Oral Health and Saliva

Question 1

List the 3 major salivary glands

Answer 1

Major salivary glands:

1. Parotid
2. Submandibular
3. Sublingual

Question 2

Where are the minor salivary glands located?

Answer 2

The minor salivary glands:

• Hundreds within the submucosa of the oral mucosa

Question 3

List the key features of Sjögren’s syndrome (9 points)

Answer 3

Key features of Sjögren’s syndrome (9 points):

1. Sjögren’s syndrome (SS) is the association of dry mouth and dry eyes
2. SS is an autoimmune disorder
3. 90% of SS patients are older females
4. Dry eyes and mouth alone are termed ‘sicca syndrome’ or primary SS (SS-1)
5. Dry eyes and mouth with a connective tissue disease are termed secondary SS (SS-2)
6. Dry mouth predisposes to dysphonia, dysphagia and dysgeusia
7. Complications may include caries, candidiasis, and sialadenitis – and lymphoma
8. Diagnosis is confirmed by detection of serum autoantibodies SS-A and SS-B, and other investigations. Diagnosis can be aided by ultrasound and a labial salivary gland biopsy
9. Management is with sialogogues and salivary substitutes, and preventive dentistry

Question 4

Recall the effects of smoking on the periodontium

Answer 4

Question 5

List 10 clinical manifestations of dry mouth (xerostomia)

Answer 5

Dry mouth (xerostomia) can cause:

1. Difficulty with eating
2. Difficulty with swallowing (dysphagia)
3. Difficulty with speech (dysphonia)
4. Trauma and ulceration of the oral mucosa
5. Gingivitis
6. Taste alteration (dysgeusia)
7. Poor oral hygiene
8. Burning mouth syndrome
9. Oral infections (including Candida)
10. Rapidly progressing dental caries

Question 6

Recall the structure of a salivary gland with reference to secretory end pieces (5 points) and the branched ductal system (3 points)

Answer 6

Structure of salivary gland

The working parts of the salivary glandular tissue:

• Secretory end pieces (acini):
  
  1. serous glands – spherical in form (parotid)
  2. mucous glands – tubular in form (sublingual)
  3. mixed glands - mucous acini capped by serous demilune (submandibular)
  4. end pieces surround a lumen - start of the ductal system
  5. myoepithelial cells surround end piece - propel secretion into the ductal system
• Branched ductal system, fluid passes through:
  
  1. intercalated ducts (low cuboidal epithelium with narrow lumen)
  2. striated ducts (columnar cells with many mitochondria)
  3. excretory ducts (cuboidal cells, terminal part lined with stratified squamous cells)
• The gland has a specialised nerve and blood supply

Question 7

Describe salivary secretion (4 points)

Answer 7

Salivary secretion:

• a unidirectional movement of fluid, electrolytes and macromolecules (e.g. glycoproteins, enzymes, immunoglobulin) into saliva in response to appropriate stimulation

Question 8

List the 2 key stages of saliva formation

Answer 8

Saliva formation involves 2 key stages:

1. Initial formation stage (primary secretion)
2. Modification stage (modified secretion)

Question 9

Describe the initial formation stage (primary secretion) of saliva

Answer 9

Initial formation stage (primary secretion):

1. Serous cells produce a watery seromucous secretion
2. Mucous cells produce a viscous mucin-rich secretion
3. Secretion of other organic constituents (e.g. amylase, lipase, IgA)
4. Pass through acinar cells, secreted into the lumen to ductal system
5. Isotonic solution (i.e. same Na+, Cl-, K+ and HCO3- concentrations as plasma)

Question 10

Describe the modification stage (modified secretion) of saliva formation:

Answer 10

Modification stage (modified secretion):

1. Modification occurs in the striated ducts
2. Secretion changes from isotonic to hypotonic solution:
   
   • Reabsorption of Na+ and Cl- out of saliva (lower than plasma)
   • But ductal cells are impermeable to water so cannot correct hypotonicity
   • Secretion of K+ and HCO3- into saliva (higher than plasma).

