Page 92 - My FlipBook
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are either reflected or absorbed. Whenever Hght is incident upon an
inlay, it is excluded from the dentin, on account of the layer of cement,
which forms an opaque body, and the color of that portion of the tooth
and inlay which is in contact with the cement may differ from the other
parts because of the unequal absorption and reflection of the rays.
Regarding reflected shades, Dr. Thompson, in the same article, says
"All illuminated bodies scatter or reflect light, and are distinguished
from each other by the kind and amount of light they send to us, their
power of selective absorption and surface reflection determining the
color. If the source of light be a point, as in the electric arc light, the
shadow is sharply defined ; if, on the other hand, it comes from a luminous
surface, as the sun, the edges of the shadow are fringed and imperfect,
due to the angular magnitude of the sun. For example, the shadows of
minute objects disappear almost immediately in sunlight, whereas the
same objects in the arc electric light cause a well-defined shadow for a
considerable distance if thrown upon a screen. This explains why porce-
lain fillings are more conspicuous in artificial light than in sunlight, the
shadows thrown appearing more definite.
When light passes from one optical medium to another, a portion of
it is always turned back, /. c. reflected. This partly explains why a highly
glazed filling that does not appear correct may be improved by grinding
or polishing. A slight roughening of its surface causes less direct ex-
terior reflection, and although it thus renders the surface slightly more
opaque, it renders the deeper coloring more prominent, because light is
reflected regularly and more fullv bv a glazed surface."
88
are either reflected or absorbed. Whenever Hght is incident upon an
inlay, it is excluded from the dentin, on account of the layer of cement,
which forms an opaque body, and the color of that portion of the tooth
and inlay which is in contact with the cement may differ from the other
parts because of the unequal absorption and reflection of the rays.
Regarding reflected shades, Dr. Thompson, in the same article, says
"All illuminated bodies scatter or reflect light, and are distinguished
from each other by the kind and amount of light they send to us, their
power of selective absorption and surface reflection determining the
color. If the source of light be a point, as in the electric arc light, the
shadow is sharply defined ; if, on the other hand, it comes from a luminous
surface, as the sun, the edges of the shadow are fringed and imperfect,
due to the angular magnitude of the sun. For example, the shadows of
minute objects disappear almost immediately in sunlight, whereas the
same objects in the arc electric light cause a well-defined shadow for a
considerable distance if thrown upon a screen. This explains why porce-
lain fillings are more conspicuous in artificial light than in sunlight, the
shadows thrown appearing more definite.
When light passes from one optical medium to another, a portion of
it is always turned back, /. c. reflected. This partly explains why a highly
glazed filling that does not appear correct may be improved by grinding
or polishing. A slight roughening of its surface causes less direct ex-
terior reflection, and although it thus renders the surface slightly more
opaque, it renders the deeper coloring more prominent, because light is
reflected regularly and more fullv bv a glazed surface."
88
