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110 THE TECHNICAX, PKOCEDUEES IN FILLING TEETH.
decay is quite certain to rebegin to the mesial or to the distal, or
both, and the filling will be lost. In these cavities there is gener-
ally no need of estension toward the occlusal farther than is
required to remove all caries and obtain a good enamel and den-
tin wall. In speaking of the smooth-surface cavities, only caries
of the enamel has been mentioned, for the reason that caries of
enamel is the first lesion and is of principal importance in the
preparation of cavities. It is sufficient to say that when caries
has entered the dentin its penetration of that tissue is the same
as in pit cavities. That is, the spreading in dentin is in every
direction along the dento-enamel junction, and the direction of
penetration is along the dentinal tubules directly toward the pulp
of the tooth.
In all of this it must be remembered that there is a general
or systemic susceptibility to dental caries, and there is also
immunity to dental caries, independently of the local conditions
discussed above. In every commimity some persons are found
who never have had a decayed tooth. In these the local condi-
tions may be just as favorable to decay as in others. Pits and
grooves in their teeth may be deep and well calculated to hold
lodgments, and yet caries does not occur. The systemic condi-
tions are such that caries does not occur even if the contacts are
broad, etc. Persons who are very susceptible to caries in their
youth, tend to become immune as they grow older. Quite a large
proportion of persons become immune to dental caries when they
arrive at adult age, provided the teeth have been properly pro-
tected, and they have continued to use them vigorously in chew-
ing food. On the other hand, if persons neglect carious cavities,
if the teeth become sensitive to such a degree that this interferes
with mastication, the tendency to caries will generally become
worse and worse and the teeth wiU be lost. This seems to be
because the teeth do not have the cleaning effect of active masti-
cation.
Oeder of Peocedtjke in Cavity Peepakation.
Geneeal peinciples. There are certain fundamental princi-
ples that are general to the excavation of carious cavities in the
teeth, the observance of which will simplify and facilitate these
operations, which may be expressed as follows
First, obtain the required outline form.
Second, obtain the required resistance form.
Third, obtain the required retention form.
Fourth, obtain the required convenience form.
110 THE TECHNICAX, PKOCEDUEES IN FILLING TEETH.
decay is quite certain to rebegin to the mesial or to the distal, or
both, and the filling will be lost. In these cavities there is gener-
ally no need of estension toward the occlusal farther than is
required to remove all caries and obtain a good enamel and den-
tin wall. In speaking of the smooth-surface cavities, only caries
of the enamel has been mentioned, for the reason that caries of
enamel is the first lesion and is of principal importance in the
preparation of cavities. It is sufficient to say that when caries
has entered the dentin its penetration of that tissue is the same
as in pit cavities. That is, the spreading in dentin is in every
direction along the dento-enamel junction, and the direction of
penetration is along the dentinal tubules directly toward the pulp
of the tooth.
In all of this it must be remembered that there is a general
or systemic susceptibility to dental caries, and there is also
immunity to dental caries, independently of the local conditions
discussed above. In every commimity some persons are found
who never have had a decayed tooth. In these the local condi-
tions may be just as favorable to decay as in others. Pits and
grooves in their teeth may be deep and well calculated to hold
lodgments, and yet caries does not occur. The systemic condi-
tions are such that caries does not occur even if the contacts are
broad, etc. Persons who are very susceptible to caries in their
youth, tend to become immune as they grow older. Quite a large
proportion of persons become immune to dental caries when they
arrive at adult age, provided the teeth have been properly pro-
tected, and they have continued to use them vigorously in chew-
ing food. On the other hand, if persons neglect carious cavities,
if the teeth become sensitive to such a degree that this interferes
with mastication, the tendency to caries will generally become
worse and worse and the teeth wiU be lost. This seems to be
because the teeth do not have the cleaning effect of active masti-
cation.
Oeder of Peocedtjke in Cavity Peepakation.
Geneeal peinciples. There are certain fundamental princi-
ples that are general to the excavation of carious cavities in the
teeth, the observance of which will simplify and facilitate these
operations, which may be expressed as follows
First, obtain the required outline form.
Second, obtain the required resistance form.
Third, obtain the required retention form.
Fourth, obtain the required convenience form.
