Injectable and Retrievable Calcium Salicylate Hydrogel Promotes Sustained Periapical Bone Regeneration in a Beagle Dog Model of Apical Periodontitis

Introduction Persistent apical periodontitis remains a clinical challenge requiring both effective disinfection and bone regeneration. This study tested the hypothesis that an injectable, retrievable F127-dimethacrylamide (DMA)/calcium salicylate (CASA) hydrogel facilitates periapical bone healing by combining antimicrobial action with osteogenic induction. Methods Periapical lesions were induced in 18 single-rooted teeth of 2 beagle dogs. After the periapical lesions were confirmed, teeth were randomly assigned to 3 groups: F127-DMA/CASA, calcium hydroxide (Ca(OH)2), or an untreated control. For the CASA and Ca(OH)2 groups, intracanal medicaments were placed and then removed after 4 weeks; in the control group, the root canals were left without the medicament. Periapical lesion volumes were tracked via cone-beam computed tomography and three-dimensional volumetric analysis for up to 10 weeks postmedication. In vitro , human osteoblasts were exposed to the hydrogel to evaluate osteogenic marker expression by reverse-transcription -quantitative polymerase chain reaction and to characterize mineral deposition by spectroscopic analysis and electron microscopy. Results The F127-DMA/CASA group achieved the highest overall mean lesion volume reduction (54%) and significantly outperformed both control (26%) and Ca(OH)2 treatment (38%) at 10-weeks ( P < .03). Healing progressed at 3 different rates. The fastest occurred at 0-2 weeks, corresponding to initial cleaning of the canal, where Ca(OH)2 and CASA were similar to each other and only moderately faster than control. Ca(OH)2 and control reached a plateau after 2 weeks, with only a small subsequent increase (10% and 6%, respectively) at week 10. In contrast, CASA continued to show a significantly higher rate (20%) between weeks 2 and 6, which slowed (6%) between weeks 6 and 10, but remained higher than Ca(OH)2 and control. A surprising result was the observation of new bone formation in two of the CASA-treated teeth. These results were further supported by auxiliary in vitro experiments in which osteoblasts exposed to CASA showed a 3- to 25-fold increase in mRNA levels of all targeted osteogenic markers and robust bone-like mineral deposition. Conclusions The F127-DMA/CASA hydrogel achieved superior, sustained periapical healing and demonstrated bone regeneration as compared with conventional medicaments in a clinically relevant animal model. These outcomes were supported in vitro , exposing the molecular upregulation of osteoblast maturation markers and deposition of bone analog minerals, suggesting that the system functions as a bioactive regenerative therapy beyond traditional disinfection.