CN115375903A

CN115375903A - Method and system for obtaining reconstruction data for reconstructing teeth

Info

Publication number: CN115375903A
Application number: CN202211321827.3A
Authority: CN
Inventors: 孙东辰; 郝鹏飞; 唐振宇; 王坤
Original assignee: Haikeshong Manufacturing Intelligent Technology Qingdao Co ltd; Tianjin University
Current assignee: Haikeshong Manufacturing Intelligent Technology Qingdao Co ltd; Tianjin University
Priority date: 2022-10-27
Filing date: 2022-10-27
Publication date: 2022-11-22
Anticipated expiration: 2042-10-27
Also published as: CN115375903B

Abstract

The invention relates to the technical field of tooth reconstruction, and particularly discloses a method and a system for acquiring reconstruction data for reconstructing teeth, wherein the method comprises the following steps: acquiring point cloud data of the outline of a certain tooth; selecting one or more points at the position of the central depression of the tooth; for each point, acquiring a plurality of different cross-sectional planes passing through the point and parallel to a longitudinal line between the gingiva and the tooth; respectively fitting the B spline curves to all the point clouds on the cross section plane to form a plurality of B spline curves; acquiring two points with the minimum curvature radius on each B spline curve to form a plurality of points; and intercepting the point cloud data by using a curved surface formed by a plurality of points to obtain reconstructed data. The invention can automatically, efficiently and accurately reconstruct the data of the teeth.

Description

Method and system for obtaining reconstruction data for reconstructing teeth

Technical Field

The invention relates to the technical field of tooth reconstruction, in particular to a method and a system for acquiring reconstruction data for reconstructing teeth.

Background

In the tooth restoration technology of modern medicine, the following four steps are roughly needed: the method comprises the steps of tooth data acquisition, tooth three-dimensional reconstruction, prosthesis processing and medical application, wherein the tooth data acquisition is to acquire tooth three-dimensional shape point cloud data through a professional intraoral measuring system or an extraoral scanning impression, the point cloud processing and three-dimensional reconstruction processes are to analyze and extract the point cloud data of the tooth to be repaired and reconstruct the three-dimensional shape of the tooth through a reverse technology, and the prosthesis needs to be precisely processed by professional medical equipment processing equipment according to the output result of the last step and is finally applied to a human body through a medical means.

When the collected tooth three-dimensional point cloud data is processed in the prior art, the tooth three-dimensional point cloud data needs to be segmented, point clouds belonging to teeth are segmented by manual frame selection in the prior art, the boundary area of the teeth and the gum needs to be judged manually and irregular shearing needs to be completed, the process is complicated, certain operation experience is needed, and the tooth reconstruction speed is low and the precision is low.

Disclosure of Invention

In order to solve the above technical problems, the present invention provides a method for acquiring reconstruction data for reconstructing a tooth, which is fast in acquisition speed and high in accuracy.

Therefore, the invention provides the following technical scheme for solving the problems:

the present application relates to a method of obtaining reconstruction data for reconstructing a tooth, comprising:

s1: acquiring point cloud data of the outline of a certain tooth;

s2: selecting one or more points at the position of the central depression of the tooth;

s3: for each point, acquiring a plurality of different cross-sectional planes passing through the point and parallel to a longitudinal line between the gingiva and the tooth;

s4: respectively fitting B spline curves to all the point clouds on the cross-sectional planes to form a plurality of B spline curves corresponding to a plurality of different cross-sectional planes;

s5: acquiring two points with the minimum curvature radius on each B spline curve to form a plurality of points;

s6: and intercepting the point cloud data by using a curved surface formed by the plurality of points to obtain the reconstruction data.

In some embodiments of the present application, an XYZ coordinate system is established when the point cloud data is acquired;

wherein the Z-axis is parallel to the longitudinal line and is directed from the gingiva toward the tooth.

In some embodiments of the present application, the plurality of different cross-sectional planes are planes formed by rotating around the point circle.

In some embodiments of the present application, two points { a, B } on the B-spline curve with the smallest radius of curvature are obtained, specifically:

when the curvature radius of the point on the B spline curve is smaller than a threshold value, the point on the B spline curve is the acquired point { A, B };

wherein the threshold is set based on a point capable of obtaining two minimum curvature radii on the B-spline curve.

