## 2 Materials and Methods  
A 5-year retrospective analysis of surgical third molar surgery carried out by third-year oral surgery specialty program students was conducted in the department of oral surgery of Policlinico Umberto I in Roma, from 2017 to 2022. The inclusion criteria for the study encompassed lower third molars requiring flap reflection and surgical extraction, while cases associated with pathological conditions such as cysts or tumors were excluded from consideration. All the third molar surgeries were performed by a third-year oral surgery student with the supervision of an experienced senior surgeon. All the surgical extractions included in the study involved a full-thickness buccal flap reflection, a full-thickness lingual flap reflection and protection (LF+), osteotomy, and odontotomy. The patients were interviewed and examined. X-ray examinations were carried out for each patient, either via an orthopantomogram (OPG) or CBCT. Routine preoperative laboratory tests (on full blood count, blood clotting tests, glycemia, azotemia, and creatinine) and a cardiologic visit with an electrocardiogram were carried out. The patient was informed of the risks and benefits of the surgical intervention. Informed consent was obtained, and the surgery was scheduled. A standardized data sheet was completed, including the name, age, gender, side of the operation, state of eruption, cause of extraction, angulation, depth of the lower third molar, tooth division, and lingual nerve injury. The orientations of the lower third molars were categorized from the radiographs in accordance with [PERSON]'s classification [24] into vertical, horizontal, mesioangular, or distoangular. Other patterns were classified as aberrant. The depth of the tooth was classified as position A, B, or C in accordance with the classification of [PERSON] [25]. A step-by-step procedure aimed at protecting the lingual flap to prevent lingual nerve injury was taught to oral surgery students during their first two years of the oral surgery program. The essential part of the program was anatomical cadaveric dissection, allowingthem to deeply understand the anatomy of the retromolar area while exploring the relation of the lingual nerve and the third molar (Figure 1), and a simulation of the intervention was carried out with the aid of a plastic model. Deep knowledge of the retromolar anatomy of the mandible is mandatory. The standardized procedure to protect the lingual flap from the harmful action of rotary instruments is composed of 4 steps:  
Step 1: Design of a vestibular full-thickness flap. Flap incision is carried out at the buccal site, respecting the anatomy of the retromolar area using a three-sided flap, also known as Ward's incision, with the distal relieving incision positioned bucally to avoid damage to the lingual nerve. The distal relieving incision is made 45 degrees to the distobuccal cusp of the lower third molar or the middle of the distal surface of the second molar in the case of a full impacted third molar. From there, an intrasulcular incision of the second molar is made; before the mesial papilla, a vertical incision line is made obliquely into the mandibular vestibule, with a variable length according to the area to be exposed. This vestibular releasing incision was carried out as a standard procedure for all patients to ensure adequate exposure for all patterns of impaction (Figure 2A). Step 2: Full-thickness elevation of the buccal flap. The elevation of the buccal flap starts from the mesial vertical releasing incision and extends to the retromolar trigone area (Figure 2B-E). Step 3: Full-thickness elevation of the lingual flap. Delicate full-thickness reflection of the lingual flap starts from the most distant part of the distal releasing incision of the vestibular flap (Figure 2E). This procedure avoids perforation or partial dissection of the lingual flap due to the tension at the insertion point in the retromolar area.