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Clinical evaluation of Root ZX II electronic apex locator in primary teeth.


A major objective of modern day dentistry is to maintain the integrity of the primary dentition until normal exfoliation [Katz et al., 1996]. Pulpectomy is an important treatment option in primary teeth with irreversibly infected or necrotic pulps due to caries or trauma. The location of the actual apical foramen in primary teeth, which are in the process of physiological root resorption, poses a great challenge to clinicians [Sim, 2004].

Traditionally radiographs have been the principal tool for determining primary root canal lengths prior to pulpectomy. However, root resorption and superimposition of permanent successors over primary root apices may obscure root canal length determination through radiographs. In addition, the quality of radiographs is highly dependent on the patient's cooperation, may lengthen appointment time and expose patients to ionizing radiation [Ghaemmaghami et al., 2008]. Technological advances have led to the introduction of digital radiography that allows a substantial reduction of radiation dose and duration of endodontic procedures. The main disadvantage of digital as well as conventional radiography is that they provide only a two dimensional image and assessment of small areas of resorption is difficult [Horner et al., 1990].

Sunada [1962] introduced an electronic method for measuring the root canal length, using a direct current device to overcome the shortcomings of the radiographic technique. His tests were based on the fact that the electrical resistance between the mucous membrane and the periodontium is constant regardless of a patient's age, or the shape and type of tooth involved [Sunada, 1962]. Yet his results were inaccurate, particularly in the presence of fluids and in wide apical foramina. To overcome these shortcomings, improvements such as alternating current apex locators were introduced. These second generation apex locators were of the single frequency impedance type and the major disadvantage was that the root canal had to be reasonably free of electro-conductive materials, as they change the electrical characteristics and lead to inaccurate measurements [Moshonov and Goldberg, 2004]. Later third generation EALs were developed to overcome inaccuracies in measurements owing to the presence of conductive liquids in the canal. They work on the principle based on the simultaneous measurement of impedance of two different frequencies as introduced by Kobayashi [Kaufman et al., 2002].

The Root ZX is the most popular and frequently tested third generation EAL. It does not require any adjustment or calibration and can be used in root canals containing electrolytes (moist) and dry canals. Several studies have shown a combined accuracy of 90% within [+ or -] 0.5mm of the apical foramen in different clinical conditions using the Root ZX [Ounsi and Naaman, 1999]. The new EAL Root ZX II is marketed with a canal measurement module as well as a low speed handpiece module which helps in the preparation of the root canal while simultaneously taking working length measurements.

Apex locators offer the potential to reduce patient exposure to ionizing radiation and serve as a useful adjunct. However, information regarding their clinical validity in root canal length determination of the primary dentition is limited. Therefore, the aim of this clinical study was to evaluate the accuracy of Root ZX II EAL in root canal working length determination of primary maxillary incisor teeth.

Materials and methods

Children aged 3-6 years attending the out-patient department of Paediatric Dentistry were included in the study. Forty primary maxillary incisor teeth with irreversibly infected or necrotic pulp tissue and completely formed roots were included in the study. Teeth with radiographic evidence of root resorption or bone loss were excluded from the study. Ethical clearance was obtained from the ethical committee of Vishnu Dental College, India. Informed written consent was signed by the parent or guardian of all the children who were included in the study.

Local analgesia was administered if required, and the study teeth were isolated with rubber dam. Endodontic access was made with #2 round carbide bur and the pulp extirpated with barbed broaches. Root canal irrigation was performed with 1% sodium hypochlorite and sterile saline and the excess fluid was removed with absorbent points. Root ZX II EAL with low speed handpiece module (J. Morita, Tustin, CA, USA) was used to estimate the working length according to the manufacturer's protocol. The lip clip was attached to the patient's lip and the electrode was connected to measuring No.15 K-type stainless steel file with a rubber stopper. The file was advanced into the canal until the LCD screen indicated "APEX" and then slowly retracted until the device signaled 0.5mm short of the apex. The rubber stopper on the inserted file was then set to the incisal reference point. Later the file was removed, measured with an Endogauge (Dentsply Maillefer) and registered as the electronic working length (EL).

