Apical Size Effect on Electronic Root Canal Length Determination

Objectives: To evaluate the influence of foramen size and electrolyte on impedance characteristics of root canal system Methods: The impedance characteristics and the effect of the apical size on the electronic root canal length measurement have been investigated by the simulated model. The impedance analyzer was employed to measure the impedance for the tubules filled with distilled water, normal saline or 5.25% sodium hypochlorite. The variation ratios of the modified impedance-quotient (SQ) have been defined as the significant indices for the impedance characteristics as well as location indications and are compared with the well-known index of impedance quotient (R) that is applied to Root ZX instrument. The location of the apex could be indicated by these two indices, irrespective of the electrolytes in the tubule. Results: It has been found from this study that the sharpness (difference between the under-apex and over-apex) of these two indications at the under-apex region would decrease with enlarged apical diameter of the tubule, especially for the impedance quotient. Conclusions: The SQ number has the ability to retard the decrease of the sharpness and to serve as a good apex position index even for the case of enlarged apical size. This index may apply to electronic apex locator (EAL) in the future to improve the accuracy of working length measurement for cases with large apical diameter during endodontic treatment.