Note: Descriptions are shown in the official language in which they were submitted.
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INTERPROXIMAL TOOTH DEFECTS DETECTION
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority on Canadian patent application
No. 2,517,252 filed August 29, 2005 and entitled "DETECTION DE LA CARIE
INTERPROXIMALE A L'AIDE D'UNE SONDE OPTIQUE EXAMINANT LA
SURFACE OCCLUSALE DE LA DENT".
FIELD OF THE INVENTION
The invention relates to the optical detection of tooth defects
and more specifically it relates to the optical detection of tooth defects in
the
interproximal area.
BACKGROUND OF THE INVENTION
There are various known methods that are used to detect the
presence of dental caries, including visual and tactile investigations using
the
usual dental explorer. These methods and instruments have their limits and
cannot detect dental caries reliably, especially when the dental caries is
proximal and when the decay is at an initial stage. X-ray investigation of
teeth
structure is also not reliable for detecting dental caries at the beginning of
their formation in regions where a too great superimposition of enamel is
present on the X-ray film. These obstructing superimpositions of teeth
structures are more typical for the occlusal aspect of the teeth, and when the
angle between the teeth alignment and the X-ray irradiation axis induces
superimposition. The X-ray evaluation technique also exposes the patient to
potentially harmful radiations.
Transillumination is another technique used to detect dental
caries. By irradiating visible light toward a tooth from an aspect (e.g.
lingual)
and by observing via another aspect (e.g. buccal) the transmitted light, the
operator can sometimes confirm the diagnosis of dental caries by observing a
luminosity contrast induced by a dental caries. This technique is not suitable
for all dental caries, especially for dental caries at their beginning phase.
Furthermore the device used for transillumination detection of caries is large
and not easy to manipulate in the mouth.
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Other devices have been devised for the detection of dental
caries using luminescence or fluorescence spectroscopy with variable
efficiencies depending, amongst others, on the cleanliness of the tooth
surface. When irradiated with one or more initial radiations at a specific
wavelength, some tooth structures generate a second radiation with a
wavelength that is different from the initial radiations. The intensity and
wavelength of such a second radiation is different for sound tooth structures
from those for decayed tooth structures. See U.S. Pat. No. RE31,815, No.
4,479,499, No. 6,186,780, No. 6,102,704, No. 6,053,731, No. 6,135,774 and
No. 5,306,144, and German Patent Publications No. DE-30 31 249-C2, No.
DE-42 00 741-Al, No. DE-U1-93 17 984, No. DE-303 1249-C2 and No. DE-
19541686-Al. In most cases, these devices include a laser to generate the
initial exciting radiation, which can be potentially harmful to the patient.
The above described optical approaches are however
sometimes inadequate for the detection of interproximal caries. Different
approaches have been suggested with a view to better detect interproximal
caries. These approaches are mostly based on special probes that try to
reach the interproximal area. The making and manipulation of such probes
are complex and not convenient.
There is therefore a need for improved optical method for the
detection of caries and in particular interproximal caries.
SUMMARY OF THE INVENTION
In a broad aspect of the invention there is provided a method for
the optical detection of tooth defects in the interproximal region. The method
advantageously enables to probe the interproximal region without having to
reach the region with on optical probe.
Thus in one aspect of the invention there is provided a method
for detection of an interproximal defect in a tooth, comprising injecting
incident
light at an injection point in a first tooth region at one or more
wavelengths,
such that said incident light can reach said interproximal defect
substantially
through enamel structure; detecting reflected/refracted or re-emitted light in
a
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second tooth region; analyzing said detected light to provide a signal
indicating a presence of said interproximal defect; and wherein said first and
said second tooth regions are other than the interproximal region.
In an aspect of the invention said first and said second region
are the occlusal surface of said tooth.
In another aspect the step of analyzing comprises obtaining an
intensity of said detected light and comparing said intensity with reference
intensities obtained from healthy interproximal tooth regions and regions
exhibiting defects.
