Postnatal Growth 2021 (PDF)

Post-natal growth of the skull Philippa Francis-West [email protected] Making room for your teeth Primary teeth replaced from year 6 e.g. 1st permanent molar by age 7 2nd permanent molar by age 12 during adolescent growth spurt 3rd molar – at maturity P.M. Som, and T.P. Naidich AJNR Am...

Post-natal growth of the skull Philippa Francis-West [email protected] Making room for your teeth Primary teeth replaced from year 6 e.g. 1st permanent molar by age 7 2nd permanent molar by age 12 during adolescent growth spurt 3rd molar – at maturity P.M. Som, and T.P. Naidich AJNR Am J Neuroradiol 2014;35:10-18 Post-natal growth of the skull Objectives Know the rates of growth of the cranial vault, cranial base and face versus the body Know the mechanisms of growth in the : 1. Cranial Vault 2. Cranial Base 3. Lower jaw 4. Upper jaw Know how growth of these regions makes room for the developing teeth The Craniofacial Complex can be divided into 3 regions Relative rates of Growth Post-natal growth of the head 6 Fontanelles present Bones are thin Midline of face not united - will do within first two years Nasal septum and orbits align Face is small - virtual absence of paranasal air sinuses and small facial bones Base of mandible - obtuse Why is the cranial vault advanced relative to the face? Brain growth much faster The face growth follows the body growth Brain versus body growth 100 X X Face follows somatic growth curve except the skeleton around the eye, middle and inner ear (petrous temporal bone) which follow neural growth pattern Development of the brain and sense organs is faster than development of the face Neural Birth 25% 6 months 40-50% 10 years 95% Face 65% Rates of growth Skull - fast - growth linked to expanding brain, almost complete by age 10 Face - same rate as general body, linked to development of teeth, sinuses and muscles. Complete with eruption 3rd molars, 18-25 years Cranial base - links brain and face - growth rate intermediate, neural rate early, somatic rate later childhood Types of Growth There are two types of bone in the head: endochondral and intramembranous What is the difference? Where are they found? Endochondral Bones Nasal capsule Meckel’s cartilage (transient) Otic capsule Cranial Base Vertebrae & Ribs (Axial Skeleton) Limb (appendicular Skeleton) Endochondral bones subsequently ossify Alizarin Red & Alcian Blue stained mouse embryos E14.5 E16.5 Intramembranous bones Frontal bone Nasal Cartilage/ capsule Parietal Bone eye Maxilla Occipital cartilage (cranial base) Mandible TYPES of GROWTH Endochondral Growth: Growth plates –interstitial growth. Remodelling – appositional growth Intramembranous bones: Suture - Important during early childhood Remodelling- Most important method of growth in late childhood and adolescence Secondary cartilage- Condylar cartilage (until adolescence) The neural crest and mesodermal contribution to the head Frontal bone Parietal bone The Cranial Vault Please also see lecture by Karen Liu on Suture development and Craniosynostosis Cranial Vault 1. How does it develop and grow? 2. What is the evidence that the cranial vault growth follows the brain? 3. What defects can occur? Cranial vault development F, Frontal bone P, parietal bone Fontanelles and Sutures Brain development controls skull development: displacement Sutural growth Remodelling - bones hollow out (reduces weight) and flatten + + - - - - -- - + + + + + + + -- - +- + - + + -+ 2 mechanisms – sutural and remodelling Brain defects linked to skull growth: Microcephaly e.g. Zika virus Macrocephaly e.g. hydrocephaly Craniosynostosis Synostosis means closure Coronal suture Metopic suture Sagittal suture Types of Craniosynostosis; Which suture is affected will determine shape of Skull The Cranial Vault END OF SECTION Please also see lecture by Karen Liu on Suture development and Craniosynostosis The Cranial Base Cranial Base 1. How does the cranial base grow? 2. When does the cranial base stop growing? 3. How does it impact on development of the upper face? Development of the cranial base alisphenoid Develops from cartilaginous precursors which will fuse Larsen’s Human Embryology, 4th edition Growth of the cranial base (fused by 3-5 yrs) (fused at birth) (closed by 20 yrs) Anterior Posterior Spheno-occipital cartilage growth plate/synchondrosis Growth is bidirectional Fusion (synostosis) starts 14 years for Females and 16 years in males Closed by 20 years Closed by 20 years The cranial base SPHENO-OCCIPITAL SYNCHONDROSIS Temporozygomatic suture Intermaxillary suture Palatomaxillary Suture As the cranial base is linked to the upper jaw, defects in cranial base development will have secondary effects on the upper jaw - there will be no space for 3rd molars Remodelling moves cranial base and face anteriorly and inferiorly Frontal Bone Cranial Base Achondroplasia Underdevelopment of cranial base -Class III occlusion Currently Phase III clinical trail (recombinant