Endodontic Intelligent Release System for Apexification using Calcium Hydroxide Microspheres

Objectives:  Apexification therapy requires repeated applications of a calcium hydroxide (CH) slurry owing to burst release of CH and loss of material in the periapical tissue. There is a need for a sustained slow release delivery system for CH. The purpose of this study was to engineer an innovative release system to deliver a steady stream of both Ca²⁺ and OH^- ions to the open apex of permanent teeth for a period of up to one year. In addition to creating a slow release vehicle for CH, the buffering effect of the teeth was also investigated.

Methods:  An oily matrix was used as a CH vehicle and to form microspheres, as well as an alginate outer coating, aiding in the slow release of ions. The CHMS were compared to a commercially available CH medicament and to CH powder as controls. The release experiments were performed in extracted teeth(n=6) and in plastic centrifuge tubes(n=3) to determine the buffering effect occurring within teeth. The calcium release was measured with ultraviolet-visible spectroscopy and the pH was monitored with a pH meter.

Results:  Results showed that the CHMS formulations showed the maximum sustained release in comparison to both controls. We were able to release Ca²⁺ for >4 months from the alginate-CHMSs in contrast to controls, which were depleted after one week under sink conditions. We also demonstrated control over the release profile of CH ions by varying the thickness of the alginate layer. The pH of samples from extracted teeth never rose above 9, whereas samples from centrifuge tubes had consistently high pH(12-14) indicating the buffering effect of teeth.

Conclusions: CHMSs present a viable alternative for currently available products for apexification. The slow release of Ca²⁺ and OH^- should eliminate the need for periodic removal and refreshing of traditional intra-canal medicaments.

Support: NIH P30DE20742 & KL2RR024983