Application of Ni-Ti rotary files for pulpectomy in ... · morphology14. All of the above ... molars (5 maxillary first molars, 9 maxillary second molars, ... the mandibular right

Original Articles

J Dent Sci 2006‧Vol 1‧No 1 10

Received: December 23, 2005 Accepted: February 18, 2006 Reprint requests to: Dr. Ming-Kuang Guo, School of Dentistry, College

of Medicine, National Taiwan University No. 1 Chang- Te Street, Taipei 100, Taiwan, ROC.

Application of Ni-Ti rotary files for pulpectomy in primary molars

CHING-I KUO 1 YIN-LIN WANG 3 HSIAO-HUA CHANG 1,3 GUAY-FEN HUANG 2,3

CHUN-PIN LIN 1,2,3 UEI-MING LI 3,4 MING-KUANG GUO 1,2,3

1 Graduate Institute of Clinical Dentistry, College of Medicine, National Taiwan University, Taipei, Taiwan, ROC. 2 School of Dentistry, College of Medicine, National Taiwan University, Taipei, Taiwan, ROC. 3 National Taiwan University Hospital, Taipei, Taiwan, ROC. 4 Cardinal Tien Hospital, Taipei, Taiwan, ROC.

Nickel-titanium (Ni-Ti) instruments are widely used in adult endodontics as an efficient technique, but are rarely used for endodontic treatment for primary molars. To explore the feasibility of using Ni-Ti rotary instruments for root canal preparation in primary molars, 51 primary molars with intact root apex in 22 children, who ranged in age from 3.2 years to 7.7 years, were treated. A modified protocol for ProTaper® Ni-Ti rotary files using only two instruments (SX and S2) was used for root canal preparation, and canals were filled with a calcium hydroxide-iodoform paste. All teeth were restored with stainless steel crowns. Postoperative radiographs were taken immediately following treatment and at 3-month intervals. Success or failure was assessed based on clinical and radiographic criteria. We found that the success rate of endodontic treatment for primary molars using Ni-Ti instrument for root canal preparation was 95% at the 12-month recall examination. We conclude that with the modified protocol, ProTaper® Ni-Ti rotary files can be safely and efficiently applied for root canal preparation in primary molars. （J Dent Sci, 1(1)：10-15, 2006）

Key words: Ni-Ti rotary files, primary molars, pulpectomy.

Pulp therapy of non-vital primary teeth has been proposed using various protocols with variable success rates1-5. However, the conventional instrumentation technique for primary teeth remains hand instrumentation which is time-consuming6. Recently, nickel-titanium (Ni-Ti) rotary instruments have been developed and are now widely used in adult endodontics as an efficient technique7. The designs and high flexibility of Ni-Ti files allow instruments to closely follow the original root canal path, especially in curved canals8-10, and procedural errors such as ledges, over-instrumentation and apical

transportation are greatly reduced as well10-12. However, the application of Ni-Ti rotary instruments is still largely limited to permanent teeth.

Barr et al. used Ni-Ti ProFile® .04 taper rotary instruments (Dentsply/Tulsa, Tulsa, OK, USA) for primary root canal preparation and concluded that the use of Ni-Ti rotary files for root canal preparation in primary teeth was cost-effective and faster, and resulted in consistently uniform and predictable fillings13. However, they reported only the results of a single incisor and a molar without follow-up results. Silva et al. reported that Ni-Ti rotary preparation for extracted teeth was faster than hand preparation but the canals were not cleaner6. A major concern of applying protocols for permanent teeth to primary molars is that they may lead to lateral perforation on the inner root surface, especially in curved molar roots. Primary tooth dentin is softer and less dense than that of the permanent tooth, and the roots are

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shorter, thinner, and more curved, often with undetectable root tip resorption. The root canal system is characterized by ribbon-shaped root morphology14. All of the above characteristics hamper the application of Ni-Ti rotary instruments in primary teeth. A practical pulpectomy technique for the primary dentition should include the following features: fast and simple procedures, with short treatment times and a minimal number of appointments; effective debridement of the root canals without weakening the tooth structure or endangering the underlying permanent teeth; few procedural complications; and maintaining tooth function until it is naturally shed.

In this study, we described procedures for root canal preparation with a modified protocol using ProTaper® Ni-Ti rotary instruments, and the outcome of using Ni-Ti rotary instruments for endodontic treatment of primary molars.

