Fumes Et Al. 2014 [Deciduous Teeth]

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Root canal morphology of primary molars: amicro-computed tomography study

ARTICLE in EUROPEAN ARCHIVES OF PAEDIATRIC DENTISTRY. OFFICIAL JOURNAL OF THE EUROPEAN ACADEMYOF PAEDIATRIC DENTISTRY · FEBRUARY 2014

DOI: 10.1007/s40368-014-0117-0 · Source: PubMed

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7 AUTHORS, INCLUDING:

Manoel Damião de Sousa-Neto

University of São Paulo

201 PUBLICATIONS 3,066 CITATIONS

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Graziela Bianchi Leoni

22 PUBLICATIONS 58 CITATIONS

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Marco Versiani


71 PUBLICATIONS 1,006 CITATIONS

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Raquel Assed Bezerra Silva


91 PUBLICATIONS 566 CITATIONS

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Available from: Marco Versiani

Retrieved on: 14 February 2016

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O R I G I N A L S C I E N T I F I C A R T I C L E

Root canal morphology of primary molars: a micro-computedtomography study

A. C. Fumes • M. D. Sousa-Neto • G. B. Leoni •

M. A. Versiani • L. A. B. da Silva •

R. A. B. da Silva • A. Consolaro

Received: 18 September 2013 / Accepted: 23 January 2014

European Academy of Paediatric Dentistry 2014

Abstract

Aim This was to investigate the root canal morphology of primary molar teeth using micro-computed tomography.

Methods Primary maxillary (n = 20) and mandibular

(n = 20) molars were scanned at a resolution of 16.7 lm

and analysed regarding the number, location, volume, area,

structured model index (SMI), area, roundness, diameters,

and length of canals, as well as the thickness of dentine in

the apical third. Data were statistically compared by using

paired-sample t test, independent sample t test, and one-

way analysis of variance with significance level set as 5 %.

Results Overall, no statistical differences were found

between the canals with respect to length, SMI, dentine

thickness, area, roundness, and diameter ( p[ 0.05). A

double canal system was observed in the mesial and mesio-

buccal roots of the mandibular and maxillary molars,

respectively. The thickness in the internal aspect of the

roots was lower than in the external aspect. Cross-sectional

evaluation of the roots in the apical third showed flat-

shaped canals in the mandibular molars and ribbon- and

oval-shaped canals in the maxillary molars.

Conclusions External and internal anatomy of the pri-

mary first molars closely resemble the primary secondmolars. The reported data may help clinicians to obtain a

thorough understanding of the morphological variations of

root canals in primary molars to overcome problems rela-

ted to shaping and cleaning procedures, allowing appro-

priate management strategies for root canal treatment.

Keywords Deciduous teeth Dental pulp cavity Micro-

computed tomography Primary molars

Introduction

The premature loss of primary teeth may cause changes in

the chronology and sequence of eruption of permanent

teeth; thus, saving teeth in children is an important concept

and frequently involves endodontic treatment (Cleghorn

et al. 2012). Root canal treatment in primary teeth includes

the removal of the pulp tissue, debridement and prepara-

tion, irrigation, and filling of the canals. The main objective

of pulp therapy in primary teeth is to maintain the integrity

and health of the teeth and their supporting tissues (Cleg-

horn et al. 2012). To accomplish this goal, a comprehen-

sive understanding of the root and the root canal

morphology of primary teeth is of utmost importance

(Hibbard and Ireland 1957; Goodacre 2003; Zoremchhingi

et al. 2005; Aminabadi et al. 2008; Bagherian et al. 2010;

Cleghorn et al. 2012).

The external and internal morphology of primary teeth

are different in many aspects from permanent successors

(Kavanagh and O’Sullivan 1998; Goodacre 2003; Johnston

and Franklin 2006; Cleghorn et al. 2012). Generally, pri-

mary teeth with fully developed roots exhibit a less com-

plex root canal system compared to permanent teeth, with

A. C. Fumes L. A. B. da Silva R. A. B. da Silva

A. Consolaro

Department of Pediatric Dentistry, Dental School of RibeirãoPreto, University of São Paulo, Av. do Café s/no, Bairro Monte

Alegre, São Paulo, Ribeirão Preto CEP 14049-904, Brazil

M. D. Sousa-Neto (&) G. B. Leoni M. A. Versiani

Department of Restorative Dentistry, Dental School of Ribeirão

Preto, University of São Paulo, Av. do Café s/no, Bairro Monte

Alegre, São Paulo, Ribeirão Preto CEP 14049-904, Brazil

e-mail: [email protected]

M. D. Sousa-Neto

Rua Célia de Oliveira Meirelles 350, São Paulo,

Ribeirão Preto CEP 14024-070, Brazil

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Eur Arch Paediatr Dent

DOI 10.1007/s40368-014-0117-0


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one canal per root. In primary molars, the complexity of

this system may increase over time due to the formation of

secondary dentine and narrowing of the canal system and

eventually the resorption process (Hibbard and Ireland

1957).

