Cataphoresis, Electrical Diffusion, and Electrical Osmosis are terms which designate a method of treatment for hypersensitive dentine, for the devitalization of pulps of teeth, for opening abscesses, for aborting abscesses, for sterilizing medications in roots of teeth, for acute periodontitis, for bleaching discolored teeth, for sensitiveness in the preparation of teeth and roots, for crown and band adjustment, etc., etc. The definition of the term cataphoresis as given by Prof. William J. Morton, M.D., is, "The movements of fluids, together with the substances they hold in solution, from the positive pole of electrodes conveying a continuous current in tissue toward the negative pole." These fluids contain elements in solution which make them medicines, and these medicines must flow from the positive to the negative pole conveyed by the current; hence if application is made to one tissue by the positive pole, and to any remote part by the negative pole, the solution has a tendency to flow with the current, and these medicines will travel in that direction.

Although any form of battery which is constant when the amperage of the individual cell is from one-fourth to five-eighths of an ampere, will answer, yet the dry chloride of silver cell is probably the best for treatment by this method, on account of its constancy and durability.

The voltage which concisely represents the pressure of the current, is indicated by the numbered attachments, and the pressure may be increased at pleasure. The milliampere dial records the flow of the current through the tissues, and a current controller furnishes in the smallest quantities further pressure upon the tissue, as may be suggested by the case in hand. Clinical experience suggests that as regards the current strength, a large voltage is not necessary in securing the desired results. Generally from one-half to one and a half milliampere registrations will be sufficient to anaesthetize perfectly. A low voltage also insures comfort to the patient. Another important element is uniform and continuous constancy of current application. If the current is spasmodic or unreliable in any degree, the result sought for will be impaired and the comfort of the patient be seriously disturbed. The continuous application of the current should be maintained to the end of the operation, and when a renewed application of the anaesthetic solution is desired, no disconnection should take place, but the solution should be added with the appliance in place.

The electrode should not be removed from the point where it is first applied until after the current is shut off. The voltage required to produce the necessary electro-motor force to produce anaesthesia of the dentine of a tooth varies from five to thirty cells. For children's teeth ten cells may answer, although from fifteen to twenty are generally required. The dry Seclauche battery is also a good form of an open cell appliance, for as long as the circuit is open there is no loss. The dry chloride of silver battery will usually give seven hundred hours of work under a high resistance of tissue.

Cocaine, in from twelve to twenty-four per cent. solutions of the hydrochlorate, is generally employed in the cataphoric method, although as high as a forty per cent. solution has been used. One and one-fifth grains of hydrochlorate of cocaine to ten minims of distilled water, will give a twelve per cent. solution ; the same quantity of the cocaine to seven and a half minims of water will give an eighteen per cent. solution, and a similar quantity of the salt to five minims of the water will give a twenty-four per cent. solution.

The citrate of cocaine, eucaine, tropacocaine, quiacolcocaine oil of cassia incorporated with a trace of pulverized soda sulphate, chloride of sodium, and cocaine and boric acid have also been used with good results in the cataphoric treatment ; and in fact any local anaesthetic mixture which is a conductor of electricity can be so employed. The instrument or rheostat, however, should be so constructed as to give the operator at all times perfect control of the current, and he must be able to raise this element from a weak to a strong current, by such minute gradations that it will be almost imperceptible to the patient.

The application of the rubber dam is necessary, so adjusted that no leakage of the current at the neck of the tooth can occur. The exposed surface of any gold or other metallic filling in the tooth should be coated with sandarac varnish, and the cavity, from which the carious matter need not be removed, is carefully dried and loosely filled with cotton saturated with the obtunding solution.

The platinum point of the anode is covered with a light layer of cotton or lint which is dipped into the obtunding mixture.

The cathode is attached to the left wrist of the patient, and its metallic surface prevented from coming in contact with the skin 38 by means of lint or cotton saturated with a solution of chloride of sodium. All being ready, the point of the anode is inserted in the cavity in contact with the cotton loosely filling it, and the switch is placed on the first contact point of the instrument, and then slowly over the contacts until the patient exhibits some indication that the current is felt. The switch should be retained at such a contact until the sensation subsides, when the resistance of the controller should be gradually lessened. This procedure is continued as long as no pain is felt, when the switch may be more rapidly moved, and if no sensation is experienced, it may then be concluded that the anaesthesia is complete. The switch is then moved back to the zero point, and the operation on the tooth commenced.