In some embodiments of the present application, the threshold is determined by an iterative method, specifically:

s1': setting an initial threshold Th;

s2': calculating the curvature radius of a point on the B spline curve;

and S3': calculating the number of points on the B spline curve with the curvature radius smaller than Th;

and S4': judging whether the number is greater than 2, if so, going to S5', if not, judging whether the number is equal to 2, if so, going to S7', and if not, going to S6';

and S5': reducing the initial threshold, assigning the reduced initial threshold to Th, and returning to S3';

s6': increasing the initial threshold, assigning the increased initial threshold as Th, and returning to S3';

s7': taking Th as the threshold.

The present application also relates to a system for obtaining reconstruction data for reconstructing a tooth, comprising:

the tooth scanning device is used for scanning teeth and acquiring point cloud data of the outline of the teeth;

a data processing center for performing the following operations:

selecting one or more points at the position of the central depression of the tooth;

for each point, acquiring a plurality of different cross-sectional planes passing through the point and parallel to a longitudinal line between the gum and the tooth;

respectively fitting B spline curves to all the point clouds on the cross-sectional planes to form a plurality of B spline curves corresponding to a plurality of different cross-sectional planes;

acquiring two points with the minimum curvature radius on each B spline curve to form a plurality of points;

and intercepting the point cloud data by using a curved surface formed by the plurality of points to obtain the reconstruction data.

In some embodiments of the present application, the system further comprises:

a coordinate establishing unit for establishing an XYZ coordinate system when the point cloud data is acquired;

In some embodiments of the present application, wherein the plurality of different cross-sectional planes are planes formed by rotating around the point circle.

s1': setting an initial threshold Th;

s2': calculating the curvature radius of a point on the B spline curve;

s3': calculating the number of points on the B spline curve with the curvature radius smaller than Th;

and S4': judging whether the number is greater than 2, if so, going to S5', otherwise, judging whether the number is equal to 2, if so, going to S7', and if not, going to S6';

and S5': reducing the initial threshold, assigning the reduced initial threshold as Th, and returning to S3';

s7': taking Th as the threshold.

Compared with the prior art, the method and the system for acquiring the reconstruction data for reconstructing the teeth have the following advantages and beneficial effects:

(1) The traditional manual point cloud segmentation mode is changed, tooth point cloud segmentation is realized through an algorithm, the point cloud acquisition of a single tooth is realized rapidly, the automation degree is high, and the operation process is simple and convenient;

(2) The tooth point cloud data segmentation is high in accuracy and beneficial to accurate tooth reconstruction.

Other features and advantages of the present invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments of the present invention or the prior art will be briefly described below, and it is obvious that the drawings described below are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a flow diagram of a method of obtaining reconstruction data for reconstructing a tooth, according to some embodiments;

FIG. 2 is a point cloud in a cross-sectional plane according to some embodiments;

FIG. 3 is a B-spline curve fitted to the point cloud plot shown in FIG. 2;

FIG. 4 is a schematic diagram of the radius of curvature of the B-spline curve shown in FIG. 3;

FIG. 5 illustrates a gingival-dental interface of a tooth according to some embodiments;

FIG. 6 is a point cloud data of extracted surfaces of a certain tooth according to some embodiments;

FIG. 7 is a three-dimensional reconstructed model of a tooth extracted according to some embodiments.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.

All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. In the description of the present invention, it is to be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, and are merely for convenience of description and simplicity of description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, are not to be construed as limiting the present invention.

In the description of the present invention, it should be noted that the terms "mounted," "connected," and "connected" are to be construed broadly and may include, for example, a fixed connection, a detachable connection, or an integral connection unless otherwise specifically stated or limited. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art. In the foregoing description of embodiments, the particular features, structures, materials, or characteristics may be combined in any suitable manner in any one or more embodiments or examples.

The terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.

If surface reconstruction is performed on a certain tooth, point cloud data of the tooth surface belonging to the tooth needs to be segmented.

The system involved herein is capable of fast, efficient and accurate acquisition of point cloud data of teeth, including primarily a tooth scanning device (not shown) and a data processing center (not shown).

The tooth scanning device is used for scanning teeth and acquiring three-dimensional point cloud data of the outline of the teeth, wherein the three-dimensional point cloud data not only comprises point cloud data of the tooth surface, but also comprises point cloud data of the gum surface.

The tooth scanning device can be a professional oral cavity scanning device or an external inverse model scanning device and the like, and the tooth scanning device is adopted to scan teeth to obtain point cloud data, which is a conventional technical means.

The data processing center is used for acquiring reconstruction data of the tooth surface according to the acquired point cloud data (namely S1 in figure 1) of the tooth outline.

See, below, fig. 1, which shows a process of a data processing center.

S2: one or more points are selected at the location of the concavity of the middle of the tooth.

