Outcome measurement in the correction of mandibular asymmetry

Quantitative evaluation of binary digital region asymmetry with application to skin lesion detection

Background

The performance of Computer Aided Diagnosis Systems for early melanoma detection relies mainly on quantitative evaluation of the geometric features corresponding to skin lesions. In these systems, diagnosis is carried out by analyzing four geometric characteristics: asymmetry (A), border (B), color (C) and dimension (D). The main objective of this study is to establish an algorithm for the measurement of asymmetry in biological entities.

Methods

Binary digital images corresponding to lesions are divided into 8 segments from their centroid. For each segment, the discrete compactness value is calculated using Normalized E-Factor (NEF). The asymmetry value is obtained from the sum of the square difference of each NEF value and corresponding value of its opposite by the vertex. Two public skin cancer databases were used. 1) Lee’s database with 40 digital regions evaluated by fourteen dermatologists. 2) The PH² database which consists of 200 images in an 8-bit RGB format. This database provides a pre-classification of asymmetry carried out by experts, and it also indicates if the lesion is a melanoma.

Results

The measure was applied using two skin lesion image databases. 1) In Lee’s database, Spearman test provided a value of 0.82 between diagnosis of dermatologists and asymmetry values. For the 12 binary images most likely to be melanoma, the correlation between the measurement and dermatologists was 0.98. 2) In the PH² database a label is provided for each binary image where the type of asymmetry is indicated. Class 0–1 corresponds to symmetry and one axis of symmetry shapes, the completely asymmetrical were assigned to Class 2, the values of sensitivity and specificity were 59.62 and 85.8% respectively between the asymmetry measured by a group of dermatologists and the proposed algorithm.

Conclusions

Simple image digital features such as compactness can be used to quantify the asymmetry of a skin lesion using its digital binary image representation. This measure is stable taking into account translations, rotations, scale changes and can be applied to non-convex regions, including areas with holes.

Correction of a severe facial asymmetry with computerized planning and with the use of a rapid prototyped surgical template: a case report/technique article

Management of significant facial asymmetry presents a challenge due to the geometric complexity of the bony and other facial structures. Manual model surgery is an essential part of treatment planning but it can be complicated, time-consuming and may contain potential errors. Computer-aided surgery has revolutionized the correction of maxillofacial deformities. The aim of this study was to report a case of facial asymmetry when computerised simulation surgery was performed instead of manual model surgery and a virtually planned wafer splint was fabricated. A 26-year-old male was presented with a severe right-sided hemimandibular elongation. Following presurgical orthodontics high-resolution computer tomography scan was performed. The stack images were reformatted into a three-dimensional structure. Virtual Le Fort-I osteotomy was performed and the symmetry of the maxilla was corrected with the help of a three-dimensional planning software. A virtual intermediate surgical wafer was designed and produced with three-dimensional rapid prototyping technology. The mandible was rotated into the correct position following virtual bilateral sagittal split osteotomy to visualize the movements of the osteotomised mandibular segments. The two-jaw procedure was performed according to the virtual plan. The facial symmetry was improved significantly and stable occlusion was achieved. This complex case shows the advantages of computer-aided surgical planning and three-dimensional rapid prototyping for the correction of facial asymmetries.

Severe facial asymmetry and unilateral lingual crossbite treated with orthodontics and 2-jaw surgery: 5-year follow-up

A 33-year-old woman with severe facial asymmetry and unilateral lingual crossbite was treated with orthodontics combined with differential maxillary impaction and intraoral vertical ramus osteotomy. After 12 months of preoperative orthodontic treatment, 2-jaw surgery was performed. The total active treatment time was 18 months. Both her occlusion and facial appearance were significantly improved by the surgical-orthodontic treatment. The occlusion was stable after 5 years of retention. Posttreatment records after 5 years showed excellent results with good occlusion and long-term stability.

Quantitative use of photography in orthognathic outcome assessment

This study reports an independent audit of two aspects of orthognathic surgery, namely control of inter-alar width and mandibular outline asymmetry. Measurements were taken from standardized photographs of a consecutive series of 27 patients, using an on-screen digitizing program (IPTool). All patients had undergone bimaxillary osteotomies involving maxillary impaction and/or advancement, by one surgeon, using a cinch suture for nasal width control. Nine-twelve months after surgery, inter-alar width had increased by just 0.08 cm mean (SD 0.3). Four patients showed an increase of just over 2mm, whilst six showed a small reduction. Based on ratios of size (area) and shape (compactness) of the right and left mandibular segments, there was a small overall improvement in mandibular symmetry (0.019 and 0.005 respectively). Whilst in most of the patients the need for surgery was primarily the correction of antero-posterior and vertical discrepancies, five patients with demonstrable asymmetry showed a clear improvement. In three patients whose asymmetry scores were very mild pre-treatment, there was a small, measured increase in asymmetry, but not to a degree that would be clinically noticeable. At a time when 3D imaging is still unavailable to many clinicians, the results of this study suggest that appropriate measurements taken from carefully standardized conventional photographs can provide a valid and objective means of assessing treatment outcome.

