A Method of Deadening Pain in Excavating a Tooth, and Apparatus for that Purpose.
Year: 1895

page_text: Date of Application, 19th Mar., 1895-Accepted, 1st June, 1895
COMPLETE SPECIFICATION.
A Method of Deadening Pain in Excavating a Tooth, and Apparatus
for that Purpose.
We, WILLIAM PERRY HORTON Junr., Dentist of 184 Arlington Street,
Cleveland, Ohio, and ANSEL B. JONES, Electrician, of 757 Scoville Avenue,
Cleveland, Ohio, United States of America, do hereby declare the nature of this
invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement :-
This invention relates to means of deadening the sensory nerves of a tooth
during its excavation, and it consists in the following steps of process; 1st, in
applying to that side of the patient's face next the tooth an electrode connected
with one pole of an electrical generator: 2ndly, in connecting the excavating
instrument with the other pole of the generator; 3rdly, in varying the external
resistance in the circuit during the operation, substantially as hereinafter
described.
The accompanying drawing represents the apparatus for carrying the process
into effect, applied in the manner hereinafter described.
An
The current employed in the process is generally that from a single cell battery,
but there are cases where the current of as many as four cells is necessary.
electrode A, connected with one pole of the generator B, (preferably the negative
pole) is secured by means of an elastic strap a, or otherwise, to. that side of the
patient's face on which is the tooth to be excavated. The other pole of the
generator is electrically connected with the excavating instrument C which is
generally a revolving burr driven by a dental engine. In order to ensure the
passage of the electric current from the excavating tool through the tooth; the
handle of the tool is made of insulating material; and the tool has to be so used
that there is no electrical connection between it and any part other than the tooth.
The reason for connecting the electrode A preferably with the negative pole is
as follows:
One source of the pain experienced by the patient is due to the laceration of the
nerve filaments in the tubuli which ramify the dentine. Another source of pain is
the heat generated by the revolution of the burr. Now, it is found that in passing
an electrical current through the human body, heat is generated at the negative
electrode. Therefore, in order that the pain due to the heat generated necessarily
by the burr shall not be increased by the heat due to the electrical current, the
electrode A is connected preferably with the negative pole.
The teeth are supplied by nerves which originate in the fifth cranial nerve.
Branches of the fifth nerve of the cranium pass from the cranial cavity througli
channels in the superior or sub-maxilary bones; and being subdivided, they enter
the several teeth, wherein they are again subdivided, forming the minute nerve
filaments which ramify the dentine. The parts of the nerve in the teeth and in
the channels in the bone, are therefore more or less completely insulated
(electrically) from each other, as well as from other parts of the anatomy; so that
a current of electricity introduced into a tooth, must pass with comparatively little
loss by the nerves as conductors into the cranial cavity. The shortest route for
the escape of the current therefrom, is through the foramina in the skull, through
which pass other branches of the fifth nerve to supply the face. In order, there-
fore, to pass by the sensory nerves of a tooth, an electrical current which will meet

page_text: with as little resistance from the body as possible, one electrode is placed, as stated
above, against the side of the face just in front of the lower lobe of the ear. By
placing the electrode here, there is not only the least possible resistance in the
body, but there is also the least variation of resistance in different patients.
The theory as to the process described is substantially as follows: In any
individual, it is necessary to pass by each of the filaments which are affected by
the operation, some amount of current which quantity cannot well be expressed in
terms of electrical measurement, for several reasons-First, no instrument has as
yet measured the quantity which passes through a patient; second, it is impossible
to determine how the current is subdivided in its passage through the dental
filaments, that is to say, to determine what part of the whole passes by any one
filament. This quantity moreover, differs in different individuals, this difference
being apparently dependent on differences in what is termed sensitiveness of nerves.
Perhaps a more accurate statement of the causes of these differences is that, the
teeth of some persons contain more nerve filaments than others, which filaments
are placed more closely together. Another cause of the personal differences may
be the fart, that owing to the differences in the structure of the teeth and bones,
the nerves are more completely insulated electrically in some persons than in
others. It is possible that the theory above outlined may be incorrect, it has been
found entirely consistent with the acts necessary to be done in order to be
practically successful in excavating teeth by the described process without pain.
In order to vary the quantity of current to compensate for the varying conditions
which arise in practice, it is necessary to connect into the circuit a resistance box
by means of which the operator may vary the resistance external to the body.
A resistance box, capable of introducing about 14,000 ohms, by increments each of
100 ohms, is suitable for this purpose.
This resistance box of which it is unnecessary to describe details is represented
by D. It is provided with two switches d and d', which can engage with any one
of the contact points 1, 2, 3 etc. and 13, 14, etc, respectively.
When switch d
touches the point 1 and switch d¹ touches the point 13 the box introduces into the
circuit approximately 14,000 ohms resistance. As the switch is moved up into
contact successively with the contact points 2, 3, 4 etc., the resistance is reduced
approximately 1000 ohms for each point. When the switch d¹ is moved
successively into contact with the points 14, 15 etc., the resistance is reduced
approximately 100 ohms for each point.
As before stated, the quantity of current required differs in different individuals,
and it also differs in different teeth of the same person, and even at different periods
during the excavation of the same tooth.
In conducting operations according to the process, it is preferred to begin with
the switches on the points 1 and 13, that is to say, with the maximum resistance,
and with a current generated by one cell of a Le Clanché battery or its equivalent.
If the resultant quantity is sufficient, and it is impossible to predetermine this
because of the personal idiosyncracies, the patient feels no sensation from the
dental nerves as when for example, the hand is not touching any external object,
there should be no sensation in it. If the current is insufficient, the patient feels a
sensation in the dental nerves affected by the revolution of the burr. The first
sensation, if the operator is watchful and careful, is not one of pain. It resembles
the sensation produced by touching an external object with the hand. The
operator then reduces the resistance by the movement of the switch d from point 1
to points 2 or 3 and so on, trying the current carefully after each movement, until
the operation may be proceeded with without producing any sensation in the dental
nerves. To attain this result, it may be necessary to move the switch d' by which
the resistance may be changed by increments of 100 ohms. It is not necessary to
proceed in the described manner in each case, but it is to be preferred because
there is then comparatively little danger thereby of employing too strong a current,
which might injure the nerve, or might produce even greater pain than would result
from excavating the cavity without any current.

