Root and Root Canal Morphology Classification Systems


A thorough understanding of root and root canal morphology is essential for successful endodontic treatments, whether surgical or nonsurgical. The external and internal morphology of roots is complex and variable, and several classification systems have been proposed to describe the various types of canal configurations that are commonly encountered.

However, recent advances in nondestructive imaging techniques, such as cone-beam and micro-computed tomography, as well as magnification in clinical settings, have revealed more complex root canal anatomy that cannot be classified using existing systems. Therefore, this article aims to present a new classification system that is accurate, simple, and reliable and can be used for research, clinical practice, and training.

Clinicians aim to achieve the best treatment outcomes for endodontic cases by diagnosing the condition well. To attain the desired treatment goals, a comprehensive understanding of root canal morphology is fundamental in clinical practice. Sound knowledge of root canal morphology classification is also essential for documentation and communication among practitioners. Despite the many existing root morphology classification systems, each has its shortcomings. Some are elaborate, while others are concise but insufficient.

In addition to normal root canal morphology, practitioners should be knowledgeable about possible variations, such as a single canal bifurcating into two canals that later combine into a single canal. This article reviews various root and root canal morphology classification systems and discusses their advantages, limitations, and research implications.

Methods

Several authors have proposed different classifications for root canal configurations. Weine et al. pioneered classifying root canal morphology within a single root and introduced an additional type in 1982. In 1974, Vertucci et al. recognized more complex root canal systems and reported eight configuration types based on the pattern of division in the main root canal from the pulp chamber to the apex of the root. Sert and Bayirli added fourteen supplemental types to Vertucci's classification system in 2004.

In 2017, Ahmed et al. proposed a new classification that is simple, easy to understand, and more accurate than earlier systems. This new system uses easy codes for students and dentists based on individual codes for tooth number, number of roots, and canal configuration. Ahmed et al. further found that final-year undergraduate students in Malaysia preferred this new system in a study conducted in 2020.

Classification Systems

Weine’s Classification

Weine et al. classified root canal morphology into four types, namely type I to type IV, as described below.

Type I refers to the presence of a single main canal running from the pulp chamber to the apex of the root.

Type II includes two separate canals that converge into one canal just before reaching the apex.

Type III has two separate canals from the pulp chamber to the root apex.

Type IV is characterized by a single canal beginning from the pulp chamber and dividing into two canals near the root apex.

Vertucci classification

The morphology of root canals was categorized into eight types by Vertucci, which are explained below.

Type I involves a single main canal running from the pulp chamber to the root apex.

Type II features two canals that depart from the pulp chamber, but then converge to form a single canal that exits at the apex.

Type III has one canal leaving the pulp chamber, which then bifurcates into two smaller canals, and finally reunites to exit through one canal.

Type IV is characterized by two completely distinct canals running from the pulp chamber to the root apex.

Type V includes a single canal exiting the pulp chamber that divides into two canals with separate apical foramina.

Type VI has two canals that meet in the middle of the root, forming one canal that extends just short of the apex, bifurcating again into two canals.

Type VII features a canal that initially starts as a single canal until the middle third of the root. It divides into two separate canals, rejoins after some distance, and then divides into two again near the apex.

Type VIII is characterized by three separate canals extending from the pulp chamber near the coronal portion to the apex.

Terminology

Root canal system

The root canal system is the hollow space inside a tooth that contains pulp tissue. It is divided into two parts: the pulp chamber situated in the anatomic crown and the root canal(s) enclosed in the root(s).

Root canal orifice

The root canal orifice is the opening of the canal system located at the base of the chamber where the root canal starts. Typically, it is at or just below the cervical line.

Root canal configuration

The root canal configuration is the pathway of the root canal system beginning from the orifice and finishing at the canal's terminus (minor apical diameter).

Major apical foramen

The major apical foramen is the outlet of the root canal that opens onto the outer root surface, generally within 3 mm of the root apex.

Minor apical foramen/apical constriction

The minor apical foramen or apical constriction is the narrowest portion of the root canal, usually 0.5–1.5 mm from the major apical foramen (Vertucci 2005). It is the benchmark frequently utilized as the apical end point for canal instrumentation and filling procedures.

Classification and Tooth Number

The new classification system applies to both root and root canal configurations. It consists of codes for tooth number, number of roots, and root canal configuration.

Any available numbering systems, such as the universal numbering system, Palmer Notation Numbering System, or FDI World Dental Federation System, can indicate the tooth number (TN). For unidentifiable teeth (e.g., extracted teeth), a relevant abbreviation like UCI for maxillary central incisor can be used.

Number of Roots and their Configuration

The superscript representing the number of roots (R) is added before the tooth number (RTN). For example, 1TN means tooth "TN" has only one root. If a root is divided into two or more parts, it will be coded as two or more roots, regardless of whether in the coronal, middle or apical third.

