An ex vivo investigation of the relationship between apical root impedance and canal anatomy.

AIM: To investigate a possible relationship between apical root impedance and canal anatomy. METHODOLOGY: Twenty-three roots from human extracted teeth with different apical anatomy (classified by number of apical canal exits) were selected. After impedance measurements, the root canals were stained and the teeth cleared to confirm their division into simple (S - Vertucci type 1; n=12) and complex (C - various Vertucci canal types with multiple exits; n=11) root types. Impedance measurements were taken using a frequency response analyser at seven apico-coronal levels in each root (0.0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 mm short of the apical terminus) at 14 frequencies ranging from 1120 to 100,000 Hz. Potential confounding factors were controlled. The impedance characteristics of individual roots were compared with 37 equivalent circuits to select best fit. The association between impedance characteristic (described by the selected equivalent circuit) and canal anatomy (S/C) was investigated using logistic regression with robust standard error to account for multiple data-sets from the same root. RESULTS: Canal anatomy had a significant (P= 0.046) effect on the equivalent circuit model. One circuit (model 10) occurred significantly more commonly in the simple canals. The odds of selecting circuit-model-10 were 2.2 times (odds ratio 2.17, 95% confidence interval 1.01-4.63) higher in canals with simple anatomy compared to those with complex anatomy. CONCLUSION: Canal anatomy had a significant effect on the equivalent circuit describing its impedance characteristics. It is theoretically possible to use impedance spectroscopy to clinically predict and image apical canal complexities.

An in vitro comparison of pH changes in root dentine following canal dressing with calcium hydroxide points and a conventional calcium hydroxide paste.

AIM: This study aimed to measure and compare pH changes at apical and cervical sites on the external root surface of extracted teeth dressed with calcium hydroxide in two different formulations. METHODOLOGY: Root canals of 45 single-rooted extracted human teeth were accessed and shaped using a step-down technique with rotary instrumentation. Standard cavities were prepared on the external root surface at specific apical and cervical sites. The teeth were randomly allocated to three groups. Teeth in group A were dressed with calcium hydroxide points, those in group B were dressed with an aqueous calcium hydroxide paste and teeth in group C were left unfilled. Following storage in humid conditions, the pH of the dentine at apical and cervical sites was measured at baseline and then at 24 h, 72 h, 1 week, 10 days, 2 weeks and 3 weeks. RESULTS: The pH of the root dentine at both apical and cervical sites was significantly greater (P < 0.001) in teeth dressed with aqueous calcium hydroxide paste compared with those dressed with calcium hydroxide points, when averaged out across all time periods. For all groups, there was a significant difference between the mean apical and cervical pH values for each tooth with lower values for the apical sites (P < 0.001). CONCLUSION: The results of this study indicate that an aqueous calcium hydroxide paste was more effective than calcium hydroxide points at raising the pH on the external root surface of extracted teeth.