Success Rate of Ultrasonic Retrieval for Separated Instruments with Different Lengths using Modified Staging Platform: A Comparative In-Vitro Study

doi:10.21203/rs.3.pex-2604/v1

Method Article

Success Rate of Ultrasonic Retrieval for Separated Instruments with Different Lengths using Modified Staging Platform: A Comparative In-Vitro Study

https://doi.org/10.21203/rs.3.pex-2604/v1

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The present study aims to evaluate the time and success rate of ultrasonic retrieval of separated instruments of 3, 5 and 7 millimeters lengths and resistance to vertical root fracture when modified staging versus conventional staging platforms techniques are used in moderately curved mesial roots of mandibular molars.

PICO:

P: Population

Mesiobuccal canals of moderately curved mesial roots of mature mandibular molars with separated instruments.

I: Intervention

I1: Ultrasonic retrieval of 5mm separated instrument by conventional staging platform.

I2: Ultrasonic retrieval of 7mm separated instrument by conventional staging platform.

I3: Ultrasonic retrieval of 3mm separated instrument by modified staging platform.

I4: Ultrasonic retrieval of 5mm separated instrument by modified staging platform.

I5: Ultrasonic retrieval of 7mm separated instrument by modified staging platform.

C: Control

C: Ultrasonic retrieval of 3mm separated instrument by conventional staging platform.

O: Outcome

• O1: Retrieval time.

• O2: Retrieval success rate.

• O3: Vertical fracture resistance.

ultrasonic retrieval

separated instruments

staging platform

vertical root fracture resistance

Through the years, endodontics has been continuously developed in terms of new technologies, materials, procedures, and scientific advancements. Because of this, root canal therapy is quite safe and has a high success rate, even in challenging clinical scenarios. However, endodontic treatment can also be difficult, with different degrees of difficulty and risks associated with the cleaning, shaping, and filling of the root canals (Amza et al., 2020).

The introduction of nickel-titanium (NiTi) rotary instruments was a revolution in the field of endodontics (Shen et al., 2013). Now, they are commonly used for root canal treatment owing to their many advantages over conventional stainless-steel instruments, such as their greater inherent flexibility and providing more centered root canal preparations and therefore, fewer procedural errors (Nakagawa et al., 2013; Short, 1997). However, the main disadvantage associated with NiTi files is the separation of the instrument during use which can happen with no warning to the operator. There are two types of failure by which rotary instruments may separate; torsional and flexural cyclic failures (Terauchi et al., 2007). Many factors were found to be associated with these two types of failure including the rotational speed, torque, operator experience, canal curvature, instrument design and technique, manufacturing procedure, repeated use and glide path preparation (Pruett et al., 1997; Bryant et al., 2002; Gambarini, 2000; Patiño et al., 2005; Al-Fouzan, 2003).

The incidence of rotary NiTi files fracture, based on only a small number of recent investigations, was found to be around 0.4% to 4.6 % (Wolcott et al., 2006; Iqbal et al., 2006a). More instruments are fractured in molars, especially mandibular molars, than in anterior teeth (Tzanetakis et al., 2008). This may be advocated for root canal accessibility, diameter and curvature (Cujé et al., 2010; Nevares et al., 2012; Shen et al., 2004).

To manage a case of a broken instrument, endodontists use either orthograde or surgical approaches. There are three orthograde approaches; instrument retrieval, bypass or preparing and obturating the root canal to the level of fractured fragment (Suter et al., 2005). The removal approach can be difficult in some cases and its success depends on several factors including the length and position of the fractured fragment, the diameter and degree of curvature of the root canal and the impaction of the instrument fragment into the canal wall (Ruddle et al., 2004). It is of great importance for the endodontist to balance the advantages and disadvantages of a fractured instrument retrieval because excessive removal of root dentin, which can happen during retrieval, causes a reduction of root strength by 30% to 40% and predisposes the tooth to vertical root fracture (Souter and Messer, 2005).

Rotary NiTi instruments were found to be more difficult to remove when compared to hand instruments because they tend to fracture at shorter lengths, at or around the curve of the canal and due to their rotation, they are usually impacted in the canal walls. (Souter and Messer, 2005). Moreover, the ultrasonic removal of NiTi-separated instruments is subjected to secondary fractures more than the stainless-steel hand instruments (Terauchi et al., 2013)

For many years, the traditional method of retrieving fractured instruments was the Masserann kit (Micro-Mega, Besancon, France) which was very effective in the retrieval of instruments fractured in the straight part of root canals. However, it cannot be used when the instrument is fractured in the middle or apical thirds of the root or in severely curved ones (Yoldas et al., 2004; Friedman et al., 1990; Nagai et al., 1986).

Recently, using ultrasonic tips has been found to be a very effective method for removing separated instruments from root canals. The combination of the dental operating microscope (DOM) with an ultrasonic device has improved the potential and safety of removing broken instruments (Traumatol, 1999).

