Tooth Development: Microscopic Structure and Stages - PDF

Here is the transcription of the image into markdown format: # Oral Histology and Embryology 114 / Midterm 2 ## (Week 6) Tooth Development and Eruption Part 1- Development of Tooth Crown - Dental professionals need to consider the importance of NCCs. In addition to assisting in the formation of the cranial sensory ganglia, they also differentiate to form most of the connective tissue of the head. - Embryonic connective tissue for most of the rest of the body is derived from mesoderm and is known as mesenchyme, whereas in the head it is ectomesenchyme, reflecting its origin from neuroectoderm - TOOTH DEVELOPMENT: - Odontogenesis is the process of tooth development. The image shows a diagram of the microscopic structure of tooth development. It highlights the stages of: > Initiation > Bell > Bud > Apposition > Cap > Maturation - Developmental disturbances can occur within each stage of odontogenesis. - These developmental disturbances can have ramifications that may affect the clinical treatment of a patient. - Dentition → NATURAL teeth in maxillary & mandibular jaws. - Primary dentition↓ - Natural teeth in a child which develops during the prenatal period - Consists of 20 teeth - These teeth are later shed/ exfoliated. - Ages: ~ 6 months to ~ 6 years old - Permanent dentition↓ - Primary teeth are shed & "replaced" by the permanent teeth as the jaws grow & mature. - Consists of 32 teeth - Our permanent teeth are the only NATURAL set we get after they erupt. - Ages: ~13 years old & after - MIXED DENTITION: - The period during childhood when teeth from both primary & permanent dentitions are present. - Ages 6 years old to ~ 12 years old - Odontogenesis is similar for both dentitions, BUT the time frame is different The image contains a dental radiograph. - ODONTOGENESIS: - Starts in 6th-7th week of prenatal development for PRIMARY dentition. - It is a CONTINUOUS process until it is completed. - Occurs in stages with no clear-cut beginning or end between the stages. - Occurs in a SEQUENTIAL fashion for BOTH dentitions. What is the order of developing teeth↓ - Mandibular anterior teeth develop first. - Maxillary anterior teeth develop next. - Then posterior teeth develop in both upper & lower arches. - STAGES OF TOOTH DEVELOPMENT: - Initiation occurs→ first. - 3 identifiable stages by shape of the tooth bud: - Bud, cap & bell stages - Apposition occurs next - the formation of partially mineralized dental tissue types - Maturation occurs last - continued mineralization - TOOTH DEVELOPMENT: - Primary dentition develops during which periods both the embryonic & fetal periods. - Most of the permanent dentition is formed during the fetal period. - Tooth development continues for years after birth. - Therefore, teeth have the longest developmental period of any organ of the body. - During the various stages of odontogenesis, several physiologic processes occur, including: - INDUCTION, PROLIFERATION, DIFFERENTIATION, MORPHOGENESIS, & MATURATION. - Except for the first step of induction, many of them overlap & are somewhat continuous during odontogenesis. - However, 1 individual process does tend to be predominant in each stage, specially marking each stage of odontogensis - First Stage - INITIATION: - Main process of initiation induction **TABLE 6.1** Tooth Development Stages | Stage and Time Span* | Microscopic Structure | Main Processes | Histologic Features | |:----------------------------------------|:----------------------------------------------|:---------------|:-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | Initiation stage at sixth to seventh week | Image shows microscopic picture of cells | Induction | Ectoderm lining stomodeum gives rise to oral epithelium and then to dental lamina with its dental placodes; adjacent to deeper ectomesenchyme, which is derived from neural crest cells. Both tissue types are separated by basement membrane | - Main process of initiation induction - Odontogenesis of the primary dentition begins between the sixth and seventh week of prenatal development, during the embryonic period - Predominantly, the main process involves the process of INDUCTION - Studies show that ectodermal tissue must influence the mesenchymal tissue in order to initiate odontogenesis - Interaction between the embryologic tissues: Tooth initiation involves Ectoderm 1st signals to mesenchyme * The image shows the cells labeled as: > Ectoderm > > Mesenchyme  - ○ Mesenchyme then responds by reciprocally inducing ectoderm to continue the developmental progression. - INITIATION STAGE: - At the beginning of the sixth week, the stomodeum of the embryo (or primitive mouth) is lined by → ectoderm. * The image depicts the Developing maxillary arch, Stomodeum, Developing tongue, Developing mandibular arch, Oral epithelium & Ectomesenchyme.  - The outer part of the Ectoderm gives rise to oral epithelium. * The image depicts the Developing tongue, Developing mandibular arch, Oral epithelium & Ectomesenchyme.  - Horseshoe-shaped bands at the surface of the stomodeum - 1 band for each future dental arch of teeth The image shows the developing tongue. And the oral epithelium, the dental lamina and the ectomesenchyme of developing mandible At the same time, deep to the developing oral epithelium, is the ectomesenchyme (mesenchyme containing the NCC's.) * The image depicts the Developing maxillary arch, Stomodeum, Developing tongue & Developing mandibular arch, the Oral epithelium & Ectomesenchyme.  - Basement membrane separates the → 2 tissues. - Next, during the latter part of the 7th week, the oral epithelium grows deeper into the ectomesenchyme & is induced to form the dental lamina. The image demonstrates the developing tongue, the Oral epithelium, Dental lamina & Ectomesenchyme of developing mandible - This growth occurs in each of the developing jaws where the two future curved dental arches of the primary dentition will form - The dental lamina begins to form initially in the midline for both arches and progresses posteriorly - At the same time, dental placodes form within each dental lamina (on both arches.) - Dental placode (know)↓ - the first organizing/signaling center of tooth / future site of tooth; They function as the first signaling centers of the tooth - Each dental placode consist of plate-like thickened epithelium associated with an underlying neural crest derived mesenchyme or neuroectoderm Here is an image of a dental placode that shows the developing tongue, with Oral epithelium. Also the dental lamina and the ectomesenchyme of developing the mandible - Formation of the oral epithelium and dental lamina are the characteristics which make up the initiation stage. - This is due primarily to the process of INDUCTION. - Note that the basement membrane is present between the oral epithelium & ectomesenchyme. - CLINICAL CONSIDERATIONS: DISTURBANCE OF INITIATION STAGE - ANODONTIA → missing teeth partial absence of 1 or more teeth - Complete absence of all the teeth - Anodontia Occurs to due to lack of initiation of the dental lamina - Patient may need tooth replacement or orthodontic treatment - CLINICAL CONSIDERATIONS: DISTURBANCE OF INITIATION STAGE PARTIAL ANODONTIA - Partial anodontia most common form of anodontia - Most common missing teeth in order of occurrence↓ ○ Permanent 3rd molar ○ Maxillary lateral incisor ○ Mandibular second premolar - Anodontia can also result from endocrine dysfunction, systemic disease, and exposure to excess radiation, such as that in radiation therapy used with cancer treatment. - ECTODERMAL DYSPLASIA: - Group of inherited disorders where there is abnormal development of structures involving ectodermal layer↓ ○ Skin ○ Hair ○ Nails ○ Teeth ○ Sweat glands The image shows an example of *Malformed teeth & extremely sparse hair* versus *Malformed teeth* The caption states: (From Ibsen OAC, Phelan JA: Oral pathology for dental hygienists, ed 6, Philadelphia, 2014, WB Saunders.) - They have no or diminished sweating; therefore, these individuals may have trouble with regulating body temperature. - Children may have difficulty controlling fevers - Anodontia is common since many components of the tooth germ is derived from ectoderm. - Teeth may be missing, pointed, widely spaced, or prone to decay because of → defective enamel - What is the treatment like?↓ - Dental treatment is almost always necessary & children may need dentures as early as 2 years old. Multiple dentures will be made as the individual grows & dental implants may be an option as they become adults. - Orthodontic treatment is usually necessary also. - SUPERNUMERY TEETH: - Abnormal initiation may result in SUPERNUMERARY TEETH/ HYPERDONTIA. - These extra teeth are initiated from persisting dental placodes within the clusters of the dental lamina. - is it Hereditary? → yes - These extra teeth are usually↓ ○ smaller. - They may be erupted or non-erupted. - They may cause displacement of the other dentition, crowding, occlusal disruption, & delayed eruption of adjacent teeth. - These teeth are often extracted during oral surgery & orthodontic treatment is usually necessary. - MOST COMMON SUPERNUMERARY TEETH (In order of occurrence)↓ - 1. Mesiodens between the maxillary central incisors The image is of a mesiodens and is labeled with the letter D - 2. Distomolar / "4th molar " distal to the maxillary 3rd molars - 3. The premolar region (permolar region) of both dental arches - BUD STAGE: - Occurs at the beginning of 8th week of prenatal development for the primary dentition - This stage is named for the extensive PROLIFERATION of the dental lamina into the ectomesenchyme, forming BUDS. Dental lamina & surrounding ectomesenchyme