A Comparative Evaluation of Root Fracture Resistance of Three Techniques of Retrieval of Separated Endodontic Instruments from Curved Root Canals 
(An In Vitro Study)

doi:10.21203/rs.3.pex-2312/v1

Method Article

A Comparative Evaluation of Root Fracture Resistance of Three Techniques of Retrieval of Separated Endodontic Instruments from Curved Root Canals
(An In Vitro Study)

https://doi.org/10.21203/rs.3.pex-2312/v1

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The separation of instruments before completion of root canal preparation especially in infected teeth was found to be associated with a high probability of failure of endodontic treatment. Retrieval of these separated instruments can aid in completion of endodontic treatment successfully. To our knowledge there are no studies on the effect of using different retrieval methods on root fracture resistance, retrieval time and success. Thus, the aim of this study is to assess and evaluate the efficiency of three different retrieval methods: ultrasonics, LeoPen loop system and XP-endo shaper in resistance to root fracture of extracted human lower molars with moderately curved roots after retrieval, success of retrieval method and retrieval time of separated instruments.

Root canal preparation is an important step of root canal treatment, it includes proper cleaning and shaping of the canals ⁽¹⁾. Root canal mechanical preparation can be carried out using manual or rotary instruments. The introduction of nickel-titanium (NiTi) instruments made a revolution in the scope of endodontics. The super elasticity and shape memory properties make nickel-titanium instruments more flexible than stainless steel instruments ^(2,3).Nickel-titanium instruments provide more centered preparation inside canals so, less procedural errors ⁽⁴⁾. There have been many innovations in the manufacturing procedures and the design features of the instruments to improve their efficiency in root canal preparation ⁽⁵⁾. Despite these advantages, separation of rotary NiTi instruments during use has become a real concern among dental practitioners especially endodontists. Separation of NiTi instruments happens without any prior warning to the operator. Rotary instruments separate due to torsional or flexural cyclic fatigue failure ⁽⁶⁾. Many factors are associated with these two modes of failure; operator experience, instrument design, manufacturing procedure, rotational speed and torque, repeated use of instrument and canal anatomy and curvature ^(6-9).

The incidence of separated rotary NiTi instrument, based on recent investigations, has been shown to be in the range of 0.4% to 4.6% ^(10-12). The separation of instruments before completion of root canal preparation especially in infected teeth was found to be associated with a high probability of failure ⁽¹³⁾. Management of separated instruments can be achieved either by orthograde or surgical approach. There are three orthograde approaches, the first is to remove the instrument, the second is to bypass it and the third is to prepare and obturate the root canal to the separated fragment ⁽¹⁴⁾. The removal approach can sometimes be difficult and its success depends on many factors including the length and position of the separated fragment, the diameter and degree of curvature of the root canal and the engagement of the instrument fragment into the root canal wall ⁽¹⁵⁾.

Rotary NiTi instruments were found to be more difficult to remove compared to hand instruments as they tend to fracture at a shorter length, more apically especially at the curve of narrow canals and usually engage in the canal wall due to their rotation motion. The position of the separated instrument has an impact on the approach to manage the case. Instruments separated at the straight portion of the canal can usually be retrieved, while those separated partially around canal curvature with their coronal aspect accessible may or may not be possible to retrieve. If the instrument was separated apical to the canal curvature and it is not applicable to be visualized or accessible, non-surgical retrieval approach can be impossible ⁽¹⁶⁾. The endodontist must balance between the advantages and disadvantages of retrieval of separated instruments as excessive root dentin removal during retrieval can reduce root strength by 30% to 40% leading to vertical root fracture ⁽¹⁷⁾.

The traditional method of retrieving separated instruments was the Masserann kit (Micro-Mega, Besancon, France) which was very effective in the retrieval of separated instrument but only in straight portion of the root canal. Attempts to use this retrieval method to remove separated instruments from middle or apical portions of root canal required removal of high amount of sound dentin leading to weakening the root structure and increasing the risk of root perforation ⁽¹⁸⁾.

Recently, the ultrasonic tips have been found to be a very effective method for retrieving separated instruments from root canal. The use of ultrasonics in combination with the dental operating microscope (DOM) has improved the efficiency and safety of retrieval of separated instruments. The vibration of the ultrasonic tip loosens the separated fragment without sacrificing a great amount of sound root dentin ⁽¹⁴⁾. Also, the time required for retrieval of separated instruments was reported to range from 3 to 40 minutes, while the Masserann method ranged from 20 minutes to many hours ⁽¹⁹⁾.

Another promising retrieval method is loop systems including: EndoCowboy (Köhrer Medical Engineering), BTR Pen (CERKAMED), Yoshi Loop (DELabs) and LeoPen (LeoDent) which can be used to engage and retrieve long loosened separated instruments through forces directed more coronally ⁽²⁰⁾. These systems do not require excessive enlargement of the root canal as the loop is usually made from nitinol which has shape memory and high elasticity ⁽²¹⁾.

