ENDODONTICS Editor: Samuel Seltzer

Passive step-back technique

Mahmoud Torabinejad, DMD, MSD, Loma Linda, Calif. DEPARTMENT OF ENDODONTICS, LOMA LINDA UNIVERSITY, SCHOOL OF DENTISTRY

Several techniques have been advocated to clean and shape pathologically involved root canal systems. Studies

have shown that most of these techniques transport the original shape of the apical portion of the root canals. This article

describes a step-by-step method, Passive Step Back Technique, which uses a combination of hand and rotary instruments to

clean and shape root canals. (ORAL WRG ORAL MD ORAL PATHOL 1994;77:3!#8-401)

The complexity and outcome of root canal therapy generally depend on diagnostic, procedural, and prog- nostic difficulties encountered during treatment. Pro- cedural difficulties can be related to obtaining ade- quate and profound anesthesia, effective rubber dam application, tooth type, physiologic age of the tooth, degree of pulpal calcification, and root canal anato- my.’ Histologic studies have shown that root canal systems can be very complex, and their shapes can be altered by age, operative procedures, decay, trauma, periodontal disease and procedures, and passive tooth eruption. 2-4 As the degree of complexity, that is, loca- tion, size, curvature, and abnormal internal anatomy, increases, the chance for complete removal of root canal contents decreases, and the incidence of proce- dural accidents, such as ledging, canal transportation, and perforation of the root canal system, increases.5 In addition, as the diameter of intracanal instruments increases, their flexibility decreases. The limited flex- ibility and increased rigidity of large reamers and files, the enlargement of small canals to large sizes, and the improper use of intracanal instruments are the main causes of procedural accidents during clean- ing and shaping of the root canal systems.’ Several . chemomechanical techmques have been proposed to clean and shape the root canal system.6-9 These tech- niques advocate the use of irrigation solutions during cleaning and shaping of the root canal system and varying degrees of coronal flaring at different stages of root canal preparation. The amount of irrigation

Copyright @ 1994 by Mosby-Year Book, Inc. 0030-4220/94/$3.00 -I- 0 7/15/529&i

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solution and the proximity of the irrigation needle to the apex play a significant role in removing root canal debris.1°-15

Coronal flaring of root canals before apical prepa- ration allows easier access of irrigation solution to the apical region of the root canal system and removal of more debris.16 In addition to providing better irriga- tion and debris removal, cervical flaring provides straighter line access to the apical foramen and reduces the chances for procedural accidents such as debris packing, ledging, straightening of the apical portion of the canal, perforation, and instrument fracture.t6, l7

The step-back technique, which was first described by Clem in 1969,1s is one of the most popular techniques for cleaning and shaping root canals. In this technique the canal is prepared to a small size at the apical region, and sequentially larger files are used to decreasing lengths. This results in a canal prepara- tion with a small apical segment and a progressively larger apicocoronal taper. Crown-down, step-down, and balanced forces techniques are essentially modi- fications of the step-back technique, a flaring prepa- ration with small apical opening and a coronal enlargement. One of the major advantages of a flared technique is the fact that it allows effective removal of canal contents and cleaner canals.” However, studies have shown that most hand instrumentation techniques transport the original shape of the apical portion of the root canals.6* 20-23 This might be largely a result of the enlargement of apical region before adequate coronal flaring or of taking small curved ca- nals to file sizes larger than no. 25 to 30. The passive

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Fig. 1. Flaring access cavity walls adjacent to the canal orifices with a thin tapered diamond bur provide direct line access to the orifice of canals.

Fig. 3. Passive step-back use of files from no. 15 to no. 40 creates a mildly flared canal and removes coronal debris.

Fig. 2. Inadequate access and coronal flare can cause procedural accidents such as ledging and perforation.

step-back technique uses a combination of hand instruments (files) and rotary instruments (Gates- Glidden drills and Peeso reamers) to achieve adequate coronal flare before apical root canal preparation.

INSTRUMENTS No. 10 to 40 K files (Union Broach, Emigsville,

Pa.), No. 2 to 3 Gates-Glidden drills (Union Broach), No. 2 to 3 Peeso engine reamers (Union Broach), and high-speed round and diamond burs (Brasseler, Sa- vannah, Ga.) were used.

CLINICAL TECHNIQUES AND RATIONALE Step one: Access preparation. A proper and ade-

quate access cavity is the key to any effective clean- ing and shaping procedure.24 A properly prepared

Fig. 4. Proper use of Gates-Glidden drills provides easy access to the apical foramen.

access should unroof the pulp chamber completely and provide the operator with a straight line to the orifice(s) of the root canal(s). With the use of an ap- propriate size round bur in a high-speed handpiece, the pulp chamber should be penetrated and unroofed completely. After locating the canal orifice with an endodontic explorer, flare the access cavity wall(s) adjacent to the orifice with a thin, tapered diamond bur (Fig. 1). Failure to create tapered wall access cavities impedes the operator’s vision and his or her control over hand- or engine-driven instruments (Fig. 2). After selection of a stable reference point and with the diagnostic film used as a guide, place a no. 15 file in the canal to establish an estimated working length of root canal either with a radiograph or an electronic apex locator.

