Cavity Lining Materials Flashcards
what are some common materials that are placed in tooth cavities
composite resin
glass ionomer
amalgam
precious metal
non precious metal
ceramic
what are disadvantages of restorative materials
- may not make intimate contact with the tooth surface, especially with dentine, which can create gaps that allow for micro leakage of oral fluids, developing caries
- heat is released during setting and curing which can fry the pulp
- release of chemicals due to any reactions, which can irritate and lead to pain or pulpal damage
how can microleakage occur with dental materials
when the material sets and does not sit tightly to the edge of the tooth, this creates a gap developing at the side
what is the solution to the issues with restorative materials and microleakage
using an intermediate restorative material called a lining material, which prevents gaps and acts as a protective barrier
what are cavity base materials and are they the same as the cavity lining materials
they are a form of intermediate restoration to put into the tooth cavity in bulk to replace as much of the dentine as possible as well as blocking undercuts for inlays and inlays. they are not the same as lining materials; those are thin coatings with exposed dentine
what is the cavity base
a thick mix placed in bulk, dentine replacement is used to minimise the bulk of the material or block out undercuts
most commonly used in metal restorations
what is cavity lining
this is a thin coating over exposed dentine, usually no more than 0.5mm
what are the purposes of liners
- pulpal protection
- therapeutic
- palliative
what does liner protect the pulp from
chemical stimuli
thermal stimuli
bacteria and endotoxins
why does liner need to protect the pulp from chemical stimuli
there can be some chemical stimuli from unreacted chemicals in the filling material or the initial pH of the filling which can irritate the pulp
what is the thermal stimuli that the liner protects the pulp from caused by
exothermic setting reaction of composite or heat conducted through metal fillings
why is there bacteria and endotoxins present that the pulp are protected from via the liners
due to microleakage, oral fluids and bacteria and toxins can enter in the gap between the restorative and cavity walls
describe the therapeutic purpose of liners
calms down inflammation within the pulp and promotes pulpal healing prior to or at the time of a permanent restoration being placed
describe the palliative function of liner
reduce patient symptoms prior to definitive treatment being carried out, which is most commonly used in patients with reversible pulpits
what are the main properties of lining materials
ease of use
thermal properties
mechanical properties
radiopaque
marginal seal
solubility
cariostatic
biocompatible
compatible with restorative materials
describe the ideal ease of use of lining materials
they are easy to mix, and the working time is usually long enough to allow easy placement, and the setting time is short due to curing lights
what does command set mean
using a curing light to set the material
describe the ideal thermal properties of lining materials
- should be low conductivity so heat is not transferred to the pulp
- thermal expansion coefficient should be similar to dentine
- thermal diffusivity should be similar to dentine or lower
what is thermal conductivity
how well heat energy is transferred through a material
how is thermal conductivity of a material determinde
heat flows through a cylinder of unit cross sectional area and unit length, with a temperature difference of 1 degree celsius between the ends
what are the units of thermal conductivity
W/m-1/degree celcius-1
ideal thermal conductivity for denture base
high
ideal thermal conductivity for restorative material
low
ideal thermal conductivity of lining base
as low as possible
why is it important that denture bases have high thermal conductivity
so that the people wearing the denture can still feel the heat of what they are consuming, therefore preventing the consumption of anything that is too hot and would burn them
what is the thermal expansion coefficient
this is the change in length per unit length for a temperature rise of 1 degree celcius
basically, apply heat to something and see how much it expands
what are the units for the thermal expansion coefficient
how should the thermal coefficient of the liner compare to the tooth and why
should match the properties to the tooth tissue as much as possible
what is the thermal coefficient value for enamel
8.3
what is the thermal coefficient value for dentine
11.4
what is the thermal coefficient value for GIC
11
