The study of head form in man has always been ofconsiderable interest to anthropologist, anatomists, &other students of human growth. In fact, the wide array of students involved in solving thecomplex phenomenon of “GROWTH” have been aptlydescribed by Krogman as early as 1943 in these goldenwords:- “ Growth was conceived by ananatomist ,born to a biologist ,delivered by a physician,left on a chemist’s doorstep & adopted by a physiologist.At an early age she eloped with a statistician, divorcedhim for a psychologist & is now being wooed , alternately& concurrently by an endocrinologist,a pediatrician , aphysical anthropologist, an educationalist , a biochemist ,a physicist , a mathematician , an orthodontist , aeugenicist & the children’s bureau”.
According to “TODD” “Growth is an increase insize.” &“Development is progresstowards maturity .”
Some definitions related to GrowthAs is the nature of growth where in the conceptskeep changing with new research findings therehas been no single definitions associated with it: Different researchers have defined growth invarious ways.-The self multiplication of living substance – JXHuxely.- Increase in size, change in proportion & progressivecomplexity.- Krogman-Entire series of sequential anatomic & physiologicalchanges taking place from the beginning ofprenatal life to senility –Meredith.-Quantitative aspect of biologic development perunit of time-Mayers-Change in any morphological parameter, which ismeasurable-Moss.
Terminology Related To Growth:GROWTH FIELDS : The outside & inside surfaces of a bone areblanketed by a mosaic-like, pattern of soft tissues , cartilage orosteogenic membrane called as Growth Fields. They when altered are capable of producing an alterationin the growth of the particular bone.GROWTH SITES : Growth sites are growth fields that have a specialsignificance in the growth of a particular bone. Eg. Mandibular condyle in the mandible, Maxillary tuberosity in the maxilla.The growth sites may possess some intrinsic potential togrowth.
REMODELING : It is the differential growth activity involvingsimultaneous deposition & resorption on all the inner &outer surfaces of the bone. Eg. Ramus moves posteriorly by a combination ofresorption & deposition.GROWTH CENTERS: Growth centers are special growth sites ,which control the overall growth of the bone. Eg. Epiphyseal plates of long bone.
Mechanism Of Bone Growth• Bone is a specialized tissue of mesodermal origin.Itforms the structural framework of the body.• Bone is calcified tissue that supports the body &gives points of attachment to the musculature.• Normal bone contains between 32-36% of organicmatter. -Bone deposition & resorption -Cortical drift -Displacement
BONE DEPOSITION & RESORPTION:Bone changes in shape & size by two basic mechanisms,bonedeposition & bone resorption.The bone deposition & resorptiontogether is called “ BONE REMODELING”.The changes that bone deposition & resorption can produceare: Change in size Change in shape Change in proportion Change in relationship of the bone with adjacent structures.
Cortical Drift Most bones grow by interplay of bonedeposition & resorption .A combination of bone deposition & resorptionresulting in a growth movement towards thedeposition surface is called “Cortical Drift”. If bone deposition & resorption on either side of a bone are equal The thickness of the bone remains constant.If in case more bone is deposited on one side & less bone resorbed on the opposite side The thickness of the bone increases.
Displacement:•It is the movement of the whole bone as a unit.•Displacement can be of two types. Primary displacement: If a bone gets displaced as a result of its owngrowth, it is called “Primary displacement”. e.g.. Growth of the maxilla at the tuberosity region results in pushingof the maxilla against the cranial base which results in pushing ofthe maxilla against the cranial base which results in thedisplacement of the maxilla in a forward & downward direction.Secondary displacement: If the bone gets displaced as a result of growth &enlargement of an adjacent bone, it is called “Secondarydisplacement.”e.g.. The growth of the cranial base causes the forward &downward displacement of the maxilla
Characteristics of Bone Growth Bone formation occurs by 2 methods of differentiationof mesenchymal tissues that may be of mesodermal orectomesenchymal origin.Accordingly 2 types of bone growth is normally seen. 1) Intra-membranous ossification : The transformation of mesenchymal connective tissue usually in membranous sheets, into osseous tissues.
2. Endochondral ossification: The conversion of hyaline cartilage prototype models into bone. The interstitial growth expansion capability of cartilage, even under weight pressure due to its avascularity precluding ischemia,(Cartilage nutrition is provided by per fusing tissue fluids that are not easily obstructed by load pressures) allows for directed prototype cartilage growth. The cartilage „template „ is then replaced by endochondral bone accounting for indirect bone growth.
