Stresses Induced by Mesially and Distally Placed Implants to Retain a Mandibular Distal-Extension Removable Partial Overdenture: A Comparative Study

Purpose: The present in vitro study compared the stresses transmitted to canine abutments and implants placed in either the first premolar or second molar areas for retaining removable partial overdentures in models of mandibular bilateral distal-extension with the six anterior teeth remaining. The study also compared horizontal to vertical reciprocation of bracing arms when the implants were placed mesially. Materials and Methods: Three overdenture models were used to represent two groups. In group 1, implants were placed bilaterally in the first premolar area (claspless denture); subgroup A dentures had horizontal reciprocal arms and subgroup B dentures had vertical reciprocal arms. In group 2, the implants were placed bilaterally in the second molar areas. Ball attachments were used to retain the partial overdenture. Eight strain gauges were cemented to the facial and lingual sides of each abutment (two canines and two implants). Static unilateral (right and left) and centric loads of 70 N were applied and the stresses were measured. All measurements were repeated five times for each loading impact, and means were calculated. Results: Group 1A showed the highest stresses around the abutments, followed by group 1B, and the lowest stresses were found in group 2. Group 1 showed statistically significant increases in the stresses induced around the implants and the abutment teeth. For group 1, although there was no statistically significant difference between subgroups, subgroup B showed lower stresses around the abutments than subgroup A in both central and unilateral loading. Conclusion: A distally placed implant can be considered a more satisfactory solution than a mesially placed implant for retention of a mandibular distal-extension removable partial overdenture.