Oral Biology

Question 1

describe the different cells found in the periodontal ligament

Answer 1

fibroblasts
- responsible for regeneration of tooth support apparatus and have a role in mechanical loading of the tooth

cementoblasts
- cells involved in secretion and maintenance of cementum

osteoblasts
- bone forming cells lining the tooth socket. only prominent when there is active bone formation

osteoclasts and cementoclasts
- found in areas where bone is being resorbed

epithelial cells
- rests of malassez are aggregations of epithelial cell rests

defence cells
- monocytes and macrophages are located near nerves and blood. mast cells are associated with blood vessels. eosinophils and dendritic cells present T antigens during primary and secondary immune responses

Question 2

describe the periodontal ligament

Answer 2

• fibrous connective tissue occupying the space between the root of the tooth and the alveolar bone
• contains collagen and is continuous with the pulp and the gingiva

Question 3

describe sharpeys fibers

Answer 3

• ends of collagen fibres within the dental follicle which become embedded in developing cementum and bone
• collagen comes from the principle fibres of the PDL
• connects the tooth to the alveolar process
• insert from PDL into cementum
• if derived from cementoblasts, they are intrinsic, running parallel to the root surface at right angles to the extrinsic fibres
• if derived from PDL, they are extrinsic, and run in the same direction as the principle fibres of the PDL

Question 4

summarise cementum

Answer 4

mineralised connective tissue lining the root of the tooth. attaches tooth to bone via the periodontal ligament

65% inorganic material, 23% organic material, 12% water by weight.

54% inorganic material, 33% organic material, 22% water by volume.

more calcium and fluoride ions than seen in dentine or enamel.
covered by a layer of tightly packed collagen, this makes the mineralised surface relatively inaccessible to odontoclasts

cellular cementum
- contains cementocytes
- apical and furcation area overlying acellular cementum
- canaliculi between the cementocytes are orientated toward the PDL
- no role in attachment due to lack of sharpeys fibres

acellular cementum
- formed first
- covers the root adjacent to dentine

Question 5

describe the innervation and vasculature of the pulp

Answer 5

pain is a subjective sensation describe as an unpleasant sensory or emotional experience. nociception describes a series of objective neuronal impulses as is defined as reception, conduction in central processing of noxious signals.

nerve fibres enter at the apical foramen and run centrally in the pulp in close association with blood vessels

afferent nociceptors: trigeminal afferents, unmyelinated. carry sharp pain and other noxious signals

• blood flow is under sympathetic nervous control , and smooth muscle arterioles are innervated by nerves which act as vasoconstrictors
• noradrenaline and neuropeptide are the neurotransmitters of the pulp
• blood vessels are closely parallel to the nerve fibres.
• arterioles and venules enter the pulp via the apical foramen. they divide and narrow in the root canal but branch out in coronal pulp

Question 6

what can happen if the pulp is infected

Answer 6

• pain
• swelling
• redness
• heat
• pus - leading to foul taste

Question 7

list the functions of the pulp

Answer 7

primary role is the production of dentine. young teeth with more pulp are more elastic than teeth where pulp has been replaced with secondary dentine
- involved in nutrition, growth, repair of dentine, defence and neural.

Question 8

list the main features of dental pulp

Answer 8

• soft connective tissue occupying the central tooth
• fibrous component is 60% type I collagen and 40% type III collagen
• peripheral cells of the pulp are the odontoblasts
• contains rich innervation and vasculature
• derived from the dental papilla
• at the apical constriction it becomes continous with the periodontal ligament
• each tooth has at least one main canal and there are smaller accessory canals that branch from the main canal with their own foramina
• made of cells embedded in ECM - 75% water, 25% organic material by weight

cells of the pulp
- odontoblast: formation of dentine. any injury or insult will result in odontoblast cell death.
- fibroblast: form a loose connective tissue network in pulp and produce ECM
- defence cells: t lymphocytes, macrophages, dendritic antigen presenting cells and mast cells

Question 9

describe peritubular dentine

Answer 9

walls of dentinal tubules are composed of mineralised type I collagen

peritubular dentine is deposited on the walls of the dentinal tubules as it matures, narrowing the lumen. the formation eventually leads to obliteration of the tubules

lacks a collagenous fibril matrix

Question 10

list the proteins found in dentine

Answer 10

• phosphoproteins are the main non collagenous protein. high calcium binding properties which is important for mineralisation
• proteoglycans - role in collagen fibril assembly and in mineralisation
• glycoproteins - acidic proteins
• gla- protiens
• growth factors
• metalloproteinases
• serum derived proteins
• lipids

Question 11

describe the cells found in dentine

Answer 11

proteoglcans - glycosaminoglycans, collagen fibril assembly and calcium binding

glycoproteins - predentine

growth factors - can be released in caries and stimulate tertiary dentine

metalloproteinases - enzymes

Question 12

describe the features of dentine and how this relates to its function

Answer 12

• pale yellow in colour and contributes to the appearance of the tooth through the translucent enamel
• dentine is harder than bone and cementum but softer than enamel
• dentine is more resistant to propagation of cracks than enamel due to association of small apatite crystals with strong protein fibres
• dentine is permeable but this declines with age

Question 13

describe the patterns of tooth wear

Answer 13

attrition
- tooth loss involving tooth to tooth contact
- seen occlusally and intraproximally
- bruxism

abrasion
- tooth loss involving friction between the tooth and outside material
- over vigorous toothbrushing

erosion
- tooth loss involving contact with acidic agents
- intrinsic due to gastric acid
- extrinsic due to soft drinks and citrus fruit

Question 14

why is young enamel whiter

Answer 14

internal reflection

Question 15

describe how dental calculus is formed

Answer 15

• Mineralised plaque, and can become attached to the enamel of the crown or the cementum.
  
