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DENTINAL ANESTHESIA BY ELECTRICAL OSMOSIS. 201

as well as the percentage of the medicament exert a considerable quali-
fying control of the resistance, as appears from the experiments of
Dr. Price. When a section of dentin partially dry on the surface had
a resistance of 30,000 ohms, after being dried and saturated with a 40
per cent, solution of cocain the resistance was reduced to 4500 ohms.
The principles here stated and the facts presented apparently demon-
strate the importance of careful selection of the degree of voltage at
the battery ; of the use of a relatively low amperage to the voltage;
of the necessity of controlling the current within the boundary of the
pain limit ; of the importance of avoiding impulses of current by rapid
advancement or by movements of or displacements of the anode ; and
of attention to the maintenance of a constantly moist state of the anodal
and cathodal contacts.
These principles and facts have led to the application of galvanic
currents for the production of a state of anesthesia of hypersensitive
dentin ; and the results of experimentation in this direction have proven
that the same eifects have followed here as have occurred in the softer
tissues.
The extreme sensitiveness of the teeth to electrical currents and their
resistance to the passage of electrical force were obstacles to the earlier
application of this method of treatment in dentistry. The absence of
means to control the current strength (the amperage) and to reduce the
pressure (the voltage) to the capacity of the teeth prevented experi-
mentation in this direction until within a comparatively recent period.
The current strength that is tolerable at the commencement of the
application is so small as to be scarcely measurable in many instances.
To produce this small current, either the battery voltage must be low
or the resistance in the controller exceedingly high.
Any form of battery whicli is constant when the amperage of the
individual cell is from one-fourtli to one-half of an ampere will have
sufficient current strength. The E. M. F. may be from one to two
volts per cell.
The voltage required to produce the necessary electro-motive force. in
an application to the teeth to produce dentinal anesthesia varies from
five to thirty. For children and Avhere the teeth are apparently not
dense, ten cells sometimes are sufficient, but generally fifteen to twenty
are needed. The cells should be arranged in series and connected in a
manner which enables the selection of any number to produce the re-
quired E. M. F. for any given case and to permit an increase of cells
during the administration.
The most important condition of the electrical force for the purpose
is that the amperage tiliall he iuconsiderahle, since high amperage is intol-
erable to the teeth. As the most efficient results are produced when the