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548 DISCOLORED TEETH AND THEIR TREATMENT.

jiblc character. The only metals Avhich may be safely used in connec-
tion Avith any chlorin ])rocess of bleaching are zinc and aluminum,
the chlorids of which arc colorless. Aluminum instruments for the
purpose may be quickly improvised out of wire or heavy plate. Gold
instruments have been recommended, but they are open to the very
(2:rave ol^jection of forming a chlorid by direct combination with chlorin,
which salt is one of the most important staining media known to the
histologist ; as a matter of fact the writer has seen several cases
where a permanent ])urple staining of the tooth has resulted from
neglect to remove gold fillings before applying the chlorin method of
bleaching, and there is certainly no reason why the same result should
not follow the using of gold instruments in the same connection.
When the tooth has been restored to its proper color it should be
thoroughly washed with very hot distilled water, dried out with bibu-
lous paper and thoroughly desiccated with a current of dry hot air,
after which the canals, Jiulp chamber, and cavities should be filled with
oxychlorid of zinc.
The final filling of the cavities of entrance and of decay should be
postponed until by a lapse of considerable time the permanence of the
operation has been established. This probationary period may with
advantage be prolonged to four or six months.
The final washing of the tooth with hot distilled water previous to
the insertion of the oxychlorid of zinc filling is a feature of the opera-
tion which requires special care and attention. As left after the appli-
cation of the bleaching agent, the pulp chamber and canals and denti-
nal structure are filled with free chlorin in solution, calcium acetate, or
other salt of calcium depending upon the nature of the acid used in
the process, and some undecomposed bleaching powder. These sub-
stances should be thoroughly removed by the hot-water douche. At
least a pint of water should be strongly injected into the interior of the
tooth l)y means of a large bulb syringe, before the dam is removed. A
towel held in close proximity to the tooth will catch the water as it re-
turns from the tooth and protect the clothing of the jxatient. Distilled
water should in all cases be used for this irrigating douche, as river
water and many other specimens of water from natural sources contain
iron in solution, which could readily become a contaminating factor
leading to subsequent return of discoloration.
Oxychlorid of zinc is selected as the permanent filling for the pulp
chamber for the reason that it is necessary to so act upon the bleached
organic residuum in the tubular structure as to prevent any alteration
of its character which may result in the production of a subsequent
coloration. Zinc chlorid possesses the property of converting many
organic substances into unalterable compounds by its coagulant action,