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Biomedical subjects

T R Meling

Publications and source records attributed to T R Meling.

At least 19 recordsLinked to original sources
PubMed2001

The effect of short-term temperature changes on superelastic nickel-titanium archwires activated in orthodontic bending.

The bending stiffness of superelastic nickel-titanium archwires is influenced by alterations in mouth temperature. The activation and deactivation phases of a load-deflection loop of superelastic wires have different stress-magnitudes. This investigation compared the effect of short-term cooling or heating on the bending force exerted by nickel-titanium archwires. Two rectangular superelastic and one conventional nickel titanium wire were tested in bending at 37 degrees C. The specimens were tested during the activation phase and during the deactivation phase. The wires were kept at constant strain and the bending force was measured continually while the activated specimens were subjected to cold (10 degrees C) or hot (80 degrees C) water. The test situation simulates a patient's archwire that is subjected to cold or hot drinks or food during a meal. The conventional nickel-titanium wire was marginally affected by brief cooling or heating, regardless of activation phase. In contrast, the superelastic wires were strongly affected by short-term application of cold or hot water. When tested in activation phase, the effect of heating was transient whereas the wires continued to exert sub-baseline bending forces after short-term application of cold water. When tested in deactivation phase, the effect of cooling was transient whereas the wires exerted supra-baseline bending forces after a short-term application of hot water. The effect of short-term temperature changes on the bending stiffness of superelastic nickel titanium archwires is dependent upon the bending phase. Cooling induced transient effects on a wire in its deactivation phase, but prolonged effects when the wire was tested in the activation phase. In contrast, the effect of short-term heating was transient when the wire was tested in the activation phase, but prolonged when the wire was tested in the deactivation phase.

Cold Temperature↗
PubMed2000

[Metotopic craniosynostoses].

BACKGROUND: Premature closure of the metopic suture leads to inhibited growth of the frontal bones, producing a keel-shaped forehead (trigonocephaly). Simple metopic synostosis is usually sporadic. Trigonocephalic patients account for 8-16% of the referrals to craniofacial centers, with a marked male predominance. Intracranial pressure (ICP) may be increased, whereas shunt-dependent hydrocephalus is infrequent. Infrequently, patients have intra- or extracerebral anomalies; one third have varying degrees of neuropsychological problems. The treatment is primarily surgical. MATERIAL AND METHODS: We present two patients who during infancy developed increasingly keel-shaped foreheads, retruded orbital rims, increased biparietal diameter and close-set eyes (hypothelorism). Both had raised ICP, but normal psychomotoric development. They were operated using radical fronto-orbital surgical remodelling. RESULTS: Recovery was uneventful. Three months post-operatively, they had pleasing cosmetic results with no symptoms of increased ICP. INTERPRETATION: Where metopic craniosynostosis is suspected, the infant should be examined clinically with palpation of fontanelles and sutures, evaluated with respect to the shape and development of the facial skeleton, as well as by X-ray of the skull sutures. Radical fronto-orbital surgical remodelling gives a stable correction of the craniofacial deformity and generally a satisfactory cosmetic result.

Cephalometry↗
PubMed2000

[Distraction osteogenesis--a new therapeutic principle in complex craniofacial synostosis].

BACKGROUND: Surgical treatment of syndromal craniofacial synostosis consists of combined neurosurgical and maxillofacial reconstructions of the neurocranium and midface. Patients often need several operations if they are to achieve a functionally and cosmetically good result. This is, in part, due to limitations in the amount of "acute" correction possible peroperatively with conventional surgical technique. MATERIAL AND METHODS: In recent years, a new method called distraction osteogenesis has been developed, by which the skeletal elements are gradually advanced. The method is based upon a process whereby the reparative callus formed between the surfaces of two bone segments is subjected to traction. This leads to new bone formation parallel to the vector of distraction. RESULTS: Distraction osteogenesis allows for greater mobilizations, hence the promise of fewer reoperations. INTERPRETATION: The method seems to be a valuable treatment modality in syndromal craniofacial synostosis, where major fronto-orbital, midface or maxillary reconstructions are often called for.

