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BDS3 - dental material science > dental luting agents > Flashcards

dental luting agents Flashcards

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1
Q

what are luting agents

A
  • all dental cements are luting agents, but not all luting agents are dental cements
  • can be
    >composite resins
    >self-adhesive composite resins
    > surface modifying chemicals
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2
Q

what is viscosity of luting agent dependant on

A
  • size of powder or filler particles in the material as well as flow characteristics of material itself
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3
Q

what should the viscosity of luting agents be

A
  • low to allow seating of the restoration without interference from cement
  • film thickness should be as thin as possible = ideally 25 µm or less
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4
Q

how easy is luting agents to use

A
  • should be easy to use
  • most are encapsulated with a clicker system
  • working time should be long to allow for seating of restoration
  • setting time should be short = ideally command set
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5
Q

why is radiopaque luting agents good

A
  • allows you to see margins easier

- easier to see marginal breakdown

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6
Q

what should the marginal seal be

A
  • ideal it should bone chemically to the tooth and the indirect restoration with a permanent and impenetrable bond
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7
Q

what colour are luting agents

A
  • tooth coloured
  • variety of shades and translucency
  • non-staining
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8
Q

what solubility should luting agents be

A
  • low

- if it is high then it will wash away under influence of saliva and fall out

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9
Q

how can luting agents be cariostatic

A
  • fluoride releasing and antibacterial

- important in preventing secondary caries around crown margins

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10
Q

what is the ideal biocompatibility of luting agents

A
  • not toxic
  • not damaging to the pulp
  • low thermal conductivity as a lot of restorations are metal based
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11
Q

what are the ideal mechanical properties

A
  • high compressive strength
  • high tensile strength
  • high hardness value
  • Young’s modulus similar to tooth
  • but no luting agents will get close to tooth values for any more than a couple of these*
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12
Q

what are the different types of materials

A
  • dental cement
    >zinc phosphate
    >zinc polycarboxylate
  • glass ionomer cement
    >conventional
    >Resin modified
  • composite resin luting agents
    > total etch for use with DBA
    > self-etch
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13
Q

what is in the powder of zinc phosphate

A
  • zinc oxide = 90%
    > main reactive ingredient
  • magnesium dioxide = <10%
    >gives white colour
    >increases compressive strength

-alumina and silica
>Improve physical properties
>alter shade of set material

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14
Q

what is in the liquid of zinc phosphate cement

A
  • phosphoric acid - 50%
  • oxides which buffer solution
    >aluminium oxide ensures even consistency of set material
    > zinc oxide slows reaction giving better working time
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15
Q

what is the reaction of zinc phosphate cement

A
  • acid base reaction initially

- followed by hydration reaction resulting in crystallised phosphate matrix

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16
Q

what does aluminium oxide do in zinc phosphate cement setting reaction

A
  • prevents crystallisation leading to an amorphous glassy matrix fo acid salt surrounding unreacted ZnO powder
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17
Q

what does the amorphous glassy matriculates of acid salt from zinc phosphate cement setting reaction do

A
  • it is almost insoluble, but it is porous and contains free water from the setting reaction
  • as it sets more it becomes harder
  • cement matures, binding this water leading to a stronger, less porous material
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18
Q

what are the problems with zinc phosphate cement

A 
- low initial pH of 2 
> cause pulpal irritation 
- exothermic reaction not good for pulp
- not adhesive to tooth or restoration 
> retention may be slightly micro mechanical but that is all 
- not cariostatic
- final set can take 24 hours 
- brittle
- opaque 
>cloudy yellow colour
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19
Q

what’s the difference between zinc phosphate and zinc polycarboxylate cement

A
  • phosphoric acid replaced by poly acrylic acid
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20
Q

what is good about polycarboxylate cement

A
  • bonds to tooth surfaces in similar way to GI
  • less heat of reaction
  • pH low to begin with but return to neutral quicker and longer chain acids don’t penetrate dentine as easily
  • cheap
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21
Q

what are the problems with zinc polycarboxylate cement

A
  • difficult to mix
  • difficult to manipulate
  • soluble in oral environment at lower pH
  • opaque = cloudy white colour
  • lower modulus and compressive strength than zinc phosphate
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22
Q

what is the difference between GI luting cement and filling material

A
  • particle size of glass which is less than 20µm to allow for suitable film thickness
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23
Q

