Flashcards in 7 - Luting Cements Deck (44):
2 types of restorations? describe how each is done + give 3 examples of each
- direct restoration: material placed in/on a cavity which hardens into a solid (chemically or by light curing)
e.g. amalgam, composite, GI restorations
- indirect restorations: a solid object made outside of the mouth which is placed in/on a prepared tooth
e.g. crowns, bridge, veneer, inlays, onlay
* can be provisional/temporary or definitive
die relief - helps to do what?
die relief helps to accommodate the thickness of luting cements
what is a luting cement? what are its 2 main purposes?
it is a material used for the
1) retention of indirect restorations, and to
2) seal the space between restoration and the tooth
choice of luting cement depends on?
- choice of luting cement depends on the type of restoration being cemented
2. material of indirect restoration:
- metal? ceramic? composite?
3. type of restoration?
- veneer? resin retained bridge? conventional bridge?
2 types of luting cement?
- active luting material
- passive luting material
active luting material: what does it do? and what are its roles?
- it bonds to the tooth and the restoration
- helps with retention
- provides a marginal seal
passive luting material: what does it do? how does it bring retention?
- it fills the gap between tooth and restoration
- there is no bond between tooth and restoration, instead retention is brought about by method of tooth tooth preparation
what are the methods of tooth preparation?
- preparation height
- surface roughness
- mechanical interlocking
general ideal properties of a luting cement?
- mechanical properties
- marginal seal
- low film thickness
- ease of use
- aesthetics: ceramic restorations
- inhibit plaque accumulation
- clear up of excess
- good shelf life
ideal luting cement: importance of biocompatibility?
able to contact with tooth tissue and periodontal tissues
ideal luting cement: importance of retention?
additional bonding for active luting cements, preparation morphology and mechanical interlocking of irregularities for passive luting cements
ideal luting cement: examples of ideal mechanical properties?
high tensile strength, fracture toughness, fatigue strength, wear resistance
ideal luting cement: importance of marginal seal?
low solubility. advantageous for active luting, reduced hypersensitivity
ideal luting cement: importance of low film thickness?
- allows full seating of restoration
- good marginal adaptation
ideal luting cement: in what ways should it be easy to use?
- powder:liquid ratios
- working and setting times
ideal luting cement: describe how it should be pseudoplastic?
it should coat the fit surface of the restoration without slumping, but it should also flow readily under pressure on fitting
ideal luting cement: how can it inhibit plaque accumulation
it should be easy to polish
it should eliminate the air inhibition layer in resin composites
passive luting cements: 4 examples? what are they based on?
- zinc phosphate
- zinc polycarboxylate
- glass ionomer luting materials
- resin modified glass ionomer luting cements
- all are water based
zinc phosphate luting cements: what is its presentation?
- powder: zinc oxide, up to 10% magnesium oxide (improves compressive strength, adds colour)
- liquid: aqueous phosphoric acid (45-64%)
how to extend setting time?
what does using a chilled glass slab help with?
- 3-6 minutes
- by slaking the fluid; small amount of powder added to fluid about 1 minute before
- increases working time
increases powder incorporated
zinc phosphate: setting reaction
- what kind of reaction?
- describe the reaction that occurs
- how does viscosity change?
- how much strength in 10 mins? how long does it take to reach full strength?
- how does the size change on setting?
- antibacterial effect?
- acid base reaction
- dissolution of surface of ZnO powder. insoluble hydrated zinc phosphate matrix crystals effective bind to the unreacted ZnO particles
- viscosity increases rapidly
- 50% strength in 10mins, 100% str in 24 hours
- shrinks slightly on setting
- no antibacterial effect
- initially unset material has what pH
- pH depends on?
- what is this relevant to?
- describe properties
- depends on thickness of mix
- relevant to vital pulp
- good compressive strength,
low tensile strength (brittle)
- alternative presentation?
- 1. powder: zinc oxide + up to 10% magnesium oxide
2. aqueous copolymer of polyacrylic acid (30-40%), high viscosity
- acid freeze dried and added to powder
- liquid: distilled water
zinc polycarboxylate - setting reaction
- acid dissolves what?
- zinc ions form cross links between what?
- unreacted powder bound where?
