mandible

GROWTH OF MANDIBLE AND

ITS ROLE IN DEVELOPMENT OF ORTHODONTIC

PROBLEMS

Growth and development of an individual is divided into two periods

Prenatal period Post natal period

THE PRENATAL LIFE IS DIVIDED INTO THREE PERIODS:

1.PERIOD OF THE OVUM2.PERIOD OF THE EMBRYO3.PERIOD OF THE FETUS

PRE NATAL GROWTH PHASE

About the fourth week of intrauterine life, the pharyngeal arches are laid down

The first arch is called the mandibular arch and the second arch the hyoid arch.

Each of these five arches contain -

1. A central cartilage rod that form the skeleton of the arch

2. A muscular component termed as bronchomere

3. A vascular component4. A neural element

INTRAMEMBRANOUS BONE FORMATION

The first structure to develop in the primodium of the lower jaw is the mandibular division of trigeminal nerve that precedes the mesenchymal condensation forming the first [mandibular] arch.

At around 36 -38 days of intrauterine life there is ectomesenchymal condensation

Some mesenchymal cells enlarges , acquire a basophilic cytoplasm and form osteoblasts

These osteoblasts secrete a gelatinous matrix called osteoid and result in ossification of an osteogenic membrane.

The resulting intramembranous bone lies lateral to meckel’s cartilage of first [mandibular ] arch.

In the sixth week of the intrauterine life a single ossification center for each half of the mandible arises in the bifurcation of inferior alveolar nerve into mental and incisive branches

During seventh week of intrauterine life bone begin to develop lateral to meckel’s cartilage & continues until the posterior aspect is covered with bone

Between eighth & twelfth week of intrauterine life mandibular growth accelerate , as a result mandibular length increases.

Ossification stops at a piont , which later become mandibular lingula, the remaining part of meckels cartilage continues to form sphenomandibular ligament & spinous process of sphenoid.

Secondary accseeory cartilage appear between tenth & fourteenth week of intrauterine life to form head of condyle , part of coronoid process & mental protuberance

ENDROCHONDRAL BONE FORMATION Endrocondral bone formation is seen in

3 areas of mandible :1) The condylar process2) The coronoid process3) The mental process

THE CONDYLAR PROCESS: At fifth week of intruterine life , an area

of mesenchymal condensation is seen above the ventral part of developing mandible.

At about tenth week it develops in cone shaped cartilage.

It migrate inferior & fuses with mandibular ramus at about 4 month.

This cone shaped cartilage is replaced by bone but its upper end persists acting as growth cartilage & articular cartilage.

THE CORONOID PROCESS: Secondary accessory cartilage appear in

region of coronoid process at about 10- 14 week of intrauterine life.

This cartilage become incorporated into expanding intramembranous bone of ramus & dissapear before birth.

THE MENTAL REGION- In mental region , on either side of

symphysis , one or two small cartilage appear and ossify in seventh week of intrauterine life to become mental ossicles.

These ossicles become incorporated into intramembranous bone when symphysis ossify completely.

POST NATAL GROWTH PHASE At birth the two rami of the mandible are

short , condylar development is minimum and there is no articular eminence in glenoid fossa. A thin layer of fibrocartilage & connective tissue exists at the midline of symphysis to separate right & left mandibular bodies.

At fourth month of age and end of first year symphysial cartilage is replaced by bone

During first year of life appositional growth is active at alveolar border, at distal & superior surfaces of the ramus, at the condyle, along the lower border of mandible and on its lateral surface.

After first year of life these changes occur:

• Mandibular growth become more selective , condyle shows considerable activities, mandible moves and grows downward & forward.

• Appositional growth occurs on posterior border of the ramus and on the alveolar process.

• Resorption occurs along the anterior border of ramus lengthening the alveolar border & maintaining the anterior- posterior dimension of ramus.

Gonial angle changes after little muscle activity.

Transverse dimension is mainly due to growth at posterior border in an expanding V pattern.

• Additive growth at coronoid notch , coronoid process & condyle

• Increased superior inter-ramus dimension.• Alveolar process of mandible grows upward & outward on

an expanding arc. This permit dental arc to accommodate the larger permanent teeth.

Scotts Theory: Scott divides the mandible into three basic types of bone:

1) Basal2) Muscular3) Alveolar

Basal portion is tube like central foundation running from condyle to the symphysis.

Muscular portion [gonial angle &coronoid process] is under influence of masseter, internal pterygoid & temporal muscle. They determine the ultimate form of the mandible in these areas.