  • Saliva is supersaturated with calcium and phosphate minerals, that have the potential to mature newly erupted enamel, protect exposed tooth surfaces from acid action and remineralise areas in the early stages of demineralisation.
  • Supragingival plaque is less mineralised than subgingival plaque (40% vs 60%)
  • Organic component of dental calculus originates from plaque, is derived from saliva, gingival crevicular fluid, desquamated epithelial cells, blood cells, food debris, bacteria and their products.
  • Supragingival calculus is cream coloured and found adjacent to the opening of the major salivary glands. Seen predominantly on the lingual surface of mandibular anteriors, near the opening of the submandibular and sublingual glands. Also seen on buccal surfaces of maxillary molars near the opening of the parotid glands.
    Subgingival calculus is darker in colour and can occur throughout the dentition from minerals in inflammatory exudate associated with periodontal disease.

Question 16

describe the stages of plaque formation

Answer 16

• Initial transport of bacteria to the tooth surface
  
  • Reversible adsorption of the bacteria on to the pellicle surface
  • Less reversible attachment of bacteria to the tooth surface
  • Build-up of new bacterial layers
  • Growth of attached organisms to produce a biofilm
    Organisms within plaque synthesise extracellular polymers

Question 17

describe how different dietary carbohydrates influence the plaque matrix and how the matrix can affect cariogenicity

Answer 17

• Early plaque is composed of gram positive, cocci and filaments. Deposit will thicken with time and accumulate in areas that lack self cleansing, like pits, fissures and the gingival third of smooth surfaces.
• Many plaque bacteria metabolise dietary carbohydrates, producing polysaccharides, which may be stored intracellularly on the cell surface and extracellularly in the matrix.
• Caries is associated with the metabolism of dietary sugar to acid by gram positive bacteria in supragingival plaque.
• Nature of plaque matrix reflects the diet and its cariogenic potential is determined by the type of carbohydrate consumed. Frequent intake of sugar induces a cariogenic plaque in which organisms capable of surviving at low pH are favoured.
  Periodontal disease is associated with persistent presence of mature plaque at the gingival margin and exacerbated by an increase in gram negative organisms. Gingival inflammation and periodontal destruction are the result of proteases and other bacterial products and indirect promotion of potentially damaging immune responses.

Question 18

describe the mechanisms of attachment of bacteria and proteins to the acquired pellicle leading to plaque formation

Answer 18

• Plaque forms from crown of the tooth toward gingivae but above the gingival margin. In the region of the gingival crevice the tooth will be covered by only the primary enamel cuticle. Below this layer the tooth is covered by junctional epithelium.
  Initial attachment is reversible, involves the formation of long range, physiochemical interactions between microorganisms and pellicle proteins. As microbes are negatively charged due to nature of the cell surface, and acidic proteins are present in the pellicle, these interactions usually involve the formation of calcium bridging between the pellicle proteins and bacterial membranes for successful interactions.

Question 19

describe the origins of the acquired pellicle

Answer 19

• Organic element of salivary origin.
  Always forms a protective coat following any wear. Derived mainly from salivary proteins but includes elements from crevicular fluid and bacteria.

Question 20

describe how dentine reacts to trauma and how it bonds to restorative materials, how it changes with age and why this is clinically important

Answer 20

• If dentine is fractured, fluid exudes from the tubules and forms droplets on the surface of dentine, which suggest pulpal tissue pressure is being exerted outward. This could help in limiting the progress of chemicals or toxins on or in dentine toward the dental pulp.
  As heat is generated during drilling, the thinner the intervening dentine the greater the dental pulp may be affected. Residual dentine thickness refers to the amount of dentine separating the floor of the dental cavity from the periphery of the dental pulp.

Question 21

describe the basis of dentine sensitivity

Answer 21

• Dentinal tubules follow a curved, sigmoid course. This is the primary curvature. they are wider at the pulp and thinner at the ADJ.
  
  • In the root and beneath the cusps, the primary curvature are less pronounced and the tubules run a straighter course.
    The tubules are more widely separated at their peripheries. - Exposed dentine is often sensitive. Nerves in dentine, odontoblast process or fluid movements in the tubules are the hypotheses for this.
  • Not nerves: they are absent in the outer dentine.
  • Not odontoblast process: no physiological evidence to date that indicates the process is analogous to a nerve fibre.
  • Most plausible is that all effective stimuli applied to dentine causes fluid movement through the tubules and that this movement is sufficient to depolarise nerve endings in the inner parts of tubules.
    Hypersensitivity is short, sharp pain arising from exposed dentine in response to thermal, tactile, osmotic or chemical that cannot be ascribed to a pathology. Most commonly associated with buccal surface of canines and premolars, especially when there is gingival recession.

Question 22

describe the different zones in dentine and the reasons for these differences

Answer 22

• Peritubular dentine - the walls of the dentinal tubules in recently formed intertubular dentine at the pulp surface are composed of mineralised type I collagen. With maturation, another type of dentine is deposited on the walls, which narrows the lumen. This is peritubular dentine, and its formation gradually leads to the obliteration of the tubule. It lacks collagenous fibrous matrix and this relates to the finding that it exhibits no piezoelectricity. It is a zone of increased radiographic and electron density lining the surface of the dentinal tubule. Found in unerupted teeth, and since it is mostly in apical dentine this indicates it is an age change and not a response tissue.
  
