International Endodontic Journal - Primary Molars Endodontic Treatment
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REVIEW
Anatomical challenges, electronic working lengthdetermination and current developments in rootcanal preparation of primary molar teeth
H. M. A. AhmedDepartment of Restorative Dentistry, School of Dental Sciences, Universiti Sains Malaysia, Kelantan, Malaysia
Abstract
Ahmed HMA. Anatomical challenges, electronic working
length determination and current developments in root canal
preparation of primary molar teeth. International Endodontic
Journal, 46, 1011–1022, 2013.
Paediatric endodontics is an integral part of dental
practice that aims to preserve fully functional primary
teeth in the dental arch. Pulpectomy of primary
molars presents a unique challenge for dental practi-
tioners. Negotiation and thorough instrumentation of
bizarre and tortuous canals encased in roots pro-
grammed for physiological resorption are the main
challenges for this treatment approach. Consequently,
numerous in vitro and in vivo studies have been
conducted to validate the application of some con-
temporary endodontic armamentarium for effective
treatment in primary molars whilst maintaining
favourable clinical outcomes. Electronic apex locators,
rotary nickel–titanium files and irrigation techniques
are at the forefront of endodontic armamentarium in
paediatric dentistry. Hence, this review aims to map
out the root and root canal morphology of primary
molars, to discuss the application of electronic apex
locators in primary molars and to provide an update
on the preparation of their root canal systems.
Keywords: apex locator, deciduous molars, irriga-
tion, primary molars, root, rotary NiTi files.
Received 5 January 2013; accepted 22 April 2013
Introduction
Despite advances in the prevention of dental caries in
paediatric dentistry, the occurrence of pulpally
involved primary (deciduous) teeth and their prema-
ture loss continues to be a common problem (Ahamed
et al. 2012). Pulpectomy of primary teeth with irre-
versibly inflamed or necrotic pulp is a reasonable
treatment approach to ensure either normal shed-
ding/eruption of the successor or a long-term survival
in instances of retention. Primary molars scheduled
for total pulpectomy continue to present a unique
challenge to dental practitioners because of the
tortuous and bizarre morphology of their root canal
systems, as well as difficulty in patient management
and isolation.
Current advances in pulpectomy procedures indicate
a remarkable paradigm shift in root canal treatment
for primary teeth. Whereas many manufacturers strive
to provide more convenient armamentarium for paedi-
atric endodontics, the potential of different diagnostic
instruments and root canal preparation techniques
used for permanent dentition to ensure accurate
assessment and proper endodontic management of
primary teeth has been examined. The use of electronic
apex locators, rotary nickel-titanium (NiTi) files and
irrigation techniques are at the forefront of advances in
pulpectomy procedures. Hence, this review aims to
map out the root and root canal morphology of
primary molars, to discuss the application of electronic
apex locators in primary molars and to provide an
update on the preparation of their root canal systems.
Correspondence: Dr Hany Mohamed Aly Ahmed, Department
of Restorative Dentistry, School of Dental Sciences, Universiti
Sains Malaysia, Kubang Kerian, 16150 Kelantan, Malaysia
(e-mail: hany_endodontist@hotmail.com).
© 2013 International Endodontic Journal. Published by John Wiley & Sons Ltd International Endodontic Journal, 46, 1011–1022, 2013
doi:10.1111/iej.12134
1011
Anatomical challenges
Root and root canal morphology
Literature search methodology
An electronic search was conducted in PubMed and
Google Scholar search engines, spanning the period
from January 1972 to September 2012, to identify
the available clinical and laboratory investigations
written in English language and published on the
number of roots and root canals in primary molars
using the following keywords: (‘deciduous molar’ OR
‘primary molar’) AND (‘root anatomy’ OR ‘root
morphology’ OR ‘root canal anatomy’ OR ‘root canal
morphology’). Cross citations of the selected articles
were identified. In addition, another search was
undertaken in endodontic textbooks to identify any
additional investigations on the root and root canal
morphology of primary molars (Tables S1 and S2).
Maxillary molars
The literature shows that primary maxillary molars
may have two to four roots, with the three-rooted vari-
ant being the most common (Table S1) (Fig. 1a,b). The
double-rooted variant, in which the distobuccal root is
fused with the palatal root, is also common, especially
in maxillary first molars (Table S1) (Fig. 1c–k).
