Biomechanical behavior of mandibular overdenture retained by two standard implants or 2 mini implants: A 3-dimensional finite element analysis

STATEMENT OF PROBLEM: Mini implants (<3 mm in diameter) are being used as an alternative to standard implants for implant-retained mandibular overdentures; however, they may exhibit higher stresses at the crestal level.

PURPOSE: The purpose of this finite element analysis study was to evaluate the biomechanical behavior (stress distribution pattern) in the mandibular overdenture, mucosa, bone, and implants when retained with 2 standard implants or 2 mini implants under unilateral or bilateral loading conditions.

MATERIAL AND METHODS: A patient with edentulous mandible and his denture was scanned with cone beam computed tomography (CBCT), and a 3D mandibular model was created in the Mimics software program by using the CBCT digital imaging and communications in medicine (DICOM) images. The model was transferred to the 3Matics software program to form a 2-mm-thick mucosal layer and to assemble the denture DICOM file. A 12-mm-long standard implant (Ø3.5 mm) and a mini dental implant (Ø2.5 mm) along with the LOCATOR male attachments (height 4 mm) were designed by using the SOLIDWORKS software program. Two standard or 2 mini implants in the canine region were embedded separately in the 3D assembled model. The base of the mandible was fixed, and vertical compressive loads of 100 N were applied unilaterally and bilaterally in the first molar region. The material properties for acrylic resin (denture), titanium (implants), mucosa (tissue), and bone (mandible) were allocated. Maximum von Mises stress and strain values were obtained and analyzed.

RESULTS: Maximum stresses of 9.78 MPa (bilaterally) and 11.98 MPa (unilaterally) were observed in 2 mini implants as compared with 3.12 MPa (bilaterally) and 3.81 MPa (unilaterally) in 2 standard implants. The stress values in the mandible were observed to be almost double the mini implants as compared with the standard implants. The stresses in the denture were in the range of 3.21 MPa and 3.83 MPa and in the mucosa of 0.68 MPa and 0.7 MPa for 2 implants under unilateral and bilateral loading conditions. The strain values shown similar trends with both implant types under bilateral and unilateral loading.

CONCLUSIONS: Two mini implants generated an average of 68.15% more stress than standard implants. The 2 standard implant-retained overdenture showed less stress concentration in and around implants than mini implant-retained overdentures.