The hunt for the hidden – Methods of locating root canals

Introduction

“Well begun is half done” quoted Aristotle, Greek philosopher, nearly 2000 years ago. This statement holds true even today- in modern day Endodontics. The importance of a well-executed access cavity preparation cannot be overemphasized. The ideal access cavity creates a smooth, straight-line path to the canal system and ultimately to the apex. When prepared correctly, the access cavity allows complete irrigation, shaping, cleaning, and quality obturation. Locating canal orifices is a crucial and critical step during access preparation.

Over the past decades, many technologies have evolved to enhance the clinical performance of dentists for start-to-finish endodontics. Many of these technological breakthroughs, however, are meaningless if a practitioner is unable to identify a specific orifice, underlying canal, or root canal system. Missed canals include pulp tissue, bacteria, and other irritants, all of which contribute to clinical complaints and endodontic lesions, ultimately leading to endodontic treatment failure.^[1]

According to an in vivo cross sectional study by Dr.Azhar Iqbal in 2014, the factors which were most responsible for endodontic failures were underfilled canals (33.3%), unfilled and missed canals (17.7%) and untreated root canals (12.2%).^[2]

In a study published in 2018-19 by Mustafa et al, inadequate root canal filling (36.8%), missed canals (14.4), over-extension root canal fillings (12.8%), perforations (9.6%), instrumentation-related (8.8%), and endodontic access preparation-related (2.4%) were found to be the most common causes of endodontic treatment failure in decreasing order of frequency.^[3]

Hence it is of paramount importance that we hunt for those hidden canals, and clean, shape and fill them for positive treatment outcomes.

Strategies for Locating Canals

The following represent, in no particular order, the important strategies for locating any given orifice, canal, and its related root canal system,

Knowledge of tooth anatomy

Radiographic diagnosis

Cone-beam computed tomography

Vision ( Magnification + Illumination)

Access cavity modification

Ultrasonics

Tests used in canal location

Knowledge of Tooth Anatomy

The clinician should be well versed with the normal as well as aberrant anatomy of individual tooth in the oral cavity, as well as racial and demographic predilection of any unique anatomical features in teeth. This basic awareness goes a long way in tracing hidden canals. The elusive root canals are easier to locate if the clinician knows what to look for and where.

As the external morphology of the tooth varies from person to person, so does the internal morphology of the crown and root. Changes in pulp cavity anatomy result from age, disease, and trauma. Although morphologic variations occur, clinical experience indicates that these changes usually follow a general pattern, and thus the study of pulp cavity morphology is a feasible undertaking.^[4]

Radiographic Diagnosis

Radiographic diagnosis has been the conventional and gold standard technique for initial diagnosis and treatment planning before starting an endodontic therapy. The most commonly used radiograph is the Intraoral Periapical Radiograph (IOPA), RVG (Radiovisiography) and the Orthopantomogram (OPG) to a lesser extent.

IOPAs and RVGs are still routinely used as one of the important investigative tools during endodontic examination and the diagnosis stage. Even though it has a few limitations, an appropriately taken and processed periapical radiograph can still provide enough information and evidence to aid in diagnosis.

A sudden shift in the radiographic density of the pulp space usually suggests the presence of an extra canal, whereas a sudden constriction or disappearance of the root canal space indicates a bi- or tri-furcation. Post-operative radiography can also reveal the presence and location of an additional root or canal. There may be a missing canal if the root filling material is not centered within the root.^[5]

Cone-Beam Computed Tomography (CBCT)

CBCT is one of the most significant advances, which has caused a radical change in diagnosis and treatment of endodontic cases in the last decade.

CBCT images always resulted in the detection of a greater number of root canals than digital radiography images, according to Matherne et al.^[6] An operating microscope and CBCT scanning were shown to be helpful for locating and identifying root canals by Baratto Filho et al, and  also that CBCT scanning can be utilized for initial identification of the internal morphology of teeth and missed canals.^[7]

In general, the use of CBCT in endodontics for root canal location should be limited to certain specific situations like-

Identification of root canal system anomalies and determination of root curvature.^[8]

During endodontic re-treatments to locate missed or extra canals for example the MB2 and the Middle Mesial.

Verifying patency of calcified canals.

