The Growth and Development of the Mandible 1/23/2013 Dr. Akshi Gvalani P.G. Dept Of Prosthodontics Terna Dental College,Nerul,Navi Mumbai The Growth and Development of the Mandible 2 CONTENTSDefinition of growth and development Mechanism of formation of boneMechanism of growth of bone and factors affecting it Theories of growth Prenatal growth Postnatal growth Anomalies of growth Age changes Applied aspect References

Growth1. Growth refers to increase in size- Todd2.Growth usually refers to an increase in sizeand number Proffit3.Self multiplication of living substance - J.S.Huxley. 4.Change in any morphological parameter which is measurable Moyers Development1.Development is a progress towards maturity Todd 2.Development connotes a maturational process involving progressive differentiation at the cellular and tissue levels Enlow3. Development refers to all naturally occurring progressive, unidirectional, sequential changes in thelife of an individual from its existence as a single cell to its elaboration as a multifunctional unit terminating in death Moyers The Growth and Development of the Mandible 3 MECHANISM OF GROWTHMORPHOGENESIS A biologic process having an underlying control at the cellular and tissue levels DIFFERENTIATION It is a change from generalized cells or tissues to a more specialized kinds during developmentMECHANISM OF BONE FORMATIONENDOCHONDRAL

INTRAMEMBRANOUS Matrix calcifies Cartilage cells hypertrophy Becomes cartilage Original mesenchymal tissue Matrix calcifies Osteoid matrix formation Osteoblasts Original mesenchymal tissue The Growth and Development of the Mandible 4 The mandible is the second bone in the body to ossify1.Intramembranous ossification Whole body of mandible except the anterior part Ramus of mandible as far as mandibular foramen 2. Endochondral ossification Anterior portion of the mandible (symphysis) Part of ramus above the mandibular foramen Coronoid process Condylar processMechanism of bone growthDisplacement 1.Primary 2.Secondary

Cortical drift The Growth and Development of the Mandible 5 Theories of growth The Growth and Development of the Mandible 6 Enlows v principle The growth and enlargement of bones occur towards wide end of v due to differential deposition and resorption Enlows counterpart principle Growth of any facial or cranial part relates specifically to other structural and geometric counterparts The Growth and Development of the Mandible 7

FACTORS AFFECTING GROWTH1.Genetic 2.Hormonal imbalance 3.Nutrition4.Systemic illness or chronic illness 5.Systemic illness in mother 6.Drugs Local factors 1. Vascular abnormality 2. Lymphatic disturbance 3. Neurologic disease 4. Local infection 5. Ear infection or mastoiditis6. Ankylosis7. Trauma or fracture 8. Birth injury 9. Habits The Growth and Development of the Mandible 8 PRENATAL GROWTHThe first arch gives rise to Dorsal and Ventral portion. oDorsal portion Maxillary process oVentral portion Meckels cartilage or Mandibular process A single ossification centre for each half of the mandible arises in the 6th week IU., in the region of the bifurcation of the Inferior Alveolar Nerve and artery into Mental and Incisive branches Development of a slender cartilage rod in the second month serves as a precursor for mandibular mesenchyme . The Growth and Development of the Mandible 9 Secondary accesory cartilages appear in the 10th to 14th week in the coronoid condylar and mental protruberance region Fate of meckels cartilageAppears 41st to 45th day of IUL Disappears 24th week of IUL MalleusIncusSphenomandibular ligament Anterior malleolar ligament Spine of sphenoid POSTNATALDEVELOPMENTThe shape and size of the diminutive fetal mandible undergo considerable change during growth and development 1.Ramus low and wide 2.Coronoid process large and protrudes above condyle3.Body open shell with buds 4.Mandibular canal lies lowThe initial separation of left and right halves disappears when the sydesmosis is converted into synostosis between 4th to 12th month after birth. The Growth and Development of the Mandible 10 Although the mandible appears in the adult as a single bone, it is developmentally and functionally divisible into several skeletal subunits. Each of these skeletal subunits is influenced in its growth pattern by a functional matrix that acts upon the bone :- The teeth act as a functional matrix for the ALVEOLAR UNIT. The action of the temporalis muscle influences the CORONOID PROCESS. The masseter and medial pterygoid muscle acts upon the ANGLE and RAMUS of the mandible. The lateral pterygoid has some influence on the CONDYLAR PROCESS.The main sites of postnatal mandibular growth are:- The condylar cartilages The posterior borders of the ramiThe alveolar ridges The condylar cartilage of mandible serves dual roles of :- An Articular Cartilage in TMJ A Growth CartilageThe GROWTH CARTILAGE may act as a Functional Matrix to stretch the periosteum inducing the lengthened periosteum to form intramembranous bone beneath it.The Growth and Development of the Mandible 11 The formation of bone within the condylar heads causes the mandibular rami to grow UPWARDS and BACKWARDS displacing the entire mandible in an opposite DOWNWARD and FORWARD direction.Bone Resorption subjacent to the condylar head accounts for the narrowed condylar neck. The attachment of the lateral pterygoid muscleIn infants the condyles of mandible are inclined almost horizontally so that the condylar growth leads to an increase in the length of the mandible, rather than increase in height. The Growth and Development of the Mandible 12 The mental neurovascular bundle emanates from the mandible at right angles or even a slightly forward direction at birth.In adulthood the mental foramen is directed backwards.This change may be ascribed to forward growth in the body of the mandible, while the neurovascular bundle drags along. It may be contributed by the differential rates of bone and periosteal growth.The ALVEOLAR PROCESS develops as a protective trough in response to the tooth buds and becomes super imposed upon the basal bone of the mandibular body The CHIN is very poorly developed in the infants The chin becomes significant only at adolescence from development of the mental protuberance and tubercles.The Growth and Development of the Mandible 13 The skeletal unit of the chin may be an expression of the functional forces exerted by the lateral pterygoid muscles that, in pulling the mandible forward, indirectly stress the mental symphyseal region by their concomitant inward pull.ANOMALIES OF MANDIBULAR GROWTHDowns syndrome Treacher-collins syndrome Pierre Robin syndrome1.Congenital i)Agnathiaii)Micrognathiaiii)Macrognathiaiv)Facial hemihypertrophyv)Facial hemiatropy2. Developmental I)Infantile cortical hyperostosis ii) Torus mandibularisiii)Stafnes cystiv)Odontogenic cyst vi)Odontogenic tumour The Growth and Development of the Mandible 14 Downs syndrome Midface hypoplasiaMost commonMaternal age >35 carries increased risk 1866, described by John Landon Down Airway and hearing problems Treacher-collins syndrome Bilateral abnormalities of 1st and 2nd branchial arches Hypoplasia of maxilla, zygoma, and mandible Downward slanting eyes with colobomas of lower eyelid and absence of eyelashes The Growth and Development of the Mandible 15 Pierre Robin syndrome Triad of palatal cleft, micrognathia, and glossoptosis AGE CHANGES IN THE MANDIBLE The Growth and Development of the Mandible 16 RESIDUAL RIDGE RESORPTION Rrr A localized pathologic loss of bone that is not built back by simply removing the causative factorChronic Progressive IrreversibleCumulative

