Microstructural Evaluation of the Mineralized Apical Barrier Induced by a Calcium Hydroxide Paste Containing Iodoform: A Case Report

Introduction: A 65-year-old man had nonsurgical retreatment using an iodoform and calcium hydroxide paste in a maxillary left canine with persistent apical periodontitis. An apical mineralized barrier (AMB) was observed 3-months postoperatively. Unfortunately, the tooth was extracted due to a cementum tear. This provided an opportunity to analyze the AMB histologically, as there is a lack of previous reports on its microstructure. Methods: After extraction and removal of the granulation tissue from the root surface, the canine was processed, and observed using micro–computed tomography (μCT) and light microscopy. Thereafter, the specimen was resin-embedded specimen was evaluated by scanning electron microscopy, micro–X-ray fluorescence spectroscopy and Raman spectroscopy to understand the mechanism and nature of the AMB formation during apical healing. Results: Nonsurgical retreatment was clinically successful based on the absence of clinical symptoms of apical periodontitis and the radiographic presence of an AMB. The AMB was opaque and could be readily differentiated from dentin under a light microscope. Micro–computed tomography analysis revealed that the AMB had the same mineral density as dentin. Scanning electron microscopy revealed that the AMB had two distinct layers based on the size of the calcified particles. Elemental mapping using micro–X-ray fluorescence spectroscopy showed that the localization of calcium and phosphorus differed between AMB and other areas of biomineralization. Raman spectral mapping revealed that the surface layer of the AMB consisted of collagen, calcium carbonate, and hydroxyapatite. Conclusions: This study explored new analytical methods for elucidating the apical wound-healing process and the nature of the mineralized repair. The findings provided detailed information on the AMB highlighting a bilaminar structure with high calcium components higher on the inside and a brightness similar to cementum not dentin and the presence of hydroxyapatite.