This study aims to present a clinical case in which the first lower left premolar (34) was opened using the Bastien technique. The intraoral clinical examination revealed extensive caries on the vestibular surface. The radiographic findings showed the presence of a radiolucent area in the cervical third and an increase in the periodontal ligament space. The instruments recommended for root canal preparation were: Prodesign Logic 30.05. The obturation was performed using the single cone technique associated with BIO-C Sealer (Angelus) cement and the vestibular wall was restored with Opus bulk fill flow (FGM) composite resin. It is concluded that the treatment with modified access using the Bastien technique, performed on a lower premolar with caries on the vestibular surface, preserves the healthy coronal dentin, resulting in clinical and radiographic success, which may represent an advantage in relation to dental longevity.