RBCs for direct restorations 4

Question 1

Composition

Answer 1

Three-phase systems:
I. organic phase (continuous)
II. inorganic phase (discontinuous) = the filler
III. silane coupling agents
The inorganic phase, after a treatment with a silane is uniformly dispersed within the organic phase
The organic phase contains monomers which, through polymerization, form a 3-D network into which is mixed
the inorganic filler

Three-phases:
I. The organic phase – the type, ratio of the components (base monomers, dilution monomers, activators)
determine polymerization shrinkage
II. The inorganic phase – type, ratio, size, distribution determine compression strength, abrasion strength,
polymerization shrinkage, thermal expansion
III. The silane coupling agents – efficient (good)
bonding

Question 2

CLASSIFICATION

1. According to initiation mechanism of polymerization

Answer 2

class 1 – self-curing
• class 2 – external energy source (light or heat)
-group 1 – intraoral application
-group 2 – extraoral application(inlay and onlay)
• class 3 – dual treatment (polymerization)

Question 3

classification

According to the organic matrix type

Answer 3

based on Bis-GMA
• based on UDMA
• mixed
• other base monomers

Question 4

classification According to initial consistency (compared with the
quantity of dilution monomers and inorganic filler)

Answer 4

for sealing (fluid)
flowable
viscous
packable

Question 5

classification According to the particles of filler

Answer 5

macrofilled (20-30 μm)
• midifilled (1 - 10 μm)
• minifilled (0,1 - 1 μm)
• microfilled (0,01 - 0,1 μm) 30-60%
• hybrid (midi + minifilled)wt 83–90%
• microhybrid (mini + microfilled) •
 nanofilled (0,005 – 0,01 μm)> 60% wt

Question 6

presentation mode

Answer 6

Bicomponent (self-cured)
⇒2 pastes: Base + Catalyst(Accelarator)
⇒ mixed according to the manufacturer’s instructions
• Monocomponent(light-cured)
=> 1 paste – inside a black plastic syringe
(containing all the necessary ingredients)

Question 7

Base monomers

Answer 7

dimethacrylate compounds with high molecular weight, low polymerization shrinkage and reduced capacity to wet the hard dental tissues

• advantages: voluminous structure => they have a reduced polymerization shrinkage.
• disadvantages: increased viscosity, high molecular weight → hard to be applied into dental cavity → new monomers with similar structure (Bis-MA, Bis- EMA, Bis-PMA) or completely different UDMA

Question 8

base monomers- ideal properties:

Answer 8

minimum polymerization shrinkage - low viscosity and volatility

• reduced water sorption
• adhesion to the hard dental tissues - minimum toxicity

Question 9

CLASSIFICATION According to base monomers type (composites:)

Answer 9

based on Bis-GMA
• based on UDMA
• mixed
• other base monomers (e.g. siloranes

Question 10

Dilution monomers

Answer 10

mono-, di- or trifunctional compounds (with 1, 2, 3 reactive groups) with reduced molecular weight, so with reduced viscosity, being mixed into organic phase to dilute the base monomers with high viscosity
e.g.=> TEGDMA, HEMA
the properties of the RBCs are influenced by the
type and ratio of the dilution monomers:
very fluid monomers or high amounts of them increase of polymerization shrinkage with unpleasant effects – low adhesion, poor marginal adaptation

Question 11

Initiation systems of polymerization

Answer 11

substances which release free radicals
- Self-curing
- Initiator – organic peroxide (BPO) (within
base)
- Accelerator – aromatic tertiary amine (N,N – diethanol p-toluidine) (within catalyst)
- Light-curing
- CQ (camphorquinone)
- N,N-dimethyl-aminoethylmethacrylate (DMAEM)

Question 12

CLASSIFICATION According to initiation mechanism of polymerization

Answer 12

class 1 – self-curing
• class 2 – external energy source (light or heat)
group 1 – intraorally (using direct composites) applied
group 2 – extraorally (using indirect composites) applied (inlay and onlay)
• class 3 – dual treatment (polymerization) (Self- + Light-curing treatment)

Question 13

Additives

Answer 13

chemical compounds with different functions
(under 0.5% from organic phase):
- inhibitors of polymerization – assure a long storage time of the RBCs (hydroquinone)
- UV stabilizers – absorb the UV radiations, which may lead to the RBCs’ aging
- pigments - impurities

Question 14

The inorganic phase (the filler)

Answer 14

quartz, colloidal silica, glasses, Li aluminosilicates, Li boronsilicates, glasses based on Ba oxide
• the filler’s ratio may vary within large limits: 30 - over 90% weight

Question 15

Silane - coupling agents

Answer 15

assure the uniform dispersion of the filler within organic phase and a strong and stable bond in time between 2 phases (A174)
• treatment of the inorganic filler with silanes will form chemical bonds between silanes and the surface of the filler particles = silanization.
• thus the treated inorganic filler is dispersed within organic phase
• for the composite’s polymerisation, the reactive groups of the silanes participate to the polymerisation reaction together with the monomer group, making the chemical bond with the organic matrix