properties part 2 6

Question 1

Mechanical properties

Depend on:

Answer 1

The type and proportion of the inorganic filler Conventional and hybrid composites - good
Composites with microfiller (under 50%) - low

Efficiency of the bond between the filler and the resin matrix
Inefficient silane coupling agent – resistance to compression decreases with 30%

The porosity of the material after setting Light curing composites
Self curing composites

Question 2

hardness of a RC is influenced by the

Answer 2

filler ratio
type of the organic matrix

If the RC has a reduced hardness it will be abraised
faster rough surface = accumulation of bacteria » Air inclusion during working with the material
» Finishing and polishing of the filling material using
different rotative instruments

Question 3

hardness effect

Answer 3

Reduced hardness of RBCs → Abrasion (rapid process)
(much higher in enamel)
(higher in hybrid than microfilled)

Question 4

Difference between roughness and abrasion

Answer 4

The roughness of the surface may be caused by:
air included in the material => voids on the surface of self
cured composites
mechanical finishing techniques
Repolish the rough surface (apply a thin layer about 100 μm of adhesive) –not resistant → quick abrasion

Question 5

Negative effects of incorrect finishing

Answer 5

Changes in the aspect of RBC fillings:
- dullness
- surface stain due to food pigments
- color changes
in hybrid with bigger particles—>bigger defects
in micro hybrid where the filler is lower—>reduced defects

Question 6

Finishing and polishing recommended procedure

Answer 6

1. Diamond burs to adjust the surface morphology Must be followed by the use of
2. Tungsten carbide finishing burs (12-30 blades)
3. Aluminium Oxide bonded finishing discs (+finishing strips) 4. Al2O3 bonded polishers
   can be associated polishing with
4. Brushes and polishing paste - do not diminish the roughness but make the filling ‘‘shiny’’

Question 7

Biocompatibility of the RBC

Answer 7

RBCs have a moderate cytotoxicity, usually reversible after 5-8 weeks because the secondary dentin layer is produced
light cured RBCs are less toxic than self cured RBCs ( different initiators and accelerators)
Reducedcytotoxicity after24-48hfromthecompositessetting time and in the presence of a 1mm protective layer of dentin
Toxic components:
2-hydroxi-4-benzophen (3mm dentin) benzoic peroxide (

Question 8

Advantages of RBCs

Answer 8

Esthetic materials, maintain the colour in time
– Conservative cavity preparation
– Reduced thermal conductivity
– Various clinical use
– Good bond to the dental tissues through adhesive systems
– Low microleakage (when a proper application technique is used)
– Reduced peripheral staining
– Reinforcing dental structures
– The composite fillings can ‘‘be repaired’’

Question 9

Disadvantages of RBCs

Answer 9

Improper marginal fit,usually, gingival mainly because of :
– Polymerization shrinkage
– Difficult handling (viscosity)
– Must be used rubber dam isolation !!!!
– More difficult to be made and more expensive than the amalgam fillings :
– Involves more stages
– Difficult handling (viscosity)
– Difficult reconstruction of the contact points – Care when finishing and polishing
– Higher wear rate especially in the lateral zones

Question 10

Indications of RBCs

Answer 10

– Pit and fissure sealents
– Changes of tooth volume and colour
– Direct veneers
– Closing interdental diastema
– T ooth coloured fillings
– Indirect veneers and inlays
– Core build-up(abutment reconstruction)

Question 11

indications for microfilled(or nano filled)

Answer 11

Composite fillings class III, IV, V

In the functional contact areas – can be replaced with hybrid RBC (oral surfaces, incisal margins)
Good to use transparent matrices, well adapted to the tooth contour, finishing the restoration with burs
Opaque RBCs to hide discolorations brings extra light curing time

Question 12

indications for hybrids(or nano hybrids)

Answer 12

Composite fillings class I and II

Never RBCs with microfiller
Avoid situations when the interproximal contacts are on the composite material
2nd class cavities – could have notable wear
For the big cavities the polymerization shrinkage causes
problems within the bond between adhesive-dental structure
Vertical placing technique / or zig-zag technique + proper direction of the light source

Question 13

contraindications

Answer 13

–Improper isolation of the operating field

–When the occlusal contact area is on the composite –Alergies

Question 14

Alternative to direct RBC restorations

Answer 14

RBC Inlay

Ceramic Inlay