In yet another aspect the intensity is detected at two or more
wavelengths to provide intensity coordinates in two or more dimensional
space, and wherein said coordinates are compared to reference coordinates
of healthy tooth regions and tooth regions exhibiting defects.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the present invention will
become apparent from the following detailed description, taken in
combination with the appended drawings, in which:
Figure 1 is a schematic diagram of teeth arrangements in the mouth;
Figure 2 is a cross-sectional view of a tooth revealing the internal
structures;
Figure 3A is a schematic representation of the path of light within the tooth
when probed according to an embodiment of the invention;
Figure 3B is an interproximal view of figure 3A;
Figure 3C is an occlusal view of figure 3A;
Figure 4A is a graphic of the intensity of reflected/refracted light at one
wavelength vs. intensity of reflected/refracted light at a different
wavelength
for healthy teeth (white symbols) and teeth exhibiting occlusal (gray symbols)
or interproximal (black symbols) caries; and
Figure 4B is a graphic of the intensity of reflected/refracted light in the
infrared
region vs. the red region of the spectrum for extracted teeth that have been
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inspected via the occlusal region, the symbols above the line represents
carious teeth in the interproximal region and the symbols below the line are
from healthy tooth.
DETAILED DESCRIPTION OF THE INVENTION
In the present description the term "defect" or "tooth defect" is
used to refer to alterations in the tooth structure or physiology such as
caries
(demineralization), plaque, dental concretion (e.g.calculus), fracture in
tooth
structure, blood in gingival or bone, tartar and the like.
A schematic representation of teeth with reference to their
anatomy is shown in Figure 1. The surfaces of the teeth comprise the facial
10, lingual 12, mesial 14 and distal 16 surfaces. The facial surface of a
tooth
faces the cheeks or lips. The lingual surface faces toward the tongue. There
are two proximal surfaces: The mesial surface is the proximal surface closest
to the front of the mouth and the distal surface is the proximal surface
opposite the mesial surface (towards the back of the mouth). Between the
mesial surface of one tooth and the distal surface of the next tooth is the
interproximal space. The top of the tooth comprises the occlusal surface 18
(for the bicuspids and molars). A typical cross-sectional view of a tooth
structure is shown figure 2 revealing the internal structure of the tooth.
Shown
in this figure is the enamel 20 which comprises the outer surface of the
tooth,
the dentin 22 which is a hard and porous tissue located under the enamel and
the pulp 24 which comprises blood vessels and nerves.
The interproximal space and the mesial and distal surfaces are
particularly difficult to inspect to assess the presence of defects such as
caries. In the present invention it has been surprisingly found that light
injected in a tooth can be used to detect interproximal tooth defects without
having to position a light probe in the interproximal area. It is therefore
shown
in the present invention that optical detection of a defect such as a carie
can
be achieved using reflection/refraction or luminescence detection without
having to inject the light directly on or in the immediate neighborhood of the
defect .
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It has been found that by injecting light at the occlusal, facial or
lingual surface such that the path of at least some of the photons between the
point of light injection and the mesial or distal proximal surface remains
substantially in the enamel portion of the tooth, it is possible to detect a
light
signal characteristic of the dental defect in the proximal surface. Without
wishing to be bound by theory, the reflection/refraction or luminescence
signal
can be detected when the path of the light substantially avoids the dentin.
Light that is injected in the tooth will be reflected/refracted by
tooth structures including at the site of the defect or it can excite natural
molecules resulting in the generation of luminescence (fluorescence or
phosphorescence) if a proper wavelength is used. The detected light from the
reflection/refraction or luminescence provides a signal indicative of the
presence or absence of the defect on the proximal surface (interproximal
area).
In one embodiment of the invention light is injected with a light
probe 28 at the mesial or distal edge of the occlusal surface of a tooth as
shown in Figure 3A and the light reaches the defect 30 (such as a carie) in
the interproximal region and is reflected/diffracted, or a luminescence signal
is
generated, and the signal is detected. Interproximal and occlusal view of
figure 3A are shown in figures 3B and 3C.
When operating in the reflection//refraction mode, the point of
light injection and the point of light detection can be the same. However in a
preferred embodiment they are spaced apart so as to avoid interference
between the injected and the detected light. Optimal spatial separation
between injection and detection point will depend on factors such as the
intensity of the light, structure of the tooth, configuration of the light
source
and detector of the probe and the like. In a preferred embodiment the
separation is between 01um and 10mm. In a more preferred embodiment the
separation is between 150 m and 5mm.
When operating in the luminescence mode the point of injection
and the point of detection can be the same since injection and detection are
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effected at different wavelengths, i.e. at different excitation and emission
wavelengths. Thus the probe can be equipped with appropriate optical filters
so as to only allow light at the excitation wavelength to reach the detector.
It
will be appreciated however that the injection and detection points may also
be separated as in the case of the reflection/refraction mode. in such a case
a
filter at the detector may still be required to filter out reflected/refracted
light.
