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ABSTRACT

Nickel-titanium rotary files have become a standard tool to shape root canals, but they tend to unexpectedly break because of cyclic fatigue. For this reason, important changes have been combined to make NiTi instruments safer. Today new single-use systems have been introduced for complete root canal shaping with only one file. This case report present a difficult lower first molar with four narrow canals treated with OneShape instrument.

KEYWORDS

NiTi instruments, Rotary files, Single-use instruments.

A Complex Case Treated with OneShape Single-Use NiTi Instrument

Case Report

INTRODUCTION

The Nickel-titanium (NiTi) instruments are commonly used for endodontic practice today.1 They offer many advantages over conventional stainless steel files, because they are more flexible and have increased cutting efficiency, so they improve root canal preparation.2,3 The super elasticity of NiTi rotary files allows to produce the desirable tapered root canal form with a reduced tendency to canal transportation.2-4 Despite these advantages, NiTi instruments appear to have a high risk of separation.5,6 Fracture may be caused by normal cyclic stresses caused by bending (fatigue failure) and to shear stresses exceeding the elastic limit of the alloy caused by torque (ductile failure).7-10 Both the clinician and the instrumentation technique used play a significant role in preventing large shear stresses caused by torque. These stresses dramatically increase when an excessive pressure is applied on the handpiece,11 when the contact area between the canal walls and the cutting edge of the instrument widens,12,13 or when the canal cross-section is smaller than the non active or non cutting tip of the instrument.12,13 The latter case can cause what has been described as taper lock, a phenomenon usually occurring with regularly tapered instruments.14 This risk may be reduced by performing coronal enlargement15,16 and by creating a manual and/or mechanical glide path before using NiTi rotary instrumentation.17-19

Very little can be done to prevent or reduce these stresses.20 Therefore, it has been recently proposed that the single-file shaping technique may simplify instrumentation protocols, drastically reduce stresses and avoid the risk of cross-contamination.20 However, to shape root canals with only one file, the instrument will be subject to a great deal of stresses, both torsional and

cyclic fatigue.21 So, this instrument is not used for further canals and not requires thermal sterilization in autoclave, so it will be not exposed to other stresses.

OneShape (Micro Mega, Besancon, France) represent a new concept of single-file instrumentation developed for a full clockwise rotation. The OneShape system consists of only one instrument, which has a tip size of 25 and a constant taper of 0.06, and is characterized by different cross-sectional designs over the entire length of the working part. This instrument is made of a conventional austenite 55-NiTi alloy. In the tip region, the cross section represents three cutting edges while in the middle of the cross-sectional design progressively changes from a three-cutting-edge design to two cutting edges. At the shank, the S-shaped cross section shows two cutting edges. Moreover, OneShape instruments have variable pitch length along the working part. OneShape instruments are used in a continuous clockwise rotation. As recommended by the manufacturer, the rotational speed for OneShape is 350-450 rpm and the torque setting should be 4 Ncm.

CASE REPORT

A 38-year-old female was treated for pain referred to lower right mandibulary region. She was having pain especially when chewing tough foods, with high sensitivity to cold.

Radiograph showed a big carious process on tooth 46, the first lower right molar (fig 1). Teeth 45 and 47 were non-vital.

Single-visit endodontic treatment of tooth 46 was the elected therapy.

Alberto DagnaAssistant Professor in Endodontics, Department of Clinical-Surgical, Diagnostic & Pediatric Sciences, Section of Dentistry

University of Pavia, Italy – alberto.dagna@unipv.it

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TREATMENT

The first step of treatment was caries removal and complete old restoration removal, in order to build up the mesial and distal walls with composite resin and access to the pulp chamber with a high-speed diamond bur (fig 2).

With the aid of an ultrasonic tip the access cavity was prepared, cleaned and refined (fig 3). Four orifices were visualized and detected. A #10 stainless steel K File was used to scout the anatomy of 4 root canals (fig 4). In distal root 2 separated and tight canals were scouted. All orifices were enlarged with Endoflare (Micro Mega, Besancon, France) (fig 5). Endoflare is a short 12% NiTi instrument with a total length of 15mm, a working length of 10mm and a tip size of 25. It’s developed for widening of coronal third of canal and for removing coronal constrictions. It was used with a speed of 400 rpm and inserted into the canal for a depth of 3mm using a gentle back and forth motion. It produced many dentinal debris (fig 6), so an abundant irrigation with 17% EDTA and 5% NaOCl was required (fig 7). Figure 8 shows both mesial orifices and figure 9 shows both distal orifices after shaping with Endoflare.

