Enamel Lecture 4 - PDF Petra University

Faculty of Dentistry ‫كلية طب األسنان‬ Enamel Petra University  ‫‪Faculty of Dentistry‬‬ ‫كلية طب األسنان‬...

Faculty of Dentistry ‫كلية طب األسنان‬ Enamel Petra University  ‫‪Faculty of Dentistry‬‬ ‫كلية طب األسنان‬ ‫رؤية الكلية ‪:‬‬ ‫أن تكون ُكلِّيَّة طبِّ األسنان في جامعة البترا الخيار األفضل للعلماء والمتعلمين في مجال طبِّ األسنان‬ ‫والرائدة في نوعية وجودة التعليم والبحث العلمي وخدمة المجتمع‪.‬‬ ‫رسالة الكلية ‪:‬‬ ‫توفــر بيئــة تعليميــة وتدريبيــة وبحثية متميــزة‪ ،‬تثير التســاؤل والفضــول في االكتشافات العلميــة‪،‬‬ ‫وتأهيــل كفايات مهنيــة وعلميــة متميــزة في علــوم طـب األسنان‪ ،‬ملتزمــة بتطويــر المهنة وتنفيــذ‬ ‫أبحاث نظريــة وتطبيقيــة وتقــديم خدمــات طبِّيــة وفــق أعلــى معايــر الجودة لتلبيــة احتياجــات ســوق‬ ‫العمــل والمجتمع المحلي‪.‬‬  Faculty of Dentistry ‫كلية طب األسنان‬ Title: - Enamel Presented By: Atef I. Ahmed Professor of Oral Biology  Faculty of Dentistry ‫كلية طب األسنان‬ By the end of this lecture, the student would be able to: 1- Discuss the structural features of enamel. 2- Examine the histological slides that showcase histological structure of enamel. 3- Explain the life cycle of ameloblasts 4- Identify the stages of amelogenesis  Enamel 1-ECTODERMAL TISSUE COVERING THE ANATOMICAL CROWN. 2-HIGHLY MINERALIZED, RISIST MASTICATORY FORCES. 3-ACELLULAR, NONVITAL AND INSENSITIVE. 4-CANNOT REPALCED OR REGENERATED.  1-COLOUR 2-THICKNESS PHYSICAL PROPERTIES 5-PERMEABILITY 3-HARDNESS 4-BRITTLNESS 6- Density 1 - COLOUR YELLOWIH WHITE TO GRAYISH WHITE 2 - THICKNESS - 2 – 2.5 mm. at the cusps of the molars and premolars. - Thinning down to Almost knife edge at the cervical margin of the tooth (100 µm)  3 – HARDNESS IT IS THE HARDEST + + CALCIFIED TISSUE IN THE + BODY DUE TO: + - 1- HIGH CONTENT OF THE - MINERAL SALTS 2- ITS CRYSTALLINE - ARRANGEMENT. 4 - BRITTLNESS ITS STRUCTURE AND HARDNESS RENDER IT BRITTLE, SPECIALY WHEN IT LOOSES ITS ELASTIC FOUNDATION OF HEALTHY DENTIN ASG  5- PERMEABILITY -ENAMEL HAS A CERTAIN DEGREE OF PERMEABILTY DEMONSTRATED BY DYES AND RADIOACTIVE ISOTOPES. - IT ACTS AS A SEMIPERMEABLE MEMBRANE FOR CERTAIN IONS AND DYESTUFFS OF SMALL MOLECULAR SIZE THROUGH PORES BETWEEN THE CRYSTALS. ASG  CHEMICAL PROPERTIES INORGANIC ORGANIC BY 96% 4% WEIGHT BY EQUAL EQUAL VOLUME ASG INORGANIC MATERIAL 92-96 % CRYSTALLINE CALISIUM PHOSPHATE ( HYDROXY APATITE) 3 Ca3 (PO4)2. Ca (OH)2  ORGANIC MATERIAL 4% (1-2% ORGANIC MATERIAL AND 2-3% WATER) - BETWEEN THE CRYSTALS, - ENVELOP SURROUNDING EACH CRYSTAL - AMINO ACIDS PRESENT ARE COLLECTIVELY CALLED ENAMEL PROTEIN 1- Amelogenin protein. 2 – Non amelogenin protein (ENAMELIN and ameloblastin). ASG HISTOLOGICAL STRUCTURE 1-ENAMEL rod ENAMEL PRISM 2-rod SHEATH ENAMEL ENAMEL PRISM 3-INTER rod SUBSTANCE DENTIN ASG  HISTOLOGICAL STRUCTURE HIXAGONAL OVAL ROUND FISH SCALES KEY HOLE ASG Rods….L/M ….hexagonal, fish scales, round, oval. E/M….T.S…key hole or paddle shaped…… L.S…..tails & bodies. Crystals ……parallel to long axis in bodies and tails…deviate 65 far out from tails.  ENAMEL PRISM LOWER CENTRAL INCISOR 1 - NUMBER 5-7.5 MILLIONS UPPER FIRST MOLAR 12.5 MILLIONS Wavy Perpendicular to 2 - DIRECTION DEJ  ENAMEL PRISM 3 - COURSE STRUCTURELESS ENAMEL GNARLED ENAMEL DENTINO-ENAMEL MEMBRANE ASG  ENAMEL PRISM 2 4 - DIAMETER : 1 4-5 um / 8 um 5 –Length 0.2 mm longer at cusps  SHORT INCREMENTAL LINES ( CROSS STRIATION ) BETWEEN SEGMENT OF 4 u LENGTH, DAILY RATE OF SECRETORY ACTIVITY OF AMELOBLASTS ASG Structural features of enamel  LONG INCREMENTAL LINE ( INCREMENTAL LINE OF RETZIUS ) BROWN STRIA OF RETZIUS 4 DAYS ARE NEEDED FOR THE FORMATION OF THE ASG ENAMEL MATRIX BETWEEN TWO BANDS  concentric growth rings  brownish bands  more in the permanent teeth  great numbers or as a broad band it indicates periods of metabolic disturbance or disturbance in amelogenesis.  