RADIOGRAPHIC STENT
5mm metal beads
A radiographic stent will enable the surgeon to visualize
anatomic landmarks and their dimensional relationship to each
other in two dimensions. X-rays taken with a radiographic stent
can then be used in conjunction with a implant transparency
overlay to determine implant diameter and length. First a vacuum
form with 5mm metal beads (Attachments International, catalog
# 40-000050) in the edentulous area of the proposed
implant site is produced by the laboratory (Tutorial) and a x-ray or panograph
is taken by the surgeon or dentist with the radiographic guide seated in the
patients mouth.
6.25mm measurement
Each x-ray machine and panograph produces some
dimensional distortion (magnification) on its own in addition to
producing varying degrees of distortion with each periapical or
pano taken, depending on the focal length of the x-ray beam and
the subject areas physical relation to the x-ray beam. To compensate
for the distortion, implant manufacturers offer implant
transparency overlays
printed with outlines of their implants in different
levels of magnification.
Transparency overlay
To determine the rate of distortion the
metal bead in the x-ray or pano is measured with a boley gauge. The value of the
measurement is then used to calculate the rate of distortion against the known
dimension (5mm) of the actual metal
bead, expressed as a percentage value. For example, if the actual
titanium bead dimension is 5mm and the measured dimension of the
bead from the x-ray is 6.25mm, then the rate of magnification is 25%.
Now the appropriate rate magnification implant transparency
overlay can be used to determine pertinent implant dimensions.