Page 206 - My FlipBook

204 PRELIMI^'ABY PREPARATION OF CAVITIES, ETC.
of lint .saturated witli tlic solution of eocain. The anode, the ])oint of
which is of platinum, is covered with a thin stratum of lint Avhicli is
dipjxHl in the solution and inserted in the cavity in contact with the
pledo-et ])reviously introduced. The cathode, which should he at least
one and a half inches in diameter, is placed at a convenient place on
the face or neck. The desired number of cells are placed in circuit
with the controller at zero.
All being ready, the switch is placed on the first contact point. At
this moment, however great the resistance of the controller, a slight
sensation is sometimes experienced, but at once the switcli may be
passed slowly over the contacts until some sign from the patient indi-
cates that the current is being felt. Here it is retained until subsidence
of the sensation occurs, when the resistance of the controller should
be very gradually lessened. This process is continued, keeping con-
stantly within the limit of pain ; at length the switch may be more
rapidly advanced. AVhen this can be done without thrill, the indication
is that anesthesia is complete. The switch is then carried back to the
zero point, when the excavation may be conducted.
Where it is necessary to remove the rubber (as the solution of eocain
is strong) the preparation should be previously w^ished away to prevent
any of it from being swallowed.
The i^eriod of administration varies from eight to fifteen minutes
in ordinary cases where the indicated amperage is from y'^ to -^-^ milli-
ampere. When, however, the dentin is dense, as where denudation has
taken place by attrition, a longer time is required to efi^ect penetration
bv the eocain. Also where from any condition the indicated amperage
at first is ^j^j- milliampere or less, time and patience are demanded.
The loss of time is more apparent than real, since there usually is a
direct relation between the pain limit at very low amperage and high
sensitivity what is ap])arently lost in the time of the application is
;
gained in the after facility of instrumentation.
The sphere of the action extends throughout the cavity, but to a
somewhat less degree at the extreme lateral margins, and more particu-
larly at the occlusal margin. Here usually no more than a normal
degree of sensitivity is found, which appears to be due to the fact that
in making the retentive undercutting this procedure may extend beyond
the sphere of the complete influence of the eocain. The eifect is most
pronounced when the application is made directly to the carious matter.
In this case the diffusion is greater than when the caries is freely re-
moved, for the reason that in the latter case the current seeks the line of
least resistance toward the pulp. It follows from this that when all
parts of the cavity are equidistant from the pulp, the action should be
more effective throughout upon the surface of the dentin. This is