Three-dimensional data generation device and three-dimensional data generation method

Abstract

This three-dimensional data generation device captures images of an abutment tooth and the edges of the gums of the abutment tooth by means of optical coherence tomography, and generates three-dimensional data of the abutment tooth and the edges of the gums, on the basis of the images of the abutment tooth and the edges of the gums.

Description

Three-dimensional data generation device and three-dimensional data generation method

[0001] The present invention relates to a three-dimensional data generation device and a three-dimensional data generation method. This application claims priority to Japanese Patent Application No. 2024-209054 filed in Japan on November 29, 2024, the content of which is incorporated herein by reference.

[0002] An optical coherence tomography (OCT) device is applied in the field of biomedicine, such as ophthalmic medicine for tomographic measurement of the cornea and retina of the eye. The OCT methods are broadly classified into TD (Time Domain)-OCT and FD (Frequency Domain)-OCT. The latter FD-OCT is further classified into SD (Spectrum Domain)-OCT and SS (Swept Source)-OCT. Patent Document 1 discloses a technique for imaging oral tissues (such as the anterior teeth and molar teeth) using a laser light source for the SS-OCT method and displaying an optical coherence tomography image (hereinafter referred to as an OCT image).

[0003] Japanese Patent No. 5839894

[0004] However, although Patent Document 1 discloses displaying an OCT image, it does not disclose generating three-dimensional data (such as STL: Stereolithography) of abutment teeth necessary for manufacturing, for example, a prosthetic device. Since high dimensional accuracy cannot be obtained from an image simply obtained by irradiating oral tissues with a laser light source, even if three-dimensional data can be output, the dimensional accuracy of a prosthetic device (such as a crown) obtained by processing based on the three-dimensional data is not very high. In particular, if the dimensional accuracy of the mating surface is low, the meshing also deteriorates.

[0005] An object of the present invention is to provide a three-dimensional data generation device and a three-dimensional data generation method that can improve the dimensional accuracy of three-dimensional information of abutment teeth using the optical coherence tomography method in order to solve the above-described problems.

[0006] One aspect of the present invention is a three-dimensional data generation device that captures images of an abutment tooth and the gingival margin of the abutment tooth by optical coherence tomography, and generates three-dimensional data of the abutment tooth and the gingival margin based on the images of the abutment tooth and the gingival margin.

[0007] According to the present invention, it is possible to provide a three-dimensional data generation device and a three-dimensional data generation method that improve the dimensional accuracy of the three-dimensional information of abutment teeth and gingival margins.

[0008] This figure shows the configuration of the three-dimensional data generation system 1 according to this embodiment. This figure shows an example of the configuration of the three-dimensional data generation device 12. This figure shows an example of the probe 11 and OCT device 13. This is an example of the structure of the probe 11. This figure shows the operation of the control unit 14 according to this embodiment. This figure shows the abutment tooth and gingival margin that are the target of measurement. This figure shows the results of STL data generated in this embodiment and conventionally generated STL data.

[0009] (Three-Dimensional Data Generation Device) Embodiments of the present invention will be described in detail below with reference to the drawings. Figure 1 is a diagram showing the configuration of a three-dimensional data generation system 1 according to this embodiment. The three-dimensional data generation system 1 comprises a probe 11 and a three-dimensional data generation device 12.

[0010] The three-dimensional data generation system 1 acquires tomographic images of the abutment teeth and gingival margins of subject S using optical coherence tomography (OCT). The optical coherence tomography is, for example, spectral domain optical coherence tomography (SD-OCT). The optical coherence tomography is, for example, wavelength-swept optical coherence tomography (SS-OCT).

[0011] Figure 2 shows an example of the configuration of a three-dimensional data generation device 12. The three-dimensional data generation device 12 comprises an OCT device 13 and a control unit 14. The OCT device 13 outputs light to a probe 11 and performs optical coherence tomography based on the light returned from the probe 11. The OCT device 13 comprises, for example, a light source 131, a beam splitter 132, a reference mirror 133, and a detection unit 134.

[0012] The light source 131 outputs light to the beam splitter 132. The beam splitter 132 outputs the light input from the light source 131 to the probe 11 and the reference mirror 133. The probe 11 irradiates the oral cavity of the subject S with light input from the three-dimensional data generation device 12. By irradiating the oral cavity with light, reflected light is generated due to light scattering, and this reflected light is incident on the probe 11. The reflected light incident on the probe 11 is input to the beam splitter 132. In addition, the light output to the reference mirror 133 is reflected by the reference mirror 133 and input to the beam splitter 132. The beam splitter 132 combines the reflected light from the probe 11 and the reflected light from the reference mirror 133 and outputs it to the detection unit 134. The detection unit 134 detects the light input from the beam splitter 132.