Craniofacial Dysostosis↗
PubMed2000

[Frontoethmoidal meningoencephaloceles].

Frontoethmoidal meningoencephalocele is a rare congenital disease where intracranial masses protrudes through a midline defect at foramen coecum from the anterior cranial fossa into the facial skeleton. The patient presents at birth with a soft-tissue swelling at the nasal bridge. In the majority of cases, the cele is completely covered by skin. The face is elongated, the nasal bridge is broad, the upper part of the nose is long, and the patients have telecanthus. Frequently, the patients have a normal psychomotor development, but may have intracerebral malformations and a shunt dependent hydrocephalus. Spinal fluid leakage may result in meningitis. Anosmia is infrequent. The patients may have a wide range of ophthalmological problems. Newborns with meningoencephalocele should be examined by a neurosurgeon. The investigation and work-up commences with a multidisciplinary approach. We present two patients with meningoencephaloceles.

Child↗
PubMed2000

Monobloc and midface distraction osteogenesis in pediatric patients with severe syndromal craniosynostosis.

We present 2 children with severe syndromal craniosynostosis who were in need of urgent midface advancement surgery due to recurrent ocular dislocations (Pfeiffer's syndrome type II) or severe upper respiratory obstruction (Crouzon's syndrome). They were operated using distraction osteogenesis, with gradual midface or monobloc advancements. In the Pfeiffer patient, a maxillary distraction of 25 mm achieved effective cessation of ocular dislocations, whereas a 23-mm monobloc advancement in the Crouzon patient achieved cessation of nocturnal arterial desaturations. No major postoperative complications were recorded. Distraction osteogenesis has become a versatile and safe technique that allows for large skeletal advancements.

Acrocephalosyndactylia↗
PubMed1999

[Young males have scant knowledge of anatomy and physiology].

When communicating with patients, doctors make assumptions as to their ability to comprehend and adjust the complexity of the information accordingly. We studied the knowledge of anatomy and physiology among young men. 150 men, 18 to 26 years old, serving mandatory military service, were interviewed during doctor consultations. The patients had a minimum of nine years of education; 93% had completed upper secondary school or started education at college level. In order to locate organs and indicate organ size, the patients were asked to draw an outline of the heart, kidneys, liver, spleen, appendix and thyroid gland on a pre-drawn outline of the human body. The patients were also asked to explain the major function(s) of these organs in lay terms. Responses were judged as "correct", "partially correct" and "incorrect" against pre-set criteria. The percentage of correct replies with respect to organ location ranged from 9% (spleen) to 49% (appendix), from 4% (liver) to 53% (appendix) with respect to organ size, and from 0.7% (thyroid gland) to 92% (heart) with respect to organ function. Young men have deficient knowledge of the locations and functions of important internal organs. In addition to correct diagnosis and the start of optimal treatment. consultations should include patient education.

Adolescent↗
PubMed1998

Short-term temperature changes influence the force exerted by superelastic nickel-titanium archwires activated in orthodontic bending.

BACKGROUND: Alterations in mouth temperature may lead to changes in the force exerted by an activated superelastic wire. It has been assumed that variations in archwire stiffness associated with short-term cooling or heating are transient. This investigation studied the effect of short-term cooling or heating on the bending force exerted by nickel-titanium archwire. MATERIAL AND METHODS: Six rectangular superelastic wires and one conventional nickel-titanium wire were tested in bending at 37 degrees C. The test specimens were deflected 0.5 mm, and the bending force was measured continually. The activated specimens were subjected to cold (10 degrees C) or hot (80 degrees C) water under constant deflection, simulating an inserted archwire that is subjected to cold or hot drinks or food during a meal. RESULTS: The conventional nickel-titanium wire was marginally affected by brief cooling or heating. In contrast, some of the superelastic wires were strongly affected by short-time application of cold or hot water. Whereas the effect of brief heating disappeared quickly, some wires continued to exert sub-baseline bending forces (up to 32% less) after short-time application of cold water and showed little or no tendencies toward increase even after 30 minutes of postexposure restitution (up to 43% less). CONCLUSIONS: Short-term exposures to hot liquid increased the bending force exerted for a given deflection transiently. The effect of short-term exposures to cold liquid was not always transient; the bending force remained sub-baseline for a number of the thermosensitive wires tested for a prolonged time.

