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Biomedical subjects

B Melsen

Publications and source records attributed to B Melsen.

At least 19 recordsLinked to original sources
PubMed1992

Craniomandibular dysfunction following surgical correction of mandibular prognathism.

Craniomandibular function was studied in 36 adult patients in whom mandibular prognathism was corrected with a combination of surgical (vertical ramus osteotomy) and orthodontic procedures. Each patient was examined up to 1 week before surgery and again 6 months later. Mandibular mobility, impaired function of the temporomandibular joint, and pain in the masticatory muscles and temporomandibular joint were evaluated. Data were classified according to a numerical scale and patients were divided into three groups: symptom free, mild symptoms and severe symptoms. Although there was no difference in the overall frequency of the three functional groups during the two phases of examination, 20 patients showed a change in functional status following surgery. Before surgery, decreased mandibular mobility was found in 19 patients; after surgery, four additional patients were included in this group. Temporomandibular joint function improved in 10 patients and three patients had less pain. The frequency of muscle pain did not change. Postoperative maximal interincisal opening was reduced by 5.4 mm (p less than 0.001) but lateral excursive movements did not change significantly. No significant relationships were found between pre- and postoperative mandibular mobility, temporomandibular joint function and muscle pain. Females experienced mild or severe dysfunction more often than males at both examinations, but the difference was not statistically significant.

Adolescent↗
PubMed1991

Determination of stress levels and profiles in the periodontal ligament by means of an improved three-dimensional finite element model for various types of orthodontic and natural force systems.

This study was undertaken to investigate the stress-strain levels and distribution within the periodontal ligament for various types of physiological and orthodontic force systems, assuming that the bone resorption process, leading to tooth movements, is partly controlled by those conditions. Two finite element models were developed, simulating a full and partial mandibular morphology, respectively. Both models were based on morphology and physical parameters of human autopsy material. The effect of changing material parameters and structure, type of boundary conditions, calculation method and fineness of the model on the stress levels and profiles in the periodontal ligament was evaluated by a series of tests. A structure optimization technique was used to investigate the load bearing characteristics of the mandible and the influence of the anisotropic material properties of both the mandible and the segment. A 'multiple modelling' technique based on both the mandible and the segment was developed to test various types of boundary conditions in the analysis of the segment. Results presented as 'stress profiles' showing the correlation between the applied force system and the stress distribution in the periodontal ligament, based on the improved finite element models, were established.

Biomechanical Phenomena↗
PubMed1991

Material parameters and stress profiles within the periodontal ligament.

Levels and profiles of initial stress in the periodontal ligament after application of various force systems were studied. Two finite-element models, based on sections of human autopsy material, were developed to simulate one full and one partial mandible. The validity of the finite-element model was improved by identification of material parameters; the mechanical properties of the tissue were described by means of strain-gauge measurements of initial tooth movements in human autopsy material. The multiple modeling technique, in which data from a coarse global model are transferred to a more detailed one, was used to identify bone structure and boundary conditions. Parameters known to influence the results were varied to establish the validity of the finite-element model. Iterative calculation methods were used to gain stable results. However, optimizing features of the bone structure and boundary conditions did not influence the results significantly. The elastic stiffness of the periodontal ligament was determined to 0.07 MPa and tau = 0.49 (tau being the Poisson's ratio). Stress profiles were obtained for various force systems--as in tipping, translation, and root movement. As we expected, there was a marked variation in the stress distribution from cervix to apex when tipping forces were applied. Bodily movement of the tooth produced an almost uniform stress distribution; root movement produced stress patterns opposite to those observed during tipping; and masticatory forces alone produced stress patterns almost identical to those achieved by masticatory force in combination with orthodontic forces.

Adolescent↗
PubMed1991

Tooth displacement analysed on human autopsy material by means of a strain gauge technique.

Tooth displacement was analysed on human autopsy material for various types of orthodontic force systems using an electronic strain gauge technique. Tooth movements were registered in two dimensions with low force clip gauges on three sections of the mandible, containing the first premolar and the first molar. The sensitivity was 0.1 microns when horizontal forces of 50, 100, and 150 cN were applied at different horizontal levels producing different M/F ratios. The relationship between a force system and the resulting tooth movement was described by the position of the centre of rotation, CR, and the angle of rotation. The centre of resistance was determined for the three autopsy specimens, and depended on tooth geometry, root length, and level of bony margin. Important differences in location were found. The dynamics of initial tooth movement were analysed within the first minute of load application. Force/displacement curves were generated to evaluate the behaviour of the periodontal ligament. There was a linear correlation between the two variables. Freezing the autopsy material some days before testing had no detectable effect. The results from measurements on human autopsy material were compared with previously derived in vivo measurements.

Adolescent↗
PubMed1991

Occlusal contacts in maximum intercuspation and craniomandibular dysfunction in 16- to 17-year-old adolescents.

