Odontogenesis and Eruption PDF

To accompany Illustrated Dental Embryology, Histology, and Anatomy & Workbook for Illustrated Dental Embryology, Histology, and Anatomy...

To accompany Illustrated Dental Embryology, Histology, and Anatomy & Workbook for Illustrated Dental Embryology, Histology, and Anatomy 1 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Table 6-1 2 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Table 6-1 (cont) 3 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Stages and Discussion with Developmental Considerations 4 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Tooth Development Tooth development, or odontogenesis, takes place in many stages, which occur in a stepwise fashion for both dentitions. Odontogenesis of the primary dentition begins between the sixth and seventh week of prenatal development, during the embryonic period. Mature Tooth Figure 2-5 5 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  6 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Initiation Stage  This first stage is the initiation stage.  This involves the physiological process of induction, which is an interaction between the embryological tissue types.  At the beginning of the sixth week, the embryo's stomodeum, or primitive Figure 4-1 mouth, is lined by ectoderm. 7 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Initiation Stage  The outer part of the ectoderm gives rise to oral epithelium. The oral epithelium consists of two horseshoe‑shaped bands of tissue at the surface of the stomodeum, one for each future jaw or arch.  At the same time, deep to the forming oral epithelium, there is a type of mesenchyme originally from the ectoderm, Figure 6-1 the ectomesenchyme, which is influenced by neural crest cells that have migrated to the area. 8 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Initiation Stage A basement membrane separates the oral epithelium and the ectomesenchyme in the stomodeum. During the later part of the seventh week, the oral epithelium grows deeper into the ectomesenchyme and is induced to produce Figure 6-2 a layer called the dental lamina. 9 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Standring S: Gray's Anatomy, ed 40, Edinburgh, 2009, Churchill Livingstone 10 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Developmental Disturbances During Initiation Stage  Lack of initiation within the dental lamina results in the absence of a single tooth (partial) or multiple teeth (complete) produces anodontia.  However, partial anodontia (hypodontia) is more common and most commonly occurs (listed in order of occurrence) with the permanent  Third molars  Maxillary lateral incisors  Mandibular second premolars. 11 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Partial Anodontia 12 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Partial Anodontia Ibsen OAC, Phelan JA. Oral Pathology for Dental Hygienists, ed 5. WB Saunders, Philadelphia, 2009 13 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Anodontia can be associated with the syndrome of ectodermal dysplasia because many parts of the tooth are indirectly or directly of ectodermal origin.  Abnormal development of the skin, hair, nails, teeth, or sweat glands.  Can see partial or complete anodontia  People with ectodermal dysplasia may not sweat or may have decreased sweating because of a lack of sweatFehrenbach, glands. MJ, Weiner J. Saunders Review of Dental Hygiene, ed 2. Saunders, Philadelphia, 2009 14 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Developmental Disturbances During Initiation Stage Abnormal initiation may result in the development of one or more extra teeth, or supernumerary teeth (hyperdontia). These extra teeth are initiated from the dental lamina and have a hereditary etiology. 15 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Developmental Disturbances During Initiation Stage  Certain areas of both dentitions commonly have supernumerary teeth, such as (listed in order of occurrence)  between the maxillary central incisors (mesiodens),  distal to the maxillary third molars (distomolar or “fourth molar”), and  in the premolar region (perimolar) of both dental arches. 16 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Supernumerary Teeth Ibsen OAC, Phelan JA. Oral Pathology for Dental Hygienists, ed 5. WB Saunders, Philadelphia, 2009 17 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Supernumerary Teeth Ibsen OAC, Phelan JA. Oral Pathology for Dental Hygienists, ed 5. WB Saunders, Philadelphia, 2009 18 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  19 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Bud Stage  The second stage is called the bud stage and occurs at the beginning of the eighth week of prenatal development for the primary dentition.  This stage is named for an extensive proliferation or growth of the dental lamina into buds or oval masses penetrating into the ectomesenchyme.  