1,721,241 research outputs found
Soft-tissue facial anthropometry in three dimensions : from anatomical landmarks to digital morphology in research, clinics and forensic anthropology
No full textThe quantitative assessment of the dimensions of human facial soft-tissue structures (eyes, nose, mouth and lips, chin, ears), their reciprocal spatial positions and relative proportions, has an interdisciplinary perspective: anatomical and anthropometric descriptions, medical evaluations (clinical genetics, orthodontics,
maxillo-facial and plastic surgery), forensic medicine, they all need reference three-dimensional data collected on healthy, normal individuals selected for sex, age, ethnic group, to be compared to those obtained on the single individual. The data collection technique should be non-invasive, fast, as simple as possible, performed directly on the subjects using low-cost instruments. Data should be collected in digital format, so to allow the creation of
computerized data bases, and the use of the computerized techniques of visualization and simulation of treatment. Independent of classic direct anthropometry, various three-dimensional image analyzers are increasingly being used in clinical investigations and research. The instruments can be divided into two main categories: optical, non contact digitizers, and contact instruments. The first kind of instruments (mainly, laser
scanners and stereophotogrammetric devices) perform a fast digitization of the face, providing a detailed analysis of the soft-tissue surface. Contact instruments (electromagnetic and electromechanic digitizers) use a landmark representation of the soft-tissue facial surface. Landmark coordinates are coupled to a mathematical and
geometric model of the face, and angles, distances and ratios similar to those measured in conventional anthropometry can be obtained. Additionally, multivariate methods of analysis, obtained either from geometric morphometry or from other analytical methods, could be used. Optical instruments provide a larger amount of
information but they cannot assess all the actual anatomical landmarks obtained by contact instruments. Motion artifacts are more common with contact instruments, but they can be easily transported, and they are less expensive. Overall, contact instruments seem sufficiently reliable, simple and fast to be used also in a clinical context, thus providing useful quantitative information to allow a better patient care, without submitting the subjects to potentially harmful procedures
Biomechanical model of the human mandible in unilateral clench: Distribution of TMJ reaction forces between working and balancing sides
No full textIn a previous article we reported on our development of a biomechanical analog of the human mandible and a simple support model was introduced. The model has been further developed to calculate the relative degree of load on the working and balancing sides of the temporomandibular joint during unilateral clench. The relative load on each joint is a function of the biting force, the geometric setting (subject's anatomy, points of application of the biting force on the dental arch and of the resultant of the forces of the masticatory muscles), and the value of the electromyographic asymmetry (relative contribution of working-versus balancingside muscles) and activity indexes (relative contribution of masseter versus anterior temporal muscle of both sides). The proposed biomechanical model showed that the reaction forces that act on the temporomandibular joint during unilateral clench do not always load the balancing-side joint more than the working-side joint. Modifications of the asymmetry index changed the relative load between the two joints, and a higher temporal muscle activity increased the joint load on both the working and the balancing sides
Anatomy of emotion : a 3D study of facial mimicry
No full textAlterations in facial motion severely impair the quality of life and social interaction of patients, and an objective grading of facial function is necessary. A method for the non-invasive detection of 3D facial movements was developed. Sequences of six standardized facial movements (maximum smile; free smile; surprise with closed mouth; surprise with open mouth; right side eye closure; left side eye closure) were recorded in 20 healthy young adults (10 men, 10 women) using an optoelectronic motion analyzer. For each subject, 21 cutaneous landmarks were identified by 2-mm reflective markers, and their 3D movements during each facial animation were computed. Three repetitions of each expression were recorded (within-session error), and four separate sessions were used (between-session error). To assess the within-session error, the technical error of the measurement (random error, TEM) was computed separately for each sex, movement and landmark. To assess the between-session repeatability, the standard deviation among the mean displacements of each landmark (four independent sessions) was computed for each movement. TEM for the single landmarks ranged between 0.3 and 9.42 mm (intra-session error). The sex- and movement-related differences were statistically significant (two-way analysis of variance, p=0.003 for sex comparison, p=0.009 for the six movements, p<0.001 for the sex x movement interaction). Among four different (independent) sessions, the left eye closure had the worst repeatability, the right eye closure had the best one; the differences among various movements were statistically significant (one-way analysis of variance, p=0.041). In conclusion, the current protocol demonstrated a sufficient repeatability for a future clinical application. Great care should be taken to assure a consistent marker positioning in all the subjects
Biomechanical model of the human mandible : a hypothesis involving stabilizing activity of the superior belly of lateral pterygoid muscle