what is the reaction for GI

A
  • acid base reaction between glass and acid
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24
Q

what is the glass in GI

A
  • SiO2, Al2O3 and CaF2
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25
Q

what is the acid in GI

A
  • mixture of acrylic, malice and itaconic acid and their copolymers
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26
Q

how does GI cement bond to tooth surface

A
  • ion exchange with calcium in enamel and dentine

- hydrogen bonding with collagen in dentine

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27
Q

does GI bond to restoration

A
  • no
  • there is no chemical bond to restoration surface
  • the surface of the restoration should be sandblasted to allow for mechanical adhesion
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28
Q

what is good about GI cement

A
  • low shrinkage
  • long-term stability
  • relatively insoluble once fully set
  • aesthetically between then zinc phosphate
  • self-adhesive to tooth substance
  • fluoride releasing
  • cheap
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29
Q

what is different with resin modified GI cement

A
  • chemistry the same as RMGI filling material
  • glass particle size smaller
  • liquid contains a hydrophilic monomer along with GIC powder and liquid
  • monomer is hydrophilic as GIC is water based
  • monomer - HEMA
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30
Q

what is HEMA

A
  • hydroxyethyl methacrylate
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31
Q

what is the setting reaction of RMGI

A
  • same acid base reaction
  • light activation causes polymerisation of HEMA and any copolymers in the material leading to a rapid initial set
  • need a REDOX reaction
  • some materials have a secondary curve via REDOX reaction
  • allows ‘dark curing’ where material not exposed to light still sets
32
Q

how does the incorporation of resin in RMGI better properties

A
  • shorter setting time
  • longer working time
  • higher compressive and tensile strengths
  • higher bond strength to tooth
  • decreased solubility
  • cheap material and use often
33
Q

what are the problems with RMGI

A
  • HEMA is cytotoxic
    > damage the pulp
  • HEMA swells
    > can’t be used for porcelain crowns as could crack
    > hydrophilic
  • doesn’t bond to indirect restorations
34
Q

what are composite luting agents-

A
  • the simplest of these materials are variants on composite filling material with suitable viscosity and filler particle size
  • used in conjunction with suitable DBA
  • light cured or dual cured
35
Q

why are composite luting agents good

A
  • better physical properties, lower solubility and better aesthetics
36
Q

how does composite luting agents bond to indirect composite restorations

A
  • composite bonds to composite
  • bond strength is lower to inlay fitting surface than to new composite
  • bond is micro mechanical to rough internal surface of inlay
  • bond is also chemical to remaining C=C bonds on fitting surface of inlay
37
Q

why do we use dual curing composite cement

A
  • light penetration through inlay will be poor
38
Q

how is composite cement bonded to porcelain

A
  • porcelain is brittel and required to be bonded to tooth to prevent fracture
  • treat ed with HF to etch the surface
  • produced a rough retentive surface
  • BUT is still not hydrophobic and compatible with composite resin luting agents
39
Q

how do we make porcelain hydrophobic to bond to composite luting agents

A
  • use a surface wetting agent

- silane coupling agent

40
Q

how does a silane coupling agent work

A
  • applied to etched porcelain surface
  • very strong bond between oxide group on porcelain surface and silane
  • the other end of the silane molecule is C=C bond which reacts with composite resin luting agent
  • hydrophilic end of it bonds to porcelain and other end is then hydrophobic to bond to composite
41
Q

why should you only use a light cured composite luting agent if porcelain is thin

A
  • increase curing time if thicker

- if restoration thicker then need to use a dual cured composite

42
Q

what is the advantage of using light cured composite luting agents rather than dual cured

A
  • stain less over time
43
Q

how do you bond composite luting agents to metal

A
  • metal surface doesnt bond to composite luting agent
  • metal surface needs to be roughened
  • ## done by etching or sandblasting
44
Q

how is metal etched

A
  • electrolyte etching
  • removes different phases of alloy at different rate
  • gives a very retentive surface

