GROWTH AND

DEVELOPMENT

• Growth can be defined as an increase in size or number.

• Development can be defined as an increase in complexity.

• Growth is largely an anatomic phenomenon whereas development is physiological and behavioral.

Patterns Of Growth

• Pattern of growth refers to changes in proportions over time.

• Example All the tissues of the body do not grow at the same rate.Scammons curve for growth for the four major tissue systems of the body shows that growth of the neural tissues is nearly complete by 6 or 7 years of age. General body tissue including muscle bone and viscera show an s shaped curve with a definite slowing of the rate of growth during childhood and acceleration at puberty. Lymphoid tissues proliferate far beyond the adult amount in late childhood, and then undergo involution at the same time that growths of the genital tissues accelerate rapidly.

Timing of Growth

• Timing in growth refers to the fact that the same event happens for different individuals at different times or in other words the biologic clocks of different individuals are set differently.

• In human adolescence, some children grow rapidly and mature early, completing their growth quickly and thereby appearing on the high side of development charts until their growth ceases and their contemporaries begin to catch up.

METHODS OF STUDYING PHYSICAL GROWTH

Craniometry

• This was the first of the measurement approaches for studying growth based on measurements of human skulls. It has the advantage that rather precise measurements can be made on dry skulls and has the important disadvantage that it provides cross sectional data which is not supportive for growth studies.

Anthropometry

In this technique, various landmarks established in studies of dry skulls are measured in living individuals’ simply by using soft tissue points overlying these bony landmarks. Although the soft tissue introduces variation, anthropometry does make it possible to follow the growth of an individual directly, making the same measurements repeatedly at different times. This produces longitudinal data which is advantageous for growth studies.

Cephalometric Radiology• This method is not only important

in the study of growth, but also in the clinical evaluation of orthodontic patients. This technique allows a direct measurement of bony skeletal dimensions, since the bone can be seen through the soft tissue covering in a radiograph, but it also allows the same individual to be followed over time. Growth studies are done by superimposing a tracing or digital model of a later cephalogram on an earlier one, so that the changes can be measured. The disadvantage of this technique is that it produces a two dimensional image of a three dimensional structure therefore all measurements are not possible.

3 D Imaging• CT allows the 3D constructions of

the cranium and face, to plan surgical treatment for patients with facial deformities. CBCT has been applied to facial scans reducing the amount of radiation dose and allowing scans of patients with radiation dose much closer to hat of cephalograms. MRI also provides 3D images that can be used in studies of growth, with the advantage that there is no radiation exposure with this technique. This method has already been applied to analysis of growth changes produced by functional appliances.

Vital staining

• This is a technique in which dyes that stain mineralized tissues are injected into an animal. These dyes remain in the bones and teeth of the animal and can be detected later by the sacrifice of the animal. A dye called alizarin which is still is used for vital staining studies reacts strongly with where bone calcification is occurring. Since these are the sites of active skeletal growth, the dye marks the location at which active growth was occurring when it was injected. These studies are not possible in human beings. Tetracycline a drug used to treat infections is an excellent vital stain that binds to calcium at growth sites in the same way as alizarin. With the development of radioactive tracers, it has been possible to use any almost any radioactively labeled metabolite that can be incorporated in tissues as a vital stain. The gamma emitting isotope Tc99 can be used to detect areas of rapid bone growth in humans.

Implant Radiography• In this technique applicable to

studies of human beings, inert metal pins are placed in bones anywhere in the skeleton, including the face and the jaws. If metallic implants are placed in the jaws, a considerable increase in the accuracy of a longitudinal cephalometric analysis of growth pattern can be achieved. Superimposing cephalometric radiographs on the implanted pins allows precise observation of both changes in the position of one bone to another and changes in the external contours of individual bones.

THEORIES OF GROWTH CONTROL

Growth site and growth centre

• Three major theories have attempted to explain the determinants of craniofacial growth.

• The first one is based upon bone as the primary determinant, second on the cartilage while the third one is based upon soft tissue matrices.

• Growth Site is a location at which growth occurs• Growth Centre is a location at which

independent (genetically controlled) growth occurs.

Growth Centre

Growth Centre- site of endochondral ossification with tissue-separating force (genetically controlled) growth occurs. , contributing to the increase of skeletal mass.

i.e. location at which independent growth occurs

Growth Site

Growth site: regions of periosteal or sutural bone formation and modeling resorption adaptive to environmental influences.

i.e. merely location at which growth occurs.

Sutural Dominance Theory

• SICHER – studies using vital dyes – sutures caused much of growth

• “….the primary event in sutural growth is the proliferation of the connective tissue between the two bones. If the sutural connective tissue proliferates it creates the space for oppositional growth at the borders of the two bones.”

• Connective tissue in sutures of nasomaxillary complex & vault – separated bones like synchondrosis & epiphyseal plate

• 2 differing views concerning the structure of the sutures – 1. Three-layer structure: - Connective tissue between the two bones - same as cartilage at the base of the skull, epiphyses, and articular surfaces of long bones - "spreading" of the suture, initiated by the proliferation of the middle layer cells of the sutural tissue. -"tissue-separating force" in the sutural tissue.