  • The mineral content of dentine decreases and the thickness of mineral crystals increases toward the EDJ. Hardness and elasticity decrease toward the junction.
  • Mantle dentine: first formed layer. Differs from circumpulpal in four ways: %5 less mineralised, collagen fibrils are orientated perpendicular to ADJ, dentinal tubules branch profusely in this region, and it undergoes mineralisation in the presence of the matrix vesicles.
  • Mantle dentine has two morphologically recognisable outer regions known as hyaline and granular layer. Granular is beneath hyaline. Hyaline is the outermost part of the root dentine. Granular dentine is hypo mineralised.
  • Circumpulpal dentine: the bulk of dentine in the crown and the root.
  • Secondary dentine: innermost layer of dentine formed between circumpulpal dentine and predentine
  • Tertiary dentine: inner layer of dentine formed mainly in the crown in response to serious insult.
  • Interglobular dentine: typically in the outer part of the crown. Outer part of circumpulpal beneath the mantle layer is often incompletely mineralised and has a characteristic appearance in groudn sections.
  • Predentine: innermost unmineralised layer, where new dentine is being deposited throughout life.
    Dentine in the root apex has more accessory canals, and apical dentine often deviates from the long access of the tooth. There may be localised areas of dentine resorption and repair.

Question 23

compare and contrast dentine with enamel

Answer 23

• The combination of enamel and dentine provides a rigid, hard structure suitable for tearing and chewing that resists both abrasion and fracture.
  
  • Dentine is sensitive, and is formed throughout life, whereas enamel is not sensitive and stops forming as soon as the tooth erupts.
    Hydroxyapatite crystals are the same shape but they are much smaller in dentine than in enamel.

Question 24

describe the composition and main structural features of dentine

Answer 24

• Rigid but elastic tissue consisting of small, parallel tubules in a mineralised collagen matrix
  
  • The tubules contain the odontoblast process, a small volume of extracellular fluid, a dendritic process from an antigen presenting cell and an unmyelinated nerve fibre.
  • Inorganic components: 26.9% calcium, 13.2% phosphorus, 4.6% carbonate, and sodium and magnesium as well.
  • Composite material consisting of apatite crystals on an organic scaffold, predominantly composed of collagen. 70% inorganic, 20% organic and 10% water by weight. 50% inorganic, 30% organic, 20% water by volume.
  • Compared to pure hydroxyapatite, the crystallites are calcium poor and carbonate rich. They are found on and in between the collagen fibrils.
  • Organic matrix of dentine: where the crystallites are embedded, composition is similar to bone. Fibrils embedded in an amorphous ground substance, fibrils are collagen and comprise of 90% of the organic matrix.
    Principle collagen fibre of dentine is type I. dentine collagen has more hydroxylysine than the equivalent in soft tissue collagen. Type III and V are very abundant in the pulp and have been reported in the dentine as well. Most fibrils run parallel to the pulpal surface and in mineralised dentine, the collagen fibrils are of larger diameter and are more closely packed than in predentine.

Question 25

describe why knowledge of enamel structure and age changes are important in many clinical situations

Answer 25

• Acid etching technique
  
  • Progress of dental caries
  • Amelogenesis imperfecta
  • The water component and its distribution are importance because ions such as fluoride travel through it.
  • Whitening agents like hydrogen or carbamide peroxide produce reactive molecules (free radicals) that penetrate the enamel pores and act as both oxygenator and oxidant. This reduces the large chromogenic organic molecules in the enamel matrix to smaller, less noticeable molecules that may diffuse out from the enamel and they will absorb less light which makes the teeth seem whiter.
    Enamel wears with age and darker in colour - due to reduced tranlucency, stains and surface coatings. Composition of surface enamel alters as a result of additions and exchanges with the oral fluids. Fluoride can be benefically incorporated into surface enamel, reducing porosity and susceptibility to caries.

Question 26

describe enamel pearls

Answer 26

enamel pearls are small isolated spheres of enamel that are occasionally found in the root toward the cervical margin. Particularly common in the root bifurcation region where they may predispose a plaque accretion following gingival recession.

Question 27

describe how the current knowledge of enamel structure and biology relates to the design of restorations

Answer 27

• Surface enamel is harder and less porous, less soluble and more radio opaque than subsurface enamel. Because it is prism less it is highly mineralised and more resistant to caries which is why acid etching may not always enhance adhesion.
  Different acids at different concentrations can produce a variety of patterns for partial prism dissolution to provide a roughened suitable surface for adherence of restorative materials

Question 28

list the features of enamel that are pertinent to the progress of dental caries

Answer 28

• In the body of carious lesions, there can be 30-50% loss of mineral. When mineral is dissolved, the loss begins at the periphery of the prism.
  
  • During carious attack, a repeating cycle of demineralisation and remineralisation occurs, and if demineralisation dominates, caries progresses.
    Fluoride can make enamel more stable and enhance remineralisation. Can form a calcium fluoride like material at the enamel surface and protect the underlying enamel from demineralisation. Maximum effect is obtained when 50% of the hydroxyl groups are replaced with fluoride.

Question 29

describe the difference between enamel spindles, enamel tubules and enamel lamellae

Answer 29

• ACJ is scalloped and has enamel spindles and tufts located here. Convexities of the scallop are in the enamel region and concavities of the scallop are in the dentinal region.
• Spindles: narrow, round, club shaped. Result of odontoblast processes that insinuated between the ameloblasts. Most common beneath the cusps where most crowding of odontoblasts would have occurred. not aligned with the prisms.
• Tufts: junctional structures in the inner third of enamel that in ground sections look like tufts of grass. Travel in same direction as prisms.
• Lamellae: sheetlike apparent structural faults that run through the entire thickness of the enamel. Hypo mineralised and narrow, longer and less common than tufts. Best visualised in transverse sections of enamel. May arise developmentally or after eruption

Question 30

describe the nature of the two types of incremental markings in enamel, namely the cross striations and enamel striae

Answer 30

• Incremental lines exist due to the phasic development
  
  • Short period are cross striations - lines that cross enamel at right angles to their long axis, and are formed parallel to the secretory face of the ameloblast.
  • Long period are enamel striae. - prominent lines that run obliquely across the enamel prisms to the surface. Form concentric rings in horizontal sections. Striae overlying the cusps and incisal edges do not reach the surface unless there is enamel loss.
  • 7-9 cross striations between adjacent striae in any one individual.
  • Enamel striae each the surface in a series of fine grooves running cirumferentially around the crown. These features are known as perikymata ridges. They are close together near the cervical margin but as they reach the surface obliquely they can be further apart.
    Neonatal lines reflect metabolic changes at birth and there is just one line.

