168 Australian Dental Journal, June, 1966

Posterior root canal therapy”

Part I

B. C. W. Barker, M.D.S. (Syd.), F.D.S.R.C.S. (Eng.), H.D.D,R.F.P.S. (Glas.),t R. W. Hession, M.D.S. (Syd.),tt and B. C. Lockett, A.A.1.M.L.T.S

Introduction

A recent study of the literature revealed few comprehensive reports which deal with the histological appearance of human teeth follow ing successful root canal therapy. Reports by such authors as Hatton,(1)(2) Skillen,(*) Blayney,(’) and Coolidge,(G)(o) were published during a period when root treated teeth were strongly suspected as foci of infection, and were recom- mended for extraction even though they had

4 This investigation was aided in part by Uni- versity of Sydney Research Grant, AC 43/64/71 , 1964.

f Senior Lecturer in Dental Anatomy, University of Sydney.

t t Part-Time Teaching Fellow-, Faculty of Den- tistry, University of Sydney.

$ Chief Technical Offlcer, Department of Ana- tomy, University of Sydney.

Received for publication, October, 1965. (1) Hatton. E. H.-The possibility of apical regene-

ration after root-canal filling from the histo- pathological point of view. J.A.D.A., 9 : 3, 192- 198 (Mar.) 1922.

(2) Hatton. E. H.-Histologic studies of living tissue reactions associated with pulpless teeth that may be taken as evidence of satisfactory or physiologic healing. J.A.D.A.. 18 : 8, 1502- 1510 (Aug.) 1931.

(8) Skillen, W. G.-Hard tissue changes noted within the canals of treated teeth, and their possible significance. J.A.D.A., 11 : 4 , 350-359 (Apr.) 1924.

1 ’ ) Blayney, J. R.-Present conception of vital re- actions which occur within apical tissues after pulp removal. J.A.D.A., 16 : 5, 851-860 (May) 1929.

(a) Coolidge, E .D. -The reaction of cementum in the presence of injury and infection. J.A.D.A., 1 8 : 3, 499-625 (Mar.) 1931.

(“)Coolidae. E. D.-The status of DulDless teeth as interpreted by tissue tolerance and repair- fol- lowing root canal filling. J.A.D.A., 20 : 12, 2216-2228 (Dec.) 1933.

been clinically symptomless since the time of root filling and the periapical bone appeared radiographically intact.

In view of the limited opportunities avail- able these days to gain such material, i t is con- sidered of value to present a detailed histo- logical analysis of a successfully treated posterior tooth for addition to the literature on this subject. In Par t I1 of this paper, a comparison will be made with the histo- pathology and histobacteriology observed in a similar posterior tooth, extracted following failure of root canal therapy.

bstby‘” states: “The histological examina- tion of the apical par t of the root and the apical periodontium after treatment is the only method of obtaining knowledge about the biologic reactions to our surgical procedures in the root canal, and of realizing the general requirements for the attainment of healing and regeneration of these tissues”.

The acquisition of blocks of human tissue which include the apical periodontium, as advocated by bstby, is dimcult, and the extension of reaction into the apical region must be conflned in the main to animal experi- mentation. However, the examination of any human tissue which becomes available, even if limited to the apical portion of the root, provides valuable data which may be correlated

ostby, B. N.-Report : The treatment of infected root canals. disrussion. 2. Internat. D. J.. 3: 4, 607-617 (June) 1953.

Australian Dental Journal, June, 1966

with that obtained from animal investigation. This information also supplements the ex- tensive literature concerning success or failure in root canal therapy where the control methods of investigation are essentially clini- cal, comprising bacteriologic examination of the canal prior to root fllling, and post-treat- ment radiographic examination.

Case report The maxillary right second pre-molar depicted

in Fig. 1 had been root fllled for approxi- mately twenty years, during which time it had been Arm in the alveolus and symptomless.

169

Fig. 1.-Upper right second premolar with root filling, approximately 4 mm. short of the apex. An intact lamina dura can be traced around

the apex.

There is an intact lamina dura circumscribing the root end. and the canal is fllled to a level which is approximately 4 mm. short of the apex. Details of the condition of the pulp prior to root fllling are not available, although the patient flrmly stated that the treatment was performed without a rubber dam. The tooth was extracted for prosthetic reasons, and immediately placed into a 10 per cent formal saline solution.

