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BDS2 CLINICAL Dental Materials > Cavity linings > Flashcards

Flashcards in Cavity linings Deck (65)
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1

what are the disadvantages of restorations

• May not make intimate contact with the tooth surface (especially dentine) and any gap may allow ingress of fluids and bacteria
• Heat is released during setting/curing
• Release of chemicals that may be pulpal irritants and lead to pain or pulpal damage

2

what is the solution to the disadvantages

The solution to these disadvantages is using an intermediate restorative material - a lining material prevents gaps and acts as a protective barrier

3

what is a cavity base

A cavity base is a thick mix of material that is placed in bulk. A definition of a cavity base is a dentine replacement used to minimize the bulk of the restoration or black out undercuts

4

what is a cavity liner

A cavity lining is a thin coating (<0.5mm) which is placed over exposed dentine. A definition of a cavity liner is a dentine sealer able to promote the health of the pulp by adhering to the tooth structure or by an anti-bacterial action

5

what is the purpose of a liner

provide pulpal protection
therapeutic
palliative

6

what does a liner protect the pulp from

chemical stimuli
thermal stimuli
bacteria and endotoxins

7

what is the chemical stimuli that can harm the pulp

o Chemical stimuli from unreacted chemicals in the filling material or the initial pH of the filling as some materials have an adverse pH

8

what is the thermal stimuli that can harm the pulp

it can protect from the heat of some setting reactions which are exothermic e.g composite or heat conducted through metal fillings

9

what is the bacteria and endotoxins that can harm the pulp

microleakage (the penetration of oral fluids and bacteria and their toxins between the restorative and the cavity walls. It does this by providing an impermeable bond which bacteria cannot pass through

10

how are cavity liners therapeutic

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

11

how are cavity liners palliative

o Reduce patient symptoms prior to definitive treatment being carried out – it is most commonly used in patients with reversible pulpitis
o Rather than putting them under the filling you put them in on their own

12

what are the properties of lining materials

• Easy to use
• Thermal properties
• Mechanical properties
• Radiopaque
• Marginal seal
• Solubility
• Cariostatic
• Biocompatible
• Compatible with restorative material

13

describe ease of use

• It should be easy to mix
• The working time should be long to allow easy placement
• The setting time should be short and ideally command set

14

what are the thermal properties

thermal conductivity
thermal expansion coefficient
thermal diffusivity

15

what is thermal conductivity

o The thermal conductivity is how well heat energy is how well heat energy is transferred through a material
o It is the heat flow through a cylinder of unit cross-sectional area and unit length, with a temperature difference of 1 degrees celcius between the ends
o The units are W/m-1/degrees celcius-1

16

what should thermal conductivity be

o It should be high for a denture base so that patients can tell whether what they are eating is hot or cold
o It should be low for a restorative material
o It should be as low as possible for a cavity lining as the whole point of the cavity lining is to protect the pulp from thermal stimuli, so we want the poorest thermal conductivity

17

what is thermal expansion coefficient

o Thermal expansion is change in length per unit length for a temperature rise of one degree Celsius
o Units are ppm degrees celcius-1

18

what should thermal expansion coefficient be

similar to dentine

19

what are the thermal expansion coefficients

o It is 11 for GIC
o 20 for RMGIC
o 25 for amalgam

20

what is thermal diffusivity

o Similar to the conductivity
o Measured in cm2/sec

21

what should thermal diffusivity be

o Ideally at least as low as tooth if not lower
 Enamel is 0.0042
 Dentine is 0.0026

22

what is the thermal diffusivity of liners

o all commercially available liners have similar or lower thermal diffusivity than tooth enamel

23

what are the mechanical properties of liners

• High compressive strength to allow placement of filling without breaking it
o Dentine has a compressive strength of around 275MPa, closer the values are to the tooth the better
• We want a modulus similar to dentine – around 15GPa – so that it moves the same way the tooth does

24

what are the radiopacity of liners

• Should be easy to see the difference between lining and tooth as this makes it easier to see if there is leakage or secondary caries
• If it is radiolucent then the restoration can look like caries and we cannot see if there is caries or if it is the lining

25

how is the marginal seal of liners

• Ideally the lining should form a chemical bond to dentine
• This bond should be permanent and impenetrable

26

what do we want the solubility of liners to be

• We want it to be low as we do not want it to dissolve away

27

what do we mean when we want a liner that is cariostatic

• We want it to be fluoride releasing and antibacterial – this is important in preventing secondary caries around the restoration

28

what do we mean by biocompatibility

• We want it to be non-toxic
• Not damaging to the pulp by
o Having a neutral pH
o No excessive heat during setting
• Low thermal conductivity

29

what are the types of intermediate materials

• Setting calcium hydroxide: liner
• Zinc oxide based cements: base
• Glass ionomer and Resin Modified Glass Ionomer cements: base or liner
• Palliative cements: base (seldom used nowadays, mainly historic)

30

what is setting calcium hydroxide liner

• Consists of two pastes
• Examples include Life, Dycal