The prevalence of a second canal in the mesiobuc-
cal roots of maxillary molars varies considerably.
A second mesiobuccal root canal reportedly occurs
between 75% and 95% of the mesiobuccal roots in
maxillary molars (Sarkar & Rao 2002, Camp & Fuks
2006). In addition, three mesiobuccal canals have
been documented (Carlsen 1987) (Fig. 1h–k).
By contrast, Aminabadi et al. (2008) did not
observe any second mesiobuccal canal in 76 maxil-
lary molars treated by a single paedodontist, and
Zoremchhingi et al. (2005) found only 6.67% and
53.3% of maxillary first and second molars with sec-
ond mesiobuccal canals, respectively. Bagherian et al.
(2010) observed only two samples of 27 cleared max-
illary first molars with a second mesiobuccal canal
(Type IV(2-2), Vertucci’s classification), and maxillary
second molars did not have additional root canals in
the mesiobuccal root.
The distobuccal root in maxillary molars normally
has a single root canal; however, the occurrence of a
second distobuccal canal has been reported (Table
S1), which can reach 27.8% (Aminabadi et al. 2008).
Similarly, the palatal root usually has one root canal;
however, the occurrence of a second palatal canal
has been reported in primary second molars (Carlsen
1987), which can be rather common (Zoremchhingi
et al. 2005). Fusion of the distobuccal and palatal
roots is a common anatomical variation that report-
edly represents one-third of maxillary molars
(Zoremchhingi et al. 2005, Camp & Fuks 2006), The
encased root canals range from one to three (Table
S1) (Fig. 1e–g).
Mandibular molars
Primary mandibular molars can have one to three
roots; the double-rooted variant is the most common
(Table S2). Accessory roots in primary mandibular
molars, especially in second molars, were reported
amongst Danish, Japanese, Chinese, Taiwanese and
Korean population groups (Song et al. 2009, Liu et al.
2010, Tu et al. 2010). Song et al. (2009) demon-
strated the concurrent existence of an additional root
in the permanent first molar and either in the second
or in both second and first primary molars. Using the
field developmental theory, the authors explained this
relationship in which the formation of accessory roots
are controlled by certain fields affecting genes that
are mainly transcribed in the first permanent molar
area and often in primary molars because of their
similar period of development and crown morphology
(Song et al. 2009). Teeth that are distant from a key
tooth exhibit few characteristics of the field they
belong to, which is the reason for its common occur-
rence in primary second molars.
The mesial roots of primary mandibular molars
usually have two root canals (Table S2). Bagherian
et al. (2010) reported all double canals in the mesial
root of mandibular molars as type IV(2-2) (Vertucci’s
classification). However, Sarkar & Rao (2002) obser-
ved a high prevalence of three canals in the mesial
roots of mandibular first molars. In addition, the
occurrence of a single root canal, with less frequency,
in the mesial roots of mandibular molars has been
documented (Table S2). The distal root in mandibular
molars usually has one or two canals (Table S2).
Similar to the mesial root, Bagherian et al. (2010)
reported all double canals in the distal root of
mandibular molars as type IV(2-2) (Vertucci’s classifi-
cation). Distal roots with three canals have also been
reported (Table S2).
Clinical considerations
Based on the above, it can be concluded that the root
canal anatomy of primary molars varies considerably.
This could be explained by (i) secondary dentine
Primary molars: endodontic challenges and recent advances Ahmed
© 2013 International Endodontic Journal. Published by John Wiley & Sons LtdInternational Endodontic Journal, 46, 1011–1022, 20131012
formation and physiological root resorption can rec-
onfigure the root canal system (Rimondini & Baroni
1995) that may reach up to six canals (Fig. 1c–k).
(ii) The pulp and/or periodontal inflammation can
cause pathologic changes in this programmed physio-
logical root resorption and further complicate the
root–root canal morphology (Rimondini & Baroni
1995, Sarkar & Rao 2002). These important facts
should be taken into consideration prior to commenc-
ing root canal treatment in primary molars.