After orifices enlargement, canal scouting and preliminary working length (WL) detemination, mechanical preflaring was performed. Gfile G1 (Micro Mega, Besancon, France) is a 3% NiTi instrument with a tip size of 12 (fig 10). It was introduced into each canal, progressing with a slow pecking movement without any apical pressure until the WL was reached (fig 11). Frequent irrigation with 17% EDTA was necessary. One G1 file was discarted because of its deformation after removal from the disto-vestibular canal (fig 12). A total of two G1 Gfiles was used for mechanical preflaring.

(Fig. 1) Pre-operative radiograph

(Fig. 2) Access cavity after caries removal and composite resin build-up of mesial and distal walls

(Fig. 3) Ultrasonic finishing of access cavity. A: introduction of ultrasonic tip. B-C: removal of roof. D: aspect of access cavity at the end of finishing, 4 orifices are visible

A B

C D

(Fig. 4) Canal scouting with a #10 stainless steel K File. A: mesio-lingual canal. B: mesio-vestibular canal. C: disto-vestibular canal. D: disto-lingual canal)

A B

C D

(Fig. 5) Endoflare is introduced into the orifices 3mm below the pulp chamber floor

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EDTA (fig 15) and placed down to the 2/3 of the WL using an in and out movement without pressure and performing an upward circumferential filing movement in order to pre-enlarge the canal. So it was frequently withdrawn from each root canal and cleansed, alternating

After the glyde path was established and the WL was determined (fig 13), root canals were ready for shaping with OneShape (fig 14). OneShape was introduced in each canal with the chamber completely filled with 17%

(Fig. 6) Orifices enlargement with Endoflare. A: mesio lingual canal. B: spect of mesial orifices after shaping with Endoflare. C: disto-lingual orifice. D: aspect of disto-lingual orifice after shaping with Endoflare

A B

C D

(Fig. 7) Irrigation after orifice enlargement

(Fig. 8) Particular of mesial orifices after enlargement with Endoflare

(Fig. 9) Particular of distal orifices after enlargement with Endoflare

(Fig. 10) Gfile G1 ready to use

(Fig. 11) Gfile G1 is working into the root canals

(Fig. 12) Deformed Gfile G1 after removal from the disto-vestibular canal

(Fig. 13) Electronical WL determination with Root ZX (Morita Corporation, Japan)

(Fig. 14) OneShape Ready to use

(Fig. 15) Canal shaping with OneShape in presence of 17% EDTA

(Fig. 16) Final rinse and sonic activation of 5% NaOCl

(Fig. 17) Obturation after backfilling. A: particular of distal canals. B: particular of mesial canals)

A B

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(Fig. 18) Post-operative radiograph

copius irrigation with 17% EDTA and 5% NaOCl. In this way OneShape was reintroduced and withdrawn until the WL was reached. At each removal of OneShape from root canal patency with a #10 K File was checked.

At the end of root canal shaping the apical gauging was verified with a #25 stainless steel K File. Each canal was rinsed with abundant 5% NaOCl (fig 16), activated with a sonic tip (SF 65, Komet Dental Gebr. Brasseler GmbH & Co. KG, Lemgo, Germany).

Canal obturation was performed with warm guttapercha continuous wave technique (fig 17). Apical third of each canal was sealed using #25 .06 master cone (MM-GP Point, Micro Mega, Besancon, France) compacted with System B size M plugger tip (Sybron Endo, Orange CA, USA). Back filling of each canal was obtained with Obtura III (Spartan Endodontics, Algonquin IL, USA). Final radiographic control confirmed the complete obturation of four root canals (fig 18).

DISCUSSION

The new single-use systems have been introduced to shape root canals with only one file. OneShape are made by the conventional austenite 55-NiTi alloy, but the design is really innovative. Thanks to its different cross-sectional designs over the entire length of the working part OneShape shows a high flexibility. It’s safe, because the risk of fracture /separation is very low: for each treatment a new sterile instrument is used and the fatigue along the length of the file is minimal, thanks to its geometry. After each treatment the instrument is discarted and not sterilised in autoclave. It simplify the treatment, because its protocol requires only one instrument for canal shaping. Asymmetrical section of OneShape allows for curved canal negotiation with an instrumental and easy dynamic. Its non-working (safety) tip ensures an effective apical progression avoiding obstructions which are often preceded by instrument separation.

Asymmetrical section also guarantees an increased space for debris removal. It’s economic, because it’s developed for continuous rotation and it work with each conventional endodontic engines, so it doesn’t require a specific motor.

CONCLUSION

OneShape single-use NiTi file is a simply and safe instrument. Respecting the protocol it allows to treat difficult cases with good results and low risk of separation into the root canal.

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