Membership in General Dental Surgery (MGDS)

Correct: The infraorbital nerve is a branch of the maxillary division (V2) of the trigeminal nerve that exits the infraorbital foramen to provide sensation to the lower eyelid, lateral nose, and upper lip. Its proximity to the surgical site for zygomatic implants makes it susceptible to injury during retraction or osteotomy preparation, and the symptoms described perfectly match its sensory distribution.

Correct: In the management of facial soft tissue injuries, the vertical line through the lateral canthus of the eye serves as a critical landmark for risk assessment. Lacerations lateral to this line are more likely to involve the facial nerve at a point before it has branched extensively or formed anastomotic plexuses (particularly the zygomatic and buccal branches). Consequently, injuries in this lateral zone carry a higher risk of permanent functional loss and generally warrant microsurgical exploration and repair within a 48-72 hour window for optimal results.

Incorrect: Lacerations medial to the lateral canthus (Option B) typically involve terminal branches that have significant cross-innervation, often making surgical repair unnecessary as function frequently returns spontaneously. A salivary fistula (Option C) suggests injury to the parotid ductal system (Stensen’s duct) rather than being a primary diagnostic indicator for nerve trunk transection. The Bell phenomenon (Option D) is a clinical sign used to assess the protective mechanism of the eye and the integrity of the upper facial nerve branches (temporal/zygomatic), but it is not the standard criteria for determining the need for surgical repair of a buccal branch injury.

Takeaway: Facial nerve injuries lateral to the lateral canthus carry a higher risk of permanent deficit due to the lack of distal anastomoses and typically require surgical intervention.

Correct: The cricothyroid muscle is the only intrinsic laryngeal muscle innervated by the external branch of the superior laryngeal nerve. All other intrinsic muscles of the larynx are supplied by the recurrent laryngeal nerve. This distinction is vital during surgical procedures near the thyroid gland and in the management of the airway, as the cricothyroid muscle tenses the vocal folds to adjust pitch and maintain the patency of the glottis.

Correct: The mental nerve is the terminal branch of the inferior alveolar nerve (V3), providing sensation to the lower lip and chin. Standard postoperative management for a neurosensory deficit involves objective, serial testing—such as light touch (Level A) and two-point discrimination (Level B)—to document the severity and monitor for recovery or the need for surgical intervention.

Correct: Herpes Zoster (shingles) is caused by the reactivation of the varicella-zoster virus (VZV) within a sensory ganglion. When the trigeminal ganglion is involved, the lesions follow the dermatomal distribution of one of its divisions. Lesions on the hard palate and maxillary gingiva that do not cross the midline are characteristic of the Maxillary division (V2) involvement, which provides sensory innervation to these areas via branches like the greater palatine and nasopalatine nerves.

Correct: Sialendoscopy is the current gold standard for the management of proximal or hilar sialoliths that are refractory to conservative treatment. This minimally invasive technique allows for direct visualization of the ductal system and the use of specialized tools like baskets or lasers for lithotripsy, which facilitates the removal of the obstruction while preserving the secretory function of the submandibular gland and avoiding the risks associated with more invasive surgery.

Incorrect: Transoral sialolithotomy is typically indicated for stones located in the distal portion of the duct; attempting this for hilar stones significantly increases the risk of injury to the lingual nerve and may lead to ductal stenosis. Transcervical submandibular gland excision is an invasive procedure that should be reserved for cases where gland-preserving techniques have failed or the gland is chronically fibrotic. Long-term antibiotic therapy does not address the mechanical obstruction and is not a definitive management strategy for sialolithiasis, while simple dilation is often insufficient for a stone of this size and location.

Takeaway: Sialendoscopy is the preferred gland-preserving surgical intervention for proximal submandibular sialoliths that do not respond to conservative management.

Correct: The fibula free flap is the workhorse for mandibular reconstruction. Its primary blood supply is the peroneal artery, which provides both endosteal and periosteal circulation. When a skin paddle is required for intraoral or extraoral soft tissue coverage, the surgeon must carefully preserve the perforating vessels (septocutaneous or musculocutaneous) that arise from the peroneal vessels and travel through the posterior crural septum to reach the skin.

Incorrect: The anterior tibial artery is not the pedicle for the fibula flap; using it would compromise the blood supply to the anterior compartment of the leg. Furthermore, the proximal and distal 6 to 8 centimeters of the fibula must be preserved to maintain the stability of the knee and ankle joints, respectively. The bone does not rely solely on endosteal supply; the periosteal supply is vital, especially when performing osteotomies to shape the bone to the mandible. The sural nerve is a sensory nerve and is not required for ‘autonomic’ metabolic support of the bone graft.

Takeaway: Successful fibula free flap reconstruction depends on the peroneal vascular pedicle and the preservation of septocutaneous perforators for skin paddle viability.

Correct: In the management of salivary gland malignancies, certain high-risk features necessitate adjuvant treatment even when surgical margins are clear. Perineural invasion (PNI) is a significant prognostic factor associated with increased rates of local recurrence and regional metastasis. For a low-grade mucoepidermoid carcinoma, surgery alone is often sufficient; however, the discovery of PNI on permanent sections shifts the management toward post-operative radiation therapy (PORT) to optimize local control and address potential microscopic disease along the nerve sheath.

Incorrect: Completion total parotidectomy is not indicated if the tumor was confined to the superficial lobe and clear margins were already obtained. Elective neck dissection is generally reserved for high-grade tumors or cases with clinical evidence of nodal involvement (N0 to N+ conversion), rather than as a response to perineural invasion in a low-grade lesion. Routine surveillance alone is insufficient in this scenario because the presence of perineural invasion significantly elevates the risk of recurrence beyond what is acceptable for observation only.

Takeaway: The presence of perineural invasion in salivary gland malignancies is a primary indication for post-operative radiation therapy, regardless of the tumor grade or the adequacy of surgical margins.

Correct: The Gow-Gates technique is considered a ‘true’ mandibular nerve block because the anesthetic is deposited at the neck of the condyle. This anatomical location allows the solution to bathe the main trunk of the mandibular nerve (V3) before it divides into the inferior alveolar, lingual, mylohyoid, and auriculotemporal nerves. By anesthetizing the trunk higher up, accessory innervation from the mylohyoid nerve or the auriculotemporal nerve—which often causes failure in the traditional Halstead IANB—is effectively blocked.

Incorrect: Targeting the pterygomandibular space at the level of the mandibular foramen describes the traditional IANB, which frequently fails when accessory innervation is present. Utilizing the coronoid notch is the standard landmark for the IANB, not the Gow-Gates, and does not address the trunk of V3. Directing the needle to the anterior border of the ramus targets the long buccal nerve but does not provide the high-level trunk anesthesia necessary to overcome accessory innervation of the mandibular teeth.

Takeaway: The Gow-Gates technique achieves a higher success rate by targeting the mandibular nerve trunk at the condylar neck before it branches into terminal nerves like the mylohyoid.