Page 190 - My FlipBook

188 PRELIMINARY PREPARATION OF THE TEETH.

perchu nuiy not bo readily retained. Oxychlorid of zinc should be used
when the cavities are shallow but sensitive,— the reason for which
w'ill appear later. It is generally advisable to introduce a thin wedge
of wood at the cervix and in contact with the gum to ])revent the re-
taining material from impinging upon this tissue and to give a base to
su]ij)()rt the introducing force.
Exposure of Cervical Margins.—When cavities extend beneath
the gum, which frequently is the case when caries has recurred above
the cervncal margins of fillings, it becomes necessary to force the gum
somewhat above the carious border. This should be done quickly
ratlier than slowly, otherwise in adult subjects the continued pressure
may arouse diffused inflammatory disturbance of the contiguous tissues.
Generally it is preferable first to cut away the gum between the teeth
with a straight, narrow bistoury, and gently force red gutta-percha
against the gum, gradually moulding it to the form of the depression.
Cotton pellets for this purpose are not admissible unless they are auti-
septically charged, for which purpose an admixture of aristol with the
cotton is the most suitable, since not being soluble in water it better
maintains the asepsis. Cotton may be conveniently charged with aris-
tol by saturating it with a solution of aristol in chloroform and allow-
ing the greater portion of the solvent to evaporate before introducing
the pledget.
When hypersensitiveness of the gum tissues exists it is admissible to
paralyze the sensation with a suitable solution of cocain, previous to
introducing the pellet of either gutta-percha or cotton fiber. A four
per cent, solution of cocain hydrochlorid applied upon cotton to the
sensitive tissues will speedily relieve the condition.