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Biomedical subjects

Birte Melsen

Publications and source records attributed to Birte Melsen.

At least 19 recordsLinked to original sources
PubMed2005

How does temperature influence the properties of rectangular nickel-titanium wires?

Thermodynamic nickel-titanium (NiTi) wires have become increasingly popular. The relationship between the temperature variation within the mouth and the force level delivered is, however, far from elucidated. The aim of this study was to evaluate the influence of possible intraoral temperature differences on the forces exerted by seven commercially available 0.019 x 0.025 inch NiTi archwires. As mouth temperature ranges from 33 to 37 degrees C most of the time, all wires were tested at five different temperatures between 30 and 40 degrees C in an orthodontic wire-testing device, a so-called Force System Identification (FSI) apparatus, placed in a climate chamber. In the FSI a two-bracket system using self-ligating Damon brackets simulated first order displacements up to 4 mm. At each temperature five samples of each archwire brand were tested. The following variables from the activation/deactivation curves were calculated: force and displacement at the yield point, maximum force level, total energy up to maximum displacement, energy loss after deactivation, force and displacement at the beginning and at the finish of the plateau, and the slope of the plateau. Any statistically significant differences in these variables for the different brands and temperature levels were analysed using one-way analysis of variance. The results showed that: (1) The behaviour of all wires was different. (2) Copper NiTi40 showed the lowest and the most constant force level, followed by NeoSentalloy 200 g. On the other hand, these wires may not work properly in mouth breathers as no forces were exerted below 35 degrees C. (3) If the use of superelastic characteristics and low force levels are the reasons for utilizing rectangular NiTi wires, austenitic NiTi wires should be avoided.

Copper↗
PubMed2005

Treatment of an ankylosed central incisor by single tooth dento-osseous osteotomy and a simple distraction device.

When teeth are replanted after being avulsed, the repair process sometimes results in ankylosis. In a growing child, the ankylosed tooth fails to move along with the remaining alveolar process during vertical growth, resulting in a tooth that gradually appears more and more impacted and requires several reconstructive procedures to correct. Ankylosed teeth can, however, serve as anchorage for orthodontic correction of a malocclusion and as a point of force application for a dentoalveolar segment during alveolar distraction osteogenesis. This case report describes the treatment of a 13-year-old girl whose maxillary left central incisor had been avulsed and replanted 5 years earlier. The tooth had become ankylosed, and it was used to provide "free anchorage" during distalization of the maxillary dentition. The underdeveloped alveolar process adjacent to the ankylosed tooth was reconstructed by dento-osseous segment distraction osteogenesis, by using the ankylosed tooth as the point of force application.

Adolescent↗
PubMed2005

Factors of importance for the development of dehiscences during labial movement of mandibular incisors: a retrospective study of adult orthodontic patients.

PURPOSE: Labial movement of mandibular incisors has traditionally been considered a risk factor for gingival recession. The aims of this study were to assess changes in prevalence and severity of gingival recession of mandibular incisors during orthodontic treatment of adults in whom the incisors had been moved labially and to identify parameters that could predict recession. MATERIAL: The sample consisted of 150 adult patients (aged 33.7 +/- 9.5 years, mean +/- SD) treated nonextraction with fixed appliances. Pretreatment overjet, overbite, degree of crowding, presence of tooth rotation, canine relationship, vertical face height, and position of the mandibular incisor to A-pogonion and mandibular lines were registered on study casts and lateral headfilms. Pretreatment gingival recession, width of keratinized gingiva, gingival biotype, gingival inflammation, and visible plaque accumulation were recorded, as was posttreatment gingival recession. Labial movement was determined by measuring pretreatment and posttreatment casts. Descriptive statistics were used to describe gingival recession at baseline and follow-up. Variables to be included in a logistic regression analysis as possible predictors of recession were identified with a bivariate correlation analysis. RESULTS: No significant increase in the mean gingival recession was observed during treatment. The prevalence of gingival recession greater than 0.1 mm increased from 21% before treatment to 35% after (P < .05). Only 2.8% of the subjects developed recession greater than 2 mm, and 5% of the pre-existing gingival recessions improved. The presence of baseline recession (P < .001), gingival biotype (P < .0179), and gingival inflammation (P < .003) were identified as possible predictors of recession. None of the orthodontic variables was significantly associated with recession. CONCLUSIONS: Gingival recession of mandibular incisors did not significantly increase during orthodontic treatment. After treatment, fewer than 10% of subjects had gingival recession greater than 2 mm, and, at follow-up, 5% of the pre-existing gingival recession had improved. Thin gingival biotype, visual plaque, and inflammation are useful predictors of gingival recession.

