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Biomedical subjects

B Melsen

Publications and source records attributed to B Melsen.

At least 37 records · Page 2Linked to original sources
PubMed2000

Immediate loading of implants used for orthodontic anchorage.

The healing around an immediately loaded screw was described and related to the bone type, manner of loading and observation time. In four adult macaca fasicularis monkeys, 16 titanium vanadium screws were inserted into the infrazygomatic crest and two in the symphysis region. Immediately after insertion, screws were loaded with 25- and 50-g Sentalloy springs extending to the canines. Following an observation period of 1, 2, 4 and 6 months, the screws and the surrounding bone were removed. Undecalcified serial sections perpendicular to the long axis were made and the degree of osseointegration studied. Two of the screws were lost immediately after insertion. Of the remaining screws, osseointegration was present around all, but two. The integration was independent of bone type, trabecular or cortical, but increased with time. Based on the results of this study, the use of screws described in the report can be recommended as anchorage units in cases where conventional anchorage is not possible.

Journal Article↗
PubMed2000

The design of custom orthodontic mechanics.

The straightwire appliance promises prescribed tooth positions within the arches. Unfortunately, such an outcome is not necessarily achieved, especially in the adult patient. Teeth do not always move according to a template. Continuous archwires do not allow for differentiation between active and reactive units; consequently, the correct force system is never developed. These shortcomings could be overcome by custom-designed mechanics. Here we report on the use of Dental Movement Analysis (DMA) software supported by two clinical examples. On the computerized occlusogram, DMA stimulates the desired tooth movements and computes the force vectors and moments necessary to achieve the planned result. These images enable the clinician to fabricate a custom appliance for maximum efficiency. Maximum efficiency results in minimal treatment time.

Journal Article↗
PubMed2000

The rate and the type of orthodontic tooth movement is influenced by bone turnover in a rat model.

The influence of bone metabolism on both the rate and the type of orthodontic tooth movement was investigated. A rat model in which high (n = 16) and low (n = 17) bone turnover was pharmacologically induced was used. A non-pharmacologically treated group (n = 19) served as the control. A mesially directed constant single force of 25 cN was applied to the upper left first molar for a period of 3 weeks. The study was performed as a split-mouth design, the contralateral side of each animal serving as its control. The displacement of the molar crown was measured with an electronic calliper, while changes in inclination of the teeth were measured from micro-CT scans of the excised maxillae. The bone turnover significantly affected the rate of tooth movement. In the case of high turnover, the rate of tooth movement was increased while it was reduced in the case of low turnover. A controlled mesial tipping in all three groups was observed, but the actual location of the centre of rotation seemed to be influenced by the metabolic state of the bone. Based on the results it can be concluded that deviations in bone turnover influence the response to orthodontic forces, and should be taken into consideration when planning orthodontic treatment in patients with metabolic bone disease or those on chronic medication influencing bone metabolism.

Analysis of Variance↗
PubMed1999

Effect of variation in tooth morphology and bracket position on first and third order correction with preadjusted appliances.

Major effort is put into the design of brackets to accomplish an optimal completion of orthodontic treatment with respect to 1st, 2nd, and 3rd order corrections. Because such brackets are standardized, the intraindividual variation of the teeth is not taken into consideration. The influence of vertical bracket displacement on 1st and 3rd order corrections was studied on the plaster models, including all teeth from central incisors to first molars, of 28 young persons. The facial contours were evaluated at the mesial, central, and the distal aspect of the bracket. The contours were calculated with the formula of a parabola, and the fit was found sufficient. Intertooth variation was extreme, the biggest curvature was found among the first mandibular molars. The variation was also marked between corresponding teeth. It can be concluded that the intraindividual variation in tooth morphology is larger than the variation between the different types of preadjusted appliances. Thus, if the straight wire approach should be followed, the bracket would have to be custom made. All the calculations were made with the precondition that full size wires were used. If this is not the case, the discussion concerning individual prescription is only of limited importance.

