FUNCTIONAL ANATOMY OF MAXILLA AND MANDIBLE

FUNCTIONAL ANATOMY OF MANDIBLEFarakath khan

EMBRYOLOGY ANATOMIC UNITS OF MANDIBLE MUSCLES RELATED TO MANDIBLE TRAGECTORIES OF FORCE APPLIED ANATOMY AGE CHANGES

MECKEL`S CARTILAGEForms at 6 th week of developmentSolid hyaline cartilage surrounded by fibro-cellular capsuleExtends from otic capsule to midline of the fused mandibular processCartilages of each side do not meet at midline, seperated by thin band of mesenchyme.

A central cartilage rod that forms the skeleton of the archA muscular component-bronchomereA vascular componentA neural component.Each of the five arches contain

A single ossification centre for each half of the mandible arise in the region of the bifurcation of inferior alveolar nerve into mental and incisive branches.

SECONDARY GROWTH CARTILAGES

CONDYLAR PROCESS

5 th week mesenchymal condensation above developing mandible.10 th week - Develops into a cone shaped cartilage. 14 th week- starts ossification4 th month- migrates inferiorly and fuses with mandibular ramus by 4 months.

Post-natally mandible exhibits largest amount of growth and variability.

RAMUS

The functional remodeling of ramus areTo accommodate the increasing mass of masticatory muscleTo accommodate the enlarged breadth of the pharyngeal space.To facilitate the lengthening of the mandibular body. (erupting molars)

Genetic theory - BRODIE (1941)Cartilaginous theory- JAMES SCOTTFunctional matrix concept- MELVIN MOSSEnlows expanding V principle

THEORY OF GROWTH

ANATOMIC UNITS OF MANDIBLELower jaw boneU- shaped body2 vertically directed rami condylar process coronoid processOblique lineMental foramen

INTERNAL ANATOMYMandibular ForamenLingulaPterygoid FoveaMylohyoid LineFossaeSubmandibularSublingualDigastricMental SpinesGenioglossusGeniohyoid

MUSCLES RELATED TO MANDIBLE

Muscles of facial expressionMuscles originating from the inner aspect of mandible ( mylohyoid, geniohyoid, genioglossus, ant belly of digastric fractured fragments collapse posteriorly or medially)Lateral pterygoid- condylar head displaced anteriorly and medially.The mandible anterior to a line passing through the anterior margin of the masseter muscle, is influenced by the depressor group of muscles, while the ramus is influenced by the elevator group.

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ELEVATORS MasseterTemporalis Medial PterygoidDEPRESSORSLateral PterygoidMylohyoidDigastricGeniohyoid

FUNCTIONS Mastication Deglutition Speech Profile.

MUSCLES OF MASTICATION

TMJLIGAMENTS

MECHANICS OF MANDIBULAR MOVEMENT

BIOMECHANICS OF THE TMJ

NORMAL MOVEMENT

MANDIBLE

To meet function , mandible is designed as a strong central bar, like the shaft of long bone, running forward in a continuous curve from condyle to condyle.Reinforced in the midline symphysis by the bulging chin, which resists the squeezing action of lateral pterygoids at the condylar ends Senile jaw-loss of teeth- alveolar process disappears. Masticatory function is severely reduced, extensive resorption of mandibular insertions. Coronoid and angular plates recede, and little but the central bar of bone remains.

TRAJECTORIES OF FORCE

The bony trajectories transmit and disperse the forces of mastication towards the condyles from the body, thus preventing injury to middle cranial fossa.

Benninghoff stated that the stress trajectories or lines of orientation of bony trabeculae involve not only the cancellous bone but also the compact bone.Minor trajectories effects of muscle attachmentsMajor trajectories trabecular columns originate from beneath the teeth in the alveolar process and join together into a common stress pillar or major trajectory system.

AREAS OF WEAKNESS (VULNERABLE FOR FRACTURE)

Junction of alveolar bone and basal bone Symphysis Parasymphysis Angle Presence of impacted teeth Neck of condyle

MUSCLE SLINGAngle and condylar neck are not entirely protected by sling.Bony trabecular crests, ridges, lines.