Dental practitioners should also be aware of the
various pulp and periodontal tissues intercommunica-
tion pathways in primary molars. In addition to the
apical foramen and large accessory canals (lateral
and furcation canals), dentinal tubule exposure due
to physiological root resorption may also cause struc-
tural alteration and increase the permeability of the
root surface to microbial toxins. Consequently, the
inter-radicular bone lesion in primary molars can be
found anywhere along the root or in the furcation
(a)
(d)
(h) (i) (j)
(e) (f) (g)
(k)
(b) (c)
Figure 1 (a,b) Three-rooted primary maxillary molar with root resorptions at the apex (black arrow) and middle third of the
root (white arrow). (c,d) Double-rooted primary maxillary molar with fused Db and P roots. (e) The orifice of the fused Db/P
root is ribbon in shape. (f,g) The fused Db/P root has three root canals. One in the Db and two in the P [Type IV(2-1)]. (h,k)
The Mb root of the double-rooted variant has three separate Mb canals. Total number of root canals is six. (Mb: Mesiobuccal,
Db: Distobuccal, P: Palatal).
Ahmed Primary molars: endodontic challenges and recent advances
© 2013 International Endodontic Journal. Published by John Wiley & Sons Ltd International Endodontic Journal, 46, 1011–1022, 2013 1013
area (Kramer et al. 2003, Dammaschke et al. 2004,
Koshy & Love 2004, Ahmed 2012).
The dental operating microscope can be used
adequately with cooperative children (Kotlow 2004).
However, some children are restless and/or unable to
sit still, scared of the equipment, or not willing to
submit to a long session. In cases with such chil-
dren, the use of dental loupes is preferred. After
placement of the rubber dam and complete deroofing
of the pulp chamber, a thorough exploration via an
endodontic explorer or size 8 or 10 K-file between
the root canal orifices is essential (Ahmed & Abbott
2012a, Ahmed & Luddin 2012). A small pre-curved
endodontic file can be used to identify root canal
bifurcations.
Other root and root canal abnormalities
In addition to the above-mentioned anatomical varia-
tions in primary molars, the occurrence of other root
and root canal anomalies has been documented.
Taurodontism, which is caused by the failure of Her-
twig’s epithelial sheath diaphragm to invaginate at
the proper horizontal level (Jafarzadeh et al. 2008),
was reported in primary molars, either unilateral or
bilateral in normal children or as a part of a syn-
drome (Terezhalmy et al. 2001, Johnston & Franklin
2006, Rao & Arathi 2006, Jafarzadeh et al. 2008,
King et al. 2010, Venugopal et al. 2010). Interest-
ingly, the prevalence of taurodontism in the primary
dentition can reach 9.0% in some population groups
(King et al. 2010). Rao & Arathi (2006) observed that
taurodontism, can affect the primary and permanent
molars simultaneously. This finding supports the field
developmental theory that was described with acces-
sory roots.
In extremely rare occasions, single-rooted primary
maxillary molars may occur (Ackerman et al. 1973,
Nguyen et al. 1996). Interestingly, Ballal et al. (2006)
reported on an endodontic management of a retained
single-rooted primary maxillary second molar with a
C-shaped canal. Fusion of primary molars has been
documented (Caceda et al. 1994). Dens invaginatus
in the primary dentition has also been reported (King
et al. 2010) and can affect primary molars (Eden et al.
2002).
Clinical considerations
Primary molars with abnormalities such as taurodon-
tism can be identified and classified from periapical
radiographs. Endodontic treatment of a primary
taurodont requires copious irrigation with sodium
hypochlorite (NaOCl) to ensure complete dissolution
of the pulp tissues that usually show excessive bleed-
ing (Jafarzadeh et al. 2008, Venugopal et al. 2010).
Ultrasonic irrigation can also be helpful. Magnifica-
tion and auxiliary illumination are preferred methods,
especially in meso- and hyper-taurodont categories.
The application of the resorbable paste using a dispos-
able injection technique can be useful (Bhandari et al.
2012).
The fusion of the distobuccal and palatal roots
in primary maxillary molars may result in the for-
mation of a ribbon like or C-shaped canal orifice
(Fig. 1e), which may extend to the apical portion.
With the exception of the isthmus, the root canals,
ranging from one to three, can be prepared nor-
mally. Careful enlargement of the orifice of the isth-
mus using a small ultrasonic tip would enhance the
penetration of the irrigant. Extravagant use of small
files and NaOCl is essential for proper debridement of
the isthmus (Jafarzadeh & Wu 2007). This should
predictably facilitate the penetration of the resorbable
paste into the isthmus.