MATERIALS AND METHODS

The total study sample consisted of 51 primary molars (5 maxillary first molars, 9 maxillary second molars, 16 mandibular first molars, 21 mandibular second molars) in 22 children whose ages ranged from 3 years 2 months to 7 years 8 months (mean 4 years 8 months). The teeth selected for this study included restorable carious primary molars with acute

pulpitis, chronic pulpitis, periapical abscess, or pulp necrosis. In some cases, pulpal or periapical disease-induced cellulitis was also noted. The diagnostic criteria are listed in Table 1. However, all teeth had adequate bony support without obvious external or internal apical root resorption. Patients with a congenital heart defect or other severe systemic diseases were excluded from this study. All of the children were seen by a single operator and were treated under local anesthesia without sedation in the Pediatric Dental Clinic of the National Taiwan University Hospital. Informed consent was obtained from each patient’s parents prior to the study after explaining the clinical procedures and the risks and benefits involved, and clarifying all questions raised by the parents.

Instruments

The original protocol suggested by ProTaper® (Dentsply Maillefer, Ballaigues, Switzerland) for permanent teeth was simplified for this study. ProTaper® rotary files, SX (19 mm) and S2 (21 mm) (Figure 1), with an 18:1 Axxess Spring-Head handpiece (SybronEndo, Kerr, Montreuil, Italy) was utilized for root canal preparation. The rotational speed was 300 rpm, at the lowest torque setting. The files were frequently inspected for flute unwinding or distortion. When flute unwinding or distortion was found, the file was discarded. Otherwise, files were

Table 1. Criteria for pulpectomy of primary molars

Clinical Radiographic

Acute pulpitis

Deep carious lesion or a defective restoration. Spontaneous, continuous or intermittent severe toothache, especially at night.

Deep carious lesion or defectiverestoration.

Chronic pulpitis

Deep carious lesion or a defective restoration. Dull toothache over an extended period of time. Uncontrollable bleeding from radicular pulp stump when the treatment was planned for pulpotomy. Sometimes outgrowth from radicular pulp (pulp polyp).

Deep carious lesion or defectiverestoration. Furcation radiolucency orthickening of PDL

Periapical abscess

Deep carious lesion or defective restoration. Painful tender or painless swelling adjacent to affected tooth and possibly a sinus tract.

Furcation or periapical radiolucency

Pulp necrosis

Pain history that subsides. Large carious lesion or defective restoration. Dry pulp chamber when the treatment was planned for pulpotomy.

Same as chronic pulpitis.

Cellulitis

A painful swelling of the mouth and face (usually unilateral). Acute, rapid onset and progression sometimes accompanying fever. Swelling and tender on mucobuccal fold adjacent to the affected tooth.

Furcation or periapical radiolucency

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discarded after use in five teeth.

Clinical procedures

Under appropriate local anesthesia and rubber dam isolation, the pulpectomy procedure began with complete caries removal, a standard access opening, and removal of the coronal pulp tissue. The shelf of dentin overlying most canal orifices was reduced using a high speed round bur, until all canal orifices could be clearly identified. An approximate working length was derived by superimposing the file over a periapical radiograph, terminating approximately 1 mm above the root apex15. Before instrumentation, the pulp chamber was copiously irrigated with 2.5% sodium hypochlorite. A No.10 K-file (Dentsply Maillefer, Ballaigues, Switzerland) was first used to explore the canals and to make sure that no intra-canal calcification was found. Then, the SX file was inserted into the canal to about 3 mm beyond the root canal orifice with a slight (buccolingual) brushing motion to remove any remaining overlying dentin and to improve straight-line access. The S2

file was then inserted into the canal while rotating and taken to the working length as previously determined. If a point of resistance was encountered, no attempt was made to go beyond it, to avoid risk of instrument separation. Pulp stumps were commonly wrapped around the S2 file when it was withdrawn (which is uncommonly found with stainless steel files). Copious irrigation with 2.5% sodium hypochlorite and normal saline was used during each file change. A dry cotton pellet moistened with one-fifth-diluted Buckley’s formocresol (Nippon Shika Yakuhin KK, Shimonoseki, Japan) was placed over the root canal orifices and the tooth was then sealed with intermediate restorative material (IRM, L.D. Caulk, Dentsply International, Milford, DE, USA).

