PARTIAL CERAMIC CROWNS. ESTHETIC AND TISSUE CONSERVATIVE
RESTORATIONS – PART I: POSTERIOR TEETH
Table 4. Etching and silanization regimens for different ceramic and luting materials.
Ceramic
Self-adhesive resin
Feldspatic ceramic, leucit reinforced
glass ceramic 60s HF, silane treatment 60s HF, silane treatment, Adhesive
Lithium disilicate ceramic 20s HF, silane treatment 20s HF, silane treatment, Adhesive
ZrO 2 reinforced Lithiumsilicate-ceramic 30s HF, silane treatment 30s HF, silane treatment, Adhesive
Resin containing materials 60s HF, silane treatment 60s HF, silane treatment, Adhesive
following preparation. Furthermore, contamination
of the tooth structure during impression taking
and temporization is reduced, thus enhancing
the establishment of the adhesive bond. Indeed,
marginal seal could be improved compared to
conventional luting 31 but this technique has not
become very popular as it is rather technique
sensitive and complex. When using the resin coating
technique, final luting must be executed with a luting
composite (and not with a self-adhesive material).
Before luting leucite reinforced and lithium disilicate
ceramics, they need to be etched and then a silane
couple agent has to be applied. The details differ with
the ceramic and the luting material (Table 4) These
procedures are important, because they significantly
improve the bond of the luting composite to the
ceramic.
Biocompatiblity
Ceramics are generally considered to be
biocompatible and no adverse effects like allergies
have been reported. However, luting materials
(often resin-based) are needed, and for resin-based
materials cases of allergic reactions have been
reported. Therefore, care should be exercised to not
use luting materials in patients who have a history of
allergic reactions to components of this material. 39
Furthermore, luting materials come into close and
prolonged contact with dentin and – in deep cavities
– potentially with the exposed pulp. Postoperative
sensitivity has been observed in few cases in our
clinical studies, which abated with time. 10,40 However,
in deep cavities with the possibility of pulp exposure,
a protective layer of calcium hydroxide cement or
a hydraulic tricalcium silicate cement is strongly
recommended. 39,41
8. Light curing: irradiance, time?
Light curing is facing two problems: too little light
applied, which may res ult in insufficient curing, less
retention, wash-out and marginal discoloration or
too much light applied, which may lead – especially
when applied in a short time – to overheating.
Insufficient light output may be due to insufficient
instruments 42 or due to an insufficient technique; 43
e.g. when the tip of the light guide is not directed
correctly to the restoration. Secondary caries has
been associated with insufficient curing of resin-
based composites but also increased release of
substances from the materials and thus increased
cytotoxicity. 44,45 Too much energy delivered by the
light curing units may result in heat damage adding
to the heat produced by the exothermic setting
reaction of the luting composite. High energy light
curing units have recently been marketed with an
278
Adhesive/luting composite
irradiance of > 6000 mW/cm 2 .
Dentin has a low thermal conductivity. 46 As a rule of
thumb, 16 J/cm 2 are needed for optimal curing of
a resin-based composite (e.g. 800 mW/cm 2 for 20
seconds, or 1600 mW/cm 2 for 10 seconds. However,
this rule (increasing irradiance while reducing
irradiating time) cannot be extrapolated to very high
energy levels and very short times like few seconds. 47
Compressed air reduced temperature increase. 48
Polymerization rate is dependent on the light
energy which reaches the luting material. Thus color,
translucency and thickness of the ceramic and the
distance between the tip of the light guide and the
ceramic surface play an essential role when choosing
the right amount of energy. 49,50
Ceramic thickness
In an in vitro study measuring the depth of cure and
the Vickers hardness of a standard luting composite,
Jung et al. 51 found that with a leucite reinforced
silicate ceramic (IPS Empress) and 2 mm ceramic
thickness, at 40 sec 800 mW/cm 2 dual curing leads to
a significantly better polymerization than light curing
only. For a leucite reinforced ceramic of a thickness
of 1 mm, light curing alone resulted in the same cure
as that with an additional chemical cure. 49,52
Translucency
For leucite reinforced silicate ceramic and for lithium
disilicate ceramic, which is less translucent than the
leucite reinforced material, similar curing of a dual
curing luting composite occured with a ceramic
thickness of 1 mm. For a larger thickness, significant
differences were observed. 49 Follow meticulously
the information of the manufacturer: ceramics with
little translucency or dark colors require extended
irradiation times.
Recommendation
• Generally, eyes of the dental personnel should
be protected, e.g. by a shield at the end of the light
guide.
• For posterior teeth, the use of a dual curing luting
composite is highly recommended. For a standard
light curing unit with an irradiance of around 800
mW/cm 2 , an irradiation time of 40 seconds from
occlusal and additional from oral and vestibular are
recommended. 49
• Irradiance levels of 800 to 2000 mW/cm 2 are
regarded as standard. With light curing units emitting
higher radiances, little clinical experience exists, and
heat effect on the pulp or burning of lips should be
prevented; rubber dam provides no protection. 53
9. Step by Step checklist
• Case selection/Prevention program: as luting
resins may enhance bacterial growth and biofilm
Stoma Edu J. 2017;4(4): 270-281
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