Question 31

describe the directions of enamel prisms and appreciate the appearance of hunter schreger bands

Answer 31

• arrangement of crystallites and prisms determines the strength and resistance to fracture
• 10-13 prisms will go in the same direction and the layers above and below will be in different directions. these periodic changes in prism direction give rise to the banding pattern called hunter schreger bands
• arranged in a spiral pattern , and in areas beneath the cusps and incisal edges the change in direction of the prisms seems more marked and irregular. groups of prisms seem to spiral around the others giving the appearance of gnarled enamel.

Question 32

describe the significance of the term prismless enamel and where it is found

Answer 32

found at narrow surface zone

- Enamel crystallites are all aligned at right angles to the surface and parallel to each other. Surface layer is more mineralised than the rest of the enamel because of the absence of prism boundaries, where more organic material is located. 
- Occurs as a result of the absence of tomes processes from the ameloblasts in the first and final stages of enamel deposition

Question 33

describe the concept of enamel prism and its appearance in different planes of enamel

Answer 33

each rod is wrapped in a sheath of organic matrix, but the crystals within the rod abut one another and there is discontinous organic matrix in between.

rods run from the DEJ to the surface of enamel, with their trajectories undulating in the inner enamel layer, creating hunter schreger bands, which makes it 10 times more resistant than bone to crack growth.

each rod consists of several million crystallites, and they run from the ADJ to the surface. at the boundaries of the prisms, the crystallites deviate by 40-60 degrees from those inside the prism, and there is increased microporosity because of this, so this means there is also more organic material.

there are different types of rods: type 1 - found at ADJ and near the surface, enamel in this region is formed slowly and has clear boundaries.
type III - keyhole pattern, where the tail of one prism is lying between the heads of the adjacent prisms, and pointing cervically .

most prisms travel in sinusoidal line from ADJ to the surface, and prisms meet the surface at varying angles.

above the cervical margin, prisms meet the surface at an angle of 60 degrees. within fissures, prisms make surface angles as acute as 20 degrees.

Question 34

describe the characteristis of enamel crystallites and their changing orientation and understand how the structure of enamel can withstand the forces of mastication

Answer 34

extremely hard and stiff, exceptional resilience, allows enamel to withstand hundreds of masticatory cycles with biting forces of up to 770N.
the intricate organisation of enamel is the key to its mechanical performance.

enamel rods are the building blocks of enamel, and are composed of an array of aligned carbonated apatite crystals which are thought to be orientated with their c axex along the rod axes. the boundaries of each rod are a result of sudden changes in crystallite orientation. the boundaries are incomplete in the cervical region and there is also a gradual change in orientation between crystals.

enamel crystals are long flat ribbons that are rhomboidal in cross section, and the core of the crystals is more soluble than the periphery. the crystals increase in width frmo the EDJ to the surface

the elongated crystals in each rof run parallel to one another, and each rod is associated with an interrod, which consists of crystals arranged at a 60 degree angle to the rod axis.

misorientation of adjacent enamel crystallites provides a toughening mechanism. if all crystals are co orientated a transverse crack can propagate across the crystal inferfaces, but if the crystals are mis orientated, then the there is material toughening via the crack deflection mechanism

interrod crystals are predominantly co orientated throughout large areas of enamel. each ameloblast cell deposits one rod-interrod complex with a head and a tail, and all tails form a joined, co orientated interrod continuum.

Question 35

describe the inorganic and organic composition of enamel, and how this links to its physical properties

Answer 35

• 95% inorganic hydroxyapatite crystals - carbonated calcium hydroxyapatite crystals that are larger than in any other mineralised tissue. Comprises 88-90% by volume, and 95-96% by weight.
  
  • Water comprises 2% weight of enamel and 5-10% volume. Presence is related to the porosity. Fluoride ions travel through it.
    1-2% weight is organic matrix, can contribute to the fracture toughness. Composed of amelogenines, enamelins and other minor compotents. Goes from 90% amelogenins during development to less than 10% in adults.

enamel is hard but because of its thinness it is brittle and requires cushioning from dentine. translucent as well - light shines through it, this is why ACJ is more yellow than incisal edge, as it is thinner enamel there.
- Surface enamel is harder, denser and less porous than subsurface enamel, hardness and density also decreases from the surface toward the interior and from incisal tip to ACJ
Fluoride can substitute the hydroxyl ions which confers greater stability and resistance to dissolution. Fluoride is acquired during enamel maturation, and so it declines as you go from the outer surface to the enamel

organic matrix is composed of peptide groups - ametogenins and non amelotogenins eg enamelin and other minor components.

