TOOTH DEVELOPMENT, HISTOLOGY AND ERUPTION PATTERNS..pdf

TOOTH DEVELOPMENT (EMBRYOLOGY) Tooth development is embedded within craniofacial development. It originates from pluripotential cephalic neural crest cells which subsequently migrate towards the rst pharyngeal arch, to trigger (in co...

TOOTH DEVELOPMENT (EMBRYOLOGY) Tooth development is embedded within craniofacial development. It originates from pluripotential cephalic neural crest cells which subsequently migrate towards the rst pharyngeal arch, to trigger (in combination with mesodermal cells) the development of many elements of the craniofacial structures. 1. NEURAL CREST CELLS : ( Migration at day 22 or by week 3) - Neural crest cells are derived from the neural fold, - They are highly migratory and specialized cells that capable of predetermined di erentiation. - This di erentiation occurs after their migration and is essential for the development of face and teeth. 2. BRANCHIAL ARCHES : ( BY WEEK 4) - By week 4 the primitive mouth or the stomatodeum is formed, and the 5 facial prominences are formed between weeks 4-5. - Each arch has a derived cartilage rod ,muscular, nervous , and vascular component. - The rst two arches and their associated components are central to the development of the facial structures. - This period is also characterized by the development of the organs of hearing, sight , and smell. - Facial development starts at 4 weeks and continue to 10 weeks. 1 of 9 fi fi ff ff 3. FACIAL DEVELOPMENT : ( By the end of week 4) - Thickening starts to develop in the frontal process. - The medial and lateral frontonasal processes develop from these together with the nasal placodes. ORDER: - The maxillary process develop from the rst pharyngeal arch - then It grows forward to meet medial and nasal processes - then Upper lip , incisor teeth and the primary palate forms - then Lower lip is formed by fusion of the mandibular arch * By week 8 , the odontogenic epithelium which will di erentiate into tooth forming cells will be determined on the maxillary process , lateral aspect of medial process and the superior border of the mandibular process. WHY IS IT IMPORTANT? 1. Failure of cells migration and or fusion during the facial development face will result in di erent anomalies/abnormalities. 2. Of all the babies born with birth defects, approximately one-third display anomalies of the head and face. including cleft lip cleft palate small or absent facial and skull bones improperly formed nose, eyes, ears, and teeth. A failure in fusion resulting in cleft lip/palate TOOTH DEVELOPMENT (Histology) : 1. Teeth start to from during the 5th to 6th week of the embryonic life, and continues until the roots of the third permanent molars are completed about 20 years of age. 2. Whether the tooth is of the primary or the permanent dentition the stages of tooth formation are the same, but obviously the teeth will develop at di erent times. 2 of 9 fi ff ff ff  TOOTH DEVELOPMENT (Histology) Continues……. Primary epithelial band: A Horse shoe shaped thickening of the ectodermal epithelium underneath the oral ectoderm at about the 6th week of intrauterine life. The earliest event in the origin of each dental organ begins from the oral epithelium. It di erentiates into the vestibular band, which eventually forms the lips and cheeks, and the dental lamina from which the tooth germs develop. Tooth development is a continuous process. Based on the developmental history of tooth. - Morphology of the enamel organ - morphological stage of development - Physiologic activity of the tooth bud – physiological stage of development STAGES OF TOOTH DEVELOPMENT : - initiation stage – 6th to 7th week - bud stage – 8th week - cap stage – 9th to 10th weeks - bell stage – 11th to 12th weeks - apposition stage – varies per tooth - maturation stage – varies per tooth 3 of 9 ff BUD STAGE : (PROLIFERATION) Marked by the incursion of epithelium into the mesenchyme. The enamel organ in the bud stage appears as a simple, spherical to ovoid, epithelial condensation that is poorly morphodi erentiated and histodi erentiated. It is surrounded by mesenchyme This developing tooth forms from both the ectoderm and mesenchyme and from neural crest cells that have migrated into the mesenchyme. The epithelial component is separated from the adjacent mesenchyme by a basement membrane. - Characterized by continuation of the ingrowth of the oral epithelium into the mesenchyme. tooth bud of the dental lamina proliferates unequally in di erent parts of the bud - By the 11th week, morphogenesis has progressed, the deeper surface of the enamel