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Chapter 32: Mentoplasty & Facial Implants

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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

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background
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
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
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
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
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
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 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 m entoplasty
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
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
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
Mentoplasty Algorithm

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

complications rare
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
anatomical considerations
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
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
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