International Endodontic Journal - Primary Molars Endodontic Treatment

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REVIEW Anatomical challenges, electronic working length determination and current developments in root canal preparation of primary molar teeth H. M. A. Ahmed Department 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 nickeltitanium 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: [email protected]). © 2013 International Endodontic Journal. Published by John Wiley & Sons Ltd International Endodontic Journal, 46, 1011–1022, 2013 doi:10.1111/iej.12134 1011

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Anatomical challenge, electronic working length determination and current developments in root canal preparation of primary molar teeth

Transcript of International Endodontic Journal - Primary Molars Endodontic Treatment

Page 1: International Endodontic Journal - Primary Molars Endodontic Treatment

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: [email protected]).

© 2013 International Endodontic Journal. Published by John Wiley & Sons Ltd International Endodontic Journal, 46, 1011–1022, 2013

doi:10.1111/iej.12134

1011

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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

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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

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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

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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

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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

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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

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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

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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