Biomechanical analysis of 4 types of short dental implants in a resorbed mandible

Short implants have been increasingly used in the aging society. However, studies which explain the difference of stress distribution according to different connections in short implant treatment are scarce.

The purpose of this finite element (FE) analysis was to evaluate the stress and strain distribution of short implants and surrounding bone under static and cyclic loading conditions with 4 different connections.

Three-dimensional models of 4 types of implant systems were considered: internal tissue level, internal tissue level wide, internal bone level (IB), and external bone level. Each system had different types of abutment, implant, and screw with the resorbed mandibular segment of the bone block. Static FE analysis was performed under external loads of 200 N (vertical or 30-degree oblique) to each cusp tip. The strain distributions of the peri-implant bone and von Mises stress fields in the abutment, implant, and screw were evaluated. Based on the static FE results, a computational fatigue analysis was performed to predict the risk of fracture caused by fatigue accumulation of repetitive mastication.

Bone tissues in fatigue failure level (greater than 4000 με) were observed in the alveolar ridge and the plateaus close to the implant apex in all situations. Under the oblique loading condition, the total volume of the bone tissue in hypertrophy and fatigue failure levels (greater than 2500 με) was the largest at IB and the smallest at external bone level. Among the 4 situations, the highest stress occurred in the abutment (506.9 MPa) and implant (311 MPa) of IB. In fatigue analysis, fracture was only predicted in the IB abutment model (588 301 cycles), and cracking occurred in the lingual direction, where stress concentration occurred when the oblique load was applied.

The abutment of IB showed the highest stress of the implant component, and internal tissue level model showed the highest strain of bone. In all groups, the bone strain values mostly appeared within physiologic capacity (under 4000 με). Various mechanical situations should be considered when using internal bone-level connections in short implants for replacing posterior teeth.