L

OCAL anesthesia in its various forms successfully employed is the greatest practice-builder at our command, as it enables a dentist to do thorough work with a minimum amount of pain. The public knows that this is being done by ethical practitioners, and is beginning to demand it more and more.

The remark is often made that nerveblocking is difficult and complicated. It is, if a man thinks he can employ the same careless technique that is usually employed when an injection is made into the peridental membrane for a simple extraction. It is not, if the proper technique is carried out.

If we know the nerve supply to the different teeth and surrounding tissues, and are familiar with the anatomical guides that will enable us to inject a sterile solution around these nerve trunks, then all we need is practice. Of course, I do not mean that a man can start into this work and get gratifying results without some preparation, but I do mean that any dentist of ability along other lines, who will apply himself and will observe carefully the smallest details of asepsis, can and will get gratifying results.

It is my desire to make this paper absolutely practical, and for that reason I shall not discuss the various technical methods of producing anesthesia, nor any phase of the subject except those which are concerned in our everyday use of local anesthesia. This paper therefore is intended for four classes of men:

First: Those who use nerve-blocking frequently with success.

Second: Those who have used nerveblocking frequently without success.

Third: Those who have learned something about the technique but for some reason have not tried it.

Fourth: Those who are not familiar with the technique.

The first practical discussion of nerveblocking I ever heard was at our meeting in Jackson, by Dr. S. L. Silverman of Atlanta. He made it appear so easy and practical that I was extremely interested, and asked him this question at the close of the lecture: "Is there a textbook on the market that will enable a man that is unfamiliar with this work to get sufficient practical information to enable him to do nerve-blocking successfully?" He said "Yes," and recommended Fischer's book. I bought one of Fischer's books, read just enough to know that I did not know anything, and blocking until two years later. laid it aside. I did not attempt nerveI have

since learned that if a man will get Fischer's book on local anesthesia and study it carefully, and will get just a little practical demonstration from someone, he can do nerve-blocking.

INSTRUMENTARIUM.

Now let us take up the practical aspect. The first thing to do is to get a suitable equipment. It is not necessary to buy everything the experts say, but if you are going to economize on the essential parts of the equipment you had better let conduction anesthesia alone. The next thing needed is a place to keep that

equipment. If it is stored away in a cabinet drawer it will be necessary to boil everything each time you use it. Purchase a sterilizing jar made for the purpose and fill it with 70 per cent. alcohol. The other essential parts of the equipment consist of a suitable hypodermic syringe without washers that will hold at least 3 cc. of solution; a short needle 15 mm. in length; a straight needle 30 mm. in length; a 30 mm. needle with curved shank for tuberosity injections; a 3 cc. novocain dissolver, and a 10 cc. dissolver. It is best to use iridio-platinum needles, because they will not corrode and can be heated to a cherry red as often as desired.

It is also desirable to have a study skull. I do not believe a man can make a success of nerve-blocking unless he has a skull to use in his study when he begins. I suspect there are men present who have made failures in their injections who would have been successful if they had had a skull to freshen the memory in regard to the anatomy of the region before making those injections.

The E tablet will meet all require ments, so we will not discuss the different tablets, which vary in suprarenin content. Only distilled water and Ringer's tablets should be used for making the solution to which the E tablet is to be added. I use a Silverman still and distil my water fresh every day and usually immediately before making solutions.

PREPARATION OF THE SOLUTION.

Let us now describe the preparation of the solution. I first remove the 10 cc. dissolver from the sterilizing jar, fill with freshly distilled water, boil thoroughly, and then empty it. This is done to remove all traces of alcohol, and, as an additional safeguard against infection, before placing the distilled water with which I am to make the Ringer solution in the dissolver. We then place a little more than 10 cc. of distilled water in the dissolver, and boil. If freshly distilled water is used, it is not necessary to boil for any length of time.

One

Ringer tablet is placed in the 10 cc. of distilled water, which gives a physiologic salt solution. We then pour 3 cc. of this solution in the 3 cc. dissolver, which has been previously prepared for it by boiling distilled water in it, just as with the 10 cc. dissolver, before making the Ringer solution. We now add 3 E tablets, or 1 E tablet to each cc. of solution, which gives a 2 per cent. solution, the strength usually employed in making the injection.

