Dental translucency analyzer and method

The invention relates to a dental device which measures the translucency of the anterior tooth that is adjacent to the tooth to be restored and gives the translucency factor that is used for the creation of a natural looking repaired tooth. The device illuminates the incisal part of the tooth with white light and detects the light from the opposite side of the tooth. Signals indicating the values of transmitted light, the calibrated light, and the ambient light are processed and displayed on the LCD as a translucency factor. The device comprises a handpiece with a U-shape distal holder. One part of the holder includes several illuminating fibers, whereas another part carries a corresponding number of detecting fibers. The device is applied to the tooth by touching the edge of the tooth with a bottom and one side of the holder which carries the detecting fibers.

BACKGROUND OF THE INVENTION
 1. Field of the invention
 The invention relates generally to esthetic dentistry, and more
 particularly, to the technical means that measure the translucency of
 dental materials and natural teeth in order to create naturally looked
 dental prostheses.
 2. State of the Art
 Translucency is a main factor that indicates the quality of the restorative
 dental procedures. A common situation frequently occurs when a patient
 gets a well color-matched restored anterior tooth, but it looks like a
 nonvital shade tab. This situation happens because the practitioner was
 not able to determine the translucency level in teeth that were adjacent
 to the damaged tooth and served as references for color matching. A
 translucency mismatch is most crucial for an incisal part of the anterior
 tooth which contributes mostly to the natural appearance of the patient's
 teeth.
 A procedure for proper color matching is performed by the visual comparison
 of teeth against shade guide color standards. A significant problem with
 the visual method is that its success depends upon the color vision of the
 practitioner. Moreover, even in the case of perfect color vision, the
 dental color matching procedure can be quite anxiety provokingfor the
 practitioner because color and translucency change along the tooth. In
 order to be normalized, standard dental color shades are classified by
 considering the color only in the central part of the shade tab. The
 variation of translucency is not included in the shade description because
 it will affect the visual perception of the teeth and shade tabs. As a
 result, for matching the incisal translucent part, the practitioner must
 guess which central part of the nontranslucent shade tabs looks closer to
 the natural translucent tooth.
 The recent prior art aimed to overcome the problem associated with the
 visual analysis of dental translucency by applying fiber optics for
 illuminating the tooth and for detecting the light scattered from the same
 side of the tooth. The idea was to determine the translucency factor by
 separate illuminating of different areas of the tooth with a few light
 sources, as described in U.S. Pat. No. 5,798,839 or by detecting the light
 scattered at different distances from a single light source as described
 in U.S. Pat. No. 5,851,113. There is one major technical obstacle to
 successful clinical implementation of these techniques. It is explained
 below without being bound by theory.
 A translucent object appears like a milky glass. The higher the
 translucency, the more transparent object seems. The translucency
 parameter may be defined as a difference between color parameters that
 were taken when the object was analyzed against two backings, one ideally
 white and another absolutely dark. Consider an absolute transparent
 object, such as optical glass, for instance, and use a Lab color system
 that is based on the use of L, a, b color parameters. If the glass is
 measured against the white backing, the color parameters will be L.sub.w
 =100, a.sub.w =0, and b.sub.w =0 which corresponds to an ideal white
 standard placed under the glass (reflection from the glass is neglected).
 When the same glass is measured against an absolutely dark backing, all
 color parameters will be zero, L.sub.b =a.sub.b =b.sub.b =0, because no
 light is transmitted at all. Therefore, the color difference will be
 .DELTA.L=L.sub.w -L.sub.b =100, .DELTA.a=a.sub.w -b.sub.b =0, and
 .DELTA.b=b.sub.w -b.sub.b =0, and thus, the transluce absolute transparent
 glass equals 100.
