324 Australian Dental Journal, August, I962

. . Asepsis in root canal therapy

6. C. W. Barker, M.D.S. (Syd.), F.D.S.R.C.S. (Eng.), H.D.D.R.F.P.S. (Glasg.)*

Sterilization of the root canal is a basic requirement prior to root filling and efforts to achieve i t are hampered if a n aseptic method of working is not maintained. This implies: sterility of all the instruments and materials used in the root canal; the area of operation in the mouth must be isolated so as to exclude endogenous contamination ; the operator must himself avoid the introduction of contaminants into the area by inadvertent handling of unsterile surgery equipment. This is a real problem in the dental surgery where conditions are not conducive to the maintenance of com- plete surgical sterility. However, a workable "chain of asepsis" is possible and procedures for accomplishing this will be outlined.

The importance of maintaining asepsis is recognized. Various w ~ r k e r s ( ~ ) ( * ) ( ~ ) have shown that a large proportion of infected root canals may be effectively sterilized by mechanical preparation of the root canal aided by irriga- tion. The full value of adequate mechanical

Received for publication November, 1961. * Lecturer in Operative Dentistry, University of

Sydney. (1) Auerbach M. B.-Antibiotics vs. instrumentation

in endddontics. New York D. J., 19: 225-228 ( N a y ) 1953.

(2) Ingle, J. I., and Zeldow, B. J.-An evaluation of mechanical instrumentation and the negative culture in endodontic therapy. J.A.D.A.. 57 :

( 8 ) Stewart. G. G.-Imuortance of chemomechanical 471-476 (Oct.) 1958.

preparation of the root canal. Oral Surg., Oral Med., & Oral Path., 8 : 993-997 (Sept.) 1955.

preparation can only be realized, however, if contamination of the root canal from external sources is avoided. Cahn") suggests that there is no reason why a vital pulpectomy cannot be followed by an immediate root filling after reaming and filing, provided a n aseptic method of working is maintained. While the author still feels that the method of culturing is desirable prior to judging a root canal ready for filling and that apical periodontitis may often occur following immediate root filling, the validity of the above statement basically cannot be questioned.

The following discussion is divided into three sections. Firstly, the preparation of the field, and this not only includes the isolation of the area by means of rubber dam, but also the very important preliminary procedures for preparing the tooth itself i n order that contamination of the root canal will not occur from leakage during treatment. Secondly, sterilization procedures must be considered both for the specialized metal instruments used in the root canal and also for the many disposable items required. Methods of main- taining sterility during storage will also be considered. Thirdly, a method of aseptic working, which is readily adaptable to the dental surgery.

(4) Cahn, L. R.-Pathology and treatment of peri- apical disease. Brit. D. J., 111 : 57-61 (July) 1961.

Australian Dental Journal, August, I962

Preparation of the field

Following the decision to undertake root canal therapy, due consideration must be given to the state of the tooth crown. All caries must be removed prior to any instrumentation of the canal and a seal of zinc oxide and eugenol cement placed in the prepared cavity. I t must be stressed that this seal remains undisturbed during the entire root canal treat- ment, a separate lingual or occlusal opening to the canal being subsequently prepared. Any attempt to gain access via the proximal surface can only lead to difficulty, not only during instrumentation but also in the maintenance of a n hermetic seal during treatment.

With incisor teeth where excessive break- down of the proximal and incisal area has occurred, in order to provide a reasonably strong temporary and hermetic seal, i t may be necessary to build up zinc phosphate cement over a subsea1 of zinc oxide cement. In some instances when both proximal surfaces are lost, the cementing of a festooned copper band or an orthodontic band, may be necessary to prevent breakdown of the temporary seal and subsequent leakage. Such a step also facilitates the application of rubber dam, even when the greater portion of the crown is lost. If aesthetic factors are important during treatment, and the complete crown is lost, the technique of McGibbon,‘j) whereby a temporary acrylic crown is built around a wide bore tube cemented into the opening of the root canal, may be utilized.

Root canal therapy in posterior teeth, where the proximal surfaces are involved, should be commenced only after the application of a copper band, which remains during the course of treatment. The complete removal of tem- porary cement at each appointment invites leakage during and between treatment.

