A novel endodontic extractor needle for separated instrument retrieval: A new patent technology

Saaid Al Shehadat; Colin Alexander Murray; Sunaina Shetty Yadadi

doi:10.4103/abhs.abhs_21_21

TECHNICAL REPORT

Year : 2022 | Volume : 1 | Issue : 2 | Page : 116-119

A novel endodontic extractor needle for separated instrument retrieval: A new patent technology

Saaid Al Shehadat, Colin Alexander Murray, Sunaina Shetty Yadadi
Department of Preventive and Restorative Dentistry, College of Dental Medicine, University of Sharjah, Sharjah, United Arab Emirates

Date of Submission	19-Dec-2021
Date of Decision	13-Mar-2022
Date of Acceptance	15-Mar-2022
Date of Web Publication	21-Apr-2022

Correspondence Address:
Saaid Al Shehadat
Department of Preventive and Restorative Dentistry, College of Dental Medicine, University of Sharjah, P.O. Box 27272, Sharjah
United Arab Emirates

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/abhs.abhs_21_21

Abstract

A novel needle that can be used to retrieve endodontic separated instruments (SIs) from the root canal of a tooth is described in this article. The needle tip is fabricated with a thermomechanically treated NiTi alloy exhibiting both shape memory and super-elasticity. The alloy demonstrates martensitic phase at certain low temperatures (25°C or less) and austenitic phase at certain slightly higher temperatures (35°C or more). These properties facilitate the needle to be straight at room temperature but incorporate a specific snakelike shape when inserted in the root canal of the tooth from which the endodontic SI is to be removed. The suggested lengths for the needles are 21, 25, and 31 mm with five different sizes of the lumina (the internal diameter is 0.25, 0.40, 0.60, 0.80, or 1 mm). The wall thickness of the needle is 0.20 for the last 3 mm of the needle then gradually increases to 0.35 for the coronal aspects. The design of this needle has the US patent application number US 2020/0129268 A1, April 30, 2020.

Keywords: Broken file, NiTi alloy, novel instrument, root canal preparation, separated instrument

How to cite this article:
Al Shehadat S, Murray CA, Yadadi SS. A novel endodontic extractor needle for separated instrument retrieval: A new patent technology. Adv Biomed Health Sci 2022;1:116-9

How to cite this URL:
Al Shehadat S, Murray CA, Yadadi SS. A novel endodontic extractor needle for separated instrument retrieval: A new patent technology. Adv Biomed Health Sci [serial online] 2022 [cited 2023 Jun 9];1:116-9. Available from: http://www.abhsjournal.net/text.asp?2022/1/2/116/343629

Background

Root canal preparation is an essential component in dental root canal treatment. It is achieved using hand and rotary shaping instruments. However, separation of instrument (SI) or instrument fracture in the root canal system may occur during endodontic root canal preparation [Figure 1]. This mishap impedes the suitable cleaning of the root canal and may lead to failure of the endodontic treatment [1,2]. The mean prevalence of retained fractured endodontic instruments ranges from 1.0% for rotary NiTi instruments to 1.6% for hand instruments, which are predominantly stainless-steel files [3].

Figure 1: Failure in endodontic treatment of a lower molar caused by poor cleaning of the apical part due to the presence of a separated (broken) file in one of the mesial root canals.

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In the majority of cases, removal of broken instruments from the root canal is difficult and often irretrievable [4]. To date, no standardized procedure for the safe removal of fractured instruments exists, although various techniques and devices have been developed. Currently, retrieval of broken endodontic instruments is attempted under operating microscope magnification using ultrasonic specific endodontic tips. In this clinical procedure, the first step involves exposing the tip of the broken endodontic instrument and loosening it by removing dentine in specific areas around the broken instrument. However, root canals are seldom straight and frequently have curvatures and twists [5], thereby making it difficult for removal of SI. Short SI in straight root canals may be removed by ultrasonic activation. However, removal of longer SI, usually more than 4.5 mm, or instruments separated in curved canals by ultrasonic activation is not recommended as it results in extra removal of dentine, which in turn weakens the tooth structure [6,7].

