Tooth Development and Growth (2024) PDF

Oral Biology Department Faculty of Dentistry Tanta University By Prof. Dalia Zahran ▪ Objectives: - By the end of this lecture, students should be able to: 1. Define and describe the sequence of events of the stages of tooth development. 2. Describe the stages of root formation. ▪ Tee...

Oral Biology Department Faculty of Dentistry Tanta University By Prof. Dalia Zahran ▪ Objectives: - By the end of this lecture, students should be able to: 1. Define and describe the sequence of events of the stages of tooth development. 2. Describe the stages of root formation. ▪ Teeth are formed from: ▪ Oral epithelium (dental lamina). Enamel ▪ Ectomesenchyme (Neural crest). Dentin, pulp &cementum.  ORIGIN OF DENTAL TISSUE ▪ Neural fold close. ▪ Neural crest cells migrate down the sides of the head underlying the skin. ▪ These cells called Ectomesenchymal cells. ▪ These cells constitute the CT of head, neck & dental structures except enamel. ▪ Neural crest cells give rise to: Chondrocytes Osteoblasts Fibroblasts Cementoblasts Odontoblasts **The development of the tooth involves many complex biologic processes, including epithelial mesenchymal interactions. From this interaction 20 deciduous and 32 permanent teeth develop, The fundamental process is similar for all teeth.  Flat cells Columnar cells A ECTODERM ( St.Sq.E. ) Stomodeum Ectomesenchy Basement mal tissue membrane Ectoderm Neural Crest Cells Dental lamina Future dental papilla Stomodeum  DEVELOPMENT **STAGES OF TOOTH DEVELOPMENT MAY BE DESCRIBED ACCORDING TO: 1- MORPHOLOGICAL STAGES. According to changes in the morphology of the developing tooth. 2- HISTOPHYSIOLOGICAL STAGES. According to physiological changes i.e. function changes of the developing tooth. 1- Dental Lamina. 1- Dental Lamina. 2- Bud stage. 1- Dental Lamina. 2- Bud stage. 3- Cap stage. Early cap. Late cap. 1- Dental Lamina. 2- Bud stage. 3- Cap stage. Early cap. Late cap. 4- Bell stage. Early bell. Late bell.  1- Initiation of Dental lamina *Primary epithelial band: after about 37 days of development, a continuous band of thickened epithelium forms around the. These bands are roughly horseshoe-shaped.  The formation of these thickened epithelial bands is the result not so much of increased proliferative activity within the epithelium as it is a change in orientation of the mitotic spindle and cleavage plane of dividing cells Odontogenesis is initiated first by factors resident in the first arch epithelium influencing ectomesenchyme, but that with time this potential is transferred to and is assumed by the ectomesenchyme. Primary epithelial band ( formed at 6 w.i.u.) PEB proliferates to give two subdivisions which grow into the underlying mesenchyme. They are Dental lamina & Vestibular lamina. ▪ Dental lamina, which forms first, (General Lamina): 1- Lateral lamina ( primary teeth) 2- Succesional lamina (permanent successional teeth). 3- Distal Proliferation of Mother (generalized) lamina (Permanent molars). 4- Rudimentary lamina (epithelial pearls or Glands of Serres) ▪ Vestibular lamina The Vestibular lamina, forms shortly afterwards, is a wedge of epithelium facial to dental lamina  Vestibular and Dental laminae A: Mandibular dental organ; B: Mesenchymal cells; C; Mandibular vestibular lamina; D: Alveolar process; E: Maxillary dental organ; F: Maxillary vestibular lamina.  Oral epithelium and Oral ectomesenchyme Initiation of Dental lamina Bud stage Cap stage Bell stage 1- Initiation Of The Entire Deciduous Dentition facial to dental lamina ( 6-8 w.i.u.). 2- Initiation Of The Permanent Successors (lingual & apical to its predecessors ( from 5 m.i.u. for Incisors until 10 months of age for Premolars). 3- Initiation of the Permanent Molars (grow posteriorly to give the EO of permanent molars which have no deciduous predsessors). (1st Molar at 4 m.i.u., 2nd Molar at 1 Year, 3rd Molar at 4 Years), so the life span of the dental lamina is about 5 years. It is thus evident that the activity of the dental lamina extends over a period of about five years and disintegrates completely or remains as epithelial rests of Serres. Def.: The determination of specific tooth types at their correct positions in the jaws Two hypothetical models have been proposed: The Field model The Clone model Factors responsible Eeach tooth class is for tooth shape derived from a clone of reside within the ectomesenchymal cells ectomesenchyme in programmed by distinct graded and epithelium to produce overlapping fields for teeth of a given pattern each tooth family 2-BUD STAGE 2-BUD STAGE The enamel organ, dental papilla and dental sac together constitute the tooth germ 1- Low columnar basal cells. 