3 - Ossification, Lines of fusion + defects in formation of the maxillofacial region Flashcards
Formation of maxilla/upper jaw
Upper Jaw
- Day 28 - Olfactory placodes develop as a thickening within ectoderm of frontal prominence
- Then a proliferation of mesenchyme around the placodes converts them into nasal pits, formed by a lateral + medial nasal process
- Frontal prominence is now the frontonasal process
- frontonasal process + medial nasal processes = middle nose, middle upper lip, anterior maxilla + primary palate
Maxilla
- Centres of ossification develop in the mesenchyme of maxillary processes of 1st brachial arch
- The ossification spreads:
- Posteriorly - below orbit towards developing zygoma
- Anteriorly - toward future incisor region
- Superiorly - To form frontal process
- In the palatine process - To form hard palate
- At union between palatal process + main body of developing maxilla = medial alveolar plate - together w/lateral plates - development of maxillary teeth
- A cartilage appears in developing zygomatic processes + contributes to the development of maxilla
Formation of mandible/lower jaw
- Formed from 2 mandibular process that arise from mandibular arch
- These 2 processes grow forward + out until they meet at midline around day 30-35
- They join by fusion of 2 streams of ectomesenchyme of mandibular processes - gives rise to lower lip
- Cartilage of 1st brachial arch associated w/mandible formation = Meckel’s cartilage
- Between 2 mandibular processes is a thin layer of cartilage called symphysis (disappears at 1 yr of birth)
- On the lateral aspect of this symphysis - a condensation of mesenchyme forms
- Week 7 - Intramembranous ossification begins in this mesenchyme + spreads anteriorly + posteriorly to form mandible bone
- Ramus develops from rapid ossification posteriorly into mesenchyme of first arch
- Lateral dimensions of mouth formed by connection point of mandibular + maxillary processes
Palatal Development
Week 7-9
- Palate develops from an anterior wedge-shaped medial part + 2 lateral palatine processes
- Medial = primary plate ⇢ develops 1st and is floor to nasal pits
- Lateral palatine processes develop from maxillary tissue laterally + grow to midline ⇢ further limits oral cavity from nasal cavity posteriorly to the nasopharynx
- As palatine shelves grow medially ⇢ they contact tongue, which grew upwards into nasal cavity during week 7
- When contact is made, shelves grow downward on either side of tongue
- Only after development of 2° palate can oral + nasal cavities be distinguished
3 outgrowths appear in oral cavity
- Nasal septum ⇢ grows down through oral cavity + encounters 1° + 2° palates + 2 palatine shelves
- 2 palatine shelves ⇢ Closure of 2° palate is likely to involve hardening of palatine shelves + withdrawal of tongues
Derivatives of facial components
Frontonasal prominence forms:
- Forehead
- Bridge of nose
- Frontal + Nasal bones
Maxillary Prominence:
- Upper cheek region
- Most of upper lip
- Maxilla
- Zygomatic bone
- 2° palate
Mandibular Prominences
- Fuses to form chin, lower lip, lower cheek region + mandible
Lateral nasal prominences
- Fuses to form alae nasi
Medial Nasal Prominences
- Fuses to form intermaxillary segment of palate
Genetic + Congenital Defects
Face develops during 4th - 7th prenatal weeks
Environmental factors can cause facial/pharyngeal arch defect ⇢ probably affects these tissues before 4th week
Embryonic period is a time to be cautious of the following factors:
- Irradiation
- Chemical
- Hormonal
- Dietary
- Stress-related
Mild developmental defects of face are common
Failure of facial prominences to merge/fuse = abnormal developmental clefts
Clefts ⇢ due to disruptors of many integrated processes of: induction, cell migration, local growth + mesenchymal merging
Types of clefts
Unilateral cleft lip
Bilateral Cleft lip
median cleft lip
oblique facial cleft
median cleft/frontonasal dysplasia
lateral facial cleft
mandibular cleft
cleft of lip + alveolus
cleft of lip + 1° palate
unilateral cleft of lip + palate
bilateral cleft of lip + 1° palate
bilateral cleft of lip + palate
cleft palate
Unilateral cleft of lip
Located in line of fusion of medial nasal + maxillary process
Most common congenital defect + commonly on left side
Has a strong family tendency
Bilateral Cleft lip
Rare defect ⇢ Significant midline defect of upper lip + may produce a protuberant mass
Medial labial processes did not fuse on either side of developing maxillary processes + anterior extrusion of medial labial process
Cleft lip + palate
Bilateral cleft of upper lip = medial nasal prominence’s failure to merge w/maxillary processes on either side of midline
Median Cleft lip
Very rare ⇢ due to incomplete merging of 2 medial nasal prominences
Leads to most cases to various forms of bifid nose
2 parts of 1st pharyngeal arch, including bony mandible are separated at birth
