ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

For the implant/bone interaction assessment the strain intensity distributions in the
buccolingual cross sections for all analyzed cases are shown in Fig. 4. The strain
intensities range typically from 0.0001 to 0.004.
4. DISCUSION
The dental implant displacement results reveal that lower BVF models (1 st and 3 rd
cases) allow more limited movement than the higher BVF models (2 nd and 4 th cases). It
is caused by the stronger cortical bone in the region of the implant neck in the first and
third cases. In these cases the implant is connected to the cortical bone in the alveolar
process via three threads and the rest of the screw is in contact with the trabeculae only
locally. On the contrary, higher BVF models have denser trabecular architecture and
weaker cortical bone in the implant neck region; in addition the cortical bone is
relatively porous in this region. In these cases the implant is not so rigidly fixed in the
cortical bone as in the previous cases. This fact allows a larger implant movement.
Moreover, the implant is in a larger contact with the trabecular architecture which has a
positive impact on the implant primary stability. The implant primary stability is not
guaranteed in the lower BVF cases because of the local-only connections. If these
connections failed it would lead to complete failure of the implant anchorage. Besides,
the cortical bone in the implant neck region can face to another problem: This region is
located on the gingiva-implant interface which is highly prone to infection. Therefore
the primary stability of the implant is highly required.
The bone layer around the implant surface modeled in 3 rd and 4 th cases allows lower
displacements than the corresponding models without this layer. The reason is that this
layer increases the stiffness of the implant anchorage.
The average coronoapical displacement (3.6±0.6 µm) corresponds to the lower level of
commonly accepted experimental values of the implant displacements which range from
4 µm to 27 µm [4]. The comparison with these experimental values is helpful also since
there are very limited possibilities of the model validation. The agreement with these
values shows that the model is valid from the implant movement point of view.
Strain intensity results confirm the significant differences between the models with the
lower and the higher bone density. In case of the model with BVF=0.149 the higher
strain intensity occur in the neck region, i.e. in the region of the implant-to-cortical-bone
connection. In this case a special attention must be paid to the loading because if the
strain intensity exceeds certain limit a tissue necrosis will occur which will result in
problems with the primary stability. In addition, the cancellous bone in the lower part of
the implant might worsen even more because of too uneven strain distribution (and
therefore bone remodeling) focused mainly on the cortical bone. In this case, the dental
implant would be finally anchored in the cortical bone only and the cancellous bone
density would more decrease. This is not an ideal state and it should be avoided. In
case of the model with BVF=0.377 the strain intensity is distributed more evenly along
the implant. According to the limits introduced by Frost the bone is slightly overstrained
which causes higher activity of bone cells (osteoclasts). The bone will increase in the
bone density, therefore the condition for osseointegration will be better. The bone layer
around the implant surface (3 rd and 4 th cases) causes lower strain intensity than in the
models without this layer. Besides, the strain intensity is distributed more evenly than in