Comparison of the rheological properties of four root canal sealers

Abstract

The flowability of a root canal sealer is clinically important because it improves the penetration of the sealer into the complex root canal system. The purpose of this study was to compare the flowabilities of four root canal sealers, measured using the simple press method (ISO 6876), and their viscosities, measured using a strain-controlled rheometer. A newly developed, calcium phosphate-based root canal sealer (Capseal) and three commercial root canal sealers (AH Plus, Sealapex and Pulp Canal Sealer EWT) were used in this study. The flowabilities of the four root canal sealers were measured using the simple press method (n=5) and their viscosities were measured using a strain-controlled rheometer (n=5). The correlation between these two values was statistically analysed using Spearman's correlation test. The flow diameters and the viscosities of the root canal sealers were strongly negatively correlated (ρ=−0.8618). The viscosity of Pulp Canal Sealer EWT was the lowest and increased in the following order: AH Plus<Sealapex<Capseal (P<0.05). All of the tested root canal sealers showed characteristic time- and temperature-dependent changes in their rheological properties. The viscosities measured using the strain-controlled rheometer were more precise than the flowabilities measured using the simple press method, suggesting that the rheometer can accurately measure the rheological properties of root canal sealers. The ability of root canal sealers to flow into and seal a root canal can best be measured with a strain-controlled rheometer. Researchers usually measure sealer viscosity using the simple press method, that is, by pressing the material between two glass plates and measuring the diameter of the resulting disc. Rheometers, however, can measure the viscosity of a complex fluid as it changes with strain, time and temperature. Kwang Shik Bae of the Seoul National University School of Dentistry, Korea, and colleagues tested four sealers (Capseal, AH Plus, Sealapex, and Pulp Canal Sealer EWT) using both methods. The rheometer measured sealer viscosity more sensitively than the simple press method. The rheometer data also showed how the viscosity of sealers changed as they set, indicating effective working times, and how increased temperature affected their chemical properties.