will form the → future tooth germ & associated supporting tissue. The image shows the oral epithelium, dental lamina. And the tooth bud and ectomesenchyme while also developing the alveolar process. At the end of the proliferation process involving the dental placodes of the primary dentition, both the future maxillary arch and the future mandibular arch will each have → 10 buds - All the teeth and their associated tissue types develop from both → ectoderm and the mesenchymal tissue, ectomesenchyme, the latter of which is derived from NCCs. - In the bud stage, ectoderm & ectomesenchyme are PROLIFERATING & INDUCING each other. - only proliferation of these two tissue types occurs during this stage. NO other structural processes are occurring yet. - In areas where teeth won't develop, the dental lamina remains uniformly thickened because it lines the stomodeum but does not produce buds. - Later, this non tooth-producing part of the dental lamina disintegrates as the developing oral mucosa comes to line the maturing oral cavity. - These other areas will later disintegrate. Cells surrounding the bud (ectomesenchyme) will condense & change form to become the future dental papilla (condensation of ectomesenchymal cells called odontoblasts) & dental sac structures. (From Nanci A: Ten Cate's oral histology, ed 8, St Louis, 2013, Mosby.) The image is an example of the cells and epithelium that make up a tooth The oral epithelium with the epithelial invagination The ectomesenchymal condensation - CLINICAL CONSIDERATIONS: BUD STAGE DISTURBANCES - Macrodontia → abnormally large teeth - Microdontia → abnormally small teeth A radiographic image of a *Peg molar* is shown. - Abnormal proliferation can cause a single tooth or multiple teeth (partial) or all teeth (complete) to be an abnormal→ size. - MICRODONTIA: - With true partial microdontia, what are involved → hereditary factors are involved. - Teeth that are commonly affected are the → permanent maxillary lateral incisor (known as a peg lateral) and the permanent third molar (known as a peg molar) - Complete microdontia is rare & associated with endocrine dysfunction / hypopituitarism or Down syndrome. - Microdontia Can lead to esthetic & spacing complications - Can be treated with → full restorative crowns (for peg laterals) or extraction (3rd molars) - Cap Stage: - Occurs between the 9th-10th weeks during the fetal period. - There is an unequal growth in different parts of the tooth bud, leading to the formation of a 3-dimensional cap shape. The image shows a primordium of the succedaneous tooth. The successional dental lamina as well The enamel knot and the enamel organ with the dental papillae there is also the dental sac and the tooth germ while it is developing the alveolar process. This stage involves PROLIFERATION, DIFFERENTIATION, & MORPHOGENESIS to form the tooth germ. Tooth Germ consists of↓ o Enamel organ (ectoderm) o Dental papilla (ectomesenchyme) o Dental sac (ectomesenchyme) The primodium of the succedaneous tooth the successional dental lamina enamel knots enamel organ dental papilla dental sac tooth germ developing alveolar process - Tooth germ is considered the primordium (earliest) of the tooth; it means that the tooth germ represents the very first stage in the development of a tooth. - At the end of the cap stage, these three embryologic structures, the enamel organ, dental papilla, and dental sac, are now considered together to be the tooth germ - A depression occurs in the deepest part of each tooth bud of the dental lamina, forming the cap shape of the ENAMEL ORGAN. *The image shows a primodium of the succedaneous tooth* *There is also the successional dental lamina enamel knot enamel organ dental papilla dental sac tooth germ *developing alveolar proces*s - The enamel organ was originally derived from ectoderm, making enamel an ectodermal product. - Where does enamel originate from? →enamel organ and ectoderm - In future development, the ENAMEL ORGAN will produce enamel on the outer surface of the crown of the tooth. EARLY CAP STAGE: * The image shows the oral epithelium, with Invagination, * There's also the Ectomesenchymal condensation * (From Nanci A: Ten Cate's oral histology, ed 8, St Louis, 2013, Mosby) * Enamel knot * Cap-shape starting to form LATE CAP STAGE: Tooth * the enamel knot Alveolar bone Tongue Enamel organ appears more cap-shaped now. Meckel cartilage (From Nanci A: Ten Cate's oral histology, ed 8, St Louis, 2013, Mosby.) -ENAMEL KNOT↓ A group of cells found in the innermost margin of the cap shape of the enamel organ : The image displays a diagram of Successional dental lamina which appears on a diagram near other parts like Primordium of the succedaneous tooth ,Enamel knot,Enamel organ,Dental sac,Dental papilla,etc. - ODONTOGENESIS-ORGANIZING CENTERS↓ 1. Dental placodes - Enamel knots; present in