Microscopic structure of alveolar process and clinical aspects of its remodelling Periodontium Jan Křivánek 22. 3. 2022 Two main functions: Structural – forming skeleton Storage of Ca2+ in our bodies (99 %) - releasing calcium from bone into blood and vice versa Compostion: Cells Extracelullar matrix (ECM) - bone matrix Overview of bone microstructure, and bone plasticity Osteoblasts Synthesize organic component of extracelullar bone matrix: Collagen I, proteoglycans, glycoproteins Deposit inorganic salts in matrix During development forms one layer of cells on the surface Osteocytes „Resting“ forms of osteoblasts, have small oval bodies with thin cytoplasmic processes Inhabit bone lacunea and its procesess are in canaliculi ossium Osteoclasts Large cells (diameter around 100 um), with multiple iregular procesess Multinuclear – number of nuclei may be 50 or more, originate by the fusion of monocytes/macrophages Digest/decompose bone matrix. Essential for bone remodelling Cells in bone osteoblasts a osteocytes; osteoclasts Inorganic (+- 45 %) and Organic (+- 30 %), rest is Water Inorganic component Responsible for hardness and stiffness of bones Formed by hydroxyapatite crystals – have shape of flat plates of hexagonal profile measuring 40 x 25 x 3 nm, deposited parallel to collagen fibrils Organic component Mainly Collagen I, then proteoglycans (glycosaminoglycans associated with proteins) and adhesive proteins – sialoprotein, osteocalcin, osteopontin, osteonectin Important role in calcium deposition during bone growth and remodelling Extracellular matric (ECM) – Bone matrix Inorganic components are responsible for bone hardness while collagenous fibres determine the resilience and flexibility of bone The ration bewteen inorganic and organic component is essential for the right mechanical behaviour Woven bone (primary) Lamellar bone (secondary) Primitive structure Developmentally and functionaly better developed Resembles calcified fibrous connective tissue Bone lamellae = 3-7 µm Firstly developer (during growth and remodelling) Collagenous fibres in lamellae always in the same direction Osteocytes between lamellae Histologically we divide 2 types of bone tissue All bones of skeleton (long, short, flat, irregular) – are composed only by lamellar type Lamellae are present in both forms: Compact (dense) bone and Spongy (cancellous, trabecular) Long boneFlat bone External and internal surfaces are covered by a connective tissue coats – the periosteum (well developed) and the endosteum (less obvious) Compact bone consists of three types of lamellae Concentrically arranged lamellae around longitudinal haversian canals, number: 4 to 20 Form cylindrical units called osteons that run parallel to longitudinal axis of bone In cross sections, osteons appear as concentric rings around circular opening (Haversian canal), In longitudinal sections lamellae resemble closely spaced bands Interstitial lamellae Are lamellae without relations to blood vessels Supposed to be rests of old non-fuctional Haversian systems which are just being resorbed Circumferential lamellae Located at outer and at inner surface of bone Run in parallel to the periosteum or parallel to endosteum (around the central cavity ) Outer circumferential lamellae Inner circumferential lamellae Osteon Diaphysis transversally (HE) Haversian canals In the centers of Haversian systems Contain one or two blood vessels Volkmann's canals Are not surrounded by lamellae and traverse the bone in perpendicular or oblique direction to the Haversian canals Function: connect Haversian canals with one other and serve for vessels entering the compact from the periosteum or the marrow cavity 2 types of vascular channels in the compact bone Haversian and Volkmans canals Cancellous/Trabecular bone composed by trabeculated bone tissue The course of depends of forces from outer environment Periostem Around the bone – from outside Highly innervated (pain) 2 layers: Stratum fibrosum, Sharpey‘s fibres Stratum osteogenicum – osteoprogenitor cells Endosteum On the inner surface Same structure as the periosteum, but thinner Bones as organs can remodel the internal structure to match the actual mechanical load Remodelling: interaction/equilibrium between osteoblasts and osteoclasts activity Remodeling is rapid in childhood - it is reported that about 10% of skeletal bones are rebuilt each year Bone remodeling can be induced by artificial stimuli: by the action of tension