Recently the XP-endo shaper (FKG) file can be used in retrieval of separated instruments based on the expandability of the file whilst being rotated clockwise inside the canal, facilitating an unscrewing movement of the fractured instrument in the coronal direction⁽²⁰⁾.

Rationale for conducting the research

The efficiency and the time required for retrieval of separated instruments using ultrasonics with DOM was studied by Ward et al.,⁽¹⁴⁾ and Nagai et al., ⁽¹⁹⁾. Also, the efficiency of the loop systems as BTR Pen was reported by Dulundu et al., ⁽²¹⁾. However, to our knowledge there are no studies on the effect of using different retrieval methods on root fracture resistance, retrieval time and success. Thus, the aim of this study is to assess and evaluate the efficiency of three different retrieval methods: ultrasonics, LeoPen loop system and XP-endo shaper in resistance to root fracture of extracted human lower molars with moderately curved roots after retrieval, success of retrieval method and retrieval time of separated instruments.

1- extracted human mandibular molars collected from surgery department in Faculty of Dentistry, Cairo University, Egypt.

2-5.25% sodium hypochlorite solution (Clorox, Tenth of Ramadan City, Egypt)

3-dental operating microscope

4- high speed diamond round bur and Endo-Z bur (Dentsply, Maillefer, Ballaigues, Switzerland).

5- size 10 K-file (Mani Inc., Kiyohara, Tochigi, Japan).

6- size 15 K-file (Mani Inc., Kiyohara, Tochigi, Japan).

7- Engine-driven Plex-V rotary NiTi files (Orodeka LTD, Jining City – Shandong Province, China)

8- acrylic resin molds

9- size 25, taper 0.6 (Mpro) rotary file (China)

10- Gates-Glidden drill (Mani Inc., Kiyohara, Tochigi, Japan)

11- Ultrasonic tip Ed4 (Guilin Woodpecker Medical Instrument Co., Ltd, China)

12- XP-endo shaper (FKG, Switzerland)

13- LeoPen (LeoDent, Egypt)

14- Universal testing machine

15- Stopwatch

Preparation of samples

· Access cavities is prepared under the dental operating microscope, using high speed round bur and Endo-Z bur

· Patency is established in the canals using a size 10 K-file (Mani Inc., Kiyohara, Tochigi, Japan).

· Glide path is formed using #15 K-file (Mani Inc., Kiyohara, Tochigi, Japan).

· Engine-driven Plex-V rotary NiTi files (Orodeka LTD, Jining City – Shandong Province, China) are used to prepare the canals.

Placement of samples in the resin molds
The teeth are mounted in acrylic resin molds with standardized vertical and horizontal positions.

- In each root, the apical 4mm of size 25, taper 0.6 (Mpro) file is fractured in the middle third of the root canal.

Fracturing the instruments

- Instruments are notched using a low-speed 0.3-mm-thick diamond disk.

- The notched instruments are introduced into canals at 250 rpm to fracture

Staging platform

- creating of a staging platform using a modified Gates-Glidden drill (Mani Inc., Kiyohara, Tochigi, Japan)

- then ultrasonic tips are used to trephine dentin around coronal tip of separated instrument.

Ultrasonic retrieval

Ultrasonic tip Ed4 (Guilin Woodpecker Medical Instrument Co., Ltd, China). The ultrasonic tip is activated

XP-Shaper retrieval

XP-endo shaper (FKG, Switzerland) is inserted in Endo motor and rotation motion is applied

LeoPen retrieval

LeoPen (LeoDent, Egypt) loop device is used to engage the head of the fractured file.

Resistance to root fracture
Crowns and distal roots of teeth are removed using high speed diamond stone.

- Teeth are tested using the Universal Testing Machine

Retrieval time and success

- Retrieval is considered successful when the whole fractured NiTi instrument is removed from the root canal

- Time is recorded from the beginning of staging platform preparation until the instrument is either successfully removed or until failure

problem 1: fracture of tooth during preparation

reason 1: dehydration of tooth

solution1: storage of teeth in solution until preparation and using irrigating solution during preparation

preparation of teeth may take about 15 mins

retrieval time from beginning of staging platform is 45 mins

according to literature ultrasonics and loop systems have proven to be successful in separated instruments retrieval, limited studies on XP-shaper files used in retrieval so results of this method isn't expected

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Associate Professor Dr. Nehal Nabil (Main supervisor)

Dr Nermine Hassan (Co-supervisor)

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A Comparative Evaluation of Root Fracture Resistance of Three Techniques of Retrieval of Separated Endodontic Instruments from Curved Root Canals
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A Comparative Evaluation of Root Fracture Resistance of Three Techniques of Retrieval of Separated Endodontic Instruments from Curved Root Canals (An In Vitro Study)

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Abstract

Introduction

Reagents and Equipment

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Troubleshooting

Time Taken

Anticipated Results

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Associated Publications

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A Comparative Evaluation of Root Fracture Resistance of Three Techniques of Retrieval of Separated Endodontic Instruments from Curved Root Canals
(An In Vitro Study)