Select the needle indicated, adapt it to the syringe, and wash the syringe out several times to clean it of alcohol by drawing in and expelling sterile distilled water several times. The needle is then heated to a cherry red and the syringe filled with anesthetic solution ready for the injection. We now have a 2 per cent. sterile solution that is isotonic.

METHOD OF MAKING INJECTION.

We are now ready to prepare the field for the injection. We must always remember that we are going to inject this solution into the deep tissues. Spray the mouth thoroughly with some antiseptic used in routine work; dry the point well where the needle is to be inserted, and wipe the tissue with tincture of iodin. The needle should always be heated to a cherry red before making the injection and before drawing the solution into the syringe. The solution should be as near the temperature of the body as is practicable. I test it by dropping a few drops on my forearm. If I cannot feel the temperature of the solution, it is a fairly safe guide that the temperature is approximately correct. I may say just here that there are two points that will prove of invaluable assistance if one will carry them out in every instance. These two points were deeply impressed upon me by Dr. Silverman: If in making an ordinary injection the patient should show any unfavorable symptoms, the first step would be to place him in a reclining position; so why not do this before making the initial puncture? The other point is, to

avoid making the injection too rapidly. Dr. Silverman says that sixty seconds by the watch should be the minimum time required for making the injection. When I make an injection, my assistant stands behind the chair with a watch in hand, and my minimum time is nearer two minutes than sixty seconds in most cases. You should be careful to distribute the solution equally for the entire time. If you consume sixty seconds in injecting one-half of the solution and then inject the other half at once, you have destroyed the effect of the slow injection.

There is another important point. When a patient presents himself for an operation with a well-defined area of infection, we should not attempt a nerveblocking injection if it is necessary to pass the needle through the infected area to reach the point necessary for anesthesia. Do one of three things: Hurt the patient as much as is necessary, administer a general anesthetic, or do not attempt to operate.

I shall now hurriedly describe the fields covered by the various injections. In the upper jaw the tuberosity injection will produce anesthesia of the second and third molars, and in some instances the first molar. We cannot rely upon anesthesia of the first molar in a tuberosity injection, on account of the distribution of the middle superior dental branches. Infiltration anesthesia should be em

ployed for the two bicuspids and the first molar when necessary.

If a nerve-blocking injection instead of infiltration is made for the six anterior teeth, it should be made at the infraorbital foramen, but remembering that the success of this injection depends upon the solution getting back into the infraorbital canal. If infraorbital injection is used for only one side, infiltration must be employed at the median line if an operation is to be performed on a central incisor, to block off sensation from the nerves anastomosing from the other side. If the lingual surface is involved in an operation on the upper jaw, a lingual injection is necessary to block off the naso-palatine or anterior palatine branches. In the lower jaw, infiltration may be employed for the six anterior teeth, but the mandibular and mental injection should be used for the posterior teeth. The lingual nerve is blocked in making the mandibular injection, which produces anesthesia practically to the median line, where it meets the injection from the opposite side. If anterior teeth only are to be removed, the lingual nerve may be blocked at any point along the lingual surface.

I realize that one cannot do nerveblocking successfully simply from listening to what I have said, but I believe I have suggested some points which may be of some assistance to each of the four classes for which this paper was intended.

TO THE EDITOR OF THE DENTAL COSMOS:

Sir,-As Dr. S. J. Kessler has brought forward the question of the respective self-limiting action of sulfuric acid and of the sodium and potassium alloy in your October issue, I avail myself of the privilege of replying to his communication through the same channel.

In this instance, as is often unfortunately the case, a sentence lifted from a paragraph loses the identity, and in particular the significance, it possessed in the original text. In my article in the June issue of the DENTAL COSMOS spoke of the fact that we should use only sodium and potassium as we approach the apical end of the canal, and that we should use it only in almost microscopic amounts. Then the sentence immediately preceding the one quoted by Dr. Kessler reads, "On this account we may safely go through the apical opening." This would of course indicate that I was speaking of the relative action of the two agents upon the immediately surrounding periapical tissues, and these are soft tissues.

The point at issue is then further clouded by creating the impression that I am at variance with Dr. Callahan, by quoting from him to the effect that sulfuric acid is self-limiting in cancellous tissue, and that sodium and potassium is not. Here lies the apparent difference. Dr. Callahan spoke of cancellous tissue, by which he meant hard tissue, and I spoke of periapical tissue, by which I meant soft tissue.