The relationship between number, distribution and intensity of occlusal tooth contacts and the craniomandibular functional status was investigated in 56 subjects aged 16-17 years. The photocclusion technique was used for the qualitative and quantitative evaluation of occlusal contacts, and a clinical examination was performed to assess the function of the stomatognathic system. According to a matched-pairs design two groups were formed, one consisting of individuals with signs of craniomandibular disorders, and the other consisting of functionally healthy adolescents. The pairs were matched according to morphological occlusal characteristics. The results of the present study emphasize the importance of occlusal contacts in relation to craniomandibular function. In particular the posterior occlusion appeared to be related to function, since statistically significant differences between the two groups were detected with regard to the number and load of contacts. Symmetry of intensity rather than symmetry of contact distribution per se seemed to be important in relation to craniomandibular function.

Adolescent↗
PubMed1991

The nasal septum in relation to the development of the nasomaxillary complex: a study in identical twins.

The influence of the nasal septum and respiration, evaluated by the total nasal resistance (TR) on the development of the nasomaxillary complex, was studied in 42 identical twins. An understanding of this influence is important for a determination of whether surgery involving the nose should be performed in children. Comparison within and between twins with different septal deformities indicated that the cartilaginous nasal septum influences the development of the nose and the anteroposterior dimensions of the maxilla. Anterior septal deformities resulted in underdeveloped cartilaginous noses and a shorter anteroposterior dimension for the maxilla. No relation was found with regard to posterior septal deformities, which may be considered as part of the development of the midface. Vertical dimensions of the face were related to TR. Increased values of TR were significantly related to a shorter maxillary height. This may not express a causal relationship but rather genetically determined shorter facial dimensions.

Adolescent↗
PubMed1991

Postnatal craniofacial skeleton development following a pushback operation of patients with cleft palate.

A longitudinal growth study of the craniofacial skeleton in 52 (19 males, 33 females) Danish individuals with cleft palates was performed. Thirty (13 males, 17 females) had clefts of the soft palate only or clefts extending into the posterior third of the hard palate. Twenty-two (6 males, 16 females) had more extensive clefts including up to two-thirds of the hard palate. The cleft was closed with a pushback operation at 22 months of age. Orthodontic treatment was included in the early mixed dentition. Lateral cephalometries were obtained at 5, 8, 12, 16, and 21 years of age. Twenty-four variables were digitized and analyzed. The results indicated that patients with more extensive clefts demonstrated significantly smaller anterior cranial base length (N-S), total cranial base length (N-Ba), maxillary dentoalveolar base length (A-PMP), mandibular length (Cd-Pgn), upper anterior and posterior facial heights (N-ANS and P-PMP), and total facial height (N-Gn). Patients with the more extensive clefts reached maximum growth spurt later than patients with less extensive clefts in all dimensions except the A-PMP and the lower and total facial heights.

Adolescent↗
PubMed1991

[Can attachment gain be achieved by means of orthodontic measures?].

The influence of intrusive movement was analyzed in an animal experiment. The results indicate that the periodontal status previously observed might in fact be related to a clinically significant amount of new attachment. Since the intrusion is carried out in case of horizontal bone loss, this treatment is specially focusing on the situation which has the most doubtful prognosis by means of the current new attachment procedures. A possible explanation of the attachment gain demonstrated may be that the stretching of the periodontal ligament fibres at the marginal level generates a sort of natural filter reducing the down growth of the epithelium. Another possible explanation may be that the orthodontic stimulation increased the turnover in the periodontal ligament and thereby improved the chances of the periodontal ligament to repopulate the previous infected root surface. There is, on the basis of the results presented reason to believe that a combination of a prevented colonarization from gingival tissue and a stimulation of the periodontal ligament cells showed open new perspective in the treatment of heavily involved periodontal patients.

Analysis of Variance↗
PubMed1991

[Biomechanics--where are we today?].

The development within the field of orthodontics is taking place within both the "hardware" (the brackets and wires) and within the "software" (the concepts behind the design of biomechanics). A survey of the physical characteristics of the new wires is presented. Within the "software" section the differentiation between appliance-guided and orthodontist-guided force systems is important. While the first is a standardized system, the second is goal-oriented and individualized. The advantage in segmented- contra straightwire-technique is discussed in relation to the limitation of orthodontics.

Dental Stress Analysis↗
PubMed1991

Effect of biteblocks and repelling magnets on root formation of unerupted premolars in Macaca monkeys.

The effect of repelling magnets on the root formation of unerupted teeth was studied in monkeys. Four controls, four monkeys with acrylic biteblocks and four monkeys with repelling samarium magnets embedded in biteblocks were observed for 12 weeks. After the monkeys were killed the teeth were examined histologically and the root formation evaluated. A clear influence on both the predentine formation and the Hertwig's root sheath was observed. The results clearly indicate the need for more long-term studies on the tissue reactions produced by repelling magnets.

Animals↗
PubMed1990

TMJ function and the effects on the masticatory system on 14-16-year-old Danish children in relation to orthodontic treatment.

