Indian Journal of Dental Research

: 2008  |  Volume : 19  |  Issue : 3  |  Page : 267--271

Curved canals: Ancestral files revisited

Nidhi Jain1, Suneja Tushar2,  
1 Senior Resident, Safdarjung Hospital, New Delhi, India
2 Formerly Junior Resident, Safdarjung Hospital, New Delhi, India

Correspondence Address:
Nidhi Jain
Senior Resident, Safdarjung Hospital, New Delhi


The aim of this article is to provide an insight into different techniques of cleaning and shaping of curved root canals with hand instruments. Although a plethora of root canal instruments like ProFile, ProTaper, LightSpeed etc dominate the current scenario, the inexpensive conventional root canal hand files such as K-files and flexible files can be used to get optimum results when handled meticulously. Special emphasis has been put on the modifications in biomechanical canal preparation in a variety of curved canal cases. This article compiles a series of clinical cases of root canals with curvatures in the middle and apical third and with S-shaped curvatures that were successfully completed by employing only conventional root canal hand instruments.

How to cite this article:
Jain N, Tushar S. Curved canals: Ancestral files revisited.Indian J Dent Res 2008;19:267-271

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Jain N, Tushar S. Curved canals: Ancestral files revisited. Indian J Dent Res [serial online] 2008 [cited 2021 Oct 27 ];19:267-271
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Two important objectives to be kept in mind during the instrumentation of a root canal are the development of a continuously tapered form and the maintenance of the original shape and position of the apical foramen. However, the presence of curvatures may pose difficulty in root canal instrumentation. The final results of the instrumentation of curved root canals may be influenced by several factors such as the flexibility and diameter of the endodontic instruments, instrumentation techniques, location of the foraminal opening, and the hardness of dentin. [1] Ledge formation, blockages, perforations and apical transportation are undesirable accidents that have been observed to occur after the preparation of curved root canals. [2],[3],[4] Therefore, several instrumentation techniques have been introduced to deal with the complex problems of preparing curved root canals. Traditionally in these situations, various hand files were employed in different instrumentation techniques. But in the modern era of endodontics, the role of these conventional hand files has been limited to only being scouting files. Expensive rotary Ni-Ti file systems have taken over the endodontic arena from conventional hand-held files.

Apart form the cost of rotary instruments, there are other deterrent factors like inexperience with rotary instruments and improper handling that prevent a general dentist from using them. In such situations, hand instruments can come to the rescue, but it should be borne in mind that routine canal preparation techniques may not give successful results in variously curved root canals. This article will try to revive the role of hand files in successfully completing instrumentation in various cases with curvatures ranging from a simple curvature in the apical third to maximum curvature encountered in the whole canal system.

 Case reports

Case 1: Gradual curvature of the mesial canals in the apical third

A 20 year-old male patient presented with a history of acute pain in the lower right posterior region since two days. Clinical examination showed a large carious lesion on the right mandibular second molar, which was correlated with the radiographic finding of pulp exposure and widening of the periodontal ligament [Figure 1]. The X-rays revealed curved mesial canals with a relatively straight distal canal; medical history was noncontributory.

