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BDS2 - dental material science > cavity lining materials > Flashcards

cavity lining materials Flashcards

1
Q

what materials are placed in cavities

A
  • composite resin
  • glass ionomer
  • amalgam
  • precious metal
  • ceramic
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2
Q

what are the disadvantages of restorative materials

A
  • 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
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3
Q

what is the solution to the problems of restorative materials

A
  • intermediate restorative material

- a lining material = prevents gaps, acts as a protective barrier

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4
Q

where does the lining sit

A
  • below the restorative material at the base of the cavity, protects the pulp
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5
Q

what is a base

A
  • a thick lining (lining and base are the same thing)
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6
Q

what is a lining

A
  • a thin base (lining and base are the same thing)
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7
Q

how does a cavity base work

A
  • 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
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8
Q

how does a cavity lining work

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 or by an antibacterial action
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9
Q

what is the purpose of a liner

A
  • pulpal protection
  • therapeutic
  • palliative
  • want something bond to surface of tooth and be impenetrable
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10
Q

how does the liner protect the pulp

A
  • 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
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11
Q

how is the liner therapeutic

A
  • to calm down inflammation within the pulp and promote pulpal healing prior to or at the same time of a permanent restoration being placed
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12
Q

how is the liner palliative

A
  • to reduce patient symptoms prior to definitive treatment being carried out
  • most commonly in patients with reversible pulpitis
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13
Q

how is a lining material easy to use

A
  • 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
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14
Q

what is the thermal conductivity of lining materials

A
  • 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)
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15
Q

what is thermal’s conductivity

A

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
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16
Q

what is the thermal coefficient

A

change in length per unit length for a temperature rise of 1oC
- units are ppmoC-1

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17
Q

what should be the thermal coefficient for a lining materials

A
  • 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)
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18
Q

what is the thermal diffusivity

A

similar to conductivity

- measured in cm2/second

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19
Q

what should the thermal diffusivity of a lining material be

A
  • 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)
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20
Q

what are the mechanical properties of a lining material

A
  • 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
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21
Q

are lining material radiopaque

A

yes

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22
Q

what is good about lining materials being radiopaque

A
  • should be easy to see difference between lining and tooth

- makes it easier to see if there if any leakage or secondary caries

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23
Q

what is the marginal seal formed by lining materials

A
  • ideally lining should form a chemical bond to dentine

- bond should be permanent and impenetrable

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24
Q

what is the solubility of a lining material

A

low

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25
Q

what does a cariostatic lining material do

A
  • releases fluoride
  • is antibacterial
  • is important in preventing secondary caries around the restoration
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26
Q

what is the biocompatibility of a lining material

A
  • non-toxic
  • not damaging to the pulp = ph neutral, no excessive heat during setting
  • low thermal conductivity
  • compatible with restorative materials
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27
Q

what are the different types of lining material

A
  • palliative cement
  • setting calcium hydroxide liner
  • zinc oxide based cements
  • zinc polycarboxylate cement
  • zinc oxide eugenol (ZOE)
  • ethoxybenzoic acid (EBA)
  • glass ionomer lining materials
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28
Q

what is palliative cement

A
  • base
  • seldom used nowadays
  • contain antibiotics or steroids
  • dampen down inflammation of pulp or bacteria
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29
Q

what is setting calcium hydroxide

A
  • 2 pastes = Life, Dycal
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30
Q

what are the constituents of setting CaOH

A
  • 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%
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31
Q

what does setting CaOH smell like

A

germolene

32
Q

what is the setting reaction of CaOH

A
  • 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
33
Q

what is the mode of action of a CaOH liner

A
  • 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
34
Q

what are the properties of CaOH

A
  • 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
35
Q

what are the zinc oxide based cements

A
  • zinc phosphate, zinc polycarboxylate, zinc oxide eugenol (ZOE), resin modified ZOE, ethoxybenzoic acid (EBA) ZOE
36
Q

what is zinc phosphate cement

A
  • 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
37
Q

what is the powder in zinc phosphate cement made up of

A
  • 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
38
Q

what is the liquid of zinc phosphate cement

A
  • 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)
39
Q

what is the initial reaction of CaOH liner

A

acid base

ZnO + 2H3PO4 -> Zn(H2PO4)2 + H2O

40
Q

what is the second reaction of CaOH liner after the initial

A
  • 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
41
Q

what does the aluminium oxide in CaOH liner do

A

prevent crystallisation leading to an amorphous glassy matrix of the acid salt surrounding unreacted ZnO powder