The effect of orthodontic treatment on the functional status of the masticatory system was analysed in 706 children from three Danish communities. Three-hundred-and-eighty-eight (48 per cent) of the children were treated orthodontically and the 295 (37 per cent) of the total population had terminated the treatment and were included in the analysis. Fifty-seven cases (7.1%) of the total population were discontinued before the orthodontic treatment was considered finished by the orthodontist. Discontinuation did not, however, seem to influence the functional status. Increasing the orthodontic treatment frequency from 38 to 51 per cent did not decrease the functional problems of a young population. On the contrary, the community with the lowest treatment frequency (38 per cent) demonstrated fewer functional problems among the orthodontically treated subjects than did the two communities with higher treatment frequencies, indicating paradoxically that it may be a functional risk to treat the last 13 per cent with minor discrepancies. Tenderness on palpation of the musculature and the TMJ capsule were generally more prevalent among orthodontically treated subjects. Children who had their treatments performed by either orthodontist or paedodontist alone demonstrated more muscular problems than children who had been treated by a team of orthodontists and paedodontists. Related to the severity of the malocclusion these findings stress the importance of more consideration to establish a functionally satisfactory occlusion after orthodontic treatment. Functional status was not related to the type of orthodontic treatment, including extraction therapy, use of either fixed or removable appliances.

Adolescent↗
PubMed1990

Buccal mucosa fibroblasts and periodontal ligament cells perturbed by tensile stimuli in vitro.

Human buccal mucosa fibroblasts and periodontal ligament cells grown in tissue culture were subjected to tensile forces approximating those used for orthodontic bodily tooth movement. The cells were synchronized into pre S phase and positively tested for response to nonmechanical physical stimuli. Two-dimensional gel analysis and immunohistochemical analysis of the three cytoskeletal components showed a lack of response. Similar negative results were found when the cells were perturbed in the presence of substance P. We hypothesize that perhaps these cells respond more readily to injury, a secondary effect of the forces of tooth movement, than to tensile forces.

Cell Membrane↗
PubMed1990

Postsurgical change of mandibular position in patients following Le Fort I osteotomy.

Mandibular displacement during and following maxillary osteotomy was observed. Cephalometric data obtained from radiographs produced before, immediately after, and at a minimum of 6 months after were analyzed. The displacement of the maxilla and of the mandible during and after surgery was studied, and the predictive value of maxillary displacement on the changes occurring in the mandibular region was evaluated by a stepwise regression analysis. The results indicated that as the maxilla was displaced superiorly, the mandible also displaced anterosuperiorly without significant relapse. The rotation and the vertical displacement of the maxilla during the Le Fort I osteotomy accounted for two thirds of the total mandibular change. Vertical displacement of the maxilla and mandible were significantly correlated, indicating that mandibular displacement and rotation can be predicted from maxillary displacement.

Adult↗
PubMed1990

Calvarial sutural abnormalities: metopic synostosis and coronal deformation--an anatomic, three-dimensional radiographic, and pathologic study.

The purposes of this study were (1) to evaluate the histologic differences between synostotic versus deformational suture abnormalities and (2) to correlate these histologic findings with anatomic and three-dimensional computed tomographic (CT) scans. We examined three infants with premature metopic synostosis; one infant also had microcephaly trisomy 13 and curious overriding of the coronal sutures. The three-dimensional CT scans demonstrated obliteration of the metopic suture inferiorly. Histologic sections of this suture showed complete bony stenosis. The same pattern was found in all three infants, including the two infants with trigonocephaly who did not have trisomy 13 or microcephaly. In the trisomy 13 infant, the overlapped inferior coronal suture was obliterated on CT examination. However, histologic sections in this region showed a merging of bone; there was no synostosis. In summary, three-dimensional CT re-formation correlated with metopic suture histology. "Stenotic" fusion existed in all infants with trigonocephaly, those with normal and abnormal karyotypes, with and without microcephaly. However, three-dimensional CT re-formation of the trisomic infant showed opacification of the coronal suture in the areas of greatest overlap, whereas histology revealed a curious bone remodeling pattern, possibly a precursor to "deformational" craniosynostosis.

Abnormalities, Multiple↗
PubMed1989

Force system developed by V bends in an elastic orthodontic wire.

The force system generated by a simple V bend in a straight wire was studied by means of the principles for small deflection of a beam and a model developed for the description of the forces and moments. The relationship between the size of the bend and the interbracket position on the force system developed is analyzed and discussed in relation to clinical problems. The parallel between positioning of a V bend and the "geometries" developed between a straight wire and angulated brackets is drawn. Four principally different force systems could be developed by the V bend and a method for the predetermination of the force systems is provided. The general principles are exemplified for wires with different moduli of elasticity, varying materials, and cross-sectional dimensions. Stainless steel and beta titanium (TMA) wires in dimensions of 0.16 inch and 0.017 x 0.025 inch are given as examples.

Dental Stress Analysis↗