Traditionally, root canal anatomy of primary teeth has

been described in case reports (Badger 1982; Falk and

Bowers 1983; Caceda et al. 1994; Winkler and Ahmad1997; Kavanagh and O’Sullivan 1998; Eden et al. 2002)

and in ex vivo studies using injection of materials (Simp-

son 1973), dye perfusion (Ringelstein and Seow 1989),

digital radiographs, longitudinal and transverse cross-sec-

tioning, histology (Poornima 2008), clearing technique

(Bagherian et al. 2010), scanning electron microscope

(Wrbas et al. 1997), and conventional computed tomogra-

phy (Zoremchhingi et al. 2005). These methodologies have

been successfully used for many years in the anatomical

study of the root canal system; however, most of them are

invasive or only provide a two-dimensional image of a

three-dimensional structure, and therefore may not accu-rately reflect the morphology of the object being studied.

Thus, these inherent methodological limitations encour-

aged the search for new methods able to produce improved

results (Peters et al. 2000).

In recent years, significant technological advances for

imaging teeth have been introduced. Their non-invasive

nature allows the use of teeth for other purposes or as

controls for further treatment procedures. The development

of the high-resolution X-ray micro-computed tomography

(micro-CT) has gained increasing significance in the study

of dental tissues. Micro-CT offers a non-invasive repro-

ducible technique for three-dimensional assessment of the

root canal system and it can be applied both quantitatively

and qualitatively (Peters et al. 2000; Siqueira et al. 2010;

Versiani et al. 2011, 2012, 2013).

Even though there has been a growing body of research and

publicationson the dental anatomy of primary teeth (Goodacre

2003; Cleghorn et al. 2012), a detailed quantitative description

of the anatomy of their root canal system is still lacking.

Therefore, the purpose of this study was to describe the mor-

phometric aspects of the external and internal anatomy of

primary mandibular and maxillary molars, using high-resolu-

tion three-dimensional micro-CT analysis.

Materials and methods

Sample selection

After approval from the local ethics in research committee

(CAAE #0072.0.130.000-09), primary mandibular (n = 20)

and maxillary (n = 20) molars, extracted for reasons not

related to this study and stored in 0.1 % thymol solution,

were selected. For each group of teeth, ten first and ten

second primary molars were evaluated. The inclusion cri-

teria comprised only molars with no physiological root

resorption or at its initial stages, i.e. in which resorption did

not exceed 1/3 of root length.

Micro-CT scanning and reconstruction

Each tooth was slightly dried, mounted on a custom

attachment, and scanned in a micro-CT scanner (SkyScan

1174v2; Bruker-microCT, Kontich, Belgium) at an isotro-

pic resolution of 16.7 lm. The X-ray tube was operated at

50 kV and 800 mA, and the scanning was performed by

180 rotation around the vertical axis with a rotation step of

1, using a 0.5-mm-thick aluminium filter. Images of each

specimen were reconstructed with dedicated software

(NRecon v.1.6.6; Bruker-microCT) providing axial cross

sections of the inner structure of the samples.

Quantitative analysis

DataViewer v.1.4.4 software (Bruker-microCT) was used

to evaluate the length (in millimetres) of the root from the

apex, and the length of the main root canals from the apical

foramen to the level of the cementoenamel junction. Three-

dimensional evaluation of the root canals (volume, surface

area, and structure model index) was performed from the

apex to the canal orifice using CTAn v.1.12 software

(Bruker-microCT). Volume was calculated as that of bi-

narised objects within the volume of interest. For the

measurement of the surface area of the 3D multilayer

dataset, two components to surface measured in 2D were

used: first, the perimeters of the binarised objects on each

cross-sectional level, and second, the vertical surfaces

exposed by pixel differences between adjacent cross sec-

tions. Structure model index (SMI) involves a measure-

ment of surface convexity in a 3D structure. SMI is derived

as 6.(S ’.V)/ S 2), where S is the object surface area before

dilation and S ’ is the change in surface area caused by

dilation. V is the initial, undilated object volume. An ideal

plate, cylinder and sphere have SMI values of 0, 3 and 4,

respectively (Peters et al. 2000).