The foveal position may refer to the position of the center point of the tooth, or the position of a point near the center point position.

One or more points at the depressed position in the middle of the tooth can be manually selected, the more the number is selected, the more the operation process is complicated, correspondingly, the higher the segmentation precision is, and the higher the accuracy of the acquired reconstruction data is.

In the previous scanning, an XYZ coordinate system for scanning the tooth is first established by the coordinate establishing unit.

The XYZ coordinate system can be established according to requirements, the plane of the cross section of the tooth can be taken as an XY plane, and the axis parallel to the longitudinal connecting line between the gum and the tooth is taken as a Z axis.

For convenience of calculation, in the embodiment of the present application, the XYZ coordinate system takes the plane of the cross section of the tooth as the XY plane, and the direction from the tooth to the gum as the positive Z-axis direction.

Thus, the selected point cloud can be denoted as a set P, including P1 (x, y, z) through Pn (x, y, z).

S3: a plurality of different cross-sectional planes passing through each Pi and parallel to the Z-axis are taken.

For each point Pi, a plurality of different cross-sectional planes (denoted as m planes, L1 to Lm) passing through the point Pi and parallel to the Z axis are acquired, the cross-sectional plane equation being AX + BY + CZ + D =0.

Since the cross-sectional plane is parallel to the Z-axis, the direction vector of the cross-sectional plane is (0, 1), plus the passing point Pi, one of the cross-sectional plane equations can be determined.

Using the determined plane equations, m planes can be obtained by rotation in a circular rotation around the point Pi.

For the convenience of calculation, the angle of each rotation may be set to acquire a rotated cross-sectional plane by a rotation matrix.

In this way, a plurality of cross-sectional planes L1 to Lm passing through the point Pi and parallel to the Z axis can be acquired.

Similarly, a plurality of cross-sectional planes, that is, n × m cross-sectional planes, of each remaining point cloud in the set P may be obtained and denoted as Lij, where i is 1 to n, and j is 1 to m.

S4: and acquiring point clouds on all cross-sectional planes.

As described above, the plane equation of the cross-sectional plane of each point in the set P can be obtained, and therefore, the point clouds located on each cross-sectional plane are determined by screening all the point clouds.

The description will be given by taking the example of obtaining a point cloud on one of the cross-sectional planes.

For example, one of the cross-sectional planes of points Pi is Li: a 'X + B' Y + C 'Z + D' =0.

A distance threshold d is set.

And screening all point clouds belonging to the teeth, calculating the distance D between the point and the cross-sectional plane Li, judging the relation between the distance D and the distance threshold value D, and if the distance D is smaller than the distance threshold value D, determining that the point is positioned on the cross-sectional plane Li.

Thus, a series of point clouds on the cross-sectional plane Li are obtained and recorded as a point cloud group Si.

Similarly, for the remaining m-1 cross-sectional planes of the point Pi, m-1 point cloud sets corresponding to each cross-sectional plane are also acquired.

For each of the (n-1) xm cross-sectional planes corresponding to the remaining n-1 points in the set P, m point cloud sets are also acquired.

Referring to fig. 2, point cloud data on one cross-sectional plane is acquired.

S5: and respectively fitting the B-spline curves to all the point clouds on the cross-sectional planes to form a plurality of B-spline curves corresponding to a plurality of different cross-sectional planes.

All point clouds on the cross-sectional plane are the point cloud group as found in S4.

For each group of point clouds, a B-spline curve is fitted.

In the present application, a third-order B-spline curve may be fitted, and of course, other B-spline curves may be used for fitting.

In this way, for the n × m point cloud groups, n × m B spline curves are obtained.

Referring to FIG. 3, which shows a third order B-spline curve fitted to the point cloud data on the cross-sectional plane of FIG. 2, the X-axis represents the abscissa and the Y-axis represents the ordinate.

S6: two points with the smallest curvature radius on each B-spline curve are obtained to form a plurality of points.

For each B-spline curve, two points are obtained at which the radius of curvature is smallest.

In this way, 2 × n × m points can be acquired for n × m B-spline curves.

The smaller the curvature radius of a point, the sharper the curve is at the point; generally, the side surfaces of human teeth are relatively flat (the curvature radius of the corresponding point is also relatively large), and if the point is located at the junction of the tooth and the gum, the turning is relatively sharp, and therefore, the corresponding curvature radius is also low.

The judgment of the curvature radius may adopt a threshold definition judgment.

The threshold value may be set through an empirical value or an iterative method, so as to obtain two points with the minimum curvature radius on the B-spline curve.

