Distal-extension removable partial dentures (RPDs) derive support from teeth and mucosa, which have different resiliency and
viscoelastic responses. Under load, the extension base rotates around a fulcrum line that connects the abutment teeth and is
displaced towards the residual ridge. The insertion of dental implants in the edentulous span to provide support and retention to the
RPDs stabilizes the denture in a vertical direction, improving the load distribution and reducing bone resorption.
The primary objective of our study was to determine whether the use of dental implants underneath the base of a distal-extension
RPD (placed medially or distally) reduces the displacements of the prosthesis and improves strain distribution in the abutment teeth,
cortical bone and soft tissue.
Three mandible models were prototyped from the CAD model obtained from the CBCT of a Kennedy Class I patient. The models
were prepared separately to receive: one conventional RPD (CRPD), one implant-assisted RPD with a mesially placed implant in the
position of the second premolar (IARPD PM) and one implant assisted RPD with a distally placed implant in the position of the molar
(IARPD M). Two implants were inserted in the corresponding sites of the implant-assisted RPD models and the ball attachments
fitted. The edentulous ridges were covered with a silicone layer to simulate the oral mucosa. The dentures were built with two ball
matrix in the implant-assisted prostheses.
Two strain gauges were fixated in the left hemi-mandible of each model to measure strain at the cortical bone, and a speckle pattern
was sprayed over the surface of the right hemi-mandible of each model for digital image correlation (DIC) evaluation. The assemblies
underwent increasing compressive load up to 300N.
The CRPD and the IARPD PM models presented the same pattern of displacement, increasing linearly from mesial to the most distal
portion of the prosthesis. The IARPD M model presented the lowest displacement associated to the implant region in the distal
portion, and the highest displacement near the abutment tooth.
At 240N, the vertical displacement of the CRPD model was 10 times higher than that of the implant assisted models.
DIC analysis revealed that the CRPD model showed the highest tension and compression in the soft tissues and cortical bone. The
insertion of dental implants significantly reduced the major and minor principal strains.
The strain gauges indicated that the CRPD presented 146.8±4μ&#949;, the IARPD M presented 11.4±2.6μ&#949; and the IARPD PM
presented -74.6±3.3μ&#949;, reflecting traction of the buccal portion of the bone supporting the abutment teeth in the CRPD. The von
Mises strains at the buccal shelf were highest at the CRPD, followed by the IARPD M and IARPD PM models
The insertion of dental implants in the edentulous areas of distal extension removable partial dentures to promote support and
retention significantly reduces the vertical and horizontal displacements of the prosthesis. It also promotes a significant reduction of
the major and minor principal strains in the cortical bone, soft tissues and abutment teeth.

Experimental evaluation of implant-assisted mandibular kennedy class i removable partial dentures