JP2011098047A - Inspection method of periodontal disease - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection method capable of simply and highly accurately acquiring an index for objectively indicating the state of periodontal disease without inflicting pain on a patient. <P>SOLUTION: This inspection method of periodontal disease comprises: acquiring a plurality of dental X-ray CT images by capturing human or animal teeth by dental X-rays; acquiring a three-dimensional image by volume rendering of the plurality of acquired dental X-ray CT images; displaying the acquired three-dimensional image; detecting data of the cervical area, root apex and alveolar bone top on the displayed two-dimensional image; calculating at least one index out of a tooth root volume index, a tooth root surface area index, and an index of center-of-gravity of the tooth root based on the detected data of the cervical area, root apex and alveolar bone top; and inspecting the progress state of the periodontal disease based on at least the one calculated index. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for examining periodontal disease. More specifically, the present invention relates to a method for volume-rendering a dental X-ray CT image and inspecting the progress of periodontal disease based on the obtained three-dimensional image.

  Periodontal disease refers to a disease that occurs around the teeth, that is, in the cementum part under the gums (gingiva), alveolar bone, periodontal ligament, and gums. However, it generally refers to an inflammatory disease that occurs around the teeth, which accounts for more than 90% of patients. Therefore, common periodontal disease is caused by bacteria such as Profilomonas gingivalis. The present invention is also mainly intended for general periodontal diseases. Hereinafter, a general periodontal disease is referred to as “periodontal disease”, and other periodontal diseases are referred to as “special periodontal disease”.

  In the following, regarding the progress of periodontal disease, the case of the lower jaw with the root apex will be described, but the same applies to the upper jaw. FIG. 3 is a cross-sectional view schematically showing healthy teeth, and FIG. 4 is a cross-sectional view schematically showing teeth with periodontal disease. As shown in FIG. 3, the healthy tooth 30 has a root 31 supported by a periodontal membrane 32 a, an alveolar bone 35, and a gum (gingiva) 32, and a periodontal pocket (or a gap between the root 31 and the gum 32). It is simply called a pocket (gingival crevice) 45. When suffering from periodontal disease, the gums (gingiva) 32 swells red, the periodontal ligament 32a is torn, and blood and pus 48 appear from the periodontal pocket 45 and the alveolar bone 35 begins to melt as shown in FIG. Become. The depth of the pocket 45 from the gum top 46 to the pocket lower end 47 is about 0 to 1 mm in a healthy tooth, but in the case of a tooth 30 affected by periodontal disease, the depth depends on the progression of periodontal disease. It gets deeper.

  In order to start treatment for periodontal disease, it is necessary to first check how much the current symptoms are progressing and then diagnose what kind of symptoms are caused. Various methods have been developed so far. Current main inspection methods include a probing method, an inspection method using dental X-rays, an inspection method using bacterial inspection, and the like. Furthermore, in the examination, it is necessary to consider personal differences in the forms of the root and alveolar bone, personal differences in tooth occlusion, and the like.

  The probing inspection method is the simplest method in which a probe (inspection needle) is inserted into the above-described pocket 45, and the condition of the symptom is searched while measuring the depth of the pocket 45. It is excellent in that it can be applied. However, the test results differ depending on the skill level of the operator, and particularly in severe cases, there is a problem that the probe stimulates the nerve and causes pain to the patient. That is, the depth of the pocket 45 is measured by inserting a probe (inspection needle, specifically, a needle with a scale called a pocket probe) until it reaches the lower end of the pocket. It is measured and may be accompanied by bleeding, causing pain to the patient and labor. Further, as will be described later, there is a problem that it cannot be said to be sufficient as an objective index of periodontal disease. That is, even if the depth of the pocket 45 is the same, the volume of the tooth 30 below the pocket 45 varies depending on the tooth 30 and the person, so that the force that supports the tooth 30 is determined only by the depth of the pocket 45. It is not possible.

  The inspection method using dental X-rays is a method of inspecting and inspecting the bone level and the external shape of the alveolar bone 35 from X-ray photographs of the teeth 30 and periodontal tissue (three-dimensional). From the bone level and the outer shape of the alveolar bone 35, the resistance to shaking is excellent in that it can be read more accurately than the probing method. However, it cannot be used at the initial stage where the pocket 45 is formed, cannot be used frequently, and there is a problem that accuracy may be lowered when the dental X-ray image is unclear.

