Luting Agents Flashcards
1
Q
What is luting agent another word for?
A
- Dental cement
2
Q
What is the ideal film thickness of luting agent?
A
- 25um or less
3
Q
What is the ideal viscosity for luting agent?
A
- Must be low to allow seating of restoration without interference- Viscosity increases as material sets therefore must seat restoration quickly and maintain pressure
4
Q
What ease of use properties should luting agents have?
A
- Easy to mix i.e via clicker system in encapsulated ones- Working time long to allow for seating of restoration- Setting time short
5
Q
Why must luting agents be radiopaque?
A
- Some ceramic crowns are radiolucent- Makes it easier to see marginal breakdown
6
Q
Ideally how should a luting agent bond to tooth and indirect restoration?
A
- Bond chemically to tooth and indirect rest with a permanent and impenetrable bond
7
Q
What is the ideal aesthetics of luting agents?
A
- Tooth coloured with variation in shades and translucency- Non staining
8
Q
What is the ideal solubility of luting agent?
A
- Low
9
Q
What is the ideal cariostatic properties of luting agents?
A
- Fluoride releasing- Antibacterial - Important in preventing secondary caries around crown margins
10
Q
What is the ideal biocompatibility of luting agents?
A
- Non toxic- Not damaging to the pulp (inappropriate pH and heat on setting)- Low thermal conductivity
11
Q
What are the ideal mechanical properties of luting agents?
A
- High compressive strength (dentine 275MPa)- High tensile strength (dentine 50MPa)- High hardness value (dentine 70K and enamel 400k)- Young modulus similar to tooth (dentine 15GPa)* No luting agent gets close to tooth values for more than one or two physical properties*
12
Q
What are the types of dental cement?
A
- Zinc phosphate- Zinc polycarboxylate
13
Q
What are the types of glass ionomer cement?
A
- Conventional- Resin modified
14
Q
What are the types of composite resin luting agents?
A
- Total etch for use with DBA- Self etch- Requires etch but has own bonding agent incorporated
15
Q
What is zinc phosphate?
A
- In use for 100+years- Acid base reaction- Powder and liquid- Excellent clinical service- Easy to use- Cheap
16
Q
What is the constituents of zinc phosphate powder?
A
- Zinc oxide >90% (main reactive ingredient)- Magnesium dioxide <10% - Other oxides (alumina and silica)
17
Q
What is magnesium dioxide used for in zinc phosphate powder?
A
- Gives white colour- Increases compressive strength
18
Q
What are alumina and silica used for in the powder of zinc phosphate cement?
A
- Improves physical properties- Alter shade of set material
19
Q
What are the constituents of zinc phosphate liquid?
A
- Aqueous sol of phosphoric acid (approx 50%)- Aluminium oxide that ensures even consistency of set material- Zinc oxide slows the reaction giving better working time
20
Q
What are the reactions of the zinc phosphate cement?
A
- Initial acid base reaction- Followed by hydration reaction - Results in formation of crystallised phosphate matrix
21
Q
What does the aluminium oxide prevent in Zinc phosphate?
A
- Prevent crystallisation leading to amorphous glassy matrix of acid salt surrounding unreacted ZnO powder
22
Q
What happens when zinc phosphate cement matures?
A
- Matrix originally insoluble but it is porous and contains free water from setting reaction- When it matures it binds the water- Leads to stronger, less porous material
23
Q
What are the disadvantages of zinc phosphate cement?
A
- Low initial pH approx 2- Exothermic setting reaction (release heat)- Not adhesive to tooth or restoration- Not cariostatic- Final set takes 24hrs- Brittle- Opaque
24
Q
What can a low pH lead to?
A
- Pulpal irritation
25
How is zinc phosphate retained in tooth?
- Works like grout on tiles and fills spaces- Retention slightly micromechanical due to surface irregularities on prep and restoration
26
What are the constituents of Zinc Polycarboxylate cement?
- Aqueous sol of polyacrylic acid (approx 50%)- Aluminium oxide - Zinc oxide- Zinc oxide >90% (main reactive ingredient)- Magnesium dioxide <10% - Other oxides (alumina and silica)
27
What are some negatives of Zinc Polycarboxylate cement?
- Difficult to mix- Difficult to manipulate- Soluble in oral environment at lower pH- Opaque- Lower modulus and compressive strength than Zinc phosphate
28
How does the glass ionomer cement bond to tooth surface?
- Ion exchange with calcium in enamel and dentine- Hydrogen bonding with collagen in dentine- Results in fairly strong, durable bond to tooth- No chemical bond to restoration surface
29
What are the advantages of glass ionomer cements?
- Clinically easy to use and durable cement- Low shrinkage- Long term stability- Relatively insoluble once fully set- Aesthetically better than Zinc phosphate- Self adhesive to tooth substance- Fluoride release- Cheap
30
What monomer does the RMGI cement liquid have in addition to conventional GIC powder?
- Hydrophillic monomer- Must be hydrophilic as GIC is water based material- HEMA (Hydroxyethyl methacrylate)
31
How is the RMGI set?
- Light activation causes polymerisation of HEMA and any copolymers = rapid initial set- Acid base reaction continues for some time- Some materials have secondary cure via REDOX- Allows Dark curing
32
What is Dark curing?