At the end of the proliferation process involving the primary dentition's dental lamina, both the future maxillary arch and the Figure 6-3 future mandibular arch will have a total of 20 tooth buds (10 in each arch)0 buds. 20 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Bud Stage  The underlying ectomesenchyme also undergoes proliferation.  A basement membrane remains between the bud and the growing ectomesenchyme.  Each of these buds from the dental lamina, together with the surrounding Figure 6-4 ectomesenchyme, will develop into a tooth germ and its associated supporting tissue types. 21 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Nanci A. Ten Cate’s Oral Histology, ed 7. Mosby, St. Louis, 2008 22 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Standring S: Gray's Anatomy, ed 40, Edinburgh, 2009, Churchill Livingstone Developmental Disturbances During the Bud Stage 23 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Developmental Disturbances During Bud Stage Abnormal proliferation can cause a single tooth (partial) or the entire dentition (complete) to be larger or smaller than normal. Abnormally large teeth result in macrodontia; abnormally small teeth result in microdontia. 24 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  25 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Cap Stage 26 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. 26  Cap Stage  The third stage is called the cap stage and occurs for the primary dentition between the ninth and tenth week of prenatal development, during the fetal period.  Not only does proliferation characterize this stage, but also various levels of differentiation, which is Figure 6-5 unequal growth in different parts of the tooth bud, leading to formation of a cap shape attached to the dental lamina. 27 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Cap Stage Additionally during this stage, a primordium of the tooth develops with a specific form: the tooth germ. Therefore the predominant physiological process Figure 6-5 during the cap stage is one of morphogenesis. 28 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Cap Stage A depression results in the deepest part of each tooth bud of dental lamina and forms a cap, or enamel organ. The innermost margin of the cap shape of the enamel organ signals the tooth's future crown form. In the future, the Figure 6-5 enamel organ will produce enamel for the outer surface of the tooth. 29 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Nanci A. Ten Cate’s Oral Histology, ed 7. Mosby, St. Louis, 2008 30 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Cap Stage  A part of the ectomesenchyme deep to the buds has now condensed into a mass within the concavity of the cap of the enamel organ.  This inner mass of ectomesenchyme is now called the dental papilla.  The dental papilla will produce the future dentin and pulp for the inner part of the tooth.  A basement membrane still exists Figure 6-5 between the enamel organ and the dental papilla and is the site of the future dentinoenamel junction (DEJ). 31 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Cap Stage  The remaining ectomesenchyme surrounding the outside of the cap or enamel organ condenses into the dental sac.  In the future, the capsule‑like dental sac will produce the periodontium, the supporting tissue types of the tooth: cementum, periodontal ligament, and Figure 6-5 alveolar bone.  A basement membrane still separates the enamel organ and dental sac. 32 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Cap Stage  At the end of the cap stage, these three embryological structures— the enamel organ, dental papilla, and dental sac— are now considered together to be the tooth germ, the primordium of the tooth.  These initial tooth germs housed within each developing dental arch will develop into the primary dentition. 33 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Tooth Germ Components During Cap Stage Table 6-4 Enamel organ: Formation of tooth bud in a cap shape with deep central depression- Future enamel Dental papilla: Condensed mass of ectomesenchyme within the concavity of the enamel organ - Future dentin and pulp Dental sac: Condensed mass of ectomesenchyme surrounding the outside of the enamel organ - Future cementum, periodontal ligament, alveolar bone 34 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Cap Stage  Already at the tenth week of prenatal development, during the cap stage for each primary tooth, initiation is occurring for the anterior teeth of the permanent dentition.  Each primordium for these initially formed permanent teeth appears as an extension of the dental lamina into the ectomesenchyme lingual to the developing primary tooth germs.  Its site of origin is called Figure 6-26 the successional dental lamina. 