Five to 7 days after the first treatment, the cotton pellet was removed under rubber dam isolation. Following copious sodium hypochlorite and normal saline irrigation, a No. 25 or No. 30 H-file (Dentsply Maillefer, Ballaigues, Switzerland) was inserted into each canal with a brushing motion, to check the canal cleanliness. The root canals were then dried with sterile paper points, and subsequently filled by injecting a resorbable calcium hydroxide-iodoform paste (Vitapex®, Neo Dental Chemical Products, Tokyo, Japan). The tooth was then restored with a stainless steel crown.

Follow-up and evaluation

A post-treatment radiograph was taken immediately after root canal filling and at 3-month intervals (Figure 2). In each follow-up examination, both clinical symptoms and signs and radiographic appearance were evaluated, based on the criteria of Coll and Sadrian16 (Table 2). The clinical evaluation was carried out by the operator (CIK). The postoperative radiographs at the time of recalls were compared with those obtained on the day of root canal filling. The radiographic evaluations were

Figure 1. Hand files (left and right) and ProTaper Ni-Ti rotary files (center two) used for root canal preparation. From left to right: No.10 K-file, SX, S2, No. 25 H-file.

Table 2. Criteria for pulpectomy success

Clinical criteria Radiographic criteria

No pain on percussion on recall checkup No pathologic root resorption

No gingival swelling or sinus tract 6 months postoperatively A furcation radiolucency resolved 6-12 months postoperatively

No purulent exudate expressed from the gingival margin No periapical radiolucency formation postoperatively

No abnormal mobility of tooth

(Modified from Coll & Sadrian, 1996 )16

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performed by two senior pediatric dentists (YLW, HHC) who independently interpreted the radiographs. If there was a disagreement with the interpretations, the evaluators jointly reviewed the particular radiographs discussed and reached agreement on the interpretation. If disagreement still existed, treatment failure was recorded as the outcome.

RESULTS

Of the 51 treated primary molars, 21 teeth were diagnosed as having acute pulpitis, 19 as having chronic pulpitis, 6 as having periapical abscess, 4 as having pulp necrosis, and 1 as having cellulitis from the mandibular right primary first molar at the initial visit. However, 8 cases were not available for the 3-month recall and 3 cases failed to appear for the

6 to 12-month recall examinations (Table 3). The clinical and radiographic success rates were 95% at the 12-month follow-up time, and no obvious differences among different quadrants and tooth types were found. Only 4% (2/51) of the treated teeth experienced pain following the initial instrumentation, while 22% (11/51) had pain after the root canal filling. However, the pain was mild and temporary and subsided in 1~2 days. A small area of expanded radiolucency was found in the furcal area in one case at the 6-month and in another case at the 12-month recalls, which were recorded as radiographic failure, although clinically no signs or symptoms were found (Figure 2F).

The entire first visit, including local anesthesia, rubber dam placement, root canal preparations, canal medication and temporization, was generally

Figure 2. Examples of radiographic success (top row) and failure (bottom row) of pulpectomies using Ni-Ti rotary files. Success case: (A) preoperative, (B) immediately postoperative, and (C) 12-month follow-up. Failure case: (D) preoperative, (E) immediately postoperative, and (F) 12-month follow-up. Twelve-month follow up radiograph (F) showing increased area of furcation radiolucency, and partial resorption of the filling material from the canals of teeth #74 and #75.

A B C

FED

Table 3. Outcome of the treatment on different quadrants and tooth types

Tooth position 54/64 55/65 74/84 75/85 Total

No. treated initially 5 9 16 21 51

Month observed F/S F/S F/S F/S F/S

Success rate S/Total (%)

3 0/5 0/8 0/13 0/17 0/43 43/43 (100)

6 1/4 0/8 0/12 0/15 1/39 39/40 ( 98 )

9 1/4 0/8 0/12 0/15 1/39 39/40 ( 98 )

12 1/4 0/8 0/12 1/14 2/38 38/40 ( 95 )

F: Failure S: Success

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completed within 30 minutes. Of this time, canal preparation using rotary instruments only took approximately 4~5 minutes. Ledges or over- instrumentation were not encountered, and neither instrument separation nor lateral perforation occurred. With regard to canal filling quality, 28 cases (55%) were flush-filled, eight cases (16%) were under-filled, and 15 cases (29%) were over-filled. The over-filled Vitapex® was gradually resorbed within 9 months with no clinical symptoms or signs. There were no cases in which temporary restoration was found to be defective prior to crown placement.

