JOURNAL OF ENDODONTICS I SPECIAL ISSUE, JANUARY 1982, VOLUME 8

Chapter 13

Preparation of the root canal

Root canal therapy may be divided arbitrarily into three phases: (1) mechanical preparation; (2) chemical preparation; (3) chemical (or electro- chemical) disinfection. Mechanical preparation is often carried out simul- taneously with chemical preparation. Disinfection follows only after the canal has been thoroughly cleansed and prepared.

Adequate mechanical preparation of the root canal, rather than reliance on antiseptics, cannot be stressed too strongly. In examining many pulpless teeth histologically , Hat ton s found that the canals had been only superficially cleansed. At times, not even all of the pulp tissue had been removed. This has also been amply demonstrated by the experiences of the author in clini- cal researches at a dental institute and in private practice. In some cases, with a history of several consecutive positive cultures, negative cu l t u r e s were obtained after only one or two treat- ments following thorough curettement and cleansing of the root canal.

M E C H A N I C A L

P R E P A R A T I O N

Mechanical preparation of the root canal is the attainment of free access to the periapical region, through the root eanal, by mechanical means.

This includes the removal of pulpal d~bris, and enlargement of the root canal for the reception of a medicated

dressing and ultimately of a root canal filling. Mechanical preparation pre- supposes a knowledge of the anatomy of root canals, which it is assumed is already possessed by the operator.

Ins t ruments . Root canal instru- ments may be arbitrarily divided into three kinds: (1) Exploring, used for locating the canal orifice and for deter- mining, or assisting in obtaining, patency of the root canal. Examples: Smooth broaches, diagnostic wires, Rhein picks, root canal picks. (2) Pulp removing, used for removing the entire pulp or fragments of it. Examples: barbed broaches, apical curettes. (3) Enlarging, used for enlarging the canal laterally or for gaining access to the apex. Examples: files, reamers. In addition, engine driven instruments, intended to be used in difficult cases for opening root canals through to the apex, are available.

In the mechanical preparation of a root canal, engine-driven instruments should not be used except as a last resort. The rapid revolution of an engine-driven instrument (about 3200 r.p.m.) causes the instrument to break suddenly when it binds. This is partic- ularly true in the apical region where the root canal is extremely narrow and the instrument has no leeway. An engine-driven instrument is also less apt to follow the course of a root canal than a hand-operated instrument. It is less likely to bend and conform to the shape of the root canal because it revolves so rapidly, and may cause

perforation either alongside the natu- ral course of the root canal or at some distance from it. More often, however, the instrument will break. In using an engine-driven instrument, the dentist is always between the Scylla of break- age and the Charybdis of a perfora- tion. If an engine-driven instrument is used as a last resort for gaining access to the periapical region, it should be run in a reducing handpiece which reduces the speed to about one-tenth the usual number of revolutions. With reduced speed, breakage is minimized. Where a reducing handpiece is not available, the engine should be run at the slowest possible speed.

An adequate supply of instruments should be available for any eventuality in the course of a root canal operation. This refers not only to various kinds of instruments needed, but to an ade- quate number as well. The latter is especially true of barbed broaches which should be used lavishly for pulp removal, if one is to avoid breaking an occasional broach in the root canal. It is far safer to use five broaches in removing one pulp, than one broach in removing five pulps.

Root canal instruments, like other dental instruments, become dull with use. We are less apt to realize this because the blades of a file or reamer are so small and because they do not end in a knife-edge but in a square, sharp edge. When a dull instrument is used in a root canal it tends to bind and become twisted rather than cut. As a

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result it breaks. Root canal cutting instruments (reamers, files, picks, etc.) should therefore be examined

frequently and if the cutting edges of an instrument appear to be dull or bent out of line, the instrument should be discarded.

In mechanical preparation of the root canal, the following rules should be observed: (1) direct access should be obtained along straight lines; (2) smooth instruments should precede barbed or rough instruments; (3) nar- row instruments should precede wide ones; (4) reamers, if used, should pre- cede files; (5) files should be used with a pull stroke; (6) no root (:anal instru- ment should be totted when it binds; (7) short-handled instruments should preferably be used in posterior teeth; i] (8) root (:anal picks should not be used l near the apical foramen; (9) apical tissues should not be traumatized; (10) d~bris should not be forced beyond the apex.

