J Bagh College Dentistry Vol. 33(4), December 2021 Root and Root Canal Morphology

Root and Root Canal Morphology: Study Methods and

Classifications

Duaa M. Shihab (1), Anas F. Mahdee (2)

https://doi.org/10.26477/jbcd.v33i4.3014

ABSTRACT
Background: Morphology of the root canal system is divergent and unpredictable, and rather linked to clinical complications,

which directly affect the treatment outcome. This objective necessitates a continuous informative update of the effective clinical

and laboratory methods for identifying this anatomy, and classification systems suitable for communication and interpretation

in different situations.

Data: Only electronic published papers were searched within this review. Sources: “PubMed” website was the only source used

to search for data by using the following keywords "root", "canal", "morphology", "classification".

Study selection: 153 most relevant papers to the topic were selected, especially the original articles and review papers, from

1970 till the 28th of July 2021.

Conclusions: This review divided the root canal analysis methods into two approaches; clinical and in vitro techniques. The

latter has shown more precise non-subjective readings, on the other hand; the clinical methods provide direct chair side diagnosis

for the clinical cases. The classification systems reviewed in the present study, started with the oldest trials that simply presented

the root canal systems, according to the degree of angulation, or by coded Latin numbers or English letters. Then, the most recent

systems were also presented that were persisted with continuous editions up to date. These new systems could briefly describe

the root and root canal’s internal and external details in a small formulation, without confusion and in an easily communicated

manner, highly recommended specially for students, teachers, and researchers

Keywords: root canal, root morphology, canal configuration, root canal classification, endodontic. (Received: 20/8/2021,

Accepted: 22/9/2021)

INTRODUCTION
Tooth development is a complex biological

process moderated by a series of epithelial-

mesenchymal interactions (1). These biological

factors can abnormalize the ultimate process of

odontogenesis causing a developmental anomaly.

“Anomaly is a Greek word, meaning irregular; or

in other words, it is a deviation from what is

regarded as normal” (1).

Depending on the stage of tooth development,

various anomalies in root/canal number, size

and/shape can occur (1). The most common root

malformations in humans arise from either

developmental disorder of the root alone, such as

root dilaceration and Taurodontism or disorders

of root development as a part of general tooth

dysplasia, such as dentine dysplasia type 1 (2).

There is a direct association of such

developmental variations with pulp and peri-

radicular diseases that may necessitate a

multidisciplinary treatment approach (3-8).

Lack of knowledge about normal and abnormal

(1) Master Student, Department of Restorative and Aesthetic

Dentistry, College of Dentistry, University of Baghdad.

(2) Assistant Professor, Department of Restorative and Aesthetic
Dentistry, College of Dentistry, University of Baghdad.

Corresponding author, a.f.mahde@codental.uobaghdad.edu.iq

root and root canal morphology is often

associated with many failures to locate,

instrument, irrigate and fill canals adequately (9,

10), therefore; identifying normal versus

abnormal (aberrant) morphology of the human

dentition is essential for effective root canal

treatment procedures (9).

With the increased range of anatomical

complexities being reported and the deficiencies

of existing systems for categorizing

morphological variations, a new system for

classifying root and canal morphology has been

proposed, which provides detailed information on

tooth notation, roots number and configuration, in

addition to accessory canals and tooth anomalies,

in simple a practical manner which will be

focused on in this review (11-14).

The presently available systems for describing the

root and root canal morphology both under

normal and abnormal conditions are plentiful and

divergent with many interrelations in authors

proposals, as they continue making their new

additions depending on the preceding trials. The

aim of this review is to do an electronic search and

to collect most if not all of the reported methods

for analyzing root canal morphology and
classification systems, and summarizing them.

https://doi.org/10.26477/jbcd.v33i4.3014

J Bagh College Dentistry Vol. 33(4), December 2021 Root and Root Canal Morphology

METHODS
In the present literature review, a comprehensive

search has been made depending on electronically

published peer-reviewed resources using the

“PubMed” website, from 1970 till the 28th of July

2021. The used keywords were "root", "canal",

"morphology", "classification", which revealed

about 153 relevant papers. After filtering, only 67

papers, all in English language, were included in this

review. The filtering process included papers

striving most if not all of the available root and root

canal classification systems, and methodologies are

applied to dental morphological identification. The

selected classification systems and methodologies

were ensured to have well defined and standardized

guidelines and steps in their criteria of work.

