Cavity Linings Flashcards
What are examples of materials that are places into tooth cavities? (5)
- composite resin
- glass ionomer
- amalgam
- precious metal
-ceramic
One disadvantage of restorations is that they may not make intimate contact with the tooth surface (especially dentine0 What can this lead to?
Any gaps may allow ingress of fluids and bacteria
a disadvantage of restorations is that heat may be released during setting/curing. What can this have an effect on?
Potentially detrimental effect on the pulp
A disadvantage of restorations is that there may be a release of chemical. What may this lead to?
- they may be pulpal irritants and lead to pain or pulpal damage
What are the functions of a lining material? (2)
- Prevents gaps
- Acts as a protective barrier
What is a cavity base?
A thick mix placed in bulk
What is a cavity base used for?
Dentine replacement used to minimise the bulk of material or block out undercuts
Where are cavity bases more common?
In metal restorations (direct or indirect)
What is a cavity lining?
- A thin coating (<0.5mm) over EXPOSED dentine
-“A dentine sealer able to promote the health of the pulp by adhering to the tooth structure of by an anti-bacterial action” - RMGI does this to a certain extent
One purpose of a liner is for pulpal protection. What is the protection from? (3)
- Chemical stimuli from unreacted chemicals in the filling material or the initial pH of the filling
- Thermal stimuli e.g. exothermic setting reaction of composite or heat conducted through mental fillings
-bacteria and exotoxins. Microleakage ( the penetration of oral fluids and bacteria and their toxins between the restorative material and the cavity walls)
What is microleakage?
The penetration of oral fluids and bacteria and their toxins between the restorative material and the cavity walls
One purpose of a liner is to have a therapeutic effect. What does this mean?
- to calm down inflammation within the pulp and promote pulpal healing
- prior to or at the time of a permanent restoration being placed
One purpose of a liner is to have a palliative effect. What does this mean?
- to reduce patient symptoms prior to definitive treatment being carried out. Most commonly in patients with reversible pulpitis
- More insulation before placing a final restoration
What are the properties of lining materials? ( 9)
- ease of use
- thermal properties
- mechanical properties
- radiopaque
- marginal seal
- solubility
- cariogenic
- biocompatible
- compatible with restorative materials
What makes lining materials easy to use?
- easy to mix
- working time should be long to allow easy placement
- setting time short- ideally command set
What should the thermal properties of lining materials be? (3)
- thermal conductivity should be low
- 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
What is the thermal expansion coefficient?
- change in length per unit length form a temoerature rise of 1 degree
- units are ppm/degree celcius^-1
Ideally what should the thermal expansion coefficient of a lining material be?
Ideally a liner should match the thermal coefficient of a tooth
- enamel = 8.3
- dentine = 11.4
- GIC = 11
- RMGIC =20
- Composite = 25
- Amalgam = 25
What is thermal diffusivity?
- the thermal conductivity of a substance divided by the produce of its density and its specific heat capacity
-IT is similar to conductivity
What unit is thermal diffusivity measured in?
cm^2/sec
Ideally what should the thermal diffusivity of a lining material be?
- ideally at least as low as the tooth
- enamel= 0.0042cm^2/sec
- dentine= 0.0026cm^2/sec
What is the thermal diffusivity of liners like compared to tooth enamel?
All commercially available liners have similar or lower thermal diffusivity than tooth enamel
What is the thermal diffusivity of amalgam?
- 1.7cm^2/sec
- amalgam is 500x more than dentine
What are the mechanical properties of lining materials (2)
- High compressive strength
- modulus is similar to dentine
What do lining materials need a high compressive strength?
- to allow the placement of a filling on top without it breaking
- Dentine is about 275MPa
What does the modulus of elasticity of a lining material have to be similar to dentine?
- If the tooth bends and flexes, want the lining material to do the same
- want it to be around 15MPa
What do lining materials need to be radiopaque?
