The purpose of this in vitro study was to evaluate effect of
implant location on initial retention values of palateless complete
overdentures retained by four o-rings at different inter-implant
distances.

Two standard acrylic
models representing completely edentulous maxillary arches were used.
Four single piece ball type implants were placed in each model. Models
were divided into two groups according to the distance between anterior
and posterior implants. Two canine implants with 32 mm inter-implant
distance were placed in both models. In one model (G1), two posterior
implants were placed in second premolar region away from canine implants
by 14 mm on both sides, while in the other model (G2), the two
posterior implants were placed in first molar region away from canine
implants by 22 mm on both sides. Eighteen palateless complete
overdentures were constructed for each model. Overdentures were retained
by four o-rings. Initial axial (central), and para-axial (anterior,
posterior, and lateral) retention values of overdentures were estimated
and compared using a universal testing machine.

Independent
t-test revealed that implant location has a significant role in
palateless complete overdenture retention with a level of significance
set at P < 0.05.

For in vitro
simulated palateless implant overdentures retained by four o-rings,
increasing the inter-implant distance between anterior and posterior
implants is favourable for a more retentive prosthesis.