Relationship between calcium hydroxide pH levels in the root canals and periodontal healing after replantation of avulsed teeth

Calcium hydroxide [Ca(OH)₂], when used as a root canal dressing, has been shown to promote periapical healing, induce formation of an apical hard tissue barrier (apexification), and arrest infection‐related root resorption. The main mechanism of action is thought to be the high alkalinity of Ca(OH)₂ ensuring a bactericidal or bacteriostatic effect upon microorganisms in the root canal and dentinal tubules. Several anatomical factors related to the root canal, such as the coronal access cavity, the apical foramen, the dentinal tubules, and existing resorption cavities on the root surface, all allow leakage of hydroxide ions from the root canal. The purpose of the present clinical study was to analyze pH changes in 63 permanent anterior teeth in which Ca(OH)₂ (Calasept^®) was used as an initial canal dressing after replantation and subsequent pulp necrosis had developed. The pH changes in the pulp canal were studied with relation to observation period, stage of root formation, healing of any periapical radiolucency, infection‐related root resorption, formation of an apical hard tissue barrier, and finally the radiographic appearance of Ca(OH)₂ in the canal (i.e. present or not). The study showed that several factors determined the pH level: the observation period (i.e. observation periods exceeding 6 months showed a significant drop in pH level below a pH of 10), an initial active inflammatory root resorption (tendency to be related to a drop in pH), and a subsequent progression of infection‐related resorption (the same tendency to be related to a drop in pH to below 10). The size of the apical foramen and the length of the pulp had no relation to pH change. The radiographic disappearance of Ca(OH)₂ in the root canal (loss of radiopacity of the canal dressing) was found to be significantly associated with a drop in pH (P=0.001). It was concluded that radiographic monitoring of the Ca(OH)₂ presence in the root canal is essential for endodontic treatment planning (i.e. when to replace Ca(OH)₂ or perform a permanent root filling). Furthermore, continuous activity of inflammatory root resorption may indicate a drop in pH and should result in replacement of new Ca(OH)₂. It should be noted that these findings apply to a Ca(OH)₂ product (Calasept^®) with no added radiopaque material.