Bone growth occurs through the balanced processes of deposition and resorption, known as bone remodeling. This allows for changes in bone size, shape, proportion and relationships. Two types of bone formation are endochondral, where cartilage precedes bone, and intramembranous, where bone forms directly in fibrous membranes. Several theories have attempted to explain craniofacial growth, including genetic influences, growth at sutures, roles of cartilage, and functional relationships between bones and surrounding tissues. Enlow's expanding V principle and neurotrophism further describe how functional demands can influence bone growth patterns.

1. GROWTH AND DEVLOPMENT-
GENERAL PRINCIPLES AND CONCEPTS
SURBHI YADAV
FINALYEAR
ARMY COLLEGE OF DENTAL SCIENCES

2. MECHANISM OF BONE GROWTH
•Bone growth is based on certain basic
principles .
•Bones do not grow symmetrically but
grow by complex differentiation
mechanism .

3. • All bone growth is a complicated
mixture of the two basic principles
deposition and resorption .
• the process of deposition and resorption
together is called bone remodelling

4. •E.g.The ramus
moves posteriorly
by the combination of
deposition and
resorption.
• so the anterior
part of the ramus
gets remodeled

5. Changes that bone remodelling can
produce are:
•Change in size
• Change in shape
•Change in proportion
•Change in relationship of bone with
adjacent structures

6. CORTICAL DRIFT
 Combination of bone deposition and
resorption resulting in growth
movement towards the depositing
surface is called cortical drift.
 bone deposition and resorption on
either side of bone are equal thickness of
bone remain constant
 More bone is deposited on one side
and less bone is resorbed on opposite
side then thickness of bone increases

7. DISPLACEMENT
 Movement of whole bone as a unit
1. PRIMARY : displaced as a result of its own
growth ( eg. Growth of maxilla at
tuberosity region against cranial base
results in forward and downward
displacement )
2. SECONDARY :displaced due to growth
and enlargement of adjacent bone
(growth of cranial base causes forward
and downward displacement of maxilla)

8. OSTEOGENESIS
Process of bone formation takes place in 2 ways
1. ENDROCHONDRAL BONE FORMATION
2. INTRA MEMBRANOUS BONE FORMATION

9. ENDOCHONDRAL BONE FORMATION
 In this type of osteogenesis bone formation is
preceded by formation of cartilage which is later
replaced by bone
 Stages:
mesenchymal cells differentiate into
chondroblasts and lay down hayline
cartilage
Intercellular substance becomes cacified due
alkaline phasphatase secreated by cartilage cells
nutrition to cartilage cells is cutoff leading to
their death (primary areole)

10. formation of secondary areolae due to inervation
of calcified matrix with blood vessels and
osteogenetic cells
Osteogenetic cells from perichondrium become
osteoblasts and line along the surface of bars of
cacified matrix
Osteoblast lay down osteoid that gets calcified to
form lamella of bone

12. INTRA MEMBRANOUS BONE FORMATION
 In this type of ossification bone is laid down
directly in a fibrous membrane
 Stages
mesenchymal cells gets aggregated at site of bone
formation
Some mesenchymal cells lay down bundles of
collagen fibres
Some cells enlarge; acquire basophillic cytoplasm
to form osteoblasts and secreate osteoid

13. Deposit calcium salts in osteoids leading to
conversion of osteoid into bone lamella
Osteoblasts move away from lamella and
add new layer of osteoid that later gets
calcified
Some osteoblasts gets entrapped in the
matrix and are called osteocytes

15. THEORIES OF GROWTH
GENETIC THEORY
 Genetic theory was given by Brodie
 One of the earliest theories put forward
 It simply states that growth is controlled
by genetic influence and is preplanned
 genes determine and control the whole
process of craniofacial growth

16. SUTURAL THEORY
 Given by Sicher andWeinmann in 1947 .
 he believed that craniofacial growth occurs at
sutures
 Acc to him, paired parallel sutures that
attach facial areas to skull and cranial base
region push nasomaxillary component
forward to pace its growth with that of
mandible

