Some cases of asymptomatic traumatic cyst can be sizeable; therefore, they require complete curettage and grafting with bone substitution materials. This case report presents a sizeable traumatic mandibular cyst in a young man treated by surgical exploration and flled with autologous dentin graft (ADG) prepared from extracted an impacted tooth 48 (FDI tooth-numbering system) and advanced platelet-rich fbrin (A-PRF). Initially, an A-PRF membrane was used to cover the apices of teeth 42 and 43, which were protruding into the defect to protect their periapical structures. Then, a grafting strategy was introduced to achieve two fronts of bone formation: one by stimulation of bone outgrowth from the periphery due to A-PRF cellular activity, and a second by bone deposition directly on dentin particles in the center of defect. On CBCT scans performed 7 months postoperatively, arrays of trabeculae that were extending from bone boundaries of the cyst defect were merged with more condensed bone deposited on ADG residuals in the center, thus flling the defect. It was found that autologous dentin combined with cellular A-PRF activity is a powerful tool to restore even sizable bone defects in a relatively short time frame with adequate bone remodeling.