Biomedical Engineering Reference
In-Depth Information
in the bone-implant interface provide valuable relative comparisons between different
implant surfaces.
Measurable indicators of the host/implant response have been utilized in cases where
two different surface designs are compared. However, to decrease the degree of specula-
tion with respect to the most critical mechanisms of the host/implant response between
different surface designs, the largest possible number of biological response indicators
(static and dynamic histomorphometric parameters, plus biomechanical testing) should be
evaluated to establish correlations.
Substantial data have been published concerning the temporal evolution of various
bone-biomaterial interfaces. Yet, whether the increased mechanical stability of different
surfaces is due to an increased mechanical locking of tissue within the surface rough-
ness, increased bone-implant contact, increased surrounding bone density, biologically
modified bone bonding, or the interplay between such variables is still controversial or
unknown (Lemons, 2004). Often, a combination of factors exists.
In vivo comparisons between different implant surface designs typically have a his-
tomorphometric and/or a biomechanical component. The histomorphometric part of the
study typically evaluates static parameters such as the amount of bone-to-implant con-
tact (BIC), bone density, amount and type of cellular content, among others. Less often
reported, but not less valuable than the static measurements, dynamic histomorphomet-
ric parameters, such as MAR, have also been utilized. The biomechanical testing compo-
nent usually evaluates the push-out force, pull-out force, or torque-to-interface failure of
implants in bone (Coelho et al., 2009).
It has been established that general tissue response to implants, biocompatibility, and
osseoconductivity information may be obtained through static histomorphometric mea-
surements. However, any of the previously mentioned parameters alone does not address
the tissue healing events that lead to the measured parameters evaluated at a given period
in vivo (Coelho et al., 2009). For example, if a given surface results in higher BIC percentage
relative to another at early implantation times, it is impossible to determine the relevance
of such observation unless extreme differences in BIC values were observed or a series
of other supporting histomorphometric and biomechanical parameters were also mea-
sured. From a structural perspective, the BIC amount may be overwhelmed by the quality
of the structural support, and implants surrounded by less bone with higher magnitude
mechanical properties may be more desirable than an implant surrounded by more bone
presenting lower magnitude mechanical properties. This concept should be taken into
account especially as bone has the ability to model and remodel under microstrain thresh-
olds (bone deformation under a given load),
and bone regions of high stress concentrations
in the proximity of the implant may be unfavorable if low-magnitude bone mechanical
properties exist.
Because BIC has been the most often measured parameter in in vivo investigations,
meticulous histomorphologic and biomechanical testing (preferentially nanoindentation
along and away from the implant surface) should also be performed to decrease the degree
of speculation concerning the benefit of increased BIC for one surface relative to another. In
this case, dynamic measurements such as MAR would be desirable to temporally evaluate
bone modeling/remodeling kinetics around different implant surfaces. This would pro-
vide insight on how different histomorphologic, histomorphometric, and bone mechanical
properties evolved as a function of implantation time.
Studies concerning the effect of different surfaces in bone healing kinetics have been
successful in indicating relationships between MAR and static parameters such as den-
sity (Suzuki et al., 1997). Unfortunately, the literature concerning bone healing dynamics