The working length obtained with EAL was evaluated using digital radiography (intra-oral sensor, size #0, dimension of 32.5 x 25.6 mm, (Dr. Suni, Medical Imaging Incl, Sanjose, CA, USA) with the measuring file set to EL. Paralleling cone technique was practiced by using an extended cone paralleling (XCP) holding device (Dentsply) with a custom made sensor holder. Based on the position of the file tip to the radiographic apex on the digital radiographic images, the samples were categorised using the following criteria: Group 1: "Acceptable" indicating file tip 0-1mm short of the radiographic apex; Group 2: "Short" indicating file tip > 1mm short of the apex and Group 3: "Long" indicating the file tip beyond the apex. In the digital radiograph, the distance between the file tip and the radiographic apex was measured by using XvA3 Software (3.5version). Digital radiographic working length (RL) was derived by adjusting the distance measured from the file tip to the radiographic apex using digital radiography software.


The above mentioned procedure was performed for all of the 40 teeth and they were categorised accordingly. The assigned calibrations were tabulated (Table 1) and subjected to Pearson correlation coefficient statistical analysis.

Group 1 included 28 teeth out of 40 in the "Acceptable" range where the file tip was 0-1mm short of the radiographic apex. The file tip fell "Short" by >1 mm (Group 2) from the radiographic apex in 10 teeth and in 2 teeth it was found to be beyond "Long" the apex (Group 3) (Table 2).

When the clinical tolerable range of 0-1mm short of radiographic apex was applied, the Root ZX II EAL located the radiographic apex within the acceptable range in 28 teeth for a clinical accuracy of 70%. In 10 teeth the files were positioned short of the apex which accounted for 25% and only in two teeth which accounted for 5% of the cases were longer than the defined limit.

Pearson correlation coefficient statistical analysis was performed for assessing the relationship between the EL and the derived RL which showed a strong correlation (r = +0.82; p = <0.001) among the groups (Figure 1).



The working length determination is a critical step during root canal treatment in primary teeth due to possible damage to the permanent successor tooth germ [Katz et al., 1996]. The root canal anatomy of primary teeth is difficult to predict because of the possible presence of physiological root resorption. In addition, pulp and periodontal inflammation may further complicate the anatomy [Kielbassa et al., 2003].

The increased concern over radiation exposure and the use of electronically stored patient records have led to the introduction of digital radiography [Gordon and Chandler, 2004]. Utilising an intra-oral sensor in place of the radiographic film. Their advantages over the conventional radiographs are: computers can enhance the contrast and brightness of the image, magnify the apical zone, store and transmit the image. Other advantages include the ease of repetitions, elimination of chemical usage and use of the image for patient education [Versteeg et al., 1997]. Hence, digital radiography was considered over conventional radiography to assess the accuracy of EAL in the present study.

In recent years, EALs have been developed for determining the length of the root canal, which may be helpful to overcome the shortcomings of radiographic examination in teeth with resorption [Athar et al., 2008]. However, the use of EALs in teeth with apical resorption is under question because of the possible destruction of the apical constricture and the loss of the surrounding periodontal tissue. Goldberg et al. [2002] showed that the accuracy of the Root ZX in determining working length measurements in teeth with apical resorption was accurate in 62.7% of the cases with a clinical tolerance of [+ or -]0.5mm. However, Shabahang et al. [1996] reported that the Root ZX could locate the root end consistently, even with the resorption lacunae'. In addition, the root canal working length determination with EAL is easier, faster, painless and can be indefinitely repeated without exposure to radiation. It is extremely useful in children who gag during radiography [Subramaniam et al., 2005].

Primary maxillary incisors with irreversibly infected or necrotic pulp tissue and without any radiographic evidence of root resorption were included in this study because of their single root canal and ease of accessibility. Furthermore, previous studies emphasised that factors like the type of root canal (incisor or molar), status of the pulp (vital/necrotic) and status of periapical region (partial resorption) did not influence the working length determination [Angwaravong and Panitvisai, 2009]. The Root ZX as well as the newer Root ZX II units were able to accurately determine the root canal lengths of single rooted as well as multi-rooted primary teeth with or without physiological root resorption [Leonardo et al., 2008; Odabas et al., 2011]

Several previous investigations indicated that the accuracy of the Root ZX EAL was not influenced by the kind of electrolyte, type or size of the metal file in the canal [Ebrahim et al., 2006]. In the present study, 1% sodium hypochlorite was used for irrigating the root canals following pulp extirpation because of its widespread use as an intra-canal irrigant.