35 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  36 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Succedaneous vs. Nonsuccedaneous  Permanent teeth formed with primary predecessors are called succedaneous and include the anterior teeth and premolars, which replace the primary anterior teeth and molars, respectively. The permanent succedaneous tooth's crown will erupt lingual to its primary predecessor's root(s) if the primary tooth has not been fully shed or lost (discussed earlier).  The permanent molars are nonsuccedaneous and have no primary predecessors. These six permanent molars per dental arch develop from a posterior extension of the dental lamina distal to the primary second molar's dental lamina and its associated ectomesenchyme for each quadrant. 37 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  38 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. 38 Developmental Disturbances During Cap Stage During the cap stage, the enamel organ may abnormally invaginate into the dental papilla, resulting in dens in dente or dens invaginatus. 39 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Developmental Disturbances During Cap Stage Gemination occurs as the single tooth germ tries unsuccessfully to divide into two tooth germs, which results in a large single‑rooted tooth with a common pulp cavity. 40 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Gemination Ibsen OAC, Phelan JA. Oral Pathology for Dental Hygienists, ed 5. WB Saunders, Philadelphia, 2009 41 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Developmental Disturbances During Cap Stage Fusion results from the union of two adjacent tooth germs, possibly resulting from pressure in the area, which leads to a broader, falsely macrodontic tooth similar to gemination. 42 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Fusion Ibsen OAC, Phelan JA. Oral Pathology for Dental Hygienists, ed 5. WB Saunders, Philadelphia, 2009 43 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Case Study 6.1 Age 5 YRS Scenario Sex Male A new patient has “My son has a his first dental Chief really large appointment. The Complaint baby tooth!” father, a patient None of record, is Medical concerned about History a large “baby” Current None tooth. Medications Likes to sing. A clinical Social photograph was History taken of the tooth. There is one less tooth noted in the arch of the primary dentition. An attempt was Fehrenbach, MJ, Weiner J. Saunders Review of Dental Hygiene, made to take a ed 2. Saunders, Philadelphia, 2009 periapical radiograph of the region, but it will need to be scheduled for the future. 44 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  45 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Bell Stage  The fourth stage is the bell stage, which occurs for the primary dentition between the eleventh and twelfth week of prenatal development.  It is characterized by continuation of the ongoing processes of proliferation, differentiation, and morphogenesis. However, differentiation on all levels occurs to its furthest extent, and as a result, four different types of cells are now found within the enamel organ.  Thus the cap shape of the Figure 6-7 enamel organ evident during the last stage assumes a bell shape. 46 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Bell Stage  The outer cuboidal cells of the enamel organ are the outer enamel epithelium (OEE).  The OEE will serve as a protective barrier for the rest of the enamel organ during enamel production.  The innermost tall columnar cells of the enamel organ are the inner enamel epithelium (IEE).  In the future, the IEE will differentiate into enamel‑secreting cells, ameloblasts. A basement Figure 6-7 membrane remains between the IEE and the adjacent dental papilla. 47 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Bell Stage  Between the outer and inner enamel epithelium are two layers: the  stellate reticulum  stratum intermedium.  The more outer-placed stellate reticulum consists of star‑shaped cells in many layers, forming a network.  The more inner-placed stratum intermedium is made up of a compressed layer of flat to cuboidal cells.  Both of these two intermediately placed layers of Figure 6-7 the enamel organ help support the production of enamel. 48 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Stellate Reticulum The stellate reticulum is a cellular group located in the center of the enamel organ of a developing tooth. These cells are star shaped and synthesize glycosaminoglycans. As glycosaminoglycans are produced, water is drawn in between the cells which stretches them apart. As they are moved farther away from one another with the production of glycosaminoglycans, the stellate reticula maintain contact with one another through cell junctions by way of desmosomes, resulting in their unique star-shaped appearance. 49 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Stratum Intermedium The stratum intermedium in a developing tooth is a layer of two or three cells, like a layer cake, between the inner enamel epithelium and the newly forming cells of the stellate reticulum. It first appears during the early bell stage of tooth development, at around the fourteenth week of prenatal development. The stratum intermedium has a notably high alkaline phosphatase activity. This layer, along with the inner enamel epithelium, is responsible for the tooth enamel formation. 