organ invaginating to form a cap-shaped structure. BUD STAGE SUMMARY : Characterized by - Formation of a tooth bud. - The epithelial cells begin to proliferate into the ectomesenchyme of the jaw. CAP STAGE : (PROLIFERATION) - A depression forms in the deepest part of each tooth bud and forms the cap or enamel organ (or dental organ) – produces the future enamel (ectodermal origin) - The adjacent mesenchymal cells continue to proliferate and surround the enamel organ. - The part of the mesenchyme lying beneath the internal enamel epithelium is termed the dental papilla, while that surrounding the tooth germ forms the dental follicle (dental sac). - Below this cap is a condensing mass of mesenchyme – dental papilla - produces the future dentin and pulp tissue (mesenchymal origin) - The basement membrane separating the dental organ and the dental papilla becomes the future site for the dentinoenamel junction (DEJ) - Remaining mesenchyme surrounds the dental/enamel organ and condenses to form the dental sac or the dental follicle. - Enamel knots are clusters of nondividing epithelial cells visible in sections of molar cap stage tooth germs. - They play an important role by the cuspal morphogenesis. BUD STAGE SUMMARY - Formation of dental papilla. - The enamel organ & dental papilla forms the tooth germ. - Formation of ameloblasts. - Formation of odontoblasts. 4 of 9 ff ff ff  BELL STAGE (HISTODIFFERENTIATION and MORPHODIFERNATION): Cap shape then assumes a more bell-like shape Di erentiation produces four types of cells within the enamel/dental organ 1. inner enamel epithelium 2. outer enamel epithelium 3. stellate reticulum 4. stratum intermedium 1. Outer enamel (dental) epithelium (OEE): - Cuboidal shape - Protective barrier during enamel production - very little cytoplasm - cells are separated from the dental follicle by a basement membrane. 2. Inner enamel (dental) epithelium (IEE) - Short, columnar cells - Di erentiates into the enamel - Secreting cells = ameloblasts - Separated from the dental papilla below it by a basement membrane.. 3. Cervical loop: - The IEE and OEE are continuous - Region where they connect – curved rim of the EO = cervical loop. 4. Stellate reticulum - Star-shaped cells in many layers - Center of the enamel organ - Forms a network = reticulum - Supports production of enamel. APPOSITION - Appositional growth is the result of a layer-like deposition of a nonvital extracellular secretion in the form of a tissue matrix. - This matrix is deposited by the formative cells, ameloblasts, and odontoblasts, which line up along the future dentinoenamel and dentinocemental junction at the stage of morphodi erentiation. - These cells deposit the enamel and dentin matrix according to a de nite pattern and at a de nite rate. - The formative cells begin their work at speci c sites that are referred to as growth centers as soon as the blueprint, the dentinoenamel junction, is completed. Initiation stage abnormalities : - The congenital absence of a tooth is the result of a lack of initiation or an arrest in the proliferation of cells. - The presence of supernumerary teeth is the result of a continued budding of the enamel organ. The following dental anomalies can occur during the proliferation stage : 1.Hypodontia 4.Fusion 2.Hyperdontia 5.Gemination 3.Missing Tooth 5 of 9 ff fi ff ff fi fi CAP STAGE ABNORMALITIES : (Proliferation Abnormalities) - As with a de ciency in initiation, a de ciency in proliferation results in failure of the tooth germ to develop and in less than the normal number of teeth. ( SIMILAR TO INITIATION STAGE) The degree of di erentiation of the cells determines whether the following things will form : 1. Cyst 2. Odontoma 3. Supernumerary tooth BELL STAGE ABNORMALITIES (MORPHODIFERNATION) - Disturbances and aberrations in morphodi erentiation lead to abnormal forms and sizes of teeth. Resulting conditions include : - Peg teeth. - Microdontia. - Macrodontia. BELL STAGE ABNORMALITIES (HISTODIFFERENTIATION) Disturbances in the di erentiation of the formative cells of the tooth germ result in abnormal structure of the dentin or enamel. One clinical example of the failure of ameloblasts to di erentiate properly is amelogenesis imperfecta. The failure of the odontoblasts to di erentiate properly, with the resultant abnormal dentin structure, results in the clinical entity dentinogenesis imperfecta. APPOSITION ABNORMALITIES - Any systemic disturbance or local trauma that injures the ameloblasts during enamel formation can cause an interruption or an arrest in matrix apposition, which results in enamel hypoplasia. 