BASIC STRUCTURE AND FUNCTION OF ORAL AND DENTAL ANATOMY Flashcards
FUNCTIONS OF THE TEETH:
- to cut up and masticate food into suitably sized portions before swallowing
- to expose the food structures to enzymes and allow digestion to begin
- to support the oral soft tissues of the cheeks and tongue, and therefore enable clear speech
ENAMEL
this is a highly calcified, protective outer covering of the crown and is the hardest substance in the body.
- made up of 96% mineral crystals (inorganic) arranged as psims in an organic matrix called the INTERPRISMATIC SUBSTANCE
- the main mineral crystals are CALCIUM HYDROXYAPATITE
- the prisms lie at right angles to the junction with the next tooth layer, the DENTINE
- the junction between these two layers is called the AMELODENTINAL JUNCTION (ADJ)
- enamel is formed before tooth eruption by the ameloblast cells, which lie at the ADJ7
- it contains no nerves or blood vessels and therefore cannot experience any sensation
- it is a non-living tissue that cannot gwoe and repair itself, so progressive damage caused by injury or tooth decay is permanent
- it can, however, remineralise its surface after an acid attack, by taking in minerals from saliva and from oral health products such as toothpaste and mouthwash
- the crystal structure can also be altered without undergoing acid attack, by the exchange og hydrpxyl ions in the hydroxyapatite with FLUORIDE, to form FLUORAPATITE CRYSTALS - these make the enamel surface harder and more resistant to acid attack
- the enamel layer is the thickest over the biting surface of the tooth and thinnest at the neck of the tooth - the cervical margin
- it is translucent in appearance, so the shade of a tooth is determined by the colour of the underlying dentine
DENTINE:
this tissue forms the main bulk of a tooth and occupie the interior of the crown and root. it is also mineralised, but to a lesser extent than enamel, and is covered by enamel in the crown of the tooth and by cementum in the root of the tooth.
- it consists of up to 80% inorganic tissue, mainly CALCIUM HYDROXYAPATITE crystals
- it is composed of HOLLOW TUBES that originally surrounded the cells within the dentine structure as it was first being formed
- in a fully formed tooth, these ODONTOBLAST cells lie along the inner edge of the pulp chamber only, but are present throughout life and can lay down more xentine as required
- in this way, it can repair itself by laying down secondary dentine
- this type of dentine is also formed as part of the natural ageing process, and its formation gradually narrows the pulp chamber
- the hollow tubes contain sensory nerve endings called FIBRILS, which run from the nerve tissue within the pulp chamber
- dentine is therefore a living tissue and can transmit sensations of pain and thermal changes to the brain
- its hollow structure allows it a degree of elasticity do that it can absorb normal chewing forces without breaking
- however, it also allows tooth decay (CARIES) to spread more raapidly through its hollow structure
- dentine is a yellowish colour, and gives teeth their individual shade
CEMENTUM
this is the calcified protective outer covering of the root and is similar in structure to bone. cementum meets enamel at the neck of the tooth, and normally lies beneath the gingivae.
- around 65% mineralised, with calcium hyrdroxyapitite cyrstals
- the crystals lie within a matrix of fibrous tissue, with the ends of colagen fibres from the periodontal ligament inserted into the outer layer of the cementum
- this allows the attachment of the root to the periodontal ligament inserted into the outer layer of the cementum
- the cementum is formed by cells called CEMENTOBLASTS and they can continue laying down more tissue layers when required
- the thickness of cementum may vary at different parts of the root, and changes throughout life, depending on the forces exerted on individual teeth
- the cementum contains no nerves or blood vessels itself, so it recieves nutrients from the periodontal ligament
PULP
unlike enamel, dentine and cementum, the pulp contains no mineral crystals and is composed purely of soft tissue. it lies within the very centre of every tooth, from the crown as the coronal pulp and into each root as the radicular pulp. the radicular pulp is often referred to as the “root canal” of the tooth.
- the pulp contains sensory nerves and blood vessels
- the sensory nerves are end sections of the trigeminal nerve (fifth cranial nerve), either as the inferior dental nerve for the lower teeth or one of the superior dental nerves for the upper teeth
- they allow the tooth to feel hot, cold, touch and pain by the stimulation of its sensory nerve endings which run as fibrils in the hollow dentine tubules
- these pulp tissues enter the tooth through the APICAL FORAMEN, lying at the root apex of every tooth
- the pulp chamber is lined by the odontoblast cells which form dentine
- the chamber gradually narrows with age, so that it can become completely obliterated in older patients, making endodontic treatment very difficult
- it can become blocked by PULP STONES which are formed by lumps of calcium-containing crystals
- the point where the cementum and the root dentine are in contact with each other is called the DENTINOCEMENTAL JUNCTION
- some teeth have additional contact between the pulp and the surrounding periodontal ligament via accessory canals, the presence of which can make successful endodontic treatment of the tooth very difficult to achieve
HOW MANY TEETH ARE IN THE PRIMARY DENTITION?