Adolescent↗
PubMed1999

Differences in static cortical bone remodeling parameters in human mandible and iliac crest.

Knowledge of the baseline turnover characteristics, and of possible general and local factors influencing alveolar bone responses, is particularly important in the planning of oral rehabilitation. The conventional tool used to obtain information on bone turnover is the iliac crest biopsy, but it is not clear whether it mirrors the situation involving the jaws. The aim of this study was to compare static bone remodeling parameters in the mandible and in the iliac crest to obtain baseline values for the mandible and to test the hypothesis of site specificity of bone remodeling. Bone specimens were obtained from 50 subjects (mean age 64 +/- 17) at autopsy. Three sites were sampled: iliac crest; jaw angle; and foramen mentalis area. In addition, occlusal status was recorded. On undecalcified thin sections, cortical porosity (Ct.Po), eroded sites (ESi), formative sites (FSi), osteonal diameter (On.Dm), Haversian canal diameter (H.Ca.Dm), and wall width (W.Wi) were measured. Ct.Po in the jaw angle and in the foramen mentalis area was lower (48% and 50%, respectively) than in the iliac crest, as was ESi and FSi (80% in the jaw angle and 74% in the foramen mentalis area). In the foramen mentalis area, Ct.Po was greater in subjects with occlusion. On.Dm, H.Ca.Dm, and W.Wi were significantly larger and mutually correlated within the mandible, whereas no correlation was found between mandibular sites and iliac crest. Static cortical bone remodeling parameters are different in the mandible and the iliac crest, thus confirming the hypothesis of site specificity of bone remodeling. Within the mandible, the parameters were correlated, whereas there was no correlation between the mandible and the iliac crest. This could be ascribed to the different functional demands to the mandible and the iliac crest, which was also reflected in the observed influence of functional occlusion on bone remodeling in the mandible. It can thus be concluded that bone reaction to dental intervention is more dependent on the local environment than on general bone turnover as reflected by the iliac crest.

Analysis of Variance↗
PubMed1999

3-D experimental identification of force systems from orthodontic loops activated for first order corrections.

Intra-arch irregularities can be corrected using wire of low stiffness, wires of increasing stiffnesses, or by the activation of loops built into the appliance. While the orthodontist controls only the magnitude of force when leveling with continuous arches, the configuration and positioning of loops offer the possibility of controlling the type and direction of force. In the present study, force systems developed by the L-loop, the T-loop, and the rectangular (R-) loop were analyzed with respect to the force systems acting for first order irregularities, buccolingual movement, and rotation along the long axis of the tooth. An interbracket distance of 21 mm was chosen, and the loops were analyzed in a testing machine that made it possible to register forces and moments simultaneously in three planes of space. The activations included a symmetrical translation of 1 mm made in steps of .2 mm, corresponding to a buccolingual movement, and 10-degree rotations clockwise and counterclockwise in steps of one degree. Force systems were recorded during activation and deactivation. Loops made of TMA wire delivered 40% of the force delivered by the same loops made of stainless steel wire. The T-loop generated a force system that deviated qualitatively only slightly from that delivered by a straight wire. The L-loop generated a force system that was dependent on orientation; constancy was better corresponding to the anterior part of the loop. It was evident that the rectangular loop was capable of generating any desired moment-to-force ratio, and the R-loop demonstrated a high degree of constancy of the force system. Rectangular loops should, therefore, be preferred for making first order corrections.

Dental Alloys↗
PubMed1999

Biological reaction of alveolar bone to orthodontic tooth movement.

