Nano eggshell based slurry as a direct pulp capping material: In vitro characterization and histopathological assessment in an experimental animal model.

Abstract

Pulp vitality is essential for tooth integrity. Following pulp exposure, choosing a suitable pulp capping material is crucial to maintain pulp vitality. However, the reparative dentine bridge created by calcium hydroxide is generally porous and incomplete. To assess the in vitro and in vivo bioactivity of nano eggshell-based slurry (NES), using NES as direct pulp capping material, compared with calcium hydroxide (Ca(OH)2 ) in rabbit animal model. Nano eggshell powder (NE) was characterized for particle morphology, chemical composition, and ion release. In vitro bioactivity was tested by immersion in simulated body fluid (SBF) for 7 days. For histopathological evaluation, 36 adult New Zealand rabbits (72 pulp exposures) were divided into nine groups (n=8) according to the pulp capping material (NES, Ca(OH)2 and no capping as negative control group) and the animals were sacrificed after 7, 14 or 28 days. The pulps of the two lower central incisors were exposed then directly capped by Ca(OH)2 or NES, or left untreated. The cavities were then sealed with a glass ionomer cement. Teeth were collected for histopathological evaluation using optical microscope. Pulp haemorrhage, inflammation, fibrosis and calcific bridge formation were assessed. Results were statistically analyzed using ANOVA and Tukey's test. NE particles were spherical with 20 nm diameter and were composed mainly of calcite. Statistical analysis showed that there was significant increase in the release of all investigated ions between day 1 and 28, except for copper. NES group showed significantly higher release of all elements as compared to Ca(OH)2 . ESEM micrographs of NES incubated for 7 days in SBF showed the formation of HAp with Ca/P ratio (1.686). For histopathological evaluation, the difference between groups was statistically significant. At day 28, 75% of the pulps of Ca(OH)2 group showed mild calcific bridge in comparison with 100% moderate calcific bridge in NES group. The NES group showed significantly less inflammation at days 7 and 28, and higher fibrosis at day7 as compared with Ca(OH)2 . NES represents a promising novel direct pulp capping material with favourable pulp tissue response.