Application of the dam should include at least one tooth on each side of the tooth to be treated with clamps positioned over unperforated dam more posteriorly. Attempting to work in a root canal where the single tooth only is isolated, gives rise to difficulties of access and vision, and tension of the dam in this area may cause leakage. Turning in the edges of the dam around the necks of the teeth is important and is readily accomp-

(6) McGibbon, D. &I.-Stainless steel tubing as a n aid in the treatment of crownless upper and anterior teeth. D. Practitioner & D. Record., 6 : 338-341 (July) 1956.

325

lished by directing a jet of compressed air at the cervices of the teeth, and then using a plastic instrument to fold the edge of the dam over the dry tooth surface. Ligatures may often be necessary.

Thorough swabbing of the surface of the teeth and dam with untinted metaphen is effective in decontaminating the area, while 70 per cent alcohol is preferred when silicate restorations are present.

Sterilization of endodontic equipment and their storage

Time will not be spent reiterating the basic principles of sterilization. Articles by Rubbo(6)(7) and Crowley(8) provide a n excellent review of the methods available, and this discussion will be limited to the practical application of these methods for the sterilization of all the diverse equipment required during endodontic work.

I t is important to realize that commonly used methods of “sterilization” in the dental surgery for general operative procedures are really only aimed a t destroying the vegetative forms of bacteria and preventing cross infection from possible carriers. The procedures of boiling instruments and the use of “cold sterilization” solutions generally achieve “sanitization”, but not true sterilization, i.e., destruction of all organisms both vegetative and sporing. Procedures which allow true sterilization will therefore be discussed first as preferable methods.

The following methods deal with the steriliza- tion of all the specialized equipment used in the root canal. Additional metal instruments, such as excavators, mirrors, dam instruments are sterilized immediately prior to the appoint- ment and placed on a covered tray. Details of their arrangement and use will be discussed in the section on “aseptic working”.

Method I Mechanical cleansing is a n essential pre-

requisite to any form of sterilization procedure. Grease, mucous secretions, and debris reduce the effectiveness of heat sterilization and pre- liminary scrubbing is necessary.

(6) Rubbo. S. D., and Pierson, Barbara-Calculated risks in sterilization in dentistry. Austral. D. J. 5 6 ’ 1-10 (Feb.) 1952.

(7) Rubbo, ’S. D.-Asepsis and antisepsis in dentistry. Austral D. J., 6 : 61-69 (April) 1960.

(6) Sommer. R., Ostrander, F., and Crowley, Mary- Clinical endodontics. Philadelphia, W. B. Saunders & Co., 2nd Ed. 1961 (p. 62-77).

D. J., 56 : 1-10 (F (7) Rubbo. S. D.-Asensis

Austral D. J., k : 61-69 (Apii l ) 1960. (6) Sommer. R., Ostrander, F., and Crowley, Mary-

Clinical endodontics. PhiladelDhia. W. B. Saunders & Co., 21

326 Australian Dental Journal, August, 1962

trays. Record syringes for irrigation may be sterilized wrapped in calico or cloth. They are subsequently withdrawn from their wrap- ping as needed.

Sterilization of the handpiece is a problem and ideally a hot oil sterilizer is required or the use of a n emulsion as advocated by Crowley.@J Alternatively, a boiling water bath with the addition of A.C.10 with sodium carbonate, autoclaving at 30 Ibs. pressure for two minutes or storage in the hot a i r oven along with the other endodontic instruments may be used. After these procedures, however, the handpiece should be lubricated with sterile oil.

One of the most effective ways of sterilizing all the necessary instruments and expendable items used in endodontics is by means of hot air. The type of sterilizer used may be a simple thermostatically controlled oven or the more elaborate Omniclave (Pelton U.S.A.). This latter apparatus is a combined hot air sterilizer and autoclave (Fig. 1). Sterilization is effected by storing the materials a t 160" C. for a minimum of one hour. The advantage of this method is that the wide variety of instruments and materials used in the root canal may be effectively sterilized together.

Fig. 1.-The Omntclnre combined hot n i r sterilizer and autoclave. In preparation €or hot air sterilizing, endodontic equipment has been arranged in a special Endodontic Tray

(P.D.) and petri dishes.

