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Biomedical subjects

G Andreasen

Publications and source records attributed to G Andreasen.

At least 19 recordsLinked to original sources
PubMed1997

A change in viewpoint promotes use of height-in-picture as a depth cue in 5- to 7-year-olds' drawings of a simple depth relationship.

Height-in-picture emerges between 6 and 7 years of age in children's drawings as the first indication of portrayal of depth relationships, but can be promoted earlier by the use of a number of experimental manipulations. The present studies investigate whether changing, and hence drawing attention to, the child's viewpoint promotes use of height-in-picture. In the first study, 5/6- and 6/7-year-old children were asked to draw two blocks, arranged in depth. Following this, the child-array relationship was altered, either by moving the child through 90 degrees or by rotating the array through 90 degrees. Children then drew again what was now a left-right arrangement, whereupon the transformation was reversed and they made a final drawing. Only when children moved to a new standpoint was there a significant increase in vertical portrayal between first and third drawings. It was not simply the movement of the child that prompted use of height-in-picture because there was no such effect in conditions in which the child was moved but made an unrelated drawing from the new position. These results indicate that making viewpoint salient by asking for a drawing from a new position prompts young children to portray a simple depth relationship.

Age Factors↗
PubMed1994

Processes underlying young children's spatial orientation during movement.

Children between 1.5 and 4 years old were tested for their ability to relocate a hidden object after a 180 degrees self-produced movement around an array of four locations. In one task the object's location relative to the other locations could be uniquely defined within one dimension, while in another two dimensions were needed to do this. No differences emerged between conditions, and by 3 years few errors occurred, despite the fact that children were unable to view the array during movement. This indicates either that young children encounter no specific difficulty in coordinating dimensions or that they solved the task without recourse to such a system. An error analysis supports the second possibility. Children apparently tackled the task by a system directly related to body movement, since errors were frequently the result of incomplete compensation for movement around the array. In a second study in which the four containers were placed in contact, children's performance declined and the relation between direction of movement and error was replaced by some evidence for updating on the near-far dimension accompanied by failure to update the left-right dimension. Thus children appear to change strategy when the problem requires more precise specification of target location.

Child, Preschool↗
PubMed1990

Protraction of the maxillofacial complex.

The purpose of this study was to evaluate the orthopedic effects of reverse headgear therapy in children with skeletal Class III malocclusions. Data based on pretreatment and posttreatment lateral cephalometric radiographs of seven boys and five girls, ages 4 through 14 years, were used. Comparison of the pretreatment and posttreatment cephalograms revealed a significant (p less than 0.05) increase in the SNA angle that indicated the maxilla was positioned farther forward after reverse headgear therapy. Both the maxillary and the mandibular effective lengths increased significantly from pretreatment to posttreatment, as did anterior and posterior total face height. These linear increases are most likely a reflection of growth rather than a direct result of the therapy. There was no significant change in the anteroposterior position of the mandible, although there was a tendency for the mandibular plane angle and the gonial angle to decrease. The results of this study indicate that maxillary protraction with a reverse headgear should be considered an alternative to orthognathic surgery in the treatment of children and adolescents with skeletal Class III malocclusion characterized by maxillary retrognathism.

Cephalometry↗
PubMed1985

Stiffness changes in thermodynamic Nitinol with increasing temperature.

The purpose of this study was to measure and describe the physical properties of a recently-developed thermodynamic Nitinol alloy, type A-138, at intervals of temperature between room and body temperatures. The properties of stiffness, flexure yield strength and permanent deformation were measured, demonstrating that the working range of Nitinol A-138 is directly related to increases in temperature between 75 degrees F and 100 degrees F. As stiffness of the .017'' round A-138 Nitinol wire increases, the yield point decreases. In the loading cycle, yield points dropped from 36 degrees angular deflection at 75 degrees F to 25 degrees at 100 degrees F. In the unloading cycle, the yield point at 75 degrees F was 41 degrees of deflection, with force dropping to zero at 35 degrees; at 100 degrees F, yield point was only 12 degrees and force did not drop to zero until unloaded to 3 degrees angular deflection.

Alloys↗
PubMed1983

Third molars: a review.

The influence of the third molars on the alignment of the anterior dentition is controversial. There is no conclusive evidence to indict the third molars as being the major etiologic factor in the posttreatment changes in incisor alignment. Various aspects related to the management of thd molars are discussed, and specific situations in which third molar extractions are contraindicated are illustrated.

Humans↗
PubMed1980

A clinical trial of alignment of teeth using a 0.019 inch thermal nitinol wire with a transition temperature range between 31 degrees C. and 45 degrees C.

Nitinol has a unique property which is of practical use to the orthodontist. That property is its extreme elasticity when it is drawn into high-strength wire. Nitinol wire is much more difficult to deform during handling and seating in bracket slots than stainless steel wire. At the time of this writing, it is nitinol's extreme elasticity that offers the clinician an advancement in the application of orthodontic materials. This characteristic reduces the loops formerly needed to level a dentition. The wire can be used for longer periods of time without changing it, and it can shorten treatment time needed in leveling the dentition. Nitinol has another remarkable characteristic, that of being able to return to a previously manufactured shape when it is heated through a transition temperature range (TTR). If we are to take advantage of this property, the wire must first be set into the desired shape while undergoing a high-temperature heat treatment. After the wire has cooled to room temperature, it may be deformed within certain strain limits. When heated to its unique TTR, it will "remember" its shape and return to the original configuration. It is this type of wire that is being reported on in the case report that follows.

Adult↗