[0013] If the OCT device 13 is an SD-OCT, the light source 131 outputs light with a broadband wavelength, and the detection unit 134 includes a spectrometer (e.g., a grating) and a linear image sensor. If the OCT device 13 is an SS-OCT, the light source 131 outputs light by sweeping the wavelength over time, and the detection unit 134 includes a differential detector.

[0014] Figure 3 shows an example of a probe 11 and an OCT apparatus 13. The probe 11 uses a small, two-axis galvanometer mirror system that ensures accuracy. Light emitted from the light source 131 enters the probe 11 through a single-mode optical fiber. A collimator lens is mounted on the exit end of the single-mode optical fiber, and the parallel light beam with a diameter of approximately 2.8 mm is reflected twice by two galvanometer mirrors that are positioned to prevent vignetting, and then focused by a scanning lens before illuminating the sample. Here, the two galvanometer mirrors are adjusted so that the OCT image of the gold mirror is as much a single-plane image as possible.

[0015] Figure 4 shows an example of the structure of the probe 11. The probe 11 comprises, for example, a single-mode optical fiber 101, an achromatic lens 102, a fixed mirror 103, a plano-convex lens 104, a MEMS mirror 105, a glass window 106, a nozzle 107, and a nozzle-internal mirror 108. The nozzle 107 is detachable. Measurement light is input to the single-mode optical fiber 101 and output from the nozzle-internal mirror 108 via the achromatic lens 102, fixed mirror 103, plano-convex lens 104, MEMS mirror 105, and glass window 106. As a result, light is irradiated onto the abutment tooth and gingival margin, which are the targets of measurement. The reflected light from the target of measurement is input to the single-mode optical fiber 101 via the nozzle-internal mirror 108, glass window 106, MEMS mirror 105, plano-convex lens 104, fixed mirror 103, and achromatic lens 102.

[0016] For example, a longer nozzle 107 is preferable to increase the operator's freedom of movement within the oral cavity. To lengthen the nozzle 107, the focal length of the plano-convex lens 104 is increased (for example, to 100 mm), and the plano-convex lens 104 is positioned close to the nozzle 107. Furthermore, since optical resolution deteriorates as the focal length increases, it is preferable to widen the effective diameters of the fixed mirror 103, the MEMS mirror 105, and the nozzle-internal mirror 108. For example, to image a wide area within the oral cavity, the MEMS mirror 105 is positioned as close to the plano-convex lens 104 as possible. The distance from the MEMS mirror 105 to the focal plane is, for example, 87 mm. Also, for example, the effective diameter of the MEMS mirror 105 is 2.0 mm, and the calculated beam diameter at the focal plane is 224 μm in the long axis direction and 182 μm in the short axis direction, resulting in an elliptical beam shape. To accommodate various applications and purposes, it is desirable that the MEMS mirror 105 has a replaceable structure.

[0017] The control unit 14 is composed of a processor such as a CPU (Central Processing Unit) and memory (main memory). The control unit 14 performs tomographic image acquisition processing, three-dimensional data generation processing, and three-dimensional data output processing by having the processor execute a program. Note that all or part of each function of the control unit 14 may be implemented using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The above program may be recorded on a computer-readable recording medium. Computer-readable recording media include, for example, portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, semiconductor memory devices (e.g., SSDs: Solid State Drives), and memory devices such as hard disks and semiconductor memory devices built into computer systems. The above program may be transmitted via a telecommunications line.

[0018] The tomographic image acquisition process involves acquiring tomographic images of the abutment tooth and gingival margin using optical coherence tomography (OCT). The control unit 14 controls the OCT device 13 through the tomographic image acquisition process, causing it to output light to the probe 11. This generates an interference light signal by combining the reflected light from the probe 11 with the output light, which in turn generates tomographic images of the abutment tooth and gingival margin.

[0019] The 3D data generation process generates 3D data of the abutment tooth and gingival margin based on the generated tomographic images of the abutment tooth and gingival margin. The generated 3D data is, for example, STL (Stereolithography) data.

[0020] In the tomographic image acquisition process, the abutment tooth and gingival margin may be imaged for each divided area. In this case, different tomographic images are acquired for each area. In the three-dimensional data generation process, a three-dimensional image of the abutment tooth and gingival margin is generated by overlapping and compositing the boundaries of the images for each divided area, and three-dimensional data of the abutment tooth and gingival margin is generated based on the generated three-dimensional image.