Question 11

Recall the overall process of saliva formation (primary and modified secretion)

Answer 11

Question 12

List the 3 key neural pathways of saliva secretion

Answer 12

Autonomic neural pathways of saliva secretion (3 key neural pathways):

1. Parasympathetic afferent pathways
2. Parasympathetic efferent pathways
3. Sympathetic efferent pathway

Question 13

Describe the parasympathetic afferent neural pathways of saliva secretion

Answer 13

Parasympathetic afferent neural pathways:

1. Primary afferent stimuli for salivation are taste and mastication
2. Afferent taste input carried to medulla oblongata via the facial (VII) and glossopharyngeal (IX) nerves
3. Input from mastication smell, sight and thought are also integrated in the medulla oblongata

Question 14

Describe the parasympathetic efferent neural pathways of saliva secretion

Answer 14

Parasympathetic efferent neural pathways:

• Sublingual and submandibular glands innervated by the facial nerve (VII) via submandibular ganglion
• Parotid gland innervated by the glossopharyngeal nerve (IX) via otic ganglion

Question 15

Describe the sympathetic efferent neural pathway of saliva secretion

Answer 15

Sympathetic efferent neural pathway:

• Via the cervical ganglion of the sympathetic chain to all glands

Question 16

Recall the autonomic effects on salivation with reference to neurotransmitters and receptors

Answer 16

Question 17

Recall the parasympathetic and sympathetic receptor action

Answer 17

Both receptors (β-adrenoceptors and M3 AChR):

• Belong to large and diverse G-protein coupled receptor (GPCR) superfamily
• GPCRs known to mediate responses to many hormones, neurotransmitters, and drugs
• Generate second messengers (IP3, Ca²⁺, cAMP)
• Second messengers are intracellular signalling molecules released by the cell to trigger physiological changes e.g. saliva secretion

Question 18

Describe the G protein-coupled receptor (GPCR) mechanism of action (4 points)

Answer 18

Mechanism of action of GPCRs (4 key stages):

1. Resting state – three subunits (α, β, γ) of the G protein are anchored to the membrane via lipid residues
2. Coupling of α subunit to agonist-occupied receptor causes bound guanosine diphosphate (GDP) to exchange with intracellular guanosine triphosphate (GTP)
3. The α-GTP complex then dissociates from the receptor and the βγ complex, and both complexes interact with their respective target proteins (enzymes or ion channels)
4. The intrinsic GTPase activity of the α subunit increases when it is bound to the target protein, leading to hydrolysis of bound GTP to GDP (switch off), and the α subunit reunites with βγ.

Question 19

Describe the mechanism of sympathetic stimulation and salivary production​ (7 points)

Answer 19

Sympathetic stimulation – synthesis and release of secretory proteins:

1. Neurotransmitter – noradrenaline (present as neurotransmitter across CNS and PNS)
2. Binds to GPCR on cell membrane – adrenoceptors
3. Activates G-protein – G-αs
4. Activates target enzyme – adenylyl cyclase
5. Adenylate cyclase converts intracellular ATP to secondary messenger – cAMP
6. The secondary messenger cAMP binds to and activates protein kinase A
7. Protein kinase A phosphorylates and activates cellular proteins responsible for the synthesis and secretion of salivary macromolecules (and decrease in flow rate as sympathetic stimulation)

Question 20

List the 3 key stages of the secretory process of salivary proteins (3 points)

Answer 20

The secretory process of salivary proteins is divided into 3 key stages:

1. Synthesis
2. Packaging and storage
3. Release

Question 21

Describe the secretory process of salivary proteins and protein regulation (4 points)

Answer 21

Each stage of the secretory process of salivary proteins is regulated by phosphorylation of target proteins by cAMP-dependent protein kinase A:

“The Proteins Must Release”

Therefore an increase in cAMP stimulates:

1. Transcription of genes for salivary proteins in ER of acinar cells – e.g. proline-rich proteins
2. Post-translational modification – glycosylation (folding, structure, function)
3. Maturation and translocation of secretory vesicles to the apical membrane
4. Release of salivary proteins via exocytosis

Question 22

Describe the mechanism of parasympathetic stimulation and salivary production (7 points)

Answer 22

Parasympathetic stimulation – fluid and electrolyte secretion (7 points):

