MFDS Oral Surgery 2 — Questions and Answers
Question 1: A patient presents with a swelling in the floor of the mouth that is fluctuant, translucent blue, and recurrent. It collapses on aspiration and refills. What is the most likely diagnosis?
- Ranula (Correct answer)
- Dermoid cyst
- Sublingual gland tumour
- Ludwig's angina
Correct answer: Ranula
A ranula is a mucous extravasation cyst or retention cyst arising from the sublingual gland. It presents as a fluctuant, translucent blue swelling in the floor of the mouth that may recur after aspiration. A simple ranula is confined to the floor of the mouth; a plunging ranula extends below the mylohyoid muscle into the neck. Definitive treatment usually requires excision of the sublingual gland.
Question 2: What are the boundaries of the 'anatomical snuffbox' and which artery is at risk during surgical procedures in this region?
- Bounded by the tendons of abductor pollicis longus/extensor pollicis brevis and extensor pollicis longus; the radial artery passes through its floor (Correct answer)
- Bounded by the masseter and medial pterygoid; the facial artery is at risk
- Bounded by the sternomastoid and trapezius; the external jugular vein is at risk
- Bounded by the buccinator and orbicularis oris; the buccal artery is at risk
Correct answer: Bounded by the tendons of abductor pollicis longus/extensor pollicis brevis and extensor pollicis longus; the radial artery passes through its floor
The anatomical snuffbox is bounded laterally by the tendons of abductor pollicis longus and extensor pollicis brevis, and medially by the tendon of extensor pollicis longus. The radial artery crosses its floor, and the cephalic vein crosses superficially. While not directly related to oral surgery, knowledge of upper limb anatomy is tested in MFDS Part 1 as part of general surgical anatomy.
Question 3: Which nerve is most commonly damaged during a sagittal split osteotomy of the mandible, and what are the typical symptoms?
- The facial nerve, causing motor paralysis of the lower lip
- The inferior alveolar nerve, causing altered sensation (numbness or paraesthesia) of the lower lip, chin, and teeth on the affected side (Correct answer)
- The lingual nerve, causing loss of taste on the anterior two-thirds of the tongue
- The hypoglossal nerve, causing deviation of the tongue
Correct answer: The inferior alveolar nerve, causing altered sensation (numbness or paraesthesia) of the lower lip, chin, and teeth on the affected side
The inferior alveolar nerve is at greatest risk during bilateral sagittal split osteotomy (BSSO) because the osteotomy cuts pass in close proximity to, or directly over, the nerve canal within the mandibular body. Damage results in altered sensation (hypoaesthesia, paraesthesia, or anaesthesia) of the lower lip, chin, and mandibular teeth. The incidence of temporary IAN disturbance ranges from 30-85%, with permanent damage in approximately 3-5% of cases.
Question 4: A 45-year-old patient on long-term bisphosphonate therapy for osteoporosis requires extraction of a non-restorable lower molar. What is the primary concern and how should it be managed?
- Risk of excessive bleeding — obtain a coagulation screen first
- Risk of medication-related osteonecrosis of the jaw (MRONJ) — assess risk factors, consider antibiotic prophylaxis, perform atraumatic extraction, and achieve primary closure (Correct answer)
- Risk of anaphylaxis to the bisphosphonate — have adrenaline available
- No additional concerns — proceed with routine extraction
Correct answer: Risk of medication-related osteonecrosis of the jaw (MRONJ) — assess risk factors, consider antibiotic prophylaxis, perform atraumatic extraction, and achieve primary closure
Bisphosphonates inhibit osteoclast activity and reduce bone turnover, increasing the risk of medication-related osteonecrosis of the jaw (MRONJ) following invasive dental procedures. Management includes assessing the patient's MRONJ risk (duration and route of bisphosphonate therapy, other risk factors), providing prophylactic antibiotics, performing the extraction as atraumatically as possible, achieving primary soft tissue closure, and close follow-up monitoring.
Question 5: What is the most appropriate management for a displaced and mobile zygomatic arch fracture causing trismus?
- Conservative management with soft diet only
- Open reduction and internal fixation with titanium plates
- Closed reduction using a Gillies temporal approach with elevation of the depressed fragment (Correct answer)
- Intermaxillary fixation for six weeks
Correct answer: Closed reduction using a Gillies temporal approach with elevation of the depressed fragment
A displaced zygomatic arch fracture causing trismus (due to impingement on the coronoid process of the mandible) is typically reduced using the Gillies temporal approach. An incision is made behind the hairline in the temporal region, an elevator is passed beneath the temporalis fascia and deep to the arch, and the depressed fragment is lifted outward. This closed technique avoids facial scarring and is effective for isolated arch fractures.
Question 6: Which type of incision is most commonly used for surgical removal of an impacted lower third molar, and what structures must be carefully protected?
- A midline mandibular incision, protecting the mental nerve
- A triangular or envelope mucoperiosteal flap with a relieving incision distal to the second molar, protecting the lingual nerve and inferior alveolar nerve (Correct answer)
- A submandibular (Risdon) incision, protecting the marginal mandibular branch of the facial nerve
- A vestibular incision only, with no nerve structures at risk
Correct answer: A triangular or envelope mucoperiosteal flap with a relieving incision distal to the second molar, protecting the lingual nerve and inferior alveolar nerve
The standard approach uses a triangular mucoperiosteal flap with a relieving incision distal and buccal to the lower second molar, extending forward along the buccal sulcus. The lingual nerve is at risk as it lies in close proximity to the lingual plate of bone in the third molar region, and the inferior alveolar nerve runs in the canal beneath the roots. Careful flap design, controlled bone removal, and avoidance of lingual soft tissue retraction minimise nerve injury risk.
MFDS Oral Surgery 2
A patient presents with a swelling in the floor of the mouth that is fluctuant, translucent blue, and recurrent.
It collapses on aspiration and refills.
What is the most likely diagnosis?