Histologic Study of a Human Immature Permanent Premolar with Chronic Apical Periodontitis after Regenerative Endodontic Procedures.

The histologic outcomes of regenerative endodontic procedures (REPs) in humans remain debated, with evidence varying between cementum-/bone-like tissue and true pulp-dentin complex regeneration. Here, we present a case of a 10-year-old girl who underwent REPs for a maxillary premolar (tooth #4) diagnosed as symptomatic irreversible pulpitis with symptomatic apical periodontitis. At the 8-month follow-up, the patient was asymptomatic with radiographic evidence of apical closure and dentinal wall thickening; the tooth was subsequently extracted due to orthodontic indications, along with the sound contralateral premolar (tooth #12) as control. Micro-computed tomography confirmed apical closure and dentinal wall thickening with heterogeneous intracanal mineralization in tooth #4. Histologic examination revealed dentin-like tissue with tubular structures, surfaced by flattened, dentin sialophosphoprotein-positive cells. Neurovascular regeneration assessed by CD31/PGP9.5 co-localization was sparse and disorganized compared to the normal control. Osteoid tissue ingrowth was present in the apical region. This case demonstrates that REPs can yield structurally disorganized pulp-dentin-like tissue, highlighting the key challenge of achieving true histologic regeneration.