Effect of different implant positions on strain developed around four implants supporting a mandibular overdenture with rigid telescopic copings

Objective: To evaluate and compare the effect of three different implant positions on strain developed around four implants supporting a mandibular overdenture with rigid telescopic attachments. Method and Materials: Three experimental acrylic resin overdentures were fabricated on three edentulous mandibular acrylic casts. Four implants were placed in each cast. According to the implant positions, the casts were classified into three groups: in group I (quadrilateral design) the implants were placed at canine and first molar areas; in group II (curved design) the implants were placed at canine and second premolar areas; and in group III (linear design) the implants were placed at lateral incisor and first premolar areas. Overdentures were connected to the implants with rigid telescopic attachments. Eight linear strain gauges were bonded to the acrylic resin around each implant at two sites (mesial and distal). Strains were measured for anterior (lateral incisor and canine) and posterior (premolar and molar) implants at both mesial and distal sites during bilateral and unilateral load applications. Results: For bilateral and unilateral load applications, group II recorded the highest strain values while group I recorded the lowest. In group II and group III, strain values at distal sites were significantly higher than values at mesial sites. Strain values of posterior implants were significantly higher than values of anterior implants in all groups. The greatest strain values were recorded at the loading side during unilateral load application. Conclusion: Quadrilateral design showed minimal peri-implant strain compared to curved or linear designs. This design may be recommended when rigid telescopic crowns are used to connect mandibular overdentures to four implants.