GROWTH OF MANDIBLE ANDITS ROLE IN DEVELOPMENT OF ORTHODONTIC PROBLEMS
Growth and development of an individual is divided into two periodsPrenatal periodPost 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 arch2. A muscular component termed as bronchomere3. A vascular component4. A neural element
INTRAMEMBRANOUS BONE FORMATIONThe first structure to developin the primodium of the lowerjaw is the mandibular divisionof trigeminal nerve thatprecedes the mesenchymalcondensation forming the first[mandibular] arch.
At around 36 -38 days of intrauterine life there isectomesenchymal condensationSome mesenchymal cells enlarges , acquire abasophilic cytoplasm and form osteoblastsThese osteoblasts secrete a gelatinous matrixcalled osteoid and result in ossification of anosteogenic membrane.
The resulting intramembranous bone lies lateral to meckel’scartilage of first [mandibular ] arch.In the sixth week of the intrauterine life a single ossificationcenter for each half of the mandible arises in the bifurcationof inferior alveolar nerve into mental and incisive branches
During seventh week of intrauterine life bonebegin to develop lateral to meckel’s cartilage &continues until the posterior aspect is coveredwith boneBetween eighth & twelfth week of intrauterinelife mandibular growth accelerate , as a resultmandibular length increases.
Ossification stops at a piont , which later becomemandibular lingula, the remaining part of meckelscartilage continues to form sphenomandibular ligament &spinous process of sphenoid.Secondary accseeory cartilage appear between tenth &fourteenth week of intrauterine life to form head ofcondyle , 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 butits 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 lifeappositional growth isactive at alveolar border,at distal & superiorsurfaces of the ramus, atthe condyle, along thelower border ofmandible and on itslateral 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) Basal 2) Muscular 3) 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 andTheir 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
Hypognathism • Restricted growth of mandiblePrognathism • Common in pirre robbin sequence andUnilateral condylar patients of cleft lip and palatehypertrophyBilateral Condylar • Convex Facial Profilehypertrophy • Hypo divergent faceTMJ Ankylosis • Skeletal and Dental Class II malocclusionImbalanced Growth • Poor airwayExcessive Transverse • Increased chances of Cleft lip and PalateGrowth • Increased Nasolabial AnglePoor Transverse Growth • Deep biteProblems of Ramal Growth • Lip in competencyProblems of Chin GrowthProblems of Angle Growth
Hypognathism • Excessive growth of mandiblePrognathism • Common in males and inUnilateral condylar conditions like acromegalyhypertrophyBilateral Condylar • Concave facial Profilehypertrophy • Hyper divergent faceTMJ Ankylosis • Dental and Skeletal Class IIIImbalanced Growth mal occlusionExcessive Transverse • Anterior and Posterior CrossGrowth bitePoor Transverse Growth • Anterior cross bite resultingProblems of Ramal Growth in restricted growth of maxillaProblems of Chin Growth • Increased mandibular corpusProblems of Angle Growth length on Ceph
Hypognathism • Due to some developmental or genetic reasonsPrognathismUnilateral condylar • Facial Asymmetryhypertrophy • Chin divergent on side opposite toBilateral Condylar hypertrophyhypertrophy • Excessive growth at TMJTMJ Ankylosis • Lingual cross bite on one side and buccal crossImbalanced Growth bite on the other sideExcessive Transverse • Can be corrected with BSSOGrowthPoor Transverse GrowthProblems of Ramal GrowthProblems of Chin GrowthProblems of Angle Growth
Hypognathism • Genetic or Hormonal causesPrognathismUnilateral condylar • Common in maleshypertrophy • Usually expresses in late teen age when theBilateral Condylar growth of mandible continues at condylehypertrophy • Clinical feature similar to mandibularTMJ Ankylosis hypertrophyImbalanced Growth • More likely to be a high angle caseExcessive TransverseGrowthPoor Transverse GrowthProblems of Ramal GrowthProblems of Chin GrowthProblems of Angle Growth
Hypognathism • Usually because of trauma that results inPrognathism intracapsular bleeding in TMJUnilateral condylar • Can be eight unilateral or bilateralhypertrophy • Can be osseous for fibrousBilateral Condylarhypertrophy • Clinical Features similar to HypognathismTMJ Ankylosis • Limited mouth openingImbalanced Growth • Airway embarrassmentExcessive TransverseGrowthPoor Transverse GrowthProblems of Ramal GrowthProblems of Chin GrowthProblems of Angle Growth
Hypognathism • Local Areas of imbalances growthPrognathismUnilateral condylar • Results in minor facial asymmetryhypertrophy • Shift of midlineBilateral Condylar • Local malocclusionshypertrophy • Crowding or spacing of teethTMJ AnkylosisImbalanced GrowthExcessive TransverseGrowthPoor Transverse GrowthProblems of Ramal GrowthProblems of Chin GrowthProblems of Angle Growth
Hypognathism • Due to genetic reasonsPrognathism • Common in Prognathic patientsUnilateral condylarhypertrophy • Brachiofacial AppearanceBilateral Condylar • Bilateral Cross bitehypertrophy • Anterior Divergent faceTMJ Ankylosis • In severe cases there can be total lingual nonImbalanced Growth occlusion – Crocodile biteExcessive TransverseGrowthPoor Transverse GrowthProblems of Ramal GrowthProblems of Chin GrowthProblems of Angle Growth
Hypognathism • Common in Hypognathic patientsPrognathism • Clinical features similar to hypognathicUnilateral condylar patientshypertrophyBilateral Condylar • Usually class II caseshypertrophy • Posterior Divergent facesTMJ Ankylosis • In severe cases there can be complete buccalImbalanced Growth non occlusion – Broodie’s BiteExcessive TransverseGrowthPoor Transverse GrowthProblems of Ramal GrowthProblems of Chin GrowthProblems of Angle Growth
Hypognathism • Excessive Vertical Ramal Growth:Prognathism ▫ Bracheofacial PatientsUnilateral condylar ▫ Low angle caseshypertrophy ▫ Anterior deep biteBilateral Condylar • Poor Vertical Ramal Growth:hypertrophy ▫ Dolicofacial PatientsTMJ Ankylosis ▫ High Angle CasesImbalanced Growth ▫ Anterio open biteExcessive Transverse • Excessive Horizontal Ramal Growth:Growth ▫ More broad oropharynxPoor Transverse Growth • Poor Horizontal Ramal Growth:Problems of Ramal Growth ▫ Narrow oropharynxProblems of Chin Growth ▫ Chances of airway embarrassmentProblems of Angle Growth
Hypognathism Prominent ChinPrognathism •Common in malesUnilateral condylar •Due to late gonial bone depositionhypertrophy •Due to excessive mental bone resorptionBilateral Condylar •Can be treated with genioplastyhypertrophyTMJ AnkylosisImbalanced GrowthExcessive TransverseGrowthPoor Transverse GrowthProblems of Ramal GrowthProblems of Chin GrowthProblems of Angle Growth
Hypognathism • Excessive transvers growthPrognathism ▫ Common in malesUnilateral condylar ▫ Due to excessive bone deposition at angleshypertrophy ▫ Can be corrected with surgeryBilateral CondylarhypertrophyTMJ AnkylosisImbalanced GrowthExcessive TransverseGrowthPoor Transverse GrowthProblems of Ramal GrowthProblems of Chin GrowthProblems of Angle Growth
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.