  Moreover, the test | inspection method using a microbe test | inspection is the method of test | inspecting the causative microbe of periodontitis, and test | inspecting the activity and progress of a periodontal disease. That is, it is thought that the strength of pathogenicity varies depending on the bacterial species, and the activity is determined by identifying the bacterial species, but it takes time and money to identify the bacterial species, and it is not so easy There's a problem.

  In order to cope with such a problem, a residual tooth prediction system has been proposed in which the degree of decrease in the total effective root surface area is obtained from the current total effective root surface area, and the reduction in the number of remaining teeth is predicted based on the result (Patent Document 1). ). This technology can predict the number of remaining teeth easily by outputting a decrease curve or a decrease line of the total effective root surface area, and is a document for long-term tooth prevention, treatment and guidance. Although it has the advantage that it can be used as the root surface area, the surface area of the root is calculated from the attachment level (proportion of the part where the gingiva adheres to the teeth) by probing, it is difficult to obtain high accuracy, and the alveolar bone Absorption was not always fully satisfactory in that it was not considered.

  In addition, the plaque score, periodontal pocket depth and tooth mobility are compared with past data to calculate the degree of progression of periodontal disease. An electronic medical auxiliary device that displays information has been proposed (Patent Document 2). Although this technique has the advantage that the patient can be motivated to make the patient aware of the importance of periodontal disease treatment, it can always be fully satisfied in that alveolar bone resorption is not considered It wasn't.

JP 2001-061873 A JP 11-047095 A

  The present invention has been made in view of the above-described problems, and provides an inspection method that can easily and accurately obtain an index that objectively indicates a periodontal disease state without causing pain to a patient. The purpose is to do. More specifically, the index indicating the progress of the periodontal disease of the patient is collected without causing pain and trouble to the patient, and the root volume calculation method for obtaining the objective index is actually operated. It is an object of the present invention to provide an inspection method capable of realizing a simple and highly accurate instruction and improving the accuracy of automatic detection measurement.

  In order to achieve the above object, according to the present invention, the following method for examining periodontal disease is provided.

[1] Obtaining a plurality of dental X-ray CT images by imaging a human or animal tooth with dental X-rays;
Volume rendering of the obtained plurality of dental X-ray CT images to obtain a three-dimensional image,
Display the obtained 3D image, detect the data of the tooth neck, apex and alveolar crest on the displayed 3D image, and based on the detected data of the neck, apex and alveolar crest Calculating at least one of a root volume index, a root surface area index, and a root centroid index, and examining the progress of periodontal disease based on the calculated at least one index Inspection method.

[2] The root volume index is calculated based on the data of the cervical part, root apex, and alveolar crest, and the root volume (V ₀ ) supporting healthy teeth and the root volume (V _C ) supporting current teeth. Is calculated as a ratio (V _C / V ₀ ) of the root volume (V _C ) supporting the current tooth to the calculated root volume (V ₀ ) supporting the healthy tooth The method for examining periodontal disease according to [1] above.

[3] The root surface area index is based on the data of the cervical part, root apex, and alveolar crest, and the root surface area (S ₀ ) supporting healthy teeth and the root surface area (S _C ) supporting current teeth. Is calculated as a ratio (S _C / S ₀ ) of the root surface area (S _C ) supporting the current tooth to the calculated root surface area (S ₀ ) supporting the healthy tooth The method for examining periodontal disease according to [1] or [2].

[4] The root-center-of-gravity index is based on the data of the cervical part, root apex, and alveolar crest, and the root-center of gravity (M ₀ ) supporting healthy teeth and the center of root of roots (M _C ) supporting current teeth. Is calculated as a ratio (M _C / M ₀ ) of the root centroid (M _C ) supporting the current tooth to the calculated root centroid (M ₀ ) supporting the healthy tooth. The method for examining periodontal disease according to any one of [1] to [3].

  ADVANTAGE OF THE INVENTION According to this invention, the test | inspection method which can obtain the parameter | index which objectively shows the state of periodontal disease objectively with high precision, without giving a patient pain can be provided. In addition, the index indicating the progress of the patient's periodontal disease should be collected without causing pain to the patient and without trouble, and when actually operating the root volume calculation method to obtain an objective index. It is possible to provide an inspection method capable of realizing a simple and highly accurate instruction and improving the accuracy of automatic detection measurement.