or pressure The action of tension creates new bone tissue, Opposite, it is resorbed under the action of pressure The role of osteocytes - they act as mechanosensors, they transmit a signal to osteoblasts in the endost or periosteum, and they transmit it to osteoclasts Bone plasticity Cycle of bone remodelling Summary Alveolar process (processus alveolaris) Part of the jaw which form the bony support for teeth (alveoli dentales) The protrusion, like other anatomical sections of the jaws, is composed of lamellar-type bone tissue - dense and spongy Compact bone structure 2 plates: • Cortical (external alveolar) - forms the vestibular or oral side of the alveoli • Cribriform (internal alveolar, os alveolaris, lamina dura) - forms the wall of alveoli Cortical (outer alveolar) plate Thicknes: 1,5 - 3,0 mm Divided into: • Lamina vestibularis • Lamina oralis Both are covered by periosteum Osteons in different directions In the area of mandibular molars is lamina oralis usually thickened lamina oralis lamina vestibularis Cancellous bone Cortical lamina vestibularis Cortical lamina oralis Cribriform os alveolare Forms the wall of alveolus, is thinner – 0,5 - 1,0 mm Perforated by Volmanns channels (for interalveolar vessels and nerves) Structure similar as in cortical plate, but no periosteum The function of periosteum has peridontium with nondifferentiated mesenchymal cells (diferentiate into different -blasts) kribriformní ploténka podélně Cribriform plate (inner alveolar plate = os alveolare) In cribriform plate are anchored PDL endings – Sharpey‘s fibres Cribriform plate is more mineralized – on X-ray has higher density – lamina dura In teeth of primary dentition and young secondary the lamina dura is flat, later has wavy structure Trabeculae - filling between the plates, high variability in the arrangement of the trabeculae (mostly horizontal direction) Located between plates and in interdental and interradicular septae High variability in the arrangement of trabeculae Horizontal course Between the trabeculae is a hematopoietic bone marrow Cancellous / Spongy bone In the area of maxillary and mandibular incisors: both lamina oralis and vestibularis fuse with the cribriform plate Different alveoli separates: Interalveolar septae = septae interdentalia Perpendicularly oriented partitions formed by the fusion of mesial and distal parts of cribriform plates of adjacent alveoli The ridges of the interdental septae are usually rounded and reach the CEJ level Above interdental septae are transseptal fibres vlákna (lig. interdentalia) – forms the shape of crests When teeth are inclined the pressure of fibres causes the tilt of crest in the direction of inclination (secondarily, the septum may be shortened) Transseptal fibres Present only in teeth with more roots Cribriformn plate together with trabecules of cancellous bone forms interradicular septs - septa interradicularia Septa interradicularia Edge of tooth alveolus – Alveolar crest – is the plase where the coronal end of cribriform plate meets lamina vestibularis or lamina oralis The structure and arrangement of the alveolar ridge is affected by a number of factors such as: • Overall nutritional status • Hormones (hyper-, hypo- production) • Masticatory forces during food processing • Growth of dental roots and tooth eruption • Infection • Tooth extraction Clinical relevance of alveoli plasticity 1. Because of different effect of long-lasting tension and pressure on the bone remodeling the bone structure can be achieved Long-lasting tension – tooth formation (tension zone) Long-lasting pressure – tooth resorbtion (pressure zone) This is widely used in orthodontics 2. When the bone is not adequately loaded for a long time, structural changes occur Applies for both the upper and lower jaw REMEMBER: When antagonists are lost – if this condition last for a longer period of time (in the order of months) - there are changes in the alveolus and periodontal ligaments 2 conclusions: - Carefully indicate teeth extractions - Fill missing or extracted teeth Clinical relevance of alveoli plasticity A – changes after removal of antogonizing teeth B – control normal loading changes from inactivity Microscopic structure of the periodontium, its function and clinical significance Consists of: • Alveolus • Periodontal ligament – dense collagenous tissue which ensure tooth stability and its attachment inside the alveolus • Cementum – covering roots • Gingiva Periodontium (in