LEC6-ORAL-ANATOMY.pdf

ORAL ANATOMY Module 6: Dentition Odontogenesis - the process of tooth development. Enamel Enamel...

ORAL ANATOMY Module 6: Dentition Odontogenesis - the process of tooth development. Enamel Enamel Organ Definition of Terms: Three Layers Dentin Dental Ectoderm → From the outer covering of the Papilla body and lining of the oral cavity. Tooth Germ Pulp Mesoderm → From the skeletal and muscular systems and also structures Cementum including the cementum, dentin and pulp of the tooth. Dental Periodontal Endoderm → Lining of the internal organs. Follicle ligament Alveolar Development of Teeth bone Development of a tooth is a complex process initiated by the interaction between ectoderm Development of Teeth: An Overview and ectomesenchyme. Ten tooth germs arise in each dental arch to Primitive oral cavity (stomodeum) is lined by oral form the primary dentition. ectoderm with ectomesenchymal connective Tooth germs that give rise to permanent tissue derived from neural crest. successors (i.e., the permanent incisors, canines, First sign of tooth development – the and premolars) develop on the lingual aspect proliferation of oral ectodermal cells to form of their deciduous predecessors in the same epithelial thickening called a primary epithelial bony crypt. band. Primary epithelial band is formed by the 6th week of intrauterine life. (Determines the future position of the future dental arches.) Primary epithelial band that gives rise to two subdivisions: o One buccal – vestibular lamina o One lingual – dental lamina → Dental lamina contributes to the formation of the developing teeth. → Vestibular lamina or lip furrow band forms the oral vestibule. In some areas of dental lamina, cells undergo proliferation to form small round structures called dental placodes. These round epithelial swelling form the enamel organs of the deciduous teeth. Stages of Tooth Development The earliest evidence of tooth formation occurs during the 6th week of embryonic life. Bud stage (Initiation) Development of the teeth begins with the The enamel organ at first resembles a small bud, development of dental lamina. which is surrounded by the condensation of The development of each individual tooth starts ectomesenchymal cells. with the formation of a tooth germ (tooth bud) Enamel organ consists of low columnar cells in o Tooth germs are small clumps of cells the periphery and polygonal cells in the center. that have the ability to form tooth tissues. o The enamel organ, dental papilla, and dental sac together constitute a tooth bud or tooth germ. Development of Teeth Enamel organ = enamel Dental Papilla = dentin and pulp Dental Follicle = Cementum, periodontal ligament, and alveolar bone. DRUA, EUGENE EARL P. |DDM 2-B (A.Y. 2022-2023) 1 ORAL ANATOMY Module 6: Dentition Cap Stage (Proliferation) Advance Bell Stage The enamel organ then proliferates to form a Characterized by the beginning of cap over the central condensation of mineralization and root formation. ectomesenchymal cells – the dental papilla. First, a layer of predentin is secreted by the The dental papilla and the dental sac become odontoblasts. The ameloblasts begin to form well-defined. enamel following the reciprocal induction. The The enamel organ differentiates to form three deposition of enamel and dentin continues until layers namely: the crown formation is complete. o Inner Enamel Epithelium – cells that outline the concavity in the deepest part of the cap stage. o Stellate reticulum – star-shaped branch- like network. o Outer Enamel epithelium – cells in the convex portion of the cap; cuboidal in shape. Stages of Tooth Development Overlapped on these morphological stages of tooth development are a series of physiological processes that occur in a sequential manner. These physiological processes are: Early Bell Stage ( Histodifferentiation & o Initiation: Dental Lamina and Bud stage Morphodifferentiation) o Proliferation: Bud stage and Cap stage The enamel organ acquires a bell shape o Histodifferentiation: Early bell stage resulting in deepening of the undersurface of o Morphodifferentiation: Advanced bell stage the epithelial cap. Another cell layer forms in between the inner Root Development dental epithelium and stellate reticulum, called Root formation begins in advanced bell stage once the the stratum intermedium. dentin and enamel formation reaches future The inner dental epithelium differentiates into cementoenamel junction. tall columnar cells called ameloblasts which are enamel forming cells. Enamel organ gives rise to Hertwig’s Epithelial root The peripheral cells of the dental papilla sheath which molds the shape of the roots and initiates differentiate into odontoblasts which form the radicular dentin formation. dentin. Stages of Tooth Development 1. Initiation – this process includes the dental lamina and bud stages, and affects the presence or absence of tooth buds. 2. Proliferation – occurs during the bud, cap, and bell stages, and influence the general size and proportions of the tooth germs. 3. Histodifferentiation – takes place from the advanced cap stage through the bell stage, involves the formation of potential enamel and dentin forming cells. 