Biomechanical analysis of short implant under static and dynamic load protocols in atrophic mandible

Background

To gain mechanical advantages, the use of shorter implants in the tilted implant concept has become popular. However, clinicians may have concerns about the durability and function of short implants. Also, studies which show the stress and strain distribution according to different combinations in implant treatment are scarce.

Aim/Hypothesis

The aim of this study was to analyze stress and strain distribution of different implant combinations in the atrophic mandible.

Material and Methods

A case of appropriate quality from the CT records was selected and used as reference for the modeling. Four groups including tilted, vertical and short implants were constituted. Group I and II consisted of a combination of tilted and vertical implants whereas Group III and IV had additionally short implants. Static analysis was performed under oblique loads of 200 N to first molar cusp tip. Von Mises, minimum principal and maximum principal stress fields in the implant, prosthesis and bone were evaluated. Based on the static finite element results, a computational fatigue analysis was performed to predict the risk of fracture caused by fatigue accumulation of repetitive mastication.

Results

Among all situations, the highest stress occurred in the tilted implant (91.155 MPa) and in the cortical bone surrounding the tilted implant (−35.787 MPa). In fatigue analysis, fracture was only predicted between the abutment and neck of the implant in all models. Although cracking initially occurred in the short implants (in Group 3- 133.569 cycles+ in Group 4- 145.045), combination with short implants increased the lifetime of more anteriorly positioned implants in Group 3 and 4 (#5- 180.039, #2- 187.335 and #4- 172.687, #2- 192.307, respectively) when compared with Group 2 (#5- 141.819, #2- 150.736).

Conclusion and Clinical Implications

In all groups, the implant stress and strain values appeared within physiologic capacity. The length of implant is known as an important factor to increase the success of rehabilitation. However, in case of atrophic mandible, the use of posteriorly placed short implant can be considered to reduce the stress and strain values.