general meaning) gingiva cementum Periodontal ligament alveolus Hold teeth inside the alveolus – Balance and compensate the forces acting during mastication (thecodontn dentition) Transforms compressive forces during chewing into tensile, which the dental bed better resists and is also better adapted to Fills the space between the cribriform plate of dental socket and root (cementum) Dense collagenous tissue with higher amount of ECM (extracellular matrix) Periodontium thickness - 0.18 - 1.0 mm, the thinnest in the middle part of the root Collagenous fibers - fiber bundles - periodontal ligaments (ligaments) Ends anchored in dental cementum and lamellar bone of cribriform plate (as Sharpey fibers) They are of different thicknesses and have a wavy course Periodontal ligaments Development Cellular: Fibroblasts a Fibrocytes ECM: Collagen fibres (I, III a XII) Fast turnover Organized into bundles Elastic fibres Oxytalan fibres (immature elastic fibres) Microscopic structure Arrangement of periodontal ligaments 3 main groups: Gingival fibres Transseptal (interdental) fibres Alveolar fibres (fibrae principales) 4 directions (groups): Dentogingival – from cementum at the tooth neck to gingiva afixa and libera. Most abundant Alveologingival - from the edge of the alveolus gingiva afixa and libera Circular - placed in free gingiva and they surround the neck of the tooth Dentoperiostal - from the neck through the edge of the alveolus on the vestibular surface or lingual plate Gingival fibres – attach the gingiva to the neck of the tooth they are not actually part of the periodontium (they lie in the lamina propria of the gingiva) Dentogingival Dentoperiostal Mesiodistally above the interalveolar septa They strengthen the linear alignment of the teeth in the arch and form the basis for interdental papillae They form the shape of the ridges of theinteralveolar septum X-ray configuration (with inclination of septal tilt and depression) Transseptal fibres – connect necks of neighboring teeth Between root and cribriform plate of alveolus (os alveolare) Most abundant Alveolar fibres Alveolar crest group – from the neck to periosteum of interalveolar septum or periosteum of coronal edge of alveolus. Function: They prevent the tooth from moving out of the alveolus (sometimes missing) Horizontal group – in coronal third of tooth root and alveolus Perpendicular to the longitudinal axis of the tooth Function - Prevents lateral (horizontal) movements of the teeth Alveolar fibres Oblique group – in the middle and apical third of root/alveolus Diagonal course - the attachments on the cement positioned more apically than the insertion in the cribriform plate Function - Prevents the root from being pushed into the bed Apical – from the tooth apex to the bottom part of alveolus Radial course Function – Prevent the tooth from moving out of the alveolus (sometimes missing) Interradicular – only in teeth with more roots At the place of root branching Attached to the alveolar septum between roots Function – prevent the tooth from moving out of the alveolus and the rotation interradicular septum Interradicular septum Summarization Intermediate plexus Some fibres has only one attachment – either in cementum or in cribriform plate of alveolar bone and the other is free From this fibres is constituted Intermediate plexus Function: - Morphological and functional supply for potential reorganization of periodontal ligament - Support for interstitial areas Interstitial areas Regions of loose collagenous tissue Separate bundles of ligaments Space for blood vessels and nerves which are responsible for periodontal space vitality On samples they are paler tissue with obvious blood vessels and surrounded by amorphous tissue Highly innervated and numerous blood vessels in this region Arterioles derived from gingival, „pulpal“ and interalveolar branches In interstitial areas they form a dense capillary network which branches can be found also between the ligaments Lymphatic vessels Blood and nervous supply of periodontal space Innervation Three types of nerve endings • Free nerve endings (pain) – from unmyelinated or from myelinated nerve fibers) • Ruffini-like endings – In apical part of PDL • Lamellated corpuscles ERM (Epithelial rests of Malassez) • Epithelial remnants from disintegrated HERS (Hertwig Epithelial Root Sheat) • Pool of stem cells, interactive support for adjacent cells • Can undergo EMT (Epithelial to Mesenchymal