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BDS3 DMS > Luting Agents > Flashcards

Luting Agents Flashcards

1
Q

luting agents aka (4)

A
  • dental cements
  • composite resins
  • self adhesive composite resins
  • surface modifying chemicals
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2
Q

properties of luting agents (9)

A

Viscosity and film thickness

Ease of Use

Radiopaque

Marginal seal

Aesthetics

Solubility

Cariostatic

Biocompatible

Mechanical properties

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3
Q

viscosity and film thickness importance for luting agents

A

Must be low to allow seating of the restoration without interference.

Viscosity increases as material sets, so must seat restoration quickly and maintain pressure.

Film thickness should be as thin as possible ideally 25um or less.

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4
Q

viscosity and film thickness of luting agents dependent on

A

Dependant on the size of powder or filler particles in the material.

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5
Q

ideal viscosity and film thickness luting agents

A

thin as possible ideally 25um or less.

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6
Q

ease of use of luting agents importance

A

Easy to mix

  • Many products encapsulated
  • Clicker system

Working time should be long to allow for seating of the restoration

Setting time should be short

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7
Q

radiopaque of luting agents importance

A

some ceramic crown are radiolucent

makes it easier to see marginal breakdown

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8
Q

marginal seal of luting agents importance because

A

Ideally the luting agent should bond chemically to the tooth and the indirect restoration with a permanent and impenetrable bond.
- Some of the newer materials approach this, but not quite

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9
Q

aesthetics of luting agents importance

A

tooth coloured - variation in shade and translucency

non-staining

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10
Q

solubility of luting agents should be

A

low

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11
Q

cariostatic nature of luting agents should be

A

F releasing

antibacterial

imp in preventing secondary caries around crown margins

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12
Q

biocompatibility of luting agents

A

non toxic

not damaging to pulp

  • inappropriate pH
  • heat on setting low

low thermal conductivity

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13
Q

mechanical properties of luting agents

A

High compressive strength
- Dentine around 275 MPa

High tensile strength
- Dentine around 50MPa

High Hardness Value

  • Dentine around 70K
  • Enamel around 400K

Young’s Modulus similar to tooth
- Dentine around 15 GPa

No luting agent gets close to tooth values for more than one or two physical properties

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14
Q

types of luting agent material (3)

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
  • Requires etch but has own bonding agent incorporated
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15
Q

dental cement - zinc phosphate

A

In use for 100+ years

Acid base reaction

Powder and liquid

Excellent clinical service

Easy to use

Cheap

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16
Q

zinc phosphate cement - constitutes

A 
Powder
- Zinc Oxide >90% 
(Main reactive ingredient)
- Magnesium Dioxide <10%
(Gives white colour
Increases compressive strength)
- Other Oxides (Alumina and Silica)
Improve physical properties
Alter shade of set material

Liquid

  • Aqueous solution of phosphoric acid (approx. 50%)
  • Oxides which buffer the solution

Aluminium oxide
- Ensures even consistency of set material
Zinc Oxide
- Slows the reaction giving better working time

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17
Q

liquid component of zinc phosphate cement

A
  • Aqueous solution of phosphoric acid (approx. 50%)
  • Oxides which buffer the solution

Aluminium oxide
- Ensures even consistency of set material
Zinc Oxide
- Slows the reaction giving better working time

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18
Q

powder component of zinc phosphate cement

A 
- Zinc Oxide >90% 
(Main reactive ingredient)
- Magnesium Dioxide <10%
(Gives white colour
Increases compressive strength)
- Other Oxides (Alumina and Silica)
Improve physical properties
Alter shade of set material
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19
Q

reaction for zinc phosphate cement

A

The initial reaction is acid base
ZnO + 2 H3PO4 -> Zn(H2PO4)2 + H2O

This is followed by a hydration reaction resulting in the formation of a crystalised phosphate matrix

ZnO + Zn(H2PO4)2 + 2H2O -> Zn3(H2PO4)2.4H2O
(Hopiete)

The aluminium oxide prevents crystalisation leading to an amorphous glassy matrix of the acid salt surrounding unreacted ZnO powder.

This matrix is almost insoluble, but it is porous and contains free water from the setting reaction.
- The cement subsequently matures binding this water leading to a stonger, less porous material

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20
Q

problems with zinc phosphate cement (7)

A

Low initial pH approx. 2
- Can cause pulpal irritation as pH can take 24hrs to return to neutral

Exothermic setting reaction

Not adhesive to tooth or restoration

  • It works like grout on tiles just filling in any spaces.
  • Retention may be slightly micromechanical due to surface irregularities on prep and restoration

Not cariostatic

Final set takes 24hrs

Brittle

Opaque

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21
Q

zinc polycarboxylate cement

A

Similar material to zinc phosphate but phosphoric acid replaced by polyacrylic acid.

