2BackgroundChin anatomy/deformity should be thoroughly examined in any patient requesting facial plasticsEspecially in relation to the lips, teeth, and noseMalocclusion and dental abnormalitiesMay need to be addressed first with orthodontic therapyMentalis muscle evaluation
3When to get radiographs If the chin deformity is complex, (e.g., vertical chin excess with horizontal deficiency or transverse bony asymmetry)AP and Lateral xraysWhen considering bony genioplastyPanorexShows mandible, mandible height, tooth roots, mental foramen, inferior alveolar canal
4Ideal Chin PositionThe 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 lineFor females, the pogonion should be slightly posterior to this lineThis technique misses vertical and transverse deformities
5Vertical Analysis of the Chin Simple technique divide the face into thirdsTrichion GlabellaGlabella SubnasaleSubnasale MentonDivide the lower third into 2 equal parts:subnasale vermilion of the lower liplower lip vermilion mentonTrichion – Frontal hairline meets the foreheadMenton – Lowest point of chin
6Transverse AnalysisLook for asymmetry of the bony midline in comparison to dental midlineCan occur in pts with Goldenhar’s syndrome or traumaGoldenhar’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
7Soft tissue deformity Witch’s Chin: Weakening of the muscular attachments of the mentalis and depressor labii inferioris musclesSoft tissue pad of the chin falls below the mandibular line deep horizontal crease in submental regionTx: Remove ellipse of skin in submental region, elevate elliptical flap, plicate tissue, re-approximate mentalisA, B, C : Pre-opD: Post –op (Face lift and surgical correction of mentalis muscle)
8Chin ImplantsChin implant augmentation good for minor chin deformitiesFor vertical/transverse chin deformities, an implant can make the appearance worseTypes: Silastic, Goretex, Medpor, Bone SourceComplications of Silastic, Goretex, Medpor extrusion, malpositionMedpor more resistant to infectionComplications of Bone Source Exposure, infection
9Chin Implant Technique (Mentoplasty) Extraoral incision (submental incision) = 2-3 cmDivide mentalis muscles, get on top of the periosteumStay supraperiosteal centrally and go subperiosteal laterallySubperiosteal is good in that it prevents migration of the implant but can cause resorption/erosion of the mandible….so this is a compromisePreserve mental nerves when doing subperiosteal dissxnImplant should be at inferior border of mandibleReapproximate mentalis muscleChin strap dressing***For intraoral route, use gingivolabial incision initially
10Osseous Genioplasty Horizontal osteotomy & down fracture of chin Advancement or retrusion in the AP planeLengthening and shortening in the CC planeAllows you to correct transverse asymmetries
11Osseous Genioplasty Technique Gingivolabial incision, go more towards labial sideElevate subperiosteally, preserve mental nervesMark osteotomy sitesHorizontal osteotomy for AP advancementOblique osteotomy for vertical manipulationWhen going laterally, stay at least 5mm below mental foramenFor vertical lengthening, bone graft can be placedFor vertical shortening, parallel osteotomy or burr away boneFixation with plates, screws, or interosseus wiresIntraoperative photograph of the preformed rigid genioplasty plate. Note that two small wires are used in this patient to ensure stability of the bony movement.
12Mentoplasty Algorithm Horizontal (Anteroposterior)Deformity VerticalTransverseProcedureDN or sl DNChin implant or genioplastyEGenioplasty (advancement with possible ostectomy if significant vertical excess)Bony advancement (with down-grafting for chin lengthening)AsymmetricBony osteotomy (with resection of down-grafting)Bony osteotomy (with setback)Bony osteotomy (with ostectomy)N – Normal. D = Deficient. E = Excessive. Sl = Slight
13Complications (rare) Mentoplasty Complications: Malpositioning of implantsExtrusion, migrationBothersome to patientsInfection (w/ intra-oral or extraoral incision)Anterior mandible resorptionGenioplasty complicationsMental nerve injuryMalunion, non-union of bone segments
15Anatomical 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 premolarThe 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.
16Occlusion GradingGrade 1 (proper occlusion): The mesiobuccal cusp of the upper first molar should align with the buccal groove of the mandibular first molarGrade 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