CERECDoctors.com-Q2-2017 - page 25

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an enamel-ceramic bonded interface will provide the strength
adhesive assembly needed for structural integrity. The beauty of
e.max HT or MT is the ability to create a multi-preparation shine-
through effect by designing the restoration thinner at the margin
and then gradually thickening it toward the body and cusp portion
of the tooth (Fig. 4).
In addition to material minimal thickness, preparation reduction
protocolsshouldtakeintoconsiderationdesiredocclusalmorphology
for the final restoration, functional dynamics of the patient’s occlu-
sion and support base under the IPS e.max restoration.
For instance, an onlaywith a rimof peripheral enamel support will
provide a greater sub-restorative support than a fully prepared crown
preparationwithacompositebuildupunder thefinal restoration. The
author uses the 1.0 mm restorative thickness protocol when there is
solid tooth support and a healthy rimof enamel on themargins.
When considering occlusal reduction, take into account the
occlusal morphological appeal and desired occlusal contact place-
ment. For 1.0 mm minimal thickness to be at the depth of the
primary and secondary grooves, preparation reduction will need
to take in to account the clearance needed for triangular ridge
morphology and avoid lateral interferences.
A high percentage of occlusal coverage restorative upgrades
are in aging, worn dentitions with minimal remaining occlusal
anatomy. These circumstanceswill require 1.5 to 2.0mmreduction
to keep the minimal restorative thickness at 1.0 mm; and a prepa-
ration occlusal reduction style that is not flat, but rather mirroring
the desired cusp angles on either side of the central groove zone.
As a clinician, it is assuring to know that after 10-plus years, IPS
Fig. 2:
1.0 MM MATERIAL THICKNESS
FOR MINIMALLY INVASIVE
RESTORATIONS WHEN
ADHESIVELY CEMENTED
At least 1.0 mm
axial
reduction
Modified
shoulder or
deep chamfer
of at least
1.0 mm
Rounded
internal
line angles
Occlusal material
thickness of at
least 1.0 mm
Fig. 3:
IPS E.MAX LITHIUM DISILICATE
BIAXIAL FLEXURAL STRENGTH
VALUES
Production testing over the last
decade shows that IPS e.max CAD
lithium disilicate has an average
biaxial flexural strength of 500MPa
600
500
400
300
200
100
0
 Flexural strength minimum
 Flexural strength average
Fig. 4: IPS e.max HT A1 characterized with Ivocolor
e.max performance has been proven. And, with additional analysis
and collective sample data of 500MPa flexural strength and surface
toughness of 2.0 to 2.5 MPam, the clinical theater has a broad range
of functional and esthetic restorative options. The more conser-
vative preparation option — when functionally indicated — will
provide an adhesive assembly with more abundant tooth base and,
when applicable to the case, using the dentin optical color shine
through will provide vitality and depth to the final restoration.
For questions and more information, Dr. Klim can be reached at
james@jamesklim.com.