Dental Alloys↗
PubMed1998

The effect of second-order couple on the application of torque.

Complex combinations of linear forces, moments, and couples are developed by the arch wire during orthodontic treatment. For instance, application of torque to a canine during distal driving may create force interactions if the tooth tips distally toward the extraction site. This investigation studied the effect of second-order couples and bracket angulations on the application of torque to a single tooth. By using a test apparatus to simulate application of torque to a single tooth, 0.016 x 0.022 inch stainless steel wires were tested in longitudinal torsion simultaneous to fixed amounts of second-order couples or fixed degrees of second-order bracket angulation. Application of a second-order couple through a bracket to a longitudinally twisted arch wire produces a third-order couple, since the bracket slot walls exert forces on the wire, tending to detwist it. This third-order couple will usually be small as the distance between the two couple members is short. Nevertheless, it may have a restraining effect on the third-order wire-bracket interaction. The results show that application of second-order couples or bracket angulations lead to an increase in exerted torque for angles of twist below 22 degrees. Because of torsional play, a wire twisted 18 degrees in a 0.018-inch bracket slot did not exert any torque unless it was subjected to a second-order couple. Thus, in an in vivo situation where forces interact, the actual torsional play may be substantially less than predicted from theoretical models only regarding third-order mechanics. The restraining effect of second-order couples tapered when the torque created by longitudinal twisting became much larger than the torque exerted by the second-order couple. Second-order couples of biologically acceptable magnitudes had little effect on the level of torque after the third-order clearance had been eliminated.

Cuspid↗
PubMed1998

On bracket slot height: a methodologic study.

Effective bracket slot height is estimated by using a formula that describes the relationship between bracket slot height, wire dimensions, wire edge bevel, and torsional play (third-order clearance). With a torque measuring instrument, the torsional play was estimated for 10 different brackets (0.018-inch stated slot) of the same manufacturer and type. One arch wire with known dimensions and edge bevel was used for all the measurements. With known torsional play, wire dimensions and edge bevel, the bracket slot height could be calculated. This was performed five times for each bracket and the method error for estimation of torsional play for a single measurement was 0.04 degrees, corresponding to 0.36 mm in slot height. The brackets tested had a mean slot height of 0.476 +/- 0.003 mm, with a range of 0.470 to 0.481 mm (0.0187 +/- 0.0001 inches, range 0.0185 to 0.0189). The variation in bracket slot height was much greater than the method error. The method used to measure bracket slot height seems to have a high degree of accuracy and is easier to implement than conventional methods.

Analysis of Variance↗
PubMed1998

The effect of cross-sectional dimensional variations of square and rectangular chrome-cobalt archwires on torsion.

The purpose of this investigation was to study the control of cross-sectional dimensions and edge bevel by various manufacturers in the production of chrome-cobalt archwires and this effect on transmitting torque through an .018 inc slot bracket system. Twenty-seven different square and rectangular chrome-cobalt wires commonly used in the edgewise technique supplied by five different manufacturers were studied with respect to dimensions, edge bevel, and mechanical properties in torsion. The mechanical study simulated application of torque to an individual tooth. Standard brackets with .018 inch slot heights were used. The results show that variation in cross-sectional dimension and edge bevel leads to variable torsional play (third-order clearance). As an example, .016 x .016 wires have a mean torsional play of as much as 26.8 degrees, with a range of 21.0 to 32.3 degrees. When using .016 x .016 wires, one must apply from 34.8 to 48.6 degrees of twist to get 20 N-mm of torsional moment. This variation is primarily due to the rather wide range in torsional play. As a result, the prediction by which a predetermined torsional moment can be delivered becomes uncertain. The results also show that because the working range in torsion of chrome-cobalt wires is somewhat limited due to high torsional stiffness, precise delivery of torsional moment based on the condition present in the oral cavity is difficult. The torsional stiffness varies between manufacturers within the various dimensional groups as a result of differences in cross-sectional geometry and material properties.

