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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
what is the acid in GI
- mixture of acrylic, malice and itaconic acid and their copolymers
26
how does GI cement bond to tooth surface
- ion exchange with calcium in enamel and dentine | - hydrogen bonding with collagen in dentine
27
does GI bond to restoration
- no - there is no chemical bond to restoration surface - the surface of the restoration should be sandblasted to allow for mechanical adhesion
28
what is good about GI cement
- low shrinkage - long-term stability - relatively insoluble once fully set - aesthetically between then zinc phosphate - self-adhesive to tooth substance - fluoride releasing - cheap
29
what is different with resin modified GI cement
- 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
30
what is HEMA
- hydroxyethyl methacrylate
31
what is the setting reaction of RMGI
- 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
how does the incorporation of resin in RMGI better properties
- shorter setting time - longer working time - higher compressive and tensile strengths - higher bond strength to tooth - decreased solubility - cheap material and use often
33
what are the problems with RMGI
- 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
what are composite luting agents-
- 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
why are composite luting agents good
- better physical properties, lower solubility and better aesthetics
36
how does composite luting agents bond to indirect composite restorations
- 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
why do we use dual curing composite cement
- light penetration through inlay will be poor
38
how is composite cement bonded to porcelain
- 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
how do we make porcelain hydrophobic to bond to composite luting agents
- use a surface wetting agent | - silane coupling agent
40
how does a silane coupling agent work
- 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
why should you only use a light cured composite luting agent if porcelain is thin
- increase curing time if thicker | - if restoration thicker then need to use a dual cured composite
42
what is the advantage of using light cured composite luting agents rather than dual cured
- stain less over time
43
how do you bond composite luting agents to metal
- metal surface doesnt bond to composite luting agent - metal surface needs to be roughened - done by etching or sandblasting -
44
how is metal etched
- 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
how is metal sandblasted
- roughens surface but does not give the undercut surface of etching
46
how do we bond composite luting agents to non-precious metals
- 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
how is tooth turned hydrophobic to bond to composite luting agent
- hydrophilic tooth is turned hydrophobic by DBa, non-precious metal which is hydrophilic is turned hydrophobic by metal bond agent
48
what type of composite luting agent must be used for metal
- 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
how do we bond to precious metal
- 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
what are self-adhesive composite luting agent
- 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
what is an example of self-adhesive composite luting agent
- panavia
52
what is Rely X Unicem
- self-etching composite resin cement | - combination of a composite resin cement and a self-etching dentine bonding agent
53
what is the problem with Rely X Unicem
- 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
how do self-etching composite resin luting agents work
- 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
what are the mechanical properties of self-etching composite luting agents
- quite good but not as good as conventional composite resin materials
56
how is bonding to enamel with self-etching composite luting agents
- lower than to dentine | - should be etched with acid period to application
57
how is boning to dentine with self-etching composite luting agents
- better than to enamel | - should not be etched with acid prior to application
58
how is boning to ceramic with self-etching composite luting agents
- branch specific | - Rely X Unicem seems to bond quite well to sandblasted zirconia
59
how is bonding to metal with self-etching composite luting agent
- better to non-precious than precious | - not good enough to cement ortho brackets
60
what is the problem with self-etching composite luting agents
- do not get round the problem of moisture control
61
what should be used when doing a MCC | only going to list the things that were green in the tables xoxo
- GIC | - RMGIC
62
what should be used for a metal post
- GIC
63
what should be used for a fibre post
- dual cure composite and DBA | - self adhesive composite
64
what should be used for a veneer
- light cure composite and DBA
65
what should be used for a adhesive bridge
- anaerobic cure composite
66
what should be used for a zirconia crown
- GIC - RMGIC - dual cure composite DBA - anaerobic cure composite - self-adhesive composite
67
what should be used for a composute inlay
- dual cure composite and DBA | - self adhesive composite
68
what should be used for a porcelain inlay
- dual cure composite and DBA | - self-adhesive composite
69
what should be used for a gold restoration
- GIC | - RMGIC
70
what are temporary cements
- 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
how are temporary cements supplied
- two paste systems of a base and a catalyst or accelerator
72
what does the base in a temporary cement contain
- ZnO, starch and mineral oil
73
what does the accelerator in a temporary cement contain
- resins, eugenol or ortho-EBA and carnauba wax | - wax weakens the structure of the set cement and makes it easier to remove
74
what are the two main types of temporary cements
- 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
why can't eugenol temporary cement be used if permanent cement is going to be resin based
- it interferes with setting of this type of luting agent

BDS3 - dental material science (9 decks)

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