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