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HISTORY OF DENTAL SURGERY 191

the profession everywhere. It is true that the practice of extension for pre-
vention was not new, but had been practiced to a greater or less extent for
twenty or thirty years previously. (Probably there was very little extension
previous to the advent of tlie dental engine except for tlie removal of decay
and the obtaining of strong walls and margins. Occlusal cavities are an ex-
ception to this statement, however.)
A very little observation served to show that decay would often occur in
the sulcus at the border of an occlusal filling if only the central decayed
portion were cut out, forming the cavity by a rotating cut with a round bur,
as some careless operators have lieen known to do. All good operators soon
learned to cut in such a case to tlie end of the sulcus, to a place where the
margin could be finished smoothly, with no crevice running to it, and this
cutting is done quite regardless whether there is decay in the sulcus or not.
This is the simplest case of "extension for prevention,'' and was generally
practiced by all good operators for thirty years before these articles on the
subject were written by Dr. Black.
Many operators liad also noticed the frequency of recurrent decay at the
buccal and lingual gingival margins of proximal cavities of bicuspids and
molars, and, noticing also in many cases the lines of incipient decay running
out from proximal cavities in these directions, had learned to extend the
cavities more or less into sound or comparatively sound enamel and dentine.
In the "Cosmos" (Vol. XXI, p. 212, 1879) Dr. SafTord Q. Perry, of New
York, in a paper on the "Management of Proximate Surfaces of Bicuspids and
Molars," states pretty clearly the doctrine of extension for prevention, and
also the protection of the gum in the interproximate space by the restoration
of full contours as again.?t permanent separations. Marshall H. Welib also,
in an article in the "Cosmos" (Vol. XXIII, p. 593, 1881) entitled, "Restora-
tion of Contours and Prevention of Extension of Decav," states distinctly the
necessity of extension for prevention of proximal cavities toward buccal and
lingual, and protection of interproximate gum by restoration of full contours.
In view of these and other similar facts and circumstances the question has
been asked as to what especial value or originality there was in Dr. Black's
presentation of these subjects. To this it may be replied that his statement of
facts was so complete, his deductions from them so reasonable and convincing,
his descriptions of tooth structures and of operative procedures were given
with such minute details, and their application to most of the cases arising
in practice so fully and clearly set forth that the knowledge, and the practice
founded upon it, have since that time merited the designation of scientific,