It is very useful to have some form of special endodontic tray, e.g., the P.D. endo- dontic tray, which may be stocked with all the required equipment. Provision is made in the tray mentioned for reamers, Ales, broaches, burs, paper points, and cotton wool, so that the initial appointment of pulpectomy and mechanical preparation of the canal may be carried out entirely from it. The tray is also provided with a lid which will effectively maintain sterility during storage. I t is prefer- able to have a number of these trays so that a stock of them may be sterilized at the one time, If such a tray is not available, a series of petri dishes may be stocked with the various instruments and materials required.

For dressing appointments, the use of a full tray is wasteful, and i t i s advisable to have a number of petri dishes filled with cotton pellets, cotton rolls, and paper points. These a r e sterilized at the same time as the full

Fix. 2.-The D.S.1.. Minor Aiitnrlnvc and suggested arrangement for sterilization of endo-

dontic equipment by steam under pressure.

M e t h o d 11

The introduction of the small D.S.L. Minor Autoclave (Atherton's Pty. Ltd., Aus- tralia) and the more expensive Omniclave for dental use has made the use of steam under pressure a more practical proposition for routine sterilization of instruments and other materials. The D.S.L. Minor operates at 27 Ibs. pressure and requires about three minutes for effective sterilization. However, i t does not possess a vacuum device for drying out after sterilization. Practically, after the sterilizing time mentioned, the materials are only slightly damp and seem to dry out completely as they cool. Expendable materials such as cotton wool are therefore no problem, but there is a possibility that metal instruments stored

(9) Crowley. Mary C . . Charnemeau, G. T., and Aponte, A. J.-Preliminary investigation of some basic problems of instrument sterilization. J.A.D.A., 5 8 : 4 5 - 4 9 (Jan.) 1 9 5 9 .

Australian Dental Journal, August, I962 327

over a period will rust. I t seems preferable to sterilize the special metal endodontic instru- ments in separate petri dishes, subsequently covering them with Hibitane, or some similar chemical bactericide for storage. The set up in Figure 2 is therefore advocated when using steam under pressure for sterilization of endo- dontic equipment. A series of petri dishes are prepared, some with divisions to keep separate the metal instruments such as broaches, reamers, and files, and others for such expendable items as paper points, cotton rolls, and cotton wool. After sterilizing, the dishes

Fig. 3.--Propylene oxide gas sterilizer for endo- dontic equipment.

of instruments are covered with a bactericidal solution and on these, as well as the other dishes, the lids are replaced for maintenance of sterility during storage. In addition, several syringes may be sterilized for irrigation and a r e wrapped in calico or cloth so as to enable sterile storage. Saline for irrigation, if required, and root filling paste materials may be sterilized in separate containers.

Method 111 Recently the first endodontic gas sterilizer

has been marketed (Atherton’s Pty. Ltd.) which utilizes propylene oxide vapour as the sterilizing agent. I t is very simple to use and has the advantage that all the various instruments and materials used in endodontics may be sterilized at the one time in the same container (Fig. 3). Propylene oxide liquid is placed in a receptacle in the base of the plastic container and the loaded petri dishes are stacked above it. The container is sealed, placed inside the thermostatically

controlled heating unit, and left for four hours or overnight. During this time the liquid is vapourized and the propylene oxide gas circulates through the petri dishes by means of small perforations in the side. Once sterilized, the stock of instruments may be stored in their containers without fear of contamination or rusting.

The possibilities of this method are very great and preliminary investigations carried out a t the United Dental Hospital of Sydney indicate that the vapour will effectively sterilize endodontic equipment. Various instruments and materials were heavily contaminated with a wide variety of bacteria and after four hours were found to give negative cultures.

Fig. 4.--Glass bead sterilizer.

Other aids to sterilizatiovi An excellent aid to endodontic practice is

the bead sterilizer, which is available in this country (Fig. 4 ) . A modification of the original molten metal sterilizer, this apparatus uses small glass beads heated to a temperature of approximately 450°F. and is most useful for “on the spot” sterilization of endodontic equip- ment. Reamers and other metal instruments are effectively sterilized in about 10 seconds as are paper points and cotton pellets. The beads tend to adhere to the latter materials, however, and the apparatus finds its main use in the sterilization of reamers, files, broaches, and the working points of plastic instruments and probes which may become contaminated during use.