Electronic working length determination
Determining the working length is an essential step
prior to pulpectomy in primary molars. This step
aims to maintain chemo-mechanical instrumentation
and subsequent filling within the confines of the
root canals, thus preventing any harm to both per-
iradicular tissues and the succeeding permanent
tooth germ (Gordon & Chandler 2004, Beltrame
et al. 2011).
Besides its crucial role in preoperative assessment,
periapical radiography is the most widely used
method for measuring the working length in primary
teeth. Despite this, studies recently demonstrated the
advantage of using various types of EALs as adjunct
measurement tools to overcome the limitations of the
radiographic procedure, which can only provide a
two-dimensional image (Table S3). This is of particu-
lar importance in roots programmed for uneven
physiological resorption which will often not be
detected accurately during radiographic interpretation
resulting in an increased risk of overinstrumentation
and overfilling (Harokopakis-Hajishengallis 2007,
Leonardo et al. 2008) (Fig. 2). EALs also reduce
radiation exposure and time. Thus, the treatment
procedure is more convenient to both the operator
and the child.
Primary molars: endodontic challenges and recent advances Ahmed
© 2013 International Endodontic Journal. Published by John Wiley & Sons LtdInternational Endodontic Journal, 46, 1011–1022, 20131014
Literature search methodology
An electronic search was conducted in PubMed and
Google Scholar search engines to identify the avail-
able clinical and laboratory investigations written in
English language and published on the application of
electronic apex locator in primary molars until
September 2012 (Table S3). The following keywords:
‘deciduous molar’ OR ‘primary molar’ AND ‘apex
locator’ were used. Cross citations of the selected
articles were also identified.
Numerous in vitro studies (Table S3) examined the
accuracy of EALs in primary molars at different envi-
ronmental conditions (dry, saline, and NaOCl) (Katz
et al. 1996), as well as with unresorbed roots and
roots at different levels of resorption. Roots with one-
sixth to one-third (Angwaravong & Panitvisai 2009),
one-third (Bodur et al. 2008, Odabas� et al. 2011),
one-half (Leonardo et al. 2009) or even up to two-
third root resorption (Pinheiro et al. 2012a) have
been examined. Most in vitro investigations reported
the high accuracy of different types of EALs at differ-
ent levels of resorption (Table S3). However, Bodur
et al. (2008) found that Root ZX (Morita, Tokyo,
Japan) and Endex (Osada, Tokyo, Japan) exhibited
only 63.4% and 48.4% accuracy within � 1 mm of
the visually determined root canal measurements in
resorbed roots, respectively.
In addition, Kielbassa et al. (2003) performed a
clinical investigation on 71 teeth, including 34
primary molars, of preschool children. The results
showed that the measurements were affected signifi-
cantly by different operators; however, the readings
were not affected by the tooth type, root canal type,
apex morphology (with or without resorption) or clin-
ical condition (vital or necrotic pulps). Other in vivo
studies demonstrated high levels of accuracy of EALs
with and without root resorption (Beltrame et al.
2011, Odabas� et al. 2011).
The Root ZX and Root ZX II (Morita) are the
most common EALs used in primary teeth (Table
S3). Related investigations of this brand did not fol-
low a single criterion in determining the working
length. For instance, Katz et al. (1996) mentioned
that the Root ZX was used as calibrated by the
manufacturer to measure the tooth length minus
0.5 mm. Meanwhile, Beltrame et al. (2011) evalu-
ated the working length by the indicated ‘0.0’ mark.
Angwaravong & Panitvisai (2009) compared the
Root ZX measurement metre readings at ‘0.5 bar’
and ‘Apex’ and found that the error in locating the
apical foramen was smaller at metre reading ‘Apex’
than ‘0.5 bar’. Leonardo et al. (2008) and Odabas�et al. (2011) selected the ‘1’ reading on the apex
locator’s display, which was based on the results of
a pilot study reported by Leonardo et al. (2008).
The results showed that this reading presented the
best correlation with the actual root canal length
measurement (visual method) at 1 mm short of the
root apex. The absence of a standardized measure-
ment technique led to conflicting results. Kielbassa
et al. (2003) reported the accuracy of Root ZX at
64%, whereas Odabas� et al. (2011) observed a
86.4–95.8% accuracy, with both findings showing
precision measurements at � 1 mm of the visually
determined root canal lengths.
