Cements 1 Flashcards
Define ‘cement’
- a material that’s initially fluid
- sets through series of complex reactions
- forms hard, stone-like mass
Define ‘dental cements’
- a range of materials that are initially fluid and set through a series of complex reactions
- not always forming hard, ston like masses
What range of setting reactions is possible with cements?
- hydraulic reaction - like builder’s cement
- acid-base reactions
- polymerisation
… are set by hydraulic reactions
calcium silicate-based cements
Which setting reaction is most common in dentistry?
acid-base reaction
Dental ‘resin-cements’ aren’t really cements. They’re set by … and are closer to … and …
- polymerisation
- dental composites and bonding resins
Uses of cements in dentistry
- 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)
What are pulp capping materials used for?
- to protect the pulp after accidental or traumatic pulp exposure
- may be used if a thin layer of dentine is protecting the pulp
Requirements of pulp capping materials
- 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
What’s the most commonly used pulp capping material?
calcium hydroxide cements
Calcium hydroxide can be mixed with …
It’s strong/weak?
- water
- weak
How is calcium hydroxide most commonly used?
- as a 2 paste system
- paste 1 is calcium hydroxide, zinc oxide and oil
- paste 2 is alkyl di-salicylate and filler
Setting of calcium hydroxide is not well understood. What’s the idea?
- chelation between zinc oxide and di-salicylate most likely
- accelerated by moisture
Freshly mixed calcium hydroxide cement is acid/alkaline?
Explain properties
- highly alkaline
- pH 11-12
- neutralizes acids
- secondary dentine growth - irritates pulp leading to inflammation, calcified layer forms leading to pulp capping
- antibaterial
The mixed calcium hydroxide cement is low/high viscosity
Explain
- low
- thin layer produced
- too thin to provide insulation
Mixed cement is very strong/weak. Explain
- 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
Calcium hydroxide cements are soluble/insoluble. What does this mean?
- soluble
- may disappear over time
2 alternative cements to calcium hydroxide
- light activated calcium hydroxide
- calcium silicate-based cements
How does the light activated calcium hydroxide cement differ to the normal?
- 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
Explain calcium silicate-based cements compared to calcium hydroxide
- 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
Why are varnishes, liners and bases needed?
- 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
Difference with varnishes, liner and base
- varnish is a very thin layer
- liner is a thin layer
- base is a thick layer
Cavity varnishes are used on what kind of cavity?
- shallow cavities
- where there is lots of residual dentine e.g
What does cavity varnish do?
- seal dentine tubules
- protects from leakage
- little thermal protection/thin layer
- dentine bonding agent too possibly - won’t bond to all amalgam though
Cavity varnish is applied how?
- resin in a volatile solvent
- forms very thin film
- several layers may be needed
Requirements for cavity liners and bases
- protect the pulp (thermal, chemical, electrical, biological barrier)
- biocompatibility
- withstand placing filling material
Desirable features of cavity liners and bases
- adhere to dentine
- radio-opacity
- low solubility
- compatibility with filling materials
Oral temp changes may be caused by …
- exothermic reaction of filling materials (like composites can lead to an increase of 30 oC or more)
- hot and cold food/drink
The amount of thermal protection to temp change in the mouth depends on …
- thickness of residual dentine
- thickness of lining/base
- thermal conductivity/diffusivity (materials which are conductors are more likely to need a liner/base)
Conductors are more or less likely to need a base
more
How do liners and bases provide chemical protection?
- 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
How do liners/bases give electrical protection?
- galvanism/corrosion prevented
- can lead to pulpal pain
How do liners and bases give bacterial protection?
- reduce effect of microleakage
- anti-bacterial action (desirable but most cements don’t do this)
To protect the pulp, cements must be …
- non-toxic
- non-irritant
Many cements contain toxic and irritant ingredients. Why when this doesn’t protect pulp?
- set material needs to be biocompatible but need a convenient WT and ST
- moisture affects both
- temp affects both
How much protection of pulp is needed changes. What does it depend on?
- 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
Mechanical requirements of cements during filling placement
- 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
In a class 1 cavity where the lining hasn’t fully set, what will happen?
- lining will flow under pressure
- filling material makes contact with basal dentine
- full set liner doesn’t flow
In a class 2 cavity, what’s the additional problem of an unset lining compared to a class 1?
- flow of the liner leads to thinner sections of amalgam
- amalgam will fail
- AND fully set liner doesn’t flow
A class 2 cavity is being packed. What technique is used so as to not fracture it?
- edge of liner is not supported so may fail if a void is left
- interproximal box must be packed first
Which needs more packing force? Amalgam or composite?
- amalgams
Why do you want liners/bases to adhere to dentine?
can potentially reduce microleakage
Why do you want liners/bases to be radioopaque?
- aid in detection of caries
- radiolucent cement can look like caries
- complete filling of canals
Why do you want liners/bases to be soluble?
base cements insoluble in dentinal fluid
Why do you want liners/bases to be compatible with filling material?
- no discolouration of filling/surrounding tissues
- no interferance with setting
