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SYSTEMIC CONDITIONS. 125
over fifty years old, who had reared a family of children, but
had never had a decayed tooth. The teeth were lost because of
disease of the peridental membranes. I split these with a fine
saw and examined carefully the pits found in them. They were
unusually deep and sharp, forming what seemed to be unusually
favorable places for caries to begin, yet the enamel was perfect
in the bottoms of all of these pits. Still, from my experience,
I am convinced that a well-fitted band of some considerable
width, immovably fixed, but with a buccal surface left without
cement, would have produced caries in that mouth. There are
certainly differences in the saliva that favor microorganisms
becoming fixed upon and clinging to the teeth of some persons,
while in other persons there is that which opposes this, and every
part is washed so freely as to carry away all acid formed by any
growths that may temporarily lie upon the enamel. The band
prevents this dissipation.
These pits occur in the occlusal surfaces of the teeth of all
animals that are omnivorous in their diet, and should not be
regarded as abnormal in man. The fact, however, that decay
in them occurs so frequently, gives abundant evidence that they
furnish the opportunity for its beginning. Therefore, if the
teeth are really faulty in their structure so that there are open
fissures as well, decay is the more certain to occur. There are
some faults in structure within the dentin which give rise to
unusual forms of cavities. Sometimes the granular layer of
Tomes is very much more considerable under some parts of the
enamel than others, inviting the burrowing of decay in special
directions, causing irregular forms of cavities. Often, also, we
find irregular groups of interglobular spaces in the dentin into
which microorganisms grow very readily and in that way pro-
duce irregularities in cavity forms. This occurs when there is
no appearance of atrophy upon the enamel. In cases of atrophy,
particularly where the occlusal surfaces of the first molars have
been wrecked, caries is very likely to run through the sheet of
interglobular spaces in the dentin, usually only a little below the
dento-enamel junction. This often forms a broad, open cavity
with the decay still following this sheet of interglobular spaces
until finally the whole occlusal surface is cut away, the decay
having extended but little in depth. The result is that the whole
occlusal surface of the tooth has decayed, leaving a blackened
stump, which may come to occlude with its fellow of the opposite
jaw and do excellent service in mastication. It too often hap-
pens, however, that decay persists in those portions of the sheet