 However, the foregoing prior arts are entirely based on measurement of the
 backscattered light. They will indicate zero signals for both types of
 glasses mentioned above no light is scattered back in the direction from
 where light came. In other words, the prior arts are not able to
 distinguish between transparency and darkness because absorption which is
 independent of scattering contributes equally to transmittance and
 reflection. In the case of teeth, nonsensitivity to absorption will
 increase the color difference due to the spectral dependence of light
 propagation into the enamel and dentin. As described elsewhere, different
 color components have different absorption and scattering parameters. This
 example shows that translucency of the teeth has to be measured in a
 direct mode, namely by measuring the light (flux F.sub.t,) that passed
 through the tooth and has continued in the same direction as the incoming
 light. If F.sub.O is the incoming flux, the translucency factor, TR, can
 be expressed as a ratio, TR=F.sub.t /F.sub.O.times.100.
 Earlier prior art was connected to the direct measurement of tooth
 transmission as described in U.S. Pat. No. 4,881,811. The technique has
 employed an integrating sphere that touched the external surface of the
 tooth while the tooth was illuminated from the internal side using a
 flexible fiber optic. The sphere was mounted in a probe that was connected
 to a remote spectrophotometer. The main disadvantage of this prior art is
 that it measures the total transmittance of the tooth because it collects
 the light that is scattered at all possible angles, from 0 up to 90
 degrees. Another disadvantages of this prior art was the complexity and
 enlarged size of the probe. These do not allow for measuring a portion of
 the tooth that is necessary for the restoration of natural looking teeth.
 In addition, this prior art is not portable because it requires a cable
 connection with the remote spectrophotometer.
 Another prior art that can be implemented for the translucency measurement
 of teeth is the fiber optic transillumination (FOTI) technique used for
 detecting cavities. It is comprised of an illuminating fiber bundle that
 illuminates the tooth from a powerful polychromatic light source and
 receiving fiber bundle that transfers a projection of the tooth to a
 screen or videocamera. This prior art is very complex and non-portable as
 it requires a powerful light source, and cannot provide an accurate
 measurement of translucency because the projective image is formed mostly
 by light scattered from the entire body of the tooth, not from the portion
 of the tooth that must be analyzed.
 It is, therefore, an object of the invention to provide a dental
 translucency analyzer that is small and portable. It is also an object of
 the invention to provide a dental translucency analyzer able to measure
 translucency in a small portion of teeth and dental materials.
 SUMMARY OF THE INVENTION
 The foregoing objects are achieved by this invention which provides a
 dental translucency analyzer and method for measuring translucency of
 teeth that are adjacent to the damaged tooth.
 According to the present invention, a dental translucency analyzer measures
 translucency in a small portion of the tooth by employing an illuminating
 fiber optic which is positioned at the back side of the tooth and a
 receiving fiber optic which is positioned at the front side of the tooth.
 The number of illuminating and receiving fibers is the same. Both fiber
 optics comprise low aperture optical fibers that transmit light within a
 relatively narrow angle. The proximal ends of the illuminating fiber optic
 are coupled to white light emitting diodes (LED), while distal ends of the
 receiving fiber optic are coupled to photodetectors. The distal ends of
 the illuminating fiber optic and the proximal ends of the detecting fiber
 optic surround the tooth via a U-shape holder, each distal end of an
 illuminating fiber faces a corresponding proximal end of a receiving
 fiber. Such a pair comprises a measuring channel that transilluminates the
 tooth at a certain position and detects the light that passes through the
 tooth in the same direction with illuminating light. In order to provide
 measurements in different portions of the tooth, the fiber optics may
 consist of several fibers that are located in a row at different distances
 from the edge of the tooth.
 The photodetectors are connected to an electronic unit that processes
 signals indicating the translucency of the tooth and displays the result
 on an LCD display. The electronic unit is comprised of a microcontroller,
 a converter, a power supply, and drivers.
 All fiber optics, LEDs, photodetectors, LCD and electronic components may
 be mounted in one handpiece that can be easily manipulated and kept as a
 conventional practitioner's tool without using a cable connection. The
 practitioner touches the tooth with one side of the U-shaped holder, and
 the device will automatically give a value of translucency. Because of the
 portability of the device, it may be possible to measure translucency
 along the crown of the tooth.
 An advantage of the present invention is that the dental translucency
 analyzer is small and portable and can be easy operated by one hand.
