cavity lining materials Flashcards
what materials are placed in cavities
- composite resin
- glass ionomer
- amalgam
- precious metal
- ceramic
what are the disadvantages of restorative materials
- may not make intimate contact with the tooth surface (especially dentine) = gaps allow ingress of fluids and bacteria
- heat is released during curing/setting reaction
- release of chemicals = may cause pulpal irritation and lead to pain or pulpal damage, often happens if not cured well
- micro leakage = when doesn’t bond well and gaps form
what is the solution to the problems of restorative materials
- intermediate restorative material
- a lining material = prevents gaps, acts as a protective barrier
where does the lining sit
- below the restorative material at the base of the cavity, protects the pulp
what is a base
- a thick lining (lining and base are the same thing)
what is a lining
- a thin base (lining and base are the same thing)
how does a cavity base work
- thick mix placed in bulk
- dentine replacement used to minimise the bulk of the material or block out undercuts
- more common in metal restorations = direct or indirect
how does a cavity lining work
- thin coating (<0.5mm) over exposed dentine
- a dentine sealer able to promote the health of the pulp by adhering to the tooth structure or by an antibacterial action
what is the purpose of a liner
- pulpal protection
- therapeutic
- palliative
- want something bond to surface of tooth and be impenetrable
how does the liner protect the pulp
- chemical stimuli = form unreacted chemicals in the filling material or the initial ph of the filling
- thermal stimuli = exothermic reaction of composite or heat conducted through metal fillings
- bacteria and endotoxins = micro leakage, the penetration of oral fluids and bacteria and their toxins between restorative material and the cavity walls
how is the liner therapeutic
- to calm down inflammation within the pulp and promote pulpal healing prior to or at the same time of a permanent restoration being placed
how is the liner palliative
- to reduce patient symptoms prior to definitive treatment being carried out
- most commonly in patients with reversible pulpitis
how is a lining material easy to use
- easy to mix = if it was made difficult then a mess would be made of it
- working time should be long enough to allow easy placement
- setting time is short = but ideally would want on command set which we don’t have yet
what is the thermal conductivity of lining materials
- should be low
- denture bases should be high, restorative material should be low, cavity lining as low as possible
- want as little heat as possible going to pulp (especially under metal restoration)
what is thermal’s conductivity
how well heat is transferred through a material
- heat flow through a cylinder of unit cross-sectional area and unit length, with a temperature difference of 1 degree between the ends
- units are W/m-1/oC-1
what is the thermal coefficient
change in length per unit length for a temperature rise of 1oC
- units are ppmoC-1
what should be the thermal coefficient for a lining materials
- ideally a liner should match the thermal coefficient of the tooth
- enamel = 8.3 ppmoC-1
- dentine = 11.4
- GIC = 11
- RMGIC = 20
- composite and amalgam = 25 (not very good)
what is the thermal diffusivity
similar to conductivity
- measured in cm2/second
what should the thermal diffusivity of a lining material be
- similar to dentine or lower
- ideally at least as low as tooth - enamel = 0.0042, dentine = 0.0026
- all commercially available liners have a similar or lower thermal diffusivity than tooth enamel
- amalgam is 1.7cm2/sec (500 x more than dentine)
what are the mechanical properties of a lining material
- high compressive strength = needs to be as filling going to packed on top so needs to not break (dentine around 275MPa)
- modulus similar to dentine = around 15GPa, if material bent too much bond would eventually break and restoration would fracture
are lining material radiopaque
yes
what is good about lining materials being radiopaque
- should be easy to see difference between lining and tooth
- makes it easier to see if there if any leakage or secondary caries
what is the marginal seal formed by lining materials
- ideally lining should form a chemical bond to dentine
- bond should be permanent and impenetrable
what is the solubility of a lining material
low
what does a cariostatic lining material do
- releases fluoride
- is antibacterial
- is important in preventing secondary caries around the restoration
what is the biocompatibility of a lining material
- non-toxic
- not damaging to the pulp = ph neutral, no excessive heat during setting
- low thermal conductivity
- compatible with restorative materials
what are the different types of lining material
- palliative cement
- setting calcium hydroxide liner