form of CNP) The Cranial Base END OF SECTION Now let’s look at growth of your face Face at birth: 60% width, 45% height, 35% depth adult size Which pharyngeal arch gives rise to the lower jaw Lower Jaw How does the lower jaw grow? When does the midline of the lower jaw stop growing? How does the lower jaw lengthen and widen posteriorly? How do developmental i.e. embryonic lower jaw defects affect upper jaw development? Mandible at birth and in the adult Coronoid process Anterior Posterior Condylar process Key changes 1. Increase in length 2. Increase in height - alveolar bone 3. Increase in width 4. Change in angle - Birth: 140 - Adult: 115 in men, 120 in female 5. Relative size of coronoid and Condylar processes 6. Position of mental foramen Mandible development and Post-natal Growth Step 1: Formation of Meckel’s cartilage Step 2: Ossification of the mandible and development around Meckels cartilage and developing teeth Step 3: Change in shape and growth by (a)Formation and growth of secondary cartilages (b)Remodelling Development of the lower jaw Mandible Development Meckel’s cartilage Malleus & Incus Alveolar nerve Perichondrium Sphenomandibular and sphenomalleolar ligaments Initial Site of Osteogenesis Incisive Branch Mental nerve Site of initial osteogenesis - week 6 of development, mandible ossified by 10 weeks Pierre-Robin Sequence Micrognathia Cleft Palate Glossoptosis (airway obstruction) Secondary cartilage & Mandible development Week 10 Condylar Cartilage **** Very important, Gradually ossifies but cartilage persists at tips of condyle Week 11 Coronoid cartilage - disappears by birth Week 12 Symphysial cartilage * some contribution to width Condylar cartilage (has unique properties) Condylar cartilage Epiphyseal cartilage Condylar growth peaks early adolescent, ceases by year 20 Symphysial cartilage: unites the mandible tongue tooth bud Mandible Symphysial cartilage Ossifies within 1 year - limited growth in width Remodelling of the Mandible Anterior Posterior Coronoid - + Condylar Process + Process -- ++ - - + + + Anterior + Posterior + + + + + + + + Mandible development + + + Anterior Posterior - - + + + The post-natal mandible changes Mental Foramen Birth Primary Secondary Adult Ageing SUMMARY: MAKING ROOM FOR LOWER TEETH Remodelling - key mechanism Growth of secondary cartilage, Condylar cartilage – key The Lower Jaw END OF SECTION Upper jaw growth What is the main bone in the upper jaw that contributes to growth? What types of bone are in the upper jaw? How does the upper jaw grow? What does the nasal septal (ethmoid) cartilage do? Embryonic development of the upper jaw Post-natal growth of the Maxilla bone Frontal Process Infra-orbital groove large frontal process no alveolar bone no anterior nasal spine Zygomatic process With frontal bone frontal process with ethmoid Orbital surface Infra-orbital groove Zygomatic process & bone Anterior nasal spine canine eminence Alveolar canal openings Tuberosity Growth: Displacement at sutures – e.g.orbit & eyeballs Dentition &alveolar bone Remodelling – Formation of maxillary sinuses Addition of bone - tuberosity Upper jaw development: The maxilla is the key player Maxilla connects with many Bones: nasal, Frontal, lacrimal, Ethmoid, Zygomatic, Vomer, palatine Sutural growth in upper face includes: 10 The septal cartilage also contributes to growth Displacement causes growth at sutures Sutural growth in the Palatal Shelves tongue important increase in width (2 years) & length (7 years) Remodelling of the maxilla and development of the maxillary sinus + Ethmoid - Vomer Inferior Concha - Orbital cavity + - - Zygomatic + + - + - + - + Maxillary Sinus + + - - + - - - ++ + + + + Palatal shelves + + + Arch development in palatal shelves BIRTH 1 YEAR ADULT Addition of bone at tuberosity makes room for molars GROWTH IN WIDTH OF UPPER FACE At birth face is divided by a complete sagittal suture system. This is important for growth in width. Then the bones start to unite limiting this potential By end of year 1 Cartilage between great wings and body of sphenoid ossifies metopic suture united – a single frontal bone (doesn’t always happen in 10% of humans) By the end of year 3: ossification of the cribiform plate of the ethmoid UPPER JAW GROWTH SUMMARY I Mechanisms Suture until 10 years, contribute to height and length and width Endochondral growth (nasal septum/ethmoid) until year 7, contributes to height and length Remodelling until adulthood - contribute to height and length and width SUMMARY II: MAKING ROOM FOR UPPER TEETH Maxilla key bone - remodelling and suture growth Permanent molars develop in alveolar bulbs at back of maxilla Linked to cranial base growth Thank you and Reading AR Ten cate Oral Histology Scott and Symons, Introduction to Dental Anatomy (Churchill livingstone press) Also look at Berkovitz, Holland and Moxham "Oral Anatomy, Histology and embryology" Mosby press and Larsen’s Human embryology for early facial development