What is the most likely cause of this radiolucency?

External cervical resorption (ECR) classically presents as a radiolucent, irregularly-bordered defect at the cervical region of the root, often with "moth-eaten" borders. Risk factors include trauma, orthodontic treatment, bleaching, bruxism and chronic acidic exposure (GERD). Internal resorption (C) appears as a symmetric, balloon-like enlargement of the canal. Root caries (A) typically occur at the CEJ externally and are associated with gingival recession. The disorganized appearance and GERD history support ECR.2. Oral Pathology & Biopsy