Evaluation of the Setting Time and pH of Nanohydroxyapatite-Chitosan as a Direct Pulp Capping Material

Calcium hydroxide (CaOH) and Mineral Trioxide Aggregate (MTA) are the most commonly used materials for Direct Pulp Capping (DPC). However, CaOH is associated with a very high pH and tunnel defects, whereas MTA has a prolonged setting time, potential tooth discoloration, low mechanical strength, and relatively high cost. Since setting time and pH are important physicochemical properties influencing clinical handling and pulp response, biocompatible alternatives are needed. Nanohydroxyapatite–Chitosan (nHA–CH) has shown potential to improve adhesion and promote dentin remineralization. Therefore, this study evaluated the setting time and pH of nHA–CH as a direct pulp capping material.

An experimental laboratory study with a post-test-only control group design was conducted using nHA–CH, CaOH, and MTA (n = 6 per group). Setting time was measured using a Gillmore apparatus, and pH was measured after 3 and 24 hours using a digital pH meter. Data were analyzed using one-way ANOVA, post hoc LSD, and paired t-tests (p < 0.05).

One-way ANOVA showed significant differences in setting time among the three materials (p < 0.05). The mean setting times of nHA–CH, CaOH, and MTA were 15.32 ± 0.09, 2.51 ± 0.01, and 17.16 ± 0.03 min, respectively. Paired t-test analysis showed significant changes in pH between 3 and 24 hours for all materials (p < 0.05). The pH of nHA–CH (6.90–7.27) remained lower than that of CaOH (10.33–11.51) and MTA (12.01–12.67).

The distinct setting and pH characteristics of nHA–CH suggest a potential balance between practical handling and a more pulp-compatible chemical environment, highlighting its potential as an alternative approach to direct pulp capping.

nHA–CH demonstrated favorable gelation characteristics and a near-neutral to slightly alkaline pH; however, further studies are required before clinical application.