DentalScout®
P2000
Comparing Mouth Mirror Cameras with Endoscope Cameras
Intraoral video cameras are proven instruments for investigative work,
documentation and marketing within dental practises. They are also being used increasingly
for ISDN image communication between dentists and laboratories. Both endoscope cameras and
mouth mirror cameras are available. In the case of endoscope cameras, there are many
different models and manufacturers but DentalScout models are almost the sole examples of
mouth mirror cameras. Taking the newly developed system DentalScout® P2000, the main
distinguishing features are listed below, together with advantages and disadvantages of
the two types of camera.
Construction principle, size and weight
With endoscope cameras, small lenses are located at the end of rod-shaped
handpieces allowing intraoral close-ups to be taken. Light for subject illumination is
supplied via optical fibres and exits directly beside the lens. Generally 0° or 90° lens
attachments are recommended for the various intraoral and extraoral shots.
With mouth mirror cameras, intraoral pictures are taken using a mirror connected
to a video camera. Lighting is provided via miniature lamps appointed around the lens.
This allows pictures to be taken of anywhere inside the mouth. If the mirror is removed,
it is also possible to take extraoral shots.
Endoscope cameras are slimmer in shape than mouth mirror cameras, but are also
generally longer.
With its camera case weighing 120 or 170 g (depending on lens attachment), the
DentalScout® P2000 is one of the lightest intraoral cameras on the market. When it comes
to effective overall weight, power leads have to be taken into account. As these tend to
be heavier and less flexible with endoscope cameras due to the fibre-optics cable, the
DentalScout® P2000 has a distinctly more favourable weight distribution.
General information on image quality
The image quality of a video camera system depends on the quality of the camera
lens and on the recording medium (CCD image sensor together with series-connected
electronics) as well as on object illumination. All components must be optimally adjusted
in relation to each other in order to achieve sharp, brilliant colour images. A further
important criterion for quality is dimensional accuracy, i.e. distortion-free
reproduction. This is an essential requirement for generating realistic and reliable
templates for dental technicians. Distortion-free reproduction is also required for
forensic purposes, for digital imaging and for orthodontic case
documentation.
Imaging optics
Endoscope lenses have very small dimensions and require additional image control
systems (e.g. internal mirrors, prisms) on the path to the image sensor. It is difficult
to correct their physical imaging errors (spherical and chromatic aberration). Due to
extremely short focal lengths of the lenses, there is also considerable distortion in
objects reproduced (fish-eye effect). Even the 0° lenses provided for extraoral shots
generally still show distinctly wide-angle characteristics, so that distortion is
inevitable e.g. with shots of anterior teeth.
With DentalScout® P2000, composite coated lenses with high light intensity
ensure optimal utilisation of the image sensor's high resolution (> 460 TV lines
hor., 440,00 pixels) as well as achieving maximum optical quality. Furthermore, the
tele-focal lengths of these lenses guarantee the physical requirement for dimensionally
accurate representation of tooth profiles and positions. This means that there is no
disruptive distortion either in long-distance shots or close-ups.
Illumination
For good representation without signal noise, the image sensor has to have
sufficient light. As the light intensity of endoscope lenses is very low due to the tiny
light penetration holes, high illumination of the object is necessary. For this reason,
fast cold light sources are used, the light of which is directed via optical fibres to the
lens where it exits directly beside it.
Uniformity of illumination may, however, suffer as a result, as light intensity
quickly reduces to ¼ (1/9 etc.) at double (treble, etc.) the distance from the
illumination source due to the 1/r2 law. As the light exit point on endoscope cameras is
located very close to the tooth, closer parts are frequently overexposed while more remote
dental areas are underexposed.
Thanks to the large lens aperture, DentalScout® P2000 does not need an external
cold light source. The light of three miniature lamps appointed around the lens falls onto
the mirror which in turn reflects it onto the object. As the lamps are some way from the
mirror and thus from the tooth to be reproduced, the distance of the object from different
dental areas is practically constant and an extremely even illumination of intraoral
details can be achieved. Besides the illuminated macro telephoto lens, an additional fast
macro standard lens is available. Even with unfavourable light conditions, this lens still
produces images of intraoral and extraoral details and overviews that are rich in colour
and contrast.