1. Neurotransmitter – acetylcholine (ACh)
2. Binds to GPCR – M₃ ACh receptors
3. Activates G-protein – G-__αq
4. Activates target enzyme – phospholipase C
5. Phospholipase C cleaves PIP₂ from inositol trisphosphate (IP₃) and diacylglycerol (DAG)
6. The second messenger IP₃ binds to and activates IP₃ receptors (calcium release channels) on ER
7. Calcium release from IP₃ receptors for ER causes increase in intracellular [Ca²⁺], leads to Ca²⁺-induced calcium release. Raised intracellular [Ca²⁺] activates channels responsible for fluid and electrolyte secretion.

Question 23

Recall the mechanism of IP₃-mediated caclium release at the endoplasmic reticulum

Answer 23

IP₃R – Inositol trisphosphate receptor

RyR – ryanodine receptor

Note: crosstalk between initial IP₃R with neighboring RyR to augment Ca²⁺

Question 24

Describe how biological tissues establish an osmotic gradient for rapid fluid movement

Answer 24

Rapid fluid movement in biological tissues occurs by osmosis and is a multi-step process:

• Na⁺/K⁺ ATPase pump (antiporter system):
  
  • Makes use of ATP to pump 3 Na⁺ out of the cell (in exchange for 2 K⁺ into the cell)
  • This creates an inwardly directed Na⁺ gradient
  • This energizes the neighboring Na⁺/K⁺/2Cl^- co-transport system
• Ca²⁺-dependent K⁺ and Cl^- channels:
  
  • Na⁺/K⁺/2Cl^- actively pumps Cl^- from blood into acinar cells
  • High [Ca²⁺] inside the cell activates the Cl^- channels in the membrane
  • Cl^- channels facilitate the transport of Cl^- into the lumen down its electrochemical gradient
  • High [Ca²⁺] also activates the K⁺ channel causing K⁺ efflux
  • This maintains negativity inside the cell and preserves the driving force of Cl^- efflux
• Osmotic gradient:
  
  • Na⁺ follows Cl^- across the cell to maintain electroneutrality
  • The high luminal [NaCl] ‘pulls’ water through by osmosis

Question 25

Describe the mechanism of bicarbonate secretion (6 points):

Answer 25

Mechanism of bicarbonate secretion (6 points):

1. Carbon dioxide (CO₂) diffuses into the acinar cells reacts with water (H2O) to produce carbonic acid (H₂CO₃^-)
2. H₂CO₃ then dissociates into hydrogen (H⁺) and bicarbonate ions (HCO₃^-)
3. The Na⁺/K⁺ATPase pump exchanges K⁺ into the cell with Na⁺ moving out of the cell
4. This Na⁺ gradient drives the Na⁺/H⁺ exchange, in which H⁺ is transported out of the cell
5. If protons (H⁺) were not lost from the cell, carbonic anhydrase would be unable to generate HCO₃^-
6. The resulting HCO₃^- diffuses down its concentration gradient into the lumen (through Cl^- channels and so will be secreted when ACh triggers increase [Ca²⁺]i

Question 26

Compare the final composition and flow rate of saliva following stimulation and without stimulation

Answer 26

The final electrolyte composition of saliva varies depending on the flow rate:

• The best way to evaluate salivary gland function is to measure salivary flow rate in stimulated and unstimulated states

Question 27

List the major factors (8 points) and minor factors (5 points) affecting unstimulated saliva flow rate

Answer 27

Question 28

Degree of hydration is the most important factor that interferes with salivary secretion.

What is the percentage body water reduction beyond which salivary flow rate stops completely?

Answer 28

↓Body water by ≥ 8% ⇒ salivary flow stops completely

Question 29

Describe the effects of circadian rhythm on salivary flow rate and composition

Answer 29

Circadian rhythms:

• Unstimulated saliva flow is not constant in a 24-hour period:
  
  • Peak flow rate occurs in the late afternoon
  • Lowest flow rate in the early morning
  • Salivary protein and electrolyte concentrations (quality of the saliva) follows this diurnal pattern
• Clinically relevant that salivary flow rate is greatly decreased during night-time:
  
  • Increased caries susceptibility in those who consume fermentable carbohydrates just prior to sleep

Question 30

Describe the effect of circannual rhythm on salivary flow rate

Answer 30

Unstimulated saliva flow rate is higher during winter than during summer

Small change in temperature by 2°C in a warm climate will inversely affect the flow rate.

