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rev port estomatol med dent cir maxilofac . 2017;58(2):79-90 81

vourable crown -to -implant ratio. Biomechanical studies high-
light the danger represented by the bending loads either for
short implants, once they have a smaller area to dissipate
tensions, 2,26 or for cortical bone because its yield strength is
lower when the load is acting on a perpendicular direction to
27
its major axis. In a location where higher masticatory loads
are produced, as the posterior arch, these findings are of ut-
28
most importance. A study from Malmstrom et al considered
the compromised crown -to -implant ratio and the lower bone-
-to -implant contact area, factors of more concern when the
masticatory loads are higher or when the patient presents risk
factors for periimplantites.
Due to all these variables, some authors still include the
implants length on the list of risk factors for implant failure. 29-31
As biomechanical methods were suggested to decrease the
stress found on the biologic structures, FEA may be beneficial
32
for the comprehension of the mechanical behaviour of all the
parts involved in such a rehabilitation. This in silico approach
has been widely used on dental implant research, allowing Figure 1. Measurements made directly on computerized
multiple combinations of critical factors in a short period of tomographys, using 3D models (c).
33
time. However, it´s accuracy is extremely dependent on fac-
tors such as the model geometry, simplifications, material
properties, boundary conditions, applied load, type of mesh
and contact definitions. 24,33 The more the virtual model resem-
bles reality, the more accurate the results will be and, to rely
34
on the FEA results, an experimental validation is required. It
must be noted that, due to those differences, an absolute co-
incidence in the magnitudes of loads, stresses and strains is
not the objective. The propose is to obtain on both, numerical
analysis and mechanical experiment, the same behaviour and
tendency. 35,36
The aim of this research was the development and exper-
imental validation of a numerical model that could be used in
the study of stresses and strains created in the different com-
ponents involved in oral fixed rehabilitations with short im-
plants.

Material and methods

A digital model considering the posterior areas of the mandi-
®
ble was designed with SolidWorks software (Dassault Sys-
tèmes SA, Vélizy, France). The dimensions were obtained con-
sidering the mean of ten direct measurements on patients
computerized tomographys, reverse engineering and product
catalogues (Figures 1 to 3). Considering the obtained meas-
urement for the overall models high (37 mm) and the clinical
case that was intended to simulate (a mandible with a re-
duced bone volume but where the placement of short im- Figure 2. Measurements made directly on computerized
plants was possible), the obtained model resulted in an ac- tomographys, using ortoradial cuts.
centuated crown -to -implant disproportion, where the
prosthetic framework (25 mm) is four times higher than the
supporting implant (6 mm) (Figures 4 and 5). In order to test
the worst -case scenario, the use of external hexagon connec- thetic framework. To save calculation time the geometries
tion implants was preferred, based on the suggestion that were simplifed.
this type of connection exhibits weaker biomechanical per- The created model followed two different procedures: a)
formance 19-21 than internal connections. The model was com- Design for manufacturing (DFM) and prototyping; b) FEA sim-
®
pleted by the design of four parts: a type II bone, with a 2 mm ulation performed with Abaqus software (Dassault Systèmes
cortical, regular platform implants, implant screws and pros- SA, Vélizy, France).