Access to the root canals should he I! obtained along straight lines. It has often been stated that the approach to anterior teeth should ahvays be from the lingual surface. In our opinion, an t, approach is a correct approach, if it is a direct approach. Where a leaky mesial or distal filling is [)resent, it ma t' be desirable to remove it and so obtain direct access through the cavity to the apical foramen. Ilowever, if a small, well-placed filling is present, it [

I

may be better judgment not to remove ! it, but to gain access lingually through i the basilar pit. See Figure 51. I

If the approach is from the lingual, I the bur should be [)laced in the center I of the cingulum and directed at almost a right angle with the hmg axis of the tooth until the pulp chamber is pene- [ trated. Following this the opening of I the pulp chamber is enlarged and the ![ bur is directed somwhat parallel with the long axis of the tooth. It is well to s

begin the drilling with a small round bur (No. I or No.2) and to increase the size of the bur as the work progresses until access along direct lines is obtained. If the approach be mesial or distal, access should be so direct that bending of the root canal instrument should not be necessary in order to enter the canal or reach the apical foramen. In this type of approach, more of the gingival floor and lateral will must often be removed than is first realized in order to obtain direct access. All pulp tissue and dentinal shavings must be removed from the pulp chamber if future staining of the tooth is to be avoided. (Fig. 52.)

i 2

rl

5 4

n

7 8 9

In posterior teeth, access ahmg straight lines must be attained even at the cost of considerable cutting of tooth structure. In some cases it may even he necessary to cut away some of the mesial surface of the tooth in order to provide proper access to the mesial canals, h should not be necessary to bend a root canal instrument, in order to insert it into a canal, because of overhanging tooth structure. For open- ing into a pulp chamber, a small round bur should be used to pierce the roof of the pulp chamber, and a larger round bur to connect the (:anal openings. A fissure bur--except for carefully enlarging the opening into the pulp

A

~E

I

P).,.,,. 50 . - - [I "~,rkmL, cn,A ,,/" tool canal ?H~lrlorlt'llt~. (1! ,%'moolh broaclt; (2) sr:'ah- tnng t, roac'/l: (3j a,hua/ cur- OIly" (41 hart)cd broach," d.5)

~riCk. (6) hatchet-cdO' /m k: r7) fib': (g/ reamer: (9/ root cana/ /)/u,~7.~,c'r; (I0) dl(l.~rTlOSllU ?:'/F/'.

iO

S 2 6

Fig. 5l.--Steps in obtaining access to apical foramen in an anterior tooth. (1) To begin preparation of the cavity, a bur or stone in straight handpiece is held almost parallel with long axis of tooth. (2) After dentin in penetrated, but in contra-angle handpiece is held almost at right angles to long axis of tooth. (3) Removal of entire pulp at this stage would be difficult, unless additional preparation were made. Widening of approach and removal of sharp corners to facilitate complete pulp extirpation is necessary. (d) Shows enlargement of root canal and direct access to periapical region has been gained by me- chanical imstrumentation.

Fig. 52.--Syringe with blunt, curved rneedle being used to sash out contents of a root canal. About 2 cc. of sterile water or hydrogen peroxide may be used. The solution is caught on a cotton roll as it drips from the tooth. No pressure should be used in ejecting the solution from the syringe. The needle may often be carried half way up the root canal. It should not be forced high enough so that it binds against the wall of the canal.

chamber--should never be used for connecting the canal orifices, since ledges will result or the pulpal floor may be damaged. Rhein picks are useful for finding the entrance to, or opening into, root canals. Or else, the points of explorers No. 17, 18, 19 may be ground off and the ends made smooth and polished. They will then serve the same purpose as Rhein picks. Pathfinders, which are delicate instru- ments and bend easily, are practically useless for this purpose.