- as it should be easy to see the difference between the lining and the tooth
- makes it easier to see if there is any leakage or secondary caries
Ideally a lining material should form a chemical bond to dentine. What properties do you want from the bond? (2)
The bond should be permanent and impermeable
What should the solubility of a lining material be like?
solubility should be low
What does cariostatic mean?
Tending to inhibit the formation of dental caries
What are the cariostatic properties of lining materials and why are they important? (3)
- fluoride releasing
-antibacterial - important in preventing secondary caries around the restoration
Why are cariostatic features of lining materials important?
They are important in preventing secondary caries around the restoration
Are lining materials toxic to the pulp?
NO
Lining materials are not damaging to the pulp. What 3 factors ensure this?
- neutral pH
- no excessive heat during setting
- they have a low thermal conductivity
Is setting calcium hydroxide a base or a liner?
Liner
Are zinc oxide bases cements a base or a liner?
base
Are Gi and RMGIC’s bases or liners?
can be either
Are palliative cements bases or liners?
A base - seldom used nowadays, mainly historic.
How man pastes are setting calcium hydroxide liners composed of?
2 pastes
What are 2 examples of setting CaOH liners?
- Life
- Dycal (used most of time in dental hospital)
What are the 2 constituents of a setting CaOH liner?
Base
catalyst
What are the 4 components of the base in a setting Calcium Hydroxide liner?
- Calcium hydroxide 50%
- zinc oxide (filler) 10%
- zinc stearate (filler) <1%
- N-ethyl toluene sulphonamide (plasticiser) 40%
What are the 4 components of the catalyst in a setting calcium hydroxide liner?
-Butylene glycol disalicylate (reactive element) 40%
-Titanium Dioxide (filler) 13-14%
-Calcium sulphate (filler) 30%
-Calcium Tungstate (filler and radiopaquer) 15%
What is the setting reaction of setting calcium hydroxide liner?
A chelation reaction between the ZnO and the butylene glycol disalicylate
The setting reaction of setting calcium hydroxide liners results in a cement with an initial pH of around 12. Why is this good?
- as all of the microbes that cause caries like to live in acidic conditions
- it also causes a degree of irritation in the pulp which causes the lay down of tertiary dentine so increases the distance between where the cavity was and the where the pulp starts
Why is a CaOH liner bactericidal to cariogenic bacteria?
Cariogenic bacterial survive in an acidic environment. The highly alkaline liner kills the bugs
Why does the irritation of the pulp by CaOH liners results in reparative dentine formation?
- The cement causes irritation to the odontoblast layer
- necrosis follows which in turn results in a layer of tertiary dentine being produced
- this eventually forms a calcified bridge walling the base from the pulp ( the calcium comes from the pulp not the cement)
What are 3 advantageous properties of CaOH?
- quick setting time
- radiopaque
- easy to use
What are 2 disadvantageous properties of CaOH?
- low compressive strength ( if try to pack amalgam filling in on top of it, it will probably break)
- it may even disappear just because it is in contact with moist dentine
What are 5 examples of zinc oxide based cements?
- zinc phosphate
- zinc polycarboxylate
- zinc oxide eugenol (ZOE)
- resin modified ZOE
- ethoxybenzoic acid (EBA) (ZOE)
How long has zinc phosphate cement been used for?
in use for 100+ years
Zinc phosphate cement is produced by an acid base reaction with a powder and a liquid. What is the power and liquid components?
powder= zinc oxide
liquid= phosphoric acid
What are 3 advantages of using zinc phosphate cement as a lining material?
- excellent clinical service
- easy to use
- cheap
What is the power in zinc phosphate cement composed of? (3)
- zinc oxide >90% (main reactive ingredient)
- Magnesium dioxide <10%
- other oxides (alumina and silica)
What 2 things does the magnesium dioxide component of the powder in zinc phosphate cements do?