Question 36

describe the different terms for the surface characteristics of enamel

Answer 36

enamelin - organic component of enamel is this protein, similar to keratin seen in the skin.

gnarled enamel
- enamel rods bent in exaggerated twisted manners at the cusp tip

hunter schreger bands
- enamel rod configuration viewing in incidental light appears as light and dark bands of rod groups called HSB

hydroxyapatite - crystallite calcium phosphate also seen in bone, dentine, and cementum

lines of retzius - enamel rods are deposited incrementally, leading to rings like seen in tree trunks, appearing as dark lines called the lines of retizius

perikymata - growth lines (striae of retzius) become apparent on surface of enamel as ridges which are the perykamata. surface manifestations of the incremental lines, some are more prominent than others

spindles - termination of dentinal tubules in enamel, seen at ACJ

striae of retzius - same as lines

tufts - hypocalcified zones caused by bending of adjacent groups of rods, seen at ACJ

Question 37

describe the various types of dentine and the structures they contain

Answer 37

primary dentine
- major component of the crown, consists of mantle dentine, globular dentine, circumpulpal dentine
- mantle dentine is deposted first, along the dentoenamel junction
- mantle is separated from the circumpulpal dentine by a zone of disturbed dentine called globular dentine
- globular dentine is through to be a result of deficient mineralisation caused during the final maturation of the odontoblast

secondary dentine
- as teeth begin to function, the dentine is termed secondary dentine and is normal circumpulpal dentine

tertiary dentine
- when caries or trauma affects the pulp, dentine is deposited underlying that area
- protects the pulp

predentine
- 90% type I collagen fibres
- 10% non collagenous proteins
- calcifies within 24 hours as the odontoblasts deposit a new band of collagen fibres

Question 38

describe the blood supply and innervation of the periodontal ligament

Answer 38

blood supply

• superior and inferior alveolar arteries
• the gingival vasculature comes from the lingual and palatine arteries, can they can also be involved
• perforation arteries passing through the alveolar bone

specialised features
- crevicular plexus of capillary loops
- presence of large numbers of fenestration in the capillaries - maybe related to high rate of turnover needing more metabolic requirements

innervation

sensory
- nociception and mechanoreception

mechanoreception
- transmission of touch and textural information when eating
- merkel cell complex and ruffini endings are associated with slowly adapting responses
- meissner endings are associated with rapidly adapting responses
- pacinian corpuscles are rare in oral tissues, but they are very rapidly adapting responses
- slow adapting means touch pressure
- rapidly adapting means flutter vibration

autonomic
- supply of periodontal blood vessels

Question 39

describe the role of inflammation in periodontal disease

Answer 39

matrix metalloproteinases degrade the extracellular matrix of collagen
inflammatio increases the expression of MMPs and this leads to aggressive loss of collagen within the periodontal ligament, leading to tissue destruction.

Question 40

describe the cellular components of the periodontal ligament

Answer 40

fibroblasts
- predominant cell
- regeneration of tooth support apparatus
- adaptive response to mechanical loading of the tooth including orthodontics

cementoblasts
- cementum forming cells lining the surface of cementum
- squat cuboidal cells rich in cytoplasm

osteoblasts
- bone forming cells lining the tooth socket
- prominent only when there is active bone formation

osteoclasts and cementoclasts
- found in areas where bone is being resorbed
- arise from blood cells of macrophage type

epithelial cell rests
- normal feature of the periodontal ligament
- remains of the developmental epithelial root sheath of hertwig
- separated from the surrounding connective tissue by a basal lamina

defence cells
- macrophages, mast cells, eosinophils
- macrophages phagocytose particulate matter and invading organisms, and synthesise a range of molecules with important functions
- mast cells produce histamine, heparin, and factors associated with anaphylaxis
- eosinophils are only occasionally seen int he normal periodontal ligament, possess granules called peroxisomes
- all capable of phagocytosis

Question 41

describe the different fibrous components of the periodontal ligament

Answer 41

collagen
- type I, 70%,
- type III, 20%

principle fibres
- bundles of collagen, 5mm in diameter
- dentoalveolar crest, horizontal, oblique, apical, inter-radicular

oxytalan/elastin
- depending on the species
- oxytalan are immature elastin fibres attached into the cementum and coursing out into the periodontal ligament in various directions

Question 42

describe the formation of the periodontium

Answer 42

developed from the dental follicel

fragmentation of HERS allows cells from the follicle to proliferate and differentiate into cementoblasts, which lay down cementum over the hyaline layer.

bundles of collagen are produced by fibroblasts in the central region of the follicle are called sharpeys fibres and they are embedded in the forming dentine and will become the principle fibres of the PDL.

cells in the outermost area of the follicle differentiate into osteoblasts to form the bundle bone that will anchor the periodontal fibres. periodontal fibroblasts produce more collagen that binds the anchored fragments together to form the principle periodontal fibres.
loose fibrous connective tissue carrying nerves and blood vessels remains between the principle fibres.
tissue specific stem cells are found in the periodontium and possess the ability to form new cementoblats, osteoblasts or fibroblasts

neural supply consists of small, unmyelinated sensory and autonomic nerves and larger myelinated sensory nerves. some of the latter terminate as unmyelinated neural structures thought to be nociceptors or mechanoreceptors

Question 43

discuss theories of dentine sensitivity

Answer 43

hydrodynamic theory - movement of the odontoblast into contact with pulpal and intratubular nerve endings

Question 44

describe the blood vessels and lymphatics of the pulp

Answer 44

terminal blood vessels in the periphery are thin walled capillaries situated among the odontoblasts, under local humoral control

larger vessels with muscle cell support in the walls exist centraly and are under post ganglionic sympathetic control

Question 45

describe both fibrous and non fibrous componennts of the extracellular matrix of the pulp

Answer 45

fibrous: thin collagen fibrils, reticular fibres, fibronctin

• 56% type I collagen
• 41% type III collagen
• 2% type V collagen

non fibrous: hyaluron, glycosaminoglycans, proteoglycans

Question 46

list all the cell types in the pulp and describe their function

Answer 46

fibroblasts are the predominant cell, existing in an extracellular matrix of glycosaminoglycans and collagen fibres

odontoblasts are the second most predominant cell, forming dentine throughout life.