Adult↗
PubMed2005

Using the finite element method to model the biomechanics of the asymmetric mandible before, during and after skeletal correction by distraction osteogenesis.

An approach was developed to evaluate the load transfer mechanism in the temporomandibular joint (TMJ) area before, during and after mandibular ramus elongation by distraction osteogenesis (DO). In a concerted approach using computer tomography, magnetic resonance imaging (MRI), and finite element analysis, three-dimensional numerical models based on a young male patient, with a dento-facial deformity were generated. The magnitude and direction of the muscle forces acting on the mandible were assessed using both values derived from the muscles volume and cross-section as retrieved from the MRI-scan data-sets and taken from the literature. The resistance of the soft tissue envelope towards elongation during the DO-phase was also included. The finite element analyses showed that before skeletal correction by DO the load transfer was asymmetrical with high peak stresses in the affected joint. Following ramus elongation a more symmetrical loading in TMJs was predicted. The reaction forces in the TMJs during DO were low.

Arthritis, Juvenile↗
PubMed2005

Changes in clinical crown height as a result of transverse expansion of the maxilla in adults.

The risk of developing bony dehiscence and gingival recession may lead clinicians to prefer extraction to expansion in borderline cases. The purpose of this research was to compare changes in clinical crown height that occur at the buccal aspect of the maxillary lateral teeth of adult patients in which the transverse dimension was increased with those occurring if no expansion had been performed. Secondly it was the intention to identify factors increasing the risk of development of gingival recessions. The material comprised the pre- and post-treatment study casts from two groups of 50 adult patients. In one group an average transverse expansion of 3 mm was performed while in the other no change in the arch width was generated during treatment. Clinical crown heights of the two groups before and after treatment were compared with a Student's t-test and correlation analysis was used to determine whether any demographic or treatment-related parameters could be applied to predict an increase in clinical crown height. The increase in transarch width was greater in males (2.4-3.4 mm) than in females (1.8-2.5 mm), and greater at the level of the premolars than at the molars. No significant increase in buccal crown height could be identified. The increase in width was, however, related to buccal tipping as a positive correlation was found between the amount of expansion and tipping (P < 0.01). No detrimental effect of slow maxillary expansion could be demonstrated.

Adolescent↗
PubMed2005

Three-dimensional finite element analysis of the mandible and temporomandibular joint during vertical ramus elongation by distraction osteogenesis.

Distraction osteogenesis has been accepted as an alternative treatment modality for hypoplastic mandibles. Knowledge about the changes occurring in the temporomandibular joint region during mandibular distraction osteogenesis is, however, limited and controversial. Stress distribution in the temporomandibular joint region during unilateral vertical mandibular ramus distraction was studied using a finite element model. The finite element model was based on computed tomography scans and magnetic resonance imaging scans of a patient with unilateral hypoplasia of the right mandibular ramus caused by juvenile idiopathic arthritis. The character of stress distribution in the temporomandibular joint and mandible was analyzed quantitatively at different intervals of the vertical mandibular ramus elongation. During the distraction phase, the condyles, articular disks, and glenoid fossa regions were loaded with a differentiated stress pattern. The affected right condyle, disk, and fossa were submitted to increasing loads with increasing elongation compared with the contralateral temporomandibular joint. Loading on the unaffected left side shifted posteriorly and slightly laterally, because the left condyle was the center of rotation. The loading of the temporomandibular joint regions was low during the active distraction phase, although local areas were subjected to elevated peak stresses.

