Sameer Ahmed
11/14/2012

• Chin anatomy/deformity should be thoroughly examined in any patient requesting facial plastics
• Especially in relation to the lips, teeth, and nose
• Malocclusion and dental abnormalities
• May need to be addressed first with orthodontic therapy
• Mentalis muscle evaluation

• If the chin deformity is complex, (e.g., vertical chin excess with horizontal deficiency or transverse bony asymmetry)
• AP and Lateral xrays
• When considering bony genioplasty
• Panorex
• Shows mandible, mandible height, tooth roots, mental foramen, inferior alveolar canal

• The most frequently used evaluation of the chin drops a perpendicular line from the vermilion border of the lower lip and compares the AP position of this line with the soft tissue pogonion (the anterior-most projecting chin point)
• For males, the pogonion should be at this line
• For females, the pogonion should be slightly posterior to this line
• This technique misses vertical and transverse deformities

• Simple technique  divide the face into thirds
• Trichion  Glabella
• Glabella  Subnasale
• Subnasale  Menton
• Divide the lower third into
2 equal parts:
• subnasale  vermilion of the lower lip
• lower lip vermilion  menton

• Look for asymmetry of the bony midline in comparison to dental midline
• Can occur in pts with Goldenhar’s syndrome or trauma

• Witch’s Chin:
• Weakening of the muscular attachments of the mentalis and depressor labii inferioris muscles
• Soft tissue pad of the chin falls below the mandibular line  deep horizontal crease in submental region
• Tx: Remove ellipse of skin in submental region, elevate elliptical flap, plicate tissue, re-approximate mentalis

• Chin implant augmentation good for minor chin deformities
• For vertical/transverse chin deformities, an implant can make the appearance worse
• Types: Silastic, Goretex, Medpor, Bone Source
• Complications of Silastic, Goretex, Medpor  extrusion, malposition
• Medpor more resistant to infection
• Complications of Bone Source  Exposure, infection

1.
Extraoral incision (submental incision) = 2-3 cm
2.
Divide mentalis muscles, get on top of the periosteum
3.
Stay supraperiosteal centrally and go subperiosteal laterally
• Subperiosteal is good in that it prevents migration of the implant but can cause resorption/erosion of the mandible….so this is a compromise
• Preserve mental nerves when doing subperiosteal dissxn
4.
Implant should be at inferior border of mandible
5.
Reapproximate mentalis muscle
6.
Chin strap dressing
***For intraoral route, use gingivolabial incision initially

• Horizontal osteotomy & down fracture of chin
• Advancement or retrusion in the AP plane
• Lengthening and shortening in the CC plane
• Allows you to correct transverse asymmetries

1.
Gingivolabial incision, go more towards labial side
2.
Elevate subperiosteally, preserve mental nerves
3.
Mark osteotomy sites
• Horizontal osteotomy for AP advancement
• Oblique osteotomy for vertical manipulation
• When going laterally, stay at least 5mm below mental foramen
4.
For vertical lengthening, bone graft can be placed
• For vertical shortening, parallel osteotomy or burr away bone
5.
Fixation with plates, screws, or interosseus wires

D
D
N
E
E
Horizontal
(Anteroposterior)
D
Deformity Vertical Transverse
N or sl D
E
D
N
N
E
N
N
N
Asymmetric
N
N
Procedure
Chin implant or genioplasty
Genioplasty
(advancement with possible ostectomy if significant vertical excess)
Bony advancement
(with down-grafting for chin lengthening)
Bony osteotomy (with resection of downgrafting)
Bony osteotomy (with setback)
Bony osteotomy (with ostectomy)
N – Normal. D = Deficient. E = Excessive. Sl = Slight

• Mentoplasty Complications:
• Malpositioning of implants
• Extrusion, migration
• Bothersome to patients
• Infection (w/ intra-oral or extraoral incision)
• Anterior mandible resorption
• Genioplasty complications
• Mental nerve injury
• Malunion, non-union of bone segments

• The inferior alveolar nerve, a branch of the third division of the fifth (trigeminal) cranial nerve, travels through the mandibular canal and exits the mental foramen as mental nerve.
• Mental foramen opposite to 2 nd premolar
• The mental nerve supplies sensation to the skin and mucous membranes of the lower lip and chin.
• The mandibular canal is often located 2 to 3 mm below the level of the mental foramen.
• Bony osteotomies should therefore be performed at least 5 mm below the mental foramen to avoid injury to the neurovascular bundle.

• Grade 1 (proper occlusion): The mesiobuccal cusp of the upper first molar should align with the buccal groove of the mandibular first molar
• Grade 2 (retrognathism): The upper molars are placed not in the mesiobuccal groove but anteriorly to it.
• Grade 3 (Prognathism): The upper molars are placed not in the mesiobuccal groove but posteriorly to it.
• Can be from large mandible and/or small maxilla

Grade 2