the region of the developing posterior teeth, the second signaling center of tooth development. - CAP STAGE: ECTOMESENCHYME Part of the ectomesenchyme deep to the bud now condenses into a mass within the concavity of the cap of the enamel organ. * The image details cells of the Maxilla : Dental papilla Outer enamel Epithelium Tongue Dental Lamina Outer enamel epithelium * Inner enamel * Epithelium * Stellate reticulumEnamel organ * Inner Enamel * Epithelium - This inner mass is now considered the DENTAL PAPILLA. < The image shows the following: Tooth crown; Tooth root Dentin; Pulp; The BASEMENT MEMBRANE still exists between the enamel organ & the dental papilla; it is the future site of the cementoenamel junction (DEJ.) The remaining ectomesenchyme that surrounds the outside of the cap of the enamel organ condenses into the DENTAL SAC/ FOLLICLE. Here,Primodium of the succedaneous tooth ,Successional dental lamina,Enamel knot Organ ,Dental papilla are visible with all tooth germs for Developing alveolar process . - In future development, the dental sac will produce the periodontium (supporting tissue types of the tooth). The image shows a Primordium of the succedaneous tooth, with successional dental lamina. There is also an enamel knot and enamel organ as well a tooth germ and dental sac/ - A similar basement membrane also separates the enamel organ & the dental sac.. - Future dental tissue  - Dental organ enamel - Dental papilla dentin and pulp - Dental sac cementum, periodontal ligament, alveolar process **TABLE 6.3** Tooth Germ During Cap Stage | | Histologic Feature | | |: |:-------------------------------------------------------------------|:--------------| | Enamel | Information of blood in cap shape with deep set the preparation | Enamel | | Dental | Condensed mass of ectomesenchyme with in concavity. | Dentin & Pulp | | Dental | Condensed. | Cementim | * CAP STAGE ~10th WEEK During the cap stage for each primary tooth, initiation is occurring for the anterior teeth for the permanent dentition & then later for the premolars of the permanent dentition. Each primordium for these initially - formed permanent teeth appears as a lingual extension of the dental lamina into the ectomesenchyme. - Its site of origin is called the SUCCESSIONAL DENTAL LAMINA * A complex image illustrates Oral epithelium (cut to show tooth buds) in relation to Successional dental lamina of permanent teeth primordia and to Tooth germs of nonsuccedaneous permanent molars The image also depicts the Vestibule and the tongue . - CAP STAGE - PERMANENT TEETH Anteriors & Premolars vs. Molars - Succedaneous teeth Permanent teeth formed with primary predecessors Includes the anterior teeth & premolars (which replace the primary anterior teeth & molars, respectively. The crown of each permanent succedaneous tooth will erupt lingual to the root of its primary predecessor if the primary tooth has not been fully shed. * In contrast, the permanent molars are nonsuccedaneous and have NO primary predecessors: Instead, the 6 permanent molars per dental arch develop much later than both anterior teeth and premolars as buds from the dental lamina distal to the primary 2nd molars FORMATION OF PERMANENT TEETH: * The successional dental lamina gives off a series of birds which includes the future permanent incisors, canines, & premolars: * However, the permanent molars are formed by buds that arise from the dental lamina posterior to the primary 2nd molars. CLINICAL CONSIDERATIONS WITH CAP STAGE DISTURBANCES: - DENS IN DENTE: During the cap stage the enamel organ may abnormally invaginate by growth into the dental papilla results in dens in dente/ dens invaginatus. : It appears clinically in deep lingual pit radiographically as "tooth within the tooth". Teeth most commonly affected are that permanent maxillary incisors, especially the lateral incisor - May be associated with hereditary factors. (Early detection is important)May lead to pupipal exposure & pathology & subsuquent endodontic therapy Most teeth with dens in dente, do NOT show any signs ohormation and may be asy. X-rays are commonly used in diagnosis with the appearance of a tooth within a tooth. - Teeth is associated with: is affected for 866 by their condition for: Endonitite treatment may be be requined Eanly defeation is Importante Cermination: occurs as as single tooth The tooth exhibits twinning in the crown, resulting in facesdly macrodontic tooth, simular to fusions However, x-ray 1-p cavity with the correst. Twinning of the crowns appears as elefts with ranging It may even manitot as 2 crowns is for a Resutity heredity is treated by orthodontic - CLINICAL CONSIDERATIONS: It from from & tooth possibity a Leads by a broads for the samething to generation

Tooth Development: Microscopic Structure and Stages - PDF

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