Anatomy and Histology of the periodontium Flashcards

Question

What is the composition of bone?

Answer 1

Bone is composed of 60% inorganic component, 25% organic component and 15% water by weight. Inorganic composition: Calcium hydroxyapatite Ca10(PO4)6(OH)2. Mainly carbonated hydroxyapatite in the form of needle-like crystallites or thin plates. Organic composition: Collagen (mainly type I) forms 90% of the extracellular matrix. There are also serum proteins, acidic glycoproteins and small proteoglycans

Answer 2

Over 90% of the organic matrix is made of collagen fibrils, mainly collagen type I. • Proteoglycans such as chondroitin sulphate and heparan sulphate glycosaminoglycans mainly in the form of decorin and biglycan. • Proteoglycans may regulate collagen fibril diameters and may have a role in mineralisation. • Glycoproteins such as osteonectin, osteopontin, thrombospondin, osteocalcin and fibronectin are also present. • Osteonectin can bind to calcium and thus is thought to be involved in mineralisation. Osteocalcin is only synthesised by osteoblasts and odontoblasts. • Exogenous proteins that circulate the blood and become locked in bone such as cytokines and growth factors have an important role in the life cycle of bone cells. • Bone morphogenetic proteins (BMP)s are present in bone. There are 8 proteins in this family (BMP-1 to BMP-8). They are part of the transforming growth factor beta (TGF-β) family (apart from BMP-1). • BMP(s) induce bone formation by influencing the movement, cell division, and differentiation of stem and osteoproginator cells.

Answer 3

• Osteoblasts secrete the organic extracellular matrix of new bone Osteoid which rapidly undergoes mineralisation to form bone. • Osteoblasts become trapped in bone in lacunae as osteocytes. • Osteoclasts are multinuclear cells involved in bone remodelling. • Bone lining cells: flat cells line bone during periods of inactivity. • Osteoprogenitor cells: Stem cells beneath the osteoblast layer.

Answer 4

Woven bone is immature bone, with random organisation of its collagen. Lamellar bone is composed of successive layers (lamellae). It may be formed as a solid mass (compact bone), or in an open sponge-like manner (cancellous bone)

Answer 5

``` Compact bone is made of parallel bone columns which are disposed parallel to the long axis of long bones (in line of stress exerted on the bone) • Columns are made of concentric bony layers (lamellae) arranged around a central channel with blood vessels, lymphatics and nerves (Haversian canals) ``` Haversian canals with their lamella form the haversian systems (osteon). • Neurovascular bundles interact with each other via Volkmann’s canals that pierce the columns at right angle or obliquely to haversian canals. • Osteocytes in their lacunae interact with each other and with the central canal via cytoplasmic extensions in canals called canaliculi. • The outermost layer of compact bone gives way to dense cortical bone Because of its position, compact bone acts as weight bearing pillars. • Compact bone is able to withstand high levels of mechanical stress. • The innermost aspect of compact bone, the lamellae merge with trabeculae of cancellous (spongy bone)

Answer 6

``` Cancellous (spongy) bone is made of a network of bone trabiculae separated by interconnected spaces containing bone marrow. • Trabiculae are thin and composed of irregular bone lamellae ``` No haversian canals are present in cancellous bone and oscteocytes get their nutrition via canaliculi connecting them to blood sinusoids in the marrow • Spongy bone gives bone its flexibility due to the presence of marrow spaces • Trabiculae are aligned along lines of stress so as to withstand forces applied to the bone while adding minimally to the mass

Answer 7

Bone resorption: Howship’s lacunae. | • Longer snail track resorption lacunae

Answer 8

``` projections marking the sites of extrinsic mineralised Sharpey’s fibres Separated by areas with intrinsic mineralised collagen ```

Answer 9

``` • Outer and inner parallel alveolar plates • Sockets are separated by interdental septa • Roots are separated by interradicular septa • Fundus: socket floor • Cribriform plate, bundle bone • In radiographs, thin white line, the lamina dura ``` ``` Cribriform plate 0.1- 0.5mm in thickness • External alveolar plates 1.5-3mm in thickness • Variable around anterior teeth ```

Answer 10

During childhood, bone deposition exceeds resorption

Answer 11

``` Bone resorption factors affect mainly osteoblasts: • Osteoblasts could stimulate the production of osteoclasts by the release of cytokines and growth factors. • Osteoblasts could produce enzymes that degrade osteoid thus exposing bone for osteoclasts to work on ``` ``` Reversal lines marks the change in bone activity. • Constant remodelling to adapt to pressure ```

Answer 12

Extrinsic fibres. • They enter the bone perpendicular to the surface. • Less numerous but thicker than those in cementum. • Two main appearances under SEM (anorganic): • Fibres remain unmineralised at their centres, resulting in hollow centres. • Fully mineralised project beyond bone surface as small calcified prominences

Answer 13

The portion of the oral mucosa that surrounds and is attached to the teeth. • Two main regions: • The attached gingiva Directly bound to the underlying bone and tooth • The free gingiva Narrow, not bound to any bone • The free gingival groove demarcates the free from the attached gingiva (40% of teeth) ``` The gingival margin is the coronal limit of the free gingiva • The gingival sulcus is the unattached region between the free gingiva and the tooth • The junctional epithelium is the area where the gingiva is bound to the tooth ```

Answer 14

The free gingival groove follows the contour of the cemento-enamel junction. • Principal fibres running from cementum to the gingiva. • Heavy epithelial ridges. • Healthy gingiva shows stippling, corresponding to epithelial ridges

Answer 15

The free gingival mucosa is identical to the attached gingiva. • The gingival sulcus is 0.5-2.0mm deep in healthy gingiva. • Sulci deeper than 3.0mm are considered periodontal pockets

Answer 16

Sulcular and junctional epithelia form the ginigval cuff. • Sulcular epithelium has a more folded interface with the lamina propria. • Sulcular epithelium is thin. • The base of the sulcus is at the same level as the free gingival groove

Answer 17

``` Junctional epithelium extends from CEJ to the sulcus base. • 2mm. • Thinner apically. •5-6 days turnover rate ```

Answer 18

The gingival crevicular fluid is the fluid within the sulcus. • Results from the permeability of the junctional epithelium. • Important in the defence mechanism

Answer 19

The interdental gingiva occupies the area between adjacent teeth. • Its shape and size depend on the shape and contact between teeth. • Wedge shaped appearance on the buccal and lingual sides. • Pointed between anterior teeth. • The interdental col a curved depression across the buccolingual plane. • It fills the contour around the contact point

Answer 20

``` The epithelium of the col is continuous with the junctional epithelium. •Spaced teeth have no col ```

Answer 21

Dense collagen bundles: • Support the free gingiva. • Bind the attached gingiva to the alveolar bone and the tooth. • Linkage of teeth to each other. • Principal fibres divided into groups according to their location

Answer 22

* Dentoginigval fibres * Longitudinal fibres * Circular fibres * Alveologingival fibres * Dentoperiosteal fibres * Transseptal fibres * Semicircular fibres * Transgingival fibres * Interdental fibres * Vertical fibres

Answer 23

Excess growth of the cementum which enters the PDL, or reduces the amount of attached gingiva