3. Techniques for root canal analysis
There are different methods that have been reported

for studying root canal morphology, ranging from in

vitro (experimental) methods, to those which are

more suitable for clinical situations (in vivo).

3.1. In vitro techniques
These are the most common techniques using

extracted teeth for laboratory analysis of root

morphology, serving scientists and authors in their

ongoing researches.

3.1.1. Root clearing and canal staining
This technique is widely mentioned in literature and

could be considered as the gold standard method for

laboratory studies of root canal anatomy, and for

comparison with readings from other techniques,

because of its high accuracy and nondestructive

approach (15).

In clean extracted teeth with fully formed roots, ink

is injected through the coronal access directly into

the root canals, then the access cavities of the study

teeth are filled and well-sealed, leaving the apical

root opening patent for ink progression. These teeth

could be stored in a high-pressure chamber to

enhance penetration of the dye into the fine details of

the tooth structure (16). Now teeth are washed and

dehydrated in an ascending concentration of ethanol

up to 100%, then decalcified in a maintained active

acidic solution over a day. Teeth are then placed in

methyl salicylate solution for a couple of hours

rendering them transparent (17). To be sure that teeth

are well decalcified, some of the samples are

exposed to conventional radiation, examination is

done by using a magnifying lens (×3). Modified

canal staining and root clearing were mentioned in

this literature as it is non-destructive and more

accurate than the conventional staining and clearing

method (17).

The main disadvantage of this method is that it

cannot be used in vivo (17). A comparable method

has the accuracy of the latter technique but at the

same time clinically feasible, not yet available in

endodontic practice.

3.1.2. Radiographical analysis with contrast

medium
In this method, water-soluble low viscosity

radiopaque medium is delivered into the root canals.

The low surface tension of the contrast medium and

subjection of the tooth to vacuum or ultrasonic

waves enable penetration of the medium into the

niches of the root canal system. Then radiographs

were taken in a buccolingual direction, in two

horizontal angulations, 0˚and 30˚, after fixing the

teeth on arch simulating models (18).

Alteration of the subject contrast is induced by

variations in transmission of the radiographic beam

between the tooth and the contrast medium, which

definitely improves the visibility of root canal

systems, in comparison with conventional

radiographs (19). These altered exposures are more

useful than plain radiographs in the assessment of

root canal anatomy, but on the other hand, as the

previous method, it cannot be used in vivo (20).

3.1.3. Histologic examination
Teeth subjected for examination in this method

should be processed by demineralization in an acidic

solution of formic acid, citric acid, or EDTA for

several weeks to be softer and ready for sectioning.

Root sections number and cutting intervals are

determined depending on the study, but most

commonly being sectioned at multiple intervals

along the root course, then simply stained with

hematoxylin-eosin for clear observation of the

canals’ shape at each section (21).

3.2. In vivo techniques

3.2.1. Two-dimensional imaging techniques
In this part of imaging techniques, there are three

different diagnostic tools including conventional,

digital, and panoramic radiography, all of which

share being a two-dimensional image of three-

dimensional structures, but differ in the imaging

quality, resolution, and practicality (19). These

diagnostic methods are still the first-line choice for

before, during, and after work usage that should

never be passed, taking into account the experience

of the operator in manipulation and interpretation of

results (19, 22).

J Bagh College Dentistry Vol. 33(4), December 2021 Root and Root Canal Morphology

3.2.2. Three-dimensional techniques
In this field, many attempts have been made to

develop systems providing an optimum three-

dimensional visualization of the tooth internal

complex and unpredictable anatomy, and to be

feasible aids available in each dental clinic.

o Nonionizing radiation, a high-resolution
magnetic resonance spectroscopy system

constitutes a powerful tool for a detailed analysis

of dental soft tissues (poor detection of hard

tissue changes) (23).

o Magnetic resonance tomography (MRT) with
stray field imaging (STRAFI) system produces

powerful proton signals in a very short time

(poor differentiation between hard tissue

structures) (24).