The smallest thickness of dentine in the internal and

external aspects of the roots, at 1, 2 and 3 mm from the

apical resorption bevel, were also recorded. Measurements

of the dentine thickness were taken from the external limit

of the root canal to the surface of the root. At these same

levels, CTAn v.1.12 software (Bruker-microCT) was used

for the two-dimensional evaluation (area, roundness,

major diameter, and minor diameter) of the root canal.

Area was calculated using the Pratt algorithm (Pratt

1991). The cross-sectional appearance, round or more

ribbon shaped, was expressed as roundness. Roundness of


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a discreet 2D object is defined as 4 A /(p.(dmax)2), where

‘‘ A’’ is the area and ‘‘dmax’’ is the major diameter. The

value of roundness ranges from 0 to 1, with one signifying

a circle. The major diameter was defined as the distance

between the two most distant pixels in that object. The

minor diameter was defined as the longest chord through

the object that can be drawn in the direction orthogonal to

that of the major diameter.

Qualitative analysis

Three-dimensional models and cross sections of the rootcanals were reconstructed based on micro-CT scans and

generated by the binarisation process using CTAn v.1.12

software (Bruker-microCT). CTVol v.2.2.1 (Bruker-mi-

croCT) and DataViewer v.1.4.4 (Bruker-microCT) soft-

ware were used for visualisation and qualitative evaluation

of the specimens.

Statistical analysis

Three-dimensional parameter results and the average

length of roots and root canals were statistically compared

using paired-sample t test within group and independent

sample t test between groups, respectively. Considering

that the data of dentine thickness and two-dimensional

parameters at 1, 2 and 3 mm from the resorption bevel

were normally distributed (Shapiro–Wilk test; p[ 0.05),

they were presented as means and standard deviations

(SD), and statistically compared using one-way analysis of

variance post hoc Tukey test. Statistical analysis was per-

formed using SPSS v.17.0 for Windows (SPSS Inc, Chi-

cago, IL, USA) with a significance level set at 5 %.

Results

Quantitative analysis

Tables 1 and 2 show the mean (±SD) of the three- and

two-dimensional data, respectively, in each root of the

primary molars. Overall, in both groups of teeth no sta-

tistical differences were found between root canals of the

first and second molars with respect to length, SMI, and the

two-dimensional analysed parameters (area, roundness,

major diameter, and minor diameter) ( p[ 0.05). Distal and

palatal canals of the mandibular and maxillary molars,respectively, presented a significant higher volume than the

other canals in the same group of teeth ( p\ 0.05). Gen-

erally, root canals of the second primary molar canals had

higher surface area than the first molars ( p\ 0.05).

Table 3 summarises the mean dentine thickness in the

apical third of each molar root. No statistical difference

was observed in the comparison of the dentine thickness, in

either internal or external aspect of each root, between the

first and second molars ( p[ 0.05). The lowest mean values

of dentine thickness were observed in the internal aspect of

the roots, in both molar groups. In general, the highest

mean thickness of dentine was observed in the distal and

palatal roots of the mandibular and maxillary molars,

respectively, in all evaluated levels.

Qualitative analysis

The analysis of the external anatomy of the mandibular first

and second molars showed that all specimens had two

roots, wider in the buccal–lingual dimension, narrower

mesio-distally, and often fluted. Deep caries with no pulp

Table 1 Mean (±SD) of the morphometric 3D data in each root of primary maxillary and mandibular molars

n Root canal Root length (mm) Canal length (mm) Volume (mm3) Surface area (mm2) SMI

