This section is from the book "Dental Medicine. A Manual Of Dental Materia Medica And Therapeutics", by Ferdinand J. S. Gorgas. Also available from Amazon: Dental Medicine.
According to Dr. Black, "infectious matter contains living particles that will grow and reproduce themselves. Septic matter may be in solution; it is poisonous. It is the product of the growth of micro-organisms, and it is this product of the dentine that is dangerous in many cases, to the exclusion of infectious matter; for while infectious matter may be in the dentine, may live there for a time, it certainly will not live there very long if communication by which it receives food is cut off. It must receive food in any case, and must get clear of its waste products or it will soon be choked. Though microbes may not be present in the dentine, there is danger of poisoning from the septic matter that is absorbed, filling the dentinal tubules. We have a different set of conditions when we leave a little bit of softened dentine over a pulp nearly exposed. We may cover in the anaerobic microbes. In a short time they produce products that will destroy the pulp, or they may pass through and penetrate into the pulp, and we may have an infected pulp presently from the microbes we have covered in. This action is brought about rapidly, and the poisonous matter escapes toward the pulp. If we have covered them in with the filling we have sealed up the elements for destroying that pulp. It is not necessary that the dentine be softened more; it may not be a class of microbes that soften dentine. It is a microbe that attacks the sarcous elements of the body; the contents of the dentinal tubes are attacked just as well. So here we need a disinfectant. What shall we use? Certainly not one of the coagulants (such as carbolic acid, creasote and chloride of zinc - agents which seal the septic matters within the teeth); certainly not one that places a barrier to its own penetration by coagulating the albumen. These are not the antiseptics you should use in this place, but something we can depend upon to penetrate in the presence of albumen, and we find that to-day in the use of the essential oils, and among them the oil of cassia is the most potent. There are many of the essential oils that when used in substance will destroy microbes just as quickly as the oil of cassia, and among them may* be mentioned the oil of turpentine, but there is none of them that will destroy microbes so rapidly and so certainly with that proportion of the oil that will dissolve in water, or the fluid with which they come in contact in their application in practice as the oil of cassia. In bacteriology, the terms germ, bacteria, microbe, schizomycetes, are used almost as synonymous names, but microbe seems preferable to germ or bacteria, and schizomvcetes is considered to be a better scientific term than either. It is also conceded that these are unicellular and assimilate nourishment apparently by absorption in the media in which they live, but they must alter their foods found proper, and yet unfit in nature for their use and appropriation. Bacteria, living or dead matter encounter no living resistance, while those feeding on living tissues, or fluids in living tissues, meet the living cells of the body and have to combat them. The diastases secreted by the various beings, whether highly organized, or unicellular and microscopic, have something in common as to their respective objects and their properties of transforming matter. The roll of microbes in existence is complex and necessary, though some are injurious. They act as scavengers, return to the air and water the organizable elements abstracted daily by the vegetables and indirectly by animals, and are indispensable to life. The bacteria that invade living organisms which happen to be fit for their nourishment and growth are considered to be parasites. The spontaneous generation of living organisms, no matter how little, is now regarded as a fallacy.
Formerly, when the root-canal of a tooth was opened and found to be empty and dry, peridental trouble resulted. But the treatment of such cases, as now pursued, consists in excluding the saliva and atmospheric microbes, the removal of every particle of debris, and the application of antiseptics and disinfectants. To render a pulp-canal permanently aseptic, it should be thoroughly cleansed with either alcohol, peroxide of hydrogen or ammonia, using a syringe to prevent septic matter being forced through the foramen. After the alcohol has evaporated, or the canal thoroughly dried of the peroxide of hydrogen or ammonia, by means of a hot-air syringe, an application of the bichloride of mercury or other antiseptic is then made, and the canal rendered permanently aseptic. In an open pulp-canal containing partly devitalized pulp tissue, the same care must be exercised to cleanse, disinfect and render aseptic. When alveolar abscess exists as the result of a devitalized pulp, similar treatment is indicated ; and in all cases where a pulp has been destroyed by therapeutic remedies or agents, the treatment consists in cleansing, disinfecting and filling the pulp-canals.
Dr. A. W. Harlan remarks: "All cavities in living and pulp-less teeth are infected through the agency of pathogenic bacteria or micrococci. (Black, Miles, Underwood and Miller.) These micro-organisms and other septic matters cannot be destroyed in excavating a cavity in a living tooth short of destruction of the pulp by coagulating drugs save in rare instances. Dilute solutions of bichloride of mercury, peroxide of hydrogen and some of the naphthol compounds, belong to this class; coagulators cannot be used in a sufficiently diluted state to accomplish disinfection without injury to the parts to which they are applied. Diffusible drugs will destroy septic materials, including cause of infection, without injury to the living hard or soft tissues. The above will apply as well to infected pulpless teeth, and this is even true with reference to the coagulation of the exposed organic matrix in the interior of a tooth partly softened by caries. Coagulating agents simply coagulate and leave the coagulum to become a source of food supply to the aerobic and anaerobic microbes."