| How
comprehensive is the clinical experience with the Lava
All Ceramic System? |
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The first fixed prosthetics
utilizing Lava zirconia were cemented by the end of 1999.
By August 2003 there were more than 15.000 units in situ.
But it must be remembered that this is the first time
that an all ceramic system of such high strength has been
available. Laboratory simulation experiments verify a
unprecedented long-term strength. There is now every indication
that Lava may be used for metal-free prosthetics in both
posterior and anterior regions! |
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What
distinguishes Lava from the other all ceramic systems
and what is its composition? |
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Lava is based on a framework made from
zirconia (Lava Frame) and a feldspathic overlay porcelain
(Lava Ceram), which has been specially designed to meet
the requirements of the framework. The zirconia ceramic
is a tetragonal polycrystalline zirconia partially stabilised
with yttria (admixture of approx. 3 mol-%) (Y-TZP = Yttria
Tetragonal Zirconia Polycrystals). |
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| How
does the accuracy of fit compare with typical porcelain
fused to metal? |
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Literature indicates a theoretically
required accuracy of 50 - 100 µm for crowns &
bridges. Internal and external investigations verify an
accuracy of fit of 30 - 100 µm with crowns and bridges
designed and fabricated using the Lava All Ceramic System.12a,
12b |
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| Is
Lava really sufficiently strong for posterior bridges? |
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With zirconia frameworks strengths
that exceed the maximum masticatory load (450 N) several
times, posterior applications are possible for the first
time. Internal and external investigations confirm that
3-unit bridges after artificial ageing (simulation of
5 years carrying time) in the mastication simulator (1.2
million cycles) with simultaneous thermocycling (10.000
x 5°-55°C) have a strength of 1.450 N to 1.200
N for 3- or 4-unit bridges, respectively. |
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| How
aesthetic are the results with Lava? Is zirconia white(-opaque)? |
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The Lava zirconia framework is ideally
translucent due to its high density (no residual porosity)
and homogeneity - no longer white-(opaque), as we know
it from the past technical/medical applications. Interestingly,
the framework wall thickness of 0.5 mm, which is possible
due to the high strength of zirconia provides ample opportunity
for aesthetic layering with the overlay porcelain. There
is the unique option of coloring the zirconia framework
in 7 VITA Classic shades. The veneer system provides a
range of intensive and characterizing materials, in addition
to 16 VITA Classic shades. |
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| What
are the preparation requirements for a successful long-term
restoration? |
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In principle, many of the requirements
for a porcelain fused to metal restoration can be applied
to the Lava All Ceramic System. Fabrication of a Lava
restoration requires a preparation having a circumferential
chamfer or shoulder. The preparation angle should be 4°
or greater. The inside angle of the shoulder preparation
must have a rounded contour. The preparation for the Lava
all ceramic restoration can be done with removal of less
tooth structure thanks to the framework’s thin wall
thickness of only 0.5 mm. Supragingival preparations are
possible due to Lava’s excellent fit characteristics
and optical properties. |
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Why
don’t Lava restorations have to be luted using adhesive?
Which cement is recommended? |
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Permanent Cementation
The strength of Lava Frame frameworks is so high that
adhesive cementation provides no additional advantages
with respect to strength! The material can neither be
etched nor directly silanized with silane coupling agent.
Conventional Cementation
For cementing use conventional glass ionomer cements,
e.g. Ketac Cem, manufactured by 3M ESPE. The use of phosphate
cements fail to provide the desired aesthetic results.
Adhesive Cementation with RelyX Unicem
For adhesive cementation of the surfaces without silanization
with the Rocatec System the new self-adhesive universal
composite cement RelyX Unicem is suitable. For adhesive
cementation with silanization with the Rocatec System
please proceed as described under point “Adhesive
Cementation with Composites”.
Adhesive
Cementation with Composites
For the adhesive cementation with composite cements,
the adhesive surfaces must be silicatized with Rocatec
Soft or Cojet Sand for 15 sec and silanized with ESPE
Sil. All products are manufactured by 3M ESPE. Soon thereafter,
place in the mouth with composite cement, e.g. RelyX ARC,
RelyX Unicem. If desired, a fit test has to be done before
silicatization/silanization. For details on processing,
please refer to the Instructions for Use of the Rocatec
System or Cojet Sand. Glass ceramics are frequently luted
with adhesive bonding, to enhance esthetics and increase
the strength of the entire tooth/restoration system. This
no longer applies with polycrystalline oxide ceramics
(Lava). This method of cementation will not result in
any further increase in strength. |
