Biomedical Engineering Reference
In-Depth Information
[Bruck, 1991]. The host response to implants placed in bone involves a series of
cell and matrix events, ideally culminating in tissue healing that is as normal as
possible, and that ultimately leads to intimate apposition of bone to the bioma-
terials, that is, the operative defi nition of osseointegration.
For this intimate contact to occur, gaps that initially exist between the bone
and implant at surgery must be fi lled initially by a blood clot, and bone damaged
during preparation of the implant site must be repaired. During this time, unfa-
vorable conditions, such as, micromotion (a biomechanical factor) will disrupt the
newly forming tissue, leading to formation a fi brous capsule [Bannon et al., 1983].
The criteria for clinical success of osseointegration are based on functionality and
compatibility, which depend on the control of several factors including:
(1) biocompatible implant material using commercially pure titanium,
(2) design of the fi xture; a threaded design is advocated creating a larger
surface per unit volume as well as evenly distribution loading forces,
(3) the provision of optimal prosthodontic design and implant maintenance
to achieve ongoing osseointegration,
(4) specifi c aseptic surgical techniques and a subsequent healing protocol
which are reconcilable with the principles of bone physiology; this would
incorporate a low heat/low trauma regimen, a precise fi t, and the two-
stage surgery program,
(5) a favorable status of host-implant site from a health and morphologic
standpoint,
(6) non-loading of the implant during healing is a basic tenet of osseointe-
gration, and
(7) the defi ned macro-microscopic surface of the implant as it relates to the
host tissue [Adell et al., 1981 ].
The implantation of any foreign material in soft tissue initiates an infl amma-
tory response. The cellular intensity and duration of the response is controlled
by a variety of mediators and determined by the size and nature of the implanted
material, site of implantation, and reactive capacity of the host [Marchant, 1986].
Dental implants vary markedly in the topography of the surfaces that contact
cells. Four principles of cell behavior fi rst observed in cell culture explain to some
extent the interactions of cells and implants:
(1) contact guidance aligns cells and collagen fi bers with fi ne grooves, such
as those produced by machining,
(2) rugophilia describes the tendency of macrophages to prefer rough
surfaces,
(3) the two-center effect can explain the orientation of soft connective tissue
cells and fi bers attached to porous surfaces, and
(4) haptotaxis may be involved in the formation of capsules around implants
with low - energy surfaces [Brunette, 1988 ].
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