Growth and development of an individual can bedivided into:- PRENATAL & POSTNATAL periods. The pre-natal period of development is a dynamicphase in the development of a human being. During this period, the height increases by almost5000 times as compared to only a threefold increaseduring the post-natal period. The pre-natal life can be arbitrarily divided intothree periods. 1. Period of the Ovum 2. Period of the Embryo 3. Period of the Fetus
1. Period of the ovum: This period extends for a period of approximately two weeks from the time of fertilization. During this period the cleavage of the ovum and the attachment of the ovum to the intra-uterine wall occurs.2. Period of the embryo: This period extends from the fourteenth day to the fifty sixth day of intra-uterine life. During this period the major part of the development of the facial & the cranial region occurs.3. Period of the fetus: This phase extends between the fifty sixth day of intra-uterine life till birth. In this period ,accelerated growth of the cranio-facial structures occurs resulting in an increase in their size. In addition, a change in proportion between the various structures also occurs.
Prenatal Growth Of MaxillaAround the fourth week of intra-uterine life, aprominent bulge appears on the ventral aspect ofthe embryo corresponding to the developingbrain. Below the bulge a shallow depression whichcorresponds to the primitive mouth appears called“ STOMODEUM”.The floor of the stomodeum is formed by thebuccopharyngeal membrane which separatesthe stomodeum from the foregut
Byaround the 4th week of intra-uterine life, fivebranchial arches form in the region of the future head& neck. Each of these arches gives rise to muscles,connective tissue, vasculature, skeletal components,&neural components of the future face.
The first branchial arch is called the mandibular arch& plays an important role in the development of thenaso- maxillary region. The mesoderm covering the developing forebrainproliferates & forms a downward projection thatoverlaps the upper part of stomodeum .This downward projection is called “FRONTO-NASALPROCESS”.
The stomodeum is thus overlapped superiorly bythe fronto-nasal process.The mandibular arches of both The sides form thelateral walls of the stomodeum.The mandibular arch gives off a bud from its dorsalend called the “MAXILLARY PROCESS”
The maxillary process grows ventro-medio-cranialto the main part of the mandibular arch which isnow called the “MANDIBULAR PROCESS".Thus at this stage the primitive mouth orstomodeum is overlapped from above by thefrontal process, below by the mandibular process &on either side by the maxillary process.
The ectoderm overlying the fronto-nasal processshows bilateral localized thickenings above thestomodeum. These are called the “NASAL PLACODES”. Theseplacodes soon sink and form the nasal pits. The formation of these nasal pits divides thefronto-nasal process into two parts: a)The medial nasal process & b)The lateral nasal process
The two mandibular processes grow medially & fuseto form the lower lip & lower jaw.As the maxillary processes undergrows growth, thefronto-nasal process become narrow so that the twonasal pits come closer. The line of fusion of the maxillary process & themedial nasal process corresponds to the naso-lacrimal duct.
POST-NATAL GROWTH Of MAXILLA INTRODUCTION Develops from a centre of ossification in the mesenchyme of the maxillary process. No primary cartilage exists. Centre of ossification is closely associated with the cartilage of the nasal capsule. Primary centre of ossification develops near the division of inferior orbital nerve into anterior superior alveolar nerve (future infra orbital region).
From the centre of ossification the bone formation extends posteriorly towards the developing zygoma and anteriorly towards the incisor region Ossification spreads superiorly to form the frontal process of maxilla A bony trough is formed for the infra orbital nerve From this trough lateral alveolar plate forms for the developing tooth germs Ossification spreads into the palatine processes to form the hard palate Medial alveolar plate develops from the palatal process Medial and lateral alveolar plates form the trough for the tooth germs
POST-NATAL GROWTH Of MAXILLA Since, the maxillary complex is attached to thecranial base, there is a strong influence of the latteron the former. Although there is no sharp line of demarcationbetween the cranium & maxillary growth gradients,yet the position of the maxilla is dependent upon thegrowth at spheno-occipital & spheno-ethmoidsynchondroses.Hence, while discussing the growth ofnaso-maxillary complex, we have to lookinto two aspects.
1)The displacement in the positionof the maxillary complex -Secondary displacement-Occurs in a downward & forward directionas the cranial base grows. -Primary displacement-occurs in a forward direction. This occurs by growth of the maxillarytuberosity in a posterior direction . This results in the whole maxilla beingcarried anteriorly.