Transition) Granulomas and cysts Cementicles Other structures in periodontal space ERM = Epithelial rests of Malassez Changes while losing an antagonist – nonfunction • Periodontal space narrowing • Weakening and loosening of fibers • Cementum thickening • Weakening of the cribriform disc Changes due to overload Acute (trauma) – blood effusions, fiber rupture, necrosis and resorption, ankylosis Chronical – hypercementosis Periodontal changes during ageing Periodontal fibres (ligaments) - terminology Gingival fibres - fibrae gingivales (fibrae gingivodentales, fibrae gingivales circulares) Transseptal fibres - fibrae interdentales Alveolar fibres - fibrae alveolodentales (fibrae principales) Alveolar cres - lig. dentale superius Horizontal - fibrae alveolodentales transversae Oblique - lig. dentale inferius Apical - fibrae apicales Interradicular - fibrae interradiculares Gingiva • Masticatory oral mucosa • Around tooth necks and covering alveolar bone. Firmly attached to adjacent hard tissues • Very stiff, pale pink color, resistant to pressure and friction • It is not movable – forming mucoperiosteum Mucogingival junction (line) • The border between gingiva and lining mucosa which covers the rest of alveolar process • Apparent on the vestibular aspect of both mandible and maxilla and on lingual aspect of mandible Gingiva Topography: 2 compartments Gingiva libera (Free gingiva) (gingiva supraalveolaris) Gingiva affixa (Attached gingiva) (gingiva alveolaris) Gingiva Sulcus gingivalis (Gingival sulcus) • Circular groove, physiological depth: 1-2 mm • Liquor gingivalis: plasma-like fluid which leaks from adjacent capillaries. The fluid has antimicrobial and anti-inflammatory properties, contains proteins and carbohydrates Interdental papillae, interdental gingiva Between neighbouring teeth, free gingiva forms a protrusion: trigonum interdentale Vestibular and lingual aspect Každá má vestibulární a linguální část, connected by intedental saddle Trigonum interdentale Stratified squamous epithelium Keratinized at vestibular and palatinal side No keratinization on the side facing teeth: Sulcular epithelium On the side facing teeth it keeps nondifferentiated epithelium characteristics. Junctional epithelium (epithelial attachment of Gottlieb) is firmly attached to teeth and seal the periodontal space from the environment of oral cavity. Microscopic structure of gingiva Gingiva affixa Dense collagenous connective tissue with papillas which are numerous and thin. Their presence causes a rough surface Gingiva libera Under the epithelium of free gingiva is lower amount of papillas and always missing under epithelium which is facing teeth Collagenous fibres are ordered into 4 groups: dentogingival, circular, dentoperiostal and alveologingival (chapter periodontium) Lamina propria Epithelial attachment, epithelial attachment of Gottlieb, Protects the periodontal space from aggresive outer environment of oral cavity resp. sulcus gingivalis (against bacteria, toxins, pieces of food) It is characteristic by the fusion of sulcular epithelium with hard tissues of teeth in the are of the neck Zone of fusion is under the sulcus gingivalis Width: 0,25 - 1 mm This epithelium is permanently actively regenerated – stem cell activity Cells are in several layers, flattened Junctional epithelium Between the innermost layer of cells and hard tissue are hemidesmosomes, between cells are desmosomes The line between epithelium and connective tissue is smooth (no papillae), connective tissue contains numerous leukocytes and B-lymphocytes, acts as an immunological barrier Narrowing ath the apical end Fast turnover: 4-6 days. Regenerates well after mechanical damage Junctional epithelium Consequence: tooth loosening and ultimately tooth loss Gingival recession in periodontitis Normal state: in primary dentition and healthy permanent dentition up to 20‘-30‘ – the apical end of the junctional epithelium at CEJ Later junctional epithelium moves more apically, until it finally moves to the cementum of the tooth neck In old age, cementum, can be exposed and a condition in which the clinical crown becomes larger than the anatomical crown Gingival recession Arterioles from aa. alveolares, a. mentalis, aa. palatinae, a. buccinatoria Branch into capillary networks with anastomosis with the periodontal network Lymphatic vessels and along the blood vessels Nerve fibres as a free nerve endings and form corpuscles Blood supply and innervation of gingiva