Tooth Development PDF

Tooth development Dr. Sándor Balázs General embriology  1. Emryonic stage ▪ Fertilization to 4th week→cellular proliferation, migration, some differentation ▪ Until the 8th week→ morphogenesis, differentation of structures  2. Fetal stage ▪ Mainl...

Tooth development Dr. Sándor Balázs General embriology  1. Emryonic stage ▪ Fertilization to 4th week→cellular proliferation, migration, some differentation ▪ Until the 8th week→ morphogenesis, differentation of structures  2. Fetal stage ▪ Mainly growth and maturation (fetus) www.aok.pte.hu General embryology  Rapid proliferation and migration until three layered (germlayer) embyo is formed  At about 8th day of development the two-layered germ disk is formed  3rd week the trilaminar embryonic disk is formed www.aok.pte.hu www.aok.pte.hu Formation of the neural tube and neural crest  Thickening of ectodermal layer→ neural plate→ raised margins→ neural groove and folds→ neural fold fuse→ neural tube  A group of cells separate from the neuroectoderm→ neural crest  Neural crest cell through epithelial-mesenchymal transition→ cells migrate away and form most of the head’s connective tissues (ectomesenchyme) www.aok.pte.hu Folding of the embryo  Folding in two planes www.aok.pte.hu Migration of neural crest cells  Provides embrionic connective tissue  First branchial arch→ cells from the neuroectoderm of the midbrain and the first two rhombomeres  Homeobox gene expression (1st branchial arch→Msx, Dlx, Barx) www.aok.pte.hu The formation of the head and mouth→ previous lectures www.aok.pte.hu Primary epithelial band  In the area of the upper and lower jaw at around the 38th day of development the epithelium of the stomodeum thickens www.aok.pte.hu Dental lamina and vestibular lamina www.aok.pte.hu Dental lamina  Dental lamina thickening of the epithelium  Localized thickening appear→ dental placodes  Proliferation→ epithelial outgrowth  Mesenchymal cells underlying have greater mitotic index, they accumulate around the outgrowth  3 further stages are distinguished→ bud, cap, bell www.aok.pte.hu www.aok.pte.hu https://youtu.be/SCP38MrccsI www.aok.pte.hu Initiation of tooth  What initiates tooth development: ▪ Oral epithelium combined with non odontogenic ectomesenchyme leads to tooth formation ▪ If oral ectomesenchyme is combined with other epithelium→ no tooth formation  Later ▪ Late first arch mesenchyme combined with plantar epithelium leads to enamel organ formation ▪ Enamel organ combined with skin mesenchyme→ organ looses its dental characteristics Tooth development is initiated by the oral epithelium, later the ectomesenchyme takes over this regulatory function www.aok.pte.hu Regulation of tooth development  More than 300 factors have already been recognized in tooth development.  The main factors are: Shh, Wnt, Fgf, BMP www.aok.pte.hu Regulation (sight into the complexity)  Initiation: epithelial Fgf-8 induces mesenchymal Lhx- 6, Lhx-7 expression ▪ 1. arch Mesenchyme combined with 2. arch epithelium→ downregulation of these genes ▪ Shh also has important role in initiation of the dental lamina ▪ Lef1 expressed in the dental lamina, later in the mesenchyme  Position of teeth: ▪ Mesenchymal Pax-9 gene co-localizes with the position of teeth ▪ Fgf-8 induces, Bmp-2 and 4 represses its expression (BMPs expressed in areas where no tooth is developing) www.aok.pte.hu Tooth type determination  Field model: ectomesenchmye contains the factors  Clone model: a tooth class is derived from clones of a measenchymal cells  Probably the models are combined→ temporal factors www.aok.pte.hu Stages  Bud stage: invasion of epithelial cells in the mesenchyme, condensed surrounding mesenchymal cells  Bud to cap transistion: ▪ Onset of morphological differences ▪ Msx-1, Pax-9 expression (lack of Msx-1 or Pax-9 arrests tooth in bud stage) www.aok.pte.hu Stages  Cap stage: ▪ Condensation of mesenchyme (cells don’t produce extracellular substance) ▪ Bud grows larger→ drags the dental lamina→ lateral lamina is formed ▪ The „cap” sitting on the mesenchyme is called the enamel organ ▪ Ectomesenchyme→ dental papilla and follicle www.aok.pte.hu Enamel knot  Non dividing epthelial cells in the epithalial organ  Expression of many signaling molecules  Every tooth germ, secondary enamel knot in the cusps of the molar teeth  Unknown fuction  Probably center of morphogenesis regulation (cusps) www.aok.pte.hu Bell stage  The enamel organ looks like a bell  Crown reaches its final shape  Histodifferentation of ameloblasts and odontoblasts  The developing tooth separates from the dental lamina and oral epithelium www.aok.pte.hu  The inner enamel epithelium is separated form the dental papilla by basal lamina From the basal lamina fine fibrils extend into acellular zone on the periphery of the papilla (see hard tissues lecture) Papilla is called pulp when the first hard tissues appear www.aok.pte.hu Formation of permanent teeth  The buds form lingually from the deciduous buds  Result of further proliferative activity in the dental lamina  The permanent molars are formed from the extensions of the dental lamina  Primary teeth development initiates at about 8th week of embryonic development  permanent about the 20th week to 10 month after birth  Permanent molars 20th week in utero to 5 years of age www.aok.pte.hu Tooth eruption  Teeth develop in bony crypts  Initiation of root formation→ teeth start to erupt  Bone over the tooth is resorbed  Cells covering the enamel→ reduced enamel epithelium (REE)  REE fuses with oral epithelium→ center cells depredate→ epithelial canal www.aok.pte.hu Mechanisms of tooth eruption  PDL forms with root development→ remodeling  Permanent teeth keep connection with lamina propria of oral mucosa→ gubernacular cord→ osteoclastic activity www.aok.pte.hu Theories  Root formation ▪ Although force is present it results apical bone resorption→ it cannot be translated into eruptive force  Bone remodeling ▪ Some remodeling occurs ▪ Dental follicle is also involved  Follicle ▪ REE- follicle signaling→ bone resorption  PDL ▪ Traction power (teeth might not erupt, having PDL, teeth can erupt without root  Innervation ▪ Innervation provoked pressure requiring PDL adaptation  Pulpal pressure ▪ Vascular pressure in the pulp increases www.aok.pte.hu Formation of hard tissues  Previous lectures→ hard tissues of the teeth www.aok.pte.hu Thank you for your attention! www.aok.pte.hu