The use of paraformaldehyde tablets for maintaining sterility of root canal instruments and materials has been suggested by

328 Australian Dental Journal, August, 1962

Kantorowicz"") (Fig. 5 ) . The photograph shows a n apparatus consisting of a large glass jar in which is placed a perforated stand contain- ing several small glass tubes. These tubes are filled with the various metal root canal instruments, gutta percha points, and cotton wool pellets. A few paraform tablets are placed in the bottom of the jar and the release of formaldehyde vapour effectively maintains sterility of the stored instruments. Tests carried nut on the efficiency of this method were impressive. Not only was the sterility of instruments maintained, but it seems that the formaldehyde vapour by itself effectively sterilized instruments, paper points, and cotton wool which were heavily contaminated with various organisms. After being sealed in the paraform sterilizer for 48 hours, paper points

Fig. %-A home made paraformaldehyde sterilizer for sterilization and storage of endo-

dontic instruments and materials.

were placed on blood agar plates innoculated with cultures of staphylococci and gram negative bacilli, and subsequently large areas of inhibition of bacterial growth appeared around these points.

While these tests were by no means exhaustive, it does seem that clean, dry metal root canal instruments may be placed directly in such a n apparatus and effectively sterilized in 48 hours, as may gutta percha points, cotton pellets, and paper points. I t must be pointed out, however, that if paper points stored in formaldehyde vapour are sub- sequently used for the purpose of culturing, false negative results are likely.

The use of cold sterilizing solutions may be required for storage, if the above methods

(10) Kantorowicz, G.-(R. D. H. London) personal communication.

are not available. The various metal instru- ments used in endodontics may be stored in petri dishes under a germicidal solution fol- lowing sterilization in boiling water for 20 minutes (Fig. 6 ) . A storage medium such as

Fig. 6.-Sterile storage of metal endodontic instruments and gut ta percha points under a bactericidal solution may be necessary. I tems such as paper points and cotton wool require sterilization by other methods as suggested in

the tes t .

Hibitane (0.5 per cent chlorhexidine in alcohol) or Zephirin (quaternary ammonium compound) is effective. Gutta percha points are also stored under such solutions and irrigation syringes, glass slabs, and medicament glasses may be decontaminated by such means.

Fig. ?.-Suggested arrangement of on the "sterile area".

equipment

Sterilization of paper points and cotton wool is possible only by one or other of the above methods, however, and storage of these iteins in a separate petri dish is shown.

Maintenance of asepsis during endodontic procedures

In order that the instruments and materials used in the root canal are sterile and un- contaminated from external sources, it i s

Australian Dental Journal, August, I962

necessary to institute a method of aseptic working. This is achieved by using two separate surfaces-a “sterile area” on which all the sterile instruments and equipment which may be used in the root canal are isolated, and a “working surface” to which the instruments are transferred from the sterile areas as required and used in the root canal. The “sterile area” is preferably a side table or a cleared portion of a side bench on which is laid a sterile towel. The working surface is usually the bracket table.

Figure 7 illustrates a typical set up for the “sterile area” in preparation for pulpectomy and mechanical preparation of the root canal. On this is placed a sterile endodontic tray or alternatively a series of petri dishes contain- ing the root canal instruments and the expendable materials. In addition is seen a tray in which is placed the various accessory instruments which are sterilized in boiling water immediately prior to the appointment. In order to avoid contamination of these instruments during their transference to the working surface, sterile tweezers are placed on top of the folded napkin enclosing the instruments, and these are used to select the instruments and materials required during the operation. Additional requisites are added to the sterile area. A syringe for irrigation during mechanical preparation, sterilized by one of the methods mentioned above, is selected and with i t the solution for irrigation. This solution varies according to the operator’s preference. Saline may be sterilized in bulk in an autoclave, alternatively sterile water may be obtained in ampoules from the pharmacist, sodium hypochlorite and hydrogen peroxide may be placed in sterile medicament glasses ready for use. It will be noted that a metal dish is illustrated in Figure 7 which contains four metal cups. This equipment is readily obtainable and is recom- mended, in view of the ease of sterilization and the fact that medicaments may be placed in them ready for use. For instance, 70 per cent alcohol or untinted metaphen for swabbing the area isolated under rubber dam is placed in one, zinc oxide and eugenol for sealing the canal in two others, and in the other is placed the medicament with which the root canal is subsequently dressed. To complete the sterile area, a sterile slab and spatula are obtained, and preferably a milli-

329

metre rule and a plastic instrument. These are handy accessories for marking the length of the root canal on the reamers and files with thin zinc oxide paste.