Methods : Figure 2 shows that root fllling of the wide

canal had been attempted with two small gutta percha points, which approximate each other in the apical third. The remainder of the canal is fllled in part with a sealer. Voids may be seen within the canal where the root fllling materials do not completely obturate the canal space, except in the area where the points almost meet. At this level, one appears to obliterate the lumen of the canal, therefore probably effecting a seal. There is no radio- graphically discernible continuation of the canal apical to the termination of the root fllling.

C

The tooth was prepared for histological examination by embedding in paraffin following decalciflcation, and serial longitudinal sections varying from 6 to 8 microns in thickness were stained.'

Observations: A study of the sections taken at didterent

levels throughout the canal and stained with Gram, indicated an absence of Gram positive bacteria.

The apical canal is seen to be obliterated with a mass of calcifled tissue extending approximately 3 mm. into the canal from the apical foramen. This tissue is shown to have staining charscteristics identical with the peripheral cementum, and the calciflc matrix, is continuous with the cementum a t the apex

Fig. 8.-Proximal roentgenogram of the pre- molar following extraction. Two small gutta percha points approximate each other in the apical third, and there is evidence that paste had been used in an effort to obturate the canal.

(Fig. 3, 4, 7). While there is continuity with the apical cementum, the calciflc tissue in the canal closely approximates, but is not fused with, the dentine of the canal wall. This is observed in Fig. 4 where retraction has occurred during preparation of the specimen. There is evidence of previous resorption of the dentine in the region of the apical foramen, new cementum subsequently fflling the irregularities.

Areas of degenerate pulp tissue are located throughout the calciflc matrix in the canal (Fig. 4) , but examination of serial sections does not reveal any channels containing vital tissue leading from the apical region. The laminations of secondary cementum covering

* Gram (saffronine 0.6% counterstain), Koneffs aniline blue and methyl green stain, Van Geison. hrematoxylin, eosin and Masson's stain.

170 Australian Dental Journal, June, I966

Fig. 3.-The sectioned root apex reveals a mass of calciflc repair tissue fllling the canal lumen apical to the root fllling, and this is continuous with the peripheral cementum. Masson x 20.

the apex appear to hermetically seal the canal. The calcifled matrix in the canal possesses lacunae, similar in all respects to those seen in secondary cementum, and these were judged to possess viable cells a t the time of flxation (Fig. 8 ) . The calciflc plug appears to have been deposited in laminations from the canal wall, progressively occluding the lumen.

The large lateral canal passing to the buccal surface of the root in the apical third, is obturated in the peripheral portion of its extent by a n ingrowth of secondary cementum (Fig. 4, 5, 6) . This also is a n intact layer.

Rig. 4.-An aptifact incurred during sectioning indicates tha t the calciflc matrix approximates, but is not attached to, the dentine wall of the canal. The large lateral canal, V, contains some debris in thfs portion of its lumen. Soft tissue remnants appear to be included in the calcific

repair tibsue, W. H & E x 2 0 .

Fig. 5.-The lateral canal, traced to the peri- phery on serial sections, is occluded by an invagination of cementum in the peripheral

third. x 20.

The several fine channels observed in addi- tion to the main lateral canal could not be traced to the periphery, and did not possess viable tissue.

Discussion The healing process following extirpation of

a vital pulp: The retention or regeneration of vital tissue in root canal ramifications, or the physiologic closure of large and small canal orifices by calcitic tissue is the aim of root canal therapy, but there are few demonstrations in the literature, of complete closure by calciflc tissue.

Fig. 6.-Lateral canal sealed by means of lacunar cementum. x 63.

Australian Dental Journal, June, 1966

The deposition of hard tissue in the unfilled portion of the canal with a tendency to ob- literate the apical lumen was observed by Grove in 1921.(*) Hatton‘” while maintaining that root fllling to the dentino-cementa1 junc- tion was ideal, stated: “The apical portions of the pulp canal with partial fillings, in the

171

, -

Fig. 7.-The calcific repair tissue is laminated and continuous with the apical cementum. The apical laminations are intact and perforating vascular bundles are not observed. Koneff x 2 0 .

absence of infection and where the distance is not too great, are occupied by living pulp tissues or are more or less completely ob- literated by calcific structures.” He illustrated a case of successful healing which was root filled to a level short of the apex by 3 mm. The closure by calcific tissue, however, is not complete, for a filament of soft tissue penetrates the calciflc deposit.