Mandibular

First molar 10 M 7.3 ± 1.5 6.1 ± 1.5 5.4 ± 3.6 36.1 ± 12.7a 2.0 ± 0.4

D 6.4 ± 1.9a 4.7 ± 2.5 4.6 ± 4.4a 28.0 ± 15.6b 1.9 ± 0.4

Second molar 10 M 8.5 ± 1.1 7.0 ± 1.8 6.6 ± 2.7 58.7 ± 20.3a 1.7 ± 0.5

D 8.9 – 2.0b 6.7 – 2.3 9.6 ± 3.5b 65.9 ± 18.3b 1.6 ± 0.3

Maxillary

First molar 10 MB 7.9 – 1.1 6.5 – 2.3 2.8 ± 2.1 24.5 ± 7.9 2.1 ± 0.6

DB 6.7 ± 1.7 5.4 ± 1.5 1.3 ± 1.6 11.4 ± 6.9a

2.1 ± 0.5

P 5.9 ± 1.8 4.6 ± 1.9 2.9 ± 2.5a 17.9 ± 7.5a 2.7 ± 0.3

Second molar 10 MB 8.5 ± 1.4 6.3 ± 1.9 3.2 ± 1.6 31.0 ± 12.0 1.8 ± 0.6

DB 6.5 ± 1.6 5.7 ± 1.4 2.0 ± 1.0 22.2 ± 11.5b

2.0 ± 0.5

P 7.4 ± 1.4 5.9 ± 1.8 5.4 ± 2.6b 31.8 ± 11.6b 2.5 ± 0.4

Different superscript letters in the same column indicate statistical significant difference between root canals in the same group of teeth

(independent sample t test, p\ 0.05); within root, values with bold letters in the same line were statistically different (paired-sample t test,

p\0.05)

M mesial; D distal; MB mesio-buccal; DB disto-buccal; P palatal


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exposure were observed in 20 % of the sample. Early

apical root resorption was observed in only one specimen

from each group of teeth. On the other hand, surface

resorption at the internal aspect of the roots was observed

in most of the teeth (n = 15). Bevelled resorption in the

apex of both roots resulted in a thinner thickness of the

dentine walls compared to the middle and cervical thirds.Three-dimensional models of the mandibular molars con-

firm that the configuration of the root canal system was

consistent with the external morphology of the root

(Fig. 1a–c). A single root canal was observed in 10 % of

the mesial roots, while a single distal canal system was

detected in 60 and 50 % of the first and second molars,

respectively. In the mesial and distal roots, the maximum

number of orifices observed in the root canal cross sections

was 8 and 5, respectively. At the furcation level, the mesial

root of the mandibular first molars showed two orifices in

eight samples, whilst all other roots presented only one

orifice. Ribbon-shaped canal systems with one or two

canals in the mesial root and one in the distal root were

present in 40 and 30 % of the first and second molars,

respectively. In the latter, a ribbon-shaped canal that sep-

arates into two or more canals from below the cemento-enamel junction was also observed.

Figure 2 shows exemplary 3D models of the external

(Fig. 2a) and internal anatomy (Fig. 2b–c) of three primary

maxillary molars. Generally, three canal systems were

present, one in each root. Two canals were observed in the

mesio-buccal (MB) root of two maxillary first molars. At

the furcation level, the MB root of the maxillary first

molars showed two orifices in two samples, whilst all other

roots presented only one orifice. The analysis of the

Table 2 Mean (±SD) of

morphometric 2D data at 1, 2

and 3 mm from the apical

resorption bevel in each root of

primary mandibular and

maxillary molars

Asterisk (*) means statistically

significant difference within

root in the same group of teeth(one-way ANOVA post hoc

Tukey test, p\ 0.05)

M mesial; D distal; MB mesio-

buccal; DB disto-buccal;

P palatal

Root

canal

n Distance

(mm)

Area

(mm2)

Roundness Major diameter

(mm)

Minor diameter

(mm)