DISCUSSION

In this study, the ProTaper Ni-Ti rotary instrument was used, which differs from the Ni-Ti files used by Barr et al.13. A study comparing torsional and bending stresses of ProTaper with ProFile showed that the ProTaper system has a lower risk of instrument separation17. The cross-section of ProTaper® Ni-Ti files has a triangular-file design rather than the traditional U-file design. A triangular- file design with a strong central core reduces friction, increases the cutting efficiency, and lowers the risk of instrument separation, which is a concern in pediatric endodontics, especially in curved root canals of primary molars.

The abrupt cervical constriction, with a shelf of dentin overlying the canal orifice and which results in an acutely curved root canal orifice in primary molars, should be removed to improve the straight-line access and reduce the risk of instrument separation. The shaft of ProTaper® files has a variable taper along its cutting surface. SX has the greatest range of taper, which not only simplifies instrumentation procedures but also replaces the use of Gates-Glidden (G-G) drills18. The gradually tapered design of the SX files can selectively remove dentin in a safe way. Using G-G drills or round burs to remove the dentin shelf, however, might cause accidental perforation of the pulpal floor or excessive removal of inner root structures, especially when treating primary molars with thinner pulpal floors. In this study, we used the SX file for early coronal enlargement and straight-line access, which made the following root canal preparation more efficient and avoided lateral perforation or over-instrumentation of the inner root structure of the middle and apical third. After

using the SX file, the S2 file could routinely be progressively taken to the full working length for final preparation of the root canals. The S2 file has a tip size of 20 and an apical taper of 4%, which approximates the root canal size of primary molars. The S1 file was not used, because it was too small to efficiently prepare the root canals of primary molars, and the F series files were not used either, because the increased taper (7%~9 %) and tip size resulted in excessive apical dentin removal in our preliminary study with extracted primary molars. However, care must be taken not to enter the primary root canal more than twice with each rotary file, for over- preparation can lead to unexpected lateral perforation, especially in severely curved canals.

The Ni-Ti rotary files now available are designed mostly for conical root canal shapes. However, most of the primary molar root canals are ribbon-shaped. It is necessary to use an additional H-file (No. 25 or No. 30) combined with copious sodium hypochlorite irrigation to remove any loose pulp tissue with a brushing motion and to ensure that all of the root canals are cleaned and ready for filling.

Recently, the number of visits needed for a pulpectomy has become an issue of discussion. Many studies tended to advocate one visit for a primary teeth pulpectomy15,16,19,20. The root canal filling material used in this study, Vitapex®, contains calcium hydroxide and iodoform which should provide adequate bacterial control in a single visit20. Nair et al. indicated that intra-canal infection can not be removed by either hand file- or Ni-Ti-prepared root canals and irrigation alone in one-visit treatment21. The two-session treatment presented in this study allowed us to enhance root canal disinfection 1253and to observe the progress of healing. However, the feasibility of a single-visit procedure using our protocol should be evaluated in a future study.

Using the modified protocol, it took only 4~5 minutes to prepare all of the root canals of a primary molar, resulting in a consistently dense fill. Although our treatment was completed in two sessions, the time spent for root canal preparation was much shorter. Overfilling the canals with a resorbable calcium hydroxide-iodoform paste is not considered a problem in primary teeth, because it will usually be resorbed within 2~9 months without damaging the underlying permanent tooth germs22-24. The partial resorption of filling material was also observed in our

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cases with no ill effect. The 12-month follow-up data of this study

indicate a success rate of 96%, which is in agreement with other studies with hand file techniques3,5,22,25. In this study, we chose only teeth with an intact root apex. With teeth already undergoing physiological root resorption (less than one third), the greater taper (8%~5.5%) and apical size of 25 of the F2 file might be a better choice than S2. A new Ni-Ti rotary instrument with a more-appropriate length, taper and tip size for the primary dentition would be advantageous. However, proper evaluation of its long-term clinical success requires further study.

ACKNOWLEDGMENTS

The authors thank Prof. Harold H. Messer of the University of Melbourne, Australia, for reviewing this manuscript and providing suggestions during its preparation.

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