Purpose: When implants are used to support a removable overdenture, the optimal stress
distribution to minimize both forces on the implants and denture movement is desirable.
This study compared the stress patterns generated around implants and denture
movement among three retention systems. Materials and Methods: Two root-form
implants were anchored in a mandibular model made of resin, and a removable
overdenture on which all experiments were performed was fabricated. The surface of the
model was covered with a layer of impression material to simulate oral mucosa. Ball/
O-ring, bar/clip, and magnetic attachments were used. A vertical force was applied to the
left first molar and gradually increased from 0 to 50 N in 5-N steps. The resultant stress
distribution and denture movement were evaluated. Results: The ball/O-ring attachment
transferred the least stress to both implants and produced less bending moment than the
bar/clip attachment. Vertical force applied to the bar/clip attachment created immediate
stress patterns of greater magnitude and concentration on both implants. Conclusion: This
in vitro study suggested that the use of the ball/O-ring attachment could be advantageous
for implant-supported overdentures with regard to optimizing stress and minimizing
denture movement. Int J Prosthodont 2003;16:128–134.