Untitled - Link 1 Link 16 Link 2 Link 17 Link 3 Link 18 Link 4 Link 19 ...

30 Osseointegration and Dental Implants
For retentive ball anchor abutments, nearly
every dental implant company offers a spherical
retentive ball anchor abutment with a
similar diameter (2.25 mm); these are generally
constructed of titanium. This abutment
allows the use of a variety of retentive attachments,
including titanium and gold cap matrices,
Preci-Clix attachments (Preat Corp.), and
a variety of O-ring attachments. The vast
majority of the gold cap matrices are manufactured
from a single company in Switzerland
(Metaux); these matrices have four
independent gold leaves that can be quickly
crimped together (to increase retention) or
separated (to decrease retention) with precision
devices to activate or deactivate the
attachment; these attachments come with a
plastic spacer around the gold leaves that
must remain in place to allow deactivation
(loosening) of the attachment when processed
in the denture base. The Clix attachment is
the spherical plastic counterpart of the plastic
Hader bar clip. It comes in three levels of
retention (yellow < white < red), and is easily
replaced when worn. Care must be taken to
place the retentive elements parallel to each
other (a dental surveyor is recommended)
irrespective of the angulation of the retentive
ball anchors, in order to maximize the retention
of the prosthesis, facilitate the prosthesis
insertion, and minimize the wear of the components
(Gulizio et al. 2005). This report may
suggest that, with off-axis implants (up to
30º), a reline impression and laboratory
processing of the attachments may be preferred
to intraoral attachment pickup
scenarios.
The resilient cap attachments (Sterngold/
Implamed ERA attachments, and more
recently Zest Locator attachments) have
experienced a long history of serving the
dental community well. Both systems provide
the opportunity to have good retention (1.5–
5.0 lbs of retentive force for both the Zest
anchors and the ERA attachments) and longterm
ease of maintenance. Unfortunately, and
unlike the universal adaptation of the retentive
ball anchor specifi cations, dental implant
companies have aligned themselves with one
or the other resilient attachment systems.
And, while the Locator system offers a single
attachment (green, 4.0 lbs of retention) for
use when the implants are off-axis, the ERA
system requires that the abutments be changed
to their angled varieties to enhance parallelism
for their attachment system to work most
effectively.
Splinted bar-retained overdentures have
been heavily advocated for use in both dental
arches, and especially in the maxillary arch
(because of poor quality of bone), due to
typical resorption patterns of the maxilla
necessitating implant placement in off-axis
locations, or when splinting is thought to be
required when removing the palatal portion
of the maxillary denture prosthesis. It is generally
not recommended to remove the maxillary
palatal portion from the overdenture
prosthesis unless a minimum of four implants
with adequate A-P spread have been placed.
When removing the acrylic palate, the use of
a cast RPD framework to provide strength to
the overdenture prosthesis is highly recommended.
When using the retentive bar system,
the biomechanics must also be considered.
The bar should allow the overdenture prosthesis
to rotate under functional occlusal
loads, rather than placing additional stress on
the implants, or on the bar or its retentive
devices. The round bar, the resilient Dolder
bar, and the Hader bar provide some level of
rotation around the bar proper. Again, in a
paired (two) implant/bar scenario, the bar
should be placed under the confi nes of the
denture base and allow rotation of the denture
in an A-P direction perpendicular to the
patient’s midline. Otherwise, undue stresses
may lead to premature failure of the retentive
elements or implant/bar components. One
must also consider the tremendous amount of
denture base acrylic resin that is lost in order
to accommodate the bar beneath it—the
astute clinician should consider metal wire/
mesh reinforcement of the overdenture prosthesis
whenever splinted bars are used. When
using bar-retained overdentures, the patient
must also be apprised of the increased initial
costs associated with the additional compo-