Question 31

List the factors affecting stimulated saliva flow rate (6 points)

Answer 31

Question 32

List the main factors affecting saliva composition (5 points)

Answer 32

Main factors affecting saliva composition:

1. Saliva flow rate (most important factor)
2. Duration of stimulus
3. Nature of stimulus
4. Circadian rhythm
5. Gland source

Question 33

Recall the relationship between saliva flow rate (mL/min) and electrolyte concentration (mEq/L)

Answer 33

Question 34

Describe the effect of low flow rates on saliva electrolyte composition

Answer 34

At low flow rates:

• More time for reabsorption and secretion, the modified saliva under resting conditions contains:
  
  • Low [Na+], ~15-20 mEq/L
  • Low [Cl-], 15-20 mEq/L
  • Low [HCO3-], 10-15 mEq/L
  • High [K+], 25-30 mEq/L
• HCO3- is an electrolyte that can also be reabsorbed by the striated ducts
  
  • Therefore, [HCO3-] in unstimulated saliva is low
  • When saliva is only needed for lubrication (less need for buffering when saliva is unstimulated between meals)

Question 35

Describe the effect of high flow rates on saliva electrolyte composition

Answer 35

At high flow rates:

• Less time for reabsorption and secretion – modified saliva is more like initial secretion by acinar cells:
  
  • [Na⁺] increases progressively to a plateau 80-90 mEq/L
  • [Cl^-] increases to ~50 mEq/L
  • [HCO₃^-] increases to 50-70 mEq/L
  • [K⁺] decreases to 15-20 mEq/L
• Increased secretion and failure to reabsorb HCO₃^- at high flow rates leads to much higher [HCO₃^-]
• High [HCO₃^-] saliva with high buffering capacity needed during and just after eating

Question 36

Compare the relative contribution of different salivary glands

Answer 36

Question 37

Describe the effects of gustatory stimulation and food intake on saliva composition (4 points)

Answer 37

Effects of gustatory stimulation and food intake on saliva composition:

1. Acidic food (e.g. citric acid) is the most effective stimulant (compared to salt, bitter and sweet)
2. Direct input from the taste receptors to the medullary salivation centres:
   
   • If food is held in the mouth without movement, the flow rate decreases
   • However if it is moved around, activating new taste receptors, flow rate increases again
3. Even the presence of very bland food in the mouth (rice) causes an increase in salivation rate.
4. Foods which stimulate multiple different receptors e.g. acid and sweet (fruit pie) can increase to ~70% of maximum flow rate.

Question 38

Recall the anatomy and neurolgy of gustatory sense

Answer 38

Question 39

Compare the effects of mechanical stimulation with gustatory stimulation on salivary flow rate (mL/min)

Answer 39

Gustatory stimulus is of more significant than the mechanical stimulus of chewing:

Question 40

Recall the major components of saliva and their function

Answer 40

Question 41

Describe the protein macromolecules which make up 1% of saliva composition

Answer 41

Saliva is about 99% water, but contains 1% protein macromolecules:

1. Mucins – heavily glycosylated glycoproteins (MUC5B and MUC7)
   
   • Submandibular, sublingual and minor mucous glands
2. Proline-rich glycoproteins (PRGs) – glycosylated
   
   • Parotid glands (P = proline-rich, P = parotid)

Provides lubrication with slimy, viscoelastic coating of all surfaces in oral cavity:

• Between opposing surfaces during mastication, swallowing and speaking
  
  • These three processes are very difficult for patients with Sjögren’s syndrome

Question 42

Recall the relationship between taste and smell

Answer 42

Taste and smell are related because they use the same types of receptors stimulated by molecules in solutions or air:

• Aromas are detected by olfactory receptors in the nose, stimuli reach these:
  
  • During the inhalation of air containing the aroma
  • Via the nasopharynx during the food consumption
• Saliva is involved in this process by incorporating into the food bolus
  