Mandibular

First molar M 10 1 0.4 ± 0.6 0.4 ± 0.2 1.0 ± 1.0 0.4 ± 0.3

2 0.4 ± 0.6 0.4 ± 0.2 1.1 ± 0.9 0.4 ± 0.2

3 0.5 ± 0.6 0.4 ± 0.2 1.3 ± 0.9 0.4 ± 0.3

D 10 1 0.5 ± 0.4 0.3 ± 0.1 1.2 ± 0.6 0.4 ± 0.22 0.6 ± 0.4 0.3 ± 0.1 1.5 ± 0.4 0.5 ± 0.2

3 0.7 ± 0.4 0.4 ± 0.1 1.4 ± 0.6 0.6 ± 0.3

Second molar M 10 1 0.4 ± 0.6 0.4 ± 0.2 1.3 ± 1.6 0.3 ± 0.2

2 0.2 ± 0.4 0.4 ± 0.2 1.0 ± 1.0 0.3 ± 0.1

3 0.5 ± 0.9 0.3 ± 0.2 1.4 ± 1.1 0.4 ± 0.2

D 10 1 0.4 ± 0.5 0.2 ± 0.2 1.8 ± 1.4 0.3 ± 0.1

2 0.7 ± 0.7 0.2 ± 0.2 2.1 ± 1.5 0.4 ± 0.2

3 1.2 ± 1.0 0.2 ± 0.2 2.7 ± 1.4 0.5 ± 0.2

Maxillary

First molar MB 10 1 0.1 ± 0.1 0.4 ± 0.1 0.5 ± 0.3 0.3 ± 0.2

2 0.2 ± 0.2 0.3 ± 0.2 1.0 ± 0.6 0.3 ± 0.2

3 0.3 ± 0.2 0.3 ± 0.2 1.0 ± 0.6 0.4 ± 0.2

DB 10 1 0.1 ± 0.3 0.5 ± 0.2 0.5 ± 0.3 0.2 ± 0.2

2 0.2 ± 0.3 0.5 ± 0.2 0.6 ± 0.3 0.3 ± 0.2

3 0.2 ± 0.3 0.4 ± 0.2 0.6 ± 0.3 0.3 ± 0.2

P 10 1 0.4 ± 0.5 0.6 ± 0.1 0.8 ± 0.4 0.5 ± 0.3

2 0.6 ± 0.5 0.6 ± 0.1 1.0 ± 0.4 0.7 ± 0.4

3 0.9 ± 0.7 0.5 ± 0.1 1.3 ± 0.5 0.8 ± 0.4

Second molar MB 10 1 0.3 ± 0.2 0.3 ± 0.1 1.2 ± 0.9 0.3 ± 0.1

2 0.4 ± 0.2 0.2 ± 0.1 1.4 ± 0.9 0.4 ± 0.1

3 0.4 ± 0.3 0.2 ± 0.1 1.6 ± 1.0 0.4 ± 0.2

DB 10 1 0.2 ± 0.1 0.3 ± 0.2 0.9 ± 0.3 0.3 ± 0.1

2 0.3 ± 0.1 0.3 ± 0.2 1.3 ± 0.6 0.3 ± 0.1

3 0.4 ± 0.2 0.3 ± 0.2 1.6 ± 0.9 0.4 ± 0.1

P 10 1 0.7 ± 0.2 0.5 ± 0.1 1.3 ± 0.3 0.6 ± 0.1*

2 0.9 ± 0.4 0.5 ± 0.1 1.5 ± 0.4 0.7 ± 0.1

3 1.1 ± 0.4 0.5 ± 0.1 1.7 ± 0.5 0.8 ± 0.1*


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external anatomy showed that six specimens from each

group of teeth had three widely separated roots, while four

presented fusion between the disto-buccal (DB) and palatal

roots. Deep caries with no pulp exposure were observed in

30 % of the sample. Early bevelled apical root resorption

was observed in two MB roots of the second molars, and

three MB and two DB roots of the first molars. The apical

resorption of the roots resulted in a thinner thickness of the

dentine walls compared to the middle and cervical thirds

and, in some cases, exposure of the root canal (Fig. 2d).

Surface resorption at the internal aspect of the roots was

observed in most of the specimens (n = 17).

Exemplary cross sections of the roots of the mandibular

and maxillary primary molars showed the complexity and

the large dimensions of the root canal system in the apical

third (Fig. 3). In the mandibular molars, mesial canal cross

sections were significantly flatter and irregularly tapered in

the mesio-distal plane. The presence of thin isthmuses,interconnecting branches, and multiples orifices were

observed. Round-shaped canals were observed when the

main canal split into multiple canals throughout the root,

which occurred in 60 and 70 % of the first and second

molars, respectively. In the maxillary molars, evaluation of

the cross sections of the roots showed generally ribbon- or

oval-shaped canals with large dimensions. However, in

both mandibular and maxillary molars, the cross-sectional

appearance of the canals varied in different levels of the

root. Table 4 summarises the percentage frequency of root

canal shape in each root of the primary maxillary and

mandibular molars.

Discussion

Although detailed descriptions of the external and internal

anatomical configuration of primary molars have been

already reported using conventional methodologies (Hib-

bard and Ireland 1957; Simpson 1973; Badger 1982; Falk

and Bowers 1983; Ringelstein and Seow 1989; Salama

et al. 1992; Caceda et al. 1994; Winkler and Ahmad 1997;

Wrbas et al. 1997; Kavanagh and O’Sullivan 1998; Fuks

2000; Eden et al. 2002; Goodacre 2003; Zoremchhingi

et al. 2005; Aminabadi et al. 2008; Poornima and Subba

Reddy 2008; Song et al. 2009; Bagherian et al. 2010; Liu

et al. 2010; Cleghorn et al. 2012), no study has been

undertaken to evaluate quantitatively their root canal sys-

tem using high-resolution micro-computed tomography.