Vision (Magnification + Illumination)

In the last 15 years, the introduction of Dental Operating Microscopes (DOM) into dentistry, notably in endodontics, has transformed how endodontics is practised around the world.^[9] The DOM has established the gold standard for exceptional lighting and magnification, making it easier to spot orifices. Because the light from a microscope is parallel to the line of sight, it provides two to three times the amount of light that a surgical headlamp does. Magnification can be achieved by two ways,

Dental Loupes

Dental Operating Microscope

Loupes are classified by the optical method by which they produce magnification. There are 3 types of binocular magnifying loupes:

a diopter, flat-plane, single lens loupe

a surgical telescope with a Galilean system configuration (2-lens system)

a surgical telescope equipped with a Keplerian system (prismroof design that folds the path of light).

Loupes have the disadvantage of having a practical maximum magnification of just around 4.5. Higher magnification loupes are available, but they are cumbersome and bulky, with a narrow field of view.

Apotheker introduced the DOM in 1981. The initial OM was poorly designed and difficult to use ergonomically. Gary Carr introduced an OM with Galilean optics and ergonomically designed for dentistry in 1999.^[9] It used a confocal illumination module to keep the light route in the same optical path as the visual path, which provided significantly better illumination than the prior scope's tilted light path. Many endodontic procedures require magnifications of x10 to x15, and some even require magnifications of x30.

The most obvious purpose of magnification in endodontics is to locate canals. Magnification can effectively help in managing calcified canals, missing canals, aberrant canals, dilacerated canals, and canals occluded by restorative materials.

Access Cavity Modification

The pulpal morphology of the tooth being treated, as well as the position of the canal orifices, are now mostly dictated by the Minimally Invasive Endodontics approach, which indicates that an access cavity is mostly dictated by the individual pulpal anatomy of the tooth being treated.

During root canal preparation, enough tooth structure should be removed to enable instruments to be placed freely into the orifice of every canal without interfering with overhanging walls. The access cavity outline form should be altered if additional roots and/or canals are suspected during the diagnosis stage. There are four stages to access cavity preparation.^[10]

Pre-treatment assessment and Isolation

Armamentarium and Preparation of the tooth for endodontic treatment

Removal of the roof of the pulp chamber and coronal pulp tissue

Creating straight line access

Ultrasonics

Ultrasonics (US) were first used in dentistry for cavity preparations with an abrasive slurry. ^[13] Richman was the first to propose the use of ultrasonics in endodontics in 1957. Martin and Cunningham coined the term endosonics, which they defined as an ultrasonic and synergistic root canal instrumentation and disinfection system.^[13]

Locating canals is one of the most difficult tasks in endodontics, especially when the orifice has become obstructed by secondary dentin or calcified dentin as a result of the placement of restorative materials or pulpotomies.

Ultrasonic cutting tips are a very useful tool for treating problematic molars because they allow visual access and greater control during access procedures. Access modification, identification of MB2 canals in upper molars and accessory canals in other teeth, location of calcified canals in any tooth, and elimination of pulp stones are all possible with ultrasonic tips.^[14], ^[15], ^[16] It is important to remember that secondary dentin is generally whitish or opaque, whereas the floor of the pulp chamber is darker and gray in appearance while troughing the floor for canal orifices.

During the initial phase of eliminating calcification, interferences, materials, and secondary dentin, larger tips with less diamond coated extension should be utilised since they offer the best cutting efficiency and control when operating in the pulp chamber. The next phase of locating canal orifices should be done with thinner, longer tips that allows us to operate in deeper locations while keeping the vision clear.^[17], ^[18]

Tests used in Locating Canals

Not all dental clinics have access to newer technologies or armamentarium. In such scenarios, chair-side tests and clinical tips can be of immense help in locating canal orifices. Some of them are-

Conclusion

The elusive root canal, entrenched within the confines of the pulp chamber challenges the expertise of even the best of the endodontists. Not detecting it can lead to failure of the treatment. The “pathways of the pulp” are varied; the responsibility falls on the clinician to locate them, so that they can be cleaned, shaped and filled. A combination of preoperative diagnostic tools, clinical tips and methods can aid the endodontist in the “Hunt for the hidden” root canals.

Source of Funding

None.

Conflict of Interest

The authors declare no conflict of interest