Skillen(*) examined 250 clinically successful root treated teeth, 58 of which possessed root fillings judged to be satisfactory. While the canals underwent marked constriction in successful cases, he was unable to flnd complete closure by hard tissue in any one instance, and maintained that the retention of a vascular core was to be expected in successful cases of root filling. Illustrations in his article lack clarity, and details of these cases are not reported. It appears from his transverse photo- micrographs that if the root filling was terminated at a high level, marked narrowing

Grove, C. J.-Nature’s method of making perfect root flllings following pulp removal with a brief consideration of the development of sec- ondary cementum. Den. Cos., 6 3 : 10, 968-982 (Oct.) 1921.

of the canal by tubular dentine and pulp stones occurred, while sealing at a level in the apical third resulted in stenosis by lacunar cementum.

Blayney(” recommended amputation of the vital pulp and root filling to the level of the dentino-cementa1 junction. Following such a procedure, he observed that slight resorption of the apex occurs initially, sometimes to the level of the root filling. This he considered necessary to accommodate the increased blodd supply coincident with repair and also ta provide a more suitable b&s for calcification, He depicted the areas of &sorption as being subsequently filled with calcified tissue, but maintained that a lumen persisted in the various calcific cores to meet the circulatory requirements of the newly formed tissue.

Hatton@’ compares the healing process in the apical region of root treated teeth to that occurring in the repair of a bone fracture. The removal of bone in the area of fracture together with other damaged tissue is a pre- liminary process to subsequent repair, first by

Fig. 8.-The region marked X, in Ftg. ?. The lacunee possess viable ceils and the tissue is morphologically identical with secondary

cementum. x 430.

flbrous callus and later by formation of bony callus. In a comparable fashion, the of pulp removal and root filling leads i to resorption of adjacent cementum and alveolar bone and replacement by Sibrous tissue, the reaorptlons being qubs repaired with hard tissue.

Coolidge@) demonstrated that traumatlc in- jury to cementum resulted in a deephy ,mne- trating resorcptfpQ of the udderlying Id&dine,

172 Australian Dental Journal, June, I966

the area being then fllled with lacunar cementum. He agreed with the above authors that slight initial resorption of the apex was a normal sequel of root fllling. Following a histological study of root treated human teeth he concludes that virtually complete closure by cementum occurs if the root fllling is terminated slightly short of the apex, but its extension to the apical opening results in flbrous scar tissue formation.

Ustby(" believes that when the level of extirpation is confined within the root canal, healing progresses more rapidly than when the periodontal membrane is traumatized. He states that deposition of cementum-like sub- stance on the canal walls apical to the root filling occurs only if vital tissue is retained in the apical part of the canal. Photomicro- graphs indicate partial occlusion, but the author remarks that complete occlusion may be the Anal result.

In the specimen described in this report, complete closure of the large and small canal orifices by calciflc tissue had occurred. This tissue is indistinguishable from lacunar cementum (Fig. 7, 8) . Observation of the deepest laminations of apical cementum indi- cate that resorption of the apex occurred prior to repair. The presence of viable cementocytes throughout the matrix suggests that hard tissue formation had commenced in close proximity to the termination of the root fllling and along the walls of the canal, pro- gressing to the apex and leaving a network of canaliculi for nourishment of the encapsu- lated cells. This calciflc repair tissue would appear to have been deposited in orderly fashion by cellular activity, but the presence of pulp debris inclusions (Fig. 3, 4 ) is re- miniscent of a picture of dystrophic calciflca- tion. Removal of such remnants by phagocytic action during the initial stages of repair would be expected.

The fate of tissue 4n lateral canals: The complexity of the lateral branching from the main canal has been demonstrated by several invest igators.(B)(~)~~~)

( 0 ) Hess, W.. and Zurcher, E.-The anatomy of the root canals of the teeth of the deciduous denti- tion and of the first permanent molars. London, J. Bale, Sons and Danielsson, 1925.

(10) Green. D.-A stereomicroscopic study of 700 root. apices of maxillary ~ and mandibular posterior teeth. Oral Surg., Oral Med. and Oral Path., 13: 6, 728-133 (June) 1960.

Meyer, W.-Anatomy of root canals. D. Abs.. 1. 3 131-132 (Mar.) 1966.

Kuitlir. Y.-Microscopic investigation of root apexes. J.A.D.A., 60 : 6, 644-562 (May) 1965.

root. apices of maxillary ~ and mandibular posterior teeth. Oral Surg., Oral Med. and Oral Path., 13: 6, 728-133 (June) 1960.

Memr. W.-Anatomy of root canals. D. Abs.. 1: 3'131-132 (Mar:) 1966.

Kuitlir, Y.-Microscopic investigation of root apexes. J.A.D.A., 60 : 6, 644-562 (May) 1965.