50 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Bell Stage  At the same time, the dental papilla within the concavity of the enamel organ is also undergoing extensive differentiation so that it now consists of two types of tissue in layers: the outer cells of the dental papilla and the central cells of the dental papilla.  In the future, the outer cells of the dental papilla will differentiate into Figure 6-8 odontoblasts, while the inner cells are the primordium of the pulp. 51 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Outer enamel epithelium (OEE): Outer cuboidal cells of enamel organ; serves as protective barrier for enamel organ Stellate reticulum: More outer star-shaped cells in many layers, forming a network within the enamel organ; supports the production of enamel matrix Stratum intermedium: More inner compressed layer of flat to cuboidal cells; supports the production of enamel matrix Inner enamel epithelium (IEE): Innermost tall, columnar cells of enamel organ; will 52 differentiate into ameloblasts that form Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  53 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Apposition and Maturation The final stages of odontogenesis include apposition, during which the enamel, dentin, and cementum are secreted in successive layers. These tissue types are initially secreted as a matrix, which is an extracellular substance that is partially calcified yet serves as a framework for later calcification. The other final stage, maturation, is reached when the dental tissue types subsequently fully mineralize. The time period of these two final stages varies according to the tooth involved, but overall involves the same chronology as the initiation of odontogenesis. 54 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Crown Formation With Enamel and Dentin Apposition and Maturation 55 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Formation of Pre-ameloblasts  After the formation of the IEE in the bell‑shaped enamel organ, these innermost cells grow even more columnar or elongate as they differentiate into pre-ameloblasts. During this differentiation, IEE cells undergo repolarization.  In the future, the pre- ameloblasts will first induce dental papilla cells to differentiate into dentin-forming Figure 6-9 cells (odontoblasts) and then will differentiate themselves into cells that secrete enamel (ameloblasts). 56 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Formation of Odontoblasts and Dentin Matrix  After the IEE differentiates into preameloblasts, the outer cells of the dental papilla are induced by the preameloblasts to differentiate into odontoblasts.  These cells also undergo repolarization. These cells are also lined up adjacent to the basement membrane but in a mirror‑image orientation compared with the preameloblasts. Figure 6-10  The odontoblasts now begin dentinogenesis, which is the apposition of dentin matrix, or predentin, on their side of the basement membrane. 57 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Formation of Odontoblasts and Dentin Matrix Thus the odontoblasts start their secretory activity some time before enamel matrix production begins. The dentin layer in any location in a developing tooth is slightly thicker than Figure 6-10 the corresponding layer of enamel matrix. 58 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Formation of Odontoblasts and Dentin Matrix Figure 6-11 59 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Formation of Ameloblasts, Dentinoenamel Junction, and Enamel Matrix  After the differentiation of odontoblasts from the outer cells of the dental papilla and their formation of predentin, the basement membrane between the preameloblasts and the odontoblasts disintegrates.  This disintegration of the basement membrane allows the preameloblasts to come into contact with the newly formed predentin.  This induces the preameloblasts to differentiate into ameloblasts. Figure 6-12 60 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Formation of Ameloblasts, Dentinoenamel Junction, and Enamel Matrix  Ameloblasts begin amelogenesis, or the apposition of enamel matrix, laying it down on their side of the now disintegrating basement membrane.  The enamel matrix is secreted from Tomes’ process, an angled part of each ameloblast that faces the disintegrating basement membrane created as the ameloblasts move away from the dentin interface. Figure 6-12 61 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Formation of Ameloblasts, Dentinoenamel Junction, and Enamel Matrix With the enamel matrix in contact with the predentin, mineralization of the disintegrating basement membrane now occurs, forming the dentinoenamel junction (DEJ), the inner junction between the dentin and enamel tissue. Figure 6-12 62 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Formation of Ameloblasts, Dentinoenamel Junction, and Enamel Matrix  The odontoblasts, unlike the ameloblasts, will leave attached cellular extensions in the length of the predentin called the odontoblastic process.  