No full textA new biomechanical analog for the human mandible is proposed. The biomechanics of the human mandible can be explained by a simple support model, where muscular forces are produced by the masseter, medial pterygoid, temporal, and superior lateral pterygoid muscle components, and reaction forces are produced by the occlusal surfaces and condyle. All forces are resolved into components orthogonal and parallel to the temporal articular plane (articular eminence). In this model, one component of muscular forces is parallel to the temporal articular plane. The influence of the inclination of the occlusal plane, the inclination of the temporal articular plane, the position of the resultant of the occlusal reactions, and the relative contribution of the different jaw elevator muscles on the parallel and orthogonal components are evaluated according to a computer model of the system. The muscular force parallel to the temporal articular plane may be produced by the superior lateral pterygoid muscle, which during clenching acts as a stabilizer of the mandibular condyle to prevent posterior dislocation and compression of nonarticular tissues
Coordinated electromyographic activity of the human masseter and temporalis anterior muscles during mastication
No full textThe present report aimed at evaluating the within- and between-subject electromyographic coordination between the masseter (M) and temporalis anterior (T) muscles during the performance of a standardized chewing task. Electromyographic activity of M and T muscles was recorded in 60 young healthy adults (30 men, 30 women) during two 15-s unilateral mastications of gum. Left-right differential potentials (delta M = MR-ML, delta T = TR-TL) were computed and the square root of (delta M2 + delta T2) moduli were calculated. The maximum modulus relative to each masticatory cycle was located, and each modulus and differential potential were expressed as a % of the maximum modulus for each subject and chewing trial. For each subject and chewing side, the masticatory frequency was computed, and statistics of the moduli as %s of the maximum were determined by means of bivariate analysis. Within-subject repeatability of the unilateral chewing patterns was good. Mean population values for the modulus position (bivariate analysis), chewing frequency, and maximum modulus of the differential potentials (univariate statistics) were computed. A significant gender difference was found for the masticatory frequency, with larger values in men than in women. Conversely, no gender or side differences were found for the mean values of the maximum modulus or for the mean position of the percentage moduli. The chewing test applied allowed the evaluation of the neuromuscular coordination during the performance of a standardized physiologic activity. In particular, it quantified the within-subject and chewing side repeatability of the muscular pattern
The influence of crossbite on the coordinated electromyographic activity of human masticatory muscles during mastication
No full textThe analysis of the masticatory muscle activity in subjects with altered occlusal relationships could provide useful data of the functional impact of morphological discrepancies. Thirty subjects aged 16-18 years, with a sound, full permanent dentition, bilateral angle class I, and an overjet and overbite between 2 and 5 mm, were examined. The control group (10 male, 10 female) had no crossbite, while the crossbite group (four male, six female) had a posterior unilateral crossbite (five on the left side, five on the right side). The electromyographic activity of the left and right masseter and temporalis anterior muscles was recorded during 15 s of unilateral (left and right) chewing of gum, and expressed as a percentage of the maximum voluntary clench on cotton rolls. For each subject, the masticatory frequency, the confidence ellipse of the simultaneous differential left-right masseter and temporal activity (Lissajous figure), and an index of muscular symmetry, were computed to assess muscular coordination. In the crossbite subjects, the four analysed muscles appeared to contract with altered and asymmetric patterns. A large variability was found, and the confidence ellipses calculated for the chewing tests performed on the crossed sides were not significant, while the confidence ellipses of the uncrossed side chewing were different from the ellipses computed in the normal occlusion group. The altered occlusal relationship influenced the coordination of the masticatory muscles during chewing on both sides. The functional alteration was more apparent when the side with the altered morphology was directly involved, i.e. when chewing was performed on the crossbite side
Statistical evaluation of monson's sphere in healthy permanent dentitions in man
No full textThe three-dimensional curvature of the mandibular dental arch was studied in 20 men and 20 women with sound dentitions and free from temporomandibular joint problems. The x, y, z coordinates of cusp lips of all but the third molars were obtained with a three-dimensional digitizer and used to derive a spherical model of the curvature of the occlusal surfaces. From the best interpolating sphere the radii of the left and right curves of Spee (quasi-sagittal plane) and of the canine arid molar curves of Wilson (frontal plane) were computed. The occlusal curvature of the mandibular arch was not significantly influenced by gender, even if, on average, all the computed variables were larger in men than women. The radii of the overall sphere, right and left curves of Spee, and curve of Wilson in the molar area were about 105 mm in men, and about 100 mm in women. A relatively large intrasample variability in arch curvature was found. The mean sphere radius in men was very close to the classical value of 4 in, confirming Monson's observations, but the relatively large intrasample variability prevented arty definitive determination of a sexual dimorphism in the three- dimensional characteristics of occlusal curvature
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