- gives white colour
- increases compressive strength
What 2 things does the oxide components (alumina and silica) of the power in zinc phosphate cements do?
- improved physical properties
- alters the shade of the set material
What is the liquid component of zinc phosphate composed of? (2)
-Aqueous solution of phosphoric acid (approx. 50%)
-Oxides which buffer the solution:
-aluminium oxide = ensures even consistency of set material
-Zinc oxide = slows the reaction giving better working time
why does the aluminium oxide component of the liquid in zinc oxide cements do?
ensures even consistency of set material
What does the zinc oxide components of the liquid in zinc oxide cements do?
slows the reaction giving better working time
What reactions are involved in producing zinc phosphate cement? (5)
- the initial reaction is acid base
- this is followed by a hydration reaction resulting in the formation of a crystallised phosphate matrix
- the aluminium oxide prevents crystallisation leading to an amorphous glassy matrix of the acid salt surrounding unreacted ZnO powder
-this matrix is almost insoluble, but it is porous and contains free water from the setting reaction - ## the cement subsequently matures binding this water leading to a stronger, less porous material
One problem with zinc phosphate cement is that it has a low initial pH of approx 2. Why is this a problem?
It can cause pulpal irritation as pH can take 24 hours to return to neutral
Is zinc phosphate cement an endothermic or exothermic reaction?
Exothermic
One problem with zinc phosphate cement is that it is not adhesive to the tooth or restoration. Why is this a problem?
Retention may be slightly micromechanical due to the surface irregularities of the cavity
is zinc phosphate cement cariostatic?
No
How long does it take for zinc phosphate cement to completely set?
- Final set takes 24 hours
- It is reasonable hard within 5 mins
Is zinc oxide cement brittle?
Yes
is zinc phosphate cement opaque?
Yes
Zinc polycarboxylate is similar to zinc phosphate. What is the difference?
Phosphoric acid is replaces by polyacrylic acid
What are the advantages of zinc polycarboxylate cement as a liner? (4)
- Bonds to tooth surfaces in similar way to GIC’s
- less heat of reaction
- pH is low to being with but returns to neutral more quickly and longer chain acids do not penetrate dentine as easily
- cheap
What are the disadvantages of zinc polycarboxylate cement as a lining ? (5)
- difficult to mix
- difficult to manipulate
-soluble in oral environment at lower pH - opaque
- lower modulus and compressive strength than zinc phosphate
What are Zinc Oxide Eugenol cements used for? (4)
Linings/base in deep cavities:
- under amalgam restorations
Temporary restorations
- resin modified of EBA ZOE
Root canal sealer
- Slow setting 24 hours
Periodontal dressings
- fast setting- 5 mins
zinc oxide eugenol cement is a base acid reaction. What is the base and what is the acid?
Base= ZnO
Acid= Eugenol
Base+ Acid -> salt + water
What is the setting reaction of zinc oxide eugenol?
- chelation reaction of zinc oxide with the eugenol to form zinc eugenolate matrix
- this matrix bond the unreacted ZnO particles
What is the working time of ZOE like?
Adequate working time
What is the setting time of ZOE like?
Relatively rapid setting time:
- sets quicker in the mouth due to moisture and heat
- can be modified by the addition of accelerators
What is the thermal conductivity of ZOE like?
Low thermal conductivity
What is the strength of ZOE like?
low strength, around 20MPa
- weak hydrogen bonds between the eugenolate molecules
- not strong enough to use as a base beneath as amalgam filling. The packing pressure would damage it
Is ZOE radiopaque
Yes
What is the solubility of ZOE like?
- highly soluble
- eugenol is constantly released:
This is good and bad:
=eugenol is replaces by water which -> disintegration of the material BUT
= eugenol when liberated has an obtundent effect on the pulp and can reduce pain
Why should ZOE materials NOT be used under composite resin materials?
