Electronic Endodontometry: Spectroscopy and Ratio method, K-File Diameter Free

During catheterism, Endodontic Impedances (EI) mainly depend on Apical Constriction Diameter (ACD) and K-File Diameter (KFD) (IADR06, IADR11). Mostly Electronic Apex Locators (EAL) measure EI with two frequencies: (≈0.4kHz and ≈8kHz) for ratio calculation (IADR03). In-vitro, the association of a low (≈0.1kHz) and a high frequency (100 kHz) allow to be ACD free (IADR07)

The aim of this work is to determine two frequencies allowing EAL to be KFD independent.

Methods:  

A resin model, 35/100^e ACD, inserted in CuSO4 gel, is catheterized from 1mm above Apical Constriction (AC), down to 0.5mm beyond (5/100^e step), using successively four K-Files (15/100^e to 30/100^e), conducted by a micrometric displacement table (Mitutoyo®). Electronic signals are treated with analog-to-digital converter and acquisition software: Labview®. 720 ratios Q_ij=Z_fj/Z_fi are computed, with f_i: frequency of reference, range [100Hz; 50kHz]; f_j: working frequency range [f_i+1; 100kHz]; Z_f: mean of 3 impedances.

Specificity of Working Length measure (WL), needs three conditions: Max(Q_-1mm)Q_-0.5mm) and Max(Q_-0,5mm)Q_AC) and Max(Q_AC)Q_+0,5mm). 

Sensibility of WL needs: differences (Q_AC-Q_-0,5mm) and (Q_+0,5mm-Q_AC) as largest as possible.

Results:  

About specificity, the last condition is never validated; the two others are verified with reference frequency ≤ 0.5kHz. About sensitivity, the largest results are obtained for both differences with Q_0.1/100kHz .With these frequencies (0.1 and 100kHz), according to Kruskall-Wallis test, there is significant difference between, Q_-0,5mm, Q_AC and Q_+0,5mm (p_value = 9.10^-5). Moreover, these ratios are linearly correlated to Catheterism (C) from -0.5mm to +0.5mm (Q_0.1/100kHz = -0,17.C + 0,54; r=0.93), so do not depend on KFD (from 15 up to 35/100^e) and allow catheterism information.

Conclusions:

In-vitro, whatever K-File Diameter (10/100^e to 35/100^e), ratio method using 0.1 and 100kHz gives the best results to determine Working Length around Apical Constriction (from -0.5mm to +0.5mm). Hence, in Electronic Endodontometry, these two frequencies, allow being K-File Diameter free.