Treatment procedure

Endodontic therapy was initiated under local anesthesia and straight-line access was gained in all the three canals (buccal and lingual in mesial and distal).Pulp chamber was irrigated with sodium hypochlorite (NaOCl).Initial scouting of all the root canals was done with K-file no. 10, one by one, and the patency of root canals was established. This negotiating file reproduced the same curvature as that of the curved root canal.File no. 10 was clipped by 1 mm and precurved in the same direction and to the same extent as the scouting file - this gave us file no. 12. [5] File no. 12 so obtained was placed in the canal till the apical third.Special emphasis was placed on frequent irrigation of the root canal to avoid blockage by dentinal debris and to remove the necrotic tissue. NaOCl and saline were used for irrigation.Simultaneously, reverse flaring was initiated in the coronal third with K-file no. 40. It was placed in the orifice position for a slight reaming of the coronal portion.Recapitulation was done with file no. 12 and coronal flaring was done in crown-down fashion with K-files no. 35 and 30.Gate-glidden (GG) drills were placed sequentially in a step-back fashion (i.e., no. 1, 2 and 3) to allow easy placement of instruments and to improve the tactile sensation of the instrument placed in the canal. Coronal flaring till (GG) no. 3 was sufficient to provide unrestricted placement of the instrument.Recapitulation with file no. 12 was done to check patency and to remove the dentinal debris thus created.File no. 12 was placed and the pulp chamber was flooded with Ethylene Diamine Tetraacetic Acid (EDTA) that provided the necessary lubricating action.A working-length radiograph was taken at this point with file no. 10 placed in the root canal to avoid over-instrumentation.Sequential filing of the curved canal was done with K-files no. 15, 17, 20, 22 and 25 until full working length was achieved. Files were selected to take advantage of the flexibility of the files up to no. 25.K-File no. 30 was placed 1 mm short of the working length.To confirm the deep shape and completeness of uniform preparation, files no. 30, 35, 40 and 45 etc were used passively in step-back fashion until 3-4 mm short of the orifice.During the whole preparation, root canals were repeatedly irrigated with irrigant and frequent recapitulation was done.A final working-length radiograph was taken.Canals were flushed with saline and dried with paper points.As the distal canal is wide and relatively straight, it was conventionally prepared by using the step-back preparation technique.The lateral condensation method of obturation was preferred [Figure 2].

Case 2: Acute curvature in the apical third

A 25 year-old male patient presented with a history of occasional dull pain in the left lower posterior region. Clinically, temporary restoration was present on the left lower first molar. Intra Oral Periapical (IOPA) X-ray showed an acute canal curvature in the apical third in the distal root of the left mandibular first molar tooth. Radiography also showed incomplete root canal treatment [Figure 3]. Endodontic therapy for the same was undertaken with flexible files to negotiate the acute curvature using a crown-down technique. Files were precurved when used in the apical third. Initial scouting was done with file no. 10. Two or three passes of the file enabled it to move freely in the canal. The coronal and middle third of the canal were easily prepared with an H-file using the crown-down technique. The apical third was prepared using file no. 25 which could successfully be curved up to the apical constriction. Copious irrigation with NaOCl and saline was carried out to remove the necrotic tissue. Root canal obturation was successfully accomplished using the lateral condensation technique [Figure 4]. A postobturation X ray taken after three months showed reduction of periapical radiolucency.

Case 3: Curvature throughout the canal

A 22 year-old female patient presented with a large carious exposure of the lower left first molar tooth. A periapical lesion could be seen on the IOPA X-ray [Figure 5]. NaOCl and normal saline were used to clean the canal. The distal canal was easily negotiated and shaped with conventional hand files. The access opening was modified for the mesial canal and taken more mesially to accommodate the coronal curvature of the canal. Initial scouting was done with file no. 10 and the working length was measured. Mesial canals were prepared using reverse flare technique with Gates-Glidden drills to obtain straight-line access to the root canal. Apical and middle curvature was negotiated with flexible files. The working length was remeasured. EDTA was used as a lubricating agent to allow the smooth movement of instruments in the canal. [Figure 6] shows satisfactory obturation of the whole canal system.

Case 4: Dilacerated root canal

This was a case of a lower third molar with dilacerated roots. The patient was a 40 year-old female with missing first and second molars. The third molar was needed for abutment preparation, hence, intentional root canal treatment was performed in this tooth [Figure 7]. Endodontic therapy was performed. Root canal access was modified to gain straight-line access up to the apical third. Canals were scouted with file no. 10 and 1 mm was clipped from file no. 10 to make it file no. 12. Sequential filing of the root canal was carried out with copious irrigation and recapitulation. Precautions were taken to avoid ledge preparation. Coronal flaring was performed with a Gates-Glidden (GG) drill. Nickel-titanium hand files were used for negotiation of curved canals. Apical preparation was done using files up to file no. 25. Obturation was performed with the help of nickel-titanium spreaders [Figure 8].

Case 5: S-shaped root canal

This case with an S-shaped curvature in the mesial root of the first molar posed great difficulties while cleaning and shaping [Figure 9].