- zinc oxide
- zinc ions form cross links with carboxyl groups on polyacrylic acid polymer chains
- unreacted powder bound in matrix of zinc polyacrylate
- how can it be extended?
what causes it to have a short working time? what can altering the ratio have an impact on?
appears viscous but is actually _____?
- extended by adding tartaric acid and mixing on a cold glass slab
- high powder:liquid ratio. altering the ratio would have an impact on the physical properties
- appears viscous but is actually pseudoplastic
initial pH? how does this relate to pulp?
how does the pH change?
- initial low pH (3-4)
- less injurious to pulp
- pH increases rapidly
- it has antibacterial properties
- adhesive to enamel, dentine, and some metals (via oxide layer)
- describe its compressive str and tensile strength
- how much strength is reached in 1 hour?
- soluble in?
- clean up?
- low compressive strength, high tensile strength
- 80% str
- soluble in acid
- messy to clean up
how is it different from the restorative glass ionomer?
- same chemistry, but luting GI has smaller glass particle size
1. powder: fluoro-alumino-silicate glass
2. liquid: aqueous poly alkenoic acid
1. acid freeze-dried, added to powder
2. liquid: distilled water
+ what element is responsible for strong cross linking?
- chemical set
1. dissolution: calcium ions released first, then aluminium
3. hardening: aluminium trivalent, slower to be released from glass, ensures strong cross linking of polymer chains
setting reaction -
- dissolution and initial set: how long?
- seated by how long?
- hardening can take up to how long?
- need protection to prevent what?
- up to 7 days
- need to prevent dissolution or contamination
glass ionomer - properties?
what may cause pulpal inflammation?
how does it compare to zinc oxide cements?
- anti-caries effect via fluoride release
- initial acidity may cause pulpal inflammation
- 1. better compressive str
2. low tensile str and fracture toughness
3. less soluble
resin modified glass ionomer:
1. components of GI + monomer (HEMA, Bis-GMA)
*no photo initiator, chemical cure only (acid base reaction of GI)
resin modified glass ionomer: advantages over GI?
- low solubility
- improved biocompatability
- improved fluoride release
- improved physical properties
- improved adhesion to tooth tissue
RMGI cements - disadvantages?
- can undergo hygroscopic expansion
- avoid under conventional all-ceramic crowns
- suitable under zirconia core / CAD-CAM crowns
resin based luting cements: what are the constituents that are in restorative composite resins as well?
why does it have lower viscosity?
how are most of them cured?
- silenated filler
- resin e.g. bis GMA
- low filler content -> low viscosity
- mostly dual cured (chemical and light)
resin based luting cements:
conventional resin luting cements - for use with?
- all ceramic restorations
- indirect composite or quartz fibre posts e.g. veneers, dentine bonded crowns
chemically adhesive resin luting cements: for?
- for adhesively bonding to metals
(resin retained bridges, metal veneers, poorly retained indirect restorations)
resin luting cements: bonding to ceramic
- how does it bond to tooth?
- when bond has to fit surface of cermic: etched with? what is applied before cementing? what kind of bond is each one?
- conventional way: acid etch, rinse, dry, DBA
- etched with hydrofluoric acid - micromechanical bond
- silane coupling agent applied and air dried - chemical bond
why lab use only?
why must it be neutralized?
why will it not etch periphery of veneers well?
- can cause damage to?
- because it is very toxic
- to prevent it from leaching out and causing tissue damage
- because it tends to slump
- to periphery of ceramic
veneers: how does try in paste change its appearance?
- it causes more light to be transmitted, less light reflected
veneers: what is applied on top of enamel to be treated?
1. etch and DBA
2. resin luting cement
- hydrofluoric acid etch fit surface + silane coupling agent
bonding to metal
- how to bring micromechanical retention?
- roughen the fit surface with 50micrometer alumina grit
bonding to metal -
chemically adhesive resin luting cement:
what kind of chemical?
name 2 monomers
both have high affinity for?
- modified bis-GMA resin
1. carboxylic monomer (4 META), e.g. C&B Superbond
2. phosphate monomer (MDP), e.g. Panavia 21, F
- both have high affinity for metal oxide on base metal alloy