o Constant-time imaging (CTI) technique shows
good resolution for both hard and soft tissue

structures (195 µm), (limited description of the

smallest components of the pulp chamber) (25).

o 1CT is a miniaturized conventional
computerized tomography offers cross- sectional

images of the roots and 3D shapes for root canal

systems with resolution (36µm), which aids to

detect geometrical changes after instrumentation

(small field of exposure, long scanning time up

to six hours) (26-28).

o High-resolution X-ray computed tomography
(HRXCT): this development gives good

quantitative data for dental structures (5-100µm)

compared with histologic sections (non-

practicality, high cost, limited availability) (29,

30).

o Flat panel-based volume computed tomography
(FP-VCT): this technique shows good qualitative

information about dental structures and exposes

several teeth at one time (low spatial resolution

(150µm), non-practicality, high cost, limited

availability) (31).

o Peripheral quantitative computed tomography
(p-QCT): this innovation produces a good

qualitative and quantitative representation of

dental structures (not fully validated technique)

(32).

o Micro-computed tomography (MCT): non-
invasive technique can evaluate internal and

external dental anatomy non-invasively in both

quantitative and qualitative values, can define

even fine root canal communications and lateral

canals (not suitable for clinical use) (22, 33).

o Cone-beam computed tomography (CBCT): As
a more recent development has been introduced

for 3D imaging of hard tissues in the

maxillofacial region, these devices are now more

available, with high diagnostic quality (75-

450µm), short scanning time (10-70s), and less

radiation dose than conventional CT (34-36).

4. Root and root canal classification systems

4.1. Old classification systems

4.1.1. Mathematical classification of root canal

curvatures

First trials began with Schneider (37) when he

classified root canals on angular bases, according to

the degree of curvature, into straight 5° or less,

moderate 10-20°, and severe 25-70°. Backman et al.

(38) classified root canals on the basis of "radius

quotient," which was obtained by dividing the root

canal angle by its radius measurement. Dobo (39)

devised a classification based on Schneider's angle

and the radius of the circle that could be

superimposed on the curved part of the root canal.

Baumann et al., Dobo, and Southard et al. (24, 39,

40) formulated their classifications using other data

besides the Schneiders angle to achieve a

"semiquantitative" method for describing the shape

of the curve of root canals, however, Schneider's

angle which depended on as a data for classification

cannot describe the course of curve of the canal

along the root.

More recently published papers demonstrated the

necessity of developing a more reliable classification

that was presented by Nagy et al. (41). This

classification is based on computer graphic analysis,

with the results described in four characteristic root

canal forms symbolled with alphabetical letters

(straight canals (I), canals curved in their apical part

(J), canals curved along their length (C), and multi

curved canals (S)).

4.1.2. Diagrammatic representation of root canal

configuration

Gupta and Sexana (42) presented with a new

diagrammatic root canal representation, which is

supposed to be simple to understand, represent, and

communicate, providing a clear picture about the

location, number, and length of most root canal

configurations. Small details should also be

included.

The proposed representation consists of five

horizontal lines, which divide the tooth into four

partitions in a corono-apical direction. The first line,

which is a dashed line signifies the point of reference

from where the length of root canal is measured

"Ref". A second line, which is continuous, marked

as ‘‘Orf.’’ at one end, represents the orifice level or
cemento-enamel junction in the case of a single canal

or Taurodont teeth. The lowermost line, which is

J Bagh College Dentistry Vol. 33(4), December 2021 Root and Root Canal Morphology

also continuous a one, represents the apical foramen

of the root canal. Then third and fourth lines (dotted

lines) divides the root canal into coronal, middle, and

apical thirds; these regions are designated as C, M,

and A, respectively.

The diagrammatic images of teeth (one

anterior/posterior single-rooted and one posterior

multi-rooted) are given for easy understanding of the

orientation of an image. The whole image has a

transparent background and is saved in a portable

network graphics (PNG) format. The image can be

rotated by 180˚ to correspond to either mandibular or

maxillary teeth. It can be imported to any word

processing document and a print of the image can be

obtained in the reporting sheet.

