjected to partial edge compression

The objective of the present paper is to investigate the influence of partial edge compression on the critical loads of moderately thick laminated plates. Towards this, an eight node isoparametric plate element is developed. The element has five degrees of freedom per node. The computer code developed accepts two sets of boundary conditions, one for pre-buckling stress analysis and the second for stability analysis. This flexibility is proposed to exploit the mid-line symmetry conditions. Two types of partial edge compression, viz., (I) uniform partial edge compression near the corners and (II) uniform partial edge compression at the middle of edges are considered. The effect of percentage of loaded edge length on the critical load of thin and thick composite plates with simply supported and clamped edge conditions is studied in detail.

Computed tomographic appearances of the pelvis following hindquarter amputation.

Bilateral and midline symmetry of the normal pelvic anatomy is an aid to the interpretation of computed tomographic (CT) examinations. Following hindquarter amputation (HQA) or partial hemipelvectomy (PHP) the normal anatomical relationships are disturbed. The CT examinations of 15 patients who had undergone either an HQA or a PHP for an advanced musculoskeletal malignancy are reviewed. The new "normal" anatomy revealed displacement of the bladder and small bowel to the side of surgery in one third of patients, more commonly in the PHP cases. There were varying degrees of wasting of the ipsilateral musculature, gluteus maximus muscle flap, erector spinae and psoas muscles, etc., because of partial denervation and disruption of their origin or insertion. Recurrent tumour was identified in eight of 10 cases in which it was clinically suspected prior to the CT examination. Invariably the recurrence arose within the muscle flap at the resection margin. Bone involvement by direct tumour spread was present in three cases. Pitfalls in differentiating recurrent tumour from scar tissue are discussed.