The accuracy of an EAL is routinely assessed by measuring the distance from the file tip to three different reference points; apical foramen, apical constriction or radiographic apex. Wrbas et al. [2002] have shown that the exact determination of the file tip or the actual root canal length is only possible if the teeth are histologically examined after extraction. Nevertheless, in the clinical situation, the radiographic apex is considered as the reliable endpoint, since the anatomical landmarks may not be detectable in the root canal [Hoer and Attin, 2004].

During electronic length determination in this study, the file was advanced into the canal until the apex locator indicated "Apex" and then slowly retracted until the device signaled 0.5mm short of the apex. Weiger et al. [1999] suggested that the use of the Root ZX meter reading '0.5 bar' gave more accurate measurements than the meter reading 'Apex' in permanent teeth. In contrast, Ounsi et al. [1999] reported that reading 'Apex' gave more accurate measurements than meter reading '0.5 bar'. An in vitro study in primary teeth showed that the 'Apex' setting tended to overestimate the root canal length [Elayouti et al., 2009].

We employed the paralleling cone technique during the radiovisiography (RVG) procedure by using a custom made acrylic sensor holder along with the XCP positioning device to minimise dimensional distortion [Sanabe et al., 2009]. The traditional method of determining the root canal working length is to place a file 0.5mm short of radiographic apex in permanent teeth [Pratten and McDonald, 1996]. In primary teeth without a well defined apical constriction, a tolerance of 1mm short of the apical constriction is regarded as clinically acceptable [Gordon and Chandler, 2004; Nelson-Filho et al., 2010].

We have determind a clinical tolerance of 0-1 mm of the radiographic apex as the acceptable range. Accordingly, it was found that in 28 (70%) of the 40 teeth the file tips were in the acceptable range and these findings are in accordance with previous studies [Ghaemmaghami et al., 2008; Leonardo et al., 2009]. However, other studies in primary teeth have shown that even 2 to 3 mm short of the radiographic apex is acceptable [Katz et al., 1996]. If a clinical tolerance of 2-3 mm short of the apex is taken into consideration in this study, 38 out of 40 teeth would fall into the acceptable range accounting for an overall success of 95%. There was a high correlation among EAL and digital radiographic readings indicating that both were equally effective in determining the root canal length.


Root ZX II EAL seems to be a reliable device for obtaining the root canal length in primary maxillary incisor teeth and can be used as an alternative to radiographic techniques. EAL can be recommended in primary incisor teeth since it is more convenient, quick, safe, painless, accurate and without radiation exposure. However, further evaluation of the accuracy of EALs is required in primary teeth under different clinical conditions.


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S. Sarithau, K.S. Uloopi, C. Vinay, R. Chandra Sekhar, V.V. Rao

Department of Paediatric Dentistry, Vishnu Dental College, Andhra Pradesh, India

Postal address: Dr.K.S. Uloopi, Dept Paediatric Dentistry, Vishnu Dental College, Bhimavaram--534202, Andhra Pradesh, India.

Table 1: Mean ([+ or -] SD) electronic apex locator (EAL) and
radiovisiographic (RVG) working length (mm) measurements (WL).

Tooth     No of       WL with EAL           WL with RVG
  No      teeth    Mean [+ or -] SD      Mean [+ or -] SD

  51        9     15.83 [+ or -] 0.75   16.83 [+ or -] 0.66
  52       10      14.7 [+ or -] 0.63    14.7 [+ or -] 0.63
  61       13     16.73 [+ or -] 1.21   17.19 [+ or -] 0.95
  62        8     14.37 [+ or -] 1.52   14.39 [+ or -] 0.99
Overall    40     15.55 [+ or -] 1.32   15.93 [+ or -] 1.49

Table 2: Distribution of teeth according
to the scoring criteria


GROUP 1      0-1 mm short of       28
ACCEPTABLE   radiographic apex

GROUP 2      > 1 mm short of       10
SHORT        radiographic apex

GROUP 3      Beyond the apex       02
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Author:Saritha, S.; Uloopi, K.S.; Vinay, C.; Sekhar, R. Chandra; Rao, V.V.
Publication:European Archives of Paediatric Dentistry
Article Type:Report
Geographic Code:9INDI
Date:Feb 1, 2012
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