The Double-Flared Technique An Alternative For Biomechanical Preparation [PDF]

Citation preview

0099-2399/83/0902-0076/$02.00/0 JOURNAL OF ENDODONTICS Copyright @ 1983 by the American Association of Endodontists



Printed in the U.S.A. MOL. 9, NO. 2, FEBRUARY 1983



The Double-flared Technique: An Alternative for Biomechanical Preparation Luiz Roberto G. Fava



Whenever endodontic treatment is performed, it must be kept in mind that three main objectives must be fulfilled (1): (a) to remove a n d / o r eliminate from the root canal all of its contents, organic or otherwise, that may lead to the growth of microorganisms or the breakdown of toxic products into the periapical tissues; (b) to remove the irregularities of the canal walls as well as obstructions such as calcifications, filling materials, etc.; and (c) to prepare the root canal not only for its disinfection but also to develop a shape that permits the simplest and most effective threedimensional filling. It, therefore, becomes obvious that biomechanical preparation must be performed as well as possible before the root canal is filled. This fact has always been recognized as an essential step in the modern practice of endodontics, and, in the opinion of many authors (2-4), this is the most important phase of treatment. Regarding these objectives, Schilder (3) states that five biological objectives increase endodontic success and decrease patient discomfort during treatment: (a) confine instrumentation to the root canals; (b) beware of forcing necrotic material beyond the foramen during canal preparation; (c) remove all tissue debris from the root canal system; (d) complete cleaning and shaping of single canals in one visit; and (e) create sufficient space during canal enlargement for intracanal medication and for potential exudate reception. Although we are aware of these objectives, success is not achieved in all cases. Many articles have been written dealing with the success of root canal therapy and have reported a variable success rate from 78 to 93% (5-14). Poor root canal filling and inadequate biomechanical preparation are two causes of endodontic failures. Ingle (15) reports that " 5 8 . 6 5 % of 104 endodontic failures were related to the poorly filled root canal . . . . Thus, it would appear that poor root canal obturation is by far the greatest cause of endodontic failure, with incorrect canal instrumentation, the next most important aspect." Until some years ago, these objectives were not achieved at all. Root canal enlargement performed in a conventional way, using endodontic



instruments in a sequence of increased diameters to the full length of the root canal, often led the professional to produce iatrogenic errors rendering the treatment a failure or leading to tooth extraction. The concept at that time was to adapt the root canal to the endodontic instrument. With the introduction of the standardized system proposed by Ingle and Levine (16), in 1958, some improvement was achieved, and in 1961 Ingle (15) stated: "there should be fewer broken instruments and root perforations, which account for about 10 per cent of our endodontic failures." However, let us turn to the realities of pulpal anatomy. Luks and Bolatin (17) affirm: " a histological examination of a root canal demonstrates that we are dealing not with a canal but rather with a root canal system complete with tortuous turns, apical foramina and, at times, with accessory canals. This 'real' picture is far different from the image evoked by the words root canal. Furthermore, this root canal system whose shape has been altered by age, operative procedures, decay and trauma is unique for each tooth and is different from tooth to tooth. A standardized root canal is non-existent." Naidorf (18) states: "the standardization system of instrumentation has become an area of controversy. However, in the practical use of any instrument, the manner in which they are used is much more important than such things as their slight difference in taper." Fava (19) in 1980 reviewed standardization in endodontics. After the analysis of results obtained by different researchers, the author concluded that endodontic instruments and filling materials are still manufactured in disagreement with the actual specifications. The coming of the flared preparation proposed by Weine (4) in 1972, and the results of many research studies regarding its use, demonstrates that all objectives of biomechanical preparation are more nearly being achieved, showing that this technique really has many advantages over the conventional technique of preparing the root canal. It may be affirmed currently that the philosophy of biomechanical preparation has been changed. While some years ago we adapted the 76



