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

5. DISCUSSION AND CONCLUSION
Initial stability is important for a successful osseointegration and high success rate for
all implants in general and mini implants in particular. Shatkin et al. [5] in their retrospective
analysis over five years of 2,514 mini implants which equally supported fixed
and removable prostheses found an overall implant survival rate of 94.2%. It is stipulated
with bone quality, implant design, and surgical technique that is used [6]. Some
authors [7] recommend bone drilling to the depth of only one third of mini implants’
length. Obvious reason was the dense bone structure of the mandible of the treated patient,
but such dense bone structure contributed to the good initial stability of the inserted
mini implants.
Ertugrul et al. [6] in their in vitro study revealed that implants of larger diameter are
more stable under lateral forces than mini implants. Implant displacements obtained in
the present study agree with these observations. Mini implants showed displacements
from 79 up to 350 µm numerically and from 39 up to 194 µm experimentally with an
applied force of 45 N. The obtained large displacement with a relatively small applied
force which was above the recommended range for the initial stability (up to 100 µm)
[8], makes the issue of the use of mini implants as a definitive treatment critical.
The extreme high experimental and numerical values of 133 µm and 347 µm observed
for the long version of the Bauer Schraube implant can be seen in conjunction with the
extreme narrow waist of the implant head. The results concerning the stress and strain
distributions, showed a clear correlation to the implant geometry rather than the diameter
and length of the implants.
The present results showed that there is a high risk of overload and fracture for mini
implants. The observed biomechanical behaviour of these implants can be considered as
additional reasons for the large number of failure cases of small diameter implants.
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