Arthritis, Juvenile↗
PubMed2005

Three-dimensional finite element analysis of the mandible and temporomandibular joint on simulated occlusal forces before and after vertical ramus elongation by distraction osteogenesis.

Distraction osteogenesis has recently become a mainstay for treatment of mandibular hypoplasia. Thorough knowledge about changes in the temporomandibular joint (TMJ) and the surrounding parts of the mandible and the skull after mandibular distraction is still lacking. The purpose of the current study was to investigate the stress distribution in the mandible and the TMJ before and after skeletal correction by intraoral unilateral vertical mandibular ramus distraction, using a finite element (FE) model. The FE models were based on computed tomography scans and magnetic resonance imaging scans of a patient with unilateral hypoplasia of the right mandibular ramus caused by juvenile idiopathic arthritis. The character of stress distribution in the mandible and TMJ before and after skeletal correction by 15 mm of vertical distraction of the mandibular ramus was analyzed quantitatively and compared during centric occlusion. Before the distraction osteogenesis treatment, the condyles, articular discs, and glenoid fossa regions are loaded with a different stress pattern. The affected right condyle, disc, and fossa are loaded diffusely and externally in comparison with the anterior and with centralized loading on the normal left side. After unilateral mandibular distraction osteogenesis, the load became more centric and symmetrical. The results suggest that correction of the mandibular deformity by distraction osteogenesis tends to normalize the stress patterns in the TMJ.

Arthritis, Juvenile↗
PubMed2004

The validity of superimposing oblique cephalometric radiographs to assess tooth movement: an implant study.

Assessment of the exact position of the posterior teeth on lateral headfilms is of limited validity because of the superimposition of the 2 sides. Lateral headfilms are also of limited use for evaluating orthodontic tooth movement, especially in cases of asymmetric mechanics. To solve this problem, the oblique cephalometric radiograph, which brings only 1 side of the image into focus, was introduced. We evaluated whether the projection of the cranial base could be used for evaluating facial growth and whether structures that were stable relative to the implants could be identified and thus replace the implants in future evaluations. Thirty sets of headfilms from growing patients with metallic implants were analyzed. Three types of superimpositions were performed. Displacement of the metallic implants in the maxillary complex and the mandible with respect to the superimposed structures of the cranial base was evaluated. When the development of the lateral parts of the facial skeleton was evaluated in relation to the cranial base, the reproducibility of the superimpositioning was significantly better in the vertical-S(e) = 0.41-than in the horizontal plane of space-S(e) = 1.35). The error of the method when superimposed on the stable structures in the maxillary complex varied between 0.31 and 0.72 and did not differ in the vertical and sagittal directions. In the mandible, the stable structures suggested for superimposition of the lateral headfilms were applicable on the oblique cephalometric radiograph-S(e) = 0.33-0.57. Oblique projection is recommended when individual analysis of the 2 sides is needed.

Adolescent↗
PubMed2004

Does the transition temperature of Cu-NiTi archwires affect the amount of tooth movement during alignment?

OBJECTIVES: To examine whether the transition temperature of Cu-NiTi archwires has an effect on the tooth movement during the alignment phase of orthodontic treatment. DESIGN: 'Split mouth' design in randomly selected patients. SETTING AND SAMPLE POPULATION: The Department of Orthodontics, School of Dentistry, University of Aarhus. Fifteen randomly selected patients with identical level of irregularity in the alignment phase of their treatment. Experiment Variable - Specially manufactured Cu-NiTi archwires for the upper arch were inserted. These consisted of two separate halves, each with its own transition temperature, respectively 27 degrees and 40 degrees C, and clamped together in the middle. OUTCOME MEASURE: The tooth movement, expressed as two translations and a rotation, in the occlusal plane was measured from the patients' intraoral photographs taken upon insertion of the archwires and again after 1 month. RESULTS: Tooth movements tended to be larger on the 40 degrees C-side, however only in case of the total translation of the premolars was this difference significant. In general, patients had not noticed any difference between the two sides of the archwire, although one patient stated the 27 degrees C-side to be more comfortable as the 40 degrees C-side had bothered her when drinking hot beverages. CONCLUSION: The transition temperature of Cu-NiTi archwires has indeed an effect on the amount of tooth movement during alignment. However, the differences are so small though that it is the question whether they can be noticed clinically. The study corroborates the trend towards the use of lower forces within orthodontics.

