Stress distribution in different tooth-implant supported mandibular prostheses rehabilitating unilateral free-end...

Utilizing Finite Element Analysis, this research biomechanically assessed three prosthetic designs for mandibular unilateral free-end saddle, specifically interrogating the magnitude and distribution of stresses transmitted to the terminal anterior abutment and the supporting posterior implant.

A mandibular unilateral free-end saddle educational cast, with the first premolar as the last standing abutment tooth, was used. The abutment teeth of the free end saddle side were prepared to accommodate two splinted crowns. Then the cast was scanned, and an implant analogue was digitally inserted at the second molar area using Blender4dental software. Three different treatment modalities were digitally designed and collected using Blender4dental software, then grouped as follows: Group 1: Tooth-Implant supported fixed-fixed bridge. Group 2: OT vertical attachment retained removable bridge. Group 3: Double OT cap retained removable partial denture. The preparatory stage involved editing the STL file within the Meshmixer software environment. Subsequent finite element analysis FEA was performed using Abaqus, where specific occlusal loads were applied over the area to be examined: 200 N (vertical) and 23.5 N (tangential) on the molars, and 140 N (vertical) and 16.45 N (tangential) on the canines and premolars. The von Misses stress levels induced around the anterior abutments, at the residual ridge area, and around the implant were measured and compared.

Regarding the stresses exerted by the whole design, it was found that, the lowest stresses were found with design 3 (Double OT cap retained removable partial denture), while the highest stresses were found with design 2 (OT vertical attachment retained removable bridge). Regarding von-Mises stresses on the prepared abutments and the residual ridge, the lowest von Mises stresses were found in design 3, while the highest von Mises stresses were found in design 1 (Tooth-Implant supported fixed-fixed bridge). Regarding von-Mises stresses on the implant, the lowest Von Mises stresses were found in design 3, while the highest Von Mises stresses were found in design 2.

RPD restored by double OT and ball and socket attachment exerted the least stress on the abutment, the residual ridge, and the implant; this design is recommended to be used with weak abutments, flat ridge, and\ or with imperfect implant stability. The fixed bridge design showed the highest stresses exerted on the anterior abutments and the residual ridge due to the absence of resiliency between the crowns and the teeth. This design could be indicated with strong abutments and well-formed ridges. OT vertical attachment retained removable bridge design showed the highest stresses exerted on the posterior implant, carrying a slight torquing force, resulting in more load concentration on the implant compared to the other two designs.