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Dental Materials > Cements 1 > Flashcards

Cements 1 Flashcards

1
Q

Define ‘cement’

A
  • a material that’s initially fluid
  • sets through series of complex reactions
  • forms hard, stone-like mass
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2
Q

Define ‘dental cements’

A
  • a range of materials that are initially fluid and set through a series of complex reactions
  • not always forming hard, ston like masses
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3
Q

What range of setting reactions is possible with cements?

A
  • hydraulic reaction - like builder’s cement
  • acid-base reactions
  • polymerisation
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4
Q

… are set by hydraulic reactions

A

calcium silicate-based cements

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5
Q

Which setting reaction is most common in dentistry?

A

acid-base reaction

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6
Q

Dental ‘resin-cements’ aren’t really cements. They’re set by … and are closer to … and …

A
  • polymerisation
  • dental composites and bonding resins
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7
Q

Uses of cements in dentistry

A
  • tooth restoration (pulp capping, cavity lining, cavity base, temp and perm fillings)
  • luting (cementation of crowns, bridges and orthodontics for attaching bands/brackets)
  • endodontics (filling and sealing root canals)
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8
Q

What are pulp capping materials used for?

A
  • to protect the pulp after accidental or traumatic pulp exposure
  • may be used if a thin layer of dentine is protecting the pulp
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9
Q

Requirements of pulp capping materials

A
  • maintain pulpal vitality
  • provide bacterial seal
  • be bactericidal or bacteriostatic
  • stimulate reparative dentine formation
    MAY
  • release fluoride to prevent secondary caries
  • adhere to dentine and restorative material
  • resist forces during restoration placement and during life of restoration
  • radiopaque
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10
Q

What’s the most commonly used pulp capping material?

A

calcium hydroxide cements

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11
Q

Calcium hydroxide can be mixed with …
It’s strong/weak?

A
  • water
  • weak
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12
Q

How is calcium hydroxide most commonly used?

A
  • as a 2 paste system
  • paste 1 is calcium hydroxide, zinc oxide and oil
  • paste 2 is alkyl di-salicylate and filler
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13
Q

Setting of calcium hydroxide is not well understood. What’s the idea?

A
  • chelation between zinc oxide and di-salicylate most likely
  • accelerated by moisture
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14
Q

Freshly mixed calcium hydroxide cement is acid/alkaline?
Explain properties

A
  • highly alkaline
  • pH 11-12
  • neutralizes acids
  • secondary dentine growth - irritates pulp leading to inflammation, calcified layer forms leading to pulp capping
  • antibaterial
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15
Q

The mixed calcium hydroxide cement is low/high viscosity
Explain

A
  • low
  • thin layer produced
  • too thin to provide insulation
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16
Q

Mixed cement is very strong/weak. Explain

A
  • weak
  • maximum compressive strength is 20MPa
  • too weak to withstand amalgam compaction - may need a second cement
  • composites don’t require high compaction forces - okay to use with composite and don’t interfere with polymerisation
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17
Q

Calcium hydroxide cements are soluble/insoluble. What does this mean?

A
  • soluble
  • may disappear over time
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18
Q

2 alternative cements to calcium hydroxide

A
  • light activated calcium hydroxide
  • calcium silicate-based cements
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19
Q

How does the light activated calcium hydroxide cement differ to the normal?

A
  • contains monomers of BisGMA, UDMA, HEMA
  • no zinc oxide
  • HEMA absorbs water to release calcium hydroxide
  • significantly less calcium hydroxide release than in the two paste system
  • stronger than the above too
20
Q

Explain calcium silicate-based cements compared to calcium hydroxide

A
  • similar to Portland cement/builders’ cement
  • contains calcium hydroxide so effect is similar
  • better mechanical properties than hydroxide
  • growing body of clinical evidence these may be better
  • often used in endodontics
21
Q

Why are varnishes, liners and bases needed?

