- Anatomy:
- Medullary branch of the inferior alveolar artery supplies the condylar head
- Maxillary alveolus sensation: nasopalantine nerve to block the palate, anterior superior alveolar nerve to block anterior teeth and mucosa
- Middle/posterior superior alveolar nerves from infraorbital nerve and innervate bicuspids to molars
- Inferior alveolar nerve: supplies lip and chin, mainly neuropraxias, found in bony canal of mandible in body of mandible
- Travels proximal to angle through body, bicuspid tooth, emerges as mental nerve
- Injuries to this nerve most commonly due to neuropraxias
- Buccal mucosa also supplied by trigeminal nerve
- Medial pterygoid: upward, medial and forward traction on mandible, inserts on medial ramus and angle
- Lateral pterygoid: has 2 heads, only muscle that inserts directly on the mandibular condyle –> acts to open the mandible and motion of the articular disk
- Condylar fractures can displace medially due to pull of lateral pterygoid
- Masseter: inserts on medial and lateral surfaces of lower border of zygomatic arch and anterolateral surface of mandibular ramus, elevates mandible
- Temporalis inserts on coronoid/ramus; elevates and retracts (cause of loss of facial height)
- Distractive forces of mandible: anteriorly (geniohyoid, genioglossus, mylohyoid, and anterior digastric) (causes posterior and downward movement of mandible); rotational forces when only one fracture pattern is present
- Side to side contractions of medial/lateral pterygoid produce side-side chewing movements of mandible, simultaneous action of all four muscles results in protrusion of mandible
- Masseter and temporalis elevate the mandible
- Permanent first molars used to determine state of dental occlusion; central incisors are for overjet
- Class I: mesiobuccal cusp of maxillary lying in buccal groove
- II: mesialbuccal cusp lying anterior
- III: posterior
- Overjet horizontal (sagittal plane anterior) –> refers to the distance between the incisal aspect of the maxillary incisors to the mandibular incisors (when upper central incisor lies anterior –> overjet)
- Overbite vertical: one in which the upper central incisors overrides the lower central
- Submandibular space: located inferolateral to mylohyoid muscle and superior to hyoid bone
- Contents include submandibular gland, lymph nodes, facial vein and artery, inferior loop of hypoglossal nerve
- Typically involve infections of second and third mandibular molars, anterior to this is sublingual space
- Buccal space has second and third maxillary muscles
- Function:
- Mandibular opening:
- Articular disk separates upper and lower joint spaces
- At rest and during rotation –> condyle in lower joint space 1-2cm, 2-3mix
- During translation –> condyle moves to upper joint space 3-5
- 4-5cm maximal incisal opening
- Tumors:
- Aneurysmal bone cyst (multinucleated giant cells): resection and curettage
- Lesions present as a pseudocyst comprised of multinucleated giant cells
- Ameloblastoma: painless enlarging mass in mandible or maxilla (multilocular lucency with preservation of the cortex)
- Wide resection, vascularized bone graft
- Pediatric:
- Mandibular distraction 1mm daily, infants can undergo 2mm daily (less carries risk for premature consolidation)
- Distraction: success most dependent on stable fixation (unstable leads to too much motion and fibrous union)
- Lag period: time prior to distraction
- Distraction period 1mm per day
- Consolidation: 2 weeks
- Superiosteal dissection important
- Abnormalities in mandibular growth most associated with condyle fractures(primary growth center)
- Contributes to vertical growth
- Mandibular fractures in children:
- Symphyseal fractures: displaced require ORIF and 2 weeks MMF or absorbable (be careful with developing tooth buds)
- Condylar fractures are not fixed, they are highly vascularized sponges –> treat with MMF
- Bone anchor screws used in children to avoid damaging dentition
- Tooth buds may be injured when placing MMF (pay attention to mixed dentition, what should be erupting)
- Remove titanium plates at 2-3 months to avoid growth disturbances in children
- Trauma: (age 16 counts as skeletal maturity)
- CSI (concomitant spine injuries) occur in mandible fractures 4-10% of the time
- Chest injury or ramus/condyle unit fractures independent risk factors for CSI
- Symphysis
- Parasymphysis
- Anterior muscles include geniohyoid, genioglossus, mylohyoid and digastric muscles –> will displace parasymphyseal fracture downward, posteriorly, and medially
- Vestibular approach used for ORIF –> risk of mental nerve injury below the second premolar (mental foramen) –> gives sensation to skin and mucosa of the lower lip, skin of chin, facial gingival of anterior teeth
- Body: typically treated with ORIF
- Displacement can cause ipsilateral numbness via injury to inferior alveolar nerve
- Angle
- Angle has the highest rate of fracture in adults
- Displacement can cause ipsilateral numbness via injury to inferior alveolar nerve
- Angle fractures: foreshortening can cause posterior open bite on c/l side
- Treat with ORIF
- Coronoid
- Nondisplaced coronoid fracture= MMF for 2 weeks