It is a flowchart which shows the test | inspection method of the periodontal disease which concerns on embodiment of this invention. It is explanatory drawing which shows typically the system used for the test | inspection method of the periodontal disease which concerns on embodiment of this invention to which the X-ray imaging apparatus, the computer, and the image display apparatus (monitor) were connected. It is sectional drawing which shows a healthy tooth typically. It is sectional drawing which shows the tooth | gear of periodontal disease typically. It is explanatory drawing which shows an alveolar bone typically. It is an X-ray CT image which shows an alveolar bone typically. a to h are a plurality of X-ray CT images of the patient's teeth, indicating that the images are on the upper side from the a to the h side. FIG. 6 is an image obtained by volume rendering the plurality of X-ray CT images shown in FIGS. It is a part of volume rendering image which instruct | indicates an alveolar bone crest. It is an X-ray CT image of the number of the X-ray CT image corresponding to the location indicated in FIG. 8A, and the location corresponding to the alveolar bone crest is indicated by the intersection of crosshairs. It is a part of volume rendering image which instruct | indicates a tooth neck part. It is an X-ray CT image of the number of the X-ray CT image corresponding to the location indicated in FIG. 9A, and the location corresponding to the tooth neck is indicated by the intersection of the crosshairs. It is a part of a volume rendering image that indicates the apex. FIG. 10A is an X-ray CT image having the number of the X-ray CT image corresponding to the location indicated in FIG. 10A, and the location corresponding to the apex is indicated by the intersection of crosshairs. It is a figure which shows the outline in the X-ray CT image of a predetermined number. It is a figure which shows the outline in the X-ray CT image of a predetermined number. It is a figure which shows the outline in the X-ray CT image of a predetermined number. It is a figure which shows the outline in the X-ray CT image of a predetermined number. It is a figure which shows the outline in the X-ray CT image of a predetermined number.

[Method for testing periodontal disease according to embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Here, FIG. 1 is a flowchart showing a method for examining periodontal disease according to an embodiment of the present invention. FIG. 2 is an explanatory view schematically showing a system to which an X-ray imaging apparatus, a computer, and an image display apparatus (monitor) are used, which is used in the periodontal disease inspection method according to the embodiment of the present invention.

  As shown in FIG. 1, the periodontal disease inspection method of the present invention obtains a plurality of dental X-ray CT images by imaging human or animal teeth with dental X-rays, and obtains a plurality of dental images obtained. Volume rendering the X-ray CT image to obtain a three-dimensional image, and display the obtained three-dimensional image (step S-1). Data on the neck, root apex, and alveolar crest on the displayed three-dimensional image (S-2 step, S-3 step, S-4 step), based on the data of the detected tooth neck, root apex and alveolar bone crest, the root volume index, root surface area index and root centroid index Calculating at least one of the indicators (step S-5, step S-6, step S-7) and examining the progress of periodontal disease based on the calculated at least one indicator. . As shown in FIG. 2, in the periodontal disease inspection method of the present invention, for example, there is a system in which an X-ray imaging apparatus 20, a computer (PC) 21, and image display apparatuses (monitors) 22, 23 are connected. Used. The X-ray imaging apparatus 20 images an affected area of a periodontal disease patient. A computer (PC) 21 displays a three-dimensional image obtained by taking a captured X-ray CT image and performing volume rendering on image display devices (monitors) 22 and 23. The tooth neck, root apex, and alveolar crest are determined on the three-dimensional images displayed on the image display devices (monitors) 22 and 23, and are indicated on the three-dimensional image with the light pen 24, for example. You may instruct | indicate with a cursor instead of the light pen 24. FIG.

(CT image volume rendering display process: S-1 process)
In the method for examining periodontal disease of the present invention, first, a dental X-ray CT image is obtained by imaging a human or animal tooth with dental X-rays, and the obtained dental X-ray CT image is volume-rendered. A three-dimensional image is obtained and the obtained three-dimensional image is displayed.

  In order to obtain a plurality of dental X-ray CT images by imaging human or animal teeth with dental X-rays, the above-described system is used. In the X-ray CT images, as shown in FIGS. The alveolar bone 35 is photographed, but the gum 32 is hardly photographed. The tooth 30 is supported by an alveolar bone 35 and a gum (gingiva) 32, and in a healthy tooth 30, the cervical portion 33 and the gingival crest portion 46 coincide with each other, and the gum 32 closely contacts the cervical portion 33 to support the tooth 30. is doing. In the periodontal diseased tooth 30, the gum is peeled off from the tooth, and a pocket 45 is formed. In severe cases, blood and urine 48 are exuded, and the tooth 30 is supported from the gum top 46 to the bottom of the pocket 45. I can't. At the same time, the gingival crest 46 is lower than the cervical tooth 33, and as the periodontal disease progresses, the alveolar bone 35 also melts, and the supporting force of the teeth 30 for both the alveolar bone 35 and the gum 32 decreases.