4. Morphodifferentiation – shape and size of the tooth is determined in this process, which happens during the bud, cap, and bell stages. Disturbance in this process may influence the size and shape of a tooth but have no effect on the enamel and dentin forming process. DRUA, EUGENE EARL P. |DDM 2-B (A.Y. 2022-2023) 2 ORAL ANATOMY Module 6: Dentition Deciduous teeth are the first teeth to emerge 5. Apposition – active during the bell stage, into the oral cavity. through the completion of the root and involves Calcification of deciduous teeth begins around the regular laying down of the enamel and the 4th month of fetal life. dentin. Calcification is the hardening of tooth tissues by 6. Eruption – the emergence of teeth into the oral the deposition of mineral salts within the tissue. cavity. Calcification process first forms the crown of the 7. Exfoliation – shedding or loss of a deciduous tooth and root formation follows later. tooth. Development of Deciduous Dentition The “six/four” rule for deciduous tooth emergence 4 teeth emerge for each 6 months of age Chronology of Development of Deciduous Dentition 1. Beginning of calcification 1. 6 months; 4 teeth (lower & upper centrals) 2. Crown completion 2. 12 months; 8 teeth (+1 lower & upper centrals) 3. Emergence 3. 18 months; 12 teeth ( +2 lower & upper 1st 4. Root completion molars) 4. 24 months; 16 teeth (+3 lower & upper canines) 5. 30 months; 20 teeth (+4 lower & upper 2nd molars) A summary for deciduous teeth development 1. By 5 months in utero, all crowns started calcification. 2. By 1 year old (11-12months), all crowns completed formation. 3. By 2.5 years old, all primary teeth emerged. 4. By 4 years old, all primary teeth completed root formation. DRUA, EUGENE EARL P. |DDM 2-B (A.Y. 2022-2023) 3 ORAL ANATOMY Module 6: Dentition Chronology of the Human Permanent Dentition Key Points 1. The chronology of human dentition refers to the development timeline of teeth. 2. The timeline of calcification and eruption of tooth plays an important role in the estimation od dental age in forensic odontology. 3. The sequence of eruption is the order in which the teeth appear in the oral cavity. 4. The order of eruption of primary teeth in one quadrant is denoted as ABDCE. 5. The order of eruption of permanent teeth in one quadrant is denoted as 61245378. The Rules of “Fours” for the permanent Tooth Development (not include third molars) At birth four first molars have initiated calcification. At 4 years of age, all crowns have initiated calcification. At 8 years of age, all crowns are complete. At 12 years of age, all crowns emerge. At 16 years of age, all roots are complete. Chronology of Appositional Growth of the Teeth Group I (4-6 months in utero o All primary teeth from central incisor to the second molar. Group II ( birth – 3 months) o First permanent molar and permanent anterior teeth except the upper lateral incisor. Group III (1-1 1/1 to 3 years) o Premolars and second permanent molars. Group IV (7 – 10 years) o 3rd molars The Rules of “Sixes” in dental Development 6 weeks old in utero: beginning of dental development. 6 months old: emergence of the first primary tooth. 6 years old: emergence of the first permanent tooth. DRUA, EUGENE EARL P. |DDM 2-B (A.Y. 2022-2023) 4 ORAL ANATOMY Module 6: Dentition Emergence of a tooth is the first sign of appearance in the oral cavity. Eruption: Eruption is the movement of the teeth within and through the bone of the jaws and the overlying mucosa to appear in the oral cavity and contact the opposing teeth. The eruption begins when the crown is complete and the roots starts to form. There are 3 stages of eruption: A. Pre-eruptive stage: before the crown is formed. B. Pre-functional eruptive stage: begins at the initiation of root formation and ends when the teeth reach occlusal contact. C. Functional eruptive stage- begins when the teeth come into occlusion and continues until the teeth are lost and characterized by occlusal wear and compensating eruption. Types of Eruption 1. Active eruption – the actual movement of the teeth toward the occlusal plane. 2. Passive eruption – apical migration; the separation of primary attachment epithelium from the enamel. DRUA, EUGENE EARL P. |DDM 2-B (A.Y. 2022-2023) 5 ORAL ANATOMY Module 6: Dentition Life Cycle 13-16 weeks in utero – beginning of calcification 6-13 months of postnatal life – eruption of the primary dentition. 2-3 years primary dentition completed. 5-6 years beginning of exfoliation stage. 6-7 years eruption of first accessional and succedaneous teeth. 10-11 years complete exfoliation of primary teeth. Functions of Primary teeth Efficient mastication of food Development of Speech Aids in the development of the jaws Guidance for the eruption of the permanent teeth. Major contrast between primary and permanent teeth. The crowns of the primary anterior teeth are wider mesiodistally in comparison with their crown length than are the permanent teeth. The roots or primary anterior are narrower and longer comparatively. DRUA, EUGENE EARL P. |DDM 2-B (A.Y. 2022-2023) 6 ORAL ANATOMY Module 6: Dentition The roots of the primary molars accordingly are longer, are more slender, more flare, and extending out beyond projected outlines of the crowns. The cervical ridges of enamel of the anterior teeth are more prominent. Notes: The crowns and roots of primary molars at their cervical portions are more slender mesiodistally. The cervical ridges of the primary molars are much more pronounced. The buccal and lingual surfaces of primary molars are flatter above the cervical curvatures than those of permanent molars. The primary teeth are usually less pigmented and are whiter in appearance than the permanent teeth. The enamel of the deciduous crowns is relatively thin, when compared to permanent teeth. The dentin of primary teeth is also relatively thin in comparison to permanent teeth. The pulp chamber and pulp horns are relatively larger in the deciduous teeth. DRUA, EUGENE EARL P. |DDM 2-B (A.Y. 2022-2023) 7