Comparative assessment of a new electronic apex locator and radiographic measurement of root length in primary teeth:An in-vitro study.

INTRODUCTION

The success of pulpectomy relies upon exact measurement of the root length. Various methods are available for the measurement of root length, but the real method is not yet identified.¹ Traditionally, radiographic method was the primary tool for measuring root length. Radiologic root length measurement has several limitations. Radiographs lengthen treatment time, rely upon patient cooperation and cause radiation hazards.^1,2 The removal of entire pulp tissue, necrosed material and micro-organisms from the root canal is essential for the success of pulpectomy.³ Debridement, shaping and obturation is not successfull unless the root length is determined accurately.⁴ The determination of working length is very important in order to confine the instrumentation to the root canal system. Although radiographs are necessary and an integral part of endodontic treatment but there is an ongoing need to reduce exposure to ionizing radiation.1 Traditional methods for determining working length are (a) the anatomical averages and knowledge of root canal anatomy (b) tactile perception (c) moisture on a paper point and (d) radiographic method.³

Electronic apex locators(EALs) have attracted much attention these days. They were developed to get more precise measurement of root length and to provide the apical limit.⁵ They are widely used in permanent teeth. But very few studies are published on their usage in primary teeth. These studies have concluded that electronic apex locators are painless, safe & useful in children.^5,6 It is essential that all new apex locators should be evaluated for their accuracy in measuring the root lengths. Currently there are no reported studies on the efficiency of this new apex locator Propex Pixi (fifth generation) in determining the root length of primary teeth. Therefore, the goal of this research was to assess the accuracy of Propex Pixi and traditional radiographic method in measuring the root length of deciduous teeth by comparing with their exact root length.

MATERIALS AND METHODS:

This in-vitro research work was carried in the department of Pediatric and Preventive Dentistry after taking approval from the institutional ethical committee. Thirty extracted human single rooted (fig-1) maxillary and mandibular primary tooth samples were collected. The tooth samples were randomly selected based on the following inclusion and exclusion criterias¹ ;

Inclusion criterias¹ : a) Tooth removed because of extensive caries, serial extraction, trauma or parents unwillingness to save them, b) Presence of at least two thirds of the remaining root structure with minimal apical resorption.

Exclusion criterias¹ : a) Presence of root caries, root perforation and root fracture b) Presence of pulp calcifications c) Presence of external or internal root resorption.

Immediately after the extraction of the teeth they were cleaned under running water and then with 3% sodium hypochlorite. Then, the teeth were stored in normal saline. Later, the teeth were flattened up to cemento enamel junction to get a repeatable reference point. The canal patency was checked using a No.15 K-file (fig-2) and irrigated with normal saline. Two blinded and thoroughly calibrated examiners were then randomly selected to perform the following measurements.

Root length measurement by Propex Pixi (Dentsply Maillefer, Ballaigues, Switzerland); Simulation of in-vivo conditions was done by embedding the teeth in alginate model (1x1 inch plastic vessel) as explained by Kaufman⁷ . Stainless steel rod of 0.9mm was pierced in the alginate before it was set to give a connection to the contrary electrode (fig-3). Tooth samples were selected randomly and embedded in the alginate and numbered from 1-30. The alginate was continuously moistened by saline irrigation. The lip-clip (contrary electrode) was attached to the stainless steel rod and file holder clamped to the shaft of a no.¹⁵ K-file. The file with the rubber stopper was moved apically in the root canal till the sound beeps and the diode mark showed apex at “00” on the panel. The file was removed carefully and the readings were noted using a digital vernier caliper (0.02mm accuracy) and magnifying glass (10x) under a light illuminated viewing box. Readings were considered valid if the instrument is static for at least five seconds. Three readings were taken and average of these was recorded for each root.