page_text: The operator may be guided in the practice of the process as above set forth, or
in proceeding more directly with the application of the proper current in any case
by the following facts:
In removing what is commonly called white decay, a less quantity of current is
needed than in any other operation, because the decayed matter being soft, little heat
is developed by the revolution of the burr, and further, because the burr does not
come in direct contact with any live filament.
In removing the so-called leathery tissue, a greater current is required, because
the underside of the leathery patch enters numerous tubuli in the tooth, which are
affected more or less by the working of the burr in this tissue.
When all the decayed substance is removed, and the tool acts on the healthy
dentine, either for the purpose of thoroughly cleansing the cavity, or for drilling
retaining points for the filling, a still greater current is required. In drilling into
the dentine, it is found that the current required is greater the harder the dentine,
because more heat is generated by the revolution of the tool in hard than in soft
dentine.
Care must be taken to prevent the burr from touching any part of the tooth
other than that where the drilling is going on, because by such touching a part of
the current is diverted from the filaments which are being lacerated or otherwise
affected by the operation. If, however, the cavity is so situated that in
excavating it, it is impossible to avoid touching the side walls, the current must
be increased.
In operating under the different conditions named, it is found that, on the
average, white decay may be removed without pain to the patient by the use as
described of the electricity generated by a single cell and the introduction of
approximately 10,000 ohms external resistance into the circuit; to remove
leathery tissue, the use of the electricity generated by one cell and the introduction
of approximately 7000 ohms resistance. For drilling into the healthy dentine, a
current having the same electro-motive force with approximately 4000 ohms
resistance often producing the desired result.
It is to be understood that these figures are only approximate. The very great
difference in personal characteristics renders a more exact statement impossible.
It is recommended above that a small current be employed at the beginning of
an operation, and that it be gradually increased by reducing the resistance, until it
is sufficient. The above figures may guide the operator by informing him of the
points at which he may ordinarily expect to be successful. It sometimes happens,
however, that a less current suffices; it sometimes, though seldom, happens that
an electro-motive force of two, three or even four cells is required.
The essential feature of the invention is that, if one electrode is placed against
one side of the patient's face a tooth on that side may be excavated without pain
to the patient if a suitable electric current is passed into the tooth from the exca-
vating instrument. The foregoing directions are merely suggestions, as explicit as
the nature of the case permits as to the best method of determining the current
required.
Attempts have heretofore been made to obtund the nerves of a tooth during its
excavation by means of an electrical current; also Bonwill's American Specification
No. 22,851 of 1859 describes a method and apparatus intended for this purpose.
No claim is made herein to that process described by Bonwell who suggests that
one electrode be held in the hand. This has been tried but without any satisfactory
results. It is found to be necessary that one electrode be applied to that side of
the face where the tooth is as this makes it possible to send by the dental nerves
the proper current of an intensity not too great to be effective.
Bonwell suggests that the power of the current be graduated so as to be just
strong enough. This gives no information as to the manner in which the current
should be graduated nor as to the principles which should govern its graduation.
In what precedes are described what current approximately is required, and the
principles which should govern the operation in changing the external resistance in

page_text: the current so that the desired result shall be obtained under the varying conditions
which arise in practical work.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
:―
1. The herein described process for obtunding the sensory nerves of a tooth
during the excavation of a dental cavity therein, by (1) applying to that side of
the patient's face where the tooth is, an electrode which is connected with one pole
of an electrical generator, (2) connecting the excavating instrument with the other
pole of said generator; and (3) suitably varying the current, substantially as and
for the purpose specified.
2. The herein described process for obtunding dental nerves during the excava-
tion of a tooth by (1) applying to that side of the patient's face where the tooth
to be excavated is, an electrode connected with the negative pole of an electrical
generator; (2) connecting the excavating instrument with the positive pole of the
generator; and (3) varying the resistance in the external circuit during the
progress of the excavating operation, substantially as and for the purpose
specified.
3. In an apparatus for excavating dental cavities and simultaneously obtunding
the sensory nerves affected by the operation, the combination of an electrical
generator, an electrode connected with its one pole and secured against the patient's
face, the revolving burr of a dental engine having an insulating hand-piece,
electrical connections between said burr and the other pole of the generator, and
means for varying the resistance in the circuit by small increments, substantially
as and for the purpose specified.
Dated this 19th day of March 1895.
ABEL & IMKAY,
Agents for the Applicants.