Primary mandibular molars have been usually described

as having two grooved and divergent roots that flare to

accommodate the developing permanent premolars (Hib-

bard and Ireland 1957; Zoremchhingi et al. 2005; Baghe-

rian et al. 2010). In the literature, a considerable variation

in number and shape of canal systems has been described

in this group of teeth (Hibbard and Ireland 1957; Salama

et al. 1992; Zoremchhingi et al. 2005; Aminabadi et al.

2008; Bagherian et al. 2010; Cleghorn et al. 2012). Ana-

tomical anomalies, such as additional roots, dens invagin-

atus, and taurodontism, have also been reported, mostly in

mandibular second molars (Badger 1982; Falk and Bowers

1983; Winkler and Ahmad 1997; Eden et al. 2002; Zor-

emchhingi et al. 2005; Johnston and Franklin 2006; Song

et al. 2009; Bagherian et al. 2010; Liu et al. 2010). Overall,

it may be inferred that the external and internal anatomy of

Table 3 Mean (±SD) of dentine thickness (in mm) at 1, 2 and 3 mm

from the apical resorption bevel in each root of primary mandibular

and maxillary molars

Root

canal

n Distance

(mm)

Thickness

(internal)

Thickness

(external)

Mandibular

First molar M 10 1 0.4 ± 0.1 0.7 ± 0.1

2 0.5 ± 0.1 0.8 ± 0.2

3 0.5 ± 0.1 0.9 ± 0.2

D 10 1 0.4 ± 0.1 0.8 ± 0.3

2 0.5 ± 0.2 0.8 ± 0.3

3 0.4 ± 0.1 0.8 ± 0.3

Second molar M 10 1 0.5 ± 0.1 0.6 ± 0.1*

2 0.6 ± 0.1 0.7 ± 0.1

3 0.6 ± 0.1 0.8 ± 0.1*

D 10 1 0.5 ± 0.1 0.7 ± 0.2

2 0.6 ± 0.1 0.8 ± 0.2

3 0.6 ± 0.1 0.9 ± 0.3

MaxillaryFirst molar MB 10 1 0.3 ± 0.1 0.6 ± 0.3

2 0.4 ± 0.1 0.7 ± 0.3

3 0.5 ± 0.1 0.7 ± 0.3

DB 10 1 0.4 ± 0.2 0.6 ± 0.2*

2 0.6 ± 0.2 0.7 ± 0.2

3 0.6 ± 0.3 0.9 ± 0.2*

P 10 1 0.8 ± 0.2 1.0 ± 0.2

2 1.1 ± 0.3 1.1 ± 0.2

3 1.2 ± 0.4 1.2 ± 0.3

Second molar MB 10 1 0.4 ± 0.1* 0.6 ± 0.1

2 0.5 ± 0.1 0.8 ± 0.2

3 0.6 ± 0.1* 0.8 ± 0.2

DB 10 1 0.5 ± 0.2 0.7 ± 0.1

2 0.6 ± 0.2 0.8 ± 0.2

3 0.7 ± 0.2 0.9 ± 0.3

P 10 1 0.6 ± 0.2 1.0 ± 0.3

2 0.8 ± 0.3 1.2 ± 0.4

3 0.8 ± 0.2 1.3 ± 0.5

Asterisk (*) means statistically significant difference within root in

the same group of teeth (one-way ANOVA post hoc Tukey test,

p\0.05)



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the primary mandibular first molar closely resembles the

primary mandibular second molar (Goodacre 2003; Cleg-

horn et al. 2012). Most studies have found either one or two

canals in each of the mesial and distal roots (Hibbard and

Ireland 1957; Zoremchhingi et al. 2005; Aminabadi et al.

2008; Bagherian et al. 2010). The incidence of double

Fig. 1 Exemplary three-

dimensional models of three

primary mandibular molars

(a) showing the anatomical

configuration of the root canals

in frontal (b) and lateral

(c) views. Generally, ribbon-

shaped canal systems are

present, with one or two found

in the mesial root and one in the

distal root. A ribbon-shaped

canal that separates into two

canals from below the cemento-

enamel junction was also

observed in the distal root in

both molars


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ribbon-shaped canal system has been reported to range

from 24 to 100 % in the mesial root, and from 22.2 to 60 %

in the distal root (Zoremchhingi et al. 2005; Aminabadiet al. 2008; Bagherian et al. 2010); however, two canals in

the mesial root and one canal in the distal root comprised

the most commonly reported anatomical configuration in

primary mandibular molars (Cleghorn et al. 2012). In the

present study, this configuration was observed in 50 and

40 % of the first and second mandibular molars, respec-

tively. The lowest length of the distal roots was not

reflected in the volume and surface area of the canal, which

showed higher values than the mesial canal. An

explanation can be found in the analysis of the 2D

parameters, which showed the highest mean values of area,

major and minor diameters in the distal canals of bothmolar types. Goodacre (2003) calculated the mean

dimensions of primary teeth based on several studies and

found that the mean lengths of the mesial and distal roots of

the first and second molars were 10.5 and 8.9 mm, and 11.4

and 10.5 mm, which were higher than the present results.