- displaced with obstruction of mandibular motion = coronoidectomy
- Condyle
- Retromandibular incision: safest exposure for submandibular fractures (allows access to coronoid notch, angle, subcondylar fractures)
- Pre-auricular approach carries risk of injury to facial nerve (not good for low fractures like low subcondylar fractures)
- Condylar fracture: loss of posterior ramus height with premature contact of maxillary and mandibular molars and contralateral open bite, ipsilateral upward cant, incisal opening decrease, chin point deviated towards side of lesion (due to unopposed action of lateral pterygoid on contralateral side)
- Operative indications for peds: displacement into middle cranial fossa, impossibility of obtaining adequate dental occlusion by closed reduction, lateral extracapsular displacement, invasion of foreign body
- MMF for 2 weeks if minimally displaced
- Most common fracture pattern seen in children
- Bilateral condylar fracture: anterior open bite: premature contact of mandibular/maxillary molars posteriorly, decrease in posterior height, facial swelling, pre-auricular pain
- Medial displacement of condylar fractures due from action of lateral pterygoid muscle
- Intracapsular fractures treated with short time of MMF 2 weeks
- Comminuted condylar fractures carry the risk for TMJ dysfunction (clicking, locking pain, trismus) –> ankylosis
- Condylar neck fractures: displacement caused by lateral pterygoid (only muscle that inserts on mandibular condyle- acts to open the mandible), other head inserts on TMJ and contributes to motion of articular disk
- Unopposed force of muscle will pull head medially
- Medial pterygoid attaches to mandibular angle and ramus
- Subcondylar fractures: traditionally treated with closed reduction and MMF (heavily debated)
- Lower risk of ankylosis than condylar head
- Longer time in MMF, nondisplaced can use 4-6 weeks, followed by 2-3 weeks elastics; same with bilateral fracture
- If it is displaced –> perform ORIF (should not have answer closed reduction/MMF or ORIF together)
- Edentulous patients:
- Edentulous patients use custom-fabricated intraoral splints or dentures for rigid MMF in order to re-establish occlusion
- Mandibular atrophy can make it difficult to achieve appropriate reduction –> ORIF is necessary to provide long term stability and accurate restoration of previous anatomy (due to poor osteogenic capabilities)
- In severely comminuted fractures of mandible, blood supply comes from periosteum
- Long flat bones (facial skeleton)- nutrient arteries and periosteal vessels
- In patient who has fractures of midface and condylar neck –> ORIF of condylar fractures first followed by ORIF of midface fractures (only appropriate way of re-establishing height of posterior face)
- Indications for removal of teeth: fractures in root of tooth, severe loosening of tooth with periodontal disease, extensive periodontal injury and broken alveolar walls, displacement of teeth from alveolar socket
- Fixation Principles
- Champy’s principle: placement of miniplates along lines of tension in mandible at the site of fracture and anchored with monocortical screws
- Anterior to canine, two miniplates needed to control rotational forces of genial and digastric muscles
- Posterior just one
- Load bearing plates can be accomplished with reconstruction plate and locking screws
- Indications: comminuted fractures, segmental defects, atrophic edentulous mandible
- Locking plate: decreases postoperative malocclusion after comminuted fracture of mandible (does not require intimate contact), less cortical compression, less blood disruption, less bone resorption, less difficulty contouring
- Load sharing: frictional sharing between ends of bone –> lag screws, champy plate (at oblique ridge) compression plates, simple screws, MMF
- Spherical gliding principle: first screw goes close to fracture, second screw goes eccentrically, away from fracture across fracture line–> creates compression
- Osteoradionecrosis: doses >6500 gray and dental caries are precipitating factors
- Bisphosphonate related osteonecrosis (BRON): pathologic fractures, pain intraoral bone in those taking bisphosphonates (typically for cancer paget etc)
- Stage I: exposed and necrotic bone, otherwise asymptomatic
- Antiseptic mouth washes and observation
- Stage 2: exposed and necrotic bone with infection
- Limited debridement, mouth rinses and antibiotics
- Stage 3: plus pathologic fracture, extraoral fistula, and osteolysis extending to inferior alveolar border
- Requires surgical debridement
- Complications
- If incisions become infected and hardware is stable –> ID and abx; if hardware unstable remove
- Postoperative mandibular infections: common-1/3 –> ID and abx (IV) oral hygeine; infected teeth should be removed, rigid fixation should remain unless actively infected or osteo
- Miscellaneous:
- Mandible contouring surgery: (mandible angle reduction) uses to decrease angular contours in a square face
- First molar- 2 tooth roots!
- Incisors, canines, mandibular premolars have 1 root
- Maxillary molars have 3 roots
- Maxillary first premolars and mandibular molars have 2 roots