Copper↗
PubMed2004

A 12 month clinical study of bond failures of recycled versus new stainless steel orthodontic brackets.

The purpose of this prospective longitudinal randomized study was to compare the clinical performance of recycled brackets with that of new stainless steel brackets (Orthos). Twenty patients treated with fixed appliances were included in the investigation. Using a 'split-mouth' design, the dentition of each patient was divided into four quadrants. In 11 randomly selected patients, the maxillary left and mandibular right quadrants were bonded with recycled brackets, and the remaining quadrants with new stainless steel brackets. In the other nine patients the quadrants were inverted. Three hundred and ten stainless steel brackets were examined: 156 were recycled and the remaining 154 were new. All the brackets were bonded with a self-cured resin-modified glass ionomer (GC Fuji Ortho). The number, cause, and date of bracket failures were recorded over 12 months. Statistical analysis was performed by means of a paired t-test, Kaplan-Meier survival estimates, and the log-rank test. No statistically significant differences were found between: (a) the total bond failure rate of recycled and new stainless steel brackets; (b) the upper and lower arches; (c) the anterior and posterior segments. These findings demonstrate that recycling metallic orthodontic brackets can be of benefit to the profession, both economically and ecologically, as long as the orthodontist is aware of the various aspects of the recycling methods, and that patients are informed about the type of bracket that will be used for their treatment.

Acrylic Resins↗
PubMed2004

Microcracks in the alveolar bone following orthodontic tooth movement: a morphological and morphometric study.

Microcracks and microdamage have been associated with bone remodelling. The aim of this study was to investigate the role of microcracks as a trigger for alveolar bone remodelling after the application of an orthodontic load. In 25 3-month-old male Danish land-race pigs, the lower right first molar was moved buccally with a force of 130 cN. The contralateral molar was not treated and was used as an internal control. After 1, 2, 4, 7 and 15 days of treatment, the regions containing the right and left molars were excised and en bloc stained in basic fuchsin. The presence of microcracks on the buccal and lingual sides of both treated and untreated teeth was detected and expressed as crack density (number/mm2). The buccal treated side showed significantly more cracks than the buccal untreated side at day 1. This difference was significantly larger than that observed at days 2, 7 and 15. The same side showed significantly more microcracks than the lingual treated side at day 1, and this difference was larger compared with that observed at days 4 and 15. The presence of more microcracks on the treated side than on the untreated side suggests a role for microcracks in the initiation of bone remodelling after orthodontic loading. The increased presence of microcracks on the side towards which the tooth was moved, and where bone resorption is usually observed, suggests that microcracks could represent the first damage induced by orthodontic force that has to be repaired by bone remodelling. Finally, the strain levels in the alveolar bone during the orthodontic load transfer in the experiment were examined by finite element (FE) analysis. Although this showed that the strains were very low (10-100 microstrain), it should be noted that occlusal loading was not taken into account. In addition, high-resolution microtomography of the alveolar bone/periodontal ligament (PDL) interface revealed that the actual surface of the alveolar bone was very rough, predisposing it to high local stress/strain peaks.

Alveolar Process↗
PubMed2003

Clinical comparison between a modified light-curing denture base resin and a conventional composite resin for orthodontic bonding.