Primary maxillary molars have been described as having

three divergent and separated roots that flare to accom-

modate the developing permanent premolars (Hibbard and

Ireland 1957; Goodacre 2003; Zoremchhingi et al. 2005;

Fig. 2 Exemplary three-dimensional models of three primary

maxillary molars (a) showing the anatomical configuration of the

root canals in frontal (b–c) and apical (d) views. Generally, ribbon- or

oval-shaped canal systems were present, with one or two canals in the

mesio-buccal root and one in the disto-buccal and palatal roots. The

presence of a bevelled resorption in the apex of the roots resulted in a

thinner thickness of the dentine walls and exposure of the root canal

(arrows in d)


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Bagherian et al. 2010). Overall, it may be inferred that the

external and internal anatomy of the primary maxillary first

molar roots closely resembles the primary maxillary sec-

ond molar roots (Hibbard and Ireland 1957; Goodacre

2003; Cleghorn et al. 2012). Despite the fact that ana-

tomical anomalies have been also reported in this group of

teeth, such as additional roots and taurodontism (Caceda

et al. 1994; Kavanagh and O’Sullivan 1998; Johnston and

Franklin 2006), they were not observed in this sample. The

incidence of fusion between palatal and DB roots was

observed in 40 % of the teeth, while in the literature it was

reported as being 77.7 % (Bagherian et al. 2010), 53.5 %

(Zoremchhingi et al. 2005), and 29 % (Hibbard and Ireland

1957) of the sample. Some variations in the number and

shape of canal systems have also been described in the

primary maxillary molars (Hibbard and Ireland 1957;

Goodacre 2003; Zoremchhingi et al. 2005; Bagherian et al.

2010; Cleghorn et al. 2012). Most studies have found only

one root canal in each root of both molar types (Hibbard

and Ireland 1957; Zoremchhingi et al. 2005; Aminabadi

et al. 2008; Bagherian et al. 2010). However, the incidence

of a double canal system in the MB root was reported in

Fig. 3 Exemplary cross

sections of the M mesial,

D distal, MB mesio-buccal, DB

disto-buccal, and P palatal roots

of the mandibular (a) and

maxillary (b) primary molars,

showing the complexity and the

large dimensions of the root

canal system in the apical third

Table 4 Percentage frequency of root canal shape in each root of the primary maxillary and mandibular molars

n Root canal Round Oval Flat-oval Ribbon Irregular

Mandibular

First molar 10 M 30 – 10 50 10

D 30 10 10 40 10

Second molar 10 M 30 – – 60 10

D 40 – 20 40 –

Maxillary

First molar 10 MB 10 10 20 50 10

DB – 50 50 – –

P 20 80 – – –

Second molar 10 MB 20 10 20 40 10

DB – 40 60 – –

P 30 70 – – –



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6.7 % (Zoremchhingi et al. 2005), 7.4 % (Bagherian et al.

2010), and 35 % (Hibbard and Ireland 1957) of the sample

and, in the DB root, in 3.7 % of the specimens (Bagherian

et al. 2010). In the present study, a double canal system

was observed only in the MB root of two maxillary first

molars. A previous study has found that the mean lengths

of the MB, DB and palatal roots of the primary maxillary

first molar were 8.8, 8.2 and 7.8 mm, respectively, and inthe maxillary second molars 10.8, 9.7 and 10.8 mm,

respectively (Goodacre 2003), which were higher than the

present results. The lowest dimension of the palatal root in

the maxillary first molar (5.96 mm) reflected the volume

and surface area of the canal, which were significantly

lower than the palatal canal of the second molar. The

surface area of the DB canal in the second molar showed

significantly higher values than in the first molar, despite

the similar mean length between them. An explanation can

be found in the analysis of the 2D parameters, which

showed higher values of area, major and minor diameters

in the DB canal of the second molar.The SMI describes the plate- or cylinder-like geometry