Double-flared Technique



Vol. 9, No. 2, February 1983



root canal to the endodontic instruments, today we adapt our endodontic instruments to the root canal system. One of the advantages afforded by the use of the flared technique is the great taper in the cervical and middle thirds of the root because instruments with great diameters act much more on the dentinal walls of these areas. Thus, the removal of canal contents is more effective and the root canal is better cleansed. Studies by Coffae and Brilliant (20), Klayman and Brilliant (21), Walton (22), and Bolanos and Jensen (23) have demonstrated this statement. Considering all of the advantages of the flared technique, it has become the elected one in cases of necrotic or gangrenous teeth. Shovelton (24) has shown that bacterial invasion does not occur in all areas of the root canal, but "there is a marked tendency for bacteria to appear in smaller numbers in the root canal itself as the apical foramen was approached. In a number of teeth the canal was seen to contain many organisms at higher levels, then for a short distance organisms and pus, and at the apex no organisms." Similar findings were also detected in lateral canals. During root canal enlargement, pulp debris, dentin chips, microorganisms, and the irrigant solution may be forced into the periapical tissues. This extruded material may be responsible for periapical inflammation or an exacerbation of a chronic process with subsequent postoperative pain. This occurs because the endodontic instrument acts like a piston in a cylinder and such "piston in cylinder" effect develops a hydrostatic pressure, which may force material through the apical foramen. The extrusion of this material beyond the apex has been demonstrated by Chapman C25) and Visse and Brilliant (26). Chapman (25) has shown that both reaming and filing are capable of transmitting contaminated material through the apical foramen, but this occurs less frequently when a file is used. Hession (27) has also observed this effect, particularly when RC Prep is used, and more so when the size of the instrument approximates that of the root canal. He postulates that the early flaring of canal walls would lessen the potential for a positive apically directed hydrostatic pressure by the establishment of an adequate coronal escape way. Considering all of these observations, we tested a modification of the flared preparation in cases of teeth with necrotic or gangrenous pulps, which we decided to call the double-flared technique. DESCRIPTION



OF THE TECHNIQUE



1. Isolate the tooth with the rubber dam and make the access opening in the usual manner. 2. Irrigate the pulp chamber with sodium hypochlo-



77



rite. This irrigant will be used during all biomechanical preparation. 3. Based in the initial diagnostic X-ray film and the average length of the tooth, take a small instrument (#1 5 or 20) and introduce it progressively and carefully into the root canal. The aim of this procedure is to allow the irrigant solution to perform a quicker, more uniform, and better contact with the canal contents, thereby dislodging and neutralizing them. Two aspects are important in this phase. The first is how many milimeters the instrument should be introduced into the root canal. For a better orientation, Pucci and Reig's findings (28) about the length of the different teeth, as well as those of De Deus (29), are reproduced (Table 1). The second aspect is that the instrument must be provided with a " s t o p " to limit its penetration. In this initial phase, the stop should be set at the minimum measurement. With gentle movements introduce the instrument until the stop reaches the coronal reference point (incisal edge or a cusp tip). 4. When the stop reaches the coronal reference point, take an X-ray and estimate the root canal length (Fig. 1 ). 5. Remove the instrument and irrigate. This irrigation removes all dislodged and neutralized contents. As an example, let us imagine that the endodontic treatment will be performed in an upper central incisor, on which the estimated length measurement was 22 mm. If we consider that its crown measures about 10 mm, its root will be 12 mm in length. Therefore, the measurement to the end of the middle third will be 18 mm (10 mm of the crown + 8 mm of the root). TABLE 1. Length of different teeth



Crown length (average value in ram) Upper teeth Central incisor Lateral incisor Canine First premolar Second premolar First molar Second molar Third molar Lower teeth Central incisor Lateral incisor Canine First premolar Second premolar First molar Second molar Third molar



Tooth length Minimum



MaxiAverage mum



10,90 10,20 10,50 8,00 7,30 7,30 7,55 7,40



18,00 18,50 20,00 17,00 17,00 18,00 17,50 14,00



28,50 29,50 33,00 25,50 26,00 25,50 27,00 22,00



21,80 23,00 26,40 21,50 21,60 21,30 21,70 17,10



8,90 9,77 11,00 8,60 8,10 7,90 7,85 7,45



16,50 17,00 19,50 17,00 17,50 19,00 19,00 16,OO



27,50 29,00 32,00 26,50 27,50 27,00 26,00 20,00



20,00 22,60 25,00 21,90 22,30 21,90 22,40 18,50



78



Fava



Journal of Endodontics



FIG 1. Left, initial X-ray (step 3); right, estimating the working length (step 4).



