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Dental Material Science > Cavity Lining Materials > Flashcards

Cavity Lining Materials Flashcards

1
Q

describe 3 disadvantages of restorative materials

A
  • may not make intimate contact with tooth surface (gaps allow ingress of fluids and bacteria)
  • heat is released during setting/curing
  • chemicals which might be pulpal irritants can be released
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2
Q

what are the main aims of a restorative lining material?

A

to act as a protective barrier to the pulp
to prevent gaps between the tooth surface and the restoration

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3
Q

what is a cavity base?

A

a thick mix placed in bulk used to minimise the bulk of material or block out undercuts

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4
Q

what is a cavity liner?

A

a thin coating (0.5mm) over exposed dentine which is bale to promote the health of the pulp by adhering to the tooth structure or by an antibacterial action

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5
Q

describe 4 purposes of a cavity liner

A

-pulpal protection (PP) from chemical stimuli from unrelated chemicals in filling material/initial pH of filling material
-PP from thermal stimuli e.g. exothermic reaction of composite
-PP from bacteria and endotoxins
- to prevent microleakage
- to calm inflammation and promote pulpal healing prior to permanent restoration
-to reduce pt symptoms prior to tx being carried out

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6
Q

define microleakage

A

the penetration of oral fluids and bacteria and their toxins between the restorative and the cavity walls

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7
Q

briefly state desirable properties of lining materials

A

-ease of use
- thermal properties
- mechanical properties
- radiopaque
- good marginal seal
- low solubility
-cariostatic
- biocompatible
- compatible with restorative materials

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8
Q

describe how a cavity lining material can be easy to use

A
  • easy to mix
  • should have a long enough working time to allow easy placement
  • setting time should be short
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9
Q

define thermal conductivity

A

-how well heat energy is transferred through a material
-Heat flow through a cylinder of unit cross-sectional area and unit length, with a temperature difference of 10C between the ends

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10
Q

describe the ideal thermal properties of a cavity lining material

A
  • low thermal conductivity
  • thermal expansion coefficient similar to dentine
  • thermal diffusivity similar to dentine or lower
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11
Q

define thermal expansion coefficient

A

Change in length per unit length for a temperature rise of 1oC
Units are ppmoC-1

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12
Q

what is the thermal expansion coefficient of enamel?

A

8.3ppmoC-1

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13
Q

what is the thermal expansion coefficient of dentine?

A

11.4ppmoC-1

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14
Q

how is thermal diffusivity measured?

A

cm2/sec

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15
Q

describe the ideal mechanical properties of a cavity lining material

A

-high compressive strength to allow placement of filling without it breaking
- modulus similar to dentine (around 15GPa)

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16
Q

why is it ideal for a cavity lining material to be radiopaque?

A

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

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17
Q

why is it ideal for a cavity lining material to be cariostatic?

A

important in preventing secondary caries around the restoration

18
Q

give examples of how a cavity lining material can be biocompatible

A

-non-toxic
-non-damaging to the pulp: pH neutral and no excessive heat during setting
-low thermal conductivity

19
Q

what type of material is dycal?

A

calcium hydroxide based material

20
Q

what are the two pastes of which dycal consists of?

A

base and catalyst

21
Q

what are the constituents of the base of dycal?

A

-calcium hydroxide 50%
- plasticiser 40%
-zinc oxide (filler) 10%
-zinc stearate (filler) <1%

22
Q

what are the constituents of the catalyst of dycal?

A

-butylene glycol dvisalicylate (reactive element) 40%
-calcium sulphate (filler) 30%
-calcium tungstate (filler and radiopaque) 15%
- titanium dioxide (filler) 13-14%

23
Q

what is the setting reaction in dycal?

A

a chelation reaction between ZnO and the butylene glycol disalicylate

24
Q

what is the pH of dycal?

A

12

25
Q

what are the modes of action of a CaOH liner?

A

-alkaline liner kills bacteria
- causes irritation to odontoblast layer- necrosis results in tertiary dentine formation which forms a calcified bridge walling the base of the cavity off from the pulp

26
Q

state the properties of dycal

A

-quick setting time
-radiopaque
-easy to use
-low compressive strength
-unstable and soluble- if the cavity leaks then the lining will disappear, it may disappear from contact with moist dentine also

27
Q

name 3 zinc oxide based cements

A

-zinc phosphate
-zinc polycarboxylate
-zinc oxide eugenol (ZOE)

28
Q

how does zinc phosphate come on clinic?

A

in a powder and liquid

29
Q

what is the main reactive ingredient in the powder of zinc phosphate?

A

zinc oxide

30
Q

what is the role of magnesium dioxide in zinc phosphate?

A
  • increases compressive strength
  • gives the powder its white colour
31
Q

what comprises approx. 50% of the liquid in zinc phosphate?

A

aqueous solution of phosphoric acid

32
Q

what reactions occur when mixing zinc phosphate?

A
  • acid base reaction
  • hydration reaction resulting in the formation of a crystallised phosphate matrix
33
Q

what is the role of aluminium oxide in zinc phosphate?

A

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

34
Q

name problems with zinc phosphate

A

-pH 2 can cause pulpal irritation (can take 24hrs to return to neutral)
-exotehrmic setting reaction
-not cariostatic
-final set takes 24hrs
-brittle and opaque
-not adhesive

35
Q

what is the main difference between zinc polycarboxylate and zinc phosphate?

A

in zinc polycarboxylate, the phosphoric acid is replaced by polyacrylic acid

36
Q

give advantages of zinc polycarboxylate

A

-bonds to tooth surface in a similar way to GI cements
-less heat off the reaction than zinc phosphate
-pH returns to neutral quicker than zinc phosphate and longer chain acids don’t penetrate dentine as easily
-cheap

37
Q

give disadvantages of zinc polycarbonate

A

-difficult to mix and manipulate
-soluble in oral environment when at lower pH
-opaque
-lower modulus and compressive strength than zinc phosphate

38
Q

give 3 uses of zinc oxide eugenol (ZOE)

A

-a lining/base in deep cavities under amalgam restorations
-root canal sealer
- periodontal dressing

39
Q

what is the setting reaction of ZOE?

A

chelation reaction of zinc oxide with eugenol to form zinc eugenolate matrix
this matrix bonds the unreacted ZnO particles

40
Q
A

Dental Material Science (1 decks)

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