2) Growth at sutures:-Sutural connective tissue, - Proliferation - Ossification - Surface apposition - Resorption - Translation are the mechanisms for maxillary growth.-Maxilla is related to cranium at least partially by the, -fronto nasal suture -Fronto maxillary suture -Zygomaticotemporal suture -Zygomaticomaxillary suture -Pterygopalatine suture These sutures are all oblique & more or less parallel witheach other. The growth in these areas would serve tomove the maxilla downward & forward
3)Surface Remodeling: Remodeling occurs by bonedeposition & resorption to bring about: a) Increase in size b) Change in shape c) Change in functional relationship
Bone remodeling seen in the midfacial region
Bone remodeling of the palate resulting inits downward displacement
Growth of the palate exhibiting V pattern of growth
The naso-maxillary complex as it emerges frombeneath the cranium
SECONDARY CARTILAGE: Also known as the zygomatic or the malar cartilage, appears in developing zygomatic process of maxilla. At birth body of maxilla is relatively small as it lacks the maxillary sinus.MAXILLARY SINUS: Forms during the 16th wk as shallow groove on the nasal aspect of the developing maxilla. Still rudimentary at birth and is that of a size of a pea.
Moss Cites three types of bone growth changes tobe observed in the maxilla1) Those changes that are associated with compensations for the passive motions of the bone brought about by the primary expansions of the orofacial capsule.2) There are changes in bone morphology associated with alterations in the absolute volume, size, shape or spatial position of any or all the several relatively independent maxillary functional matrices, such as orbital mass.3) There are bone changes associated with the maintenance of the form of the bone itself. All these changes do not occur simultaneously but rather differentially or sequentially.
The palate “is the tissue that interposesbetween the oral & nasal cavities”, itdevelops from 2 parts: the primary palate & the secondary palateDevelopment of the primary palate( median palatine process, premaxilla)Appears earlier than 2ry palate at 6wiu.It is a triangular bone anterior to the incisivepapilla that supports the 4 maxillary incisors.
Primary Palate• Develops from the deep tissues of theintermaxillary segment during thedeepening of the nasal pit to form thenasal sac. Tissues beneath the nasal sacenlarge & grow inferiorly to form theprimary palate.• It acquires the triangular shape due tothe continuous growth of the maxillaryprocess in a medial direction.
• During the deepening of the nasal sac & theformation of the primary palate, the ectoderm atthe depth of the nasal sac proliferates to form athickened ectodermal plate, the nasal fin, whichthen thins down to a thin double thickenedmembrane called the “ oro-nasal membrane” ( 2layers of ectoderm from stomodeum & nasalsac).• The rupture of the oronasal membrane detachesthe 1ry palate from the nasal cavity.• 1ry palate & central parts of upper lip are oneunit at first, then by 8wiu become separated bythe vestibular lamina
Development of the secondary palate• The secondary palate forms the palate posterior to the incisive fossa that comprises both the hard & the soft palate.• The inferior medial edges of the maxillary process forms the palatine processes (shelves) at 6wiu.
The tongue is narrow & high filling all theoro-nasal cavity, so the palatine shelves grow medially & downwards (vertically) on either sides of the tongue.
Palatal shelf elevation• The fusion of the palatine shelves occursfirst just posterior to the primary palate.•From this point, the fusion of the palatineshelves with premaxilla proceeds anteriorly& fusion betweenbetween palatineshelves proceedsposteriorly.
• Fusion also between P shelves & the nasalseptum( formed from the interior parts of thepremaxilla) except posteriorly, where the softpalate & uvula remain unattached.
Hard & soft Palate Formation• The palate then becomes invaded in itsanterior 2/3 by bone (from premaxillary &maxillary palatal centers) to form the hardpalate.• The posterior part becomes invaded bymuscles to form the soft palate• The incisive suture demarcate the unionbetween 1ry & 2ry palate, while palatineraphe demarcate union between 2 palatineshelves.
•Theincisive suture demarcate the unionbetween 1ry & 2ry palate ( young skulls).•While palatine raphe demarcate unionbetween 2 palatine shelves.
Developmental anomalies Cleft Palate• Less common than cleft lip• Due to: 1. lack of growth, or failure of fusion between medial &lateral palatine process & nasal septum. 2. Interruption of the growth after initial fusion ( at anypoint). 3. Interference with palatal shelves elevation.
Cleft Palate1. Cleft primary palateClefts anterior to incisive Foramen.Results from Failure of lat. palatine Processes tomeet & fuse With primary palate Associated withmissing or malformed teeth.
2. Clefts secondary palate• Clefts posterior to incisive foramen. As fusion of 2ry palate begins at incisivepapilla& proceeds posteriorly, The degree of cleft may vary From simplestform of bifid uvula to acomplete cleft involving both hard & softpalate.
3. Cleft both primary & secondary palate• Complete palatal clefts. Results from :- failure of growth Orlack of fusion of 3 palatine processes with each other & with the nasal septum