Direct and indirect resorption are perceived as reactions to an applied force. This is in contrast to the view of orthopedic surgeons, who describe apposition as a reaction to loading of bone. A histomorphometric study of the circumalveolar bone reaction to a force system generating translation of premolars and molars of five maccaca fascicularis monkeys is described. Three force levels (100 cN, 200 cN, and 300 cN) were applied for a period of 11 weeks. Undecalcified serial sections were cut parallel to the occlusal plane, and a grid consisting of three concentric outlines of the root intersected by six radii was placed on each section. Areas anticipated to be submitted to different stress/strain distributions were isolated. A-posteriori tests were used in order to separate areas that differed with regard to parameters reflecting bone turnover. Based on these results, a new hypothesis regarding tissue reaction to orthodontic forces is suggested. Direct resorption could be perceived as a result of the lowering of the normal strain from the functioning PDL and as such, as a start of remodeling, in the bone biological sense of the word. Indirect remodeling could be perceived as a sterile inflammation attempting to remove ischemic bone under the hyalinized tissue. At a distance from the alveolus, dense woven bone was observed as a sign of a RAP (regional acceleratory phenomena). The apposition could, according to the new hypothesis, be perceived as a result of the bending of the alveolar wall produced by the pull from the Sharpey fibers. The above suggested interpretation of tissue reaction would be shared with bone biologists.

Adaptation, Physiological↗
PubMed1999

Endochondral vs. intramembranous demineralized bone matrices as implants for osseous defects.

This study focuses on the difference in regenerative capacity between endochondral and intramembranous demineralized bone matrices (DBMs) when implanted into bony defects. It also focuses on the possible influence of the type of skeletal recipient site (orthotopic or heterotopic). Of 34 Wistar rats, 10 served as a source of DBM, and 24 were divided into two groups of 12 animals. In group A identical defects were produced in the parietal bones, whereas in group B the defects were produced in each radius. The right defects were implanted with endochondral DBM and the left defects were implanted with intramembranous DBM. Descriptive and/or histomorphometric analyses were performed by means of light and polarized microscopy, and radiography (group B). Right and left data were compared to disclose differences in bone-healing capacity. The quantitative results demonstrated that endochondral DBM displays a greater regenerative capacity than intramembranous DBM when implanted heterotopically. The different clinical performances of endochondral and intramembranous bone grafts might be explained on the basis of the mechanical rather than the osteoinductive principle. The qualitative results suggest that the type of bone deposition induced by the DBMs is not related to the type of implanted DBM. Recipient site characteristics and/or environmental factors seem decisive in the occurrence of either types of ossification.

Animals↗
PubMed1999

Force systems developed by six different cantilever configurations.

OBJECTIVES: To describe the force systems developed by cantilevers with different configurations during incisor intrusion. DESIGN: A two-dimensional Finite Element model. SETTING AND SAMPLE STUDIED: Laboratories of the Department of Orthodontics, Royal Dental College, Aarhus University, Denmark. The materials studied comprised cantilevers made of 0.017" x 0.025" TMA wire. EXPERIMENTAL VARIABLE: Vertical activation of the six different modelled cantilever configurations. OUTCOME MEASURE: Force level and direction during activation and deactivation analysed at the point of force application. RESULTS: The force direction was dependent on the configuration of the cantilever. Only the cantilevers with a curvature produced combined retraction and intrusion forces. All other configurations resulted in combined protrusion and intrusion, which reversed into retraction and intrusion, according to the variations in deactivation. CONCLUSION: The choice of correct cantilever configuration is important when selecting the mechanics of intrusion for a particular patient.

Dental Stress Analysis↗
PubMed1999

Clinical comparison between a resin-reinforced self-cured glass ionomer cement and a composite resin for direct bonding of orthodontic brackets. Part 2: Bonding on dry enamel and on enamel soaked with saliva.