- zinc oxide based cements
- zinc polycarboxylate cement
- zinc oxide eugenol (ZOE)
- ethoxybenzoic acid (EBA)
- glass ionomer lining materials
what is palliative cement
- base
- seldom used nowadays
- contain antibiotics or steroids
- dampen down inflammation of pulp or bacteria
what is setting calcium hydroxide
- 2 pastes = Life, Dycal
what are the constituents of setting CaOH
- base
- calcium hydroxide 50%
*zinc oxide filler (10%)
*zince stearate filler <1%
*N-ethyl toluene sulphonamide plasticiser 40%
(has few fillers) - catalyst
*butylene glycol disalicylate (reactive part) 40%
*titanium dioxide (filler) 13-14%
*calcium sulphate (filler) 30%
*calcium tungstate (filler and radiopaque) 15%
what does setting CaOH smell like
germolene
what is the setting reaction of CaOH
- chelation reaction between the ZnO and the butylene glycol disalicylate
- results in a cement with an initial pH of around 12
- good as bacteria like acidic conditions so will die in this pH
what is the mode of action of a CaOH liner
- bactericidal to cariogenic bacteria =
cariogenic bacteria survive in acidic environment, high alkaline liner kills bugs - irritation to cause reparative dentine formation =
cement causes irritation to the odontoblast layer, necrosis follows which results in a layer of tertiary dentine to protect pulp, eventually a calcified bridge forms walling the base of the cavity off from the pulp
what are the properties of CaOH
- quick setting time
- radiopaque
- easy to use = mix bit from each tube
- but has low compressive strength, would not survive under amalgam filling
- unstable and soluble = if cavity leaks then lining will disappear, may even disappear if in contact with moist dentine
what are the zinc oxide based cements
- zinc phosphate, zinc polycarboxylate, zinc oxide eugenol (ZOE), resin modified ZOE, ethoxybenzoic acid (EBA) ZOE
what is zinc phosphate cement
- been in use for over 100 years
- acid base reaction
- powder and liquid (zinc oxide powder and phosphoric acid liquid)
- excellent clinical service = strong and hardwearing
- easy to use
- cheap
what is the powder in zinc phosphate cement made up of
- zinc oxide >90% = main reactive ingredient
- magnesium dioxide <10% = gives white colour, increases compressive strength
- other oxides (aluminium and silica) = improves physical properties, alter shade of set material
what is the liquid of zinc phosphate cement
- aqueous solution of phosphoric acid (approx 50%)
- oxides which buffer the solution = aluminium oxide (ensures even consistency of set material), zinc oxide (slows reaction giving better working time)
what is the initial reaction of CaOH liner
acid base
ZnO + 2H3PO4 -> Zn(H2PO4)2 + H2O
what is the second reaction of CaOH liner after the initial
- followed by hydration reaction resulting in formation of a crystallised phosphate matrix
ZnO + Zn(H2PO4)2 + 2H2O -> Zn3(H2PO4)2.4H2O - hydration reaction makes it stronger
what does the aluminium oxide in CaOH liner do
prevent crystallisation leading to an amorphous glassy matrix of the acid salt surrounding unreacted ZnO powder
what occurs because the matrix in CaOH is almost insoluble
matrix is almost insoluble, but is too porous and contains free water from the setting reaction
- cement subsequently matures, binding this water leading to a stronger, less porous material
what are the problems with CaOH liner
- low initial ph = cause pulp irritations
- exothermic setting reaction = gives off heat to pulp
- no adhesive to tooth or restoration = retention may be slightly micro mechanical causing micro leakeage with no bond
- not cariostatic
- final set = 24 hours
- brittle = cant use in thin section
- opaque = kind of creamy colour
what is zinc polycarboxylate cement
- similar material to CaOH but phosphoric acid is replaced with poly acrylic acid
- this material had the advantage of boding to tooth surfaces in a similar way to glass ionomer cements
what is good about zinc polycarboxylate cement
- there is little heat of reaction so damages pulp less
- the ph is low to begin with but returns to neutral/alkaline more quickly than CaOH and longer chain acids do not penetrate dentine as easily = sticks to dentine a little but to very well
- cheap
- opaque
what is not good about zinc polycarboxylate cements
- difficult to mix and manipulate
- soluble in oral environment at lower ph
- lower modulus and compressive strength than zinc phosphate
what materials for lining are seldom used nowadays
- zinc phosphate and zinc polycarboxylate
- they were important materials for many decades and were important in the development of the more modern glass ionomer cements
what are zinc oxide eugenol (ZOE) cements and related materials
- linings/base in deep cavities = under amalgam restorations (can’t use under resin)
- smell you get when you walk into a dentists
- temporary restorations = resin modified or EBA ZOE
