Biomedical subjects
C A Chan
Publications and source records attributed to C A Chan.
The role of inhibitory processes in the formation of functional properties of neurons in vibrissal projection zone of the cat somatosensory cortex.
The role of intracortical inhibitory processes in the formation of neuronal receptive fields in the vibrissal projection zone of the somatosensory cortex was studied. Iontophoretic application of picrotoxin and bicuculline blocks the inhibition and causes the loss of directional sensitivity in neurons. Activation of inhibition by distant glutamate application gives opposite results--neurons become direction sensitive. A dependence was found between spatial location of activated cells and the pattern of changes of their detector properties. Inhibitory processes caused by natural afferent stimulation lead to similar changes in the functional properties of neurons.
The polishability of posterior composites.
The polishability of six brands of posterior composites was evaluated by means of a stylus profile instrumentation and scanning electron microscopy and was compared with that of an anterior microfilled composite. A sedigraphic study was performed to estimate the size and distribution of their inorganic particles. The extent of the filler loading as well as the hardness values were also assessed to determine any relevant characteristics. Some of the findings indicated that posterior composites with large particles produced significantly higher surface roughness than those with small fiber particles. A direct correlation was also found between the hardness value and surface roughness value, indicating that a composite with higher hardness value yielded a higher roughness value.
Effects of resin-compatible cavity varnishes on the polymerization of visible light-cured composites.
The effects of three proprietary resin-compatible cavity varnishes on the polymerization of two visible light-cured composites were investigated. A conventional varnish (Copalite) was included for the sake of comparison. The four cavity varnishes showed no significant difference in average hardness values of the light-cured composites when cured against completely set varnish. It was also found there was no statistical difference in the thickness of the uncured resin layer when the light-cured composites were cured against all four partially set cavity varnishes. The average thickness of the uncured resin layer in Silux was found to be significantly higher than that of Command Ultrafine. Based upon the hardness and thickness evaluations, the data of this study suggest that none of the four cavity varnishes (including Copalite) affected the hardness of the composites when allowed to set completely before the composite was applied. In contrast, all four tested cavity varnishes showed a softening of resin at the interface when the composites were cured against a partially set varnish. It is important therefore to permit the cavity varnish to dry completely before applying composite.