Each odontoblastic process is contained in a mineralized cylinder, the dentinal tubule. The calcification or maturation of each type of matrix occurs later and is a different process for both enamel and dentin.  The cell bodies of odontoblasts will remain within pulp tissue.  The cell bodies of the ameloblasts will be involved in the eruption and Figure 6-12 mineralization process but will be lost after eruption. 63 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Dentin Matrix Formation Figure 12-2B 64 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Apposition Stage Figure 6-13 65 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Figure 12-3 66 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Standring S: Gray's Anatomy, ed 40, Edinburgh, 2009, Churchill Livingstone 67 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Developmental Disturbances During Stages of Apposition and Maturation Certain factors may interfere with the metabolic processes of the ameloblasts, resulting in enamel dysplasia, which is the faulty development of enamel dysplasia. Many different types are possible and have either a local or a systemic etiology. Local enamel dysplasia may result from trauma or infection occurring in a small group of ameloblasts. Systemic enamel dysplasia involves larger numbers of ameloblasts and may result from traumatic birth, systemic infections, nutritional deficiencies, or dental fluorosis (excess systemic fluoride level). 68 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Enamel Hypoplasia Enamel hypoplasia can be noted in the presence of Hutchinson incisors and mulberry molars, which is caused by the teratogen of syphilis. This results from a reduction in the quantity of enamel matrix. As a result, the teeth appear with pitting and grooves in the enamel surface. From the labial view, Hutchinson incisors have a crown with a screwdriver shape that is wider cervically and narrow incisally, with a notched incisal edge. Mulberry molars have enamel tubercles on the occlusal surface. 69 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Enamel Hypoplasia 70 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. A.Hutchinson’s Incisors B. Mulberry Molar’s These are associated with Congential syphyllis Ibsen OAC, Phelan JA. Oral Pathology for Dental Hygienists, ed 5. WB Saunders, Philadelphia, 2009 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Figure 3-16 71 Enamel Hypoplasia Caused by Febrile Illness or Vitamin Deficiency Fehrenbach, MJ, Weiner J. Saunders Review of Dental Hygiene, ed 2. Saunders, Philadelphia, 2009 72 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Enamel Hypocalcification Enamel hypocalcification results in reduction in the quality of the enamel maturation. The teeth appear more opaque, yellower, or even browner because of an intrinsic staining of enamel. A single affected area or white “sparkle spot” is called Turner spot and if the permanent crown is affected, Turner tooth. 73 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Dental Fluorosis Enamel hypoplasia and hypocalcification may occur together and affect entire dentitions, a common finding in dental fluorosis. Figure 12-5 74 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Amelogenesis Imperfecta A certain type of enamel dysplasia, amelogenesis imperfecta, has a hereditary etiology and can affect all teeth of both dentitions. Figure 6-16A 75 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Amelogenesis Imperfecta Figure 6-16B 76 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Dentin Dysplasia Dentin dysplasia, or the faulty development of dentin, can result from an interference with the metabolic processes of the odontoblasts during dentinogenesis. 77 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Dentin Dysplasia Ibsen OAC, Phelan JA. Oral Pathology for Dental Hygienists, ed 5. WB Saunders, Philadelphia, 2009 78 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Dentinogenesis Imperfecta One type of dentin dysplasia, dentinogenesis imperfecta, has a hereditary basis. Figure 6-17 79 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  To accompany Illustrated Dental Embryology, Histology, and Anatomy, 3rd Edition & Workbook for Illustrated Dental Embryology, Histology, and Anatomy, 3rd Edition 80 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Root Development The process of root development takes place after the crown is completely shaped and the tooth is starting to erupt into the oral cavity. Most nondental personnel find it remarkable that the tooth is formed starting with the crown and then moving to the apex of the root. The structure responsible for root development is the cervical loop. The cervical loop is the most cervical part of the enamel organ, a bilayer rim that consists of only IEE and OEE. 81 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Root Development The cervical loop begins to grow deeper into the surrounding ectomesenchyme of the dental sac, elongating and moving away from the newly completed crown area to enclose more of the dental papilla tissue and form Hertwig epithelial root sheath (HERS). The function of this sheath or membrane is to shape the root(s) and induce dentin formation in the root area, so that it is continuous with coronal 82 dentin. Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Root Development 83 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Root Development 84 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Root Dentin Formation  Root dentin forms when the outer cells of the dental papilla in the root area are induced to undergo differentiation and become odontoblasts.  Lacking the intermediate layers of the stellate reticulum and stratum intermedium, this HERS may induce odontoblastic differentiation but fails to differentiate into enamel- forming ameloblasts. This Figure 6-19 accounts for the absence of enamel in the roots. 85 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Root Dentin Formation  After the differentiation of odontoblasts in the root area, these cells undergo dentinogenesis and begin to secrete predentin.  As in the crown area, a basement membrane is located between the inner enamel epithelium of the sheath and the odontoblasts in the root Figure 6-19 area. 86 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Root Dentin Formation  When root dentin formation is completed, this part of the basement membrane also disintegrates, as does the entire HERS.  After this disintegration of the root sheath, its cells may become the epithelial rests of Malassez (ERM). Figure 6-19 87 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Cementum and Pulp Formation  The cementoblasts move to cover the root dentin area and undergo cementogenesis, laying down cementum matrix, or cementoid.  Many cementoblasts become entrapped by the cementum they produce and become mature cementocytes.  As the cementoid surrounding the cementocytes becomes calcified, or matured, it is then considered cementum. Figure 6-20 88 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Cementum and Pulp Formation  As a result of the apposition of cementum over the dentin, the dentinocemental junction (DCJ) is formed.  Also at this time, the central cells of the dental papilla are forming into the pulp.  The pulp tissue is Figure 6-20 surrounded by the newly formed dentin. 89 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Standring S: Gray's Anatomy, ed 40, Edinburgh, 2009, Churchill Livingstone 90 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Developmental Disturbances With Cemental Formation Excess cementum formation can rarely occur with concrescence. 91 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Concrescence Ibsen OAC, Phelan JA. Oral Pathology for Dental Hygienists, ed 5. WB Saunders, Philadelphia, 2009 92 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Periodontal Ligament and Alveolar Bone Development  The ectomesenchyme from the dental sac begins to form the periodontal ligament (PDL) adjacent to the newly formed cementum.  This process involves forming collagen fibers that are immediately organized into the fiber bundles of the PDL.  The ends of these fibers insert into the outer part of the cementum and the surrounding Figure 6-20 alveolar bone to support the tooth. 93 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Development of Multirooted Teeth 94 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Multirooted Teeth  Like anterior teeth, multirooted premolars and molars originate as a single root on the base of the crown.  This part on these posterior teeth is called the root trunk.  The cervical cross section of the root trunk initially follows the form of the crown. However, the root of a posterior tooth divides from the root trunk into the correct number of root branches for its tooth type.  Differential growth of HERS causes the root trunk of the multirooted teeth to divide into two or three roots. 95 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Development of Multirooted Teeth Figure 6-21 96 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Standring S: Gray's Anatomy, ed 40, Edinburgh, 2009, Churchill Livingstone 97 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Developmental Disturbances During Root Formation In some cases, misplaced ameloblasts can migrate to the root area, causing enamel to be abnormally formed over the cemental root surface, which produces an enamel pearl. Ibsen OAC, Phelan JA. Oral Pathology for Dental Hygienists, ed 5. WB Saunders, Philadelphia, 2009 98 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Developmental Disturbances During Root Formation Dilaceration results in either distorted root(s) or crown angulation in a formed tooth. It is caused by a distortion of HERS due to an injury or pressure; it can occur in any tooth or group of teeth during tooth development. 