- root canal sealer = slow setting, 24 hours
- periodontal disease dressings = fast setting, 5 mins
what is ZOE cement
- this is still an acid base reaction
= base is ZnO
= acid is eugenol
what is the setting reaction if ZOE
- chelation reaction of zinc oxide with the eugenol to form zinc eugenolate matrix
- this matrix bonds the unreacted ZnO particles
- resin in powder do not take part in setting reaction
what are the properties of ZOE
- adequate working time
- relatively raid setting time = sets quicker in mouth due to moisture and heat, can be modified by addition of accelerators
- low thermal conductivity
- low strength around 20MPa
- radiopaque
- high solubility
- released eugenol inhibits set of resin based filling materials = softens them and causes discolouration
under what material should ZOE materials not be used under
- should not be used under composters resin materials
what is the strength of ZOE
- low strength around 20MPa
- weak hydrogen bonds between eugenolate molecule;es
- not strong enough to use as a base beneath an amalgam filling = packing pressure would damage it
what is the solubility of ZOE
- high
- eugenol is constantly released
- good and bad
- eugenol is replaced by water which lead to disintegration of material (bad)
- but eugenol when liberate has an obtundant effect on the pulp and can reduce pain (good)
what is resin modified ZOE
- resins are added the powder and the liquid = polymethylmethacrylate in IRM, polystyrene in Kalzinol
- these resins do not take part in the reaction but give a stronger backbone to the set material = increases compressive strength to >40MPa making it suitable as cavity lining
- resins greatly reduce solubility
what is ethoxybenzoic acid (EBA) cement
- another modifies ZOE
- reactive
what makes up the powder of EBA
- ZnO = 65%
- quartz or aluminium = 35% (make it stronger than ZOE)
- hydrogenated resin
what makes up the liquid in EBA
- eugenol = 37%
- ethoxybenzoic acid (EBA) = 63%
what is the setting of EBA
- as with ZOE but EBA
- encourages crystalline structure which imparts greater strength to the set material
what are the properties of EBA
- stronger than ZOE or resin modified ZOE, around 60MPa
- less soluble
what are glass ionomer lining materials
- become most widely used
- glass ionomer can bond to and seal the dentine
- it then in turn can bone to the composite resin filling placed over it
- releases fluoride over time and can be cariostatic
- chemistry of conventional and light cured glass ionomer is exactly the set as the respective filling materials
is glass ionomer lining materials easy to use
yes
- mixing is simple and many materials come a two pasts ‘clicker’ system
- vitrebond = base in one tube, catalyst in the other
how are glass ionomer materials set
- generally light cured and so are common set
- gives a long working time and conventionally short setting time (30seconds)
what is the thermal conductivity and diffusivity of glass ionomer lining
- lower than for dentine for both GIC and RMGIC
what is the thermal expansion for GIC
similar to dentine
what is the compressive strength for GIC
> 170MPa
- higher than any other ZnO based material (still not as high as dentine though)
are glass ionomer materials radiopaque
- most materials are, but radiopacity varies between materials
what is the marginal seal of glass ionomer materials
is better than any of the other material as there is a chemical bond to enamel and dentine
what is the only material that can predictably seal dentinal tubules
- glass ionomer lining
- this decreases micro leakage and helps prevent post treatment sensitivity
what is solubility for glass ionomer materials
- 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
- RMGIC less soluble than any other cement
are GIC materials cariostatic
possibly as fluoride is released
what is released during the polymerisation reaction of RMGIC’s
- benzoyl iodides and benzoyl bromides are released during the polymerisation reaction
- these are cytotoxic and can be effective against residual cavity bacteria
- but complete cure of RMGICs is required as any unreacted HEMA may damage the pulp = needs to be cured well rot kill bugs but not damage pulp
what is the only lining able to bond to restorative materials
GIC
what may some conventional glass ionomers materials require before bonding
- some may require to be etched
- RMGIC’s require no surface treatment = may be possible to bond to amalgam using RMGIC’s
what are the dental hospital lining guidelines for cavities in dentine
- consider using a lining of RMGIC for amalgam and for larger cavities to be filled with composite
what are the dental hospital lining guideline with CaOH
- should be used when the cavity approaches the pulp cap over the deepest part of the cavity
- should then be covered with RMGIC prior to a final restoration being placed