Select an instrument of large diameter (#80, for example) with a stop fitted at 14 mm, equivalent to the measurement to the cervical third. Operate it loosely on the dentinal walls by filing action. It must not bind in the walls of the root canal to prevent the creation of hydrostatic pressure. Irrigate. 6. Take the sequentially smaller instrument (#70) measured at 15 mm and use it in the same way as in step 5. Irrigate. 7. Follow this procedure, decreasing the diameter of the instrument at the same time that its length is increased by 1 mm, until reaching 18 mm (end of the middle third), always using abundant irrigation between the passage from one instrument to the next. It must always be remembered that the instrument must never bind in the dentinal walls. Example of the sequence: file # 8 0 14 mm file # 7 0 15 mm file # 6 0 16 mm file # 5 5 17 mm file # 5 0 18 mm This sequence is justified based on the earlier mentioned observations by Hession (27) about the early flaring of the canal. Furthermore, if we consider Shovelton's findings (24), we conclude that microorganisms are better removed because they are located in greater quantities at cervical and middle thirds of the root. 8. With cervical and middle thirds free of their contents, and with the contents of the apical third adequately neutralized by the irrigant solution, take a small instrument ( # 1 5 or 20) with its stop at 22 mm and repeat step 3. If necessary, take another X-ray to confirm the canal length (Fig. 2). Remove the instrument and irrigate the root canal.



FtG 2. Confirming the working length, if necessary (step 8).



9. Continue in the sequence of step 7: file # 4 5 19 mm file #/40 20 mm file #/35 21 mm file # 3 0 22 mm With this procedure, we reach the full length of the canal with its contents already neutralized, dislodged, and removed, and clean and divergent canal walls with a decreased probability of forcing material beyond the foramen (Fig. 3). 10. After this, we follow with the flared preparation proposed by WeJne (4), in the following sequence: file # 3 0 22 mm file # 3 5 22 mm



Double-flared Technique



Vol. 9, No. 2, February 1983 file # 4 0



22 mm



file file file file file file



21 22 20 22 19 22



#45 #-40 #50 #40 #55 #40



mm mm mm mm mm mm



and so on. 11. Final irrigation and aspiration. 12. Drying with paper points. I N D I C A T I O N S FOR T H E D O U B L E - F L A R E D TECHNIQUE



Because of its modus operandi, this technique is indicated in cases of straight root canals or in the straight portions of curved canals of mature teeth. It is not indicated in cases of calcified canals, young permanent teeth, or teeth with an open apex because they have thin dentinal walls and great pulp volume.



conventional one, including better cleaning of the canal ( 2 0 - 2 3 ) and improved quality of the root canal filling when compared with the conventional technique (30). When the canals are prepared with the flared technique and obturated by the lateral condensation method, the induced stresses during this condensation are more evenly distributed (31). Furthermore, the flared technique maintains the root canal shape and produces neither the hourglass appearance nor the apical zip (32). Finally, with the use of instruments of large diameter far from the apical area, the potential for creation of iatrogenic errors is greatly decreased. The action of these instruments in the middle and cervical areas facilitates the irrigation procedure and permits easier confection and placement of posts (33).



POSTOPERATIVE EVALUATION The use of the double-flared preparation shows that in cases where it is indicated, the pulp canal enlargement may be completed in one visit. If the instruments with fitted stops are used in a diligent way and the radiographical control is carefully followed, posttreatment flare-ups decrease to a minimal level. Our first in vivo evaluations confirm this finding. In 30 devitalized teeth with or without periapical radiolucencies treated by this technique, there were no flare-ups, indicating that good results may be obtained. FINAL CONSIDERATIONS



A review of the literature regarding the flared technique shows that it has many advantages over the



79



FiG 3. Radiographicalaspect after step 9.



FIG 4. Final aspect, after step 12.



80



Journal of Endodontics



Fava



In addition to all the preceding advantages of the flared technique, the double-flared preparation adds two more: the potential of forcing material through the foramen is greatly diminished because of the early flaring; and the microorganisms and toxic material are removed in the initial phase, decreasing the probability of carrying them to the apex in order to produce an exacerbation. When the apex is reached, this material has already been removed. Although this technique has limitations, it may be an alternative in appropriate cases. SUMMARY I present an alternative to the flared preparation, the double-flared technique, for biomechanical preparation of root canals. After some general considerations, the technique is described along with its indications, an in vivo postoperative evaluation, and a discussion of its advantages over the standardized technique. I believe that where indicated, good results may be obtained with this technique. Dr. Fava is an endodontist in private practice. Address reprint requests to him at Rue da Consolacao, 3527, 0t 416 Sac Paulo, Brazil.



