THE CLINICAL RELEVANCE OF THE GROWTH OF THE HEAD AND JAWS AFTER BIRTH

how many bones are in the human head

28 bones

• 8 cranial

• 14 facial

• 6 auditory

• (+ 1 hyoid)

is post natal growth of the head and face proportional in each bone

no, post-natal growth is not due to simple proportional enlargement of each bone

what is the ratio of head:body at birth VS in adulthood 

• birth 1:4

• adult 1:8

what are the two types of growth occurring in the head and face 

1. intramembranous bones grow by periosteal remodelling

2. endochondral bones grow by cartilaginous replacement

what is the function of fontanelles

fontanelles give the skull flexibility as it goes through the birth canal

outline the skull at birth

• sutures

• 6 fontanelles (posterior, anterior, x2 sphenoid, x2 mastoid)

define cranial vault

• cranial vault: the part of the skull that encloses or protects the brain i.e. calvaria, skullcap

outline the growth of the brain in terms of its weight

• 1yr = 50% of what it will be in adulthood

• 3yrs = 75%

• 7yrs = 90%

• 11yrs = 100%

—

the surrounding cranium expands to accommodate it

expansion of the cranium is due to _____ ______

expansion of the cranium is due to brain growth

outline sutural growth

• at birth the 6 fontanelles are present and closing at 18 months

• bone is laid down at sutures in response to brain growth and increasing pressure

• some sutures begin to fuse at approx. 7yrs

• all mostly fused mid-late teens

outline the growth of the cranial vault in later childhood and adolescence

• development of lower 2/3 of face

• downwards and forwards growth of maxilla and mandible

• elongation of nose

• backward shift of orbits

—

• dramatic physical changes during puberty often occurs up to 2 years earlier in girls than in boys

define cranial base

cranial base: the bony floor of the skull that separates the brain from the face and neck

• involves the frontal, ethmoid, sphenoid, temporal, occipital bones

what is the post natal growth of the cranial base via

1. endochondral

2. surface remodelling

what are synchondroses

synchondroses: isolated regions of cartilage that joins bone

• once growth has ceased, the cartilage is then replaced by bone

what are the cranial base synchondroses 

• spheno-ethmoidal

• spheno-occipital

• inter-sphenoid (ISS)

outline the spheno-ethmoidal synchondroses

• anterior cranial base

• neural growth pattern - genetically controlled

• fuses at the age of 7

• stable by 8-10yrs

outline the spheno-occipital synchondroses

• posterior cranial base

• somatic growth pattern

• present into mid-late teens

• stable by late teens

outline the inter-sphenoid (ISS) synchondroses

• fuses between 2-3yrs of age

outline the nasomaxillary complex

• consist of the maxilla, some bones of the nasal cavity and parts of the orbit

outline the growth pattern of the maxilla 

• grows downwards and forwards - appears to move downwards more than forwards

• new bone added to both sides of sutures

• also grows in width due to midpalatal suture which fuses around puberty

—

• remodelling continues on bone surfaces

• floor of nose is resorbing

• bone added to FOM

why is knowledge of the growth pattern of the maxilla relevant to dentistry

• can incorporate fusion of sutures into treatment for certain patients

• expansion of maxilla can be done as a narrow arch can result in crowding of teeth (image)

  • bone will be laid down at the mid palatal suture - this takes a few months

state the direction that surface remodelling takes place in relation to bone translation in the maxilla

surface remodelling occurs in the opposite direction to bone translation

in what manner does the mandible grow

• the mandible grows in height and length

• growth appears forwards and downwards away from the base of the skull

• there is also a rotational pattern to mandibular growth (image)

  • reflections of differential growth in anterior and posterior face heights

outline the growth pattern of the mandible

• one area of growth: condyle

  • grows in length by cartilage replacement which then becomes ossified

• proliferative cell zone can differentiate into chondroblasts

• growth also seems to occur via resorption from anterior surface and deposition on posterior surface

• remodelling of glenoid fossa also occurs

what does the condylar cartilage in the mandible resemble in long bones 

the epiphyseal plate cartilage of long bones

what type of grows does the mandible undergo

appositional (increase in thickness/ width/ diameter), not proliferative

state the histological appearance of the mandible (in growth)

• not organised into parallel columns

• histologically, it has a different appearance to the organisation at the spheno-occipital synchondroses cartilage

when does growth in mandibular length cease

growth in mandibular length ceases in late teens

when does growth in mandibular height cease

growth in mandibular height continues very slowly throughout life

outline studies done by Björk in Copenhagen in the 1950-60s

• longitudinal studies

• using metal implants in the jaws to study growth

• done because sequential radiographs had no reliable reference point so metal pins were inserted as a reference point instead

• unethical: no therapeutic benefit, radiation exposure

how was growth observed in Björk’s studies

• can see internal rotation in the core of the mandible relative to the cranial base

  • done by superimposing serial radiographs with metal implants

• masked by surface apposition and resorption

Björk’s findings pt. 1

• majority had an ‘anterior’ rotation

• mandibular plane angle decreases by 2-4°

• increasing overbite

• more skeletal class III occlusion (underbite)

• leads to late lower incisor crowding?

• genetic link?

radiograph and clinical image showing anterior growth rotation of mandible

Björk’s findings pt. 2 

• minority had a ‘posterior’ rotation

• mandibular plane angle increases » anterior open bite

• more skeletal class II occlusion

• leads to late lower incisor crowding?