42
Q

what occurs because the matrix in CaOH is almost insoluble

A

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

43
Q

what are the problems with CaOH liner

A
  • 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
44
Q

what is zinc polycarboxylate cement

A
  • 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
45
Q

what is good about zinc polycarboxylate cement

A
  • 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
46
Q

what is not good about zinc polycarboxylate cements

A
  • difficult to mix and manipulate
  • soluble in oral environment at lower ph
  • lower modulus and compressive strength than zinc phosphate
47
Q

what materials for lining are seldom used nowadays

A
  • 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
48
Q

what are zinc oxide eugenol (ZOE) cements and related materials

A
  • 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
49
Q

what is ZOE cement

A
  • this is still an acid base reaction
    = base is ZnO
    = acid is eugenol
50
Q

what is the setting reaction if ZOE

A
  • 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
51
Q

what are the properties of ZOE

A
  • 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
52
Q

under what material should ZOE materials not be used under

A
  • should not be used under composters resin materials
53
Q

what is the strength of ZOE

A
  • 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
54
Q

what is the solubility of ZOE

A
  • 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)
55
Q

what is resin modified ZOE

A
  • 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
56
Q

what is ethoxybenzoic acid (EBA) cement

A
  • another modifies ZOE

- reactive

57
Q

what makes up the powder of EBA

A
  • ZnO = 65%
  • quartz or aluminium = 35% (make it stronger than ZOE)
  • hydrogenated resin
58
Q

what makes up the liquid in EBA

A
  • eugenol = 37%

- ethoxybenzoic acid (EBA) = 63%

59
Q

what is the setting of EBA

A
  • as with ZOE but EBA

- encourages crystalline structure which imparts greater strength to the set material

60
Q

what are the properties of EBA

A
  • stronger than ZOE or resin modified ZOE, around 60MPa

- less soluble

61
Q

what are glass ionomer lining materials

A
  • 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
62
Q

is glass ionomer lining materials easy to use

A

yes

  • mixing is simple and many materials come a two pasts ‘clicker’ system
  • vitrebond = base in one tube, catalyst in the other
63
Q

how are glass ionomer materials set

A
  • generally light cured and so are common set

- gives a long working time and conventionally short setting time (30seconds)

64
Q

what is the thermal conductivity and diffusivity of glass ionomer lining

A
  • lower than for dentine for both GIC and RMGIC
65
Q

what is the thermal expansion for GIC

A

similar to dentine

66
Q

what is the compressive strength for GIC

A

> 170MPa

- higher than any other ZnO based material (still not as high as dentine though)

67
Q

are glass ionomer materials radiopaque

A
  • most materials are, but radiopacity varies between materials
68
Q

what is the marginal seal of glass ionomer materials

A

is better than any of the other material as there is a chemical bond to enamel and dentine

69
Q

what is the only material that can predictably seal dentinal tubules

A
  • glass ionomer lining

- this decreases micro leakage and helps prevent post treatment sensitivity

70
Q

what is solubility for glass ionomer materials

A
  • 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
71
Q

are GIC materials cariostatic

A

possibly as fluoride is released

72
Q

what is released during the polymerisation reaction of RMGIC’s

A
  • 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
73
Q

what is the only lining able to bond to restorative materials

A

GIC

74
Q

what may some conventional glass ionomers materials require before bonding

A
  • some may require to be etched

- RMGIC’s require no surface treatment = may be possible to bond to amalgam using RMGIC’s

75
Q

what are the dental hospital lining guidelines for cavities in dentine

A
  • consider using a lining of RMGIC for amalgam and for larger cavities to be filled with composite
76
Q

what are the dental hospital lining guideline with CaOH

A
  • 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

BDS2 - dental material science (13 decks)

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