The time required to produce anaesthesia varies from eight to fifteen minutes, although a longer time may be necessary when the dentine is very dense.

The effect is better when the application is made directly to the carious matter in the cavity; and the deeper the cavity and the nearer approach to the pulp indicates a less degree of voltage. The removal of the anode while the current is on and before the anaesthesia is complete, causes great discomfort to the patient, and, hence, should be avoided.

The appliances for bleaching discolored teeth by cataphoresis are the same as those required for obtunding the hypersensitive-ness of dentine. The agents employed are a 25 per cent. aqueous solution of peroxide of hydrogen, the ethereal solution opposing too great resistance to the current.

The 25 per cent. aqueous solution of peroxide of hydrogen is readily made by shaking together in a test tube one volume of water and two volumes of 25 per cent pyrozone. The peroxide dissolves in the water, and the ether of the pyrozone is evaporated by heat. The ethereal solution of peroxide of hydrogen opposes too much resistance to the current. Adding a small quantity of acetate of sodium or sulphate of sodium will facilitate the passage of the current through the aqueous solution of the peroxide of hydrogen.

The application of the current is the same as in the treatment of hypersensitive dentine, the tooth cavity being filled with cotton saturated with the bleaching solution.

A. I. F. Buxbaum, M.D., D.D.S., gives the following as his experience in the use of cataphoresis: "Cocaine applied cata-phorically has been proven to have no systemic effects, but is entirely local in its action. Apply cocaine by cataphoresis to a central incisor, and the adjoining central or lateral will be as sensitive as if no application had been made. I can say, however, from my practical experience, that the gum immediately surrounding the anaesthetized tooth is less sensitive than normal. It has also been my observation that when a pulp is completely anaesthetized, that tooth takes on the appearance of a devitalized tooth, - namely, the tooth becomes darker; and when drilled, seems dry (pulverizing, so to speak), the dentine giving off the odor of dead bone when cut or filed. I have also observed that any slight oozing of blood from the gum immediately surrounding the tooth to be anaesthetized stops upon using cataphoresis. To test the power of cataphoresis I have used a red-hot instrument over a pulp scarcely covered with a thin layer of dentine, and no response was given; I have gone further and drilled into pulps which I wished to devitalize, and in some cases no response was made, in others only a trifle. Where I wish to devitalize a pulp by means of an arsenical application, and do it painlessly, I first use cataphoresis, then drill into the pulp and apply arsenic. The greatest objection to cataphoresis has been the time consumed in its application, which at first occupied anywhere from 30 to 40 minutes. After becoming more familiar with this method I was able to cut down the time to thirty, twenty, fifteen and twelve minutes, according to the patient and tooth. I am now able to anaesthetize in fifteen, twelve, ten, seven and five minutes. The duration of the anaesthesia varies in different cases, lasting from one-half to six and eight hours. I have yet to find a case where the result has not been favorable. The danger of cataphoresis lies not in its application to the patient, but in the care and boldness with which a dentist can operate. If a dentist be careless he could easily penetrate or expose the pulp. Not eliciting any pain, he might be careless and not protect the pulp. Another great advantage found in cataphoresis is all freedom from pain when finishing off a filling with disks, strips, stones, etc. I have found, the larger the cavity and the softer the dentine, the more readily will cocaine be transmitted." Electric Units: Ampere - the unit of measurement of an electric current; the unit of strength. Ampere-hour - a unit of electric quantity equal to one ampere flowing for one hour ; it is the equivalent of 3600 coulombs. Coulomb - the unit of measurement of electric quantity ; the quantity of electricity that passes during one second through a conductor having a resistance of one ohm, with one volt of electro-motive force. Ohm - the unit of resistance. Volt - the unit of electro-motive force, or the force sufficient to cause a current of one ampere to flow against a resistance of one ohm. Watt - the unit of power. Unit of current - a conductor one cm. long which, if bent into an arc of one cm. radius, will act with the force of one degree on a unit magnet pole at the centre. Dyne - the unit of force. Farad - the unit of electric capacity. Erg - the unit of electric work. Volt-ampere - the unit of electric work; the amount of pressure developed by a current of one ampere having an electromotive force of one volt. Volt coulomb - the unit of electric work. Weber - an ampere. Unit of work - the erg. Joule - the unit of electric energy. Milliampere - one-thousandth of an ampere.