The purposes of this investigation were to compare the clinical performance of a resin-reinforced self-cured glass ionomer cement to a standard composite resin in the direct bonding of orthodontic brackets when bonded onto: a) dry teeth and b) teeth soaked with saliva. The two bonding agents were compared using a split-mouth design. In that, both systems were used for direct bonding of stainless steel brackets in every patient. Thirty-eight consecutive patients with fixed appliances were followed for a period of 12 months. The patients were randomly divided into two groups: group A (11 patients) and group B (27 patients). In group A, the performance of 220 stainless steel brackets was evaluated: 110 brackets were bonded with GC Fuji Ortho glass ionomer cement (GC Industrial Co., Tokyo, Japan) onto dry teeth, and 110 bonded with System 1+ composite resin (Ormco Corp., Glendora, CA). In group B, the performance of 540 stainless steel brackets was evaluated: 270 brackets were bonded with GC Fuji Ortho onto teeth soaked with saliva, and 270 bonded with System 1+. In group A, GC Fuji Ortho recorded an overall failure rate (34.5%) significantly higher (p < 0.05) than System 1+ (9%) when applied onto completely dry teeth. Conversely, in group B, no statistically significant differences (p > 0.05) between the failure rates of the two bonding agents were found when GC Fuji Ortho was used on teeth soaked with saliva. It was concluded, therefore, that GC Fuji Ortho shows clinically acceptable bond strengths when bonded onto moist teeth, but not when used on dry enamel. Both bonding agents failed mostly at the enamel/adhesive interface, without causing any enamel damage.

Acrylic Resins↗
PubMed1998

Frictional forces related to self-ligating brackets.

Orthodontic tooth movement can be regarded as teeth sliding on a wire like pearls on a string, the force being supplied by springs or elastics. The movement implies friction between wire and bracket, taking up part of the force and leaving an uncontrolled amount to act on the teeth. The friction is likely to depend on bracket construction and wire material. Therefore, in this investigation the friction of self-ligating brackets and beta-titanium wires was evaluated, as opposed to more conventional configurations. Carried by low-friction linear ball bearings, a bracket was made to slide along an out-stretched archwire with minimal (and known) basic friction, either parallel or at an angle to the wire. Two self-ligating brackets were used in their closed position without any normal force. Friction was tested against four wires: stainless steel and beta-titanium, both in round and rectangular cross-sections. The force used to overcome friction and to move the bracket was measured on a testing machine at 10 mm/min, and the basic friction was subtracted. The results show that round wires had a lower friction than rectangular wires, the beta-titanium wires had a markedly higher friction than stainless steel wires, and friction increased with angulation for all bracket/wire combinations. The self-ligating brackets had a markedly lower friction than conventional brackets at all angulations, and self-ligating brackets, closed by the capping of a conventional design, exhibited a significantly lower friction than self-ligating brackets closed by a spring. The selection of bracket design, wire material, and wire cross-section significantly influences the forces acting in a continuous arch system.

Analog-Digital Conversion↗
PubMed1998

Importance of the critical-size bone defect in testing bone-regenerating materials.

A substantial interest exists in developing substitute materials and human recombinant bone-inducing factors to enhance bone regeneration both in the craniofacial complex and in other parts of the skeleton. A persistent problem has been to find an animal model that allows for the comparison of different osteopromotive materials. The purpose of this investigation was 1) to determine whether a 5-mm calvarial defect in adult rats fulfilled the requirements of a critical-size bone defect and 2) to discuss the use of this animal model in assessing bone repair in the craniofacial region. Bilateral full-thickness calvarial defects were trephined in the calvarial bone of 56 5- to 6-month-old Wistar rats. Except for minor amounts of bone formation limited to the margins of the defect, none of the defects revealed any signs of spontaneous bone regeneration 6 and 12 months after surgery. The full-thickness 5-mm calvarial defects thus fulfill the criteria for a critical-size bone defect. This animal model allows for an experiment with a paired design, it avoids inclusion of the sagittal suture in the osseous defect, and it thereby minimizes morbidity by reducing the risk of damaging the midsagittal sinus. An adequate experimental model has been developed to evaluate the efficiency of osteopromotive materials in the healing of bone defects in the craniomaxillofacial region.

Animals↗
PubMed1998

Clinical comparison between a resin-reinforced self-cured glass ionomer cement and a composite resin for direct bonding of orthodontic brackets Part 1: Wetting with water.

