dental material science need to know Flashcards
explain gaseous porosity
voids in the material occurring when PMMA is cured fast
monomer boils
usually happens in a thicker section of the acrylic
what are the constitutes of gutta-percher?
20% GP
65% zinc oxide
10% radiopacifier
5% plasticiser
what are the properties of non-setting calcium hydroxide?
high pH- antimicrobial factors
hydrolysis pf LPS reduce inflammatory potential
removal of tissue debris
what are the constitutes of stainless steel?
72% iron
18% chromium
8% nickel
1.7% titanium
0.3% carbon
what is work hardening?
work done on metal below its recrystallisation temperature causes slip
slip= dislocations collect ar grain boundaries hence stronger, harder material
the hard wire is made by drawing the metal in a cold state through a series of dies of successively smaller diameter
this makes it stronger and gives it spring properties
define springiness
can undergo large defelctions without permanent deformation
give disadvantages of self cure PMMA
poor mechanical properties
not suitable for pts w residual monomer allergy
What is the use of a cavity base?
to minimise bulk of material
blocks out undercuts
what kind of reaction takes place when mixing the base and catalyst for calcium hydroxide?
chelation reaction
what is the use of a cavity lining material
thin coat of material over the dentine and pulp
has pallative effect
what reaction occurs in ZOE cement
acid base reaction
what is the composition of the base for calcium hydroxde lining material?
- calcium hydroxide
- zinc oxide
- plasticiser
what chemicals react in ZOE cement and what is formed
ZnO and eugenol form zinc eugenolate
what is the strongest ZOE and why
EBA ZOE due to addition of quartz and aluminium
what takes part in the chelation reaction when mixing caclium hydroxide?
base- zinc oxide
catalyst- butylene glycol disalicylate
what pH is calcium hydroxide?
pH 12
what are uses of ZOE cement
lining material
temporary restoration
Root canal sealer - slow set 24 hours
what is the advantage of calcium hydroxide being highly alkaline?
kills bacteria
what are properties of ZOE
rapid set
good working time
low thermal conductivity
radiopaque
High soluble
name 4 properties of calcium hydroxide
- soluble
- alkaline
- irritant- stimulate tertiary dentine formation
- radiopaque
explain advantage and disadvantage of ZOE’s solubility
advantage - eugenol is continually released which releives pain
disadvantage - soluble in water so eugenol is released and this inhibits setting of resin materials
eugenol also discolours resin materials
what is a contraindication of using ZOE
cannot place under a composite restoration as it affects bonding
when should calcium hydroxide be used?
as a direct or indirect pulp cap under deep restorations
why does calcium hydroxide need to be covered with a RMGIC?
soluble- prevents dissolution
what kind of bond is formed when etching an GIC?
micromechanical bond
What type of ZOE is least soluble resin modified or normal
resin modified so can use under amalgam filling
What form of cement is the least soluble
RMGIC
What is a contraindication of using GI near the pulp
any unreacted HEMA is cytotoxic to the pulp
list ideal properties of lining materials
- pulpal protection
- therapeutic
- radiopaque
- bond to dentine
- low solubility
- cariostatic
- low thermal expansion and conductivity
how can a lining material give pulpal protection?
- thermal- exothermic reaction of composite/heat conducted through metal restorations
- chemical- unreacted chemicals/pH of restorative materials
- bacterial- against microleakage
what property of GI makes it bettern than other lining materials
It bonds to enamel and dentine forming a better marginal seal
how does RMGI kill bacteria
polymerisation of RMGI releases cytotoxic enzymes
what does it mean if a lining material is “therapeutic”?
- reduces inflammation
- promotes healing
what is the significance of a lining material being radiopaque?
can be viewed radiogrpahically if displaced from tooth
allows for microleakage to be seen radiographically
explain the thermal properties of GI and their significance
thermal conductivity is less than dentine (RMGI and GI)
thermal expansion is similar to dentine (GI)
during exposure to heat the GI will react similarly to dentine which will maintain seal of material
give an example of how a lining material can be cariostatic?
release fluoride
Explain GI interaction with dentine tubules and its significance
GI seals dentine tubules
this decreases micro-leakage and decreases sensitivity
what is the reason for using a lining material in a pt with reversible pulpititis?
pallitave care- eases the pts symptoms
What is an advantage of using GI over other cements
it releases fluoride = CARIOSTATIC
What does the initial gradient on a graph show
young’s (elastic) Modulus
what type of alloy is stainless steel?
wrought alloy- can be cold worked
What is indicated by the change in gradient on the stress strain curve
the proportional limit
what are the components of stainless steel?