For locating the orifice to a root canal, a pledget of cotton saturated with tincture of iodin should be placed in the plup chamber for a minute or so. The excess iodin is then removed with alcohol and the pulp chamber is exam- ined. ~he entrance to the canal will appear much darker than the rest of the pulp chamber. Where the root canal is quite narrow, the canal orifice may reveal itself only as a tiny dark spot. A modification of this method consists in placing a solution of sul- phuric or hydrochloric acid in the pulp

chamber for two or three minutes. The acid is then neutralized with sodium bicarbonate solution and the pulp chamber is afterward syringed with sterile water. The iodin solution in then applied, as described above, to disclose the root canal opening. The purpose of the acid is to disorganize the organic tissue or to decalcify the inorganic elements, so as to intensify the strain and so make the entrance to the canals obvious. A transilluminat- ing light is of inestimable help at times in detecting root canal orifices.

In gaining access to the root canal from the lingual surface of an anterior tooth, the approach should not be too far up on the tooth near the gingiva. Instead, the approach should be so planned that it will become a direct continuation of the root canal. In gain- ing access to the root canals of molar teeth, Gottlieb 4 has made the following suggestion: Where the pulp chamber is narrow in an occlusogingival direction, a perforation may be avoided by directing the bur toward the distal

canal in lower molars and toward the palatal canal in upper molars. In such cases the pulp chamber has become decreased in size due to the formation of adventitious dentin and pulp stones, and the operator, expecting the bur to sink into the pulp chamber, may cause a perforation before realizing it. If the aforementioned procedure is followed in doubtful cases, this accident may be avoided. After the distal or palatal canal is reached, it is a simple proce- dure to follow up the opening, remove the thin pulpal roof and uncover the orifices to the other canals.

Smooth instruments should precede rough or barbed ones in entering a root canal. A smooth instrument will pierce its way through soft tissue and not force infected material, if it be present, through the apical foramen. A barbed instruments may force infected d~bris through the root apex, or compress the pulp tissue in the more constricted portion of the canal if it be a case of devitalization. If a smooth instrument is used first, the soft tissue will be

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pierced or displaced so as to make room for a rough instrument.

Narrow instruments should precede wide ones. Instruments should also be used in sequence of sizes. It is desira- ble to begin with a fine instrument and follow it up with the next larger size, etc., until the largest size for that particular canal is reached. This is especially true of files and reamers.

Reamers should never be used if files alone are adequate for the opera- tion contemplated. Reamers are deli- cate twist drills which cut by being rotated. The very nature of their design predisposes them to breakage. Should the end of the reamer bind while the instrument is being rotated, breakage will occur. They should be used with great care. They are useful instruments, however, and cannot be dispensed with altogether. Reamers should preferably be used concurrently with files in sequence of sizes, i. e., No. 1 reamer followed by No. 1 file, No. 2 reamer followed by No. 2 file, etc. The working end of a reamer is so designed as to provide a purchase for the instru- ment along the root canal surface. With each turn of the instrument the cutting blades are advanced along the root canal and so dig into and cut away some dentin. A reamer should not be advanced more than a quarter turn or half turn at a time. The instrument should then be moved back a trifle, reinserted, and given another quarter or half turn to the right. Repeated removal and reinsertion of the instru- ment, and care not to give it more than half a turn at a time, will prevent binding and hence prevent breakage. From time to time dentinat dfibris clinging to the instrument should be removed by thrusting the instrument into the end of a cotton roll. The instrument should then be sterilized in a molten metal sterilizer.

Files should be used with a pull

stroke. They are relatively safe instru- ments to use from the standpoint of breakage, but may force d~bris through the apical foramen if used improperly. A file should be inserted into a root canal and be withdrawn laterally against the wall in such a manner as to file one surface of the canal at a time. Packing of dfibris should be guarded against by cleaning the root canal with a barbed broach from time to time. The file itself may be cleaned by being thrust into the core of a cotton roll and then sterilized in the molten metal sterilizer.

Under no circumstances should a root canal instrument be forced, when it binds. Hand-instruments which are revolved, such as reamers, should be revolved in the other direction in an effort to release them. Barbed broaches should be slowly worked loose without using too much force. Root canal instruments are delicate and should be discarded at the first indication of wear.

In molar teeth, where there is little working room, a short-handled instru- ment is preferable to making a bend in a long handled instrument. Not only is the latter awkward to work with, but an accurate sense of touch is interfered with, and proper control of the instru- ment is often lost. This sometimes results in the formation of a ledge due to misdirection of the root canal instru- ment.

Cutting instruments, such as root canal picks, should be used as little as possible in the apical region, so as neither to force infected material beyond the apex nor traumatize the periapical tissues.