what is the thermal coefficient value for RMGIC
20
what is the thermal coefficient value for composite
25
what is the thermal coefficient value for amalgam
25
what is thermal diffusivity
this is similar to conductivity, looking at the dissipation of heat through different areas
what is thermal diffusivity measured in
cm2 / sec
what should the thermal diffusivity value be
as low as the tooth
thermal diffusivity value of enamel
0.0042 cm2/sec
thermal diffusivity value of dentine
0.0026 cm2/sec
what is the thermal diffusivity value of amalgam
1.7cm2/sec
what should the mechanical properties of lining materials be
high compressive strength and a modulus similar to dentine
why is it important for lining materials to have high compressive strength
to allow placement of filling without it breaking
what is the compressive strength of dentine
275 MPa
what is the modulus of dentine
around 15 GPa
what is modulus
looks at how much a material distorts when you apply a force to it
describe how the radiopacity of lining materials should be
should be easy to see the difference between the lining and the tooth. this makes it easier to see if there is any leakage or secondary caries
describe how the marginal seal of lining materials should be
ideally the tooth should form a chemical bond to dentine, which should be permanent and impenetrable and strong
why is it important that the solubility of lining materials is low
if there is a gap and an ingress of oral fluid that reaches the cavity lining material, it would dissolve away and leave a gap in the lining, creating the opportunity for caries and infection within the pulp. so the lower the solubility the less likely this is to happen
describe how lining materials are cariostatic
they stop the development of caries through fluoride release, which is an antibacterial ion. this is an important property to prevent secondary caries around the restoration
describe the biocompatibility of lining materials in the ideal world
non toxic and non damaging to the pulp
pH neutral
no excessive heat release during setting
low thermal conductivity
what kind of material is setting calcium hydroxide
liner
what kind of material are zinc oxide based elements
base
what kind of material are glass ionomer and resin modified glass ionomer cements
bases or liners
what kind of material are palliative cements
bases, seldom used nowadays, and are mainly historic
what is the chemical composition of calcium hydroxide
Ca(OH)2
what are the two main calcium hydroxide liners used
Life and Dycal
describe how setting calcium hydroxide liner comes in clinic
one tube is the base and the other is the catalyst.
describe the base constituent of setting calcium hydroxide liner
50% calcium hydroxide
10% zinc oxide, acting as a filler
less than 1% zinc stearate, acting as a filler
n-ethyl toluene sulphonamide (plasticiser) at 40%
describe the constituents of the setting calcium hydroxide liner catalyst element
butylene glycol dvisalicylate is the reactive element at 40%
titanium dioxide at 13-14% to act as a filler
calcium sulphate at 30% to act as a filler
15% calcium tungstate to act as a filler and to be radiopaque
what is the reason for adding a radio pacifier to the setting calcium hydroxide liner
so it can be detected on a radiograph as a lining material and not part of the tooth or the restorative material
what is the function of the plasticiser in the base constituent of setting calcium hydroxide liner
to allow the liner to be manipulated and moved during placement
what is the setting reaction for the calcium hydroxide liner
a chelation reaction between zinc oxide and the butylene glycol dvisalicylate, which results in a cement with an initial pH of around 12
what is a chelation reaction
one in which the metal ions reacts with organic agent and this removes the metal ion from the vicinity.
what are the two modes of action for the calcium hydroxide liner
it is bactericidal to cariogenic bacteria, and it causes irritation which leads to the formation of reparative dentine
why is calcium hydroxide liner bactericidal to cariogenic bacteria
the cariogenic bacteria need to be in an acidic environment, so the highly alkaline nature of the liner kills them by creating unfavourable conditions.
how does the calcium hydroxide liner irritate and form tertiary dentine
the cement causes irritation to the odontoblast layer, and necrosis follows which in turn results in a layer of tertiary dentine being produced. this eventually forms a calcified bridge walling the base of the cavity off from the pulp. the calcium comes from the pulp, not the cement.
the tertiary dentine makes the pulp shrink away to protect it.