Kronfeld'l') maintains that when the main canal is well fllled and not infected, the perio- dontal tissues take care of lateral channels. He shows a specimen in which a large lateral canal, fllled with cementum, retains a strand of vital tissue connecting with the periodontal membrane. A smaller canal is seen to be com- pletely occluded by laminations of cementum.

In the present case, the closure of the large lateral canal by peripheral invagination of lacunar cementum is observed, with degenera- tion of the enclosed tissue (Fig. 4, 6 , 6 ) . In cases of infected root canals however, the emcacy of pulp solvents and sterilising agents are relied upon to clear the inaccessible channels of necrotic tissue and micro-organisms and allow a similar healing by the periodontal tissues.

The desirable level of obturation following vital pulpectomy: It is probable that the level of amputation of a vital pulp, which is extirpated from a wide and uncomplicated canal by means of broaches, occurs a t the dentino-enamel junction. This is demons- trated in an experimental extirpation of an intact pulp performed on a single rooted tooth

Flg. I).-Experimental extirpation of an intact pulp from an uncomplicated root canal reveals the level of separation situated at the dentino- cementa1 Junction. which is an area of constric-

tion. H & E x 20.

immediately following extraction (Fig. 9 ) . Instrumentation and subsequent root fllling carried out to this level would therefore seem to be ideal in such cases.

It is possible, in the example under con- sideration, that the tooth possessed the frequently encountered variation where there

(18) Kronfeld, R.-Histopathology of the teeth and their surrounding structures (P. E. Boyle, ed.). Philadelphia, Lea and Febiger, 3rd. ed.. 1960 (PP. 225-252).

Australian Dental Journal, June, I966 I73

is a subdivision of the single broad lumen into two in the middle third‘’’) which rejoin again as a single channel in the apical third (Fig. 10). Such a division would hinder the removal of the pulp tissue in its entirety.

The pulp tissue remnants incorporated in the calciflc repair tissue suggest that pulp- ectomy was not completed to the dentino- cementa1 junction in this case. Although in- adequate pulpectomy was possibly achieved, and the level of obturation was situated a t a distance far removed from the dentino-cementa1 junction a repair of some magnitude was effected with lacunar cementum. It appears

Fig. 10.-Pulp canal morphology of two maxil- lary second premolars revealed by injection with radiopaque elastomer. The canal division in the middle third of the root, rejoining towards the apex, is commonly seen. Note the apical

bifurcation of the canal in both specimens.

that the level a t which the canal should be obturated, at least following vital extirpation, may not be as critical as some clinicians maintain.

Sekine, Machida, and Imanishim) have pro- vided a valuable contribution to our knowledge concerning the process of healing following vital extirpation a t various levels of the root canal. Twentyfive complete pulpectomies were performed with broaches in one series, and in another, 25 partial pulpectomies were effected a t mid-root level by specially designed long- shanked burs. Each wound surface was covered with New Paste which contained a base of calcium hydroxide, and various anti- bacterial substances, and this was left in place for periods extending from 48 hours to 2 years.

Sommer. R. F., Ostrander, F. D., and Crowley, M. C.-Clinical endodontics; a manual of scientific endodontics. Phil. and London, W. B. Saunders Co., 1966 (p. 21).

Sekine, N., Machida, Y., and Imanishi, T.-A clinico-uathoiogical study on D U ~ D extiruation and pulp amputation in-the middle portion of the root canal. Bull. Tokyo D. Col., 4 : 2, 103- 135 (Dec.) 1963.

The results show that if a large amount of vital pulp tissue is left in the canal apical to the root filling, newly formed odontoblasts complete a bridge of dentine in the region of the root filling. This occurrence is to be expected when the well-known results of vital pulpotomy using calcium hydroxide as a cap- ping agent are considered. When the pulp is extirpated in the region of the apical foramen, there is an ingrowth of granulation tissue, and sealing of the apex is effected with cellular cementum.

It may be deduced from the above investiga- tions that repair by dentine bridging will in all probability occur if pulp extirpation is carried to a level short of the dentino-cementa1 junc- tion, provided that the residue of pulp tissue retains a peripheral layer of odontoblasts with maintenance of vitality by vascular connection with the apical tissues. The possibility of leaving behind vital pulp remnants after instrumentation, is to be expected most frequently when dealing with the complex canals found in adult posterior teeth in which canal subdivisions and curvatures a re often difacult or impossible to negotiate with hand instruments. I t is suggested by Kronfeld(u) that where the canal undergoes a relatively sharp curvature or constriction, there is a tendency for the pulp to separate at that point during extirpation procedures.