The Growth and Development of the Mandible 17 EtiologyAnatomic quantity quality Metaboliclocalsystemic Mechanicalfrequency intensity duration direction Consequences ofRRRDecreased sulcus width and depth Decreased VDO Exposure Of Mandibular Canal And Mental Foramen In severe situations, the superior border of the mandibular canal was resorbed under progressive residual ridge resorption. A resorbed superior border of the canal was found more often in edentulous women than in men. Asthma, thyroid disease, and thin cortex at the mandibular angle were significantly related to resorption of the mandibular canal wall. The Growth and Development of the Mandible 18 Systemic factors, gender, asthma, and thyroid disease played important roles in resorption of the mandibular canal wall of the edentulous elderly. Grade 0: The crest of the residual ridge above both the mental foramen and the mandibular canal (Fig. 1, a ) Grade I: The crest of the residual ridge above the mandibular canal and the mental foramen at the top of the residual ridge with or without a partially resorbed border (Fig. 1, b ) Grade II: The superior border of the mandibular canal at the top of the residual ridge and the mental foramen with or without a partially resorbed border (Fig. 1, c ) Grade III: The superior border of the mandibular canal partially resorbed and the borders of the mental foramen totally resorbed (Fig. 1, d ). Management of RRRIncreased denture bearing area Decreased dental units Decreased buccolingual width of artificial teeth Anatomy of teeth Increased interocclusal space Increased tongue space The Growth and Development of the Mandible 19 REFERENCESEssentials of complete denture prosthodontics Sheldon Winkler Human embryology SD GanganeB.D. Chaurasia Human osteology, 1st edition, 1984 Shafer W.G. Textbook of oral pathology, 4th edition, 1983 Pediatric dentistry Principles and practice Muthu, Muthu and SivakumarContemporary orthodontics ProffitResorption of mandibular canal wall in the edentulous aged population The Journal of Prosthetic dentistry vol 77 no 6;596-600 Qiufei Xie, DDS, MS, a Juhani Wolf, DDS, PhD, b Reijo Tilvis, MD, PhD, and Anja Ainamo, DDS, PhD d Craniofacial development Geoffrey Sperber RRR a review ,Ajay Gupta et al ,Indian journal of dental sciences March 2010 vol 2 issue 2 pg 7 Some clinical factors related to rate of resorption of residual ridges Douglas Allen Atwood ,The jour nal of prosthetic dentistry,may june 1962 ,vol 12 no 3 441-450.