A less elaborate set up is required for sub- sequent dressing appointments. After the sterile area is prepared, the clinical procedures may be commenced. The anaesthetic having been administered, the dam is applied, ligatures placed and the area swabbed. The instruments used in this procedure are transferred to the working surface and after use are grossly contaminated with the patient’s saliva. They are therefore cleared away, and the bracket table is covered with a sterile napkin in preparation for the sterile instruments that will be used in opening and preparing the

BRACtZT TABLE

Contarmnated Sectim

Patlent.

BRACtZT TABLE ( w c r u n g surface)

Sterile Oectim

Contarmnated

Patlent.

Fig. b.-A method of maintaining asepsis during endodontic procedures.

canal. The only piece of equipment remaining on the bracket immediately prior to opening into the root canal should be a sterile waste receiver.

Figure 8 illustrates how the endodontic operation is carried out so as to ensure asepsis during working. The bracket (the working surface) is visualized as being divided into a “sterile” and a “contaminated” section. Sterile instruments are transferred from the side table (sterile area) to the sterile section of the bracket. These are used in the root canal and returned to the used or contaminated section of the bracket table. This is important, for after progressive reaming and filing, the canal may be mechanically sterilized and contaminated instruments must not be per- mitted to come into contact with the sterile

330 Australian Dental Journal, August, I962

unused ones. At no time is a n instrument returned to the sterile side table after being transferred to the bracket.

Summary Various methods have been suggested where-

by the large variety of instruments and materials used in endodontics may be sterilized and stored ready for use.

A mode of operation has then been outlined for the maintenance of asepsis during the clinical procedures. It is possible in a n article on this subject to give little more than a guide

to a suitable technique, and many details must be left to the individual operator to suit his own particular technique.

I t is apparent, however, that by employing a method which effectively maintains asepsis during the endodontic procedure, contamina- tion of the root canal is avoided, and success- ful root canal therapy is attainable in a relatively short time.

United Dental Hospital, Chalmers Street,

Sydney.

A note on masticatory loads

H. F. Atkinson, M.B.E., M.Sc., D.D.S. (Manc.), M.D.Sc. (Melb.), F.D.S.R.C.S. (Edin.).

Recent research in this department on mandi- bular movement and masticatory efficiency has brought to light some interesting facts in con- nection with comparative studies. Mountfort"' records that the British hawfinch is capable of splitting cherry and olive stones to extract the kernels and quotes laboratory tests which indicate that loads of from 60 Ibs. for cherry to 159 Ibs. for olive stones are required. When the weight of the bird, approximately 0.125 Ibs., i s considered it makes this feat quite remark- able. I recently had the good fortune to observe in the natural state a flock of gang gang cockatoos (callocephalon fimbriatus) feeding on ripe hawthorn berries. The birds took the whole berry into the mouth, expelled the flesh and then held the stone length wise between the mandibles where it was split open. A deft movement of the tongue extracted the kernel and the broken shell was discarded. A s the cracking of the shells made a considerable noise I realized much force was being applied

* Professor of Dental Prosthetics, Dental School, University of Melbourne. (1) Mountfort, Guy-The Hawfinch, London, S. 31.

N. Collins, 1st ed., 1957.

and therefore collected samples of the fresh fruit and discarded shells for further study. I t was interesting to observe that the shells were all splint longitudinally and were not crushed. Four people, two children and two adults, failed to crush or split any stones when held between opposing teeth.

Anvils representing the upper and lower mandibles of the bird were made from mild steel to fit a Hounsfield tensometer and the load necessary to split the nuts determined. I t was found that a load of 50 lbs. was required to split the nut in the same way as had the bird, while, between flat plates, a crushing load of 55 to 60 lbs. was necessary. When the weight of the bird, approximately 0.5 Ibs., is considered this is indeed a remarkable feat made more interesting in view of the fact that the above children and adults weighed 80, 100, 130 and 160 Ibs. and failed in this task.

Dental School, University of Melbourne,

193 Spring Street, Melbourne.