Particle size and shape of calcium hydroxide in Endodontics

Objectives: Calcium hydroxide aqueous slurry is widely used as an interim (interappointment) antimicrobial dressing in root canal treatment. Less than 0.2 % of the slurry is dissolved into calcium and hydroxide ions, leaving mostly undissolved particles. While it is known that the penetration of particles into dentin tubules is determined by size and shape, the precise physical properties of the particle are not known. The aim of this study was to use image analysis to establish particle length, width, perimeter, and aspect ratio of calcium hydroxide powder using a flow particle image analyzer (Sysmex FPIA-3000, Japan). Methods: Five sample groups each with 10 mg calcium hydroxide (Sigma-Aldrich) were mixed with 15 mL of alcohol and sonicated. Samples were run using High Power Field mode at an effective size range of 0.5-40μm. Digital images of particle samples were taken and statistically analyzed using one-way ANOVA. Results: Overall Average±S.D. among five groups for particle length (μm), width (μm), perimeter (μm), and aspect ratio were 2.255±1.994, 1.620±1.464, 6.699±5.598, and 0.737±0.149, respectively. No statistical significance was observed among five groups in the analysis of all parameters. When the total of 46818 particles from all five groups were classified into the five length categories at 0.5μm increments, length category 2 (1.0-1.5μm) and length category 1 (0.5-1.0μm) were the highest in frequency and aspect ratio, respectively. ANOVA showed there were significant differences in width, perimeter, and aspect ratio among the five length categories (all p-values<0.0001).Conclusions: The cumulative percentage of particles length between 0.5 and 2.0 μm, which is smaller than the reported size of dentin tubules in root dentin, was 63%. Calcium hydroxide fine particles can be possible to penetrate into open dentin tubules, and its shape is not round but irregular.

Acknowledgement: Hosokawa Micron Ltd. & Malvern Instrument Ltd. /NIH KL2RR024983(TK), UL1 RR024982.