1- hypomineralized or rhythmic formation.  2- Variations in organic structure  3 – NEONATAL LINE in deciduous and 1st molars PRENATAL POSTNATAL POSTNATAL PRENATAL ENAMEL ENAMEL ENAMEL ENAMEL ASG 4 5 HUNTER SCHREGER’S BANDS - alternating dark (diazones) and light zones (parazones) seen in longitudinal ground sections - viewed under reflected light. - originate at the dentinoenamel junction and pass outward traversing more than half of the enamel They are not seen towards the enamel surface.  THE DENTIN0-ENAMEL JUNCTION scalloped interface between the enamel and dentin. Small curved convexities of enamel fit into small concavities of the dentin. ASG ENAMEL LAMELLAE - Thin, leaf like structures extend from the enamel surface towards the DEJ.  ENAMEL LAMELLAE a failure of the process of removal of the organic matrix and water a site of weakness, which may form the pathway for bacterial invasion. Types - Type A: restricted to enamel. - Type B. - Type C: Type B and C may reach the dentin.  ENAMEL TUFT -Enamel tufts are organic structures - originate at the DEJ and extend into for about ⅓ of its thickness. -It resemble tufts of grass - due to abrupt changes in the rod direction,  ENAMEL SPINDLES - Are odontoblastic processes - derived from dentin and have an organic content higher than surrounding enamel. - are randomly distributed along the DEJ.  1 – OUTER STRUCTURELESS ENAMEL REMTHERE IS AN INNER STRUCTURELESS ENAMEL 30 um thick rodless without tom’s processes. ASG The crystals are oriented at right angles to the striae of Retzius.  2 - PERIKYMATA PARALLEL TO EACH OTHER AND TO C.E.J. External manifestation of the striae of retzius. CONTINUOUS AROUND THE TOOTH. More in facial aspect 30/ mm – AT THE REGION OF C.E.J. 10/ mm – NEAR TO THE OCCLUSAL OR INCISAL EDGES. Not present in occlusal deciduous teeth ASG  3 - ROD ENDS Concave SHALLOWER CERVICALLY DEEPER OCCLUSALLY contribute to the adherence of plaque ASG  4 - CRACKS Narrow, fissure like structures. Represent outer manifestations of enamel lamellae. They originate from DEJ and, and may rich the occlusal or incisal surface. PRIMARY ENAMEL CUTICLE (Nasmyth’s membrane) -0.5 to 1.5 µm thick. - in newly erupted teeth and is lost due to mastication - Its structure is similar to the basal lamina of the epithelium. - It is the last product of the ameloblasts. ASG. Enamel cuticle is made of two cuticles, Primary is the last product of the ameloblasts and it becomes mineralized. secondary covers the primary cuticle and is a product of the reduced enamel epithelium and is not mineralized. Functional and structural features of ameloblasts: - Differentiation: The ameloblasts are derived from the IDE during bell stage. - Ameloblasts fully differentiate at cusp tips spreads towards the cervical loop. - Once the inner dental epithelium has fully differentiated there is no more proliferation as they highly differentiated cells do not divide. Induction and competence: Reciprocal induction - Factors involved in tooth development 1- genetic factors (homeobox genes) 2- growth factors(TGF,FGF,….) 3-signaling molecules(BMP)  Life Cycles of the Ameloblasts  According to their function, can be divided into 7 stages: 1. Morphogenic stage. 2. Differentiating or Organizing stage. 3. Secretory or Formative stage. 4. Transitional stage 5. Maturative stage. 6. Protective stage. 7. Desmolytic stage. ASG  AMELOGENESIS 1 - ENAMEL 2 - MATURATION secretion OF ENAMEL THE BEGINNING OF MINERALIZATION OF THE ENAMEL MATRIX DOES NOT AWAIT THE COMPLETION OF ITS FORMATION. ASG Thank YOU