Degenration and damage

Question 1

2 forms

Answer 1

chemical degeneration (corrosion and staining)
mechanical (wear and fracture)

Question 2

corrosion - chemical

Answer 2

this is errosion/demineralisaton of enamel

Causes:
chewing acidic food
bulimia as a result of stomach acid (occurs on lingual = tongue facing) surface of teeth
acidic fizzy drinks
acidic by products from plaque related bacteria

occurs at enamel-cementum junction

Question 3

protection against corrosion - chemical

Answer 3

prevent exposure to corrosive agents

increase Flourine conentent, as in enamel FA more resiistant to acid than HA –> F from water/toothpaste

Question 4

tooth staining - chemical

Answer 4

causes:
loss of vitality (nerves die)
intake of drugs
diseases during tooth development

dead teeth change colour:
loss of pulpial fluids
dentine darkens, yellow-brown, brown-grey

pink colouration: leakage from pulp

nicotine & alcohol cause staining

Question 5

mechanical degeneration

Answer 5

wear: loss of material becuase of removal & relocation of materal from a surface

3 types:
adhesive wear
abrasive wear
3 body wear

Question 6

adhesive wear - mechanical degeneration

Answer 6

pressure welds when 2 surfaces forced together:
materials (similar or disimilar) under v high stress can join together
low area of contact = v high stresses
failure in the weaker material when there is sliding
leaves a layer of weaker material behind

not common: saliva is lubricant

adhesive wear normally for 2 dismilar materials = disimilar mechanical properties

Question 7

abrasive wear - mechanical degeneration

Answer 7

hard protuberance ploughs through softer material
leads to scratches on softer surface

causes:
tooth brushes on teeth (hard/wrong direction of brushing)
soft filings/ restoration by opposite tooth
teeth against teeth (ezp.when 1 is weaked by decay)
excessive tooth brushing
grinding of teeth

Question 8

third body wear - mechanical degeneration

Answer 8

hard particle trapped b/n 2 surfaces
particle may get embeed on softer material
damages tooth surface
in microscope: appears similar to abrasive wear

not common: saliva acts as lubricant

causes:
hard food caught b/n teeth
broken bit of metals (e.g. amalgam filings)
hard particles de-bond from composite retorations

Question 9

other forms of - mechanical degeneration

Answer 9

fracture due to trauma or fatigue

fatigue fracture: cyclic loading of free particles = localised stress concentration = surface or sub surface cracks

particles break off under cyclic loading

Question 10

surface fracture - mechanical degeneration

Answer 10

chewing v hard particles = subsurface craks = tooth fracture

Question 11

crack propagation

Answer 11

each load applied = stress in area od microscopic inital flaw
energy applied breaks atomic bonds around crack tip
each load cycle = longer/ additonal microcraks
sufficent cracks = removal of section of surface