Discussion
The prosthetic rehabilitation of distal extension edentulism using
conventional RPD is a challenge to the prosthodontist as it inherently
poses several problems essentially of a biomechanical nature. Subjected
to functional solicitations, the prosthesis undergoes various parasitic
movements.6 These movements are:
-The rotation around the axis of the crest.
- The recurrent distal sinking movement due to the tissue duality, which
is characteristic of terminal edentulousness. In fact, the conventional
RPD is based on two structures of different nature and behavior, the
mucosa and the periodontal ligament surrounding the abutment tooth.
Under pressure, teeth are displaced by 0.1 mm into the periodontal
ligament, whereas the mucosa overlying the residual alveolar bone may be
displaced by as much as 2 mm depending on the thickness of the
fibromucosa. This differential is the origin of the posterior sinking
movements of the prosthetic saddle.7
- The movement of distal detachment following the absence of distal
retention.
In this clinical case, it is a mandibular unilateral terminal edentulism
bordered by a lateral incisor. The biomechanical problem is more
important given the loss of the left canine. The presence of the lateral
incisor on the edge of the edentulism is a critical factor. Neither the
almost flat shape of this tooth nor its low periodontal value allowed
satisfactory retention to be obtained using clasps.
It was then judicious to propose rehabilitation by ISRPD to the patient,
given her requirement for good prosthetic stability and the financial
constraints prohibiting the use of fixed prosthesis.
Since a small number of implants can be used in the context of ISRPD,
they had to be positioned in strategic places, hence the notion of
strategic implant.5
The biomechanical problems previously exposed can be clinically resolved
with a single implant on the distal edentulous sites that improves the
prosthetic balance and the patient satisfaction by creating a point of
support and posterior retention.
ISRPD can be suggested as an advantageous and less cost-effective
treatment option for the partially edentulous patients. Previous results
showed that the placement of an implant in the distal extension site of
the RPD can improve the distribution of the occlusal forces, limits
lateral and vertical displacement of the RPD, reduces its distal
extension, and reduces its potential rotational movement. In this case,
an implant was placed in the site of the first molar to restore the
prosthetic balance polygon.1,3,5,6,7,8,9
In a finite element analysis, it has been demonstrated that placing
posterior implants, assisting free-end RPDs improves the occlusal
support and reduces the stress in the temporomandibular
joint.10
Moreover, implant support decreases the resorption of the alveolar
ridges and the need of relining procedures in the following
years.11,12
The studies revealed an overall of 98% implant survival rate for
mandibular Kennedy class I or II cases.6,11,13
The literature review showed also increase in patient satisfaction, oral
health-related quality of life scores, and masticatory
ability.14,15
It is important to point out that ISRPD presents triple supports:
dental, implant and osteo-mucous.7 The weak link in
this triology is the implant since it has no possibility of resilience.
It was necessary to avoid overloading it by limiting the sinking of the
terminal saddle by a sectoral anatomo-functional impression technique,
with the particularity of using the frame as an impression tray to put
oneself in the same conditions of use of the future prosthesis. It also
allows to transfer the exact position of the implant in the three planes
of space.
In this clinical report, a locator attachment was used. This type of
attachment is indicated in the case of a reduced available prosthetic
space. It is a resilient attachment offering a slight freedom of
movement and avoids overloading the teeth and the
implant.16,17
Despite all interests in using implants to stabilize RPDs, some
mechanical and biological complications were mentioned such as a
marginal bone loss, implant mobility and fracture of the denture base.
The average marginal bone loss varies from 0.64 to 2
mm.6