6 of 9 fi ff ff ff fi ff ff  CALCIFICATION ( MINERALIZATION) - Calci cation (mineralization) takes place following matrix deposition and involves the precipitation of inorganic calcium salts within the deposited matrix. - The process begins with the precipitation of a small nidus, and further precipitation occurs around it. CALCIFICATION ANOMALIES ? - If the calci cation process is disturbed, there is a lack of fusion of the calcospherites. - These de ciencies are not readily identi ed in the enamel, but in the dentin they are evident microscopically and are referred to as interglobular dentin. (check slide 32) TIMETABLE FOR TOOTH DEVELOPMENT - Entire primary dentition initiated between 6 and 8 weeks of embryonic development. - Successional permanent teeth initiated between 20th week in utero & 10th month after birth. - Permanent molars between 20th week in utero ( rst molar) & 5th year of life (third molar). ROOT FORMATION - Root formation is through the formation of a cervical loop. - The CL is the most cervical portion of the enamel/dental organ – two layers consisting of - IEE - OEE. - the CL begins to grow down into the dental sac and it forms a Hertwig's root sheath. - This sheath shapes the root and induces dentin formation in the root area by the ODs of the dental papilla. 7 of 9 fi fi fi fi fi  CEMENTUM AND PULP FORMATION - Cementogenesis in the root area also occurs upon degradation of the Hertwig's root sheath. - The degradation allows contact of the dental sac cells with the dentin surface – induces the formation of cementoblast cells. - The cementoblast cover the root dentin and undergo cementogenesis – laying down cementoid only - upon mineralization of the cementoid it can be called cementum. - The region of contact between cementum and root dentin = dentinocemental junction. PERIODONTAL LIGAMENT - The surrounding tissues of the tooth also develop as the crown and root form the mesenchyme of the dental sac condenses to form the periodontal ligament. - Ends of these bers insert into the outer layer of cementum and surrounding alveolar bone - The cells of the disintegrating Hertwig's root sheath develop into discrete islands of epithelial cells which become the epithelial rests of Malassez. - They can be identi ed in the periodontal ligament and are responsible for the development of radicular cysts. WHAT ABOUT MULTIROOTED TEETH - Anterior teeth, premolars and molars all begin as a single root – root trunk. - Root of the posterior teeth divides from the trunk into the correct number of root branches. - Di erential growth of the Hertwig's root sheath results in the division of the root trunk into two or three roots. ERUPTION PATTERNS (AGE OF ERUPTION) (Varies considerably) 1. Centrals : Mandibular then maxillary 2. Laterals: Mandibular then maxillary 3. 1st Molars: Mandibular then maxillary 4. Cuspids: Mandibular then maxillary 5. 2nd Molars: Mandibular then maxillary Usually the mandibular teeth erupt rst ERUPTION PATTERNS STEPS OF ERUPTION 1. Pre-emergent eruption - Pre-eruptive phase a) Resorption of the bone & primary tooth roots. b) The eruption mechanism. 2. Post-emergent eruption - Eruptive phase a) Post-emergent spurt - Eruptive phase (Pre-functional). b) Juvenile occlusal equilibrium Eruptive phase (Functional). c) Adult occlusal equilibrium. 8 of 9 ff fi fi fi  ERUPTION PATTERNS SEQUENCE OF ERUPTION ERUPTION PATTERNS (FAILURE OF ERUPTION) - Eruption cyst can be considered a variant of the dentigerous cyst that occurs in the soft tissue overlying an erupting tooth. How is it caused ? - It is caused by separation of the reduced enamel epithelium and dental follicular tissues from the crown of the tooth. Dentigerous cyst: An odontogenic cyst that surrounds the crown of an impacted tooth. How is caused ? - It is caused by uid accumulation between the reduced enamel epithelium and the enamel surface, resulting in a cyst in which the crown is located within the lumen and root or roots outside. ERUPTION PATTERNS ABNORMALITIES OF ERUPTION TIMING ? - Natal and neonatal teeth are rare dental anomalies seen in the oral cavity of a newborn baby. - These teeth are a result of a biological disturbance in the chronology of teeth, the etiology of which is still not understood. - “Natal teeth” are teeth which are present at the time of birth, while “neonatal teeth” are those which erupt during the neonatal period (up to 30 days of age). Treatment : 1. Well implanted tooth should be left in the arch 2. Extraction is indicated if : - There is a risk of aspiration - Tooth is mobile - Causing injury to the baby ( sublingual ulcers ) - A ect feeding. 9 of 9 ff fl