The purpose of this study was to compare the clinical performance of a resin-reinforced self-cured glass ionomer cement to a standard composite resin in a split mouth design, by using both systems for direct bonding of orthodontic stainless steel brackets in every patient. Forty eight patients (34 females and 14 males, of which 29 were adults > 18 years of age) with fixed appliances were followed for a mean period of 10 months (range 4-16 months). The performance of 864 stainless steel brackets was evaluated: 404 brackets were bonded with GC Fuji Ortho glass ionomer cement (GC Industrial, Tokyo, Japan) onto teeth soaked with water, and 460 were bonded with System 1+ composite resin (Ormco, Glendora, CA). System 1+ recorded an overall failure rate (18.2%) significantly higher (p < 0.05) than GC Fuji Ortho (7.9%). There were no statistically significant differences (p > 0.05) between the failure rates in the upper and lower arches with either material. Both in the upper and lower arches, System 1+ exhibited a failure rate significantly higher (p < 0.05) than GC Fuji Ortho. When the bonding performance of the six anterior teeth was compared with first and second premolars, no statistically significant differences were found (p > 0.05) between bonding agents in either arch. System 1+ exhibited a failure rate significantly higher (p < 0.05) than GC Fuji Ortho, both in the anterior and posterior segments. Both bonding agents failed mainly at the enamel-adhesive interface, without causing any damage to the enamel.

Acrylic Resins↗
PubMed1998

Miniscrews as orthodontic anchorage: a preliminary report.

The problems related to anchorage for orthodontic tooth movements in patients with deficient dentition are discussed, and various solutions suggested in the literature, including "onplants," implants, and zygoma wires, are evaluated. A miniscrew is presented as alternative anchorage, and possible locations for placement are discussed, based on studies of bone quality in dry skulls. Application of the miniscrew as anchorage for various types of tooth movement is demonstrated. Miniscrews are easily placed and removed and can be loaded immediately following insertion. However, stability is limited after loading with torsion.

Bone Screws↗
PubMed1997

Combined intrusion and retraction generated by cantilevers with helical coils.

Combined retraction and intrusion of the anterior teeth is often needed as part of orthodontic treatment. The use of a statically determinate force system has many advantages over statically indeterminate systems. In the case of the cantilevers the orthodontist can evaluate the line of action of the delivered force directly in the clinical situation. In the present paper the force system delivered by stainless steel and beta titanium cantilevers with an eccentrically placed helix was evaluated. The cantilever consisted of a straight piece of wire bent to form a helix with an external diameter of 3 mm. The wire was fixed into a bracket of sensor 1, touching sensor 2 of a test bench with a 1-point contact to. Activation was induced by rotating sensor 1 into which the wire was tightly fixed. This was done in 2 different modes, one in the direction in which the helix was bent and one in the opposite direction. With an interval of 5 degrees the force system generated with respect to sensor 1 and the direction of the force delivered to sensor 2 (the other bracket) were registered. The results were expressed graphically and the influence of material and activation mode were evaluated statistically by comparing the coefficient of regression. As expected, the influence of the material reflected the relative stiffness of the 2 alloys. As TMA is monocrystalline (i.e. consists of homogeneous crystals) the mode of activation did not reflect any significant Bauschinger effect as seen in the case of stainless steel. Analysis of the force direction confirmed that the suggested wire configuration is useful for delivery of a predetermined combination of horizontal and vertical force. This was confirmed by a finite element analysis.

Dental Alloys↗
PubMed1997

Orthodontic treatment of a patient with multidisciplinary problems.

This report reviews the orthodontic treatment of a patient suffering from a metabolic disease controlled by medication. The patient also had periodontal problems on both hard and soft tissue support. The results of involvement of general medicine, periodontal surgery, and proper biomechanics is shown and the problems of the multidisciplinary treatment discussed.

Adolescent↗