(a) (b) (c)
Figure 2 (a) Buccolingual radiographic projection of a mesiobuccal root in a primary maxillary molar with uneven root
resorption. Radiographically, the endodontic file is located within the confines of the root. (b,c) The photographic images show
that the file (yellow arrow) is about 1 mm beyond the apical foramen (white arrow), which is located distally. The visually
determined working length is 3 mm short of the root apex.
Ahmed Primary molars: endodontic challenges and recent advances
© 2013 International Endodontic Journal. Published by John Wiley & Sons Ltd International Endodontic Journal, 46, 1011–1022, 2013 1015
Clinical considerations
Both in vitro and in vivo studies indicate that the appli-
cation of EALs in paediatric endodontics demonstrate
the following advantages: (i) accurate determination
of the working length; (ii) reduced tension amongst
the operator, child and family attributed to the
simplicity of the procedure (which is the opposite case
in radiographic examination, with cooperation from
children usually achieved with difficulty); (iii) reduced
exposure to radiation; (iv) shorter treatment time due
to favourable attitude and cooperation of children;
and (v) detection of root perforations resulting
from internal or external root resorption (Gordon &
Chandler 2004), which can be undetected radio-
graphically.
Current developments in the preparation
of root canal systems
Literature search methodology
An electronic search was conducted in PubMed and
Google Scholar search engines to identify the avail-
able clinical and laboratory investigations written in
English language and published on the application
of rotary nickel-titanium files in primary molars
until September 2012 (Table S4). The following
keywords: ‘deciduous molar’ OR ‘primary molar’
AND ‘rotary file’ OR ‘nickel titanium’ have been
used. Cross citations of the selected articles were
also identified. The irrigation techniques used in the
selected studies for rotary nickel-titanium files have
been listed (Table S4). Further electronic search was
undertaken to identify studies that used other irriga-
tion solutions–protocols. Finally, the pooled data are
discussed in the light of the American and United
Kingdom guidelines for pulpectomy procedures in
paediatric dentistry and current literature in end-
odontic research.
Mechanical instrumentation
The application of NiTi rotary systems in primary
molars has been investigated since the beginning of
the 21st century (Barr et al. 2000) (Table S4). A
study by Silva et al. (2004) examined the cleaning
ability of K-files (Dentsply Maillefer, Ballaigues,
Switzerland) and the ProFile system (Dentsply Tulsa
Dental, Tulsa, OK, USA) using a stereomicroscope and
scoring of remaining dye adhering to root canals of
the cleared samples. The results showed no significant
difference in the cleaning ability between both sys-
tems. However, the preparation time was reduced sig-
nificantly with the latter. This clinical advantage was
observed by Nagaratna et al. (2006) who found that
the canal preparation exhibited satisfactory taper and
smooth walls with the ProFile system; however,
instrument fracture was reported. The significant
reduction in the preparation time also was demon-
strated with other NiTi rotary systems (Table S4). On
the contrary, Madan et al. (2011) reported a shorter
preparation time with K-files than the ProFile system,
which might be attributed to insufficient operator
experience with the rotary system.
Canoglu et al. (2006) compared the ProFile system
with hand and ultrasonic K-files. Although the results
were not significantly different in terms of shaping
effectiveness, ultrasonics significantly increased the
incidence of zip formation and decreased the working
length. Despite this occurrence, Da Costa et al. (2008)
reported a high success rate (94%) with ultrasonic
instrumentation after clinical and radiographic assess-
ment for a mean follow-up of 14.1 months.
Kuo et al. (2006) introduced a modified time-saving
protocol for the treatment for primary teeth in two
sessions. The guideline starts with a size 10 K-file fol-
lowed by two files (SX and S2) of the ProTaper NiTi
rotary system and then finishing the preparation with
size 25 or 30 H-files (Table S4). Based on both clinical
and radiographic evaluation, the 12-month follow-up
showed a success rate of 96%. Despite this favourable
finding, this protocol requires modifications for teeth
undergoing physiological root resorption in which lar-
ger sizes and greater tapers are indicated (Kuo et al.
2006).
