The necessity of making some effort to restore the color of teeth changed by devitalization was apparent to dentists very early in the present century. The constant destruction of pulps with the imperfect methods of practice then prevailing, necessarily increased this unpleasant complication to such a degree that treatment of the anterior teeth became, so far as appearances were concerned, of no value whatever. Under the defective modes of treating pulp canals then prevailing, discoloration was sure to follow the filling of teeth. Any attempt to change color is necessarily dependent for success upon preliminary measures. Without thoroughness _here_, all subsequent efforts will fail. The early attempts at bleaching, before the settled practice of filling root canals was established, was not a success, and it must ever remain a failure unless the minuter structure of dentine be carefully considered. It has been demonstrated by artificial injection, and still better by sudden congestions of the pulp, that coloring matter may be carried nearly to the final distribution of the minute ramifications of the tubuli. This is an important point, for, without this vascularity, bleaching would be impossible. With it, the possibility exists of extending the whitening process to the peripheral border of the dentine; or, in other words, to its union with the enamel on the crown, or the cementum on the roots. The diameter of the tubuli is so minute, always decreasing in size until lost in final distribution, that any agent used must necessarily require considerable time before it can penetrate to the minute tubes, therefore you must not expect to bleach rapidly and meet with good success. The change, if any change be made at all, is simply on the walls of the canal, and cannot penetrate to any depth of tissue. If the discoloration is superficial, this mode will be effected, but not otherwise. Color can be changed by several of the acids: notably, oxalic and nitric. The former destroys the color, and the latter changes dark-blue to a yellowish tinge; but as both of these are very destructive, they should never be used except in connection with an ant-acid. The first named will be found to give better results when used in connection with chlorinated lime. _Chlorine_, free, or in some of its combinations, has been and is to-day the main reliance for bleaching, and that it is the most effectual has been demonstrated. Failures have _usually_ been the result of defective manipulation. It has great penetrating power, is a thorough bleacher, is readily applied, and if handled with care, will prove harmless.