4.5
Root Canal Instrumentation 1
Jianing He
Objectives
On completion of this chapter, the reader should be able to describe the goals and principles of root canal instrumentation and perform the steps of instrumentation on routine cases.
Introduction
A 35‐year‐old Asian male patient was referred by his general dentist for evaluation and possible root canal treatment due to throbbing pain in the lower right quadrant.
Chief Complaint
The patient complained of sensitivity from the lower right side, mostly to cold. This started after his dentist placed a new filling and has been getting worse. The patient has not been able to chew on the tooth.
Medical History
The patient is generally healthy, and does not take any medications. He has no known drug allergies.
Dental History
Routine dental care. Good dental hygiene. Composite on the lower right first molar (LR6) was placed about two weeks ago.
Clinical Examination
LR6 had a disto‐occlusal (DO) composite resin restoration with intact margins. The tooth had no pain to buccal palpation, but was tender to percussion with digital pressure. Endo‐Ice elicited intense pain that lingered for more than 10 seconds.
The lower right second premolar (LR5) and second molar (LR7) were intact with no caries or restorations. Both teeth responded to Endo‐Ice and had no pain to percussion or palpation.
Radiograph interpretation: the DO composite on LR6 appeared to be of good quality, but may be approximating the mesial pulp corn (Figure 4.5.1). The disto‐lingual (DL) root (radix entomolaris) appeared to be shorter than the other roots with a moderate curvature. Periapical tissue appeared normal.
Diagnosis and Treatment Planning
Diagnosis for LR6 was symptomatic irreversible pulpitis with symptomatic apical periodontitis.
Treatment options:
- No treatment.
- Non‐surgical root canal treatment was recommended for LR6 followed by a full‐coverage crown.
- Extraction and replacement.
The non‐surgical root canal treatment was planned to be completed in a single visit.
What are some of the potential difficulties of this case?
Potential difficulties related to the case included achieving profound anaesthesia due to the presence of pulpal inflammation. Another potential challenge is the management of the complex root canal anatomy (radix entomolaris).
Treatment
Local anaesthesia was achieved with inferior alveolar nerve block followed by buccal infiltration. Soft tissue and pulpal anaesthesia were confirmed by the lack of response to probing and cold test with Endo‐Ice. Upon dental dam isolation, an access cavity was created through the existing composite using a high‐speed carbide fissure bur. Once the pulp was exposed, unroofing of the pulp chamber was achieved with a safe‐ended Endo Z bur, and the access cavity was further refined with an ultrasonic instrument. Two orifices on the mesial and two orifices on the distal were located.
What are the objectives and principles of root canal instrumentation?
Root canal instrumentation combined with chemical irrigation is a critical step in non‐surgical root canal treatment to remove the aetiology of endodontic disease and provide a foundation for root canal obturation. The main goal of mechanical instrumentation is to create a space with sufficient diameter and taper to allow adequate penetration of the irrigants to remove pulp tissue and bacteria. An important consideration during instrumentation is to respect the original canal anatomy and to avoid unnecessary removal of tooth structure whenever possible.
In the last decade, vertical root fracture has been identified as a major cause of extraction for endodontically treated teeth. Preserving more root dentine, especially in the pericervical region, is critical to maintaining the mechanical strength of the roots and reduce the likelihood of root fracture. Accordingly, aggressive canal shaping with large‐tapered instruments is no longer advocated. The improved properties and design of instruments combined with active irrigation have allowed a more conservative and biologically based root canal preparation without negatively affecting the efficacy of root canal disinfection.
What are the considerations before starting instrumentation?
Appreciation of root canal anatomy along with a careful assessment of the pre‐operative radiographs is critical in accurately assessing the complexity of the root canal system. The assessment should include an estimate of the number of canals, the configuration of the canal system, the location and severity of the curvature, and any potential obstruction. This knowledge can help the clinician to select the appropriate instruments and strategy and prepare for any potential challenges encountered during treatment.
In this case of the LR6, based on data reported in the literature and the pre‐operative radiographs, it appears that there was one mesial root with two canals and two separate distal roots. The two mesial canals may or may not join apically. The DL root is also known as the radix entomolaris. The incidence of radix entomolaris varies from 0.9% to 22.4% depending on the geographical location, with a higher prevalence among patients of East Asian descent. The radix is often thinner and shorter than the other roots and has a greater curvature towards the buccal. The orifice of the radix is typically located more lingual than the mesio‐lingual (ML) canal and more mesial than the disto‐buccal (DB) canal. Due to these characteristics of the radix, more conservative preparation of this canal is recommended.
The roots appeared to be longer than average. There was a moderate curvature located in the apical third of both the mesial and distal canals.
What are the steps of instrumentation?
While there are a wide variety of instruments and techniques available to mechanically prepare the root canal systems, the following basic steps are recommended for a case with moderate difficulty such as this LR6:
- Coronal flaring: The aim of coronal flaring is to remove the coronal restrictive dentine to create a straight‐line access to the apical portion of the canal. This step allows easier placement of subsequent instruments into the canal space, and reduces stress on the instruments and the risks of instrument separation. It also allows more accurate tactile sensation and more effective canal scouting and gauging. Coronal flaring can be achieved using Gates Glidden drills or orifice shapers, which are nickel titanium (NiTi) rotary instruments with shorter cutting flutes, a smaller tip diameter and larger tapers. Examples of orifice shapers include ProTaper® SX (Dentsply Sirona, Charlotte, NC, USA), EdgeTaper™ SX (EdgeEndo, Albuquerque, NM, USA) and ESX™ 20/08 files (Brasseler USA, Savannah, GA, USA). These instruments are typically side cutting. They should not be placed deeper than one‐third of the canal length and should be used to cut on the outstroke and directed away from the furcation in multi‐rooted teeth to minimise the risk of strip perforation.
- Canal scouting: A small hand file (e.g. no. 8 or no. 10K file) should be used to confirm the patency of the canal. The tactile feedback from the file helps the clinician to get an estimate of the size and curvature of the canal space. The file should be pre‐bent in the apical 3 mm with a gentle curve to allow the file to follow and negotiate the apical curvature better (Figure 4.5.2).
- Working length (WL) determination:
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