A randomized clinical trial on short endosseous implants in the posterior region.
The influence of platform switching on the marginal bone level.

The aging human might, due to caries or periodontal lesions, loose one or more
of their back teeth in the posterior region of the maxilla or mandible. The
major part of people does not want removable dentures, but prefer fixed
construction as an implant based crown. Frequently, the bone in this posterior
zone is resorbed and there is only enough bone to place a short (<10 mm length)
implant. In the past short oral implants have been associated with lower
survival rates. There are several presumed reasons for a lower survival rate of
short implants in the posterior maxilla or mandible. First, compared to longer
implants with a comparable diameter there is less bone to implant contact when
short implants are used, simply because there is less implant surface.
Secondly, short implants are mostly placed in the posterior zone where the
quality of the alveolar bone is relatively poor, especially in the maxilla.
Thirdly, often a very outsized crown has to be made to reach occlusion, because
of the extensive resorption in the posterior region, which causes a higher
crown to implant ratio.
To avoid the use of short implants the resorbed bone can be augmented using a
bone grafting technique. This modification in the patient*s anatomy makes it
possible to insert a longer implant, but an extra surgical intervention also
leads to greater patient*s morbidity, higher costs and a longer treatment
period. Esposito et al. (2010) concluded from their systematic review on
augmentation procedures of the maxillary sinus: *Short implants may be as
effective and cause fewer complications than longer implants placed using a
more complex technique.* And from their systematic review on horizontal and
vertical bone augmentation techniques for dental implant treatment they
concluded: *Short implants appear to be a better alternative to vertical bone
grafting of resorbed mandibles.* Complications, especially for vertical
augmentation, are common.* From the systematic review of Telleman et al. (2011)
could be concluded that there is fair evidence that short (<10 mm) implants can
be successfully placed in the partially edentulous patient, though with an
increasing survival rate per implant length.
So, short implants are increasingly used for the prosthetic solution of the
resorbed posterior zone of partially edentulous patients. But in short implants
it is important to preserve peri-implant bone, although they might be expected
to develop a greater maximum compressive stress in their coronal region in
comparison to longer implants, which could lead to bone microfracture and
peri-implant bone loss.
A new development in the implant neck design is the concept op
platform-switching; placing a smaller diameter abutment on a wider diameter
implant, which has resulted in less peri-implant bone loss. Several theories
were suggested to explain the rationale behind the concept of platform
switching for marginal bone preservation. The biomechanical rationale proposed
that by platform-switching the stress-concentration zone (from the forces of
occlusal loading) are directed from the crestal bone-implant interface to the
axis of the implant and so greatly reduces the stress level in the cervical
bone area. Another theory concerned the role of inflammatory cell infiltrate at
the implant abutment connection. The presence of peri-implant microbiota was
suggested to influence the crestal bone resorption. The systematic review of
Atieh et al. (2010) about platform switching for marginal bone preservation
around standard or long implants (>10 mm length) showed that peri-implant bone
loss around platform-switched implants was significantly less comparing to
platform-matched implants. As short implants might be expected to develop a
greater maximum compressive stress in their coronal region in comparison to
longer implants, which could lead to peri-implant bone loss, it is not cleat
yet whether platform-switching is also effective in peri-implant bone
preservation around short implants.
To our knowledge no study had been reported about the effect of
platform-switching on peri-implant bone level changes around short implants in
the resorbed posterior zone of partially edentulous patients. There is very
limited evidence regarding the effect of platform-switching (Trammell et al.
2009) on implants shorter than 10 mm in length.
Therefore, the aim of this study is to compare the outcome of short implants
(8.5 mm in length), with a conventional implant-abutment connection to a
platform-switched implant-abutment connection. Implants will be placed in the
resorbed posterior region of partially edentulous patients.

To investigate the influence of platform-switched implant-abutment connections
(smaller diameter abutment on wider diameter implant) of short implants (8.5 mm
in length) on marginal peri-implant bone levels and clinical variables.

A randomized clinical trial

This study is comprised of two groups. Patients allocated to the control group
will be treated with a platform-matched implant-abutment connection (Osseotite
XP Certain implant, Biomet 3i, Palm Beach Gardens, Florida, USA). Patients
allocated to test group will be treated with a platform-switched
implant-abutment connection (Osseotite Certain Prevail, Biomet 3i).

One implant type might lead to less peri-implant bone loss than another type.
There are no further risks involved, since it is a regular dental treatment.
The extra load for the patients is filling in questionnaires.