Page 177 - My FlipBook

PHYSICAL PHENOMENA OF DENTAL DECAY. * 151
PHYSICAL PHENOMENA OF DENTAL DECAY.

a. Decay of Enamel.

Ill making a study of the phenomena of dental decay which is
intended to be anywise complete, it will be necessary to subject
the physical, chemical, and microscopical changes of the tissues
involved to a rigid examination.
Let us begin with the physical phenomena of dental decay, in so
far as they are revealed by inspection with the unaided eye or by
examination with such simple instruments as excavators, probes,
etc. A clear insight into the macroscopical changes which occur
at the beginning of enamel-caries can be gained most easily from
a freshly extracted molar or bicuspid, decayed on the approximal
surface. Cases of fissure-decay are not serviceable for this pur-
pose, because the appearance of the decaying enamel is here
generally obscured by other processes occurring simultaneously
(precipitates, discolorations, etc.).
Suitable material is not always easily obtained, because teeth
showing the very first stages of decay are seldom extracted, and
because caries on the approximal surfaces of unextracted teeth
becomes apparent only after it has made considerable progress.
The opportunity of observing decay at its beginning is therefore
very rare.
As the first indication that the process of destruction has begun
on the external surface of the enamel, we notice that it has lost
its normal polish and transparency; then a white (not black) ir-
regular spot of chalky color appears; a sharp instrument {e.g.,
the point of a needle) will not easily glide over the surface, but
will readily detect the presence of a slight roughness caused by
a softening or disintegration of the enamel, by which it is
gradually changed into a soft cheesy powder. This dissolu-
tion of the enamel may be best observed when decay advances
from the dentine upon the inner surface of the enamel (secondary
decav); here the broken-down enamel-prisms cannot be washed
away, so that quite a thick layer of a perfectly icldk cheesy sub-
stance may often be found.
In primary decay the disorganized enamel-prisms are soon
mechanically washed away, whereljy an excavation or cavity is