• genetic link?

radiograph and clinical image showing psoterior growth rotation of mandible

(not same radiograph and clinical image) 

why may waiting until a patient is older to start treatment planning be wise (if they are showing early signs of atypical jaw relationship)

• may wait until a patient is older so we know the exact relationship between mandible and maxilla so treatment planning is more certain and stable

• this means we will not be fighting against the natural growth of the jaws

what else did Björk identify in the mandible

• ‘stable’ anatomical structures 

• these can be used as a reference point instead of the metal pins

does the maxilla also have rotational growth patterns

• small but variable rotations - majority are anterior so the upper can occlude on the lower

• there is a mean 3° anterior (rotation) - but can be backwards

• genetic link?

outline the growth pattern of soft tissues

• grow and change throughout life

• most rapid growth occurs around puberty

• these may mask or enhance hard tissue growth changes

• genetic link?

why is knowing the growth patterns of the bones that make up the head important in dentistry

• need to decide if the problem is due to underlying skeletal problems or the teeth themselves

• sometimes it may not only be limited to just the teeth

define growth site VS growth centre

• growth site: a location at which growth occurs

• growth centre: is a genetically controlled growth site where growth occurs

—

therefore all growth centres are growth sites but the converse is not true

what are the theories of postnatal head and face growth

1. remodelling theory

2. sutural theory

3. cartilaginous theory

4. functional matrix theory

5. part-counterpart principle

6. servo-system theory

outline the remodelling theory

remodelling theory

• emphasis upon remodelling as primary mechanism by which all bones witthin the craniofacial complex grow

• very little emphasis on sutures and cartilages

outline the sutural theory

sutural theory

• primary growth of craniofacial skeleton is genetically regulated and was being controlled within sutures and cartilages

outline the cartilaginous theory

cartilaginous theory

• emphasis was placed on the role of the cartilage in producing the driving force for craniofacial growth 

• nasoseptal cartilage, synchondroses, condylar cartilage etc.

outline the functional matrix theory

functional matrix theory

• growth was not genetically determined

• no real role of genetics

• more to do with function of the head and face complex as a whole

outline the part-counterpart principle

part-counterpart principle

• skull is composed of numerous structural components whose growth and development is complemented by a series of counterparts

• e.g. growth of maxilla as a component as how the mandible grows in response to it - this needs to be matched to maintain normal occlusion

outline the servo-system theory

servo-system theory

• there is genetically regulated growth of primary cartilages within cranial base and nasal septum

  • these provide a changing reference which is mediated by dental occlusion

• the mandible is to respond to this changing occlusal reference by muscle adaptation

the theories of head and face growth go from entirely _______ to entirely _____________

genetic, environmental

graph showing growth

dark green = maxilla

light green = mandible

periods of rapid facial growth occurs at about the same time as…

periods of rapid facial growth occurs at about the same time as rapid growth in height

Björk and Bergensen

if someone is tapering off in their height, what can be inferred about their jaw growth

• it can be inferred that their maxilla and mandible will also almost be at their final size for adulthood

• standing height can essentially be used as a proxy for facial growth

image of growth chart for children

graph showing increase in height overtime 

• red dots = height

• blue dots = velocity

what can be inferred from this graph

velocity of height growth is very fast in babies and during puberty

outline methods of measuring head and face growth

• hand wrist radiograph

• cervical spine maturation radiograph

outline hand wrist radiographs

• ulnar sesamoid bone ossifies at the start of pubertal growth spurt

• median bone maturity stage for each chronological age and sex identified and compiled as atlases

• limited value

• is not really done anymore

outline cervical spine maturation

• undertaken on a lateral cephalometric radiograph

• Baccetti suggested a method based on examining 3 cervical vertebrae

• not used frequently

cervical spine maturation shapes

how can radiographs be used to compare growth

• can compare rapid growth between ages by superimposing radiographic images taken 

• observe when change has stabilised so treatment can start

what are the ways growth can be affected to result in atypical postnatal growth

• congenital

• primary growth disorders - e.g. condylar hyperactivity, condylar hyperplasia, hemi-mandibular elongation

• acquired - e.g. juvenile idiopathic arthritis (can affect mandible growth)

• trauma - e.g. fractured condyle

what is the term for the early fusion of sutures

craniosynostosis

in what syndromes are craniosynostosis seen

• Crouzon

• Apert

• Pfeiffer

outline Crouzon syndrome

• birth defect

• abnormalities caused by fusing of both sides of the coronal suture

• often causes skull to be short in the front and back

• flat cheek bones and flat nose are typical

outline Apert syndrome

• craniofacial abnormality characterised by abnormal head shape

• small upper jaw

• fusion of fingers and toes

outline Pfeiffer syndrome

• birth defect

• abnormalities of skull, hands, feet

• wide-set, bulging eyes

• underdeveloped upper jaw

• beaked nose

brachycephaly is caused by the premature fusion of which suture(s)

coronal

Kleeblattschädel syndrome is caused by the premature fusion of which suture(s)

• almost all of the fibrous sutures

• results in a cloverlead skull shape

Oxycephaly is caused by the premature fusion of which suture(s)

coronal and sagittal sutures 

Scaphocephaly is caused by the premature fusion of which suture(s)

sagittal suture

Trigonocephaly is caused by the premature fusion of which suture(s)

fusion of the two halves of the frontal bones at the metopic suture

outline achondroplasia

• short stature

• large head

• prominent forehead (frontal bossing)

• small midface

• flattened nasal bridge

—

genetic link

outline cleft lip and palate

• syndromic or non-syndromic

• 1 in 700 births

• issue with pharyngeal arches rather than sutures or cartilages

cleft lip and palate statistics

• unilateral CLP 40%

• CP 30%

• bilateral CLP 10%

• CL 10%

• other 10%

which tooth is commonly affected by CLP

canine development

outline result of those who have CLP that have been operated on after birth

• lip minimal effect

• hard palate surgery » maxillary retrusion

• mandible would be small

outline result of those who have CLP that have not been operated on after birth

• (fairly) normal maxilla development

• mandible is smaller