In these more complicated cases, the use of additional tools is needed to securely capture the tip of the SI and withdraw it out of the dental root canal. Current endodontic systems used for this purpose include Terauchi loop (Dental Engineering Laboratories, Santa Barbara, California) and instrument removal system iRS (Dentsply Tulsa Dental, Tulsa, Oklahoma), File removal system kit (Dentsply Sirona, USA), Masserann kit (Micro Méga, Besançon, France) and Ruddle Post Removal System (SybronEndo, Orange, California). However, all these previous instrument removal systems have certain clinical limitations. The Terauchi loop is rather fragile, expensive and difficult to manipulate once inserted in the root canal of the tooth [8], making it very difficult for extracting broken endodontic instruments, particularly in curved root canals.

The other mentioned systems consist of two units that require to be used together, which limits their use in the curved part of the root canal which cannot be approached under the dental microscope. Thus, there is a need for the development of an optimal instrument that can effectively extract fractured endodontic instruments from curved root canals. It is a premise of the present invention to provide a simple, flexible, super-elastic, fatigue-resistant, and cost-effective instrument that can adapt to canal irregularities to access areas beyond curvatures. Thereby, this novel technology should effectively retrieve fractures endodontic instruments from dental root canals, irrespective of the canal being straight or curved.

“EXTRACTOR NEEDLE” DESIGN

The terminal tip of the proposed extractor needle is fabricated with a shape memory alloy such as a thermomechanically treated nickel-titanium (TM-NiTi) alloy. The main feature of this alloy is that it has a crystalline structure, which shows different properties in different phases. This alloy gives the extraction needle elasticity and flexibility and enables it to adapt to canal irregularities and take the specific shape of the root canal form within which the endodontic SI is to be removed. More specifically, the TM-NiTi alloy is a martensite-austenite alloy and combines both shape memory and super-elasticity in clinical application.

The suggested austenitic finishing (AF) temperature for such alloy is in a range of 25–35°C. This makes the alloy in the martensitic phase at room temperature (25°C or less) and in the austenitic phase in the body/intracanal temperature (37°C or above). Therefore, the alloy is soft, ductile, and flexible and displays high plasticity (no shape memory) at the room temperature but becomes hard, less flexible, and super-elastic (shape memory) at intracanal temperature. The needle fabricated with the aforementioned alloy is completely straight at room temperature and can be deformed as per the curvature of the canal prior to insertion as it displays high plasticity in the martensitic phase. Once it is exposed to intracanal temperature, a phase transformation from the martensitic to the austenitic phase occurs. The shape memory property is subsequently restored, and the tip of the needle becomes curved to restore a prefabricated snakelike shape [Figure 2]. Because of this transformation in shape, the needle of the present invention effectively grips broken instruments within curved dental root canals. MaxWire alloy (FKG Dentaire SA) is an example of such an alloy and can be used to fabricate the extractor needle.

Figure 2: “Extractor needle”: (A) At room temperature, the needle is plasticiable. The needle tip is straight and can be formed in any shape. (B) At body temperature (intra-canal temperature), the tip of the needle takes a specific prefabricated snakelike shape to grip the endodontic separated instrument inside the canal.

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To make the extractor needle more clinically practical and applicable in a wide range of endodontic situations, five different sizes of internal diameters of the extracted needle are suggested 0.25, 0.40, 0.60, 0.80, and 1 mm. The suggested wall thickness of the needle is 0.20 for the last 3 mm of the needle then gradually increases to 0.35 for the coronal aspects [Figure 3]. The small thickness (0.2 mm) of the needle wall at the terminal component facilitates insertion of the needle around the exposed part of the broken instrument without the need for excessive destructive removal of radicular dentine. Conversely, the increased thickness of the needle at the other parts enhances the strength and resistance of the needle in the wider part of the canal. The suggested lengths for the needles are 21, 25, and 31 mm. Short needles are more appropriate for posterior teeth or in patients with limited mouth opening. The needles can be manufactured as either single-use disposable or autoclavable for multiuse. The disposable needles are pressed into pre-prepared plastic Leur-lock hubs and used for onetime only. The Leur-lock hubs can be prepared from autoclavable materials such as copper or stainless steel so that the needle itself can be used multiple times after sterilization.

Figure 3: Tip of the extractor needle. The thickness of the needle wall is 0.2 mm for the terminal 3 mm, then increases gradually to become 0.35 mm at the 5 mm point (5 mm far from the tip) and onward.

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HOW TO USE EXTRACTOR NEEDLES?