Freehand vertical lines should be drawn from the top

dashed line to the bottom continuous line, to

represent the major root canals exist in the tooth,

with each labeled at the top. The length of the

individual canal from the point of reference to the

apical foramen can be written in millimeters,

depending on the situation, either adjacent to the

origin of its corresponding line, near ‘‘Ref.’’ line, or

at the end, adjacent to the fifth line representing the

apical foramen.

Intercommunications and isthmuses between the

canals should be drawn keeping in mind the

approximate level (coronal, middle, apical) for each.

Fusion between canals can be shown by one vertical

line merging into another or both lines joining

together at the corresponding level.

Bifurcation in the canal is represented by the division

of the line at the corresponding third. The orientation

of the resulting canals can be labeled in the area

adjacent to the fifth line. In addition, the diameter of

the canals can be represented by the relative

thickness of the lines.

Lateral and accessory canals, if identified, can be

shown as blind lines originating from the main

vertical line and running in a horizontal direction at

the corresponding locations. If the major canals,

instead of appearing at the pulpal floor as separate

orifice, continue as a single large canal and separate

below the orifice, then the same can be represented

as a thick band in the diagrammatic representation.

The lines representing the divided canals, in such

cases, can be labeled near the fifth line. If the major

canals, instead of appearing at the apex in separate

apical foramina, join and continue as single large

canal, then also can be drawn as a thick band starting

from the corresponding third. The above-mentioned
rules can be simply summarized as ‘‘to draw what

you see’’, see Figure (1).

This method still has many limitations, which are

inherent in their two-dimensional representation of a

three-dimensional network. It is not able to present

neither the exact location of the canal orifices, nor

the location and orientation of the canals. The

lengths of the canals are out of proportion in order to

simplify the procedure of drawing and segmenting

the canals.

Figure (1): Representation of canal

configuration of maxillary left second molar

having two roots, mesio-buccal and disto-

palatal. Mesio-buccal root having two

canals, MB1 and MB2 with separate orifices,

which merge at the middle level. Disto-

palatal root with two canals, DB and P with

separate orifices and merge in the apical

third, having an identifiable isthmus in the

middle third (42).

4.1.3 Number-digits root canal classification

systems

In these systems the canals configuration is coded as

number digits, to represent their number in each

section of a single root in an occluso-apical direction.

Weine (43) was the first to start classification by

producing four configurations for the root canals

course in a single root, see Figure (2).

Figure (2): Root canal configurations from

type I to type IV, (43).

Vertucci and Williams (44) identified more complex

forms of root canal systems to add eight root canal

configurations in the literature, see Figure (3).

J Bagh College Dentistry Vol. 33(4), December 2021 Root and Root Canal Morphology

Thereafter, Sert and Bayirli (45) described fourteen

additional even more complex configurations to

complement that was described by Vertucci, see

Figure (4).

Figure (3): Root canal configurations from

type I to type VIII, (44).

Figure (4): Root canal configurations from

type IX to type XXIII, (45).

4.2. New systems for root canal classification

(formulation systems)

The simple idea behind these systems is to represent

the root and root canal configuration of a tooth by

coded formula, including symbols and numbers,

easily written and identified, these systems were

developed for the first time by Ahmed et al. (11),

with useful additions to this system persisted up to

date.

4.2.1. New classification system for root and root

canal morphology by Ahmed et al. (2017).
According to this system (11), tooth number (TN)

can be written by using any numbering system (e.g.,

Universal Numbering System, Palmer Notation

Numbering System, or the FDI World Dental

Federation System). If the tooth cannot be identified

using one of the numbering systems (i.e., extracted

teeth), then a suitable abbreviation can be used, e.g.,

maxillary (upper) central incisor (UCI). Number of

roots is added as a superscript before the tooth

number (RTN). Any division of a root whether in the

coronal, middle or apical third will be coded as 2 or

more roots. Accordingly, a bifurcation is represented

as (2TN), and trifurcation is represented as (3TN),

and so on. Details of roots (RTN R1 R2 ... etc.) in

double and multi-rooted teeth are added on the right

of the tooth number.

When individual roots are fused, a slash ('/') should

be added between the initial letters of each root.

Type of root canal configuration in each root will be

identified as a superscript number after the tooth

number starting from the orifice (O), through the

canal (C), to the foramen (foramina) (F).

