Chapter 32: Mentoplasty & Facial Implants

Chapter 32:Mentoplasty & Facial Implants Sameer Ahmed 11/14/2012

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) • Extraoral incision (submental incision) = 2-3 cm • Divide mentalis muscles, get on top of the periosteum • 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 • Implant should be at inferior border of mandible • Reapproximate mentalis muscle • 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 Technique • Gingivolabial incision, go more towards labial side • Elevate subperiosteally, preserve mental nerves • Mark osteotomy sites • Horizontal osteotomy for AP advancement • Oblique osteotomy for vertical manipulation • When going laterally, stay at least 5mm below mental foramen • For vertical lengthening, bone graft can be placed • For vertical shortening, parallel osteotomy or burr away bone • Fixation with plates, screws, or interosseus wires

Mentoplasty Algorithm 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 extraoralincision) • 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

Chapter 32: Mentoplasty & Facial Implants