  Next, the obtained plurality of dental X-ray CT images are volume-rendered to obtain a three-dimensional image. FIGS. 6a to 6h show the obtained plurality of X-ray CT images of the patient's teeth, from a to It shows that it is an upper side image, so that it goes to the h side. FIG. 7 shows an image obtained by volume rendering the plurality of X-ray CT images shown in FIGS. As shown in FIGS. 6a to h and FIG. 7, in the case of step S-1, for example, a three-dimensional image 71 volume-rendered from a plurality of X-ray CT images 61 of the patient's teeth is displayed on the image display device 22. In this case, the X-ray CT image 61 that is the basis of the image 71 is also displayed on the image display device 23. Both images may be displayed simultaneously or switched on one image display device 22. FIGS. 6a to 6h show examples of 50 images from the 100th image to the 450th image among approximately 500 X-ray CT images taken at intervals of 0.5 mm. A three-dimensional image 71 is obtained by volume rendering from all X-ray CT images 61.

  Here, the X-ray CT image will be described. An X-ray CT image refers to a tomographic image obtained by data reconstruction using a computer and reconstruction of the image. In particular, in the case of dental X-ray CT, distortion caused by short-time X-ray irradiation. It is possible to observe a delicate image with little cross section. Precise diagnosis and inspection of 3D images of the hard tissue of the head and neck, such as the jaw, teeth, and oral region, and the surrounding tissues, has been made possible. For diagnosis, inspection, and treatment of implants, temporomandibular joints, apical lesions, etc. Since it is effective, and it is X-ray irradiation for a short time, the amount of exposure is smaller than that of conventional CT, and safer and more reliable treatment can be performed. The resolution of the device is approximately 0.1 mm to 0.5 mm.

  Next, volume rendering will be described. Normally, when displaying a three-dimensional image, a polygon is used as a base, texture is pasted on the surface, and the state of the object surface is drawn. Unlike this method, volume rendering expresses density data (volume data) of a three-dimensional lattice (voxel) in space by color, density, etc., and expresses it directly as three-dimensional graphics. The density is expressed by color, density, etc. without creating a three-dimensional model. By performing volume rendering with the viewpoint changed in this way, it is possible to display an image with the viewpoint turned sideways, diagonally upward, downward, or the like. That is, an image viewed from the side or viewed from an oblique direction can be seen. Compared to instructing on the two-dimensional X-ray image 52 shown in FIG. 5B, there is an advantage that a desired place can be accurately detected and instructed by changing and confirming the viewpoint. However, it is necessary to perform rendering calculation every time the viewpoint is changed, and there is a problem that the processing load becomes heavy. Therefore, it can be said that volume rendering is a method that has become widespread due to the fact that the viewpoint can be changed in real time due to the advancement of hardware.

(Dental neck, apex and alveolar crest detection (instruction) step: (steps S-2, S-3, S-4)
Next, on the two-dimensional screen displayed on the image display devices 22 and 23, the data of the tooth neck, the apex and the alveolar crest are detected (instructed). In this case, detection is performed semi-automatically. That is, when the operator gives an instruction with a cursor, the software on the computer 21 automatically detects data on the tooth neck, apex and alveolar crest, and the operator approves and corrects the detection result. More specific description will be given below.

  First, the location to be instructed will be described. As shown in FIG. 3, the tooth neck 33 indicates the curvature change point of the curve on the side surface of the tooth (in the case of step S-2). For healthy teeth, the vicinity of the top 35a of the alveolar bone is the cervical part 33. If periodontal disease has progressed and the gums have fallen, look for the curvature change point by looking at the curve on the side of the tooth and use it as the tooth. The neck 33 is used. The apex 34 indicates the lowest point of the tooth root 31 (in the case of step S-3). In addition, as shown in FIG. 5A, the alveolar crest 51 indicates the crest of the white portion between the teeth (in the case of step S-4). In FIG. 3, the alveolar bone crest is shown as an alveolar crest 35a.