mesenchymal stem cells

Question 47

describe the anatomy of pulp

Answer 47

lateral canals
- channels of communication between pulp and PDL
- form when a localised area of root sheath is fragmented before dentine formation.
- cause direct communication between pulp and PDL via a channel through the dentine and cementum carrying vasculature and innervation.
- most common in apical third of the root
- clinically significant because they represe pathways along which disease may extend from the pulp to periradicular tissues

apical foramen
- epithelial root sheath continues to extend until the full, predetermined length of the root is reached
- pulpal vessels and nerves pass here
- located at the end of the anatomical root
- can be one or multiple - the largest is called the apical foramen, and the smaller are called acccessory canals, and together they form the apical delta
- usually 0.3-0.6mm
- larger diameters are found on the distal canal of the mandibular molars and the palatal root of the maxillary molars

pulp space divisions: coronal and radicular

coronal pulp
- subdivided into pulp horns, extending from the chamber into the cuspal region
- extensive horns in young teeth
- horns decrease in height, and overall pulp chamber size decreases, due to the gradual formation of dentine

radicular pulp
- root canals
- some have more than one
- singular canal in anterior teeth, posterior have multiple
- tapered or conical, becomes smaller with age also

central zone and peripheral zone
- central has arterioles, veins, nerve trunks that enter from apical foramen and proceed to the pulp chamber

pulps of molar teeth are four times larger than incisal pulp

Question 48

describe the process of root development

Answer 48

in the developing tooth, cells of the inner and outer dental epithelium meet at the cervical loop, which then proliferates apically to form hertwigs epithelial root sheath.

HERS provides signals for the differentiation of odontoblasts and acts as a template for the root.
multiple roots result when opposing parts of the root sheath proliferate both horizontally and vertically.

after the first dentine (mantle dentine) in the root is formed, the basement membrane beneath HERS breaks up and the innermost root sheath cells secrete a hyaline material over the newly formed dentine. after mineralisation, this is called the hyaline layer of hopewell smith, which helps bind the soon to be formed cementum.

HERS then fragments, which allows dental folliscle cells to migrate and contact the newly formed dentine surface, where they will differentiate into cementoblasts and initiate accellular cementum formation.

after root development is completed, there are cell remnants of HERS that are usually functionless, but if there is inflammation they can proliferate and can cause a radicular cyst

Question 49

describe the development of the pulp

Answer 49

tooth originates in the dental lamina on the surface of the embryonic jaws. the lamina has downgrowths to form the teeth. ultimately leads to the bell shaped enamel organ (ectodermal origin, will be responsible for amelogenesis), tissue in the invagination of the bell is the dental papilla, which forms the pulp.

papilla is derived from ectomesenchymal cells from the neural crest.

Question 50

describe the structure, function, location, formation and defects of enamel

Answer 50

thin, outer, translucent covering on the crown of the tooth. hardest calcified matrix of the body.

structure
- composed mainly of hydroxyapatite and organic materials
- structural unit of interlocking columns of enamel rods. arrangement of them is crucial for enamels hardness - mammalian enamel is the rodgs and interrod enamel is found between the prisms.
- length of crystals can span the entire thickness of the enamel layer.
- not collagen based
- thickness varies: thin at cervical margin, can be 2.5mm at incisal edge: provides variation in colour because at thin regions the dentine colour can be seen

function
- protection of the underlying structures of the tooth
- withstand mechanical forces applied during tooth functioning.
- brittle: needs dentine to cushion it.

formation:
- during the bell stage of tooth development, the shape of the crown is determined
- ameloblasts are the cells responsible for their formation, they are lost when the tooth erupts.
- amelogenesis
- first formation, only 30% mineralised. as the organic matrix breaks down, the crystals grow wider and thicker. this takes the mineral content up to 96%
- three functional stages:
- presecretory
differentiating ameloblasts acquire their phenotype, change polarity, develop an extensive protein synthetic apparatus and prepare to secrete the organ matrix of enamel
- secretory
ameloblasts elaborate and organise the entire enamel thickness, forming highly ordered tissue
- maturation
ameloblasts modulate and transport specific ions required for the concurrent accretion of mineral
- enamel formation begins in the early crown development and involves the differentation of the cells of the inner enamel epithelium at the tips of the cusp outlines formed in that epithelium
- when enamel is fully mature, the ameloblast layer and the adjacent dental papilla layer regress to form the reduced enamel epithelium. the reduced epithelium found more cervically will remain when the tooth erupts to interact with the oral epithelium to form the junctional epithelium

Question 51

describe the different functions that saliva has

Answer 51

• Oral hygiene
• Antimicrobial
• Chemical digestion
• Hydrate oral cavity and food
• Increases the taste of food (lubricates food and allows absorption into taste buds).
• Decreases caries.

Question 52

describe the process of salivation

Answer 52

universal mechanism for the glands

acinus surrounded by acinar cells, lead into ducts surrounded by ductal cells

PNS produces acetylcholine and SNS produces noradrenaline to innervate the glands depending on the type of saliva that is required