Root length determination by conventional radiographic method (Ingle’s method)⁸ : The radiographic root length measurement was done with the paralleling cone technique (fig-4). An E-speed film (Intra-oral X-ray film, care stream health India Pvt. Ltd.) was used. The exposure factors 0.5sec at 60kvp and 7mA (Kodak 2100 intra-oral X-ray system) and the distances were standardized (source to film distance of 77 mm and object to film distance of 24mm). The film packet was placed in a film holder and positioned parallel to the tooth under study. The X-ray tube head was then aimed perpendicular (vertically and horizontally) to both the tooth and film packet (fig4). To make sure centered and accurate positioning of the teeth, a series of marks were made. Root length was measured on radiograph using the vernier caliper and magnifying glass(10x). Then, root length was measured on preoperative radiograph (fig-5), from this 1.0 mm was subtracted as “safety allowance” for possible image distortion or magnification. The scale was set at this tentative working length and stoppers were adjusted to this level. The instrument was placed in the canal at the point of reference plane and radiograph was taken in a bucco-lingual direction. On the intraoral periapical radiograph the difference between tip of the file and root end was measured. This difference was added (+) or subtracted (-) to the original pre-operative radiographic root length. From this adjusted length of the tooth 1.0mm was subtracted to conform to the apex at the cemento dentinal junction.

Actual working length determination by direct visual method: The actual measurements were taken by easy placement of a no.15 K-file (with stopper) within the root canal up to the apical foramen (fig6), this was observed under a magnifying glass (10x). Silicone stopper was then pushed to the upper reference limit to get the root length. The file was removed and root length was measured using digital vernier caliper and magnifying glass (10x). The procedure was repeated three times and mean was taken for each root. From this measured length 0.5mm was reduced to conform to the apical termination of the root canal.⁹ This, actual or direct visual measurement was taken as definitive standard value to which the Propex Pixi and the radiographic measurements were compared.

The comparison of Propex Pixi and the radiographic measurements with the gold standard actual value was done using student paired ‘t’ test, intra-class correlation coefficient (ICC) was done to get the confidence interval (CI) and correlation between the actual value, Propex Pixi and radiographic method. Regression analysis was carried out to anticipate the actual values using the electronic and radiographic values. The discrepancy between the two methods was calculated and statistically compared.

RESULTS:

The data entry was done and analyzed using Statistical Package for the Social Sciences (SPSS) software to obtain mean values and difference in mean values by actual, electronic and radiographic methods. The results obtained were expressed as mean ±SD and were subjected to further statistical analysis. Data was further analyzed using student paired‘t’ test, followed by regression analysis. “P” value was calculated. When “P” value was <0.05, it was taken as significant and when the “P” value was >0.05, it was taken as not significant.

Table-1 shows the mean and standard deviation of actual, electronic and radiographic measurement of root canal length. Table-2 shows the intra-group comparison of means and standard deviations of actual, electronic and radiographic methods. Average difference between electronic and actual measurement was 0.130 and “p” value of <0.019 which was significant. Mean difference between actual and radiographic measurement was 0.691 and “p” value of 0.032 which was significant.Mean difference between electronic and radiographic measurement was -0.154 and “p” value of 0.280 which was not significant.

As per the study results both the methods displayed a high correlation and agreement R= 0.947(0.904-0.986) and R= 0.826(0.667-0.913) with the actual measurement. On comparison the electronic and radiographic methods also showed high association and agreement (ICC=0.899) [table-2]. The radiographic method showed an accuracy of 60% within +0.5 mm and 83% within +1.0 mm, whereas the electronic method showed an accuracy of 96.6% within +0.5 mm and 100% within +1.0 mm. Regression analysis showed that Propex Pixi can anticipate the actual value with 94.3% accuracy [table-3] but the radiologic method can anticipate the actual value with 67.2% accuracy [table-4].

DISCUSSION:

Electronic root length measurement was first studied by Custer¹⁰ in 1918. This idea was revised by Suzuki¹⁰, he described about the flow of electric current through the dogs teeth. He found consistent values in electrical resistance between a device in the root canal and an electrode on the oral mucosa and speculated that this would measure the root canal length. Sunada¹¹ took these principles and constructed a simple device that used electric current for measuring the root length.^3,10,11 These devices attempt to locate the apical constriction, cemento dentinal junction or the apical foramen.

