Dentaltown June 2020 - 44

Fig. 6

Fig. 7

dentition.33 It is important to notify the lab
what the opposing dentition is and request
further steps to be followed in fabrication.
When possible, a screw-retained crown
is more biologically favorable than a cementretained crown because of dangers of excess
cement.35 The cement-retained crown was
once thought to be more aesthetic, but
because of all-ceramic materials such as IPS
E.max or zirconia, the screw-retained crowns
are equally aesthetic as cement-retained, and
superior to in aesthetics than older PFM
screw-retained crowns (Figs. 4 and 5, p. 43).
With all-ceramic screw-retained crowns,
it is possible to completely hide the screw
holes, if desired (Figs. 6 and 7). However,
some doctors advocate using a different
shade composite to detect the screw hole.
Once the lab is informed about the
opposing and adjacent dentitions, the
recommended occlusal fi nishing is then
requested. Teeth in the natural dentition
move both horizontally and vertically,
even in nonmobile teeth (Fig. 8).36-38 It

44

is important to understand these natural
movements and translate that to the lab
to have an implant that is protected in the
occlusion by the surrounding dentition.
When the lab fabricates the restoration
on stone models, there are no periodontal
ligaments, periodontal tissues, bone, ligaments, nerves or vascular supply to replicate
what we see in the mouth. Because of this,
teeth can move vertically 8-28 microns
(µm) and horizontally 56-108µm (Fig. 8)
within the arch. Doctors typically prefer an
occlusal clearance of 8-10µm and request
that shimstock not hold between the implant
restoration and the opposing dentition.
When the patient clenches, shimstock
should be able to slide through the occlusal
table of the implant crown (Fig. 9).
If one desires shimstock to pull through
vertically and horizontally, the mobility
figures previously reported need to be
added to the shimstock thickness on the
prescription. For example, if one is requesting
an implant crown to replace the maxillary

right first molar (#3, 16) the vertical clearance
requested on the prescription for the lab to
perform on stone models would be 28µm
(vertical movements previously stated)
plus desired occlusal clearance (8-10µm
for shimstock). 28µm + 10µm = 38µm
performed in the lab, which would then
provide the restoring dentist with 10µm
clearance in the mouth once PDL loading
of the adjacent dentition occurs.
For horizontal clearance, we notice that
the adjacent teeth move laterally nearly
70µm (Fig. 8). One would request 70µm
plus the desired occlusal clearance of 10µm
for 80µm laterally on the stone model to
provide 10µm of clearance in the patient's
mouth. If the restoring dentist would prefer
more occlusal clearance, it needs to be
added to these above figures. If you have
noticed clinically you have a lot of occlusal
adjustments to perform on your implant
crowns, changing this protocol to your
prescription may solve this problem.
If the opposing dentition/restorations are
implants, it would be wise to double these
figures to compensate for the lack of PDL
in the implants in the opposing arch. If one
is concerned about the patient's ability to
masticate food, a bolus of food is typically
up to 500µm and larger than these implant
protective guidelines.39

6. Splinting crowns
Unlike the natural dentition, which
has an increased caries rate and endodontic
risk on splinted adjacent crowns, implants
do not have these same issues and greatly
benefit from splinting adjacent implant
crowns together.
"Screw loosening of abutment or
prosthetic screws occurs more often on
individual implant crowns than on crowns
that are splinted together. For example, in
a report for single-molar replacement, the
abutment screw-loosening rate was 40%
during a three-year period. When two
splinted crowns were used to replace the
molar space, the screw loosening was reduced
to 8%.40 The stress distribution of splinted
prosthetic units results in less force applied
to the screw system. Studies have shown

JUNE 2020 // dentaltown.com

DT0620_Nosti_Implants_AG.indd 44

5/20/20 11:30 AM
http://www.dentaltown.com
Dentaltown June 2020

Table of Contents for the Digital Edition of Dentaltown June 2020