what are the properties of calcium hydroxide liner
quick setting time
radiopaque
easy to use
low compressive strength (brittle)
unstable
soluble
why is it not good that calcium hydroxide liner is soluble
if the cavity leaks then the lining will disappear, and may even disappear just because it is in contact with moist dentine
what are the zinc oxide based cements
- zinc phosphate
- zinc polycarboxylate
- zinc oxide eugenol
- resin modified zinc oxide eugenol
- ethoxybenzoic acid zinc oxide eugenol
what is ZOE
zinc oxide eugenol
what is resin modified ZOE
resin modified zinc oxide eugenol
what is EBA ZOE
ethyoxybenzoic acid zinc oxide eugenol
what kind of reaction occurs with zinc phosphate cements
acid base reaction
what are the two components of zinc phosphate cement
powder and liquid
describe the powder component of zinc oxide cement
this is the main component.
over 90% zinc oxide, which is the main reactive ingredient
less than 10% magnesium dioxide, which gives the white colour and increases the compressive strength
other oxide like alumina and silica improve the physical properties and alter the shade of the set material
describe the liquid component of zinc phosphate cement
an aqueous solution of phosphoric acid, around 50%.
also contains oxides which buffer the solution to keep it as neutral as possible and to ensure it is consistent when set
what are the oxides in the liquid component of zinc phosphate cement and what are their functions
aluminium oxide, which ensures an even consistency of the set material
zinc oxide which slows the reaction giving better working time
what is the initial reaction for zinc phosphate cement
an acid base reaction
what is the second reaction for zinc phosphate cement
a hydration reaction resulting in the formation of a crystallised phosphate matrix
what is the function of aluminium oxide in zinc phosphate cement
prevents crystallisation leading to an amorphous glassy matrix of the acid salt surrounding the zinc oxide powder
describe the glassy matrix of the acid salt surrounded unreacted zinc oxide powder in the zinc phosphate cement
insoluble, porous and containing free water form the setting reaction
the cement binds to the water to create a stronger, less porous material
what are the problems with zinc phosphate cement
- low initial pH around 2
- exothermic setting reaction
- not adhesive to the tooth or to the restoration
- not cariostatic
- final set takes 24 hours
- brittle
- opaque
describe why a low initial pH for zinc phosphate cement is not a good thing
it can cause pulpal irritation as pH can take 24 hours to return to neutral
how is the zinc phosphate cement retention increased
could be micro mechanical due to surface irregularities in the cavity but it does not adhere to the tooth or to the restoration
why is the opacity of zinc phosphate cement not ideal
if there are thin areas of enamel with the material underneath, it can shine through and compromise the aesthetic of the tooth
describe zinc polycarboxylate cement
this is a similar material to the zinc phosphate cement, but the phosphoric acid is reacted by polyacrylic acid
why is zinc polycarboxylate cement better than the zinc phosphate
it bonds to tooth surfaces in a similar way to glass ionomer cements
less heat of reaction
pH is low to begin with but returns to neutral more quickly and there are longer chain acids which do not penetrate dentine as easily
cheap
what are the disadvantages of zinc polycarboxylate cements
difficult to mix and manipulate
soluble in an oral environment at low pH
opaque
lower modulus and compressive strength than zinc phosphate
what are ZOE cements used for
linings and base material in deep cavities, under amalgam restorations
temporary restorations (RMZOE or EBAZOE)
root canal sealer (slow setting though, 24hrs)
periodontal dressings (fast setting, 5 minutes)
describe the use of ZOE in periodontal dressings
coe pak - eugenol free zinc oxide, protects wounds from being contaminated with saliva as much as possible. kept there for a week
describe ZOE
base acid reaction
base is zinc oxide
acid is eugenol
draw out the chelating reaction of zinc oxide with eugenol
describe the setting reaction of ZOE
chelation reaction of zinc oxide with eugenol to form zinc eugenolate matrix which bonds the unreacted zinc oxide particles
what are the properties of ZOE
adequate working time
rapid setting time, sets quicker in the mouth due to moisture and heat
modified by additional of accelerators
low thermal conductivity
low strength around 20 MPs
weak hydrogen bonds between eugenolate molecules
not strong enough to use as a base beneath an amalgam filling, packing pressure damages it
radiopaque
describe the solubility of ZOE
high solubility and prone to disintegration eugenol is constantly released, which is replaced by water which leads to disintegration of the material but when eugenol is liberated, there is an obtundant effect on the pulp which can reduce pain
why should ZOE materials not be used under composite resin materials
the released eugenol inhibits the set of resin based filling materials, and softens them to cause discolouration
describe RMZOE
resin modified zinc oxide eugenol
resins are added to the powder and the liquid, they do not take part in the reaction by give a stronger backbone to the set material which increases the compressive strength to over 40MPa to make it a suitable cavity liner.