O B S T R U C T I O N S I N T H E

R O O T C A N A L

The course, length and diameter of the root canal can be determined from

the roentgen-ray film. This should be carefully studied before any root canal work is begun, in order to judge how accessible the apical foramen will be, what obstructions there are, if any, and how the obstructions can best be overcome. Occasionally, a pulp stone will occlude a root canal. If the stone is in the pulp chamber, as most of them are, its removal will be relatively sim- ple. If present in the root canal itself, however, its removal may be very difficult or even impossible. In such cases where the pulp stone is attached to the root canal wall on one side and allows a fine instrument to pass through on the other, the canal should be widened at the expense of the stone rather than an attempt be made to remove the stone in its entirety. Where the pulp stone lies free in the canal, but becomes wedged in an effort to remove it, it is permissible to use an engine-driven instrument to grind away some of the pulp stone in order to free it. The drill should be heavy and wide, almost the width of the canal, s0 that it will not break by becoming wedged between the canal and pulp stone. Where the pulp stone almost occludes the root canal, a simi- lar procedure must be followed, in an effort to reach the apical foramen. This type is rather rare, however, and is seldom encountered in practice.

Where the apical end of the root canal is apparently closed off so as to present an effective barrier against the passage of a fine root canal instru- ment, the presence of cementum clos- ing off the apical foramen should be suspected. A close scrutiny of the roentgenray film should be made for any sign of a root canal. If none is apparent, and no area of rarefaction is present, and the tooth is comfortable, no attempt should be made to create an opening through the apical foramen. In such cases the foramen has become

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closed over with secondary cementum and is sealed more effectively than we could hope to do it with a root canal filling. If the tooth is uncomfortable, however, or presents an area of rare- faction, apical access must be obtained in order to treat the periapical tissues. This is another instance where, at times, rather than sacrifice the tooth because access to the apical tissues cannot be attained by hand instru- ments, it is permissible to use an engine-driven instrument.

Broken Instruments in the Root Canal. Another obstruction which sometimes makes apical accessibility impossible, is a broken instrument in the root canal. Nothing is more annoy- ing, nothing so disheartening to a den- tist, than to discover that he has just broken an instrument in the root canal. And yet, this anxiety can very easily be prevented by the extravagant use of new root canal instruments. The extra cost is negl[gible when compared with the anxiety, time and difficulty involved in attempting to remove a fragment of an instrument.

There are times, however, when knowing how to remove a broken instrument is indispensable. There is no sovereign remedy or technic, but several methods may be tried. The method will depend somewhat On the size of the fragment, its position in the canal, and what it is wedged against. A very small fragment that extends beyond the apical foramen will offer great difficulty in its removal and should not be attempted. A root ampu- tation, if in an operable tooth, should be do~ae instead. More often the frag- ment remains entirely within the canal and an attempt should be made to remove it by mechanical or chemical means. The use of a magnet, which is sometimes recommended, is not often Successful. If the fragment is so loose that a magnet can withdraw it, it can

be removed by simpler means as well.

A roentgen-ray picture should first be taken to localize the fragment before any attempt is made to remove it. Then with picks, smooth broaches, or other fine smooth instruments, an attempt should be made to dislodge the fragment. If these means fail, rough instruments such as files, should be used to engage the coronal end of the fragment and withdraw it. If it hap- pens to be a fragment of a barbed broach, another barbed broach may be used to dislodge it. A small wisp of cotton is wound around a fine barbed broach, which is inserted in the canal and turned so as partly to unwind the cotton in order to engage a barb on the fragment. The instrument is now slowly withdrawn, and if one is fortu- nate enough to have engaged the frag- ment with the cotton, it will often become loosened or come away entire- ly with the cotton. Grinding around the periphery of the instrument with a fine bur in an effort to dislodge it may also be tried, but usually the fragment is too far up in the root canal to be reached with a bur. Where the frag- ment is caught against a ledge and cannot be removed, but access can still be had to the apical foramen, the fragment may be left in the root canal and treated as a partial filling, pro- vided the canal has been thoroughly sterilized. This, however, happens but rarely.

