European Archives of Paediatric Dentistry

, Volume 14, Issue 6, pp 369–374 | Cite as

Formulating a regression equation for determination of working length in primary molars using apex locators: a clinical study

  • A. DandempallyEmail author
  • R. Muppa
  • M. K. Duddu
  • P. Bhupatiraju
  • S. Nallanchakrava
Original Scientific Article



The aim of this study was to formulate a regression equation for calculating working lengths in primary molars using EAL (Root ZX and Ipex) for teeth with and without resorption and to evaluate, in vivo, the accuracy of the electronic apex locators in determining working lengths in primary teeth with and without resorption in comparison with Ingles radiographic method.

Study design

The study was a cross-over study. Fifty children undergoing pulpectomy in primary mandibular molars (total 150 root canals) with and without resorption were evaluated. The actual length of each root was measured with Ingles radiographic method followed by the use of two generations of apex locators. The distances were measured with radiographs, apex locators and working lengths tabulated. Frequency distribution of working length from radiographic apex and their percentages were calculated. Pearson’s correlation coefficient was used to assess the closeness of the measurements to radiographic apex with or without resorption followed by formulating regression equations.


It was observed that 131 (87.33 %) of the 150 readings with Root ZX, and 122 (81.33 %) of the 150 readings with IPEX were within 0.0–1.0 mm of the radiographic readings. Root ZX gave 96.77 % (30) and IPEX gave 90.32 % (28) of 31 acceptable readings (within 0.0–1.0 mm of the radiographic apex) in resorption cases. Measurements with apex locator and radiographic methods were highly correlated.


Apex locators are reliable when compared with Ingles radiographic method and can enhance the safety of treatment in specific situations such as presence of root resorption. In case of non-availability of apex locators, the equations given in our study can be of use.


Primary teeth Resorption Working length Regression equation 


Conflict of interest

The authors deny any conflicts of interest.


  1. Angwaravong O, Panitvisai P. Accuracy of an electronic apex locator in primary teeth with root resorption. Int Endod J. 2009;42:115–21.PubMedCrossRefGoogle Scholar
  2. Elayouti A. The ability of Root ZX apex locator to reduce the frequency of overestimated radiographic working length. J Endod. 2002;28(2):116–9.PubMedCrossRefGoogle Scholar
  3. Ghaemmaghami S, Eberle J, Duperon D. Evaluation of the Root ZX apex locator in primary teeth. Pediatr Dent. 2008;30:496–8.PubMedGoogle Scholar
  4. Ingle J, Bakland L, Buchanan S, et al. Endodontic cavity preparation. 4th ed. Philadelphia: Williams & Wilkins; 1994. p. 92–227.Google Scholar
  5. Ingle J, Himel T, Hawrish C, Bakland L. Cavity preparation. In: Ingle J, editor. Endodontics. 5th ed. Hamilton: Decker; 2002. p. 517–25.Google Scholar
  6. Martinez MAL, Forner-Navarro L, Sanchez-Cortes JL, Llena-Puy C. Methodological considerations in the determination of working length. Int Endod J. 2001;34:371–6.CrossRefGoogle Scholar
  7. Mente J, Seidel J, Buchalla W, Koch MJ. Electronic determination of root canal length in primary teeth with and without root resorption. Int Endod J. 2002;35:447–52.PubMedCrossRefGoogle Scholar
  8. Neena IE, Ananthraj A, Praveen P, Karthik V, Rani P. Comparison of digital radiography and apex locator with the conventional method in root length determination of primary teeth. J Indian Soc Pedod Prev Dent. 2011;29:300–4.PubMedCrossRefGoogle Scholar
  9. Nelson-Filho P, Romualdo PC, Bonifacio KC et al. Accuracy of the ipex multi frequency electronic apex locator in primary molars: an exvivo study. Int Endod J. 2011;44:303–6.PubMedCrossRefGoogle Scholar
  10. Nguyen HQ, Kaufman AY, Komorowski RC, Friedman S. Electronic length measurement using small and large files in enlarged canals. Int Endod J. 1996;29:359–64.PubMedCrossRefGoogle Scholar
  11. Prattern DH, McDonald NJ. Comparison of radiographic and electronic working lengths. J Endod. 1996;22(4):173–6.CrossRefGoogle Scholar
  12. Riccucci D, Langeland K. Apical limit of root canal instrumentation & obturation, Part 2. A histological study. Int Endod J. 1998;31:394–409.CrossRefGoogle Scholar
  13. Saritha S, Uloopi KS, Vinay R, Sekhar RC, Rao VV. Clinical evaluation of Root ZX II electronic apex locator in primary teeth. Eur Arch Paediatr Dent 2012;13:32–35.Google Scholar
  14. Stober EK, Duran Sindreu F, Mercade M et al. An evaluation of Root ZX and IPEX apex locators: an invivo study. J Endod. 2011;37(5):608–10.PubMedCrossRefGoogle Scholar
  15. Spangberg SF. Instruments, materials & devices. In: Cohen S, Burns RC, editors. Pathways of pulp. 8th ed. St. Louis: Mosby; 2002. p. 521–72.Google Scholar

Copyright information

© European Academy of Paediatric Dentistry 2013

Authors and Affiliations

  • A. Dandempally
    • 1
    Email author
  • R. Muppa
    • 1
  • M. K. Duddu
    • 1
  • P. Bhupatiraju
    • 1
  • S. Nallanchakrava
    • 1
  1. 1.Department of Paediatric DentistryPanineeya Mahavidyalaya Institute of Dental Sciences and Research CentreHyderabadIndia

Personalised recommendations