  • Melting, warming, cooling and liquefying action on food
• More liquefied bolus - favours flavour release
  
  • Increases the contact area between the bolus and the oral and pharyngeal mucosa
• Saliva acts is a solvent – allows interaction of foodstuff with taste buds to facilitate taste
• Interaction of taste substances in solution with specific taste receptors present on taste buds
• Once tastant is close to a taste bud it diffuses through the salivary film which normally coats the oral mucosa

Question 43

List the 5 recognized basic taste groups in order of their effectiveness as salivary stimulants

Answer 43

There are five recognised basic tastes groups – in order of their effectiveness as salivary stimulants:

1. Sour
2. Salt
3. Bitter
4. Sweet
5. Umami

Question 44

Describe the first and second lines of defence exhibited by taste receptors

Answer 44

Reflex stimulation of salivary flow, especially bitter taste receptors (noxious taste)

1. First-line of defence → spit out
2. Second-line of defence → cough and vomit it out

The first line of defence – saliva and taste receptors on tongue:

• Dilutes any material taken into the mouth e.g. noxious taste
• This is actively spat out before reaching the rest of the digestive tract
• Bitter taste of poison > sour taste of spoiled foods

The second line of defence – taste receptors on airways and digestive tract

• Expelling noxious substances from the body by way of initiating coughing or vomiting

Patients with Sjögren’s syndrome - the oral mucosa is very dry:

• Damaged taste buds may exhibit elevated taste thresholds and so may have reduced taste perception (and potentially reduced defensive reflex)

Question 45

Describe the role of saliva in digestion

Answer 45

Saliva and digestion:

• Initial chewing of a portion of food causes formation of a cohesive food bolus:
  
  • Covered by a mucin film, which facilitates the swallowing process
• The main protein and (digestive enzyme) in saliva is α-amylase:
  
  • Acts on the α-1,4-glycosidic bonds to breakdown starch into maltose (disaccharide), maltotriose (trisaccharide) and other oligosaccharides
  • Primarily present in parotid saliva
  • Concentrations in submandibular and sublingual saliva are < ¼ of those in parotid saliva
• Lingual lipase (von Ebner glands in the human tongue) can theoretically initiate lipid digestion:
  
  • Hydrolyses long-chain triglycerides into partial glycerides and free fatty acids
  • However quantities are insignificant compared to gastric lipase.

Question 46

Recall the role of salivary carbonic anhydrase in carbonic acid equilibrium

Answer 46

Buffering action

Question 47

Describe the role of saliva and related mucosal secretions in the protection of the oesophagus (4 points)

Answer 47

Protection of the oesophagus:

1. Saliva softens and lubricates food bolus:
   
   • Reduces sharp edges
2. Oral mucosal pellicle:
   
   • Thin layer of salivary proteins including mucins attached to oral mucosal cells
   • Acts as lubricant between tissues – teeth, tongue, cheeks to provides protection
3. Oesophagus (protection during gastric reflux):
   
   • Oesophagus mucous glands secrete mucins and bicarbonate
     
     • Forms protective layer, swallowed salivary mucins contribute
4. Epidermal growth factor (EGF) secreted from parotid saliva
   
   • Acts on oesophagus EGF receptors to promote mucosal cell proliferation

Question 48

List 3 key drug groups associated with drug-induced gingival overgrowth (DIGO)

Answer 48

Key drug groups associated with DIGO:

1. Anticonvulsants
2. Caclium channel blockers
3. Immunosuppressants

Question 49

Describe the anticonvulsants associated with DIGO and the clinical manifestations

Answer 49

Phenytoin:

• Phenytoin is indicated in grand mal, temporal lobe, and psychomotor seizures
• Estimated prevalence of phenytoin-induced gingival overgrowth is ~50%
• Clinical onset occurs as early as 1 month, and increasing severity is seen in 12 to 18 months
• Phenytoin-induced gingival overgrowth lesions frequently occur on the anterior buccal maxilla and mandible
• The entire dentition may be involved in severe cases
• Phenytoin-induced gingival overgrowth is characterized by enlargement of interdental papillae and increased thickening of the marginal tissues, → aesthetic and functional problems:
  
  • Malpositioning of teeth
  • Difficulty in speech
  • Impaired oral hygiene.
• Phenobarbital and sodium valproate have been associated with DIGO less often than phenytoin.