The extractor needle is indicated to remove parts of endodontic instruments separated within root canals during randomized controlled trial (RCT) procedures. Before placing the needle in the target root canal, the part of the canal coronal to the SI should be enlarged to at least 0.70 mm to allow for proper visualization of the SI through an operating microscope. This can be achieved using a Gates-Glidden bur (size 2) or any size 70 rotary instrument with a gentle brush motion. Subsequently, the upper end of the SI is exposed using Endodontic ultrasonic tips [Figure 4]A. At least 2–3 mm of the broken endodontic instrument should be exposed for efficient removal. If the SI does not become free and loose in the canal, further removal of dentine is indicated in the internal surface of the canal curvature.

Figure 4: (A) To retrieve a broken fragment, exposure of the coronal part of the fragment is achieved using a suitable ultrasonic tip. (B) Extractor needle is inserted around the exposed part of the fragment. (C) Extracted needle becomes in austenitic phase after injection of hot irrigant and engage the fragment. (D) Extracted needle is withdrawn out of the canals together with the fragment.

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The terminal end of the extraction needle is then inserted and placed around the exposed tip of the endodontic SI. If the SI is lodged in a curved canal, the shape of the terminal tip of the needle should be modified to follow the curvature of the canal, prior to insertion. This modification in the shape of the tip of the needle can easily be achieved, as the needle is fabricated with an alloy that exhibits high plasticity at room temperature in the martensitic phase and hence can be easily deformed to follow the root canal curvature.

Once in place [Figure 4]B, the needle is connected to a syringe and a warm irrigant such as saline or sodium hypochlorite is injected into the tooth root canal. As a result of the change in temperature, the terminal tip of the needle transforms from the martensitic to the austenitic phase. The straight shape of the needle transforms to a specific curved shape, thereby securely engaging the upper end of endodontic SI [Figure 4]C. As a result, the needle is able to tightly engage the endodontic SI. The needle along with the gripped endodontic instrument is then pulled and/or twisted out to remove both the needle and the endodontic SI from the dental root canal [Figure 4]D. For endodontic instruments, which were broken through clockwise rotation, the needle can be rotated counterclockwise prior to withdrawal or vice versa.

ADVANTAGES OF THE “EXTRACTOR NEEDLE”

The extractor needle can be used in endodontics in the context of procedures for the retrieval of SIs with a wide range advantage; the needle is simple and cost-effective, flexible, excellent resistance to cyclic fatigue, ability to retrieve broken endodontic instruments from the dental root canals, and the possibility to adapt to canal irregularities. Finally, the needle tip can be adapted to change shape to become straight at a room temperature of 25°C or less and can become curved at a body temperature of 37°C or more.

Study limitations

The extraction needles described in this article need to be fabricated and tested in vivo to confirm the proposed advantages.

Authors’ contributions

SA conceived the design of the extraction needle and applied for the US patent. CM and SY contributed to manuscript writing and reviewing. All authors reviewed and approved the final draft of the manuscript. All authors are responsible for the content and integrity of this manuscript.

Ethical statement

Not applicable.

Financial support and sponsorship

Not applicable.

Conflict of interest

There are no conflicts of interest.

Data availability statement

All data generated during this study are included in this published article.

References

1.	Lin LM, Rosenberg PA, Lin J. Do procedural errors cause endodontic treatment failure? J Am Dent Assoc 2005;136:187-93; quiz 231.
2.	Eleazer PD. Lack of corrosion of stainless steel instruments in vivo by scanning electron microscope and microprobe analysis. J Endod 1991;17: 346-9.
3.	Parashos P, Messer HH. Rotary NiTi instrument fracture and its consequences. J Endod 2006;32:1031-43.
4.	Hülsmann M. Methods for removing metal obstructions from the root canal. Endod Dent Traumatol 1993;9:223-37.
5.	Walton RE, Vertucci FJ. Internal anatomy. In: Endodontics: Principles and Practice. St Louis, MO: Saunders/Elsevier; 2009. p. 216-29.
6.	Al Shehadat S. Needle for extracting endodontic separated instruments. US Patent: US 16/169,267. 2020 Apr 30.
7.	Brito-Júnior M, Normanha JA, Camilo CC, Faria-e-Silva AL, Saquy PC, Ferraz MÃ, et al. Alternative techniques to remove fractured instrument fragments from the apical third of root canals: Report of two cases. Braz Dent J 2015;26:79-85.
8.	Pruthi PJ, Nawal RR, Talwar S, Verma M. Comparative evaluation of the effectiveness of ultrasonic tips versus the terauchi file retrieval kit for the removal of separated endodontic instruments. Restor Dent Endod 2020;45:e14.