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Biomedical subjects

M F Land

Publications and source records attributed to M F Land.

At least 37 records · Page 2Linked to original sources
PubMed1994

Disturbance of the dentinal smear layer by acidic hemostatic agents.

The pH of nine commonly used hemostatic agents was measured. Three measurements were recorded for each solution, and values ranged from 0.7 to 2.0. The effect of exposure to one hemostatic material, ferric sulfate solution (Fe2(SO4)3), on the dentinal smear layer was investigated. Prepared extracted teeth were exposed for periods ranging from 30 seconds to 5 minutes to an acidic ferric sulfate-based hemostatic agent. A smear layer was clearly demonstrated on a control specimen; however, the dentinal smear layer was rapidly removed by exposure to the hemostatic agent, and peritubular dentin was lost after prolonged exposure.

Acid Etching, Dental↗
PubMed1992

Predictable eye-head coordination during driving.

Large changes in the direction of gaze are made with a combination of fast saccadic eye movements and rather slower head movements. Since the first study on freely moving subjects, most authors have agreed that the head movement component of gaze is very variable, with a high 'volitional' component. But in some circumstances head and eye movements can be quite predictable, for example when a subject is asked to shift gaze as quickly as possible. Under these conditions, laboratory studies have shown that the eye and head motor-systems both receive gaze-change commands, although they execute them in rather different ways. Here I reconsider the way gaze direction is changed during free movement, but in the performance of a task where the subject is too busy to exert conscious control over head or eye movements. Using a new portable and inexpensive method for recording head and eye movements, I examine the oculomotor behaviour of car drivers, particularly during the large gaze changes made at road junctions. The results show that the pattern of eye and head movements is highly predictable, given only the sequence of gaze targets.

Automobile Driving↗
PubMed1992

Bond strength and accuracy of combined reversible-irreversible hydrocolloid impression systems.

This study investigated the bond strength and accuracy of irreversible and reversible hydrocolloids that were modified by the manufacturer to bond to each other for use in the combination impression technique. One conventional type irreversible hydrocolloid was used because of previously reported favorable results obtained in several investigations. Tensile strength of each individual material was tested as well as the adhesive bond between reversible and irreversible hydrocolloids. Tensile bond strength was then measured for each combination of materials. Subsequently, all the materials were tested individually and in combination for dimensional accuracy.

Alginates↗
PubMed1992

The fit of fixed partial dentures joined by infrared soldering.

This study determined the accuracy of fit of three-unit fixed partial dentures joined by an infrared soldering technique compared with one-piece fixed partial denture castings and individually cast crowns. Wax patterns of prepared Ivorine teeth, maxillary left central incisor and maxillary left canine, were injection molded; a plastic rod was used as a pontic. One group of patterns was cast as one-piece dentures; the other group was sectioned in the connector area, cast individually and then joined by infrared soldering. Castings were seated on their respective dies, embedded in epoxy resin, and sectioned. Gap distances between the casting and the die were measured at specified marginal sites with a profile projector. Results showed that the fit of infrared-soldered fixed partial dentures was significantly better than that of one-piece castings and was comparable with the fit of single crowns. The gap openings measured in all castings were within the range of clinical acceptability.

Crowns↗
PubMed1990

Direct observation of receptors and images in simple and compound eyes.

The relation between the quality of the optical image and the fineness of the retinal mosaic has been studied in eyes of three different optical types: the simple eyes of spiders, the superposition compound eyes of moths, and the apposition compound eyes of butterflies. In all three it is possible to observe both the receptor mosaic and the image in the living eye, using appropriate ophthalmoscopic techniques. Whereas in humans the retinal sampling frequency approaches the optical cut-off frequency quite closely, in diurnal insects of both types the image is undersampled by a factor of 2-3, and in crepuscular spiders this factor may be greater than 100. Reasons for these differences are discussed.

Animals↗
PubMed1985

Cone mosaic observed directly through natural pupil of live vertebrate.

Using a simple ophthalmoscopic technique, the cone mosaic of a live garter snake was clearly visible when viewed directly through its natural pupil, providing the first definitive cone map in a vertebrate eye. The optical MTF was also measured in natural conditions by projecting gratings in the snakes' field of view. Marrying these two results gives, unequivocally, the interrelation of optical image quality and the photoreceptor mosaic.

Animals↗
PubMed1980

Compound eyes: old and new optical mechanisms.

Over the last twenty years classical views of how compound eyes work optically have undergone a series of overhauls. Exner's central concept of an optically inhomogeneous lens cylinder has survived, and such devices are now made commercially. He was wrong, however, about some crustacean eyes. They produce images by a mirror mechanism that was not discovered until 1975, and which now shows promise as an optical system capable of development.

Coleoptera↗