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Functional anatomy of mandible
- 2. EMBRYOLOGY ANATOMIC UNITS OF MANDIBLE MUSCLES RELATED TO MANDIBLE TRAGECTORIES OF FORCE APPLIED ANATOMY AGE CHANGES
- 3. MECKEL`S CARTILAGE •Forms at 6 th week of development •Solid hyaline cartilage surrounded by fibro-cellular capsule •Extends from otic capsule to midline of the fused mandibular process •Cartilages of each side do not meet at midline, seperated by thin band of mesenchyme.
- 4. 1. A central cartilage rod that forms the skeleton of the arch 2. A muscular component-bronchomere 3. A vascular component 4. A neural component. Each of the five arches contain
- 5. 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.
- 8. CONDYLAR PROCESS 5 th week mesenchymal condensation above developing mandible. 10 th week - Develops into a cone shaped cartilage. 14 th week- starts ossification 4 th month- migrates inferiorly and fuses with mandibular ramus by 4 months.
- 9. Post-natally mandible exhibits largest amount of growth and variability.
- 10. RAMUS The functional remodeling of ramus are • To accommodate the increasing mass of masticatory muscle • To accommodate the enlarged breadth of the pharyngeal space. • To facilitate the lengthening of the mandibular body. (erupting molars)
- 13. • Genetic theory - BRODIE (1941) • Cartilaginous theory- JAMES SCOTT • Functional matrix concept- MELVIN MOSS • Enlow’s expanding ‘V’ principle THEORY OF GROWTH
- 14. ANATOMIC UNITS OF MANDIBLE Lower jaw bone U- shaped body 2 vertically directed rami condylar process coronoid process Oblique line Mental foramen
- 15. INTERNAL ANATOMY Mandibular Foramen Lingula Pterygoid Fovea Mylohyoid Line Fossae •Submandibular •Sublingual •Digastric Mental Spines •Genioglossus •Geniohyoid
- 16. MUSCLES RELATED TO MANDIBLE Muscles of facial expression Muscles 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.
- 20. TMJ LIGAMENTS
- 21. MECHANICS OF MANDIBULAR MOVEMENT
- 22. BIOMECHANICS OF THE TMJ
- 23. NORMAL MOVEMENT
- 24. 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.
- 25. 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.
- 26. • 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 attachments • Major trajectories – trabecular columns originate from beneath the teeth in the alveolar process and join together into a common stress pillar or major trajectory system.
- 27. AREAS OF WEAKNESS (VULNERABLE FOR FRACTURE) Junction of alveolar bone and basal bone Symphysis Parasymphysis Angle Presence of impacted teeth Neck of condyle
- 28. MUSCLE SLING • Angle and condylar neck are not entirely protected by sling. • Bony trabecular crests, ridges, lines.
- 31. CHAMPY`S LINE OF IDEAL OSTEOSYNTHESIS • Masticatory muscles produce tension at upper border and compression at lower border. • Torsional forces produced anterior to canine.
- 32. Monocortical tension banding osteosynthesis neutralizes distraction and torsion during physiologic stress, while normal basilar compression is restored CHAMPY
- 33. 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.
- 34. MUSCLES OF FACIAL EXPRESSION
- 36. FACIAL NERVE
- 38. OLD AGE
- 39. 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 viens INFLAMMATION RICH CAPILLARIES
- 40. MICROGNATHIA Insufficient 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 syndrome Congenital cardiac anomalies Skeletal dysplasia-achondrogenesis. COMPROMISE NEONATAL RESPIRATION
- 41. • 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
- 42. ABNORMALLY LARGE JAW Paget’s disease of bone Acromegaly Fibrous dysplasia
- 43. • CORONOID HYPERPLASIA • Rare developmental anomaly • Result in limited mandibular movement • Unknown etiology. • M:F ratio 5:1 • May be unilateral or bilateral • Bilateral is more common • CONDYLAR HYPERPLASIA • Excessive growth of one of the condyles • Cause is unknown, but local circulating problems, endocrine disturbances, and trauma have been suggested as possible etiologic factors.
- 44. CONDYLAR HYPOPLASIA Congenital or acquired • CONGENITAL: Mandibulofacial Dysostosis Goldenhar Syndrome Hemifecial Microsomia
- 45. • Rare • Most of have medial and lateral head divided by an antero posterior grooves. • Some condyles may be divided into an anterior and posterior head • Cause is uncertain • Antero-posterior may be traumatic origin. BIFID CONDYLE
- 47. EVOLUTION
- 48. EVOLUTION • SOME SCIENTISTS BELIEVE JAW SIZE INHERITED • SOME STUDIES CONFIRMED THAT HUMAN JAW SIZE AND SHAPE VARY ACCORDING TO DIET. • HUNTER-GATHERER GROUPS—including 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
- 49. CONCLUSION
- 50. REFERENCE • Jeffrey P. Okeson. Management of TemporoMandibular Disorders and Occlusion. 6th Edition • Richard L. Drake. Wayne Vogi. Adam W.M. Mitchell. Gray’s Anatomy for Students • Human embryology- Inderbir Sing Eight edition • Contemporary orthodontics Williams R. proffit fifth edition • Facial Growth – Donald H. Enlow third edition • Gray’s Anatomy – Fortieth edition • Human anatomy-BD Chaurasia Forth Edition • Shafer’sTextbook of Oral pathology sixth edition • Oral and maxillofacial Pathology- Neville third edition THANK YOU