Effect of variations in buccal bone thickness, implant diameter and thread pitch on stress distributions upon implant placements at high insertion torques: a three-dimensional finite element analysis

ABSTRACT

The objective of this study was to investigative the influence of high insertion torques on the stress distribution around dental implants with variations in thread pitch and reductions in buccal cortical bone thickness. Two bone level dental implants [3.8mm and 5.0mm diameters and a standard length of 10mm] were modeled each having a thread pitch of 0.4mm and 0.65mm. Each implant was placed in two mandibular bone segments having buccal cortical bone thickness set at 2.0mm and 1.5mm. A total of 8 such models were created and discretized with hexahedral mesh elements with an average element size of 0.2mm. Implant-bone interface was simulated with non-linear contacts and friction. Static torque values from 50Ncm to 90Ncm were applied with an increment of 5Ncm on each fully inserted implant. Maximum von-Mises along with maximum frictional stresses were used to record stress distribution within each model. Maximum stresses seem to follow a linear relation with insertion torque showing an over-all increase in stress magnitudes with 1] a reduction in the diameter of the implants 2] decrease in thickness of the buccal cortical bone and 3] decrease in pitch of the dental implant threads from 0.65mm to 0.4mm. The maximum stress of 171.4 MPa was recorded at 90 Ncm for the 3.8mm diameter implant adjacent to a buccal bone thickness of 1mm with a thread pitch of 0.4mm. With an increase in insertion torque there is a corresponding increase in the magnitude of stress production. Maximum stresses are primarily distributed in the peri-implant region in particularly the buccal cortical bony plates. The use of profile drills to coronally flare the osteotomy especially in dense bone is highly recommended if the diameter of the final widening drills to place progressively tapered implants is narrower as compared to the diameter of the implants at the neck