 Another advantage of the present invention is that translucency of the
 tooth is measured in a direct mode without affecting the results by
 uncertain absorption and scattering parameters of the tooth. Yet another
 advantage is that translucency of the tooth can be measured in a small
 area of the tooth or several small areas of the tooth, thus, providing the
 possibility of an exact color restoration for the repaired tooth.

DETAILED DESCRIPTION OF THE INVENTION
 With reference to FIG. 1, the general design of a dental translucency
 analyzer according to the present invention shall be further explained.
 Essentially, the analyzer is designed as a handpiece that comprises a body
 (10) and a distal tip (15). The distal tip comprises a U-shaped holder
 (16) that is applied to a tooth (20) in such a way that the tooth is in
 contact with a bottom (22) and a right side (24) of the holder as shown in
 FIG. 2A. The right side of the holder carriers a plurality of receiving
 optical fibers (only three fibers (30), (32), and (34) are shown in FIG.
 2A). A left side of the holder carriers a plurality of receiving optical
 fibers (only three fibers (40), (42), and (44) are shown in FIG. 2A). The
 distal end of each illuminating fiber faces the proximal end of the
 corresponding receiving fiber, and thus, the axes between the ends of the
 fibers create a plurality of measuring points (50), (52), and (54) as
 shown in FIG. 2B. The detecting fibers are coupled with a corresponding
 number of photodetectors, and the illuminating fibers are coupled with the
 corresponding number of light sources (both not shown in FIG. 2A).
 Both illuminating and receiving fibers are preferably low aperture optical
 fibers. An illuminating fiber irradiates the tooth within a narrow solid
 angle (60) as shown in FIG. 3. A corresponding receiving fiber detects
 light transmitted through the tooth (flux Ft) within a narrow solid angle
 (62). The fibers are located at various distances from the bottom of the
 holder with increments from 0.5 to 2.0 mm, preferably 1.0 mm.
 A schematic of the preferred embodiment of the electronic unit is shown in
 FIG. 4. The illuminating fibers (40), (42), and (44) are coupled to white
 polychromatic light sources (70), (71), and (72), respectively. The light
 sources are powered from a power supply (73) through a driver (74).
 Preferably, the light sources are white LEDs with operating voltages from
 3 to 5 volts. The receiving fibers (30), (32), and (34) are connected to
 photodetectors (75), (76), and (77), respectively. The photodetectors are
 preferably silicone photodiodes. The photodetectors (75), (76), and (77)
 are connected to amplifiers (78), (79), and (80), respectively. The
 amplifiers are connected to an analogto-digital converter (84). The
 analog-to digital converter is connected to a microcontroller (86). The
 microcontroller indicates the results of the measurement on a
 liquid-crystal-display (LCD) (88). The indication results preferably
 include two lines of data, distances h1, h2, h3, ((90), (92), (94),
 accordingly), and the corresponding calculated data of translucency (96),
 (98), (100). The distances h1, h2, h3 are fixed for the design of the
 distal tip. In another embodiment, LCD may indicate "standby", "ready",
 "calibration" and other similar modes that make the device more user
 friendly.
 The mode can be chosen by a switch (102) that is connected to the
 microcontroller (86). The switch can be located at any convenient place on
 the handpiece, preferably closer to the distal tip (15) as shown in FIG.
 1. It can be activated by a finger or automatically when a proper contact
 of the holder (16) with the tooth (20) is achieved. In another embodiment,
 the LCD may show additional useful information such as the preferable
 composition of the restorative materials that gives the desired
 translucency. This data is processed in the microcontroller (86) by
 comparing the measured translucency with data stored in memory (104). The
 stored data may consist of values for translucency and standard recipes
 that combine a certain percentage of clear and opaque porcelains or
 plastics. A port (106) may be connected to the microcontroller. The port
 may be used for communication with dental image software, a patient
 database, communication with the dental lab performing the restoration,
 and other related purposes. A power switch (103) that connects the battery
 with the electronic circuit may be located at any convenient place on the
 handpiece, preferably on the front side of it as shown in FIG. 1. A
 connector (108) may be optional to the dental translucency analyzer if a
 rechargeable battery is used. Preferably, it is located in the bottom of
 the body as shown in FIG. 1. A speaker (110) can be connected to the
 microcontroller signaling the powering, calibration, and measurement.