Recently, Azar et al. (2012) suggested another
modified sequence for ProTaper (S1, S2, F1) and com-
pared the cleaning capacity of that sequence with
Mtwo NiTi rotary system (VDW, Munich, Germany)
and hand files using a method similar to that
described by Silva et al. (2004). All systems were
found to have acceptable cleaning ability. A study by
Pinheiro et al. (2012b) compared another sequence of
ProTaper (S1, S2, F1, F2) with hand files and a
hybrid system comprising a number of hand K-files
and ProTaper rotary files (Table S4). The hybrid tech-
nique required a longer preparation time than the
manual and rotary systems, but showed the greatest
reduction in Enterococcus faecalis. This reduction may
be due to increased exposure of the organism to the
irrigant [Endo-PTC (urea peroxide + Tween 80 + Car-
bowax, Formula & Ac�~ao, S~ao Paulo, Brazil) and 0.5%
Primary molars: endodontic challenges and recent advances Ahmed
© 2013 International Endodontic Journal. Published by John Wiley & Sons LtdInternational Endodontic Journal, 46, 1011–1022, 20131016
NaOCl], supplemented by the simultaneous action of
the manual and rotary instruments.
Another study evaluated the instrumentation
behaviour of Hero 642 (Micro-Mega, Besanc�on,France) in primary teeth (Kummer et al. 2008). In
addition to the significant decrease in instrumentation
time reported, canal instrumentation exhibited regu-
larity and uniformity. However, iatrogenic perfora-
tions in the middle third of some resorbed roots were
observed in both rotary and manual systems, espe-
cially in mesial and distal roots of mandibular molars
as well as the mesiobuccal roots of maxillary molars
having second mesiobuccal canals.
Moghaddam et al. (2009) compared the FlexMaster
rotary NiTi system (VDW, Munich, Germany) with
the manual K-files (Dentsply Maillefer). The mean
preparation time–canal was reported as short as
2.07 min in the rotary system compared with
5.55 min for the manual. The cleaning efficacy was
examined for all cleared samples after scoring the
remaining dye observed via a stereomicroscope. The
results showed that the cleaning efficacy in the apical
and middle thirds was comparable; however, the
coronal third was more efficiently cleaned with hand
files than with the rotary system.
Root canal irrigation
Experimental studies summarized in Table S4 indicate
that NaOCl, especially at 1% concentration, is the
most commonly used irrigant in primary molars
(Silva et al. 2004, Canoglu et al. 2006, Kummer et al.
2008, Madan et al. 2011, Ochoa-Romero et al. 2011,
Pinheiro et al. 2012b), which is recommended by the
American Association of Pediatric Dentistry (AAPD
2012). The use of normal saline is also common
(Nagaratna et al. 2006, Moghaddam et al. 2009, Azar
& Mokhtare 2011, Azar et al. 2012), which is docu-
mented in the United Kingdom national guidelines in
paediatric dentistry (Rodd et al. 2006).
The literature also demonstrates the application of
other irrigation solutions in paediatric endodontics
such as hydrogen peroxide (Moskovitz et al. 2005),
Dakin’s solution (0.5% NaOCl neutralized with boric
acid) (Pascon & Puppin-Rontani 2006, Pascon et al.
2007) and chlorhexidine (CHX), which has the ability
to reduce the bacterial loading in pulpectomized pri-
mary teeth (Ruiz-Esparza et al. 2011). In addition, the
combination of CHX with NaOCl was attempted to
maintain both tissue-dissolving capacity and antimi-
crobial substantivity (Ramar & Mungara 2010). A
comparison by Tirali et al. (2012) indicated that 0.1%
octenidine dihydrochloride exerted more antibacterial
activity against E. faecalis cultured in extracted
primary teeth compared with 2% CHX and 5.25%
NaOCl. The application of CarisolvTM (MediTeam,
Goteborg, Sweden) has also been investigated, and
the SEM images at the middle and coronal thirds con-
firmed its ability to obtain comparable results with
1% NaOCl at liquid and gel formulations; however,
NaOCl solution showed the least mean debris score at
the apical third (Singhal et al. 2012).
The smear layer is an amorphous layer with a
thickness of 2–5 lm and consists of inorganic and
organic components, including remnants of odonto-
blastic processes, pulp tissue, microorganisms and
their metabolic products (Violich & Chandler 2010).
The differences in the micromorphological features
between primary and permanent teeth indicate that
the thickness and composition of the smear layer of
the instrumented root canals in both dentitions may
vary. Current practice prefers the removal of smear
layer with necrotic pulps. Consequently, smear layer
removal from pulpectomized anterior and posterior
primary teeth was investigated (Salama & Abdelmegid
1994, G€otze et al. 2005, Canoglu et al. 2006, Nelson-
Filho et al. 2009, Hariharan et al. 2010, Tannure
et al. 2011, Barcelos et al. 2012, Pascon et al. 2012).