[0021] In the tomographic image acquisition process, multiple optical coherence tomography (OCT) scans are performed multiple times within the oral cavity by linearly moving the probe 11, thereby acquiring multiple tomographic images taken from different positions. At this time, in the three-dimensional data generation process, the multiple tomographic images are synthesized three-dimensionally based on the amount of movement of the probe 11 during OCT scanning, thereby generating a three-dimensional image of the abutment tooth and gingival margin. By extracting the surface position near the maximum brightness value, three-dimensional data of the abutment tooth and gingival margin is generated. The three-dimensional synthesis of multiple tomographic images can be performed, for example, using the switching function of image processing software (such as ImageJ).

[0022] In tomographic image acquisition processing, it is desirable that the abutment tooth and gingival margin be imaged in divided areas relative to the occlusal surface of the abutment tooth. In this case, in the three-dimensional data generation processing, a three-dimensional Fourier transform is performed on the overlapping region of the images from each divided area to generate a three-dimensional image of the abutment tooth and gingival margin, and three-dimensional data of the abutment tooth and gingival margin is generated based on the generated three-dimensional image. For superimposing the images from each divided area, for example, the Fourier transform based phase correlation method (PCM) is used. By performing a three-dimensional Fourier transform on the overlapping region, extracting the peak in the Fourier region, and correcting the position of that peak as a positional shift, the multiple tomographic images acquired are synthesized three-dimensionally.

[0023] Furthermore, there are no particular limitations on the number of divisions, number of compositing cycles, field of view size, or overlap amount; you should apply appropriate values ​​that improve dimensional accuracy.

[0024] When compositing three-dimensional images, the boundaries of the images may be smoothed. For example, boundaries can be smoothed by calculating a moving average for each pixel. Types of moving averages include the simple moving average, which simply averages multiple pixel values ​​while moving them; the weighted moving average, which linearly decreases the weight of individual pixel values; and the exponentially smoothed moving average, which exponentially decreases the weight of individual pixel values.

[0025] In generating three-dimensional data from three-dimensional images, a point cloud of the abutment tooth surface may be extracted based on predetermined thresholds. The threshold may be, for example, brightness, and a point cloud brighter than the threshold may be extracted. If there are two thresholds, and they are brightness, a point cloud between the two thresholds (lower threshold and upper threshold) may be extracted. In this case, a point cloud with brightness from the lower threshold to the upper threshold is extracted. In other words, point clouds darker than the lower threshold and point clouds brighter than the upper threshold can be treated as noise (removed), thereby reducing noise. Three or more thresholds may be set.

[0026] The coordinates of each point may be corrected according to the resolution of each axis in the three-dimensional direction. Furthermore, the computational complexity can be reduced by downsampling to decrease the number of points. Additionally, points in anomalous positions may be statistically removed. An anomalous position is defined as a point outside the range determined by the standard deviation from the mean position μ.

[0027] As a surface extraction method, the clustering algorithm DBSCAN (Density Based Spatial Clustering of Applications with Noise) is used to set a threshold and retain only the clusters on the tooth surface. Then, the normal vectors of the point cloud are estimated, normalized, and adjusted to a single direction for each predetermined region (e.g., 100 points). After that, a mesh is generated, smoothing is performed, and the normal vectors of the mesh are calculated. This allows the 3D image to be converted into STL data. Shading can be applied to the 3D model by calculating the normal vectors of the mesh.

[0028] In the above explanation, it was described that a three-dimensional image is captured and the captured three-dimensional image is converted into STL data. However, a two-dimensional image may be captured and a three-dimensional image may be generated based on the captured two-dimensional image. For example, the OCT device 13 may capture a two-dimensional image and generate a three-dimensional image by stitching together the captured two-dimensional images in another dimension.

[0029] Alternatively, the two-dimensional images captured in segments may be combined, and a three-dimensional image may be generated based on the combined two-dimensional image. In the combination of three-dimensional images, a three-dimensional Fourier transform is performed in the overlapping region, while in the combination of two-dimensional images, a two-dimensional Fourier transform is performed in the overlapping region. In addition, in the combination of two-dimensional images, processing similar to that for three-dimensional images, such as boundary smoothing, may be performed.

[0030] The 3D data output process is the process of outputting the generated 3D data of the abutment tooth and gingival margin. The generated 3D data of the abutment tooth and gingival margin is output to an external display device and the 3D data is displayed. Multiple formats of 3D data of the abutment tooth and gingival margin may be superimposed and displayed. For example, STL data and CAD data of the abutment tooth and gingival margin may be superimposed and displayed. Also, for example, the generated 3D data of the abutment tooth and gingival margin may be superimposed and displayed with 3D data generated based on images acquired by a method other than OCT. Images acquired by a method other than OCT are, for example, images generated by scanning the abutment tooth and gingival margin with a conventional intraoral scanner.

