Parents of a 3-year-old child report that the child has constant pain in the upper front teeth. Objectively: the coronal part of the 61 tooth is gray and decayed. Probing of the root canal orifice is pai- nful and accompanied by bleeding. The tooth percussion provokes acute pain. Mucosa is hyperemic, edematic and painful. Palpation in the region of the 61, 62 teeth reveals a fistula. What is your provisional diagnosis?