As follows, setting the threshold value in an iterative manner will be described.

(a) An initial threshold Th is set.

(b) And calculating the curvature radius of each point on the B spline curve.

(c) And calculating the number of the curvature radiuses smaller than the initial threshold Th.

(d) And (e) judging whether the number is larger than 2, if so, proceeding to (e), and if not, proceeding to (f).

(e) The initial threshold is decreased and the decreased value is assigned to Th and returned to (c).

A step down can be set, one step down each time the initial threshold is decreased.

(f) And (e) judging whether the number is equal to 2, if so, going to (g), and if not, going to (h).

(g) Th is taken as a threshold.

(h) The initial threshold is increased and the increased value is assigned to Th, and returns to (c).

An increase step size may be set, one step size being added each time the initial threshold is increased.

Referring to fig. 4, which shows the radius of curvature of 180 points on a cross-sectional plane, the abscissa in fig. 4 represents the number of points and the ordinate represents the radius of curvature of the points.

As can be seen from fig. 4, the two points with the smallest radius of curvature are points a and B, i.e. corresponding to the two corners shown in fig. 3: one (-46.6521, -103.655) and one (-34.9418, -104.582).

Note that the viewing angles in fig. 3 and 4 are different.

S7: and intercepting the point cloud data by utilizing a curved surface formed by a plurality of points to obtain reconstructed data.

The 2 × n × m points obtained in S6 are the boundary points between the gum and the teeth.

In order to improve the accuracy of tooth reconstruction, the intersection points are filtered, and outliers are removed.

Referring to fig. 5, the intersection points obtained from the scanned point cloud data of a certain tooth are shown, wherein the black points of the larger squares are the intersection points.

Several junctures around the junctures can be used to fit the facet, and if a point is located on one side of the tooth of the facet, the point is considered to belong to a point cloud on the tooth surface.

As such, fitting multiple facets may be employed to obtain a point cloud on the tooth surface.

All the acquired point clouds on the tooth surface are then reconstructed data, see fig. 6, which shows the reconstructed data on the tooth surface.

That is, point cloud segmentation between teeth and gums is achieved.

From the acquired reconstruction data, a three-dimensional model of the tooth can be reconstructed, see fig. 7.

The method for acquiring the reconstructed data changes the traditional manual point cloud segmentation mode, is high in automation degree and high in segmentation speed, is verified through actual operation, is good in segmentation effect, and ensures the accuracy of acquiring the tooth reconstructed data.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. A method of obtaining reconstruction data for reconstructing a tooth, comprising:

s1: acquiring point cloud data of the outline of a certain tooth;

s3: for each point, acquiring a plurality of different cross-sectional planes passing through the point and parallel to a longitudinal line between the gum and the tooth;

2. The method of claim 1, wherein an XYZ coordinate system is established when acquiring the point cloud data;

3. The method of claim 1, wherein the plurality of different cross-sectional planes are a plurality of planes formed by rotation around the point circumference.

4. The method according to claim 1, wherein two points { a, B } on the B-spline curve with the smallest radius of curvature are obtained, specifically:

5. The method according to claim 4, wherein the threshold is determined using an iterative method, in particular:

s1': setting an initial threshold Th;

and S2': calculating the curvature radius of a point on the B spline curve;

s6': increasing the initial threshold, assigning the increased initial threshold to Th, and returning to S3';

s7': th is taken as the threshold.

6. A system for obtaining reconstruction data for reconstructing a tooth, comprising:

a data processing center for performing the following operations:

for each point, acquiring a plurality of different cross-sectional planes passing through the point and parallel to a longitudinal line between the gingiva and the tooth;

and intercepting the point cloud data by utilizing a curved surface formed by the plurality of points to acquire the reconstruction data.

7. The system of claim 6, further comprising:

8. The system of claim 6, wherein the plurality of different cross-sectional planes are a plurality of planes formed by rotation around the point circle.

9. The system according to claim 6, wherein the two points { A, B } on the B-spline curve with the smallest radius of curvature are obtained by:

when the curvature radius of the point on the B-spline curve is smaller than a threshold value, the point on the B-spline curve is the acquired point { A, B };

10. The system according to claim 9, wherein the threshold is determined using an iterative method, in particular:

s1': setting an initial threshold Th;

s2': calculating the curvature radius of a point on the B spline curve;

s4': judging whether the number is greater than 2, if so, going to S5', otherwise, judging whether the number is equal to 2, if so, going to S7', and if not, going to S6';

s7': taking Th as the threshold.