The access opening was modified as the first step to successfully accomplish the root canal treatment. To negotiate the acute curvature in the middle third of the root, the access opening was inclined more mesially.Shaping the orifice with GG drills reduced coronal interference in a step-back fashion.A precurved K-file no. 10 was used to scout the canal. The tentative length of the canal was noted from the X-ray and file no. 10 was again inserted into the canal. Two passes of the same file in the canal were successful to facilitate free gliding of the file and decrease the binding of the file in the middle third. More emphasis was put on eliminating any coronal binding of the file up to the middle third.Trimming off a 0.5 mm segment from file no. 10 and increasing its width by 0.01 mm made it file no. 11. Rasping and reaming actions were avoided. Recapitulation with file no. 10 was done and the working length was measured.Sequential filing was done with 12, 15, 17, 20, 22 and 25 files. [6] The various files were created by trimming the preceding file in this sequence by 1 mm. All files were placed in a curved fashion and rotation was avoided inside the canal.A working-length X-ray was taken with taken with a no. 20 K-file.Obturation was done using lateral condensation with the help of Ni-Ti spreaders [Figure 10].


There is no doubt that the preparation of curved canals presents one of the greatest challenges in endodontics and is fraught with difficulties. Only the curvatures in the mesio-distal plane can be seen on a radiograph, yet it is well known that curvatures in the bucco-lingual plane are also evident in many teeth. [7] Failure of root canal treatment in curved canals is mainly due to procedural errors such as ledges, fractured instruments, canal blockage, zip and elbow creation.

The cases presented above were treated completely with hand-held instruments. The canal preparations were described in detail to highlight how the use of hand files can be modified to get excellent results. Some important points regarding the preparation of variously curved canals that may help the operator are: [8],[9],[10],[11],[12]

The size and shape of the access cavity will be dictated by the degree of curvature of the canals. This procedural nuance is quite critical as it simplifies all subsequent instrumentation procedures and eliminates many cleaning and shaping frustrations.The significance of retaining original canal shape should always be given due consideration. The original shape includes includes the apical foramen, the sealing of which is a prime objective of endodontic therapy. [13],[14],[15] . In curved canals, a mild variance in the center portions of the root may lead to severe alteration at the tip. A lost or relocated foramen represents one of the greatest causes of endodontic failure. [4],[12],[16] Foramen should be kept as small as possible because overenlarging the foramen contributes to a number of iatrogenic mishaps. [17],[18] Small canals should be negotiated initially with a size no. 10 K-file called a scouting file, [19] which fits quite snugly at the apex. [20] Always precurve the instrument before placing in a curved canal to retain the original shape of the canal and prevent transportation to the apical side of the apical foramen.Avoid overuse of reaming action.Avoid excessive use of chelating agent.Preenlarging [21] or reverse flaring and crown-down preparations [22],[23] should be routinely employed to improve tactile control when directing smaller, precurved negotiating files so as to promote removal of dentinal debris, thus enhancing the cleaning of the canal.Incremental instrumentation should be done as it verifies the deep cleaning and shaping of the root canal - a process called tuning and gauging.Use of flexible hand files should be done because they can flex over the curvature and prevent lateral perforation.

It is important to understand the advantages of hand files over rotary files before we decide to use them for a case:

They afford more control to the operatorTactile perception is betterFlutes can be clipped or the flutes can be dulled according to the needs of canal preparation as for narrow canals and curved canalsFiles can be precurved according to the curvature as noted on the radiographLess expensiveThe hand-held technique is easy to master

Although rotary files are more efficient and aggressive than hand-held files and ensure that taper of the canal can be easily obtained, they can be expensive and require experience in handling them. Hence, it is wise to utilize conventional files for successful results.

The underlining fact remains that a thorough knowledge of instrumentation is very important when using any canal preparation technique. The author suggests that it will be good idea to compare similar cases treated with rotary instruments with those treated with hand files, to test the efficiency of both techniques.


The author firmly believes that expensive rotary files are not a panacea for all kinds of root canal treatments. Instead, the author wishes to emphasize that with the necessary modifications in technique, excellent results can be obtained with just hand files only, even in cases with dilacerated canals. Hence, it is technique that assumes importance over instruments.[24]


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