Until recently, evaluation of bone as a
recipient site for endosseous implants has
been limited to two-
dimensional radio-
graphic analysis,
and clinical assessment. The advent of
tomography, followed by CT scan
technology has
given clinicians a
true, accurate and
meaningful view of
this third dimension17,18. The CT
scan creates a digital map of the maxillary or mandibular
arch. This digital image can then be divided into sagittal, pan-
oramic, and
cross-sectional
views which are
translated to the conventional CT radio
graphic film. Each
section can be represented in intervals
as small as one millimeter, generating
a highly accurate assessment of the
bony anatomy. The
CT scan allows for precise measurements
of height, width, and depth of bone, in
addition to diagnostic information regarding bone density. Recent advances in
technology allow interactive CT scan computer-based treatment planning prior to
surgery. This innovative software gives
the clinician the most accurate appraisal
of proposed implant sites by simulating
fixture location, fixture height, and width
(Sim/PlantTM, Columbia Scientific,
Inc., Columbia, Maryland). CT
scans are usually not indicated or
recommended for single tooth implant
placement. However, the concepts presented in this article can be applied to the
treatment plans in which a CT scan is not
utilized.
The CT scan for dental implants has
brought a new awareness and technology to accurately evaluate proposed implant sites in a true three-dimensional
format.
This technology has made it
possible to visualize a "triangle of bone"
or a concept which will allow for the most
favorable placement of the implant which
will take greatest advantage of bone
anatomy.
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Fig. 7 (above left) The proposed "triangle of bone"
placed over the cross-sectional image. Note that the base of
the triangle demarcates the widest available bone.
Fig. 8 (above right) The implant should "bisect"
the triangle of bone. This should allow for a longer implant
fixture, increased volume of bone, and increased chance of
attaining bicortical stabilization.
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It is postulated that the ideal
placement of the fixture should bisect
this triangle.
Other "triangles of bone"
can also be visualized in the two-dimensional plane as a diagnostic tool to help
treatment plan and accomplish successful implant reconstruction. In the true
three-dimension sense, these triangles
make up a pyramid of bone which surrounds the implant fixture with a volume
of support.
If a natural tooth is viewed on a CT scan
from a cross-sectional view, the true
quantity of bone existing buccal or lingual
to the root can be clearly documented
[FIG.3,4]. The computer enhanced cross-
sectional view reveals the fragile, thin nature of the
buccal and
lingual cortical plates of
bone [FIG.5].
It is imperative
that both the
surgical specialist and the
restorative
dentist be
aware of this
natural state in
order to properly diagnose
and treatment
plan.
The conventional two-
dimensional
periapical radiograph will
not enable the
clinician to
fully appreciate the actual
bony anatomy.
Measuring the
potential
height of bone
for fixture
placement using a two-dimensional radiographic interpretation,
could lead to a misinterpretation of the
existing anatomy followed by improper
fixture selection. If the natural tooth were
to be extracted, and an osteotomy prepared following the path of the residual
socket, the fixture could perforate the
buccal plate of bone. Once perforated,
infection, loss of bone and ultimate failure of the implant could occur [FIG.6].
The three dimensional view of the bone,
especially in the maxillary anterior arch
demonstrates an inherent buccal trajectory. The natural tooth root does not sit
parallel to this trajectory. On the contrary,
due to buccal location of the natural tooth, the tooth actually exists at an
angle to the bone projection.
N E X T+
P A G E |
The Triangle of Bone
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