[0031] Figure 5 shows the operation of the control unit 14 according to this embodiment. The control unit 14 acquires tomographic images of the abutment tooth and gingival margin captured by optical coherence tomography through tomographic image acquisition processing (step S11). The control unit 14 generates three-dimensional data of the abutment tooth and gingival margin based on the generated tomographic images of the abutment tooth and gingival margin through three-dimensional data generation processing (step S12). Here, if the abutment tooth and gingival margin are imaged in divided ranges, a three-dimensional image of the abutment tooth and gingival margin is generated by overlapping and compositing the boundaries of the images for each divided range, and three-dimensional data of the abutment tooth and gingival margin is generated based on the generated three-dimensional image. The control unit 14 outputs the generated three-dimensional data of the abutment tooth and gingival margin through three-dimensional data output processing (step S13).

[0032] The following describes the comparison results between the three-dimensional data generated in this embodiment and conventionally generated three-dimensional data. Figure 6 shows the abutment tooth and gingival margin that are the target of measurement. Figure 6(a) shows the abutment tooth. Figure 6(b) shows the subgingival margin line (below the gum) of the abutment tooth.

[0033] Figure 7 shows the results of STL data generated in this embodiment and conventionally generated STL data. Figure 7(a) is the STL data generated in this embodiment, which is three-dimensional data generated based on tomographic images obtained by optical coherence tomography of the abutment tooth shown in Figure 6(a) as described above. Figure 7(b) is the conventionally generated STL data, which is three-dimensional data generated based on images obtained by scanning the abutment tooth shown in Figure 6(a) with a conventional oral scanner (IOS).

[0034] Conventional STL data generates information about the visible portion of the abutment tooth, but does not include information about the subgingival portion, which is not visible. The STL data generated in this embodiment can include information about the subgingival portion. Therefore, the dimensional accuracy of prosthetic devices and the like obtained by processing based on the STL data generated in this embodiment can be improved.

[0035] According to the present invention as disclosed herein, it is possible to provide a three-dimensional data generation device and a three-dimensional data generation method that can improve the dimensional accuracy of the three-dimensional information of abutment teeth using optical coherence tomography.

[0036] 11 Probe, 101 Single-mode optical fiber, 102 Achromatic lens, 103 Fixed mirror, 104 Plano-convex lens, 105 MEMS mirror, 106 Glass window, 107 Nozzle, 108 In-nozzle mirror, 12 Three-dimensional data generation device, 13 OCT device, 131 Light source, 132 Beam splitter, 133 Reference mirror, 134 Detection unit, 14 Control unit

Claims

1. A three-dimensional data generation device that captures images of an abutment tooth and its gingival margin using optical coherence tomography, and generates three-dimensional data of the abutment tooth and its gingival margin based on the images of the abutment tooth and its gingival margin.

2. A three-dimensional data generation device according to claim 1, comprising: imaging the abutment tooth and the gingival margin in divided ranges; generating a three-dimensional image of the abutment tooth and the gingival margin by overlapping and compositing the boundaries of the images for each divided range; and generating three-dimensional data of the abutment tooth and the gingival margin based on the three-dimensional image of the abutment tooth and the gingival margin.

3. The three-dimensional data generation apparatus according to claim 2, comprising: imaging the abutment tooth and the gingival margin in sections divided with respect to the occlusal surface of the abutment tooth; performing a three-dimensional Fourier transform in the overlapping region of the images for each section; and generating a three-dimensional image of the abutment tooth and the gingival margin.

4. A three-dimensional data generation device according to any one of claims 1 to 3, wherein three-dimensional images of the abutment tooth and the gingival margin are captured.

5. A three-dimensional data generation device according to any one of claims 1 to 3, wherein a two-dimensional image of the abutment tooth and the gingival margin is captured, and a three-dimensional image of the abutment tooth and the gingival margin is generated based on the two-dimensional image.

6. The three-dimensional data generation apparatus according to any one of claims 1 to 3, wherein the probe that irradiates the abutment tooth and the gingival margin with light by optical coherence tomography is equipped with a MEMS mirror.

7. A method for generating three-dimensional data, comprising: capturing images of an abutment tooth and its gingival margin using optical coherence tomography; and generating three-dimensional data of the abutment tooth and its gingival margin based on the images of the abutment tooth and its gingival margin.

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