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 Trichion – Frontal hairline meets the forehead Menton – Lowest point of chin

Transverse Analysis Look for asymmetry of the bony midline in comparison to dental midline Can occur in pts with Goldenhar’s syndrome or trauma Goldenhar’s Syndrome -- Oculo-Auriculo-Vertebral (OAV) syndrome) is a rare congenital defect characterized by incomplete development of the ear, nose, soft palate, lip, and mandible. It is associated with anomalous development of the first branchial arch and second branchial arch. Common clinical manifestations include limbal dermoids, preauricular skin tags, and strabismus

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 A, B, C : Pre-op D: Post –op (Face lift and surgical correction of mentalis muscle)

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 Intraoperative photograph of the preformed rigid genioplasty plate. Note that two small wires are used in this patient to ensure stability of the bony movement.

Mentoplasty Algorithm Horizontal (Anteroposterior) Deformity Vertical Transverse Procedure D N or sl D N Chin implant or genioplasty E Genioplasty (advancement with possible ostectomy if significant vertical excess) Bony advancement (with down-grafting for chin lengthening) Asymmetric Bony osteotomy (with resection of down-grafting) Bony osteotomy (with setback) 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