PRIMARY SALIVA

the primary ions in the acinus that make up the isotonic, primary secretions are: sodium, potassium, chloride, bicarbonate, calcium, water and phosphate. they have different mechanisms of entering the cell.
- Entry of water: aquaporin 5 allows water to leak from the apical membrane into the acinus. Water can move between the cells and enter the acinus through paracellular transport. Basolateral membrane has aquaporin 3 transporters to let water enter the cell and then go into the acinus through aquaporin 5.
- Entry of sodium: via paracellular transport.
- Entry of potassium: potassium enters the acinar cell via NaK pump on basolateral membrane, and the transporter that channels sodium, potassium and 2 chloride ions. to enter the acinus from there, on the apical membrane take the potassium ions out into the acinus in exchange for a proton or through leakage channels.
- Entry of chloride: sodium potassium 2 chloride (NaK2Cl) cotransporters pump in two chloride ions. on apical membrane there are CFTR (cystic fibrosis transmembrane receptor proteins) which allow chloride ions to leak into the acinus.
Entry of bicarbonate: cells produce carbon dioxide, which combines with water in the cells in presence of carbonic anhydrase it becomes carbonic acid, carbonic acid is broken down into protons and bicarbonate. Bicarbonate is excreted into the acinus. As a result, some chloride ions go into the cell to maintain electrical activity.
- isotonic solution as the volume of water is equal to sodium and chloride concentration

SECONDARY SALIVA - ductal modification

- Decrease sodium: Sodium molecules are taken into the ductal cells from the primary secretion. Proton is pumped out in exchange. 
- Chloride decrease: chloride is pulled into ductal cells in exchange for bicarbonate. 
- Sodium and chloride concentration is now less than the water volume, making the secondary secretion, if the solute concentration is less than the water, then is it hypotonic. 
- Modified saliva is hypotonic. 
- Other things in the saliva is dependent on the ions. - Special IgA antibodies are found in saliva, and cystatins, histatins (kill bacteria and fungi), lysozyme (break down bacterial cell walls and digest food) and proline rich proteins to remineralise the teeth.

Question 53

describe the innervation of the salivary glands

Answer 53

parasympathetic innervation of the glands

• brainstem has superior and inferior salivatory nuclei.
• superior is in part with facial, moves with taste fibres and salivary fibres to make up chordae tympani, innervates tongue and the sublingual and submandibular gland
• inferior salivatory nucleus is glossopharyngeal, supplies the parotid gland
• innervation produces watery, electrolyte rich saliva

sympathetic innervation of the glands
- thoracolumbar region. T1-T4 goes to head and neck, forming superior cervical ganglion to innervate the glands
- SNS produces thick, protein rich saliva

acetylcholine is produced from the parasympathetic nervous system to produce saliva that is watery and full of ions. Acetylcholine binds to muscarinic M3 receptors on the basolateral membrane of the acinar cells and stimulate it to release Gq. Normally bound to GDP and binds GTP, which stimulates phospholipase C which then increases calcium levels in the cell. Increased calcium levels activates CAM kinases, which will phosphorylate certain channel types to increase secretion of water, sodium, chloride, potassium, bicarbonate. This increases the water and electrolyte

noradrenaline is produced from the sympathetic nervous system to produce saliva that is viscous and full of different proteins like mucin. binds to beta 2 adrenergic receptor which activates g stimulatory proteins to bind GTP and stimulate adenylyl cyclase to convert ATP to cAMP which activates protein kinase A. there are granules in the cells with proteins and enzymes. Protein kinase A stimulates exocytosis of the granules which releases many enzymes and proteins into the primary secretion - mostly mucin, and salivary amylase. So this makes the saliva thicker and more viscous.

Question 54

describe the features of the lower first permanent molar

Answer 54

groove starting on the buccal surface deepens into the transverse fissure across the occlusal surface and ends as a groove on the lingual surface

deepens in the centre of the crown to form a pit

pulp chamber has five pulp horns corresponding to the five cusps. the root canals open at the mesial and distal borders of the pulp floor.
the distal root contains a single wide canal and the mesial root has two narrow canals

Question 55

describe the features of the upper second molar

Answer 55

the roots are the much less divergent than that of the first, the lingual root can be partially fused with either of the buccal roots

Question 56

describe the features of the upper first molar

Answer 56

there is a single lingual root in the same plane as the distobuccal root
single lingual root is the longest and strongest of the three
the mesiobuccal root apex is curved distally
the distobuccal root is the most slender

the pulp chamber is roughly cuboidal and the walls bulge convexly into the space, especially in the roof and the floor

one pulp horn extends into each of the four cusps

Question 57

describe the features of the lower second premolar

Answer 57

crown is much larger than the first premolar. lingual cusp is much larger than that of the first and is displaced mesially. there can sometimes be two lingual cusps, but the mesial one is larger

single root is stronger than that of the first and is more circular

the pulp is slightly compressed mesiodistally

Question 58

describe the features of the lower first premolar

Answer 58

occlusal surface is round, there is a much greater difference in buccal and lingual cusp height
lingual cusp is displaced distally
small groove runs from the mesial pit onto the mesiolingual surface

buccal surface in inclined strongly lingually so the tip lies almost above the centre of the tooth

lingual surface is narrow and much lower than the buccal surface

contact point of the mesial surface is more buccally placed than the distal surface, so the mesial surface is set at more of an acute angle to the buccal surface than the distal

single root that is grooved mesially and distally

usually only one pulp horn corresponding to the buccal cusp.