In primary teeth the exact root length measurement is essential to prevent injury to the underlying permanent tooth bud. Several radiographic limitations have been overcome by the use of electronic devices. The new generation electronic apex locators have high accuracy, high reliability and repeatability in locating the apex.¹ With the advancement of technology there are several modifications in apex locators, with limited information provided by manufacturers the classification of apex locators is a matter of controversy and ignorance.¹² Apex locators are classified into different generations (from first to fifth) depending on their working principles.^3,10,11,13 The shape of the apical portion is considered to be an inverted cone; its base is located at the major apical foramen and apex of the inverted cone coincides with the apical constriction which is present at or near the cemento dentinal junction.¹⁴

Electronic apex locators have become an indispensable component of root canal treatment. Radiographic methods have radiation hazards, technicalities and over instrumentation issues. Thus, electronic working length measurement has gained popularity among the endodontists. More accurate apex locators have been developed in recent years. In the present study Propex Pixi (Dentsply Maillefer, Switzerland) was used. It is a fifth generation device and it uses multiple frequencies, in addition to calculating the root mean square (RMS) values of the electrical signals. RMS symbolizes energy of the electrical signals. Propex Pixi may be used in both dry and wet root canals, however it has not been extensively studied.^12,15,16 In Propex Pixi, file clip and lip hook completes the circuit and on entering the apical region of the root canal the first blue bar lights up indicating that the file is in the canal. With the file movement subsequent bars light up (with beeps) until a steady zero reading is illuminated by a thicker yellow bar “00” mark indicating that the file tip is resting at the constriction (as per manufacturer’s instructions). At this point the sound becomes solid and continuous. Going beyond this point “00” results in a warning notice ‘beyond apex’ with a rapid intermittent signal to alert the operator. Measurements were considered as correct if remained constant for at least fiveseconds.^17,18,19

In the present research, variations were observed between Propex Pixi and actual measurements (p=0.019), and between radiographic and actual measurements (p=0.032). However the comparative evaluation between Propex Pixi and radiographic measurements showed no significant difference (p=0.280). These findings are in agreement with Kaufman AY, Sivadas et al and Subramaniam P.^7,20,21 The electronic method showed an accuracy of 96.6% within +0.5 mm and 100% accuracy within +1 mm. However, radiographic method showed an accuracy of 60% within 0.5 mm and 83% within +1 mm. The probable reason for this is because of digital vernier caliper which had an accuracy of 0.02mm. These values are in analogous with Sara Ghaemmaghami and Mello et al study.^22,23

The radiographs are generally used to obtain information about root canal anatomy, working limit and apical tissues. However, the exact measurement of root length is difficult using the radiographs because of anatomical variations, overlapping of anatomical structures or errors in projection.²⁴ The intra-class correlation coefficient between radiographic method and Propex Pixi showed high correlation and agreement. Regression analysis gives an equation which is used to anticipate the actual length. Regression analysis suggested that Propex Pixi can anticipate the actual value with 94.3% accuracy and radiographic method with 67.2% accuracy. The equations are as follows:

Actual value=0.917+0.923 x (Electronic value)………. (table- 3).

Actual value=2.295+0.800 x (Radiographic value)……. (table- 4).

Previous studies by Sara Ghaemmaghami²², G. Sivadas et al²¹ and Mello-Moura²³ have shown good performance of electronic apex locators in primary teeth. The outcome of this research corroborates the good performance and accuracy of fifth generation Propex Pixi in determining root length in deciduous teeth. The use of apex locators is quick, comfortable, accurate, safe, painless and does not expose the patient to the hazards of ionizing radiation. Although questions still exist on whether the accuracy of Propex Pixi can be affected by different types of electrolytes and root resorption. Study conducted by Shree kaluva et al²⁵ showed that Propex Pixi is accurate with a file diameter size of 0.6mm. Propex Pixi was not affected by the alloy type of the file used to determine the working length. Ravichandra C. et al¹⁵ showed no significant difference in the accuracy between the radiographic and Propex Pixi root length measurement in teeth with periapical lesions.

CONCLUSIONS:

• Propex Pixi is as effective as radiographic method in measuring the root length of primary teeth.

• Regression analysis suggested that Propex Pixi can anticipate actual root length with 94.3% accuracy and radiographic method with 67.2% accuracy.

Thus, considering the radiation hazards and difficulty in placement of radiographic film, it is advisable to use Propex Pixi in children. However a diagnostic radiograph may be required for endorsing the electronic method in determining the root length.

Limitations of the study: In this in-vitro study only single rooted primary teeth were considered. Hence, the efficacy of Propex Pixi should be assessed in multi rooted primary teeth.

Recommendations: Further in-vivo studies using Propex Pixi with large samples of single and multirooted primary teeth are recommended.

Financial support and grants:

nil.

Conflicts of interest:

nil.