Analysis of Variance↗
PubMed1998

The effect of temperature on the elastic responses to longitudinal torsion of rectangular nickel titanium archwires.

To investigate responses to longitudinal torsion and the effect of temperature on the torsional stiffness of superelastic nickel titanium archwires, eight batches of rectangular wires were tested at 18, 27, 37, and 40 degrees C ambient temperature. The wires were twisted 25 degrees and studied in deactivation. The resulting torque-twist diagrams show that only half the wires had discernible deactivation plateaus at body temperature. The plateaus were generally narrow (1 to 3 degrees) and started at 20 to 23 degrees of torsional twist. The clinical significance of these deactivation plateaus is debatable. Only one wire had a well-defined plateau that was fairly wide (6 degrees) and started at a lower level of twist (17 degrees). The wires without plateaus when deactivated from 25 degrees of twist were retested at body temperature. All exhibited deactivation plateaus subsequent to activating twists of 45 and 60 degrees, and the plateaus became more distinct as the degree of prior activation increased. This indicates that the stress imparted on the alloys by 25 degrees of activating twist is insufficient to induce martensitic transformation at body temperature. As prescriptions advocate bracket pretorque of less than 25 degrees for a maxillary central incisor, the clinical relevance of alloys requiring large activations before they demonstrate deactivation plateaus is questionable. Half the wires tested were markedly influenced by ambient temperature changes; the other half were relatively insensitive to temperature. Responsiveness to thermal stimuli seemed closely related to superelastic tendency.

Copper↗
PubMed1998

The effect of short-term temperature changes on the mechanical properties of rectangular nickel titanium archwires tested in torsion.

Due to their exceptional temperature sensitivity, superelastic nickel titanium wires may be affected by temperature changes associated with ingestion of cold or hot food. It has been assumed that the alterations in archwire stiffness associated with short-term cooling or heating are transient. This investigation studied the effect of these temperature changes on the torsional stiffness of nickel titanium alloys. Eight rectangular superelastic wires were activated to 20 degrees, in longitudinal torsion at body temperature and subjected to cold (10 degrees C) or hot (80 degrees C) water with the strain held constant. The torsional stiffness of some wires was strongly affected. The effect of hot water disappeared quickly, but the wires remained at a level of reduced torsional stiffness (up to 85% less than baseline) after short applications of cold water. The most thermodynamic archwires showed incremental reductions in torsional stiffness when cold water was repeatedly applied. Furthermore, the torsional stiffness remained low (up to 50% less than baseline) and showed no tendency to increase even after 2 hours of post-exposure restitution. It is conceivable that some wires may provide inadequate forces for tooth movement after ingestion of cold liquids.

Beverages↗
PubMed1998

On the variability of cross-sectional dimensions and torsional properties of rectangular nickel-titanium arch wires.

Twenty-five rectangular superelastic or conventional work-hardened nickel-titanium alloy wires, commonly used in the 0.018-inch edgewise technique, supplied by seven different manufacturers, along with one braided nickel-titanium and two beta-titanium wires, were studied with respect to wire dimensions, edge bevel, and mechanical properties in longitudinal torsion at 37 degrees C. The wires were twisted 25 degrees and studied in deactivation, simulating application of torque to an individual tooth. Standard Siamese brackets. with stated slot heights of 0.018 inches and measured slot heights of 0.0187 inches, were used. Most wires were within +/-0.0005 inches of the stated dimensions, but had more edge bevel than previously reported for stainless steel and chrome-cobalt alloy wires. Variations in wire dimensions and edge bevel led to variable torsional (third-order) clearance. The torsional stiffness varied among manufacturers within the various wire sizes, this being the result of differences in actual cross-sectional geometry and material properties. None of the tested wires exhibited superelastic properties under the current conditions, and only one wire had a superelastic tendency.