- 72% iron
- 18% chromium
- 8% nickel
- 1.7% titanium
- 0.3% carbon
what is the role of chromium in stainless steel?
corosion resistance
what is the role of nickel in stainless steel?
corosion resistance
increase strength
What is proportional limit and explain it
The stress applied before a material behaves inelastically
> proportional limit will result in deformation
< proportional limit - the material will return to the original shape
what is the role of titanium in stainless steel?
prevents precipitation of chromium carbide at grain boundaries
what does the end of a line in the stress strain curve show?
fracture stress
What is translucency
Ability for light to pass through a material but be scattered, at one of the surfaces or internally, leading to blurring of transmitted light
give 3 properties of stainless steel
- springiness
- ductile
- corrosion resistant
how does weld decay affect stainless steel?
makes it brittle
What is opalescence
the ability of translucent material to appear blue in reflected light and orange/yellow in transmitted light
define springiness
the ability to undergo large deflection WITHOUT deformation
what makes steel classed as “stainless” steel?
contians at least 12% chromium
Define cold working
Shaping a material below its recrystallisation temperature
Define slip
Defects in a grain move to grain boundaries this results in fewer defects in the lattice structure
what does it mean by classing iron as ‘allotropic’?
undergoes 2 solid state changes due to temperature
What is an alloy
2 or more metals that form a common lattice structure and are soluble in one another
define creep
repetitive small forces that cause gradual dimensional change
define Fatigue
Repetitive small stresses that because fracture
what are the 2 types of acrylic used in dentistry?
self cure
heat cure
give an advantage of heat cure PMMA
has a higher molecular weight than self cure
this means better mechanical properties
what are ideal properties of luting agents
low viscosity - increases as it sets
low film thickness - <25 um
easy to use
Radiopaque
Good marginal seal
Low solubility
Cariostatic
Non-toxic
High compressive strength
High hardness
give a disadvantage of heat cure PMMA
gaseous porosity occurs if cured too fast
results in process taking far to long to avoid this
What does dual cure material mean
cured by:
- light
- cures on its own by REDOX reaction
what are the ideal properties of acrylic?
- non-toxic
- non-irritant
- unaffected by oral fluids
- high softening temperature
- low density- lightweight
- low thermal conductivity
What are issues with HEMA
- cytotoxic to the pulp
- swells
when can you not use RMGI as a cement
for porcelain - it swells cracking the crown
for posts - it will swell and split the root
give an advantage of self cure PMMA
polymerisation doesnt require heat- less thermal contraction means a better fitting denture
RMGI does not bond to indirect restorations so what chemical is needed
composite luting agent
how does dentine bonding agent bond composite luting agent to the tooth
hydrophilic end bonds to tooth
hydrophobic end bonds to composite
give 2 disadvantages of self cure PMMA
polymerisation is less efficiant, meaning there are more unreacted monomers
irritant/allergy issues
lower molecular weight= reduced transverse strength
how can self cure PMMA dentures become oversized?
they absorb water and expand
what is free radical polymerisation?
chemical union of 2 molecules to form a larger molecule without elimination of the smaller molecule
How does composite luting agent bond to indirect restorations
chemical bond forms between C=C
micro-mechanical bond forms between composite luting agent and the rough inside surface of indirect restoration
what type of bonds are present in the molecules that undergo free radical polymerisation?
C=C
How do you improve bonding to porcelain
etch the surface with hydrofluric acid
what are the 4 stages of free radical polymerisation?
activation
initiation
propagation
termination
What is required to bond composite luting agent to porcelain/ceramics
Silane coupling agent
How does silane coupling agent bond to composite luting agent and porcelain/ceramics
C=C bonds from silane coupling agent react with similar groups in the composite luting agents
hydroxyl groups in the silane coupling agent react with oxide groups on the porcelain surface
What is needed to bond composite luting agent to metal
Metal bonding agent
What are examples of metal bonding agents
MDP and 4-META
What is important when using compoosite luting agent to bond to metal
must use a self cure composite as light cannot penetrate through metal
How does metal bonding agent bond metal to composite luting agent
C=C bonds in metal bonding agent react with similar groups in the composite luting agent
Acid end of metal bonding agent reacts with metal oxide
What is a self adhesive composite resin
composite luting material with metal bonding agent in it
What is an example of a Self adhesive composite resin luting agent
Panavia
How do you bond an indirect retention to the tooth
Tooth
DBA
Composite luting Agent
Indirect retention
How do you bond porcelain/ceramic to the tooth
Tooth
DBA
Composite luting agent
Silane coupling agent
Porcelain/Ceramic
How do you bond metal to the tooth
Tooth
DBA
Composite luting agent
Metal bonding agent
Metal