2. Five-layer structure : -Each bone at the suture has its own two-layer periosteum covering + opposing surfaces of the bones -fifth layer between these periosteal layers - allows for slight adjustments between the bones during growth -active proliferating role - layers of the periosteums of each bone.

Evidence against Sutural dominance theory

1. Subcutaneous auto transplants of the zygomaticomaxillary suture area in the guinea pig have not been found to grow – lack of innate growth potential.

2. Growth of sutures – respond to external stimuli.3. Extirpation of facial sutures - no appreciable effect on

growth of the skeleton.4. Shape of sutures - depends on functional stimuli5. Closure of sutures -extrinsically determined. 6. Sites of sutures - not predetermined .

CONCLUSION:

• Sutures are growth sites not centres.

• Adaptive, compensatory or secondary growth occurs in these sutures.

Cartilaginous theory

SCOTT’S HYPOTHESIS:• Intrinsic growth-controlling factors in cartilage &

periosteum. • Sutures are secondary & dependent on

extrasutural influences.• Cartilaginous part of skull must be recognised as

primary centres of growth, with nasal septum being a major contributor in maxillary growth, per se.

• Sutural growth – responsive to synchondrosis proliferation & local environmental factors.

Cranial Base Synchondroses

• Removal of spheno-occipital synchondrosis - results in an arrest of growth in length of the cranial base .

• Pressure & tension – little effect on cartilage.

• Intramembranous bone- immediate response.

• Endochondral cranial base – lesser response to brain growth than intramembranous cranial vault.

• Primary centres of growth – Sarnat, Burdi, Baume, Petrovic & others.

• Endochondral ossification at the synchondroses- only a response to external stimuli?

• Cartilage- lacks same amount of independent growth potential as transplants of epiphyseal cartilage under similar experimental conditions.

• Spheno-occipital synchondrosis appears to close much earlier than is usually stated in the textbooks -11 to 16 years of age

Nasal septal cartilage

• Scott- primary cartilage in nasal septum – primary mechanism for growth of nasomaxillary complex.

• Latham- ligament extending from nasal septal cartilage to to anterior premaxillary region – SEPTOPREMAXILLARY LIGAMENT.

• This is an important relation between midfacial & nasal septal growth – especially before birth.

• Histologic examination - endochondral ossification at the septo-ethmoidal junction and area of proliferation at the vomeral edge of the cartilage

• In the palatal area - resorption on the nasal side and apposition on the oral side of the bony palate.

Condylar cartilage

• Growth of the condylar cartilage is responsible for the anteroposterior growth of the mandible- primary growth centre.

• Scott- growth of the condylar cartilage enables the condyle "to grow upwards and backwards so as to maintain the contact at the temporomandibular joint as the mandible is carried downwards and forwards by the growth of the upper facial skeleton."

• If the condylar cartilage is transplanted to a relatively nonfunctional site, such as the subcutaneous or brain tissue, it does not maintain its structure and does not behave like the condylar cartilage in situ.

• Bilateral condylectomy, congenital absence of the rami- no appreciable effect on the growth of the rest of the mandible in humans.

Functional Matrix Theory

• According to this theory the control growth lies within the adjacent soft tissues.

• This theory was put forward by Moss in 1960.• This theory holds that neither the cartilage of the

mandibular condyle nor the nasal septum is a determinant of jaw growth. Instead the growth of the face occurs as a response to functional needs and is mediated by the soft tissue in which the jaws are embedded i.e. the soft tissue grows and both bone and cartilage react.

• Growth of the cranial vault is a direct response to the growth of the brain. Pressure exerted by the brain separates the cranial bones at the sutures, and new bone passively fills in at these sites so that the brain case fits the brain. cranium is also very small, and the condition of microcephaly

• In hydrocephalus, the absorption of CSF is impeded, fluid accumulates and intracranial pressure builds up. This pressure does not allow the brain to grow and these patients have small brains but this condition leads to an enormous skull.

• Other example is the relationship between the eye and the orbit. An enlarged eye will cause a corresponding change in the size of the orbital cavity and the eye acts as functional matrix.

• According to Moss, the major determinant of growth of the maxilla and mandible is the enlargement of the oral and nasal cavities which grow in response to functional needs.

• In summary, it appears that growth of the cranium occurs almost entirely in response to growth of the brain. Growth of the cranial base is primarily the result of endochondral growth and bony replacement at the synchondroses, which have independent growth potential but perhaps are influenced by growth of the brain. Growth of the maxilla occurs from a combination of growth at sutures and direct remodeling of the surfaces of bone. The maxilla is translated downwards and forwards as the face grows, and new bone fills at the sutures. Growth of the mandible occurs by endochondral proliferation at the condyle and apposition and resorption of bone at its surfaces. It seems clear that that the mandible is translated in space, by the growth of the muscles and other adjacent soft tissue structures, and that addition of new bone at the condyle is in response to the soft changes.