Microscopic structure of the alveolar process, clinical aspects of bone remodelling Anatomy and histology of temporomandibular joint Jan Křivánek 21. 4. 2021 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 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 Osteon 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 Cortiaal 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 Temporomandibular joing (art. temporomandibularis, TMJ) The connection between the mandible and the fixed temporal bone of the cranial base Fossa mandibularis + Tuberculum art. of temporal bone Caput mandibulae (condylus mandibulae) Discus articularis – cartilage plate Caput mandibulae (condylus mandibulae) – elongated ellipsoidal shape, elongated axis oriented horizontally on the condyle surface - thin plate of compact Inside is cancellous bone – trabeculles diverge from the center of the condyle radially to the surface During childhood trabeculles can contain islands of hyaline cartilage Microscopic structure of TMJ Fossa mandibularis • Plate of compact bone • The anterior border of mandibular fossa constitutes the tuberculum articulare - it has a similar structure to the caput mandibulae TMJ surfaces - fibrous cartilage • It is reinforced on the back of the tuberculum articulare • Cartilage better resists degeneration and has a good ability to regenerate Discus articularis • Ligament plate 3 - 4 mm thick • Its edges are fixed in a joint • Thinner in the middle - intermediate zone (1 - 1.5 mm) • Dense collagen tissue of a irregular type • In adulthood, it may contain islets of hyaline cartilage • Function: Stabilization and absorbtion of shocks and vibrations functions A: Articular layer B: Proliferative layer C: Chondrogenic layer D: Hypertrophic layer Mandibular condyle Complex inner structure Dorsal section is divided in 2 lamellae: Superior retrodiscal lamella of elastic fibers, which are inserted to dorsal edge of the fossa Inferior retrodiscal lamela inserts to the rear edge of condyle Between lamellae the retroauricular pillow of Zenker is present - areolar connective tissue with rich venous plexus (it is continuous by pterygoid plexus - plexus pterygoideus) Ventral section is thickenned and ends in places of insertion of lateral pterygoid muscle Thickened compartments act as stabilizing regions (wedges): stabilize condylus in the fossa Dorsal section Ventral section Discus articularis Retroauricular pillow of Zenker Joint capsule - free, especially on the medial side externally supported by the lateral and medial ligaments 2 layers: stratum fibrosum and stratum synoviale Articular cavity contains synovial fluid and is divided in two sections: upper - discotemporal lower - discomandibular Joint biomechanics: TMJ (articular disc) movements: https://www.youtube.com/watch?v=mB46 8Jh9aAY&ab_channel=AlilaMedicalMedia MRI: https://www.youtube.com/watch?v=ZnNg MnSfAws&ab_channel=SpringerVideos Temporomandibular joing (art. temporomandibularis, TMJ) Final form takes between 20 -25 years of age Adaptability of TMJ – the ability to adapt to new functional requirements Very good in cartigale Poor in discur articularis a) Degenerative changes in the discus articularis, rupture or disintegration b) After the 5th decade perforation of the central disc part and connection of both sections of the articular cavity can occur Age changes in TMJ TMJ clicking: https://www.youtube.com/watch?v=Opgz2EUyI0w&ab_channel=WellingtonVillageOrthodonticsOttawa https://www.youtube.com/watch?v=bq2mXyHz5uA&ab_channel=HackDentistry