Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
2002-03-18
2003-02-18
Stafira, Michael P. (Department: 2877)
Optics: measuring and testing
By polarized light examination
Of surface reflection
C356S364000
Reexamination Certificate
active
06522407
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the detection of dental disease using polarized light by optically measuring the depolarization of incident light backscattered from dental tissues.
2. Description of Related Art
Dental caries, or tooth decay, is a pathological process of destruction of tooth structure by oral microorganisms, which can lead to tooth loss if untreated. In coronal caries, lesions begin in the enamel and cause demineralization of the enamel. This demineralization changes the scattering properties of the enamel, resulting in chalky or “white spot” lesions visible when the caries occurs on smooth, unstained enamel surfaces. If the carious lesion is detected before it reaches the dentin, remineralization is still possible. After the carious lesion has reached dentin, however, inflammation of the pulp occurs, requiring a filling and leading to serious tooth decay and eventual tooth loss if untreated. Restorative dentistry is most effective when the progression of caries is detected early before it reaches the dentin.
Current techniques for diagnosing caries are visual inspection, mechanical probing with a sharp dental explorer, and radiographic imaging. The tooth can be tactilely and visually explored to determine the presence of indicators of tooth decay such as surface irregularities, crevices, or discoloration. However, the practice of probing all accessible tooth surfaces with a sharp explorer is coming under increased scrutiny since it can further damage enamel already weakened by decay and may also cause cross-contamination between teeth. As tooth decay primarily affects the region of calcium below the tooth surface, detection of caries before significant damage occurs in the tooth is very difficult.
By the time caries is evident under visual and tactile examination of the tooth, the disease is usually in an advanced stage, requiring a filling and occasionally leading to tooth loss. As a consequence of conservative diagnoses and treatment, there are false positives leading to unnecessary drilling and placement of restorations in healthy teeth. Currently there is no accurate device for determining whether restorations are in need of replacement, resulting in enormous costs from the unnecessary replacement of good restorations and complications such as root canals from not replacing defective or aged restorations.
Radiography is often used for detection of cavities, since it provides integrated views of tooth structure that in certain orientations can isolate carious lesions. The sensitivity of radiographic systems, however, is limited by visible changes in film density, making identification of small carious or precarious regions difficult. Since radiographs are two dimensional, precisely locating the position of such decay is impossible. Moreover, due to the orientation of the x-ray imaging, only interproximal lesions (between the teeth) are easily detected, while early occlusal lesions (top of the tooth), are difficult to detect. In addition, radiography uses harmful ionizing radiation.
Given the disadvantages of current detection techniques, a need exists for a device that provides safe, early diagnosis of caries. This invention applies the technique of polarimetry to image dental hard tissue and detect the presence of caries based on the depolarization of incident light. The invention also has the potential for detection of disease in bone.
Polarimetry is a well-established tool for non-invasive material characterization and involves comparison of the polarization states of light before and after the light interacts with the material. The use of polarized light for characterization and imaging of highly scattering media, such as biological tissue, has been studied. The effect of scattering on the polarization state of light has been found to be useful for imaging of surface or subsurface structures in scattering media, and for transmission imaging of deep structures. See Rowe et al., “Polarization-difference imaging—a biologically inspired technique for observation through scattering media”,
Optics Letters
20:608-610 (1995). It has also been shown that the scattering parameters of turbid tissue, including the scattering coefficient &mgr;
s
and anisotropy factor g, can be determined from diffusely scattered polarized light. See Hielscher et al., “Diffuse backscattering Mueller matrices of highly scattering media”,
Optics Express
1:441-453 (1997).
Polarimetry may be combined with a second method, optical coherence domain reflectometry (OCDR), which was developed as a high resolution ranging technique for characterization of optical components and was based on bulk optics. See Youngquist et al., “Optical coherence-domain reflectometry: a new optical evaluation technique”,
Optics Letters
12(3):158-160 (1987). The first fiber optic based OCDR system was constructed by the U.S. National Bureau of Standards for micro-optic technology. See Danielson et al., “Guided-wave reflectometry with micrometer resolution”,
Applied Optics
26(14):2836-2842 (1987).
OCDR uses a low coherence Michelson interferometer to probe the sample, generating reflection signals as a function of depth. When the probe beam is transversed across the sample, a series of axial scans can be stacked together to form a high-resolution two-dimensional optical coherence tomogram. See Lee et. al, “Profilometry with a coherence scanning microscope”,
Applied Optics
29(26):3784-3788 (1990). Optical coherence tomography (OCT) was developed to produce cross-sectional images of biological microstructure by combining transverse scanning with a fiber optic OCDR system. See Huang et al., “Optical Coherence Tomography”,
Science
254:1178-1181 (1991). U.S. Pat. No. 5,321,501 discloses the general means for construction of an OCT system, specifically as it applies to OCT imaging of the eye for diagnosis of ocular diseases. U.S. Pat. No. 5,459,570 discloses OCT imaging of biological tissue, including measurement of tissue optical properties and the use of polarization sensitive OCT (PS-OCT) to measure tissue birefringence. These OCT devices provide imaging in the eye and circulatory system.
PS-OCT has also been used for measuring birefringence in teeth in an unsuccessful attempt at caries detection. This attempt was unsuccessful because caries causes light to become depolarized by changing the scattering coefficient of the enamel rather than significantly affecting the birefringence of the enamel. See Baumgartner et al., “Optical coherence tomography of dental structures”, Proc. SPIE 3248; Lasers in Dentistry IV, John D. Featherstone, Peter Rechmann, Daniel S. Fried, eds., pp. 130-136 (1998).
The application of OCT for dental applications was pioneered by the University of California at Lawrence Livermore National Laboratory. U.S. Pat. No. 5,570,182, assigned to the University of California, discloses the use of OCT for diagnosis of dental caries and periodontal diseases. Co-pending U.S. patent application Ser. No. 09/315,000 assigned to the same assignee, describes a dental explorer device for detecting caries and periodontal disease using OCDR, and is incorporated herein by reference. In order for OCT to be practical and convenient for clinicians to use on patients, an OCDR dental device was developed in the form of a hand-held, portable explorer tool for non-invasively probing teeth and other dental tissues. The OCDR explorer was designed to safely and accurately collect intraoral OCT images of dental tissue and microstructure in vivo for evaluation of dental health.
The capabilities of the dental explorer device have been further expanded and improved in the present invention by the incorporation of polarization sensitive diagnostics. The invention uses PS-OCT to measure the depolarization of light associated with optical scattering, rather than changes in polarization state associated with birefringence, to detect demineralization and caries. By taking advantage of the ability of polarimetry to both image tissue and detect changes in its scatterin
Colston, Jr. Billy W.
Da Silva Luiz B.
Everett Matthew J.
Fried Daniel
Sathyam Ujwal S.
Scott Eddie E.
Stafira Michael P.
The Regents of the University of California
Thompson Alan H.
LandOfFree
Optical detection dental disease using polarized light does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical detection dental disease using polarized light, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical detection dental disease using polarized light will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3182246