Effect of canal preparation and residual root filling material on root impedance.
OBJECTIVE
To investigate the effect of root canal preparation and residual root filling material on the impedance characteristics of extracted human roots.


METHODS
Thirty extracted, human single-rooted teeth were mounted in a custom-made apparatus that allowed strict temperature control. Impedance measurements of the roots were made with a file acting as the internal electrode, using a frequency response analyser. The measurements were made under three canal conditions: (i) before chemo-mechanical preparation; (ii) after chemo-mechanical preparation; (iii) after root filling removal to re-establish patency (following placement of root filling). The measurements were taken at 0, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 mm coronal to the apical terminus and also at 0.5 and 1 mm past the apical terminus. Impedance values were viewed using Nyquist plots and comparisons made within each tooth, between measurement points along the length of the canal, as well as under the different canal conditions. Equivalent circuits were modelled for different test conditions.


RESULTS
The impedance decreased from the coronal to the apical levels in all canal conditions in a characteristic way, with an exaggerated drop at the apical terminus. Impedance decreased after chemo-mechanical preparation, but gave higher values compared with before or after instrumentation, once canal filling had been removed. Equivalent circuits remained consistent at the tested positions within the canal, regardless of canal condition, but the circuit component values changed with the impedance.


CONCLUSIONS
Impedance was influenced by corono-apical position, chemo-mechanical preparation and residual root canal filling material.
Al-bulushi
A
A
UCL Eastman Dental Institute, University College London, London, UK.
Levinkind
M
M
Flanagan
M
M
Ng
Y-L
YL
Gulabivala
K
K
D002614:Chelating Agents / Q000627:therapeutic use; D003722:Dental Alloys; D003786:Dental Pulp Cavity / Q000033:anatomy & histology*; D004492:Edetic Acid / Q000627:therapeutic use; D017097:Electric Impedance; D004566:Electrodes; D004867:Equipment Design; D006171:Gutta-Percha / Q000627:therapeutic use; D006801:Humans; D009532:Nickel; D009811:Odontometry / Q000295:instrumentation; D019233:Retreatment; D012387:Root Canal Filling Materials / Q000737:chemistry* / Q000627:therapeutic use; D012388:Root Canal Irrigants / Q000627:therapeutic use; D018915:Root Canal Preparation / Q000295:instrumentation / Q000379:methods*; D012973:Sodium Hypochlorite / Q000627:therapeutic use; D013696:Temperature; D013997:Time Factors; D014025:Titanium; D019227:Tooth Apex / Q000033:anatomy & histology*; D015035:Zinc Oxide-Eugenol Cement / Q000627:therapeutic use
D002614:Chelating Agents; D003722:Dental Alloys; D012387:Root Canal Filling Materials; D012388:Root Canal Irrigants; D015035:Zinc Oxide-Eugenol Cement; C040654:titanium nickelide; C074935:Roth's 801 Sealer; D009532:Nickel; D006171:Gutta-Percha; D004492:Edetic Acid; D014025:Titanium; D012973:Sodium Hypochlorite