As the release of eugenol inhibits the set of resin based filling materials. It softens them and can cause discolouration
Resins can be added to the powder and liquid of ZOE to make resin modified ZOE. What resins are added to IRM and Kalzinol?
IRM= Polymethylmethacrylate
- Kalzinol = polystyrene
Resins added to ZOE do not take part in the reaction. What do they do?
They give a stringer back bone to the set material
Adding resins to ZOE increases the compressive strength to >40MPa. What does this make ZOE suitable for?
suitable as a cavity lining
What does adding resins to ZOE do to the solubility of it?
greatly decreases the solubility
Ethoxybenzoic acid (EBA) cement is a modified ZOE. What is the composition of the powder component of this ? (3)
- ZnO 65%
- Quartz or Alumina 35%
- Hydrogenated rosin (around 6%)
EBA cement is a modified ZOE. What is the composition of the liquid component of this ? (2 points)
- Eugenol 37%
- ethoxybenzoic acid EBA 63%
What does the inclusion of quartz and alumina in EBA do?
- makes the cement stronger
- it is reinforcing
The setting reaction of EBA is similar to that of ZOE. What is the difference ?
EBA encouraged a crystalline structure which imparts greater strength to the set material
EBA is stronger than ZOE or Resin modified ZOE. What is the strength of EBA?
around 60 MPa which is more than strong enough to place an amalgam filling onto it
is EBA more or less soluble than ZOE?
Less soluble
What are the most widely used lining materials ?
Glass ionomer lining
Can glass ionomers bond to dentine ?
Yes, can bond to and seal dentine
Can glass ionomer bond to composite?
Yes
Is glass ionomer cariostatic?
Yes, as it releases fluoride over time
Are glass ionomer lining materials easy to use?
yes, mixing is simple and many materials come as a two paste ‘clicker’ system
Glass ionomer lining materials are generally light cured and so are command set. What does this allow?
Gives a long working time and a conveniently short setting time (30 seconds)
What is the thermal conductivity and diffusivity of glass ionomer lining materials like compared to dentine ?
Lower than dentine for both GIC and RMGIC
What is the thermal expansion of GIC and RMGIC’s like compared to dentine
similar to dentine
-RMGIC is a little bit less so
What is the compressive strength of GIC’s ?
> 170MPa, higher than any of the ZnO based materials
- not quite as high as dentine though
Are GIC’s radiopaque?
Yes, most of them are, but the radiopacity varies between materials
What is the marginal seal of GIC’s to dentine like?
Better than any other materials as there is a chemical bond to enamel and dentine
What features of GIC’s decreases micro-leakage and helps to prevent post treatment sensitivity?
As GIC’s are the only material to predictably seal dentinal tubules
What is the solubility of GIC and RMGIC’s like compared to other lining materials? (3)
- Solubility is greater for GIC than RMGIC and is greatest initially
- However, GIC materials are less soluble than any of the other liners apart from Zinc phosphate cement
- RMGIC is less soluble than any other cement
Benzoyl iodides and benzoyl bromides are released during the polymerisation reaction of RMGIC’s. What does this lead to?
These are cytotoxic and can be effective against residual cavity bacteria
What is complete cure of RMGIC’s required?
As any unreacted HEMA may damage the pulp
Which lining material is the only one able to bond to restorative materials?
GIC’s
What do some conventional glass ionomers require prior to bonding?
Some require to be etched
Do RMGIC’s require any surface treatment
No
Is it possible to bond amalgam to a tooth using RMGIC?
Yes
What are the dental hospital guidelines for cavities in dentine?
Consider the use of a lining RMGIC (such as vitrebond) for amalgam and for larger cavities to be filled with composite
What are the Dental Hospital lining guidelines for Calcium hydroxide? (2)
- It should only be used when the cavity approaches the pulp
- either as a direct or indirect pulp cap ober the deepest part of the cavity
- calcium hydroxide should be covered with RMGIC prior to the final restoration being places