Colour and brilliance
Due to the electronic post-amplification of the image signal that is necessary
as distance increases, colour saturation quickly decreases with endoscope cameras and
signal noise increases, and thus brilliance is significantly reduced.
Here the DentalScout® P2000 shows a noticeably better performance due to its
faster lenses. It also allows a white balance to be performed at the touch of a button,
for optimal adjustment of the camera's colour reproduction in relation to ambient light.
An on-screen menu also allows you to set colour and contrast specifically to individual
requirements. Furthermore it is possible to choose between integral and selective
measurement.
Image detail and enlargement
Endoscope cameras do have advantages over mirror cameras when it comes to
selecting intraoral details and enlargement scale. The extremely wide-angled
characteristics of their lenses allow you to enlarge or reduce image detail by altering
distance. Higher enlargement can also be achieved by going very close to the object. But
when extremely close to the object and with a high degree of enlargement, it is
particularly difficult to maintain definition as the depth of field is then minimal. With
a mouth mirror camera with attached mirror, the enlargement scale can only be slightly
varied by altering distance.
The enlargement factor (image size/object size) also naturally depends on the
size of monitor used. With normal-sized monitors, approximately 20-fold enlargement is
achieved with mouth mirror cameras, while some endoscope cameras enlarge up to 40
times.
Handling
An intraoral camera's handling and usefulness in praxis not only depends on the
design and weight, but also to a much greater extent upon how easily and efficiently
typical reproduction situations (occlusal and buccal views of teeth, oral roundups and
front views) can be negotiated.
With mouth mirror cameras, the mirror rests on the tooth for intraoral
close-ups. This immediately ensures a shake-free image that is in focus. Resting the
mirror on the tooth also helps considerably in finding intraoral details. This is where
mouth mirrors have a major advantage over endoscope cameras, which normally cannot be
rested on a tooth but must be held clear and at a distance.
A further problem occurs in that image position on the monitor depends on the
orientation of the image sensor in relation to the object. With most endoscope cameras,
the lens and image sensor are closely linked to each other so that any turning of the
longitudinal axis of the camera will rotate the image on the monitor. Thus, for example,
shifting the camera horizontally along the buccal dental area (whereby the camera has to
be turned approximately 90° around its own longitudinal axis) will result in an
unexpected vertical image shift on the monitor with a 90° turn. This is very confusing
and makes it much more difficult to find intraoral details. Enormous skill in guiding the
camera is necessary in order to locate and fix the object, while at the same time keeping
the right distance away and maintaining the level of focus, simultaneously avoiding any
poor definition due to movement, especially since there is no direct support on the
tooth.
This problem can be avoided with mouth mirror cameras as the entire mirror
attachment can be turned round the camera axis so that the image on the monitor always has
the same orientation as the object.
Hygiene
Transparent foil can be used to protect endoscope cameras from contamination
through saliva or blood. This foil does impair image quality, however. On some models, the
camera case can be removed and sterilised but wiping with disinfectant is generally
recommended.
In the case of mouth mirror cameras, you only need to exchange the sterilisable
mouth mirror and lens cap with a different patient. The body of the camera just needs to
be wiped with disinfectant, as it remains outside the mouth.
Stationary use of camera and connection to microscope
Meaningful accessories should also allow an intraoral camera to be used for
other praxis-oriented tasks. These include above all uncomplicated handling of the camera
in stationary use (e.g. recording treatment sequences when the object is far away,
standard orthodontic shots and imaging) and the possibility of connecting the microscope
for investigating microbial plaque.
Stationary use of DentalScout cameras is easily possible due to a plug-in
coupling with tripod thread. The telephoto lenses used ensure greater object distances.
Only few endoscope cameras are designed to be capable of this.
Summary
The slim 'handy' design of an endoscope camera does not automatically mean
better handling. The deciding factor is how easily and efficiently typical imaging
situations can be managed in daily praxis. On this score, the DentalScout® P2000 often
has major advantages over endoscope cameras. It also beats most endoscope cameras when it
comes to picture quality and dimensional accuracy of imaging.
Author:
Dr. Dr. Rolf Klett, physicist and dental surgeon, Wuerzburg
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