Therefore, a bifurcation is denoted as 2TN and trifurcation as 3TN, etc. The details of roots in teeth with two or more roots are added to the right of the tooth number (RTN Rn).

A brief overview of the assigned codes for teeth with one, two, or multiple roots.

Tooth Type

Code

Single-rooted 1TNO-C-F
Double-rooted 2TN R1O-C-F R2O-C-F
Multirooted nTN R1O-C-F R2O-C-F RnO-C-F

Root Canal Configuration

The root canal configuration in each root will be designated by a superscript number(s) after the tooth number. This number(s) will indicate the continuous path of the canal system from the orifice(s) (O), through the canal (C) to the foramen (foramina) (F).

The evaluation of apical canal configurations may differ depending on the diagnostic technique used for identification – whether it is experimental or clinical, which may be subjective among different observers. A consistent and standardized view of such anatomy cannot be achieved; therefore, the apical canal configuration type should be classified based on the method and criteria used for identification.

For example, based on certain experimental measurements of canal dimensions or clinical navigability, some apical bifurcations could either be classified as an apical delta/ramification (i.e. complex ramification of branches of the root canal located near, and open on, the root apex) or a division from the main canal (type 1-2).

Single-rooted teeth

If the orifice (O), canal (C), and foramen (F) numbers are equal for a canal, a single code (1TNn) is assigned. For instance, a single-rooted maxillary right central incisor with one orifice, one canal, and one foramen is described as 1111. Similarly, a single-rooted maxillary right second premolar with two orifices, two independent canals, and two foramina is represented by 1152.

In cases where the number of O, C, and/or F is not the same, the root canal configuration will be described in more detail with a code such as 1TNO-C-F. For instance, 1341-2 describes a mandibular left first premolar with a single root initially having one orifice and one canal but then bifurcating into two separate canals and two apical foramina. 1411-2-1 represents a mandibular right central incisor with a single root initially having one orifice and one canal but then bifurcating into two separate canals and terminating in one canal.

Finally, 1441-2-3 describes a mandibular right first premolar with a single root initially having one orifice and one canal but then bifurcating into two separate canals and terminating in three canals and three apical foramina.

Double-rooted teeth

In the case of a double-rooted tooth, the code used should be 2TN R1O-C-F R2O-C-F, where R1 and R2 refer to the anatomy of the first and second roots, respectively. If the number of orifices, canals, and foramina is the same in the same root, then only one code will be used. For example, 214 B1 P1 denotes a double-rooted maxillary right first premolar, with each root (B: buccal; P: palatal) containing a single root canal from the orifice to the main foramen.

On the other hand, 224 B1-2-1-2 P1 represents a double-rooted maxillary left first premolar, where the buccal root contains a single canal that divides into two canals and then joins into one canal before dividing again into two separate canals until the canal terminus, while the palatal root encases a single root canal from the orifice to the main foramen.

The code for a double-rooted tooth that bifurcates in the middle or apical third and has a different root canal configuration apical and coronal to the level of bifurcation is 2TN O-CR1C-F R2C-F. The coronal root canal configuration is represented by 'O-C', and R1C-F R2C-F represent the continuation of the canal and number of foramina apical to the level of bifurcation in the first (R1) or second (R2) roots, respectively.

An example of this is shown in Figure 5c, which illustrates a double-rooted maxillary left central incisor with the code 221 1M1 D1, indicating that the tooth bifurcates in the apical third, and the root canal configuration differs apical and coronal to the level of bifurcation.

Multirooted teeth

To describe a multirooted tooth, the code nTN R1O-C-F R2O-C-F RnO-C-F should be used. For example, if a maxillary right first molar has three roots (MB: mesiobuccal; DB: distobuccal; P: palatal) and each root has a single orifice, canal and foramen, then it can be coded as 316 MB1 DB1 P1. If the MB root encases canal type 2-1 and the other two roots encase a single orifice, canal and foramen, then it can be coded as 316 MB2-1 DP1 P1. Similarly, if the maxillary right second molar has four roots (MB: mesiobuccal; DB: distobuccal; MP: mesiopalatal; DP: distopalatal), and the MB root encases canal type 2-1 while the other three roots encase a single orifice, canal and foramen in each root, then it can be coded as 417 MB2-1 DB1 MP1 DP1.

If a mandibular right second molar has three roots (M: mesial; DB: distobuccal; DL: distolingual), and the mesial root encases 2 independent canals, whilst the other two roots encase a single root canal, then it can be coded as 347 M2 DB1 DL1. The same coding system will be applied when one of the roots bifurcates at the middle or apical third, and the root canal configuration is different apical and coronal to the level of bifurcation.

Conclusion

The proposed classification system aims to offer a straightforward, precise, and feasible method for identifying root and root canal configurations, which can be used by students, dental professionals, and researchers. It includes specific details about tooth number, number of roots, and root canal configuration types while disregarding minor anatomical variations and developmental anomalies to make it simple and universally applicable.

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