BUT

  • it is technique sensitive
  • potentially carcinogenic to lab technicians
  • seldom used now
45
Q

how is metal sandblasted

A
  • roughens surface but does not give the undercut surface of etching
46
Q

how do we bond composite luting agents to non-precious metals

A
  • metal bond agent
  • material with carboxylic and phosphoric acid derived resin monomers
  • MDP and 4-META
  • these molecules have an acidic end and a C=C bond
  • the acidic end of the molecule reacts with the metal oxide and render the surface hydrophobic as other end is C=C
47
Q

how is tooth turned hydrophobic to bond to composite luting agent

A
  • hydrophilic tooth is turned hydrophobic by DBa, non-precious metal which is hydrophilic is turned hydrophobic by metal bond agent
48
Q

what type of composite luting agent must be used for metal

A
  • dual curing as light will not penetrate the metal
  • used to cement crown, bridges and posts
  • technique sensitive and won’t work unless moisture controlled
49
Q

how do we bond to precious metal

A
  • change precious alloy composition to allow oxide formation
  • increase copper content and heat 400 degrees in the air
  • tin plate
  • sulphur based chemistry of binding agent
50
Q

what are self-adhesive composite luting agent

A
  • luting agents with an in-built metal bonding agent
  • the metal coupling agent is incorporated into the composite resin
  • simplifies the bonding process
  • anaerobic self-cured material

BUT

  • moisture sensitive
  • expensive
51
Q

what is an example of self-adhesive composite luting agent

A
  • panavia
52
Q

what is Rely X Unicem

A
  • self-etching composite resin cement

- combination of a composite resin cement and a self-etching dentine bonding agent

53
Q

what is the problem with Rely X Unicem

A
  • required good moisture control
  • there is doubt about the bond strength to enamel due to inadequate etching
  • the pH of the carboxyl monomer doesnt stay low long enough to get a good etch
54
Q

how do self-etching composite resin luting agents work

A
  • acidic groups bind with calcium in hydroxyapatite forming a stabilising attachment between the tooth and resin
  • ions from dissolution of filler neutralise the remaining acidic groups forming a chelate reinforced methacrylate network
  • good bond strength to dentine
55
Q

what are the mechanical properties of self-etching composite luting agents

A
  • quite good but not as good as conventional composite resin materials
56
Q

how is bonding to enamel with self-etching composite luting agents

A
  • lower than to dentine

- should be etched with acid period to application

57
Q

how is boning to dentine with self-etching composite luting agents

A
  • better than to enamel

- should not be etched with acid prior to application

58
Q

how is boning to ceramic with self-etching composite luting agents

A
  • branch specific

- Rely X Unicem seems to bond quite well to sandblasted zirconia

59
Q

how is bonding to metal with self-etching composite luting agent

A
  • better to non-precious than precious

- not good enough to cement ortho brackets

60
Q

what is the problem with self-etching composite luting agents

A
  • do not get round the problem of moisture control
61
Q

what should be used when doing a MCC

only going to list the things that were green in the tables xoxo

A
  • GIC

- RMGIC

62
Q

what should be used for a metal post

A
  • GIC
63
Q

what should be used for a fibre post

A
  • dual cure composite and DBA

- self adhesive composite

64
Q

what should be used for a veneer

A
  • light cure composite and DBA
65
Q

what should be used for a adhesive bridge

A
  • anaerobic cure composite
66
Q

what should be used for a zirconia crown

A
  • GIC
  • RMGIC
  • dual cure composite DBA
  • anaerobic cure composite
  • self-adhesive composite
67
Q

what should be used for a composute inlay

A
  • dual cure composite and DBA

- self adhesive composite

68
Q

what should be used for a porcelain inlay

A
  • dual cure composite and DBA

- self-adhesive composite

69
Q

what should be used for a gold restoration

A
  • GIC

- RMGIC

70
Q

what are temporary cements

A
  • made to cement temporary restorations in place while permanent restoration is fabricated
  • soft for easy removal
  • preparation must be physically retentive or they won’t work
71
Q

how are temporary cements supplied

A
  • two paste systems of a base and a catalyst or accelerator
72
Q

what does the base in a temporary cement contain

A
  • ZnO, starch and mineral oil
73
Q

what does the accelerator in a temporary cement contain

A
  • resins, eugenol or ortho-EBA and carnauba wax

- wax weakens the structure of the set cement and makes it easier to remove

74
Q

what are the two main types of temporary cements

A
  • those with eugenol and those without
  • both work fine if going to use GI as a permanent
  • if going to use RMGI then can’t use temporary with eugenol as it interferes with setting
75
Q

why can’t eugenol temporary cement be used if permanent cement is going to be resin based

A
  • it interferes with setting of this type of luting agent

BDS3 - dental material science (9 decks)

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