The Archives of Dentistry, Vol. VII, No. 4, April 1890

by Various

The next point to be considered is the insertion of the material. Before this is attempted the canals and crown should be well washed with a solution of ether, borax, sodium bicarbonate, or ammonia, to remove fatty matter. It should then be well washed with distilled aqua. The tooth is then dried, the rubber dam having been applied at the beginning of the operation. There are several methods of bringing the acid used in connection with the lime. This apparently simple matter is really quite difficult. One process is, to saturate the entire canal and pulp chamber with the acid before inserting the chlorinated lime. Another is, to dip the instrument into the weak acid solution and then into the lime, and pack rapidly into the cavity; and still another is, to make a paste by the use of distilled aqua and pack this in the tooth, and then apply a stronger acid by means of cotton wrapped around the point used. There are difficulties attending all these modes. The point desired must be kept constantly in view—that of having acid sufficient and of proper strength to break up the compound and set free the chlorine used, and to preserve as much as possible of the latter for bleaching. Before commencing the packing, everything should be ready, so the cavity can be sealed at once.

Convenience of adaptation must govern the choice of the material used for closing the cavity. Gutta-percha, oxyphosphate or oxychloride of zinc may be used with good results, but the zinc preparations are harder to remove than the gutta-percha. After sealing the cavity, the tooth must be left for a day or two. On the return of the patient, remove all of the application, avoiding the use of steel instruments. Syringe out the canal with distilled aqua. If the bleaching has not gone far enough, a second application must be made, and this be repeated until a satisfactory result is obtained. The importance of using distilled water must be insisted upon. The reason for this must be apparent, for in many waters the minerals held in solution, especially those impregnated with iron, will defeat the desired object.

The immediate bleaching effect will be observed on the lower third of the tooth where the dentine is the thinnest. In the majority of cases this will be effected by one application. The greatest trouble will be found at the gingival border. Here the dentine is very thick, and it will be slow work, and in some cases end in failure, to restore normal color. The great objection made to this operation is, that the tooth will re-discolor, but if the subsequent operations are properly performed, this danger will be reduced to a minimum. The fact that dentine is permeated by pulp prolongations throughout the tissue, increases the difficulty of bleaching, and also increases the liability of a return of discoloration; but if the oxidation of the soft contents of the tubes has been properly effected, and then an agent used to fill the canal, and also act directly upon this microscopic tissue, there is but little reason to fear a return of discoloration. The operation, simple as it is, requires close attention to details and a clear comprehension of possible results.

The tooth having been restored to a good color, the next consideration is the proper filling to place in it. In this connection the before mentioned fact still remains an important factor, that the tubuli are still filled with decomposable matter. To allow this to remain without attention to future contingencies, must result in eventual failure. To effect any good results the antiseptic must not only operate in the main canal, but penetrate deeply into the minuter conduits. This quality is possessed in a remarkable degree by chloride of zinc, and maintains the same effect when combined with the oxide of zinc, forming the oxychloride of zinc. The canal and pulp chamber should be thoroughly filled with this paste, or, it is better to line the whole cavity with it, and then finish with the oxyphosphate, using gutta-percha at the cervical margin.

Chlorine acts as a bleaching agent by reason of its strong affinity for hydrogen. Vegetable and animal colors when brought in contact with chlorine in the presence of water, is seized upon by the chlorine, and the oxygen set free, oxidizes the color and destroys it. Chlorine in this case acting indirectly as an oxidizing agent.

If you wish to try to bleach more rapidly, a solution of oxalic acid is used to liberate the chlorine. Oxalic acid is more rapid than either tartaric or acetic.

Sulphurous acid is said to be a good bleaching agent, and acts by an entirely different method from chlorine. It is therefore of great interest from a chemical point of view.

As before mentioned, chlorine acts as a bleaching agent by reason of its strong affinity for hydrogen. Sulphurous acid, on the contrary, is a reducing agent by reason of its affinity for oxygen, in combining with which it becomes sulphuric acid.

On the chemical character, therefore, of the coloring matter depends the choice of the agent to be used.

Chlorine should be used when the color is an oxidizable compound, or rich in hydrogen; while sulphurous acid should be used more particularly in substances highly oxidized and capable of being reduced.