2- Polygonal cells. 3- Ectomesenchymal condensation (around the epithelial proliferation) ENAMEL ORGAN TOOTH GERM DENTAL PAPILLA DENTAL SAC (follicle)  3- CAP STAGE ▪ a. Early cap stage; the tooth germ continues to grow (unequal growth) in the different parts of the enamel organ (i.e. differential growth) leading to a shallow invagination in the deep surface of the bud. ▪ The enamel organ assumes a cap shaped appearance with a convex outer surface and a concave inner surface Cap Stage of Tooth Development Dental (enamel) organ Dental papilla Dental follicle HISTOLOGY OF CAP STAGE Transitory structures - Enamel knot and enamel cord - Primary and secondary enamel knots initiate the bud-to-cap stage transition and tooth crown formation. ▪ The function of these two structures is not known ▪ Major signaling center for tooth development. ▪ Represent an organizational center that orchestrates cuspal morphogenesis. ▪ The enamel cord could be related anatomically to the site where the lateral lamina attaches to the enamel organ cap. Enamel niche. This structure is created by the plane of histological section cutting through a curved lateral lamina so that mesenchyme appears to be surrounded by dental epithelium.  TOOTH GERM 1-Enamel ORGAN 3- DENTAL 2- DENTAL SAC PAPILLA Outer enamel ep. 1-Enamel organ Stellate Reticulum Enamel cord Enamel knot Inner enamel ep. Cell free zone 3-Dental sac 2-Dental papilla  There are three sets of transient signaling centers in the dental epithelium. Initiation Knot: appear in the dental placode and initiate budding of the tooth epithelium, and Primary and Secondary Enamel Knots: initiate the bud-to-cap stage transition and tooth crown formation. They produce more than a dozen different signaling molecules belonging to the BMP, FGF, Shh, and Wnt families. Fgf-4 and Slit-1 may be the best molecular markers for enamel knot formation, because they have been observed in both primary and secondary knots. 4- BELL STAGE ▪ During the Bell stage, two important events occur: 1- The IEE folds determining the shape of the future crown. 2- Break up of DL. ▪ During this stage, the tooth crown assumes its final shape (morphodifferentiation), and the cells that will be making the hard tissues of the crown (ameloblasts and odontoblasts) acquire their distinctive phenotype (histodifferentiation). ▪ Morophodifferentiation: Determining the shape of a tooth. ▪ Histodifferentiation, a mass of similar epithelial cells transforms itself into morphologically and functionally distinct components ▪ The folding that occurs as the crown develops results from intrinsic growth caused by differential rates of mitotic division within the inner enamel epithelium ▪ As development continues, division ceases at a particular point because the cells are beginning to differentiate and assume their eventual function of producing enamel. ▪ The point at which inner enamel epithelial cell differentiation first occurs represents the site of future cusp development. ▪ Bell stage is divided into: A) Early bell stage : before formation of any hard dental tissue. 1- Elongation of inner enamel epithelium. 2- Differentiation of odontoblasts. 3- Predentin formation. B) Late (Advanced ) bell stage: which starts by the formation of the first layer of dentine. 1- DP changes to dental pulp. 2- The OEE invaginate & carry capillary plexus of DS near ameloblasts.  Bell-shaped enamel organ Dental lamina Outer enamel epithelium Stellate Reticulum Successional lamina Stratum Intermedium Inner enamel Dental papilla epithelium Cervical loop Dental sac Developing bone Early Bell Stage  Dental Sac Inner Enamel Epithelium Odontoblasts OEE Cell SI free zone DP SR OB IEE  DENTAL LAMINA PROPER Successional lamina LDL Cervical loop  DENTAL LAMINA PROPER SUCCESSIONAL LAMINA SUCCESSOR PRIMORDIUM LATERAL Enamel DENTAL Organ LAMINA SDL  Cervical loop - At the cervical part of the enamel organ, the IEE & OEE meet at the rim of the enamel organ to form the cervical loop (or zone of relection). - Minimal inclusion of stellate reticulum