99 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Dilaceration Figure 17-36 100 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Developmental Disturbances During Root Formation Teeth may also have extra or accessory roots (or supernumerary roots). Fehrenbach, MJ, Weiner J. Saunders Review of Dental Hygiene, ed 2. Saunders, Philadelphia, 2009 101 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Primary Tooth Eruption and Shedding 102 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Active Eruption After enamel apposition ceases in the crown area of each primary or permanent tooth, the ameloblasts place an acellular dental cuticle on the new enamel surface. In addition, the layers of the enamel organ are compressed, forming the reduced enamel epithelium (REE). Figure 6-23 103 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Nanci A. Ten Cate’s Oral Histology, ed 7. Mosby, St. Louis, 2008 104 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Active Eruption To allow for the eruption process, the REE first has to fuse with the oral epithelium lining the oral cavity. Second, enzymes from the REE then disintegrate the central part of the fused tissue, leaving an epithelial tunnel for the tooth to erupt through the surrounding oral epithelium into the oral cavity. 105 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Figure 6-25 106 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Active Eruption This fused tissue that remains near the CEJ after the tooth erupts then serves as the initial junctional epithelium of the tooth and creates a seal between the tissue and the tooth surface. This tissue is later replaced by a definitive junctional epithelium (arrows) as the root is formed. Figure 10-7 107 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Active Eruption The primary tooth is then lost, exfoliated, or shed, as the succedaneous permanent tooth develops lingual to it. Figure 6-5 108 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Active Eruption  The process involving loss of the primary tooth consists of differentiation of osteoclasts, which absorb the alveolar bone between the two teeth, and odontoclasts, which cause resorption or removal of parts of the primary's root of dentin Figure 6-28 and cementum as well as small parts of the enamel crown. 109 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Permanent Tooth Eruption 110 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Permanent Tooth Eruption The permanent tooth erupts into the oral cavity in a position lingual to the roots of the shedding or shed primary tooth, just as it develops that way. The only exception to this is the permanent maxillary incisors, which move to a more facial position as they erupt into the Figure 6-26 oral cavity. 111 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Eruption Lingual Ibsen OAC, Phelan JA. Oral Pathology for Dental Hygienists, ed 5. WB Saunders, Philadelphia, 2009 112 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Permanent Tooth Eruption  The process of eruption for a succedaneous tooth is the same as for the primary tooth: the REE fuses with the oral epithelium to create a tissue that degenerates, leaving an epithelial‑lined eruption tunnel.  The process of the nonsuccedaneous permanent tooth's eruption is similar also, but no primary tooth is shed. Figure 6-26 113 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Standring S: Gray's Anatomy, ed 40, Edinburgh, 2009, Churchill Livingstone 114 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Developmental Disturbances During Eruption An odontogenic cyst that forms from the REE after the crown has completely formed and matured is the dentigerous Figure 6-30 cyst, or follicular cyst. 115 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  Elsevier, Imaging Consult, imaging.consult.com, 2009 116 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Developmental Disturbances During Eruption If a dentigerous cyst appears on a partially erupted tooth, it is considered an eruption cyst and appears as fluctuant, blue, vesicle‑like gingival lesion. Figure 6-31 117 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.  118 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved. Problems in Spacing A permanent tooth often starts to erupt before the primary tooth is fully shed, possibly creating problems in spacing. Interceptive orthodontic therapy can prevent some of these situations. Thus it is important for children with prolonged retention of any primary teeth to seek early dental consultation. 119 Copyright © 2011, 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.