Where mechanical measures to dis- lodge the fragment fail, chemical means might be tried. For this pur- pose, iodin compounds are probably the most satisfactory. Some years ago, Waas 11 recommended a 25 per cent solution of iodo-trichlorid for dissolv- ing broken root canal instruments. While this is an effective method, great care must be exercised in handling the solution because of its strong caustic effect. The solution should be freshly

prepared each time. As large a portion of the fragment as possible should be exposed, so as to present a large sur- face area to the action of the solution. The iodo-trichlorid solution should be carried into the pulp chamber by means of a small pipette, pumped up into the root canal with a thin plati- num needle and allowed to remain there for from three to five minutes. After washing the canal with sterile water, an effort is made to remove the fragment. If unsuccessful, the technic is repeated. Generally, enough of the surface of the fragment becomes cor- roded to enable one to loosen and remove it after two or tlaree trials. In some cases it may be necessary to repeat the aforementioned technic on several visits, until all of the fragment has become dissolved.

A concentrated Lugol solution, as suggested by Prinz, ~ may also be used. The formula for the solution is:

Potassium iodid .................. 2 parts Distilled water .................... 3 parts Iodin crystals ...................... 2 parts

The solution should be pumped into the root canal so as to come into close contact with the fragment. Picking around the fragment with an instru- ment will help to bring the solution into close contact, and so assure a corrosive effect by the iodin solution. After several minutes the solution is washed out, the canal is dried, and a fresh solution is carried into the canal. After each application of the iodin solution, the canal should be syringed with sterile water. If the fragment is not displaced, the canal should be dried and the iodin solution sealed into the canal for two or three days. To retain the solution in the canal, ashes- tos fiber should be used instead of cotton which becomes dissolved by strong solutions of iodin. Difficulty

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may be encountered in sealing the iodin solution in the canal. If cement is used, the periphery of the cavity should be coated first and the cement applied from the periphery towards the center, so as not to trap air bubbles. If gutta percha is used as a sealing agent, all excess moisture should first be removed, and pressure in packing the gutta percha should be made against the periphery rather than towards the cavity, so as to assure a hermetic seal. Only those who have attempted to remove a broken instru- ment know how difficult it is. With much perseverance and patience, how- ever, the attempt will often be crowned with success.

Another obstruction to apical access is a previously filled root canal, as in retreatment cases. For removing gutta percha canal fillings, xylol or chloro- form may be used. Medicated root canal fillings of a cementitious nature will generally require some mechani- cal pressure with an instrument to break up the filling material, in addi- tion to the liberal application of xylol or chloroform. Retreatment of teeth with root canal fillings composed of oxychlorid (or oxyphosphate) of zinc cement should not be attempted because of the difficulty commonly encountered in dissolving these fillings even with strong inorganic acids.

C H E M I C A L P R E P A R A T I O N

OF T H E R O O T C A N A L

Mechanical instrumentation may be assisted by chemicals for disorganizing pulpal d~bris, removing obstructions, and enlarging root canals. The chemi- cals used may be either alkalis, e. g., sodium-potassium alloy or sodium dioxid, or acids, e. g., hydrochloric or sulphuric acid. Chemical preparation should not be attempted until the canal has been prepared as much as possible

by mechanical means alone. Alkalis are used for the purpose of

dissolving or disintegrating organic matter, thus making the dentinal material friable and less resistant to pressure from an advancing instru- ment. Acids act by dissolving the inor- ganic dentinal structure, of which about two-thirds of the dentin is com- posed. The remaining organic matrix often offers little resistance to instru- mentation, thus making it possible to enlarge the root canal in order to gain free access to the periapical tissues. When sulphuric acid is used, carboni- zation of the organic matter is, at times, an incidental but desirable effect.

Alkali Method. Two effective alkalis are available for enlarging the canal by the alkali method: (1) sod- ium-potassium alloy; (2) sodium diox- id.