References 1. Fava LRG, Caputo CA. Novas tecnicas de prepare biomecanico: prepare biomecanico escalonado e prepare biomecanico incremental. Parte I. ARS Curandi Odontol 1979;5:4-14. 2. Heuer MA. The biomechanics of endodontic therapy. Dent Clin North Am 1963; 341-59. 3. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974; 18:269-96. 4. Weine FS. Endedontic therapy. St Louis: CV Mosby, 1972. 5. Bender IB, Seltzer S, Soltanoff W. Endodontic success: a reappraisal of criteria. Part I. Oral Surg 1966;22:780-9. 6. Bender IB, Seltzer S, Soltanoff W. Endodontic success: a reappraisal of criteria. Part II. Oral Surg 1966;22:790-802. 7. Buchbinder M. A statistical study of root canal therapy. Dent Cosmos 1936;78:20-6. 8. Strindberg LZ. The dependence of the results of pulp therapy on certain factors. Acta odontol Scand 1956;14:suppl. 21.



9. Grahnen H, Hansson L. Prognosis of pulp and root canal therapy: a clinical and radiographic follow-up examination. Odontol Revy 1961 ;12:14665. 10. Seltzer S, Bender IB, Turkenkopf S. Factors affecting successful repair after root canal therapy. J Am Dent Assoc 1963;67:651-62. 11. Grossman LI, Shepard LI, Pearson LA. Roentgenologie and clinical evaluation of endodonticatly treated teeth, Oral Surg 1974; 17:368-74. 12. Seltzer S, Bender IB, Smith J, Freedman J, Nazimov H. Endodontic failures: an analysis based on clinical, roentgenographic and histological findings. Part I. Oral Surg 1967;23:500-16. 13. Seltzer S, Bender IB, Smith J, Freedman J, Nazimov H. Endodontic failures; an analysis based on clinical, roentgenographic and histological findings. Part ]l. Oral Surg 1967;23:517-30. 14. Harry FJ, Perkins BJ, Wengraf AM. Success rate in root canal therapy; a retrospective study of conventional cases. Br Dent J 197D; 128:6570. 15. Ingle JI, A standardized endodontic technique utilizing newly designed instruments and materials. Oral Surg 1961 ;14:83-91. 16. Ingle JI, Levine M. The need for uniformity of endodc,ntic instruments, equipment and filling materials. In: International conference on endodontics. 2. Transactions. Philadelphia, 1958. 17_ Luks S, Bolantin L. The myth of standardized root canal instruments. NY J Dent 1973;43:109-11. 18. Naidorf IJ. Controversies in endodontics. Oral Health 1978;68:21-4. 19. Fava LRG. Estandardizac~o em endodontia: ticc~o ou realidade? ARS Curandi Odontol 1980;6:31-43. 20. Coffae EP, Brilliant JD. The effect of serial preparation on tissue removal in the root canals of extracted mandibular human molars. J Endodon 1975;1:211-4. 21. Klayman SM, Brilliant JD. A comparison of the efficacy of serial preparation versus Giromatic preparation. J Endodon 1 975;1:334-7. 22. Walton RE. Histologic evaluation of different methods of enlarging the pulp canal space. J Endodon 1976;2:304-11. 23. Bolanos OR, Jensen JR. Scanning electron microscope comparison of the efficacy of various methods of root canal preparation. J Endodon 1980;6:815-22. 24. Shovelton DS. The presence and distribution of micro-organisms within non-vital teeth. Br Dent J 1964;117:101-7. 25. Chapman CE. The correlation between apical infection and instrumentation in endodontics. J Br Endodon Soc 1971 ;5:76-8Q 26. Visse JEV, Brilliant JD. Effect of irrigation on the production of extruded material at the root apex during instrumentation. J Endoden 1975;1:243-6. 27. Hession RW. Endodontic morphology. III. Canal preparation. Oral Surg 1977;44:775-85. 28. Pucci FM, Reig R. Conductos radiculares, vol 1. Montevideo: A. Barreiro y Ramos, 1944. 29. De Deus, QD. Endodontia. 3rd ed. Rio de Janeiro: Medsi, 1982_ 30. Allison DA, Weber CR, Walton RE. The influence of the method of canal preparation on the quality of apical and coronal ebturation. J Endqdon 1979;5:298-204. 31. Harvey TE, White JT, Loeb IJ. Lateral condensation stress in root canals. J Endodon t 961 ;7:151-5. 32. Weine FS, Kelly RF, Lie PJ. The effect of preparation procedures on original canal shape and on apical foremen shape. J Endodon 1975;1:25562. 33_ Fava LRG. Prepare biomecanico de canais alresiados e/ou curves_ Sue problematica em endodontia. ARS Curandi Odontol 19B0;6:10-32.