of an object. If a perfect plate is enlarged, the surface area

does not change, yielding an SMI of zero. However, if a

rod is expanded, the surface area increases with the volume

and the SMI is normed, so that perfect rods are assigned an

SMI score of 3 (Peters et al. 2000). In the mandibular

molars, the mean SMI values varied from 1.69 to 2.06

indicating that the root canal system of the mesial and

distal canals, in both molars, had flat cone-shaped geom-

etry. In the maxillary molars, the mean SMI values of the

canals in most of the specimens were higher than 2.08

indicating a conical shape geometry. The cross-sectional

appearance of the root canal in the apical third was eval-

uated using the so-called morphometric parameter of

roundness. In mandibular molars, mean roundness ranged

from 0.31 to 0.49, which means that the root canal was

more flat shaped. In the maxillary molars, the lowest range

of values observed in the MB root of the second molar

(0.26–0.33) indicated a ribbon-shaped canal and reflected

its SMI data (1.81 ± 0.61). On the other hand, DB and P

root canals, as well as MB canal of the first molar, were

more oval shaped considering that the roundness ranged

from 0.38 to 0.63.

The wide range of variations reported in the literature

regarding the anatomy of the root canal system of primary

molars, in comparison to the present results, has been

mostly related to the diversity in sample origin, racial

factors, the relatively small number of teeth in each group,

the presence of initial apical root resorption in some

specimens and, of course, to the methodological approach

(Cleghorn et al. 2012). On the other hand, the micro-CT

experimental model presented here overcomes several

limitations displayed by the aforementioned conventional

methods, as it provides useful 2D and 3D information

related to the root canal space without changing the ori-

ginal sample. Unfortunately, these morphometric analyses

cannot be compared to others because of the lack of similar

reports in the literature to date.

Effective root canal debridement relies on accurate

determination of the working length and adequate apical

canal enlargement, which allow for better irrigation in theapical area, optimising root canal disinfection (Fornari

et al. 2010). In the present study, major and minor diam-

eters of the root canals in the apical third indicated that the

debridement at this level could be improved with instru-

ments up to an ISO size 100. However, considering the

shape of the root canals, the reduced thickness of the

dentine walls, and the difficulty in predicting the location

of the canal terminus accurately in primary teeth (Beltrame

et al. 2011), using instruments of this size would definitely

lead to stripping or perforations of the roots. Clinically, 2D

data results have definite implications for shaping and

cleaning procedures, because only the minor diameter isevident on radiographs. Thus, clinicians must be aware of

the anatomical configuration of the canals which, combined

with the presence of thin isthmuses in the apical region,

would compromise adequate cleaning and shaping, leaving

untouched fins on the buccal and/or lingual aspects of the

canal.

The introduction of nickel–titanium rotary file systems

has resulted in a marked progress in the mechanical prep-

aration of the root canal space (Hülsmann et al. 2005).

However, shaping root canals with these systems has failed

in debriding flat- and oval-shaped canals, leaving untou-

ched fins or recesses on the buccal and/or lingual exten-

sions (Versiani et al. 2011, 2013). Besides, large tapered

rotary files should be avoided in primary mandibular

molars considering their internal anatomical configuration.

Recently, Self-Adjusting File (SAF; ReDent-Nova, Ra’a-

nana, Israel) cleaning–shaping–irrigation system was

introduced. This innovative instrument consists of a hollow

and lightly abrasive nickel–titanium file composed of a

metal lattice, which adapts itself to round, oval, or even

long-oval cross sections of root canals. During its opera-

tion, which lasts 4 min, SAF removes dentine with a back-

and-forth grinding motion by scrubbing the canal walls

with a continuous irrigation provided by a peristaltic pump,

i.e. it simultaneously performs the mechanical and chem-

ical preparation of the root canal space (Metzger et al.

2010). Previous reports have shown that the SAF system

was advantageous in promoting cleaning, shaping, and

disinfection of oval-shaped canals in permanent teeth

compared to rotary files (Siqueira et al. 2010; Versiani

et al. 2011, 2013; Ribeiro et al. 2013), and may be an

alternative for shaping procedures in primary molar teeth to

be evaluated in further studies.


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Conclusion

Under the limitations of this ex vivo study, it was possible

to conclude that external and internal anatomy of the pri-

mary first molars closely resembles the primary second

molars. Considering the morphology of the canals in the

apical third, a careful selection of instruments including the

use of additional disinfection supplements such as passiveultrasonic irrigation or negative apical pressure is advis-

able. The reported data may help clinicians to obtain a

thorough understanding of the variations in root canal

morphology of primary molars to overcome problems

related to shaping and cleaning procedures.

Conflict of interest The authors declare that they have no conflict

of interest.

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Fumes Et Al. 2014 [Deciduous Teeth]