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308 HISTORY OF DENTAL SLfEGEKY

by means of vulcanite plates with piano-wire springs attached. Piano-wire
as a means of exerting force by virtue of its great resilieucv and strength had
been employed by Headridge for several years, and vulcanite hase-plates were
not new, but the combination of the two materials in the manner devised by
Mr. Coffin was decidedly original and effective.
In the variety of its application and its consecjuent scojie of usefulnes.= it
seemed to open up a new field in orthodontic practice. Mr. C'otRn designated
his method the "expansion nu'thod" for the reason that the bringing of
malposed teeth into alignmcTit. in nearly all cases necessitated the expansion
or enlargement of the arch for their aicomtnodation. This expansion was accom-
plished coincidently witli the application of force to individual teeth so that
botli operations were carried forward without loss of time. Otlier advantages
possessed by the method were the lirm aiichoi'age of the jilate when in position;
its large field of resistance: the facility with which the wire springs could be
attached to it, and its complete supplanting of the use of screws, levers and
ligatures. Its simplicity of construction and operation. eonj almost imiversal applicability, won
for it immediate' favor. Fig. v!0, rep-
resents an upper plate designed to
expand the arch and at the same
time bring into alignment an out-
standing n]ii)er lateral incisor. The
plate is fashioned to cover the entire
vault and the posterior teeth, the lat-
ter to afford firm anchorage aiul to
Fiff. L'O
open the bite so that the movement
f'litliii Kx]i;uisi(piv Plate (upper)
of the malposed tooth may not be
interfered with. While the plate is in process of ennstruclion, a piano-wire
spring coiled a few times ii])on itself is imlieddeil hv means of its free ends in
the body of the plate, the main portion of the spring resting entirely ui>on the
surface. Any additional spring for individual movement is also placed in
position, .\fter the plate has been constructed in one jjiece, it is slit with a
jeweler's saw along its center into two .symmetrical halves. By pulling these
halves apart from titne to time, thus widening the spring, and reinserting into
position in the nmuth. fon-e is exerted laterally resulting in arch expansion.
.\t tlie same time any supplemental spring or attachment is accomplishing its
object independently.