In-vitro Criterion Difference Optimisation, K-file Diameter Free, In Electronic Endodontometry

Some Electronic Apex Locators (EAL) measure endodontic impedances using two frequencies: (1kHz and 5kHz), with a criterion of difference. In-vitro, the association of 5kHz and 100kHz allow to be Apical Constriction Diameter (ACD) free (IADR08).

The aim of this work is to determine two frequencies allowing EAL to be insensitive to K-File Diameter (KFD) with that criterion.

Method:

A resin model, 35/100^e ACD, inserted in CuSO4 gel, is catheterized from 1mm above Apical Constriction (C_R: conductance of reference) down to 0.5mm beyond (5/10^emm step), using successively four K-Files (15/100^e to 30/100^e, 5/100^estep). At each step of displacement, spectroscopy analysis, range [100Hz; 100kHz], was performed.

Electronic signals are treated in a high performance AD converter, using Labview® as acquisition software.

108 differences D_ij were computed at -0.5mm, AC and +0.5mm with D_ij=[C_fj-C_fi] - [C_Rfj - C_Rfi]; f_i: reference frequency from 100Hz to 50kHz; f_j: working frequency from i+1 to 100kHz; C_fi=mean of 3 measured conductances. Specificity of working length measures needs two conditions: Max(D_-0.5mm)D_AC) and Max(D_AC)D_+0.5mm). Its sensibility needs the largest differences (D_AC-D_-0.5mm) and (D_+0.5mm-D_AC).

Result:

About specificity, these conditions are validated with reference frequency ≤ 2kHz, and working frequency ≥ 20kHz. About sensitivity, the largest results are obtained for both criteria with 100 and 100000Hz. With these frequencies, there is significant difference between D_-0.5, D_AC and D_+0.5 obtained for every KFD (Kruskal Wallis test, p-value = 7.10^-3). Moreover, these differences (D) are linearly correlated to Catheterism (C) from -0.5mm to +0.5mm (D=140.0*C + 76.3; r² = 0,82), so do not depend on KFD (from 15 up to 30/100^e) and allow catheterism information.

Conclusion:

In-vitro, whatever K-File Diameter (10/100^e to 30/100^e), difference criterion using 100Hz and 100kHz gives the best results to determine Working Length around Apical Constriction (from -0.5mm to +0.5mm) and allows being K-File Diameter free.