If pulpecomy is incomplete but the vascular connections with the periapical tissues are traumatically severed, then i t is probable that repair will be by ingrowth of tissue from the apex with concomitant phagocytosis of pulp residue. Even if the root filling is terminated a t a substantial distance from the apex, i t is unlikely that odontoblasts will differentiate from the granulation tissue growing into the blood clot from the periodontal membrane, and healing in a successful case will be by fibrous tissue in which cementum tends to form and seal the apex.

These healing processes would account for the clinical success so frequently achieved fol- lowing the root filling of posterior teeth where complex pulp morphology prevents a thorough canal debridement and preparation.

Coolidge in 1933C6) stated: “The treatment of root canals must be considered no different from treating an open wound in any other part of the body.”. Kronfeldn*) pointed out the im- portance of maintaining pulp vitality at the level of severance and emphasized the great

I74 Australian Dental Journal, June, I966

the possibility of causing damage to mechani- cally inaccessible pulp tissue.

The principle of sealing such canals shortly after instrumentation has been completed, avoiding repeated drug applications which may attenuate the natural reparative process, must be supported. An interim period of a few days should be allowed prior to canal obtura- tion, so that any periapical edema may subside.

Definitive comment concerning the treatment of teeth which possess complicated canal morphology, and containing vital pulp tissue which is superficially infected must await the outcome of more productive research work. The principle of aseptic operation under rubber dam is basic(20) and it may indeed prove effec- tive to treat a carious exposure by initial sterilization or cautery of the pulp chamber contents. Extirpation of the pulp and the mechanical preparation of accessible canals in the accepted fashion, while the field is flooded with a non-irritant antiseptic, should be carried out wherever possible.

Summary In the light of histologic observations carried

out on a n upper second premolar tooth, which had been successfully treated by root canal therapy procedures, the nature of the healing process following vital pulpectomy and root filling has been discussed. It would appear from a close inspection of the pre-extraction and post-extraction roentgenogram, and from histological analysis that this treatment was poorly performed according to the standards accepted in modern endodontic practice. While it is considered ideal to prepare and root fill a canal to the cemento-dentinal junction, i t is probable, in the absence of infection, that healing can occur when the root filling does not reach the level of pulp amputation. The repair tissue in such cases is secondary cementum, and the occlusion of lateral canals by similar tissue may be expected.

harm which may accrue from the use of highly toxic drugs. Asepsis has taken the place of anti- sepsis, and no one would apply a n irritant drug to living tissue which is expected to heal.

Cahn(*e) has more recently elaborated on this view, pointing out the benefit of early rest to any wound area, and advocates root filling a canal as soon as possible after pulpectomy.

Fish‘’?) draws attention to the fact that in the region of a carious exposure, chronic or subacute abscess formation frequently occurs, b u t the deeper region of the pulp, though hyper- remic is sterile- €pe reasons that if the pulp can be removed without injecting bacteria from the purface into the apical region, healing of the apical tissues will necessarily follow im- mediate root canal filling. I n this contention he is supported by Kronfeld.(‘B) The technique suggested by Fish involves the application of dam, and the preliminary removal of the infected coronal pulp by cautery.

Fish recommends the use of an electric pulp desiccator to effect pulp coagulation to the apicll region by cautery and immediate robt filling following instrumentation. He furthef states: “Provided no organisms have been carried into the apical canals of the root, i t makes little difference whether the canals are weH filled or not, provided they are com- pletely and effectively sealed off from the r n ~ U t h . ’ ~ ~ ~ ) While he stresses that a short root fllling h less than ideal, he considers “It is more itnportant to fill the cervical two thirds of the canal effectively and expeditiously than to risk’ carrying infection into the apices by prolodged instrumentation.”‘lO)

The use of an electric cautery to clear the root canals in teeth possessing complex root canal morphology may be criticized regarding

(mCahn. L. R.-The pathology and treatment of periapical disease. Brit. D. J., 111: 2, 57-61 (July 1 8 ) 1961.

(l7) Fish, E. W.-Surgical pathology of the mouth. London, Sir Isaac Pitman & Sons Ltd., 1952 (pp 249-282)

(18) Fish ‘ M. w.--I’bid. (p. 280). ( p ) Fish: E: W.-Ibld. (p. 281).

(20) Barker, B. C. TV.--Asepsis in root (anal therapy. Austral. D. J., i : 4 , 324-330 (Aug.) 1962.