or stratum intermedium. - This is the point where the cells continue to divide until the tooth crown attains its full size, and it is very important for root formation. A, Cervical loop B, Inner enamel epithelium C, Outer enamel epithelium D, Stratum intermedium E, Stellate reticulum  B. ADVANCED BELL STAGE - It starts by deposition of the first layer of dentin by differentiated odontoblasts. Bell Stage Late Bell Stage  Stratum Intermedium Stellate Recticulum Inner Enamel DENTIN Ep ODONTOBLASTS  S.R. E D P.D. A O S.I Dental pulp. When dentin deposition occurs: ***Source of nutrition of the (avascular enamel organ) is cut Enamel organ off -The dental organ react to compensate this by:- 1- Shrinkage of StR 2- Flattening and folding of OEE 2- Approximation of the capillary plexus of the dental sac to ameloblasts ***Dental lamina:- -Lateral dental lamina will disappear due to its invasion by the surrounding mesoderm causing its degeneration. -Remnants of the dental lamina may persist in the form of isolated groups of epithelial cells called epithelial rests of Serres or Serres’ pearls. - These remnants may form eruption cyst, odontomes or may form supernumerary teeth  NERVE AND VASCULAR SUPPLY DURING EARLY DEVELOPMENT Vascular Supply - Clusters of blood vessels are found ramifying around the tooth germ in the dental follicle and entering the dental papilla during the cap stage. - Their number in the papilla increases, reaching a maximum during the bell stage when matrix deposition begins. - Remember that, The enamel organ is avascular, although a heavy concentration of vessels in the follicle exists adjacent to the outer enamel epithelium. Nerve Supply - Nerve fibers approach the developing tooth during the bud-to-cap stage of development, growing toward the dental follicle. - When dentinogenesis begins, the nerve fibers penetrate the dental papilla (pulp).  FUNCTIONS OF THE ENAMEL ORGAN 1- OUTER ENAMEL EPITHELIUM. a- Active transport of materials specially, after hard dental tissues formation. b. Involved in the maintenance of the shape of the enamel organ. 2- STELLATE RETICULUM. a- It act as a buffer or (cushion) against any external forces or pressure. b- it acts as a store house for the nutritive materials. c- It keeps room (space) for the developing enamel. 3- STRUTUM INTERMEDIUM. The function of this layer is not understood: a- It provides the enamel organ with alkaline phosphatase enzyme needed for mineralization. c- These cells together with the inner dental epithelium are considered as a single functional unit responsible for enamel formation.  4- INNER ENAMEL EPITHELIUM. ✓ a- It exerts an organizing influence on the undifferentiated cells of the dental papilla to differentiate into odontoblasts. ✓ b- Arranged in a pattern to determine the future morphology of the amelodentinal junction and the crown (crown shape). ✓ c- It lays down enamel matrix and helps in its mineralization. ✓ d- It forms the Hertwig's epithelial root sheath with the OEE ✓ e- It secretes primary enamel cuticle, after the full thickness of enamel is deposited, to protect the enamel of the unerupted tooth. ✓ f- It shares in the formation of the reduced enamel epithelium. ✓ g- It is involved in development of DGJ and attachment epithelium. ✓ h- The cells of the inner enamel epithelium of the Hertwig epithelial root sheath may secrete the intermediate cementum. ***The Dental Papilla gives rise to: Dentin and Dental Pulp. ***The Dental Sac gives rise to Cementum, Periodontal Ligament and Alveolar Bone Proper. Cervical loop Hertwig’s epith. root sheath Odontoblast differentiation Dentin formation Disintegration of root sheath Cementoblast differentiation Cervical loop Hertwig’s epith. root sheath  Dentin formation Odontoblast differentiation  Disintegration Cementoblast Dentin formation of root sheath differentiation  E PD AB D SI SR OB OEE DP DF  Cells of the dental follicle (forms cementocytes) Cell rest (of Malassez) ©Copyright 2007, Thomas G. Hollinger, Gainesville, Fl In MULTI-ROOTED TOOTH the same sequence of events as for single rooted teeth until the level of furcation area is reached, where the epithelial diaphragm grows horizontally forming:- two tongue like extensions (or projections) in double rooted teeth. Three tongue like extensions (or projections) in triple rooted teeth.  