Sodium-potassium alloy, for dental purposes, was introduced by Schreier m in 1892. It is a combination of metallic sodium (2 parts) with metallic potas- sium (1 part). Since these elements are very hygroscopic and decompose vio- lently in the presence of water, they are either kept under a non-aqueous liquid, such as benzene, or else in hermetically sealed containers of glass. For dental use, small glass tubes are available, sealed with paraffin wax. When fresh, the material has a silvery sheen and looks very much like mercu- ry. After the tube has been opened several times, decomposition of the alloy takes place due to absorption of moisture from the air, and a lusterless, hard, white or grayish coating forms on the inside of the tube. This coating consists of the hydroxids and oxids of sodium and potassium, and is ineffec- tive for the purpose intended. The coating may be removed with an excavator so as to expose a fresh layer of active sodium-potassium under-

neath. Tubes of sodium-potassium alloy should be hermetically sealed with utility wax when not in use.

In using the alloy, a very small quantity, about the size of a pin-head or less, is removed from the container on a smooth broach. This is quickly transferred to the previously dried canal of the tooth. At once, a violent interaction will occur between the alloy and the moisture present in the organic pulpal d~bris. If enough of the alloy is used and much moisture is present, sparks of fire with much heat and a sizzling sound will follow. The reaction results in a liberation of sod- ium and potassium hydroxid in statu nascendi, with the evolution of hydrogen, according to the following formula:

Na + K + 2H20 -- NaOH + KOH + H2

The hydroxids combine with water to form a concentrated caustic solution, which attacks the organic pulpal material and destroys it. According to Schreier, a secondary chemical reac- tion follows, whereby the fat and fatty acids contained in the pulp d~bris combine with the sodium and potas- sium hydroxids to form soaps. These are readily washed from the canal with distilled water or hydrogen peroxid solution U.S.P. As a by-product of the initial reaction, hydrogen is liberated with the evolution of much heat, which incinerates some of the organic mater- ial and accounts also for the flash of light which is sometimes observed. The end result of the reaction is: (1) disorganization and dissolution of the organic pulpal d+bris; (2) friability of the inorganic matrix, facilitating enlargement of the canal by instru- ments; (3) sterilization of the root canal, because of the powerful, caustic and antiseptic effect of the hydroxids

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of potassium and sodium. A word of caution should be given

regarding the care with which sodium- potassium alloy should be used. Because of its powerful caustic effect, great care should be exercised in carrying it into the root canal. It should never be used without protec- tion to the soft tissues of the mouth by means of a rubber dam. Cotton rolls or napkins are inadequate, since if even a pin-head of the alloy be accidentally dropped in the mouth, a flash of light, intense heat, and a severe burn will result. Also, because of its powerful caustic action sodium-potassium alloy should be used sparingly and never allowed to come into contact with the periapical tissues.

Chemical destruction of pulp tissue and incidental enlargement of the canal my also be obtained by means of sodium dioxid. Sodium dioxid was introduced by Kirk 6 in 1893. It is a yellowish, somevhat granular, highly hygroscopic powder. It is a powerful oxidyzing agent and is highly destruc- tive to organic tissue. It is marketed in screw-capped, tin containers which must be sealed tight to exclude air in order to prevent decomposition. On contact with water, sodium dioxid liberates sodium hydroxid and oxygen, according to the reaction:

Na202 + 2H20 = 2 N a O H + H20 + O

The effect of sodium dioxid is some- what similar to that of sodi- um-potassium alloy in that it also acts Upon h e organic portion of the pulp or dentin. It should be conveyed to the root canal on a broach which has previously been moistened with chlor- oform-alcohol solution (3 to 1) or an alcohol-glycerin solution (10 to 1). When brought into contact with moist pulp tissue, sodium dioxid effervesces

owing to the liberation of oxygen. It should gradually be worked into the root canal, carrying it to the apex but not beyond. If the root canal is very dry, the sodium dioxid should first be placed in the canal and then a drop of sterile water should be added to com- plete the reaction. Decomposition of the sodium dioxid will take place with the formation of caustic soda and the liberation of oxygen.

Since the chemical reaction follow- ing the use of sodium dioxid is not so pronounced as when sodium-potas- sium alloy is used, an acid is often used in conjunction with the former. In experiments carried out by the author a number of years ago, it was found that sulphuric acid left a residue when allowed to interact with sodium diox- id. On the other hand, a 10 to 30 per cent solution of hydrochloric acid left no residue. Hydrochloric, rather than sulphuric, acid is therefore recom- mended for reacting with sodium diox- id. The acid may afterward be neutral- ized with a weak solution of sodium bicarbonate. It might be added here that mechanical instrumentation should play just as important a r61e as chemical action in removing obstruc- tions and enlarging the root canal. The two may either be combined in the same operation or used in sequence, the purpose of the chemical reaction being to weaken the resistance of the dentin to mechanical instrumentation.