17. POINTS AGAINST THIS THEORY
 When area of suture trasplanted to another
location the tissue doesnot continues to grow
– shows lack of innate growth potential of
sutures
 Growth takes place in untreated cases of cleft
palate even in absence of sutures
 Microcephaley and hydrocephaley raised
doubts about intrinsic genetic stimulus of
sutures

18. CARTILAGENOUS THEORY
 Given by James Scott
 Acc . to him intrisic growth controlling
factors are present in cartilage and
periosteum with sutures only being
secondary.
 He viewed cartilaginous sites thoughout skull
as centres of growth
 Acc. to him nasal septal cartilage is
pacemaker for growth of entire naso-
maxillary complex

19.  Mandible is considered as diaphysis of long
bone bent into a horseshoe shape with
epiphysis removed so that there is cartilage
constituting half an epiphyseal plate at ends
which are represented by condyles
 Points in favour:
 In many bone cartilage growth occurs and bone
merely replaces it
 If part of endosteal plate is transplanted to
different location it continues to grow – innate
growth potential eg.Nasal septal cartilage
 Experiments on rabbits involving removal of
nasal septal cartilage demonstrated retarded
midface devlopment

20. FUNCTIONAL MATRIX THEORY
 Given by Melvin Moss
 The functional matrix concept attempts to
comprehend between form and function.
 The functional matrix hypothesis claims that the
origin, form , position, growth and maintenance
of all skeletal tissues and organ are always
secondary, compensatory and necessary
responses to chronologically and
morphologically prior events or processes that
occur in specifically related nonskeletal tissues
,organs or functioning spaces(functional
matrices).

22. PERIOSTEAL MATRIX
 Periosteal matrices act directly and actively on their
skeletal component
 Alteration in their functional demand produce as a
secondary compensatory transformation of size and
shape of their skeletal unit
 Examples of periosteal matrices includes:
 Muscles.
 Blood vessels and nerves lying in grooves or
entering or exiting through foramina.
 Teeth.
CAPSULAR MATRIX
 Capsular matrices act indirectly and passively on
their related skeletal units producing a secondary
compensatory traslation in space

23.  Example:
Neurofacial capsule and orofacial capsule
 The alteration in spatial position of skeletal
components is brought about by expansion of
enveloped capsule within which facial skull
arise, grow and are maintained
 This surrounds and protects th orophoryngeal
functioning spaces, and the volumetric
expansion of these spaces serves as a primary
morphogenetic extent in facial skull growth.

24. VAN LIMBORGH’S THEORY
Multifactorial theory put forward byVan
limborgh
Acknowleged three popular theories
 Sicher’s {cartilagenous theory}
 Scott’s [genetic theory]
 Moss’s { functional matrix theory}

25. CONTROLLING FACTORS IN CRANIOFACIAL
GROWTH

26. ENLOW’S EXPANDING V PRINCIPLE
 Most useful and basic
concept in facial growth
as many facial and
cranial bones have aV
shaped configuration.
 Bone
deposition(+)occurs on
the inner side
and resorption (-)
occurs on the outer
surface.

27.  Deposition also takes
place at the end of
two arms ofV
resulting in growth
movement towards
the end.

28. TRANSMISSION OF FUNCTIONAL STIMULUS TO THE
BONE-NEUROTROPHISM
 Neurotrophism is a non impulsive transmittive
neurofunction involving axoplasmic transport
providing for long term interaction between
neurons and innervated tissue , which
homeostatically regulate the morphological
compositional and functional integrity of those
tissues.
 Types of neurotrophism:
1.Neuromuscular
2.Neuroepithelial
3.Neurovisceral

29.  Neuroepithelial : normal epithelial growth is
controlled by release of certain neurotrophic
substances by nerve synapses
 Neuromuscular :embryonic myogenesis is
independent of neural innervation; at myobast
stage neural innervation is established without
which further myogenesis cannot continue
 Neuroviseral : salivary gland, fat tissues and
other organs are also trophically regulated