The purpose of this in vivo study was to evaluate and compare the bond failure rate of a modified visible light-cured denture base resin (Triad VLC Provisional Material; Dentsply International Inc., York, PA) with that of a conventional visible light-cured composite resin (Transbond XT; 3M/Unitek, Monrovia, CA) for the bonding of orthodontic brackets. Both adhesives were used in each patient following a split-mouth design. Thirty-five consecutive patients with fixed appliances were included in the study, and the performance of 655 stainless steel brackets was evaluated: 325 brackets were bonded with the modified Triad VLC resin and 330 were bonded with Transbond XT resin. The incidence and site of bond failures were recorded over a period of 12 months. The overall failure rate of Triad VLC (4.3%) was not significantly different (p>0.05) from that of Transbond XT (3.6%). No significant differences in the failure rates of upper and lower arches within each material or between the two materials were found (p>0.05). Transbond XT showed a significantly higher failure rate (p<0.05) in the anterior (4.8%) than in the posterior teeth (1.6%). The present findings demonstrate that Triad VLC could be used as an alternative bonding material for direct bonding of orthodontic brackets.

Acrylic Resins↗
PubMed2003

Long-term assessment of psychologic outcomes of orthognathic surgery.

PURPOSE: This long-term study of post-orthognathic surgery patients aimed at assessing perceptions of problems with physical and psychologic functioning, self-concept, body image, and satisfaction with the surgical outcome based on subjective evaluations. In addition, the patient's perception of self-concept, body image, and function was compared with the perception of pretreatment patients and controls with no treatment need. PATIENTS AND METHODS: One hundred seventeen patients who underwent orthognathic surgery 10 to 14 years earlier and participated in a psychologic study 10 years earlier received questionnaires that were composed of 4 instruments designed to assess these factors. A sample of 92 persons representing a population without treatment need and 39 patients requesting treatment for a malocclusion served as control groups. RESULTS: The findings of this study support the hypothesis that improvement in appearance brought about by orthognathic surgery is associated with improvement in psychosocial adjustment. Orthognathic surgery resulted in subjective estimation of function, appearance, health, and interpersonal relationships that was higher than that among pretreatment and no-treatment control groups. The level of body image and self-esteem approximated but did not reach that of a nonpatient population. CONCLUSIONS: In view of the current psychologic and social environment, patients should be offered the appropriate treatment to correct a disfigurement if it is subjectively perceived by them as a handicap, in part to improve the psychologic outcome.

Adult↗
PubMed2003

Distal molar movement with Kloehn headgear: is it stable?

The aim of this study was to evaluate intramaxillary molar movement after 8 months of cervical traction and posttreatment displacement 7 years later. The total molar displacements in relation to stable intraosseous reference points were compared with those observed in an untreated control group that also had intraosseous reference indicators inserted. During the headgear period, the type of molar displacement could be predicted by the direction of the force system acting on the teeth. It was noted, however, that the variation in the vertical development was related more to each patient's growth pattern than to the force system applied. After cessation of the headgear, intramaxillary displacement of the molars was noted, and the total displacement of the molars did not differ from that of the untreated group. The indication for intramaxillary displacement of the molars by means of extraoral traction is therefore questioned.

Cephalometry↗
PubMed2003

The transfer of occlusal forces through the maxillary molars: a finite element study.

The morphology of the skeleton is known to reflect functional demand. A change in the intramaxillary position of molars can be expected to influence the transfer of occlusal forces to the facial skeleton. A finite element analysis allows us to simulate the displacement of a molar in relation to the well-defined morphology of the maxilla. Three 3-dimensional unilateral models of a maxilla from a skull with skeletal Class I and neutral molar relationships were produced based on CT-scan data. The maxillary first molar was localized so that the contour of the mesial root continued into the infrazygomatic crest. When the molar was loaded with occlusal forces, the stresses were transferred predominantly through the infrazygomatic crest. This changed when mesial and distal displacements of the molars were simulated. In the model with mesial molar displacement, a larger part of the bite forces were transferred through the anterior part of the maxilla, resulting in the buccal bone being loaded in compression. In the model with distal molar displacement, the posterior part of the maxilla was deformed through compression; this resulted in higher compensatory tensile stresses in the anterior part of the maxilla and at the zygomatic arch. This distribution of the occlusal forces might contribute to the posterior rotation often described as the orthopedic effect of extraoral traction.

Alveolar Process↗