Alveolar portion exists to hold the teeth & gradually resorbed in the event of tooth loss.

MOSS say that the mandible as a group of microskeleton unit :

• Coronoid process as one skeleton unit under influence of

temporalis.

• Gonial angle is another skeleton unit under influence of

massetor & internal pterygoid muscles.

• Alveolar process is under the influence of the dentition.

THE CHIN:

• Generalized cortical recession in the flattened regions positioned between the canine teeth.

• On lingual surface, behind the chin heavy periosteal growth occurs , with the dense lamellar bone merging and overlapping on the labial side of the chin.

• In male , the apposition of the bone at symphysis seems to be about the last change in shape during the growing period. This change is much less apparent in the females.

Problems of Mandibular Growth and Their Orthodontic Significance• Hypognathism• Prognathism• Unilateral condylar hypertrophy• Bilateral Condylar hypertrophy• TMJ Ankylosis• Imbalanced Growth• Excessive Transverse Growth• Poor Transverse Growth• Problems of Ramal Growth• Problems of Chin Growth• Problems of Angle Growth

HypognathismPrognathismUnilateral condylar hypertrophyBilateral Condylar hypertrophyTMJ AnkylosisImbalanced GrowthExcessive Transverse GrowthPoor Transverse GrowthProblems of Ramal GrowthProblems of Chin GrowthProblems of Angle Growth

• Restricted growth of mandible• Common in pirre robbin sequence and

patients of cleft lip and palate

• Convex Facial Profile• Hypo divergent face• Skeletal and Dental Class II

malocclusion• Poor airway• Increased chances of Cleft lip and

Palate• Increased Nasolabial Angle• Deep bite• Lip in competency


• Excessive growth of mandible

• Common in males and in conditions like acromegaly

• Concave facial Profile• Hyper divergent face• Dental and Skeletal Class

III mal occlusion• Anterior and Posterior

Cross bite• Anterior cross bite

resulting in restricted growth of maxilla

• Increased mandibular corpus length on Ceph


• Due to some developmental or genetic reasons

• Facial Asymmetry• Chin divergent on side opposite to

hypertrophy• Excessive growth at TMJ• Lingual cross bite on one side and

buccal cross bite on the other side• Can be corrected with BSSO


• Genetic or Hormonal causes

• Common in males• Usually expresses in late teen age when

the growth of mandible continues at condyle

• Clinical feature similar to mandibular hypertrophy

• More likely to be a high angle case


• Usually because of trauma that results in intracapsular bleeding in TMJ

• Can be eight unilateral or bilateral• Can be osseous for fibrous

• Clinical Features similar to Hypognathism

• Limited mouth opening• Airway embarrassment


• Local Areas of imbalances growth

• Results in minor facial asymmetry• Shift of midline• Local malocclusions• Crowding or spacing of teeth


• Due to genetic reasons• Common in Prognathic patients

• Brachiofacial Appearance• Bilateral Cross bite• Anterior Divergent face• In severe cases there can be total

lingual non occlusion – Crocodile bite


• Common in Hypognathic patients• Clinical features similar to hypognathic

patients

• Usually class II cases• Posterior Divergent faces• In severe cases there can be complete

buccal non occlusion – Broodie’s Bite


• Excessive Vertical Ramal Growth:▫ Bracheofacial Patients▫ Low angle cases▫ Anterior deep bite

• Poor Vertical Ramal Growth:▫ Dolicofacial Patients▫ High Angle Cases▫ Anterio open bite

• Excessive Horizontal Ramal Growth:▫ More broad oropharynx

• Poor Horizontal Ramal Growth:▫ Narrow oropharynx▫ Chances of airway embarrassment


Prominent Chin•Common in males•Due to late gonial bone deposition•Due to excessive mental bone resorption•Can be treated with genioplasty


• Excessive transvers growth▫ Common in males▫ Due to excessive bone deposition at

angles▫ Can be corrected with surgery

Significance• Timely identification of growth disturbances

helps in interception of developing malocclusions and other orthodontic and esthetic facial problems.

• Knowing the timing of development of different facial structures gives you idea about the long term facial appearance of the patient.

• Timely diagnosis of growth problems gives you a chance to treat the problem with functional appliances.

mandible

Documents

alveolar process of

mental process

week of intrauterine

coronoid process condyle

region of coronoid process

week ofintrauterine

week of intruterine

alveolar border