Acid M e t h o d . - - T h e acids general- ly used in root canal work for enlarg- ing the canal and gaining access to the periapical tissues are: (1) Sulphuric acid; (2) hydrochloric acid. Phenolsul- phonic acid and dilute solutions of reverse aqua regia are also used occa- sionally.

Sulphuric acid was introduced into root canal work by Callahan 2 in 1894. It destroys pulp tissue by precipitating proteins and by abstracting water. It

literally chars organic tissue. Its sol- vent action on dentin is self-limiting because it forms an insoluble calcium sulphate, or modified Plaster of Paris, according to the equation:

CaCO3 "1"- H2804 = CaSO4 "[-

H 2 0 -[.- C O 2

For this reason it sometimes defeats its own end, since blocking of the root canal occasionally occurs from forma- tion of the fairly insoluble calcium sulphate. Sulphuric acid is used in concentrations varying from 30 to 50 per cent. Because of its corrosive action upon metals, it should not remain long in contact with a very thin broach, especially in the root canal, since it weakens the broach and may cause it to break. When used clinically, the canal should be frequently syringed with water or with a weak sodium bicarbonate solution in order to wash away the resultant calcium sulphate. The bicarbonate solution will not only neutralize the acidity, but will form a soluble salt, sodium sulphate, which is readily washed out of the canal. The resultant chemical equation may be expressed thus:

H2SO4 + NaHCO3 = NaHSO4 + H20 + C O 2

As a by-product of this reaction, an effeverscent solution is formed which helps to dislodge organic d+bris and to force it along the line of least resis- tance, i. e., out toward the pulp cham- ber.

Hydrochloric acid is generally employed in a 30 per cent solution. It is more active than sulphuric acid per se and because it is not self-limiting in its action, i. e., an insoluble product is not formed from its interaction with dentin. In in vitro experiments con- ducted by the author, dentin was found

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to be more soluble in hydrochloric than in sulphuric acid. Also, no resi- due was left from the reaction, since the resultant calcium chloride is readi- ly soluble in an excess of acid. The reaction may be expressed as follows:

CaCO 3 -1- 2HCI = CaC12 + H20 -[- C O 2

Hydrochloric acid will also interact with sodium dioxid without leaving a residue, in contradistinction to sul- phuric acid which does leave a residue. In the opinion of the author, 30 per cent hydrochloric acids is superior to sulphuric acid for opening and enlarg- ing root canals.

Phenolsulphonic acid was rec- ommended by Buckley 1 in 1917 because it is not so destructive as sulphuric acid and because its syrupy consistency facilitates its being carried into the root canal. Phenolsulphonic acid is not commonly used today. It is not so active as either sulphuric or hydrochloric acid. Also, if sodium bicarbonate is used to neutralize the acid, sodium phenolsulphonate will be formed, which being fairly insoluble, may block the root canal rather than clear it.

In recalcitrant cases, where the root

canal is difficult to open with either hydrochloric or sulphuric acid, a 50 per cent solution of reverse aqua regia, as suggested by Prinz, 9 may be tried. This solution is composed of:

Hydrochloric acid ................ 1 part Nitric acid ........................... 4 parts Distilled water .................... 5 parts

The above solution of aqua regia prob- ably possesses the greatest solvent power on dentin of any acid used in root canal work. To prevent its too rapid action and dissolution of dentin, the solution may be further diluted with an equal quantity of water. The solution should be kept in a glass- stoppered bottle, away from steel instruments, which the fumes readily attack. It should preferably be carried into the root canal with a fine, plati- num wire. Reverse aqua regia should not be used routinely, but only in cases where the application of sulphuric or hydrochloric acid has been unsuccess- ful in enlarging the root canal. What- ever acid is used, extreme care should be taken to confine the acid within the root canal.

Among other agents which have been suggested for the preparation of root canals may be mentioned: (1)

B

J

Fig. 53.--Capillary pipettes for ejecting medicaments directly into root canal. A, Glass pipettes, made by fusing iridio-pla- tinum hypodermic needle in mouth of dropper ordinarily used for silicate ce- ment liquid. B, Me- tal pipette made of stainless steel nozzle and rubber tubing.

chlorinated soda solution; (2) papain; (3) sodium methylate; (4) lactone; (5) maggots.