The procedure of ultrasonic removal of the separated instruments typically starts with establishing straight-line access to the level of the separated instrument by using modified Gates Glidden drills (GG) to enlarge the canal to a funnel-shaped coronal to the instrument fragment to the so-called “Conventional staging platform” (CSP), to allow visualization of the broken instrument with the operating microscope. The CSP is required to provide sufficient space around the instrument to allow the introduction of ultrasonics, then fine ultrasonic tips are used to trephine all around the obstruction to unlock it and free it from the canal (Ruddle et al., 2002; Souter and Messer, 2005; Garg & Grewal, 2016).

Although the previously described protocol is considered the most employed for ultrasonic removal of separated instruments, the risk of using modified Gates Glidden drills for creating a staging platform to provide straight line access to the separated instrument can be destructive to root dentin with possible occurrence of complications such as canal transportation or perforation in curved canals. (Wu et al., 2005; Iqbal et al., 2006b; Duarte et al., 2011).

Narasimhan et al., 2021, introduced a modified technique which uses a Modified Staging Platform of about 180 degrees around the instrument fragment, oriented toward the inner wall of the curvature. Allowing for minimized canal damage in situations of with instrument fragments in the middle thirds of curved canals.

Fu et al., 2019, analyzed the effects of ultrasonic removal of fractured files from the middle third of root canals using conventional staging platform on the vertical root fracture resistance. Findings showed that the ultrasonic removal of separated instruments from the middle third of canals increased the root canal volume and resulted in decreased tooth vertical fracture resistance. However no available studies analyzed the effect of modified staging platform on tooth vertical fracture resistance.

Thus, the present study aims to evaluate the time and success rate of ultrasonic retrieval of separated instruments of 3, 5 and 7 millimeters lengths and resistance to vertical root fracture when modified staging versus conventional staging platforms techniques are used in moderately curved mesial roots of mandibular molars.

· Extracted human mandibular molars (Oral Surgery Department, Faculty of Dentistry, Cairo University, Egypt)

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

· Rubber Base Putty Molds (Zhermack SpA, Badia Polesine , Italy)

· High speed Endo-Z bur (Dentsply, Maillefer, Ballaigues, Switzerland).

· Dental Operating Microscope (Zumax Medical Co., Ltd)

· K-Files sizes 10 and 15 (Mani Inc., Kiyohara, Tochigi, Japan).

· MG3 Gold Rotary NiTi files Sizes 19/.10, 2O/.04 and 25/.06 (Shenzhen Perfect Medical Instruments Co., Ltd., China)

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

· Ultrasonic tip E6 and E14D (Guilin Woodpecker Medical Instrument Co., Ltd, China)

· Universal Testing machine

1. The external root surfaces of the teeth will be cleaned with a curette to remove calculus and periodontal tissues and then will be disinfected with 5.25% sodium hypochlorite for 30 minutes, then stored in saline solution until use.

2. Each molar will be mounted in rubber base putty mold with standardized vertical and horizontal positions to facilitate handling during retrieval process. Root will be positioned upright so that its occlusal surface will be horizontal.

3. Access cavities will be prepared under the dental operating microscope, using high-speed diamond round bur and Endo-Z bur.

4. The mesiobuccal canal will be negotiated with size 10 K-file to establish apical patency and then the working length will be adjusted at 1mm shorter after the first inspection of the file at the apex.

5. Glide path will be formed using a size 15 K-file

6. The coronal 3 mm of the mesiobuccal canal will be instrumented using MG3 Gold orifice opener file (#19/.10) then enlarged to MG3 Gold rotary file (#20/.04).

7. In the mesiobuccal canal of each molar a MG3 Gold rotary file #25/.06 will be notched to half of the instrument thickness with a diamond disc at 3, 5 or 7 mm from the tip and then it will be introduced into the mesiobuccal canal at a speed of 350 rpm and a torque of 3N and rotated with pressure until separation. After that, a periapical radiograph will be to confirm the position of the separated instrument in the middle third of the canal.

8- Molars will be divided into 2 main groups according to the method of ultrasonic retrieval of the separated instrument and each main group will be further divided into 3 subgroups according to the length of the separated instrument fragment as follows:

Group 1 (G1): Ultrasonic retrieval of separated instrument using conventional staging platform.

Group one A (G1a): 3mm separated instrument

Group one B (G1b): 5mm separated instrument

Group one C (G1c): 7mm separated instrument

Group 2 (G2): Ultrasonic retrieval of separated instrument using modified staging platform.

Group two A (G2a): 3mm separated instrument

Group two B (G2b): 5mm separated instrument

Group two C (G2c): 7mm separated instrument

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Success Rate of Ultrasonic Retrieval for Separated Instruments with Different Lengths using Modified Staging Platform: A Comparative In-Vitro Study

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