Bilateral Asymmetry in the Tooth Relationships of Orthodontic Patients

Objective: To quantify the nature and extent of bilateral dentoalveolar asymmetries in routine adolescent orthodontic patients.

Materials and Methods: Eight left-right pairs of occlusal dimensions were measured from dental casts (n = 211 subjects) with proportionate samples of class I, II, and III malocclusions.

Results: Directional asymmetry is a subtle, but pervasive feature of the dental arches, with systematically larger dimensions on the left side. Prior studies attribute this sidedness to compensations for hemispheric laterality. Patient's sex did not influence the magnitude of asymmetry, but patients with class II malocclusion exhibited significantly greater asymmetries, particularly in the anterior segment. Inspection suggests that this is attributable to the lack of coupling and guidance of the teeth between the jaws. There is a significant association between the severity of class II buccal-segment relationship and the extent of left-right asymmetries.

Conclusion: Clinically, these lateralities need to be anticipated, particularly in class II malocclusions, and incorporated into the treatment plan.

Orthodontic and Surgical Treatment of Hemimandibular Hyperplasia

Correction of facial asymmetries is still a major problem in need of an adequate solution. In this case report, the differential diagnosis and treatment strategies of hemimandibular hyperplasia are described with the present patient.

Misuses of correlation and regression analyses in orthodontic research: The problem of mathematical coupling

INTRODUCTION

The aim of this article was to encourage good practice in the statistical analyses of orthodontic research data. Our objective was to highlight the statistical problems caused by mathematical coupling (MC) in correlation and regression analyses. These statistical problems are among the most common pitfalls in orthodontic research when exploring associations among clinical variables. This article will show why these problems arise and how they can be avoided and overcome.

METHODS

Four orthodontic journals were electronically and manually searched for articles that used correlation and regression analyses. Studies that seemed to suffer from MC in their statistical analyses were identified and carefully examined.

RESULTS

Several examples from our search illustrate that MC in correlation and regression analyses can potentially cause misleading results. More appropriate statistical methods are available and should be used to eliminate confusing results and improve any subsequent interpretations. Because many clinical and radiographic variables used in orthodontic research are correlated due to direct or indirect MC, interpretation of studies in the literature needs to be cautious.

CONCLUSIONS

Correlation and regression analyses are useful tools in orthodontic research when their assumptions and limitations are recognized. However, greater care is required in formulating research questions and experimental designs. It is prudent to seek statistical advice when orthodontic research involves complex data analyses.

Asymmetric mandibular prognathism: A 30-year retrospective case report

A healthy white man with marked facial and dental asymmetry, a consequence of unilateral mandibular condylar hyperplasia, was treated with conventional fixed edgewise appliance therapy combined with orthognathic surgery (bilateral sagittal split osteotomy of the mandibular ramus). Pretreatment, posttreatment, and long-term follow up records for the patient at ages 26 years 11 months, 28 years 6 months, and 58 years 7 months are presented. Thirty years after treatment, the results remain stable. The pretreatment and posttreatment records were presented to the American Board of Orthodontics in 1976 in partial fulfillment of the requirements for board certification.

Pressure oscillation amplitude after interruption of tidal breathing as an index of change in airway mechanics in preschool children

Bronchodilator reversibility testing using change in airway resistance during interruption (Rint) is feasible in preschool children. Analysis of postocclusion oscillations of the mouth pressure-time transient (Pmo(t)), recorded during airflow interruption, may offer an alternative index of change in airway mechanics. We analyzed Pmo(t) oscillation amplitude in three different ways: 1) difference between the first relative maximum and minimum (AMxMn); 2) detection of the dominant frequency using Fourier analysis (AFS); and 3) curve-fitting based on a mathematical model (ACurv). In 25 asymptomatic asthmatic children, aged 2.5-5.6 years, who had undertaken reversibility testing, the correlation coefficients between baseline Rint and amplitude were: AMxMn r = -0.84, AFS r = -0.82, ACurv r = -0.84. The coefficient of variation (CoV) of readings contributing to baseline Rint measurement, as median (range), was 12% (5-24%), which was not significantly different from AFS or ACurv (P > 0.05). All parameters were significantly different postbronchodilator (P < 0.001). Using the sensitivity index, i.e., the change after intervention divided by the baseline standard deviation, ACurv was the most sensitive and Rint the least sensitive, with median (range) at 2.72 (-0.84 to 12.10) and 1.91 (-1.17 to 9.50), respectively (P = 0.005). Our results suggest that oscillation amplitude analysis may provide a sensitive index of change in airway mechanics in preschool children undertaking bronchodilator reversibility testing.