  Next, an actual instruction method using a volume rendering image of an X-ray CT image will be described with reference to FIGS. 7, 8A, 8B, 9A, and 9B. FIG. 7 is a three-dimensional image obtained by volume rendering the plurality of X-ray CT images shown in FIGS. FIG. 8A is a part of a volume rendering image indicating the alveolar crest. FIG. 8B is an X-ray CT image of the number of the X-ray CT image corresponding to the location indicated in FIG. 8A, and the location corresponding to the alveolar bone crest is indicated by the intersection of the crosshairs. FIG. 9A is a part of a volume rendering image indicating the tooth neck. FIG. 9B is an X-ray CT image having the number of the X-ray CT image corresponding to the location indicated in FIG. 9A, and the location corresponding to the tooth neck is indicated by the intersection of the cross lines.

  As described above, one image display device 22 can display both the volume-rendered three-dimensional image 71 and the original X-ray CT image 61 simultaneously or by switching. In addition, the volume-rendered three-dimensional image 71 is composed of a plurality of X-ray CT images, and can be displayed with different viewpoints. A place that is difficult to see from a certain direction can be easily seen by changing the viewpoint. it can.

  Hereinafter, the case where the alveolar bone crests 35a and 51 are indicated on the image 71 will be described as an example. FIG. 8A shows a part of the image 71 and indicates the alveolar crest 81. The X-ray CT image corresponding to the designated location was No. 220. FIG. 8B, which is the 220th X-ray CT image, is displayed, and the location corresponding to the alveolar bone crest 81 is displayed at the intersection of the cross lines 91. Similarly, when the tooth neck 82 is indicated in FIG. 9A, the corresponding X-ray CT image number 239 is displayed (FIG. 9B), and when the apex 83 is indicated in FIG. 10A, the corresponding X-ray CT image 155 is displayed. The number is displayed (FIG. 10B).

(Root volume, root surface area, root primary moment index calculation step: (steps S-5, S-6, S-7)
Next, based on the detected (instructed) tooth neck, apex, alveolar crest, and if necessary, data on the lower end of the periodontal pocket, the root volume index, root surface area index, root primary moment index, etc. At least one index is calculated. That is, using the detected (instructed) tooth neck, root apex, gum tip, and if necessary, the lower part of the periodontal pocket, etc., using the X-ray CT image, the root volume, root surface area and root primary At least one of the moments is calculated and a corresponding index is calculated. Hereinafter, each index calculation process will be described in order.

(Calculation process of root volume index: (S-5 process)
First, the root volume (V ₀ ) in a healthy state is calculated as follows. That is, it is considered that the teeth are supported by the alveolar bone 35, and the root volume of the healthy portion 36 from the alveolar crest 35a to the apex 34 when the tooth is in a healthy state is the root volume of the healthy state ( V ₀ ) and calculate this. For example, the contour is automatically detected from the X-ray CT image # 239 to the CT image 155, and the area is calculated. This is continued to the apex, and the sum of all is converted into a real unit to be a volume (V ₀ ). The area is the number of pixels surrounded by the contour. 11A to 11E show the respective contours 111 of the X-ray CT images 239, 227, 220, 190, and 157. FIG. 11E shows the maximum of the three contours in FIG. 11D. Since the position of the contour (root) generally moves obliquely as the X-ray CT scan position moves, it differs from the initial position. The number of internal pixels surrounded by the contour is integrated. As shown in FIG. 11A, the coordinate axis is the xy axis, and the z axis is perpendicular to the plane of the paper and away from it. In this case, the root volume (V ₀ ) can be calculated by the following formula 1. The contour can be automatically detected by contour tracking processing or the like.

Next, the current root volume (V _C ) is calculated as follows. That is, the root volume of the healthy portion 36 from the alveolar crest 35a to the apex 34 is calculated as the current root volume (V _C ). Each contour from the X-ray CT image 220 to the CT image 155 is automatically detected and the area is calculated. In this case, the current root volume (V _C ) can be calculated by the following equation 2.

Data obtained from the above, healthy tooth root volume (V ₀ ) _, current tooth root volume (V _C ) to tooth condition index (root volume index) (K _v ), ie, supporting healthy teeth can be calculated percentage of the root volume to support the current tooth for tooth root volume _{(V 0) (V C)} (V C / V 0), with the following equation 3.