Anyone with a knowledge of chemistry would know that the action of H2SO, would be limited in action in bony tissue, because the acid radical would be quickly

satisfied by combining with the high calcium content of cancellous structure. In fact, in looking over Dr. Callahan's original paper (Items of Interest, August 1915) I find that Dr. Prinz in his discussion went into detail on that point. There is a percentage of cases where the canal contents have completely dried out in which the application of Na-K, without the proper previous application of water, will result in a very gradual saponification of these contents and of the canal walls. In these cases the action is not, strictly speaking, so limited, and this was probably the case with the specimen Dr. Callahan presented. But with the proper technique this is not the case. However, in dentin the inorganic content is about 75 per cent. of the mass, and I spoke then only of its limited action on all organic matter. The action of Na-K is, as has been repeatedly pointed out by Dr. M. L. Rhein, largely due to its affinity for water, and all soft tissue has a high water content. This is the reason why we can so readily open canals and with the roentgenogram find in so many cases that accessory canals, often even at right angles to the main canal, have been cleaned of their contents and we are thus enabled to properly fill them. Na-K, in the extremely small amounts in which we should use it, when it touches any soft tissue instantly enters into chemical combination with it, and both lose their original identity, leaving in this case only such a trace of sodium and potassium hydroxid that its action is negligible.

Sulfuric acid, on the other hand, acts on soft tissue as a caustic or by virtue of its ability to coagulate albumin.

Its action on such tissue will continue uninterruptedly until its acid radical is entirely satisfied, and in soft tissue the inorganic salts are so small a percentage of the mass that they have no appreciable effect in limiting the caustic action. Therefore the action of sulfuric acid cannot be viewed as a self-limiting one in soft tissues.

We must consider not only the chemical reactions of these two agents, but also their physical characteristics. Na-K is an alloy of plastic consistence, so that we may pick up any amount at will and place it in the canal with the assurance that it will not pass through an opened apical foramen. Sulfuric acid is a liquid, and we can only apply it by placing a drop in the canal, and if the apical foramen be opened it can be and often is drawn through, coming in contact with the periapical soft tissues. Therefore if one feels that he must still use an agent so dangerous to soft tissues, when working in the apical third. of root-canals, he should assuredly resort to the use of the paste form in which sulfuric acid has been recently introduced.

In order to test these reactions on living tissues, a guinea-pig was used. Making an incision through the skin, it was dissected back a short distance, exposing

healthy muscular tissue. On the one thigh so prepared was placed some sodium and potassium, much more than would ever be protruded accidentally through an apical foramen, and on the other so prepared was placed one drop of 50 per cent. sulfuric acid. The Na-K reaction was entirely confined to the point of application, while on the acid. side the reaction was spread over quite an area, and was much more violent in appearance. This rather empirical experiment goes to prove the above explanation as to the respective actions of the two agents. These experiments, to be conclusive, should of course be carried out by working the agents through the root-canals of dogs' teeth, sections being made of the tissues, but I have not at present the necessary time to carry out such a long series of experiments, and I write this in order to demonstrate more clearly to any other investigator who may be interested enough to carry the work farther, this difference between hard and soft tissue when acted upon by these agents.

In conclusion I wish to thank Dr. Kessler for his interest in the matter. Very cordially yours,

MILTON J. WAAS. CAMDEN, N. J., November 11, 1918.

TO THE EDITOR OF THE DENTAL COSMOS: Sir,-Concerning the action of sulfuric acid on teeth, the late Dr. Geo. Watt, many years ago professor of chemistry in the Ohio Medical College, and in the Ohio College of Dental Surgery, this city, affirmed before a class that this acid was self-limiting.

Dr. Callahan, who is referred to in Dr. Samuel J. Kessler's contribution to the Correspondence column in the DENTAL COSMOS for October, once asked the writer if he knew whether or not this

acid was self-limiting. I referred him to Watt's "Chemical Essays," saying I thought Dr. Watt therein affirmed what he had stated before our class.

Dr. Watt spent many years elucidating his theory of acid decay of the teeth, affirming that sulfuric acid caused the black variety of decay, accounting for the slow progress of this (alleged) form of caries on the hypothesis that a minute portion of the nascent acid attacked a tooth, the action ceasing almost instantly. Again, conditions favoring its