A
  • enamel and dentine naturally protect the pulp
  • removal of these can lead to pulpal pain
  • the more removed, the greater the chance of pain so varnishes, liners and bases reduce the chance of this pain
22
Q

Difference with varnishes, liner and base

A
  • varnish is a very thin layer
  • liner is a thin layer
  • base is a thick layer
23
Q

Cavity varnishes are used on what kind of cavity?

A
  • shallow cavities
  • where there is lots of residual dentine e.g
24
Q

What does cavity varnish do?

A
  • seal dentine tubules
  • protects from leakage
  • little thermal protection/thin layer
  • dentine bonding agent too possibly - won’t bond to all amalgam though
25
Q

Cavity varnish is applied how?

A
  • resin in a volatile solvent
  • forms very thin film
  • several layers may be needed
26
Q

Requirements for cavity liners and bases

A
  • protect the pulp (thermal, chemical, electrical, biological barrier)
  • biocompatibility
  • withstand placing filling material
27
Q

Desirable features of cavity liners and bases

A
  • adhere to dentine
  • radio-opacity
  • low solubility
  • compatibility with filling materials
28
Q

Oral temp changes may be caused by …

A
  • exothermic reaction of filling materials (like composites can lead to an increase of 30 oC or more)
  • hot and cold food/drink
29
Q

The amount of thermal protection to temp change in the mouth depends on …

A
  • thickness of residual dentine
  • thickness of lining/base
  • thermal conductivity/diffusivity (materials which are conductors are more likely to need a liner/base)
30
Q

Conductors are more or less likely to need a base

A

more

31
Q

How do liners and bases provide chemical protection?

A
  • from acid in cements like zinc phosphate w/ phosphoric acid
  • from acids in fillings like glass ionomer cements w/ polyacids
  • monomers from composites - these are potent irritants
  • mercury from amalgams
32
Q

How do liners/bases give electrical protection?

A
  • galvanism/corrosion prevented
  • can lead to pulpal pain
33
Q

How do liners and bases give bacterial protection?

A
  • reduce effect of microleakage
  • anti-bacterial action (desirable but most cements don’t do this)
34
Q

To protect the pulp, cements must be …

A
  • non-toxic
  • non-irritant
35
Q

Many cements contain toxic and irritant ingredients. Why when this doesn’t protect pulp?

A
  • set material needs to be biocompatible but need a convenient WT and ST
  • moisture affects both
  • temp affects both
36
Q

How much protection of pulp is needed changes. What does it depend on?

A
  • residual thickness of dentine (this adds protection but exposed dentinal tubules provide access to pulp)
  • is dentine freshly cut? - sclerotic dentine can have tubules occluded by salts
  • is all caries removed? - residual caries can mean residual bacteria
37
Q

Mechanical requirements of cements during filling placement

A
  • resist flow during packing (more cements need mixing before use, must wait until after setting time before packing)
  • resist fracture during packing (compressive strength, different techniques for different cavities)
  • resist fracture in function
38
Q

In a class 1 cavity where the lining hasn’t fully set, what will happen?

A
  • lining will flow under pressure
  • filling material makes contact with basal dentine
  • full set liner doesn’t flow
39
Q

In a class 2 cavity, what’s the additional problem of an unset lining compared to a class 1?

A
  • flow of the liner leads to thinner sections of amalgam
  • amalgam will fail
  • AND fully set liner doesn’t flow
40
Q

A class 2 cavity is being packed. What technique is used so as to not fracture it?

A
  • edge of liner is not supported so may fail if a void is left
  • interproximal box must be packed first
41
Q

Which needs more packing force? Amalgam or composite?

A
  • amalgams
42
Q

Why do you want liners/bases to adhere to dentine?

A

can potentially reduce microleakage

43
Q

Why do you want liners/bases to be radioopaque?

A
  • aid in detection of caries
  • radiolucent cement can look like caries
  • complete filling of canals
44
Q

Why do you want liners/bases to be soluble?

A

base cements insoluble in dentinal fluid

45
Q

Why do you want liners/bases to be compatible with filling material?

A
  • no discolouration of filling/surrounding tissues
  • no interferance with setting

Dental Materials (17 decks)

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