40 Torabinejad ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY April 1994

Fig. 5. Confirmation of root canal working length with a patency file (no. 15) prevents overextension of files after initial flaring of the root canal.

Fig. 7. Apical root canal preparation with sequential use of progressively larger files from the working length.

Fig. 6. Proper use of Peeso reamers in the coronal portion (2 to 3 mm) of the root canal can provide straighter access for final apical preparation.

Step two: Passive step-back hand instrumentation. After depositing a 2.25% solution of sodium hy- pochlorite in the pulp chamber, place a no. 10 or 15 K-type file to the radiographic apex with a very light one eighth to one quarter turn and push-pull strokes to establish apical patency with little or no resistance. With the same motion, no. 20, 25, 30, 35, and 40 K-type files are carried into the canal as far as they can be inserted passively. After passage of these files, the canal is irrigated with sodium hypochlorite solu- tion. The passive step-back hand instrumentation provides the operator with an initial insight into the root canal anatomy, removes debris and minor ob- structions from the root canal, and creates a mildly flared canal for insertion of Gates-Glidden drills (Fig. 3).

Step three: Passive use of Gates-Glidden drills. A no. 2 Gates-Glidden drill is inserted into the mildly flared canal to a point where it binds slightly. It is then pulled back about 1 to 1.5 mm and the slow-speed handpiece is activated. With an up and down motion and slight pressure, the desired canal wall(s) is planed and flared. A similar technique is used to plane and flare the higher portions of the coronal region of the root canal with the use of a no. 3 Gates-Glidden reamer. A no. 4 Gates-Glidden reamer can be used in large canals. The root canals should be irrigated with 2.25% sodium hypochlorite solution between uses of the engine-driven instruments. Proper execution of this phase of treatment provides the operator with straighter line access to the apical region of the canal than an unflared canal (Fig. 4).

Step four: Confirmation of working length. Be- cause flaring and removal of curvatures reduce the working length, it is essential to confirm the correct working length before apical preparation. After plac- ing a no. 15 (Patency file) or 20 file in the canal, the working length should be confirmed either with a ra- diograph or an electronic apex locator (Fig. 5). Stab- holz et a1.25 have shown that preflaring of root canals makes detection of apical constriction easier and more predictable.

Step Jive: Passive use of Gates-Glidden drills or Peeso reamers. A no. 2 Gates-Glidden drill or a Peeso reamer is placed into the canal to a point where it binds slightly. It is then pulled back about 1 to 1.5 mm and the slow-speed handpiece is activated. With a gentle up and down motion, the coronal portion of the canal is shaped and flared further. With the use of a similar technique and at a lower depth, the higher portion of the canal (coronal 2 to 3 mm) can be flared

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with a no. 3 Gates-Glidden reamer or a Peeso reamer (Fig. 6). Application of Peeso reamers before coronal flaring with hand instruments and Gates-Glidden drills and forceful application of engine-driven in- struments can result in excessive hard tissue removal and iatrogenic perforations.

Step six: Apical preparation. After flaring and de- termining the correct working length, a no. 20 file should penetrate the full working length without any resistance. The root canal is then prepared with a se- quential use of progressively larger instruments placed successively further from the working length (Fig. 7). Narrow or curved root canals should not be enlarged beyond the size of no. 25 or 30 files. Enlargement of small root canals with large files results in adaption of root canals to rigid endodontic instruments and pro- duction of apical transportation, ledging, and perfo- ration.

The passive step-back technique provides an un- forceful and gradual enlargement of root canals in an apicalcoronal direction. In addition, it is applicable in every canal type, easy to master, reduces procedural accidents, and is convenient for the operator as well as the patient.

REFERENCES

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2. Hess W. The anatomy of the root canals of the teeth of the permanent dentition: Part 1. New York: Winwood and Co., 1925:1-47.

3. Davis SR, Brayton SM, Goldman M. The morphology of the prepared root canal. ORAL SURG ORAL MED ORAL PATHOL 1972;34:642-8.

4. Luks S, Bolantin L. The myth of standardized root canal in- struments. NY State Dent J 1973;43:109-11.

5. Torabinejad M. Procedural accidents. In: Walton RE, Torab- inejad M. Principles and practice of endodontics. Philadelphia: W.B. Saunders, 1989:300-4.

6. Weine FS, Kelly RF, Lio PJ. The effect of preparation proce- dures on original canal shape and on apical foramen shape. J Endodon 1975;1:255-62.

7. Abou-Rass M, Frank A, Glick D. The anticurvature filing method to prepare the curved root canal. J Am Dent Assoc 1981;101:792-6.

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Reprint requests: Mahmoud Torabinejad, DMD, MSD Department of Endodontics Loma Linda University School of Dentistry Loma Linda, CA 92350