Dentaltown June 2020 - 43

Fig. 4

Compressive forces push masses toward each
other. Tensile forces pull objects apart. Shear
forces cause sliding.18 The shear forces are
the most dangerous to implants and bone
when compared with other load modalities.
Cortical bone is strongest in compression
and weakest with shear.25 This off-axis load
will result in increased shearing forces on
the implant.
Second, the final restoration typically
has unfavorable contours with cantilevered
restorative material (Fig. 2). There is a direct
relationship between the length of the cantilever and the force applied to the prosthesis.26
The greater the cantilever, the greater the
tensile and shear forces that are applied to
the implant. This results in a greater increase
in the third unfavorable result: greater risk
of peri-implantitis and fracture. Because
of these unfavorable contours, there is an
increased risk of food entrapment, microbial
buildup and peri-implantitis.
Lastly, because of the increased forces on
the cantilevered segment, there is a great risk
of screw loosening. Screw loosening has been
found to be the most common postimplant
prosthodontic complication, accounting for
about 33% of all such complications.27 Screw
loosening may contribute to crestal bone
loss because bacteria are able to colonize
and harbor in the open interface. If a loose
abutment screw is not treated, fracture of the
prosthesis, implant components or implant
body may occur.

4. When possible,
platform-switch
What was once considered a novel idea
because of chance fi ndings with certain
implants has now gained popularity based
upon the clinical research.28-32 An abutment
with a platform matched to the implant
body would typically see boneless to the first
thread. This was thought to be the result
of microtensile factors18 or the microbiota
invading the first available "microgap"
(Fig. 3).32 When platform-switched, the
"microgap" is moved to the top of the
implant platform and demonstrates not
only less bone loss but also less chance of
peri-implantitis.28-32

Fig. 5

5. Lab communication
Nothing should be taken for granted
when it comes to ordering your implant
prosthesis-or any indirect restorations, for
that matter-from the lab. It is true that
most labs are very knowledgeable regarding
the fabrication of these restorations; however,
they aren't aware of your patient's particular
conditions unless you inform them. Adjacent
or opposing teeth with mobilities, adjacent
or opposing existing restorations, and even
an internal derangement in the TMJ can
cause occlusal changes that the lab should
be aware of.
The existing opposing dentition can be
responsible in the changes in the patient's
bite-force ability. These have been reported
to be less than 50 psi in patients wearing
full dentures,33 approximately 250 psi in
patients with natural dentition,34 greater
than 250 psi in patients with crown and
bridge present 34 and more than 500 psi
in patients with implants in the opposing

Want more CE credits?
Check out Dr. Nosti's
latest online courses
Dr. John Nosti's latest video CE course,
Treatment Planning and Restoring
Implants in the Aesthetic Zone, went live
on Dentaltown.com in late May. It's one
of more than a dozen video courses that
he's created exclusively for Townies about
restorative dentistry, implants, occlusion,
cosmetic dentistry, prosthodontics
and more. To check them out, head to
dentaltown.com/nosti-ce.

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Dentaltown June 2020

Table of Contents for the Digital Edition of Dentaltown June 2020