Stresses around implants and natural abutments in free end RPD

Objective:  to study the stress distribution around implants and natural abutments in long span distal extension free end saddle Mandibular partial dentures with different loading conditions either when the natural abutments are splinted or not. Method:  A 3D CT scan images obtained from a patient data were used -after his consent- in this study. The last standing abutment at each side was the first premolar. The images were imported to Mimics software to produce a 3D model. The model was exported to Solidworks software to further prepare it for testing by finite element module of the software (FEA). The manner of retention of removable partial denture to  natural abutment was extra coronal attachment; while a ball and socket attachment was used to connect the RPD with the implant. The complex nature of bone, teeth, periodontal ligament, implants, attachments, denture as well as mucosal coverage of the mandible were simulated. The model was loaded by a simulated load of 150 N vertical and oblique, and the 3D FEA was carried out. The analysis was carried out in two studies with splinting of the first premolar and canine (Study 1) and  without splinting (Study 2). Result:  Splinting in case of vertical loading reduced the maximum recorded stresses by 40-70% around the implant and periodontal ligament of the first premolar respectively. Splinting in case of oblique loading increased the maximum stresses around the implant by 10%; and decreased the maximum stresses around the periodontal ligament of premolar by more than 80% of that recorded without splinting. The values recorded at the canine also showed decrease with splinting by 30-60% in case of oblique and vertical loading respectively. Conclusion: This prelimary observation suggests that splinting the principal natural abutments in long span implant supported RPD may be beneficial to the implant and natural abutments at different loading conditions