Question 50

Describe the caclium channel blockers associated with DIGO and the clinical manifestations

Answer 50

Different types of CCBs have been associated with some degree of DIGO:

• Non-dihydropyridines:
  
  • Benzothiazepine derivatives, e.g., diltiazem
  • Phenylalkylamine derivatives e.g., verapamil
• Dihydropyridines (e.g., amlopidine, felodipine, isradipine, nicardipine, nifedipine, nitrendipine, oxodipine, nimodipine, nisoldipine)

Among patients taking the medication, the prevalence of nifedipine-induced gingival overgrowth is highly variable, ranging from 6% to 83%.

Clinically, interdental papillae are affected, and overgrowth is limited to attached and marginal gingiva, which usually is observed on the anterior segments.

Nifedipine-induced gingival overgrowth can coexist with periodontitis and attachment loss that is different from other forms of DIGO.

Question 51

Describe the immunosuppressants associated with DIGO and the clinical manifestations

Answer 51

Cyclosportin A:

• Cyclosporin A has been the immunosuppressant of choice for preventing rejection of solid organ and bone marrow transplants and for treatment of autoimmune conditions.
• The prevalence of cyclosporin A–induced gingival overgrowth has been reported to be about 30% but it can be much higher, especially for pediatric populations.
• Clinically, the lesions are more inflamed and bleed more than other forms of DIGO, and they commonly are limited to buccal surfaces.
• Severity of the lesions can be similar to those of phenytoin and nifedipine.
• They affect the entire dentition and interfere with occlusion, mastication, and speech.

Question 52

Recall the histology of DIGO with reference to phenytoin, nifedipine and cyclosporin A

Answer 52

Phenytoin:

• Fibrosis
• Thick, stratified squamous epithelium with long, thin rete pegs extending deep into connective tissue

Nifedipine:

• Similar to phenytoin-induced lesions

Cyclosporin A:

• More inflammatory infiltration and increased vascularization compared with phenytoin and nifedipine

Question 53

Define calculus (3 points) and list 2 key types

Answer 53

Calculus:

• Dental calculus is an adherent, calcified mass that forms on the surfaces of teeth and dental appliances.
• It is covered on its external surface by vital, tightly adherent, nonmineralised plaque.”

Key types of calculus

1. Supragingival calculus:
   
   • Forms on the clinical crowns of teeth above the free gingival margin ⇒ clinically visible.
   • It is also called salivary calculus because it forms from the saliva and therefore commonly forms next to salivary duct openings
2. Subgingival calculus:
   
   • Calcified deposits formed on the root surfaces below the free marginal gingiva ⇒ not clinically visible
   • It is believed to be formed from the gingival exudate and hence called
     serumal calculus

Question 54

Describe the precipitation theory of calculus formation

Answer 54

Precipitation theory:

• Loss of carbon dioxide and formation of ammonia leads to increase in the pH which leads to the precipitation of calcium phosphate salts.

Question 55

Describe the nucleation theory of calculus formation

Answer 55

Nucleation theory:

• Seeding agents induce small foci of calcification that enlarge and unite together to form calcified mass.
• The carbohydrate–protein complexes may initiate calcification by removing calcium from the saliva and binding with it to form nuclei that induce deposition of minerals.

Question 56

Describe the inhibition theory of calculus formation

Answer 56

Inhibition theory

• Calcification occurs only at specific sites because of the existence of an inhibiting mechanism at non-calcifying sites.
• Where calcification occurs, the inhibitor is apparently altered or removed.
• Inhibiting substance is thought to be pyrophosphate and among the controlling mechanism is the enzyme alkaline pyrophosphatase, which can hydrolyse the pyrophosphate to phosphate ⇒ disinhibition of calcification
• The pyrophosphate inhibits calcification by preventing the initial nucleus from growing, possibly by “poisoning” the growth centres of the crystal

Question 57

Recall the aetiology of sialorrhea associated with Parkinson’s disease

Answer 57