Considering any similar adjacent numbers for a

specific root reduced into single number

representing both. Number of canals before

furcation, written as a subscript after tooth number,

see Figure (5, 7).

Figure (5): Diagrammatic representation of

the new classification system.

4.2.2. Accessory/auxiliary root canals

classification system by Ahmed et al. (2018)
Taking into account the necessity of precise

interpreting, and well localizing the

accessory/auxiliary root canal ramifications, we

cannot go blind with the essential determining role

of this characterization in attaining favorable overall

final results in our routine practice of endodontic

treatment. As it has been reported in many cases that

apical divergent morphology is responsible for

persistent apical periodontitis and incomplete

healing after efficient well-sealed 3D root canal

obliteration from the operator's point of view (46).

On the other hand, these ramifications may be the

answer for many diagnostic questions in confusing
cases, giving explanations for lateral radiolucency of

unknown origin, or surprising devitalization after

root planning especially with the development of

J Bagh College Dentistry Vol. 33(4), December 2021 Root and Root Canal Morphology

new technologies for precise 3D characterization of

this complex morphology with ease (46-48).

The nomenclature of accessory canals is described

by several authors, with many of no clear

demarcating lines for separating the many types of

these canals. Some authors produced their

description on angular bases, as for lateral canals

meeting the main canal at a right angle, while the

accessory canals being at an oblique angle. Other

modalities depended on spatial location, lateral

canals named for those emerging from the trunk of

root in the coronal and middle thirds, accessory

canals emerging in the apical third more precisely

3.5 mm from the root end, while furcation canals

emerge from the floor of the pulp chamber. The term

apical delta/ramifications notate divergent fine

branching of the accessory canals at the apical end

of the root canal with obliteration of the main canal

just like a tree branch (45, 49-54).

With neglecting the old attentions to classify these

canals which was with much of confusion,

emphasizing on the new one that gave a nominal

notation for the accessory canals in general as a new

addition for the new classification system was

described by Ahmed et al. (14). This system gives

you a clear picture about the location of the canal

along its course without additional complex

information, making it suitable for trainees and

researchers communication.

In this system or addition, Ahmed et al. (14) divided

the root into three partitions apical, middle, and

coronal (A, M, C), respectively. Moreover, they

described the course of canal from the orifice

opening, canal penetration within the dentinal wall,

ending with its foramen on the root surface (a O-C-

a F) respectively, fused into a single number when

they are similar, writing it as a superscript after tooth

number(TN) in single-rooted tooth or when the

accessory canal located in the floor of the chamber,

or after root number(RN) in double/multi-rooted

teeth, apical delta notified as (D), when these canals

present in more than one-third of the root separate

between root divisions by comma(,), Adding straight

horizontal line among parts of canal course, one

canal may have orifice in specific root third with its

orifice opens in another third in such a case mention

both root sections with a comma in between, see

Figure (7).

4.2.3. Root canal anomaly classification by

Ahmed and Dummer (2018).

Most classification systems previously added had
been going very deep in describing root canal

anomalies in a detailed manner with much of

complexity, stands against an immediate clear

interpretation of them (44, 55-58). This limitation is

compensated for with the new addition of

classification system described by Ahmed and

Dummer (12), who allow easy simultaneous

interpretation of these anomalies along with root and

root canal morphology in the same notation.

The anomalies described in this system should be

related directly to the root canal morphology,

affecting the endodontic work. Abbreviation for the

anomaly added in capital letters between brackets

(A) before tooth number, with the subtype if present

and identified clinically added as a superscript on the

right upper corner (A2). If the anomaly includes

fusion between teeth or roots, then slash (/) is added

between them, while double slash (//)is added if root

canals have inter-canal communications. If the tooth

has more than one of the same anomalies, write the

number of repetitions on the left side to the tooth

anomaly (NA), while if the same tooth has more than

one different anomaly, then separate between them

with comma (A1, A2), see Figures (6, 7).

Figure (6): Diagrammatic representation of

tooth/root anomalies.

Figure (7): (a) Examples of symbolic

representation of the root canal system by

Ahmed et al. (11), (b) accessory root canals

formulations, merged with root canal

configuration details in the same formula

(14), (c) examples for coding some of the

common root canal anomalies (Dens

Evaginatus (DE)) (12).