Results showed that 6% citric acid as a final rinse
after irrigation with NaOCl caused no damage to the
root dentine of primary molars (G€otze et al. 2005)
and improved clinical outcomes (Barcelos et al.
2012). Final irrigation with 2% CHX, after 6% citric
acid, was recommended to potentiate the antimicro-
bial action and substantivity of CHX (Hariharan et al.
2010). In addition, the use of 17% EDTA for final irri-
gation improved the tubular penetration of sealers,
which provides a clinical advantage for retained pri-
mary molars (Canoglu et al. 2006). This was recently
confirmed by Pascon et al. (2012) who compared the
ability of NaOCl/EDTA and CHX/EDTA combinations
to remove the smear layer in the primary root dentine
and found that NaOCl/EDTA combination was the
best. However, in that study, NaOCl was used at
5.25% concentration, which is not recommended in
primary teeth.
Pascon & Puppin-Rontani (2006) investigated the
permeability of root dentine in primary molars
following the application of 1% and 2% CHX liquid,
Dakin solution alone or combined with urea peroxide.
Although 1% and 2% CHX liquid demonstrated the
highest permeability index (PI) (percentage of the dye
penetration area in root dentine), a low PI was
Ahmed Primary molars: endodontic challenges and recent advances
© 2013 International Endodontic Journal. Published by John Wiley & Sons Ltd International Endodontic Journal, 46, 1011–1022, 2013 1017
reported with 2% CHX at the gel formulation (Pascon
et al. 2007). Ultrasonic activation of CHX gel resulted
in higher PI averages than manual; however, the best
results were demonstrated with saline, Dakin solution
alone or combined with hydrogen peroxide cream
without ultrasonic activation. The effect of high PI on
the penetration of root canal filling materials and
microbial irritants requires further investigations.
The UK National Guidelines on Paediatric Dentistry
for pulpectomy procedure recommends irrigation with
normal saline (0.9%), CHX (0.4%) or NaOCl solution
(0.1%) (Rodd et al. 2006). According to the American
Academy of Pediatric Dentistry for pulpectomy proce-
dure (AAPD 2012), the chemo-mechanical procedure
with an inert solution alone cannot adequately reduce
the microbial population in a root canal system. The
same guideline also emphasized the importance of dis-
infection with irrigants such as 1% NaOCl and/or CHX
for optimal bacterial decontamination of the canals.
The related literature on irrigant concentrations
and interactions indicates that the current guidelines
and recommendations for pulpectomy in primary den-
tition should be revised. (i) NaOCl commonly used in
endodontics at concentrations between 0.5% and
5.25/6% (Zehnder 2006, Sch€afer 2007, H€ulsmann
et al. 2009, Haapasalo et al. 2010). Although the
most appropriate concentration remains controversial,
there is no evidence in the literature that NaOCl at
0.1% concentration would maintain effective tissue-
dissolving effect and potent antimicrobial activity. (ii)
The combination of NaOCl and CHX, even at small
concentrations, was found to produce a brown precip-
itate that may contain a significant amount of the
carcinogenic parachloroaniline (PCA) (either in the
precipitate or one of CHX breakdown products)
(Basrani et al. 2007, Nowicki & Sem 2011). This is of
particular concern in primary molars undergoing root
resorption where the possibility for irrigant extrusion
is high (Williams et al. 1995). This precipitate also
adheres to the tooth structure, causing tooth discol-
ouration, and acts as a residual film that may com-
promise the diffusion of intracanal medicaments and
proper adaptation of the root canal filling to the root
canal walls (Ahmed & Abbott 2012b).
Meanwhile, the combination of 2.5% NaOCl and
20% citric acid results in bubbling because of chlorine
gas formation (Baumgartner & Ibay 1987), and may
produce a white precipitate (Ahmed & Abbott
2012b), or the solution turns cloudy when 6% citric
acid is used. Further investigation is necessary to
validate the safety of the aforementioned combination.
In addition, Gonz�alez-L�opez et al. (2006) and Rasimick
et al. (2008) have reported interactions between CHX
and EDTA irrigants with the formation of white to
pink precipitate, although no PCA was detected.