 With reference to FIG. 1, FIG. 5 and FIG. 6, the action of the dental
 translucency analyzer shall further be explained. Immediately after
 turning on the power switch (103), while still not applying the distal tip
 (15) to the tooth (20), a step I (calibration, or measurement of incoming
 fluxes Fo) is performed. Each LED is powered one by one in a sequence mode
 by a normalized pulsed current. Each receiving fiber gets its incoming
 flux Fo shown in FIG. 6 that comes from the corresponding illuminating
 fiber after passing the distance between the left and the right sides of
 the U-shape holder (fluxes Fo1, Fo2, and Fo3 shown in FIG. 5 for three
 fibers design mentioned above). The fluxes Fo are not necessary the same
 in each channel as they depend of the LED-to-fiber coupling, the fiber
 transmission, the quality of fiber tips, the photodetector-to-fiber
 coupling, and other factors. Therefore, the calibration is necessary for
 providing an accurate and repeatable measurement. According with the
 present invention, the calibration is performed by measuring the fluxes Fo
 passed through the air space. Thus, the air space serves as a translucency
 standard (reasonably, the translucency of air can be accepted as 100%).
 The flux Fo is converted by the corresponding photodetector to a
 calibrated signal UC (signals UC1, UC2, UC3, respectively). The values of
 these signals are stored in the microcontroller. When these measurements
 are done, all LEDs are turned off. In order to avoid illumination coming
 straight from surrounding light sources, the distal tip can be placed in a
 dark enclosure during calibration. After applying the distal tip (15) to
 the tooth (20) and activating the switch (102) the next steps are
 performed.
 Step II (dark signals registration). The microcontroller registers dark
 signals UD (signals UD1, UD2, UD3 shown in FIG. 5). These signals are
 generated by the photodetectors mainly because of ambient illumination.
 Step III (measurement of transmitted fluxes Ft). The LEDs are powered in
 the same way as was done in step I. Each receiving fiber receives flux Ft
 which transmits through the tooth at a certain distance h from the tooth's
 edge. The microcontroller registers a set of the signals UM (signal UM1,
 UM2, UM3 in FIG. 5) from the photodetectors.
 Step IV (calculation of translucency). The translucency parameter, TR, is
 calculated by the microcontroller from the stored data for each distance h
 as
EQU TR=(UM-UD)/UC.times.100
 and is expressed a percentage for convenience.
 The calculated value TR is then displayed on the LCD, preferably as rows of
 h and TR as shown in FIG. 1. It can be used for preparing the recipes for
 the dental lab which is going to make the dental prostheses.
 The distal tip (15) can be made disposable by pulling it from the body
 (10). In another embodiment, a thin disposable protective shield (112) can
 be applied to the distal tip as shown in FIG. 7. This shield will protect
 the patient against direct contact with the dental translucency analyzer.
 The shield can be made of a transparent material, preferably polystyrene
 or polyethylene. The calibration procedure (step I in FIG. 5) is performed
 after applying the shield.
 The diameter of the illuminating and receiving fibers can be from 0.05 to
 1.0 mm, preferably from 0.1 to 0.2 mm. The diameter of the receiving fiber
 determines the size of the zone that is detected by the dental
 translucency analyzer. This zone is much smaller than the width of the
 translucent incisal part of the tooth which is typically from one to four
 millimeters.
 It should be pointed out that a great number of possible designs of the
 dental translucency analyzer according is possible within the scope of the
 present invention. For, example, a few more rows of illuminating and
 receiving fibers could be placed into the distal tip with corresponding
 LEDs and photodetectors attached in the body. This placement will allow
 the provision of translucency measurement in a lateral direction, and
 thus, more accurate data could be obtained from multiple portions of the
 tooth. In addition, a row of microlenses could be associated with the
 distal ends of the illuminating fibers for providing more directional
 illumination of the tooth.