Question 59

describe the features of the upper left second molar

Answer 59

crown smaller than upper first premolar
two cusps are similar in width and height, due to reduction in size of the buccal cusp
occlusal surface is more symmetrical and there is slight mesial displacement of the lingual cusp

15% have two rotos, although the single root is usually deeply grooved

root canal is often undivided and occupies a region wide buccolingually and narrow mesiodistally

Question 60

describe the upper first premolars key features

Answer 60

traversed by a longitudinal ridge that terminates in the buccal cusp
occlusal borders of the buccal surface meet at the cusp almost at right angles
lingual is lower and more narrow than the buccal surface
canine fossa on mesial root
buccal cusp is wider and higher than the lingual cusp
lingual cusp is displaced mesially
two cusps are joined by marginal ridges, mesial marginal ridge is higher
two cusps are separated by a sharp fissure running mesiodistally which does not reach the distal marginal ridge but extends across the mesial marginal ridge on to the mesial surface
more than 50% have two roots, one buccal and one lingual , apical part of the root shows distal curvature

pulp - narrow mesiodistally and wide buccolingually. two pulp horns extend toward the two csusp
the root canal is almost always divided into a buccal and lingual canal even if the root is only single

Question 61

describe the differentiating features between upper and lower canines

Answer 61

upper has stout crown, diamond shaped surface, pointed cusp
lower has high, narrow crown, with a less pointed cusp
upper canine has crown set in straight line with the root
lower canine has the crown set at an angle to the root and this produces a convex labial profile from the cusp to the apex
upper canine has the amelocemental junuction at the same level on the labial and lingual sides of the crown
lower canine often has enamel extending further apically on the labial side than the lingual
cingulum is skewed distally

Question 62

describe the features of lower permanent canines

Answer 62

• distal surface gets the most wear from continous movement
• more flat and symmetrical compared to uppers which are narrow and slender, and flatter mesiodistally.
• crown is not in a straight line with the root and the cingulum is less pronounced
• enamel extends further apically on the labial than on the lingual.
• labial surface is lingually inclined so the cusp tip is in a lingual position
• pulp is simple and spindle shaped, compressed mesiodistally
• root is shorter and weaker, flatter mesiodistally

Question 63

describe the featrrures of upper permanent canines

Answer 63

• mesial borders are shallower than distal which is due to contact with adjacent tooth
• mesial surface gets the most tooth wear from continuous movement
• diamond shaped crown with prominent cingulum.
• has a pointed cusp rather than an incisal edge
• labial surface is concave and divided into two shallow fossae by a ridge connecting the cusp with distally displaced cingulum.
• root is long and strong, oval. grooved mesially and distally.
• pulp is spindle shaped, compressed mesiodistally. widest at the level of the cervical margin. pulp chamber narrows to one single horn.

Question 64

describe the features of lower permanent incisors

Answer 64

• crown is chisel shaped, also has mammelons.
• labial is convex, laterals have more of a fan shape
• lingual has a cervical convexity that is distally displaced.
• root is flattened mesiodistally. grooves on mesial and distal surface.
• pulp is flattened labiolingually and flattened mesiodistally. three pulp horns.

Question 65

describe the features of the upper permanent incisors

Answer 65

• incisal edge shows mammelons (three cusplets). these wear with age - can help to identify the age of a tooth therefore.
• labial surface is convex
• lingual surface is deeply concave
• cingulum is on cervical third of lingual surface and is distally displaced
• cone shaped root
• upper lateral roots are slightly grooved
• pulp chamber is wide mesiodistally and narrow labiolingually. three pulp horns, circular in cross section

Question 66

describe the buffers in the saliva at different flow levels

Answer 66

• Bicarbonate most effective buffer when flow rates are at the highest
  
  • Phosphate is most effective as buffer in saliva at rest
  • Proteins have limited buffering effect but main effect occurs at pH less than 5
  • The salivary buffers are bicarbonate, phosphate, proteins and bacterial ammonia
    Ammonia are important buffers as they buffer plaque acid

Question 67

describe sweeteners

Answer 67

bulk cariogenic sweeteners
- sucrose
- fructose
- glucose
- lactose

low caloric sweeteners
- mannitol
- sorbitol
- xylitol

non caloric, high intensity sweeteners, non cariogenic relative to sucrose
- aspartame
- cyclamates
- saccharin
- sucralose

Question 68

describe the amount of saliva in the mouth

Answer 68

volume of saliva - 1.1ml

dispersed over an area of 200cm^2

mucosa covered by film of saliva that is 50-100 micrometers thick

flow velocity varies in different regions of the mouth

10ml produced when sleeping
250ml produced when awake or resting
360ml produced when eating
500-700ml produced overall

submandibular: 70% of saliva when sleeping, 72% when awake, 40% when stimulated

sublingual: 15% when sleeping, 4% when awake, 2% when stimulated

parotid: 0% when sleeping, 20% when awake, 50% when stimulated

minor glands: 15% when sleeping, 4% when awake, 8% when stimulated

Question 69

describe amelogenesis

Answer 69

• Made in two stages
  
  • Dentine induces the internal enamel epithelial cells to differentiate into ameloblasts which elongate and become columnar. The nucleus migrates to the basal end of the cell.
  • Secretory phase of amelogenesis: ameloblasts become secretory cells and synthesise and secrete the enamel matrix proteins called amelogenins. The matrix is then partially mineralised.
  • Maturation phase: most of the matrix is removed, mineral content is increased, mature enamel is 95% mineral.
    Protection phase: ameloblasts regress to form a protective layer called the reduced enamel epithelium. This is involved in eruption and forms epithelial attachment.

Question 70

describe the timeframe for dental development

Answer 70

Week 6 - primary epithelial band develops
Week 7 - vestibular lamina and dental lamina have formed.
Week 8 - dental lamina is horse shoe shaped structure with tooth germs.
Weeks 8-10 - dental lamina thickens into bud stage enamel organ, ectomesenchymal condensation appears - the dental papilla.
Week 11 - enamel organ forms a cap over the papilla. Cap has external and internal enamel epithelium which meet at the cervical loop.
Week 12 - extension appears on the lingual side of the dental lamina, which is the dental lamina for the permanent successor.
Week 14 - bell stage enamel organ, more cells are differentiated and tooth shape is being defined.
Week 16 - first permanent molar germ develops as a backward extension of the dental lamina.
Week 18 - late bell stage enamel organ - crown shape is well defined, apposition of enamel and dentine begins. Enamel formation begins once dentine formation is established.