20 teeth
HOW MANY TEETH ARE IN THE SECONDARY DENTITION?
32
WHAT IS - ALVEOLAR BONE?
specialised ridge of bone over the bony arch of each jaw, where the teeth sit in their sockets
WHAT IS - GINGIVA?
specialised soft tissue covering of the alveolar processes, which are also in attachment with the teeth at their necks
WHAT IS - PERIODONTAL LIGAMENT?
connective tissue attachment between the tooth and the alveolar bone
WHAT IS - CEMENTUM?
hard tissue covering of the root that anchors the periodontal ligament to the tooth
ALVEOLAR BONE IN-DEPTH
it is here that the teeth form during the growth of the foetus and later the child, and from where they erupt into the mouth at various ages
- it is a specialised bone found only in the jaws
- its outer layer is made of, COMPACT BONE, the outer surface of which is called the LAMINA DURA
- the inner layer is called CANCELLOUS BONE and is sponge-like appearance, to allow the passage of the various nerves and blood vessels that supply the jaws, teeth and surrounding oral soft tissues
- the sole purpose of the avelor bone is to support the teeth, and it is gradually lost whem a tooth is extracted as the bone slowly resorbs away
GINGIVA IN-DEPTH
this is the correct anatomical term for the gums, it is a continous layer of specialised epethelium found only in the oral cavity and which is firmly attached to the underlying alveolar bone as a MUCOPERIOSTEAL LAYER of tissue. this layer is raised as a flap during oral surgical procedures, to expose the bone below
THE THREE DISTINCT AREAS OF GINGIVAL COVERAGE:
- ATTACHED GINGIVA - that covering the majority of the alveolar process, which is firmly attached to the underlying bone as the MUCOPERIOSTEUM
- MARGINAL GINGIVA - that forming the gingival margin of the teeth, which is free from the underlying bone and follows the shape of each tooth in the arch, as well as extending between the teeth in the contact areas; the level at which these two areas meet is called the FREE GINGIVAL GROOVE
- JUNCTIONAL TISSUES - the specialised gingival tissue lying within the gingival crevice and forming the anatomical junction between the teeth and the oral epithelium; this point is called the JUNCTIONAL EPITHELIUM
THE PROPERTIES OF THE GINGIVA ARE:
- when healthy, the gingivae fit around the neck of every tooth like a tight cuff
- the GINGIVAL CREVICE exists as a shallow space of less than 3mm between the tooth surface and the gingival margin, and contains the junctional epithelium
- a natural mound of gingival tissue occurs between each tooth and is called the INTERDENTAL PAPILLA
- in health, the ginigivae are pink in colour with a stippled surface, like orange peel
- inflammation of the gingivae is called GINGIVITIS; it affects the marginal gingivae and occurs in the presence of DENTAL PLAQUE due to poor oeal hygiene control
- gingivitis appears as red and shiny gingivae that are swollen due to their inflammation and that bleed easily on touching
- the swollen appearance of the inflamed gingivae presents as “false pockets” when probed, giving the impression that the gingival crevice is depper than 3mm
- the gingiva can also be stimulated to overgrow and become HYPERPLASTIC as side-effect of various drugs being taken by the patient, including some antihypertensives and some drugs used to control epilepsy
PERIODONTAL LIGAMENT:
is a specialised fibrous tissue that attaches the teeth to the alveolar bone and the surrounding gingivae. it acts as a shock absorber to the teeth during chewing and its main fibres run between the alveolar bone and the cementum covering the root of the tooth. other fibres run between the necks of the teeth, and from the cementum into the surrounding gingivae.
THE VARIOUS PERIODONTAL LIGAMENT FIBRE GROUPS:
- Alveolar crest fibres
- Horizontal fibres
- Oblique fibres
- Apical fibres
- Transeptal fibres
- Free gingival fibres
FUNCTION OF ALVEOLAR CREST FIBRES:
run from the alveolar bone crest to the cementum at the neck of the tooth; they prevent tooth movements in and out of the socket, as well as resisting tilting and rotation
FUNCTION OF HORIZONTAL FIBRES:
run horizontally from the alveolar bone to the cementum, just below the crest fibres; they resist tilting and rotation of the tooth