Walker 12 has suggested the use of a double strength solution of chlorinated soda U.S.P. for chemical cleansing of the root canal. The solution should contain at least 5 per cent of available chlorin. In addition to being a solvent of organic tissue, the solution is claimed to be a powerful germicide.

Papain has been recommended by Wilkinson 13 as a useful means of elim- inating necrotic tissue from the root canal. Wilkinson suggests that the papain should be made up in a 10 per cent solution in 0.001 normal hydroch- loric acid to which a 0.1 per cent thymol or formalin is added to insure sterility. He claims that the pulp will be digested in from 3 to 6 days when this solution is sealed in the root canal.

A solution of sodium methylate in alcohol has been suggested by Levene. 7 Its effect is somewhat similar to that obtained from sodium-potassium alloy but is less violent in its action. He also recommends a concentrated solution of

Fig. 54.--Showing ejectzon of fluid from capillary pipette into root canal of upper tooth.

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lactone for pulp digestion. Seeding of the pulp chamber and

root canal with specially prepared maggots for puposes of cleansing was suggested by Dreher 3 as a result of in vitro tests conducted by him. The method appears to be too cumbersome and uncertain for clinical use.

References 1. Buckley, J.P.: Jour. Nat. Dent. Assn., 4,

217, 1917.

2. Callahan J.R.: Dent. Cosmos, 36, 957, 1894.

3. Dreher, G.C.: Dem. Survey, 12, 36, 1936.

4. Gnttlieb B.: "Dentistry in Individual Phases. I. The Treatment of Root Canals," Tel-Aviv, Haaretz Press, 1938.

5. ttatton, E.H.: Dent. Cosmns, 70, 249, 1928.

6. Kirk, E.C.: Dent. Cosmos, 35, 162, 1893.

7. Levene. P.A.: Dent. Cosmos, 63, 905, 1921.

8. Prinz, H.: Brit. Dent. Jnur., 43, 1167, 1922.

9. Prinz, tt.: "Diseases uf the Snft Structures of the Teeth." Philadelphia: Lea & Febiger, p. 189, 1937.

10. Schreier, E.: Oestr.-ungar. Vrtljschr. f. Zhk., 8, 119, 1892.

I1. Waas, M.J.: Dent. Cosmos, 60, 908, 1918.

12. Walker, A.: Jnur. Am. Dent. Assn., 23, 1418, 1936.

13. Wilkinson, F. C.: Brit. Dent. Jour., 50, 1, 1929.

T h i s brief note is to comment on Dr. Grossman's contributions to organizational forms of endodontics, in particular, the American Association of Endodontists, and to give a perspective on his impact on endodontic research.

The first formal coming together of a group of like-minded men who believed in root canal therapy was initiated by Louis Grossman in Philadelphia. The AAE is a direct lineal descendent of this group. Dr. Grossman was a source of nurture and enthusiasm in the early days of growth; he has been a voice of wisdom, restraint, and experience, while the AAE has flourished and expanded. His pioneering efforts are the bedrock upon which the AAE stands.

Dr. Grossman recognized early in his career that the slow, meticulous, sometimes painful path of careful research investigation, rather than bombastic rhetoric and special pleading, was the only way to truly establish the biologic validity and clinical acceptability of endodontic therapy. His early research was conducted against a background of prejudice, which was hardly favorable. Yet his insight in selecting timely and important areas for investigation and his careful methodology eventually succeeded in giving endodontics a scientific basis. Today, young graduate students embarking on a research project often find in their literature search that a similar study was done by Dr. Grossman years earlier. One cannot help but conclude that much of our research is simply thinking Louis Grossman's thoughts after h i m . . , and alas imperfectly on our parts.

When one thinks of Louis Grossman, two qualities come immediately to mind: decency and integrity. T h e y are the attributes that enabled Dr. Grossman and endodontics to prevail. In a larger sense, they are the enduring core of all civilized behavior.

Henry Van Hassel, DDS, PhD University of Maryland, Baltimore, President, American Association of Endodontics

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