Dental Alloys↗
PubMed1997

On mechanical properties of square and rectangular stainless steel wires tested in torsion.

Forty different sizes and types of square and rectangular stainless steel wires, supplied by five different manufacturers, were tested in torsion. The study simulated the situation occurring when torque is applied to an individual tooth. We used standard brackets with 0.018-inch slot heights, with an interbracket distance of 4 mm. The results show that variation in cross-sectional dimension and edge bevel leads to variable torsional play (third-order clearance). As an example 0.016 x 0.022-inch wires have a mean torsional play of as much as 18.5 degrees, with a range of 16.6 degrees to 20.4 degrees. We have shown that when 0.016 x 0.022-inch wires are used, one must apply from 24.6 degrees to 29.2 degrees of twist to get 20 Nmm of torsional moment. This variation is mostly due to a rather wide range in torsional play. As a result, the prediction by which a predetermined torsional moment can be delivered becomes uncertain. The results show that because the working range in torsion of stainless steel wires is somewhat limited, precise delivery of torsional moment, based on the condition present in the oral cavity, is difficult. Torsional stiffness varies considerable within the various dimensional groups, this being the result of variation in cross-sectional geometry and material properties.

Analysis of Variance↗
PubMed1997

The effect of friction on the bending stiffness of orthodontic beams: a theoretical and in vitro study.

The purpose of this study was to investigate the effect of friction on the bending stiffness of orthodontic beams. A theoretical and experimental model have been established where tensile and compressive forces are applied to an arch wire to simulate the effect of additional friction during activation and deactivation, respectively. The results show that tensile force increases wire stiffness, and that compressive force increases flexibility. Thus more force will be needed during activation and more force will be lost during deactivation. The amount of force lost increases nearly linearly with increasing friction. During activation, the percentage increase in force due to friction for a given deflection is about equal to the loss of force due to friction during deactivation. Friction affects thin flexible wires more than heavy wires. Careful ligation is recommended in the leveling phase to reduce the negative side effects of friction.

Compressive Strength↗
PubMed1996

[Growth hormone deficiency in adults].

Growth hormone (GH) has been in clinical use for almost 40 years to promote linear growth in growth hormone deficient children. Treatment has usually been stopped after the epiphyseal plates have fused or when the person reaches a proper height. Previously, GH replacement therapy in adults was not deemed clinically indicated. GH-deficiency in adults is now accepted as a clinical entity, manifested by cardiovascular dysfunction, dyslipidemia, reduced capacity for exercise and muscular weakness, altered body composition, increased prevalence of osteoporosis, and impaired psychological well-being. The treatment of adults used to be unrealistic, because of the limited supply of human pituitary-derived GH. Moreover, the risk of transferring Creutzfeldt-Jakobs disease led to a stop in the therapeutic use of pituitary GH preparations. The availability of recombinant human prion-free GH has made replacement therapy possible in GH-deficient adults. In this review, the GH deficiency syndrome in adults is described, together with the results of recent clinical studies of GH replacement treatment in adults.

Adult↗
PubMed1996

Growth hormone deficiency in adults: a review.

For more than 35 years, growth hormone (GH) has been used to promote linear growth in GH-deficient children. Previously, GH replacement in adults was limited to the supply of human pituitary-derived GH. In addition, until recently, GH replacement was not deemed clinically indicated. With the introduction of recombinant human prion-free GH, replacement therapy in GH-deficient adults has become feasible, and its use has burgeoned. In this review, recent studies on GH therapy in healthy and GH-deficient adults are evaluated to provide a rational basis for the widened scope of its clinical application.

Adult↗