- Material not exposed to light will cure
33
What are some advantages of RMGI?
- Shorter setting time- Longer working time- Higher compressive and tensile strengths- Higher bond strength to tooth- Decreased solubility
34
What are some potential problems with RMGI?
- HEMA is cytotoxic (can damage pulp if any remain)- HEMA swells (expands in wet environment so can't use conventional porcelain crowns as may crack - No bond to indirect restoration
35
What are the advantages and disadvantages of composite luting agents?
- Can be light or dual cured- Better physical properties, lower solubility and better aesthetics- But technique sensitive
36
What are the advantages and disadvantages to bonding to indirect composite?
- Composite bonds to composite- Bond strength lower to inlay fitting than new composite- Bond is micromechanical to rough internal surface of inlay- Bond is chemical C=C bonds on fitting surface of inlay- Use dual curing cement as light penetration through inlay is poor
37
Why does porcelain need to be treated with 10% HF in order to bond to tooth?
- Porcelain is brittle and needs to be bonded to tooth to prevent fracture- Untreated porcelain is smooth and non retentive- Treated with HF to etch surface (toxic)- Leads to rough retentive surface- Allows silane bonded coupling agent to adhere
38
What is a silane coupling agent and how does it bond?
- Gamma-methacryoxypropyltrimothoxysilane- Applied to etched porcelain surface as monolayer- Strong bond between oxide groups on porcelain surface and silane- Other end of silane molecule has C=C bond which reacts with composite resin luting agent- Works same manner as dentine bonding agent
39
When curing a composite luting agent to porcelain what should you do?
- If porcelain restoration is thin use light cured- If thick use dual cure- Remove as much of the luting resin as poss before curing
40
How does composite materials bond to metal?
- Does not bond directly to metal- Metal surface to be roughened by etching- Usually done by sandblasting
41
What does etching metal lead to?
- Electrolytic etching removes diff phases of alloy at different rates- Gives very retentive surface- But technique sensitive- Beryllium alloy works best- Can't etch precious metals at all
42
What is required after sandblasting a metal?
- Sandblasting roughen surface - Does not give undercut surface of etching- Chemical bonding required to strengthen bond
43
How are non-precious metals bonded?
- MDP and 4-META- Molecules have acidic end and C=C end- Acidic end of molecule reacts with metal oxide and surface is now hydrophobic- Use dual cure as light doesn't penetrate metal
44
How are precious metals bonded?
- Change precious alloy composition to allow oxide formation- Increase copper content and heat 400oC in air- Tin plate- Sulphur based chemistry of bonding agent- Complicated and technique sensitive
45
What are the advantages of self adhesive composites resins?
- Good film thickness- Opaque- Moisture sensitive- Expensive
46
What is a self adhesive composite resin?
- Metal coupling agent incorporated into composite resin- Simplifies bonding process
47
What are the advantages and disadvantages of Self etching composite resin cements (Rely X Unicem)?
- Stick to everything - Easy to use- Requires good moisture control- Potential inadequate bond strength to enamel due to inadequate etching- pH of carboxylic monomer doesn't stay low enough enough for good etch
48
How do Self etching composite resin luting agents work?
- Acidic group binds with calcium in hydroxyapatite- Forms stabilising attachment between tooth and resin- Ions from dissolution of filler neutralise remaining acidic groups- Forms chelate reinforced methacrylate network- Limited removal of smear layer or sig infiltration into tooth surface- Good bond strength to dentine
49
What are the properties of Self etching composite resin luting agents?
Mechanical - Compressive strength- Tensile strength- Hardness- Wear resistance*Slightly lower than conventional resin luting agent's but better than cements
50
When using a MCC what luting agent should you use?
- Glass ionomer cement- RMGI
51
When using metal post what luting agent should you use?
- GIC
52
When using a fibre post what luting agent should you use?
- Dual cure composite and DBA- Self adhesive composite
53
When using veneer what luting agent should you use?
- Light cure composite and DBA
54
When using adhesive bridge what luting agent should you use?
- Anaerobic cure composite
55
When using zirconia crown what luting agent should you use?
- GIC- RMGIC- Dual cure composite and DBA- Anaerobic cure composite- Self adhesive composite
56
When using composite inlay what luting agent should you use?
- Dual cure composite and DBA- Self adhesive composite
57
When using porcelain inlay what luting agent should you use?
- Dual cure composite and DBA- Self adhesive composite
58
When using gold restoration what luting agent should you use?
- GIC- RMGIC
59
What are temporary cements used for?
- Cement temporary restorations in place whilst permanent restoration is fabricated- Soft for easy removal and some don't even set- Prep must be physically retentive or doesn't work
60
What are temporary cements made of?
- Two paste system (base and catalyst/accelerator)- Base = ZnO, Starch and mineral oil- Accelerator = resins, eugenol or ortho-EBA and carnauba wax
61
What is the wax for in temporary cements?
- Weakens structure of set cement - Makes it easier to remove- Can be made even weaker with petroleum jelly
62
What are the two types of temporary cements?
- With and without eugenol
63
What can't eugenol containing temporary cements be used for?
- Not used to cement provisional restoration where permanent restoration will be cemented with resin cement- Any eugenol residue can interfere with setting of resin cement
