Dentistry – Apparatus – Having means to emit radiation or facilitate viewing of the...
Reexamination Certificate
1999-05-11
2001-02-13
Manahan, Todd E. (Department: 3732)
Dentistry
Apparatus
Having means to emit radiation or facilitate viewing of the...
C433S215000
Reexamination Certificate
active
06186780
ABSTRACT:
The present invention relates to a method and to a corresponding device for the recognition of caries, plaque, concretions, bacterial infection etc. on teeth in accordance with the preamble of claim
1
or
8
.
It is known to identify caries, plaque or bacterial infection on teeth through visual investigation or through employment of X-rays. However, with the aid of a visual investigation, satisfactory results frequently cannot be attained since, for example, caries in the early stage or at a difficult to observe tooth region cannot be identified. Although, on the other hand, X-rays have proved to be a very effective way of identifying an incidence of caries or other tooth diseases, this investigation method is also not optimal due to the damaging effect of the X-rays for human health. There was thus the need to develop a new technique in order to be able to identify the presence of caries on teeth.
In DE 3031249 C2 there was proposed a contactless investigation method for the identification of caries on human teeth, whereby the tooth is irradiated with practically monochromatic light. The practically monochromatic light radiation excites a fluorescence radiation at the tooth. Thereby it was discovered that the fluorescence spectrum reflected from the tooth manifests significant differences between carious and healthy tooth regions. Thus, in the red spectral range of the fluorescence spectrum of the tooth (i.e. between 550 nm and 650 nm) the intensity is significantly higher than with a healthy tooth. In contrast, in the blue spectral range of the reflected fluorescence spectrum of the tooth (i.e. between 350 nm and 450 nm) the intensity of the fluorescence radiation for carious regions and healthy regions of the tooth is virtually identical. In DE 3031249 C2 it was therefore proposed to irradiate the tooth with a wavelength of 410 nm and, by means of two filters, to detect the fluorescence radiation of the tooth for a first wavelength of 450 nm and a second wavelength of 610 nm, i.e. in the blue and red spectral region, for example with the aid of photodetectors. The fluorescence radiation intensities detected by means of this arrangement are subtracted so that on the basis of the thus obtained difference intensity a healthy tooth region can be unambiguously distinguished from a carious tooth region.
DE 4200741 A1 proposes, as an advantageous further development, to bring about the fluorescence of the tooth by means of an excitation radiation having a wavelength in the range 360 nm to 580 nm and to filter out the fluorescence radiation brought about at the irradiated tooth in the wavelength range between 620 nm and 720 nm. By means of this measure it is achieved that the spacing between the wavelength of the excitation radiation and of the received fluorescence radiation is sufficiently great such that the excitation radiation cannot corrupt the evaluation results through superposition on the fluorescence radiation.
The above-described known investigation methods or devices have in common that for the excitation of the fluorescence at a tooth to be investigated an excitation radiation having a relatively short wavelength, i.e. smaller than 580 nm, is employed. Thereby, although on the one hand a relatively greater effective cross-section for the generation of the fluorescence radiation is attained, however the fluorescence radiation for healthy tooth tissue is significantly stronger than that for carious lesions. Therefore, with the above-described investigation methods an elaborate direct comparison of the fluorescence radiation emitted in a particular wavelength range from neighbouring healthy and carious regions is necessary, or the measurement signals of the detected fluorescence radiation in two different wavelength ranges must be compared with one another in an elaborate manner.
In DE 19541686 A1, which like DE 4200741 A1 originates from the applicant of the present application, it was therefore proposed to employ for the excitation of the fluorescence at a tooth to be investigated an excitation radiation having a wavelength between 600 nm and 670 nm. For the detection of the fluorescence radiation excited at the irradiated tooth, a spectral filter arrangement is employed which lets through fluorescence radiation having a wavelength between 670 nm and 800 nm, i.e. in accordance with DE 19541686 A1 only fluorescence radiation having a wavelength between 670 nm and 800 nm is evaluated for the recognition of caries, plaque or bacterial infection at the irradiated tooth.
With the aid of the measures proposed in DE 19541686 A1 an improved sensitivity of the caries detection is attained. The excitation of the fluorescence radiation with an excitation radiation in the above-mentioned wavelength range between 600 nm and 670 nm has the advantage that the fluorescence radiation from healthy tooth regions strongly reduces with such excitation wavelengths, so that the fluorescence radiation from carious regions is only slightly superposed with the autofluorescence of the healthy tooth tissue and caries, plaque or bacterial infection of teeth can be recognised simply, in a manner not prone to disruption and with high sensitivity.
Starting from the above described state of the art the present invention has the object of further increasing the detection sensitivity in the recognition of caries, plaque, concretions or bacterial infection on teeth, i.e. to increase the difference between measurement signals from healthy tooth regions on the one hand and carious tooth regions on the other hand.
In accordance with the present invention this object is achieved by means of a method having the features of claim
1
or a device having the features of claim
8
. The subclaims describe preferred and advantageous embodiments of the present invention, which for their part contribute to an improved sensitivity or to a construction of the device in accordance with the invention which is as simple as possible.
In accordance with the present invention it is proposed, for the recognition of caries, plaque, concretions, bacterial infection etc., to evaluate fluorescence radiation having a wavelength above ca. 800 nm. In accordance with the knowledge on which the present patent application is based, with the aid of this measure there can be attained a particularly sensitive recognition of hidden caries (for example in fissures or approximal tooth regions), since in this wavelength range of the fluorescence radiation the proportion of caries specific fluorophores and other deposits is particularly high, but healthy tooth enamel or dentine does not fluoresce or fluoresces only very slightly.
The fluorescence radiation can in principal be excited with all wavelengths below 800 nm. With regard to the optical penetration depth an excitation with radiation of as long a wavelength as possible is advantageous, due to the scattering which reduces with increasing wavelength, so that in accordance with a preferred exemplary embodiment the excitation wavelength lies between 680 nm and 800 nm, in particular between 700 nm and 800 nm, and preferably is 780 nm.
In the development of the present invention it has been revealed that evidently above and below a particular excitation wavelength different groups of fluorophores are detected, so that for a differentiation (e.g. of decalcifications and lesions having organic deposits or bacterial infection) the combination of different detection ranges, i.e. of different evaluated wavelength ranges of the fluorescence radiation, and/or of excitation wavelengths, is also advantageous.
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Hibst Raimund
Paulus Robert
Kaltenbach & Voigt GmbH & Co.
Manahan Todd #E.
Scully Scott Murphy & Presser
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