The value of the root volume index is a value from 0 to 1, and is close to 1 in a healthy state. Even in a healthy tooth, the height of the cervical portion and the alveolar crest do not coincide with each other. Thus, for example, _{K V} is up to about 0.8 and health. This value of 0.8 is a provisional value, and will be verified and determined by many examples in the future. The progress of periodontal disease can be examined based on the index calculated in this way.

(Calculation process of tooth root surface area index: (S-6 process)
The root surface area can be substituted by the sum of the contour lengths of the X-ray CT image. Strictly speaking, it is not the length of the contour, but even if it is calculated strictly, it hardly changes, so this can be substituted. The root surface area can be calculated by the following formula 4.

From the root surface area (S ₀ ) of _the healthy state _{, the} current root surface area (S _C ), to the surface area index (K _S ) of the tooth state, ie, the current root surface area (S ₀ ) supporting the healthy tooth The ratio (S _C / S ₀ ) of the root surface area (S _C ) supporting the teeth can be calculated by the following formula 5.

K _S also takes a value of from 0 to about 1.0, is a health closer to 1.0. The progress of periodontal disease can be examined based on the index calculated in this way.

(Calculation step of root primary moment index: (S-7 step)
The first moment can be calculated by multiplying the area of the X-ray CT image by the length from the apex and integrating. That is, it can be calculated by the following formula 6.

From the root primary moment M _{0 in a} healthy state _{and the} current root primary moment M _C to the primary moment index (K _M ) in the tooth state, that is, the current to the center of gravity of the root (M ₀ ) supporting a healthy tooth The ratio (M _C / M ₀ ) of the root centroid (M _C ) that supports the teeth can be calculated by the following equation (7).

K _M also takes a value of from 0 to about 1.0, is a health closer to 1.0. The progress of periodontal disease can be examined based on the index calculated in this way.

  In the present invention, the progress of periodontal disease is examined using at least one of the above-mentioned indices, and the combination thereof can be determined by variously considering the examination time, examination accuracy, and the like. preferable. Further, other indexes such as an index based on the periodontal pocket depth or other methods may be used in combination.

20 X-ray machine 21 Computer (PC)
22 Image display device (monitor)
23 Image display device (monitor)
24 Penlight 30 Teeth 31 Root 32 Gum (Gingiva)
32a Periodontal ligament 33 Tooth neck (curvature change point)
34 root apex 35 alveolar bone 35a alveolar crest 36 healthy part 45 pocket (gingival sulcus)
46 Gingival crest 47 Lower pocket 48 Blood and pus 51 Alveolar bone crest 52 Two-dimensional X-ray image 61 X-ray CT image 71 Volume-rendered three-dimensional image 81 Alveolar crest 82 Dental neck 83 Apex 91 Location corresponding to alveolar crest Crosshair 111 contour

Claims (4)

Imaging a human or animal tooth with dental X-rays to obtain a plurality of dental X-ray CT images;
Volume rendering of the obtained plurality of dental X-ray CT images to obtain a three-dimensional image,
Display the resulting 3D image,
Detect the data of the neck, apex and alveolar crest on the displayed 2D screen,
Based on the data of the detected tooth neck, apex and alveolar crest, calculate at least one of a root volume index, a root surface area index, and a root primary moment index, and the at least one calculated A method for examining periodontal disease, comprising examining the progress of periodontal disease based on an index. The root volume index calculates a root volume (V ₀ ) for supporting healthy teeth and a root volume (V _C ) for supporting current teeth based on data on the neck, apex and alveolar crest. The calculated value is a ratio (V _C / V ₀ ) of the root volume (V _C ) supporting the current tooth to the calculated root volume (V ₀ ) supporting the healthy tooth. The test | inspection method of periodontal disease of description. The root surface area index calculates the root surface area (S ₀ ) supporting healthy teeth and the root surface area (S _C ) supporting current teeth based on the data of the neck, apex and alveolar bone crest, The calculated value as a ratio (S _C / S ₀ ) of the root surface area (S _C ) supporting the current tooth to the calculated root surface area (S ₀ ) supporting the healthy tooth 2. The method for examining periodontal disease according to 2. The root primary moment index is based on data on the tooth neck, apex and alveolar crest, and the root primary moment (M ₀ ) for supporting healthy teeth and the root primary moment (M ₀ ) for supporting current teeth. _C )), and the ratio (M _C / M ₀ ) of the root primary moment (M _C ) supporting the current tooth to the calculated root primary moment (M ₀ ) supporting the healthy tooth The method for examining periodontal disease according to any one of claims 1 to 3, which is a calculated value.