Clinical considerations
Clinical research proved that rotary NiTi files can sig-
nificantly reduce the instrumentation time of the root
canals (Table S4). Consequently, NiTi rotary systems
gained an increase in application amongst American
Board of Pediatric Dentistry diplomates (Dunston &
Coll 2008). Despite the advantage of reduced instru-
mentation time with NiTi application, the significance
of adequate exposure time for the irrigant must be
emphasized, particularly in necrotic cases given that
root canal preparation is essentially a chemo-mechan-
ical procedure. Sufficient exposure time is necessary
to dissolve the remaining necrotic tissues completely
and eradicate the remaining microbial irritants in the
complex anatomy of the root canal system and
dentinal tubules (Retamozo et al. 2010), especially at
lower concentrations of NaOCl.
Apart from the high cost of NiTi rotary systems,
the fracture of rotary NiTi files in primary molars has
been reported (Nagaratna et al. 2006). The occasion
of files fracture in roots programmed for physiological
root resorption and in close proximity to permanent
tooth buds is of particular concern (Kuo et al. 2006).
A number of clinical epidemiological surveys show
that file fracture is one of the most prominent compli-
cations with NiTi rotary systems amongst general
dental practitioners and endodontists (Madarati et al.
2008, Bird et al. 2009, Mozayeni et al. 2011). How-
ever, the literature lacks similar clinical surveys
amongst paedodontists. Future studies are warranted
to identify the prevalence of file fracture in the
primary dentition and usage parameters of NiTi
rotary systems in paediatric endodontics.
Likewise, dental practitioners should carefully
choose irrigating solutions (Ahmed & Abbott 2012b,
Rossi-Fedele et al. 2012). Intermediate solutions such
as saline or sterile distilled water, followed by careful
drying, can prevent the formation of brown precipi-
tate when NaOCl and CHX are combined (Krishna-
murthy & Sudhakaran 2010). When removal of the
smear layer is indicated, the use of 6% citric acid or
18% EDTA between NaOCl and CHX may also block
the formation of a brown precipitate. However, using
saline or sterile distilled water as intermediate flushes
between every two successive irrigants remains essen-
Primary molars: endodontic challenges and recent advances Ahmed
© 2013 International Endodontic Journal. Published by John Wiley & Sons LtdInternational Endodontic Journal, 46, 1011–1022, 20131018
tial to prevent the formation of any possible interac-
tions. Notably, maleic acid (MA) has been found to be
less cytotoxic and more effective in smear layer
removal than EDTA (Ballal et al. 2009a,b), and the
combination of MA and CHX has not caused any
precipitate formation or discolouration (Ballal et al.
2011). However, further research is needed to
validate its use in primary dentition.
Concluding remarks
The root and root canal morphology in primary
molars shows considerable variations. Further investi-
gations are required to identify the prevalence of, and
the correlation between, a missed root and/or root
canal anatomy and failure in root canal treatment of
primary molars.
The literature supports the potential use of elec-
tronic apex locators in primary molars, regardless of
the stage of root resorption. This advantageous find-
ing would pave the way for its adoption amongst
paedodontists.
With an experienced operator, the use of rotary NiTi
files in primary molars is advantageous. However, fur-
ther studies are warranted to examine (i) the effect of
reduction in the preparation time on the efficacy of the
chemo-mechanical procedure and clinical outcomes,
(ii) the prevalence of file fracture and (iii) usage param-
eters of NiTi rotary systems in paediatric endodontics.
Dental practitioners should be aware of the chemical
interactions amongst endodontic irrigants, which must
be highlighted in the current guidelines for pulpectomy
procedures in paediatric dentistry. The recommended
preventive strategies should be strictly followed.
Conflict of interest
The author denies any conflict of interest.
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Supporting Information
Additional Supporting Information may be found in
the online version of this article:
Table S1 Summary of studies that demonstrated
the root canal morphology of primary maxillary
molars.
Table S2 Summary of studies that demonstrated
the root/root canal morphology of primary mandibu-
lar molars.
Table S3 Summary of in vivo and in vitro studies
that demonstrated the use of electronic apex locators
in primary molars.
Table S4 Summary of in vitro and in vivo studies
that demonstrated the use of rotary NiTi instruments
in primary molars.
Primary molars: endodontic challenges and recent advances Ahmed
© 2013 International Endodontic Journal. Published by John Wiley & Sons LtdInternational Endodontic Journal, 46, 1011–1022, 20131022
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