Chapter 32:Mentoplasty & Facial ImplantsSameer Ahmed11/14/2012

Background• 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

When to get radiographs• 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

Ideal Chin Position• 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

Vertical Analysis of the Chin• 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

Transverse Analysis• Look for asymmetry of the bony midline in comparison to

dental midline• Can occur in pts with Goldenhar’s syndrome or trauma

Soft tissue deformity• 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 Implants• 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

Chin Implant Technique (Mentoplasty)1. Extraoral incision (submental incision) = 2-3 cm2. Divide mentalis muscles, get on top of the periosteum3. 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 dissxn4. Implant should be at inferior border of mandible5. Reapproximate mentalis muscle6. Chin strap dressing***For intraoral route, use gingivolabial incision initially

Osseous Genioplasty• 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

Osseous Genioplasty Technique1. Gingivolabial incision, go more towards labial

side2. Elevate subperiosteally, preserve mental nerves3. Mark osteotomy sites• Horizontal osteotomy for AP advancement• Oblique osteotomy for vertical manipulation• When going laterally, stay at least 5mm below

mental foramen4. For vertical lengthening, bone graft can be

placed• For vertical shortening, parallel osteotomy or burr

away bone5. Fixation with plates, screws, or interosseus

wires

Mentoplasty AlgorithmHorizontal (Anteroposterior) Deformity Vertical Transverse Procedure

D N or sl D N Chin implant or genioplasty

D E N

Genioplasty (advancement with possible ostectomy if significant vertical excess)

D D NBony advancement (with down-grafting for chin lengthening)

N N AsymmetricBony osteotomy (with resection of down-grafting)

E N N Bony osteotomy (with setback)

E E N Bony osteotomy (with ostectomy)

N – Normal. D = Deficient. E = Excessive. Sl = Slight

Complications (rare)• 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 End

Anatomical Considerations• 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 2nd 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.

Occlusion Grading• 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

What type of occlusion?

What type of occlusion?

Grade 2