Comparative evaluation of pattern and distribution of stresses in single- and double-implant overdenture using...

The aim is to evaluate and compare stress distribution characteristics of ball, magnet, and positioned attachment systems in single and double implant-retained overdentures using the finite element method (FEM).

In vitro (in silico study) finite element analysis (FEA).

A Styrofoam mandible with duplicated silicon mucosa was used to construct a mandibular complete denture. Implants of size 12 mm by 3.4 mm body diameter (Implantium, Dentium, Korea) were used along with ball O-ring, positioner, and magnet attachment system for constructing single and double implant overdenture. FEA models were processed defining geometry. Six models were formulated, namely, three models of central single implant and three for double implant overdenture using ball O-ring attachment, positioner attachment, and magnet attachment named B1, P1, M1, B2, P2, and M2, respectively. The FEM analysis was done using ANSYS workbench 16.0. A load of around 100N was applied bilaterally in the first molar regions, anteriorly between the two central incisors, and unilaterally on the right first molar region. Stresses were calculated according to the Von Mises stresses scale. Stress magnitude and patterns were analyzed and interpreted accordingly.

Stress patterns and maximum principal stress were described.

FEM analysis revealed that stress concentration in the B1 model was the highest. Anterior loading produced maximum stress followed by unilateral and lastly bilateral loading. In the bone, stress concentration was the highest in the crestal bone region (3-18 MPa). Mucosa showed the least amount of stress in all models (1.3-3 MPa). Stress patterns in dentures were symmetric with concentration on the mid-lingual and molar premolar area (3-18 MPa). Implants showed stress concentration near the collar and the internal connection region (7.5-24 MPa). Maximum stresses were around the head of prosthetic abutments (10.5-24 MPa). The stress concentration in the ball head was typically located in the abutment neck. In positioner attachment, stress was located in the inner open end area (11-20.1 MPa). For the keeper, stresses were at its base and stress patterns extended into the body (10.5-17.7 MPa). Less stress magnitude was seen for all models on bilateral loading (10.5-15 MPa).

Magnet and positioner attachments have a more favorable stress distribution in both single and double implant-retained overdentures. Bilateral loading conditions are more favorable for uniform stress patterns.