the resin reduces the solubility as well
what is the resin in IRM
polymethylmethacrylate
what is the resin in kalzinol
polystyrene
describe EBA ZOE
ethoxybenzoic acid cement, is another modification for ZOE
EBA is the reactive agent, and there are different filler particles to toughen the material up
what are the components of the powder part of EBA ZOE
65% zinc oxide
35% quartz or alumina (fillers)
hydrogenated rosin 6%
what are the components of the liquid part of the EBA ZOE
37% eugenol
63% EBA
describe the setting of EBA ZOE
same as with ZOE, but with EBA to encourage a crystalline structure which imparts greater strength to the set material
what are the properties of EBA ZOE
stronger than ZOE or resin modified ZOE, around 60MPa, and less soluble
describe glass ionomer lining materials
these are the most widely used lining materials, and they can bond and seal to the dentine
can also bond to composite resin filling placed over it, and can release fluoride over time to be cariostatic
describe the use of glass ionomer lining material
easy, mixing is simple and many materials will come as two paste clicker system
light cured and command set. gives a long working time and a conveniently short setting time of around 30 seconds
describe the properties of glass ionomer lining materials
thermal conductivity and diffusivity are lower than dentine for both GIC and RMGIC
thermal expansion is similar to dentine
compressive strength is over 170MPa, higher than any zinc oxide based materials
most materials are radiopaque, with radiopacity varying between each
marginal seal is better than any other materials as there is a chemical bond to the enamel and the dentine
describe the interaction of glass ionomer cements with dentinal tubules
they predictably seal the tubules, decreasing microleakage and helping prevent post treatment sensitivity
which lining cement is the least soluble
resin modified glass ionomer
what is released from GIC materials
- fluoride (cariostatic)
- benzoyl iodides and benzoyl bromides
- unreacted HEMA
describe the release of benzoyl iodides and bromides from glass ionomer lining materials
they are released during the polymerisation reaction of resin modified glass ionomer cements, and are cytotoxic which is effective against residual cavity bacteria
why is complete cure of RMGIC required
unreacted HEMA can damage the pulp
why should RMGIC never be placed over direct pulp exposure
materials released can be cytotoxic which can also kill the pulpal cells alongside bacteria.
which lining material can bond to restorative materials
glass ionomer cements
do RMGIC require surface treatment
no
what are the dental hospital lining guidelines for cavities in dentine
consider using a lining of RMGIC such as vitrebond for amalgam and for larger cavities to be filled with composite
when should calciumhydroxide be used as a lining material in the dental hospital
only when the cavity approaches the pulp, either as direct or indirect pulp cap over the deepest part of the cavity
what should calcium hydroxide be covered with prior to the final restoration being placed
RMGIC
what is an indirect pulp cap
when the cavity is close to the pulp but there is still dentine covering it
what is a direct pulp cap
when the pulp is exposed
why should calcium hydroxide be covered with RMGIC before placing the restorative material
shields the layer from any liquids that could dissolve it away
