The effect of loading conditions on a Kennedy Class I implant-assisted removable partial denture

Objective: To evaluate the strain behaviour of the Kennedy Class I implant-assisted removable partial denture (IARPD) distal extension area under various loading conditions to better understand the strain pattern. Method: A mandibular Kennedy Class I was selected with natural teeth from the 34 to 44. A duplicated model was made out of polyurethane and a conventional removable partial denture was fabricated with a cobalt chromium metal framework and acrylic base. Strain gauges were placed on the fitting side of the acrylic and metal framework to measure the strain in the partial denture structure. Two Straumann® implants were then placed in the second molar regions and the removable partial denture was modified to accommodate ball attachments. The model was loaded to 120N unilaterally and bilaterally, with three different loading areas; premolar, molar and uniform. Results: In all loading conditions the maximum micro-strains were in a bucco-lingual direction. In all loading conditions tension micro-strains were most common, except on the metal surface in the unilateral loading condition, which showed mainly compression micro-strains. Conclusions: This research highlights that lateral movement/displacement was evident during bilateral and unilateral loading of the IARPD. Molar bilateral loading showed favourable strain behaviour during bilateral loading conditions whereas uniform unilateral loading showed less destructive strain behaviour during the unilateral loading conditions