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90 PATHOLOGY OF THE HARD TISSUES OP THE TEETH.
sense, restoring the original contour perfectly but without ref-
erence to the superficial spreading of caries, may become the
cause of wider spreading of decay on the surface than would
have occurred without it. Further, in practice, it will be found
that when proximal fillings are made without separating the
teeth to gain room for the finishing of the fillings to the full
original contour, with the original fullness of the contact points,
but necessarily losing a little of the original mesio-distal breadth,
the area of near approach of the proximal surfaces is increased,
the embrasures are made shallower and the opportunity for
recurrence of caries at the bucco-gingival and linguo-gingival
angles of fillings is increased.
Penetration of the Enamel in Buccal and Labial Surfaces.
Caries beginning in the buccal and labial surfaces presents
the same characters as to penetration of the enamel and spread-
ing in definite directions as decays beginning in the proximal
surfaces. In this case the line of beginning is along the free
margin of the gum in the middle third of the surface mesio-
distally. The lines of extension in spreading are toward the
mesial and the distal angles of the tooth. The beginning of these
decays often forms a narrow whitened line, the length of
which is from mesial to distal. These, taken with the decays of
the proximal surfaces, tend to form lines encircling the teeth
along the free margins of the gum. This is very generally
defeated by the failure to spread across the angles of the teeth.
But when the angles are passed and when connected by decay
on the lingual surfaces, which sometimes occurs, the complete
girdling of the teeth is accomplished. Frequently we may find,
in the first beginning of the decay on buccal surfaces, several
starting points which later run together, forming a continuous
line of whitened enamel. This gives, in cross sections of the
tooth, appearances almost exactly similar to those shown in
Figures 92-95, inclusive. As the very general rule, the extension
of decay on the surface of the enamel is stopped at the mesial
and distal angles of the surface.
While these decays occur in a much less number of persons
than proximal decays, they often attack tooth after tooth in
quick succession, and progi'ess very rapidly in the enamel,
destroying considerable areas of enamel tissue. They become
wide-open cavities, and, in the mouths that have very little care,
are apt to run a rapid course.
This subject will be presented in greater detail under the
heading, "Caries as a Whole,"