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22
Q

zinc polycarboxylate cement advantages (4)

A

This material had the advantage of bonding to tooth surfaces in a similar way to glass ionomer cements.

There is less heat of reaction.

The pH is low to begin with but returns to neutral more quickly and longer chain acids do not penetrate dentine as easily.

Cheap.

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23
Q

zinc polycarboxylate cement disadvantages (5)

A

Difficult to mix

Difficult to manipulate

Soluble in oral environment at lower pH

Opaque

Lower modulus and compressive strength than Zinc Phosphate

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24
Q

dental cements are

A

mainly historic

seldom used nowadays

All of the more modern materials utilise chemical bonding to the tooth surface.
Many of these materials can also bond to the indirect restoration as well.

25
glass ionomer cement
Chemistry of the luting cement is exactly the same as the filling material The main difference is particle size of the glass which is less than 20um to allow for suitable film thickness – can’t be used as a filling material
26
glass ionomer cement reaction
Acid base reaction between Glass and Acid - Glass is SiO2, Al2O3 and CaF2. - Poly acid mixture of Acrylic, Maleic and Itaconic acid and their copolymers. The reaction goes through the same dissolution, gelation and hardening stages.
27
glass ionomer cement bonding
Cement bonds to tooth surface through - Ion exchange with calcium in enamel and dentine - Hydrogen bonding with the collagen in the dentine This results in a fairly strong, durable and possibly dynamic bond to the tooth. There is no chemical bond to the restoration surface. - The surface of the restoration should be sandblasted to allow mechanical adhesion
28
benefits of GIC as luting agent
Clinically easy to use and durable cement Low shrinkage Long term stability. Relatively insoluble once fully set. Aesthetically better than ZnPhos. – can come in different colours Self adhesive to tooth substance. Fluoride release. Cheap.
29
Resin modified glass ionomer cement
Chemistry is the same as RMGI filling material Glass particle size is smaller to allow acceptable film thickness In addition to conventional GIC powder and liquid the liquid contains a hydrophilic monomer The monomer must be hydrophilic as GIC is a water based material. HEMA (Hydroxyethyl methacrylate)
30
RMGI reaction
The same acid base reaction occurs. Light activation causes polymerisation of the HEMA and any copolymers in the material leading to a rapid initial set. The acid base reaction then continues for some time. Some materials have a secondary cure via a REDOX reaction - This allows ‘Dark Curing’ where material not exposed to light will cure.
31
incorporation of resin to GIC improves (5)
Shorter setting time Longer working time Higher compressive and tensile strengths Higher bond strength to tooth Decreased solubility
32
3 issues with RMGI
HEMA is cytotoxic - Very important that no monomer remains as it can damage the pulp. HEMA swells, it expands in a wet environment - It cannot be used to cement conventional porcelain crowns as they may crack - It shouldn’t be used to cement posts as it may split the root No bond to indirect restoration
33
composite luting agents
simplest of these materials are variants on composite filling materials with suitable viscosity and filler particle size
34
composite luting agents needs to be used in conjunction with
a suitable DBA
35
composite luting agents properties
light or dual cured - need light cured as properties reduced by 25% if not better physical properties, lower solubility and better aesthetics but technique sensitive
36
bonding of composite luting cements to indirect composite
Composite bonds to composite Bond strength is lower to inlay fitting surface than to new composite Bond is micromechanical to rough internal surface of inlay Bond is also chemical to remaining C=C bonds on the fitting surface of the inlay Use a dual curing cement as light penetration through the inlay will be poor
37
bonding of composite luting cements to porcelain
Porcelain is brittle and requires to be bonded to tooth to prevent fracture Untreated porcelain is smooth and non retentive. It can be treated with HF to etch the surface (v toxic). This produces a rough retentive surface but it is still not hydrophobic and compatible with composite resin luting agents. A surface wetting agent is required.
38
silane coupling agent
Gamma-methacryoxypropyltrimothoxysilane Applied to the etched porcelain surface, ideally as a monolayer Very strong bond between oxide groups on the porcelain surface and the silane. The other end of the silane molecule has C=C bond which reacts with the composite resin luting agent. This works in the same manner as a dentine bonding agent does with tooth. This is the same mechanism as bonding filler material to resin matrix in composite resin filling materials.
39
type of bond to porcelain from composite bonding luting agents
Strong durable bond Only use a light cured composite luting agent if the porcelain restoration is thin. - You must increase your curing time. - If the restoration is thick use a dual cured composite. - Remove as much of the luting resin as possible before curing.
