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MANAGEMENT OF CAVITIES BY CLASSES. 209

equal, the proximal cavities would be double the number of
either vhe first or fifth classes.
These are all smooth surface cavities — that is, they occur
in surfaces on which the enamel of the tooth is perfect and
smooth, presenting neither fissures, pits nor grooves, which serve
as starting points for decay. The conditions are therefore rad-
ically different from those presented in pit and fissure cavities.
The beginning of decay in these smooth surfaces is not confined
to a single minute point in the enamel, as when beginning in pits
and fissures, but the surface of the enamel is attacked and the
area will be great or small, coinciding with the size of the local
areas of uncleanness. The close examination of a large number
of cases shows that the size and form of these areas depend
mainly upon the forms of the proximal surfaces, and the amount
and form of those parts which closely approach each other.
When the surfaces are well rounded, the contact points small
and the embrasures wide ami deep, decay is less apt to occur and
its beginning is confined to a narrower area of surface, or often
to a small point ; while, if the proximal surfaces are flat, the con-
tacts broad and the embrasures shallow, decay is more liable to
occur and the area of enamel surface attacked will be propor-
tionately broad. Other things being equal, this matter of forms
of the surfaces, their contact points and the depth of the embra-
sures control the degree of cleanliness of these surfaces and their
liability to decay. This will be better understood by reviewing
Figures 86 to 95 inclusive, illustrating these forms, together
with the text relating to them. All of this will be modified by
the degree of susceptibility to decay and by personal artificial
cleaning. The susceptibility of the person will constantly be the
principal factor, modified and controlled to some extent by the
conditions above detailed. At the present time, we are unable in
any direct way to control this principal factor — susceptibility.
In prophylactic treatment our attention must be directed to the
removal, modification or improvement of those local conditions
giving opportunity for its manifestations.
The key to the rules of management of these classes of cases
is found by noting these local conditions, and in the study of the
influences they exert for limiting, increasing or modifying the
opportunities for the beginning and superficial spreading of
caries of the enamel.
The forms of the areas of liability to decay are different in
the molars and bicuspids from the forms presented in the incisors
and cuspids, because of the differences in the contour of proximal