Dr. lama khaled El Banna Faculty of Oral and Dental Medicine Al – Azhar University operative dentistry part two

2. College of Dentistry
Operative Dentistry II
Direct Esthetic Tooth-Colored
Restorations -4-
Dr. Hazem El Ajrami

3. • Advantages of visible light-cured over
chemical-cured composite:
1. Command setting i.e. unlimited working time:
in chemically-cured composite the reaction
starts the moment the two components are
mixed, thus the working time is restricted by
the speed of the chemical reaction. In light-
cured composites, however, light curing can
be delayed until the material is inserted and
properly shaped. This gives the dentist better
control on the curing process and longer
working time. Thus, light-cured composite
usually requires less finishing time than
chemical-cured ones.

4. 2. No incorporation of air bubbles (one paste):
during mixing of chemically cured composite
air bubbles are trapped leading to internal
porosity in the final mix (soft spots due to
oxygen inhibition of polymerization). This
affects the quality of the final restoration.
3. Improved color stability: the aliphatic tertiary
amine activator in light-cured composites is
more color stable than the aromatic tertiary
amine in chemically-cured composites.

5. 4. Better control over amount and direction of
polymerization shrinkage: chemical-cured
composites shrink towards its center, while
light cured composite shrink towards the
light because activation first takes place at
the point closest to the light source.

7. • There are two techniques for packing of
resin composite:
A. Bulk technique:
The composite is applied in one single bulk
inside the cavity. This technique is used with
chemical-cured composites. It can also be
used with light-cured composites in small
non-deep cavities, where the thickness of
composite does not exceed 2 mm. to ensure
full penetration of light and hence adequate
polymerization.

8. B. Incremental packing technique:
Used with light-cured composites only.
The restorations are placed in successive
small increments (not more than 2 mm.),
each light-cured independently. In
incremental packing the total polymerization
shrinkage is reduced because each increment
compensates for the shrinkage of the
previous one.

9. • In addition, the direction of polymerization
shrinkage could also be controlled by
directing the light curing tip so that each
increment is polymerized towards the walls
rather than away from the walls (guided
polymerization). The use of transparent
matrix and wedges aids in this process.

10. • An example for the use of guided
polymerization:
In the proximal portion of Class II, the first
increment is placed gingivally and cured
through the light-transmitting transparent
wedge. A transparent matrix should also be
used. The buccal and lingual increments are
cured through the buccal and lingual surfaces,
respectively.

12. • Disadvantages of light-cured composites:
Light-cured systems are preferred because of
their advantages. However, it also has some
disadvantages. Direct prolonged eye exposure to
light source should be avoided as it can cause
retinal damage. Heat generation from the light
source could cause pulpal irritation if the
remaining dentin thickness is very thin. However,
the most important clinical limitation of light-
cured composite is its limited depth of cure which
directly affects the degree of polymerization of
composite and hence all its properties.

13. Variables affecting the depth of cure:
1. Light curing unit:
A. Light intensity of the curing unit directly
affects the depth of cure; increasing the light
intensity increases the depth of cure. The
intensity of light should not be below 400
mW/cm² and should be checked
periodically.
B. The time of light exposure also have direct
relation to degree of cure. The curing time
for most composites under a continuous
curing mode is 20 to 40 seconds.

14. C. The distance between light source and
composite also affects the depth of cure. The
tip of the light curing unit should be placed
as close as possible from the composite (zero
distance to within 1 mm. is acceptable).
Increasing the distance decreases the
intensity and hence the depth of cure.

16. D. Angle between light curing tip and
composite should be 90°. As the angle
diverges from 90 degrees to the composite
surface, the light energy is reflected away
and penetration is greatly reduced.

17. 2. The composite itself:
A. Thickness of the composite increment is
inversely proportional to the depth of cure.
Increasing the thickness decreases the
depth of cure. Thus, composites should be
placed in increments of not more than 1.5-
2 mm. to ensure proper polymerization.

18. B. Particle size and filler loading: micro-filled
composites are more difficult to cure than
macro filled composites. Generally, the more
heavily loaded a composite is with larger
inorganic fillers, the more easily the resin
cures. However, as discussed before, nano-
filled composites achieve thorough
polymerization as the fillers do not interfere
with light.
C. Shade of the composite: darker composite
shades cure more slowly and less deeply than
lighter shades.

19. 3. Tooth-related factors:
A. Depth of the cavity preparation: in deeper
areas the distance between the light tip and
composite increases, causing attenuation of
light intensity and less depth of cure.
B. Intervening tooth structure: curing through
tooth structure decreases the depth of cure. In
such case, intensity and/or time of curing
should be increased.

21. 8. Finishing and Polishing:
The best finished and polished composite
restoration is the one that is adapted against a
smooth, well-contoured and well adapted
matrix strip; a situation which is nearly
impossible to obtain, since almost all
composite restorations need final shaping,
contouring, finishing and polishing. If a
matrix band is not used an oxygen inhibited
layer is formed on the surface. This layer
should be removed during finishing as it is apt
to discoloration and abrasion.

22. • Gross finishing can be performed with 30- to
40- fluted carbide burs or fine and micro-fine
diamond points.

23. • No. 12 Scalpel blade is very useful and
effective in removing composite flashes from
the tooth structure and in gross contouring of
the restoration. It should be used with caution
from the tooth structure to the restoration.

24. • Finishing and polishing discs (e.g. Soflex
discs) of descending coarseness (coarse,
medium, fine and extra-fine grits) can be used
at low speed. They should be used sequentially
from coarse to fine grits. The coarse grits are
effective for gross reduction and finishing
while the fine grits create a shiny, smooth,
polished surface.

26. • Proximal finishing strips are also available in
sequential grits for finishing of the proximal
portion of a composite restoration.

27. • Finishing and polishing can also be done with
special rubber tips, points or cups impregnated
with abrasive material. They come in variety
of shapes, sizes and grits.

28. Thank You