It is also possible to inject the light at an injection point that is on
a different surface than the detection. Thus it is also possible to inject the
light
at a point on one surface, say the facial surface near the proximal surface,
and detect the reflection (or fluorescence) at a different surface, say the
lingual or occlusal surface. This approach is to be distinguished from the
trans-illumination approach in which light absorption is measured as opposed
to reflection/refraction or luminescence. The magnitude of the signal detected
using a given light intensity and wavelength will depend on the actual
localization of the injection and detection points relative to the defect in
the
interproximal area as well as on the size of the defect. It may accordingly be
possible to get an approximation of the size and position of the defect by
acquiring signals at different injection/detection points configurations.
The position of the injection and detection point to be used for
detecting interproximal tooth defects may be determined by identifying the
regions at which reflection/refraction (or luminescence) from dentin is
detected and using this "map" to avoid positions at which the dentin signal
interferes with the signal from the interproximal region.
It has been found that the intensity of the reflection/refraction of
the light at given wavelengths or ranges of wavelengths is different for teeth
that exhibit defects in the interproximal region than for healthy teeth in the
same region. In one embodiment the intensity of the reflection/refraction at
one wavelength (1.1) can be plotted against the intensity at a second
wavelength (I,,2) (see for example figure 4A and 4B). Standard (reference)
plots can be generated by acquiring multiple readings at the two wavelengths
(I, l, 1.2) from teeth exhibiting a healthy interproximal region and teeth
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exhibiting a defect such as carie. The reference plots exhibit areas in which
the coordinates (I.1, 1.2) are characteristic of diseased or normal teeth.
Actual
measurements for diagnosis purposes can be compared to the standard plots.
As can be seen in figure 4 defects such as caries in different
areas of a tooth can be distinguished by establishing the relationship between
intensity measurements at two or more wavelengths. From the particular
example in figure 4A, in which intensity measurements for healthy teeth and
teeth exhibiting interproximal or occlusal caries are plotted at two
wavelengths
it can be seen that the Intensities are clustered in a specific region (or
regions).
Plots of I,,, vs 1,2 also advantageously take into accounts
variations in the signal intensity that are the results of variations in the
position
of the injection point and/or detection point relative to the position of the
defect
on the tooth. Such plots also take into account the size and position of the
defect insofar as it can affect the intensity of the signal.
It will be appreciated that more than two wavelengths can be
used. The number of wavelengths used dictates the dimensionality of the
graph. Thus, for example a three dimensional graph can be used to represent
the correlation between the intensity at three wavelengths. Increasing the
number of wavelengths at which measurements are obtained and thus the
dimensionality of the graph increases the accuracy and specificity of the
diagnosis. Without wishing to be bound by any theory, since the
reflection/refraction is wavelength dependent, each wavelength can provide
specific information about the nature of the defect.
When diagnosis measurements are obtained from a patient, the
intensities of the reflection/refraction at two or more wavelengths (i.e. the
coordinates (Ix1, I,2)) are compared to the reference graph to determine
whether there is presence of a carie or not in the interproximal area.
It will be appreciated that other approaches to analyze the
detected light may also provide indication of the presence of defects. For
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example the measurements may be reported in terms of ratios of intensities at
different wavelengths or even intensity at a single wavelength.
The range of wavelengths that can be used is preferably
between 300 and 3000 nm. In the case of luminescence specific wavelengths
may be more effective for the excitation of molecules. Optimal wavelengths
may be determined by injecting light at different wavelength and detecting the
emitted luminescence.
Injection and detection of light can be achieved using optical
instruments that are known in the art such as described in US patent
applications US20050181333, US20030143510 and US20040106081 or
other such devices. These instruments can be adapted to comprise a
processor capable of computing and comparing the intensities as described
above to provide a signal to the user when a measurement indicates the
presence of a defect in the interproximal region of a tooth.
Furthermore, polarized and/or coherent light may also be used
as the light source to be injected according to the method of the present
invention. Detection of such light for the purpose of detecting dental defects
has been described. See for example Fried et al (Journal of Biomedical
Optics; vol 7; No 4; 618-627, 2002).
While the invention has been described -in connection with specific
embodiments thereof, it will be understood that it is capable of further
modifications and this application is intended to cover any variations, uses,
or
adaptations of the invention following, in general, the principles of the
invention and including such departures from the present disclosures as come
within known or customary practice within the art to which the invention
pertains and as may be applied to the essential features herein before set
forth, and as follows in the scope of the appended claims.