Epithelial diaphragm Root Formation  epithelial rests of Malassez. *** The function of EPITHELIAL RESTS OF MALASSEZ ▪ Osteoblasts are differentiated from dental sac and form bony socket. ▪ Fibroblasts are differentiated from the dental sac and form periodontal ligament which attaches the cementum of the root to the bony socket. ▪ Bone, cementum, and periodontal ligament are formed at the same time. ▪ 1- Growth factors e.g., TGFB, FGF, EGF and BMPs. They initiate proliferation , migration, and differentiation of cells ▪ 2- Homeobox genes ( HOX); Regulatory factors that specify correct positioning of body parts during embryonic development ▪ 3- Nutrition The essential nutrients for a healthy tooth include calcium, phosphorus and vitamin A, C and D. ▪ 4- Fluoride  Clinical consideration 1- A lack of initiation results in the absence of either a single tooth or multiple teeth (partial anodontia or hypodontia), ▪ There also may be a complete lack of teeth (anodontia). 2- Abnormal initiation may result in the development of single or multiple supernumerary (hyperdontia) teeth. (Most commonly the mesiodens is seen between the maxillary central incisors). 3- Disturbances affect the size or form of the crown and roots of teeth (macrodontia or microdontia).  Clinical consideration 4- If the cells of the epithelial root sheath of Hertwig’s remain adherent to the dentin surface (i.e. failure of its degeneration) either: A) Enamel pearls. B) Bare dentin ( highly sensitive). This is most common at cervical region. ▪ 5- Accessory root canal Premature degeneration of the root sheath before odontoblasts differentiation. Present on the periodontal surface of the root. 6- If there is disturbance in the fusion of the tongue like extension of the diaphragm of the Herwig’s sheath, or if a large vessel is present that disturb the continuity of epithelial root sheath of Hertwig’s, this result in a defect leading to existence of accessory root canal.  Exposed (Bare) dentin Accessory root canal ENAMEL PEARL  HISTOPHYSIOLOGICAL STAGES OF TOOTH DEVELOPMENT ▪ This classification is based on the physiological changes during tooth development, it is divided into; 1)Initiation 2)Proliferation 3) Morphodifferentiation 4) Histodifferentiation 5)Apposition DEVELOPMENT  1- INITIATION ▪ Initiation; The dental lamina and tooth bud represent the part of the oral epithelium that has potencies for tooth formation. epithelium Initiation requires ectomesenchymal – epithelial interaction due to the stimulation effect of the ectomesenchymal cells (neural crest cells) that migrate from the region of the neural tube to the oral cavity. In the absence of Initiation, no tooth would form, and this condition is called Anodontia. 2- PROLIFERATION The proliferative activity results successively in the bud, cap and bell stages where the dental hard structure are not yet deposited. The proliferative activity causes regular changes in the size and proportions of the tooth germ. 3-MORPHODIFFERNTIATION - Begins at the end of cap stage and continuous through early bell stage. - The relative size and the morphologic pattern of the future tooth is determined. ***Disturbance in this stage results abnormal tooth form and size. e.g.: peg shape lateral incisor, macrodontia, microdontia  4- HISTODIFFERENTIATION ▪ In this stage the cells of the tooth germs undergo definite morphogenic as well as functional changes and thus achieve their functional requirements. ▪ It begins in the cap stage until the bell stage ▪ Disturbance in this stage lead to defect in enamel or dentin formation , amelogenesis imperfecta and dentinogenesis imperfecta. 5-APPOSITION The deposition of the matrices of enamel and dentin are confined to the late bell stage. The secretion of enamel and dentin takes place in an incremental pattern called Apposition. This phenomenon is regular, rhythmic and with alternate periods of activity and rest. Disturbance will lead to enamel or dentin hypoplasia ▪ Jose, Maji. Essentials of Oral Biology: Oral Anatomy, Histology, Physiology & Embryology. CBS Publishers & Distributors, 2nd Edition. ▪ Nanci A :Ten Cate Oral Histology: Development, Structure and Function ( 2013 ) ,8th edition , Mosby , Elsevier Publisher ,USA. ▪ https://www.studyblue.com/notes/note/n/tooth- development/deck/8433252 ▪ - http://www.toothpicks.info/exam_prep/module_1.html ▪ -http://pocketdentistry.com/5-development-of-teeth/