BATTLE SIGNCOLEMANS SIGN

CHAMPY`S LINE OF IDEAL OSTEOSYNTHESIS

Masticatory muscles produce tension at upper border and compression at lower border.Torsional forces produced anterior to canine.

Monocortical tension banding osteosynthesis neutralizes distraction and torsion during physiologic stress, while normal basilar compression is restoredCHAMPY

PEDIATRIC FRACTURE

Common - 39%Young bone possesses unique physical properties that coupled with space occupying developing dentition give rise to patterns of fracture not seen in adults.Majority of the fractures in children are undisplaced because of the elasticity of mandible and embedded tooth buds that hold the fragments together.Green stick fracture.

MUSCLES OF FACIAL EXPRESSION

FACIAL NERVE

OLD AGE

METASTASIS TO MANDIBLE

It was found that in 29.4% of patients with a metastatic lesion in jaw bone, it was the first indication of an undiscovered malignancy at a distant site.Site- premolar molar area (makes the diagnosis of most jaw metastasis difficult because the posterior mandible is often the area where dental inflammatory diseases occurs)Moorman and shafer most jaw metastasis occur in posterior mandible because it contains the most hematopoietic marrow.Kawast increased red bone marrow-dec rate of blood flow-risk of tumour emboli.Zetter- marrow has growth factors of metastatic tumours.Batson- metastasis along vetebral viensINFLAMMATIONRICH CAPILLARIES

MICROGNATHIAInsufficient migration of neural crest cells usually occur in 4 th week of gestation.Associated with Trisomy 13,18 Goldenhar syndrome-hemifacial microsomia Nager syndrome TAR syndrome Pierre robin syndrome Treacher collin syndromeCongenital cardiac anomaliesSkeletal dysplasia-achondrogenesis. COMPROMISE NEONATAL RESPIRATION

Hypoplasia or absent of mandible with abnormally positioned ears.Autosomal recessive .It is probably due to failure of neural crest mesenchyme into the maxillary prominence

AGNATHIA

ABNORMALLY LARGE JAW Pagets disease of bone Acromegaly Fibrous dysplasia

CORONOID HYPERPLASIARare developmental anomalyResult in limited mandibular movementUnknown etiology.M:F ratio 5:1May be unilateral or bilateralBilateral is more commonCONDYLAR HYPERPLASIAExcessive growth of one of the condylesCause is unknown, but local circulating problems, endocrine disturbances, and trauma have been suggested as possible etiologic factors.

CONDYLAR HYPOPLASIA

Congenital or acquired

CONGENITAL: Mandibulofacial Dysostosis Goldenhar Syndrome Hemifecial Microsomia

RareMost of have medial and lateral head divided by an antero posterior grooves.Some condyles may be divided into an anterior and posterior headCause is uncertain Antero-posterior may be traumatic origin.

BIFID CONDYLE

TORUS MANDIBULARIS

EVOLUTION

EVOLUTION

SOME SCIENTISTS BELIEVE JAW SIZE INHERITEDSOME STUDIES CONFIRMED THAT HUMAN JAW SIZE AND SHAPE VARY ACCORDING TO DIET.HUNTER-GATHERER GROUPSincluding populations of the Alaskan Inuit, Australians, and Central Africans tended to have more room in their mandibles (lower jaws). The diets of these populations consist primarily of unprocessed foods that require more chewing. AGRICULTURALIST GROUPS - Including Italians and Japanese, had relatively short and broad mandibles

CONCLUSION

REFERENCEJeffrey P. Okeson. Management of TemporoMandibular Disorders and Occlusion. 6th EditionRichard L. Drake. Wayne Vogi. Adam W.M. Mitchell. Grays Anatomy for StudentsHuman embryology- Inderbir Sing Eight editionContemporary orthodontics Williams R. proffit fifth editionFacial Growth Donald H. Enlow third editionGrays Anatomy Fortieth editionHuman anatomy-BD Chaurasia Forth EditionShafersTextbook of Oral pathology sixth edition Oral and maxillofacial Pathology- Neville third edition

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