J Bagh College Dentistry Vol. 33(4), December 2021 Root and Root Canal Morphology

4.2.4. Application of the new classification system

on primary teeth by Ahmed et al. (2020)
Root canal treatment or partial pulpectomy has

become part of the routine treatments of primary

teeth. To ensure normal physiological resorptive

process and exfoliation, or if tooth retention is

required for some time, and to optimize these

procedures, it is necessary to realize the anatomy of

these root canal miniatures, with all associated

anomalies and fine communications, just like in

permanent teeth (59-63).

Root canal treatment in primary teeth has challenged

with many factors, signing first one which is

aberrance from normal morphology specially in the

posteriors, as a result of dentin islands formed

continuously, in addition to physiologic resorption

that may alter the working length, moreover anterior

primary teeth normally show additional canals

specially in upper canines. On the other hand,

pathological factors such as periodontal tissue

inflammatory diseases are more complicating their

anatomy by altering the normal course of root

resorption, which itself is uneven and not predictable

(64, 65).

The present system or addition (66) sharing nearly

the same formula as has been described for

permanent teeth by Ahmed et al. (11), but with

lightening some point differences in writing formula

include (1) primary tooth number could be replaced

by any simple abbreviation if the exact number

could not be identified, (2) physiologic tooth

resorption is not included in the formula, but the

formula will be changed if the resorption altered the

anatomy during the course of treatment, (3)

accessory canals are usually coded as in permanent,

but should be omitted from the formula in specific

conditions when there is an extensive resorptive

process, or tooth is about to exfoliate (67).

CONCLUSION
The root canal analysis methods, divided into two

approaches; clinical and in vitro techniques, with the

latter has shown more precise non-subjective

readings, on the other hand; clinical methods

provide direct diagnostic methods for the clinical

cases on the chair-side.

The classification systems pointed to in the present

literature, has been reviewed, beginning with the

oldest trials to represent the root canal systems in

diagrams, according to the angulation degree, or

simply by Latin numbers or English letters, reaching
to the most recent systems, which persist with

continuous editions up to date. These new systems

could briefly describe the root and root canal’s

internal and external details in a small formulation,

without confusion and in an easily communicated

manner, highly recommended specially for students,

teachers, and researchers.

Conflict of interest: None.

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الخالصة
مختلف على نطاق واسع وغير متوقع، وكثيرا" ما يتم ربطه بالمشاكل السريرية، مما يؤثر بالتالي االهداف: تشكيل تجاويف الجذور اللبية في االسنان

بشكل مباشر على نتائج العالجات الجذرية.

ر " هي المصدPubMed: فقط الدراسات المنشورة الكترونيا" تم البحث عنها ضمن هذا االستعراض. المصادر: بوابة البحث االللكترونية "البيانات

".root ,"“canal” ,“morphology”" ,classificationالوحيد الذي تم اعتماده للبحث عن مفردات االستعراض، و ذلك باستخدام الكلمات الداللية "

ي الكتابة.فاختيار الدراسة: تم اختيار الدراسات المكتبية والبحوث االصيلة، التي لها عالقة مباشرة بموضوع االستعراض، لتكون مصادرا" معتمدة

غير متأثرة ةاالستنتاجات: الدراسات المعنية بتحليل شكل التجاويف اللبية للجذور تقسم الى قسمين؛ سرسرية ومختبرية، االخيرة اظهرت قراءات أكثر دق

نيفية التي تم االنظمة التص باسلوب الباحث، بينما بالمقابل، الطرق السريرية تعتبر وسيلة تشخيصية مباشرة للحاالت السريرية على كرسي العالج.

ذور، او جاستعراضها في الموضوع الحالي، تبدأ مع اقدم المحاوالت لتمثيل انظمة التجاويف اللبية على شكل مخططات، او بناءا" على درجة التواء ال

افات مستمرة ترميزية مفصلة، والتي ال تزال مع اضترمز باحرف باللغة الالتينية او االنكليزية، انتهاءا" مع احدث االنظمة التصنيفية التي تستخدم صيغة

الى هذا التاريخ.

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