40
bonding to metal by composite bonding luting agents
Like porcelain composite materials do not bond directly to metal Metal surface needs to be roughened. - done by etching - More usually done by sandblasting Etching metal - Electrolytic etching removes the different phases of the alloy at different rates - gives a very retentive surface ``` BUT - Technique sensitive - Beryllium containing alloys work best - Cannot etch precious metals at all Seldom Used Nowadays ```
41
sandblasting metal
roughens surface but does not give the undercut surface of etching needed for composite luting agents chemical bonding is required to stregthen the bond
42
bonding to non-precious metal surface with composite luting agents system
Materials with carboxylic and phosphoric acid derived resin monomers. MDP and 4-META These molecules have an acidic end and a C=C end The acidic end of the molecule reacts with the metal oxide and renders the surface hydrophobic. This is the same as DBA and Silane
43
bonding to metal with composite luting agents system
Must use a dual curing material as light will not penetrate metal. This system can be used to cement most crowns, bridges and posts. These materials will not bond to precious metal. Technique sensitive and will not work unless moisture control is adequate.
44
bonding to precious metal with composite luting agents system
Change precious alloy composition to allow oxide formation - Increase copper content and heat 400oC in air Tin Plate Sulphur based chemistry of bonding agent All complicated and technique sensitive.
45
self adhesive composite resin
The metal coupling agent is incorporated into the composite resin. This simplifies the bonding process MDP is used in Panavia This is an anaerobic self cured material
46
self adhesive composite resin properties
Consistent results over many years Good film thickness Opaque Moisture sensitive Expensive
47
self etching composite resin cements (e.g. Rely X Unicem)
This is a combination of a Composite resin cement and a Self etching dentine bonding agent. Sound like a great idea as it should stick to everything and it is easy to use. However as with all dentine bonding it requires good moisture control. There is also doubt about the bond strength to enamel due to inadequate etching. The pH of the carboxylic monomer doesn’t stay low for long enough to give a good etch.
48
self-etching composite resin luting agents bonding
Attaches like a self etching primer(sort of) Acidic groups bind with calcium in hydroxyapatite forming a stabilising attachment between the tooth and the resin Ions from dissolution of filler neutralise the remaining acidic groups forming a chelate reinforced methacrylate network Limited removal of smear layer or significant infiltration into the tooth surface. (only a couple of microns) Good bond strength to dentine
49
properties of self etching composite resin luting agents
mechanical properties - compressive strength - tensile strength - hardness wear resistance all slightly lower than convention resin luting agents but better than cements
50
bonding to enamel of self etching composite resin luting agents
lower than to dentine should be etched with acid prior to application
51
bonding to dentine of self etching composite resin luting agents
better than to enamel should not be etched with acid prior to application
52
bonding to ceramics of self etching composite resin luting agents
brand specific RelyX unicem seem to bond quite well to sandblasted Zironica
53
bonding to metal of self etching composite resin luting agents
better to non-precious not good enough to cement ortho brackets
54
use of of self etching composite resin luting agents
Probably the way forward - Very few clinical studies. Nothing long term enough If you can’t use a DBA and conventional resin cement, you can’t use these. They do not get round the problems of moisture control.
55
temporary cements
Made to cement temporary restorations in place while permanent restoration is fabricated. - Soft for easy removal some do not set at all. - Prep must be physically retentive, or they will not work. - Can be used for trial lute of permanent restoration to allow assessment by patient or clinician.
56
how to dispense temporary cements
Supplied as two paste systems base and catalyst or accelerator - Base contains ZnO, Starch and mineral oil - Accelerator contains resins, eugenol or ortho-EBA and carnauba wax - The wax weakens the structure of the set cement and makes it easier to remove - Material can be modified to make it weaker still by incorporating petroleum jelly into the mixture
57
2 main types of temporary cements
Two main types those with and those without eugenol Eugenol containing materials should not be used to cement the provisional restoration where the permanent restoration will be cemented with a resin cement. - Any residual eugenol may interfere with the setting of this type of luting agent.
58
what is essential to do when removing temporary cement
Irrespective of the type used complete removal of the temporary cement is essential. (eugenol or non eugenol)

BDS3 DMS (9 decks)

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