(1) Background: Among all possible causes, foreign bodies are the rarest cause of appendicitis in the pediatric population. In the majority of cases, ingested foreign bodies pass through the gastrointestinal tract without causing symptoms. However, those foreign bodies that pass through the lumen of the vermiform appendix cannot re-enter the colon and may cause acute appendicitis. So far, various foreign bodies have been described to enter the appendix and cause acute appendicitis, such as seeds, needles, toothpicks, plant material, or even hair. Tooth or dental implants as a cause of acute appendicitis have been described in only a few cases. To our knowledge, this is the first described case of the tooth causing acute appendicitis in the pediatric population. (2) Case presentation: A 14-year-old male patient presented to the emergency department complaining of pain in the right lower quadrant of the abdomen and vomiting that persisted for approximately 24 h. Until then, the patient was healthy and had no concomitant diseases. Physical examination revealed guarding and tenderness in the right lower abdominal quadrant. The white blood cell count was 17.1 × 10/L with a neutrophil count of 91.1% and a C-reactive protein of 39.3 mg/dL. Ultrasonography of the abdomen revealed a thickened, inflamed appendix with a diameter of 11 mm and free periappendicular fluid. A 9 × 6 mm foreign body at the base of the appendix was visualized. The patient was diagnosed with acute appendicitis, and an emergency laparoscopic appendectomy was performed on the same day. Intraoperatively, gangrenous appendicitis was noted and removed without complications. Upon examination of the removed specimen, it was determined that the patient's appendicitis had been caused by an ingested tooth. As it later turned out, the patient had broken a lateral incisor while playing sports the day before admission without knowing that he had swallowed it. The patient recovered well and was discharged the day after surgery. (3) Conclusion: Although an extremely rare event, acute appendicitis can be caused by a swallowed tooth. This case highlights the importance of a thorough history in pediatric patients who present to the emergency department with suspected acute appendicitis to determine if there is a precipitating event that may have caused acute appendicitis.