Construction method and equipment of root canal isthmus 3D printing research model, medium and product

Abstract

The invention discloses a root canal isthmus 3D printing research model construction method and device, a medium and a product, and relates to the technical field of root canal isthmus printing.The method comprises the steps that root canal original data and prepared root canal data are obtained; the root canal original data are screened various typical form data containing root canal isthmus; obtaining expanded main root canal diameter data according to the prepared root canal data, extracting original tooth root three-dimensional surface data according to the root canal original data, and combining the original tooth root three-dimensional surface data with the expanded main root canal diameter data to obtain a root canal isthmus 3D printing research model. The root canal original data screened out in the application contain all possibilities of the root canal isthmus, and compared with a modular stacking mode in the prior art, a mode of carrying out layer-by-layer modeling by utilizing the root canal original data obtained by scanning in the application can more accurately simulate the shape and size of the real root canal isthmus.

Description

Technical Field

[0001] The present application relates to the technical field of root canal isthmus printing, and particularly to a method, device, medium and product for constructing a 3D printing research model of a root canal isthmus. Background Art

[0002] In recent years, many scholars have designed and constructed models of root canal branches or isthmuses and carried out corresponding research.

[0003] "Visualization" is one of the common features of existing research models of root canal branches or isthmuses. Researchers use a finger spreader as the inner core of the main root canal, a thin metal wire or a thin metal strip as the inner core of the lateral root canal or the root canal isthmus, and pour transparent epoxy resin, polydimethylsiloxane or polymethyl methacrylate. After the material is cured, the inner core is withdrawn to form a root canal isthmus and lateral root canal model. The "visualization" research model makes it possible to record instantaneous changes in the experiment and can more intuitively understand the effects of different irrigation methods on the branches and isthmus.

[0004] However, the existing models of branches or isthmuses are all "patterned" models. The main root canal, isthmus or branches are composed of regular morphological combinations, and the isthmus morphology is all "band-shaped". In addition, the "numbers" of existing models are all relatively large. The distance between the two root canals of the isthmus is 3 mm to 5 mm, and the narrowest diameter of the isthmus is 0.15 mm to 0.40 mm, which can allow the tip of a file No. 15 to No. 40 to enter (while it is very difficult for root canal instruments to penetrate into the isthmus clinically). This deviation may make the corresponding research results inapplicable to clinical practice. Summary of the Invention

[0005] The purpose of the present application is to provide a method, device, medium and product for constructing a 3D printing research model of a root canal isthmus, which can accurately simulate the shape and size of a real root canal isthmus.

[0006] To achieve the above object, the present application provides the following solutions:

[0007] In a first aspect, the present application provides a method for constructing a 3D printing research model of a root canal isthmus, including:

[0008] Obtaining original root canal data and post-preparation root canal data; the original root canal data is scan data including various typical morphologies of the root canal isthmus; the post-preparation root canal data is scan data after the root canal is enlarged using dental instruments; data obtained by scanning a tooth using a scanning device;

[0009] Obtaining the diameter data of the enlarged main root canal according to the post-preparation root canal data;

[0010] According to the original root canal data, three-dimensional reconstruction is performed by the threshold segmentation method to obtain the three-dimensional surface data of the original tooth root; the original three-dimensional surface data includes: the three-dimensional surface data of the original tooth root, the root canal, and the isthmus.

[0011] The three-dimensional surface data of the original tooth root is horizontally cut in a direction perpendicular to the long axis of the root canal to obtain two-dimensional layer data.

[0012] On the two-dimensional layer data, the center points of the main root canals are sequentially marked from the root tip to the crown to obtain the data of the main root canal path.

[0013] Taking the data of the main root canal path as the center, the data of the enlarged main root canal diameter is imported to form the main root canal surface data that conforms to the main root canal path.

[0014] The main root canal surface data is subjected to Boolean addition with the original root canal data to obtain a 3D printing research model of the root canal isthmus after the main root canal is enlarged; the 3D printing research model of the root canal isthmus is a digital draft.

[0015] In a second aspect, the present application provides a computer device, including: a memory, a processor, and a computer program stored on the memory and executable on the processor, where the processor executes the computer program to implement the method for constructing the 3D printing research model of the root canal isthmus described in any one of the above.

[0016] In a third aspect, the present application provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, it implements the method for constructing the 3D printing research model of the root canal isthmus described in any one of the above.

[0017] In a fourth aspect, the present application provides a computer program product, including a computer program, and when the computer program is executed by a processor, it implements the method for constructing the 3D printing research model of the root canal isthmus described in any one of the above.

[0018] According to the specific embodiments provided by the present application, the following technical effects are disclosed by the present application:

[0019] The present application provides a method, device, medium and product for constructing a 3D printing research model of a root canal isthmus. The method includes: obtaining original root canal data and post-preparation root canal data; the original root canal data includes various typical morphological data of the root canal isthmus; the post-preparation root canal data is data obtained by scanning a tooth using a scanning device; according to the post-preparation root canal data, obtaining the enlarged main root canal diameter data; according to the original root canal data, performing three-dimensional reconstruction by means of threshold segmentation to obtain the original root three-dimensional surface data; the original three-dimensional surface data includes: original root, root canal and isthmus three-dimensional surface data; horizontally cutting the original root three-dimensional surface data in a direction perpendicular to the long axis of the root canal to obtain two-dimensional layer data; sequentially marking the center points of the main root canal from the root apex to the root crown on the two-dimensional layer data to obtain the main root canal path alignment line data; extracting the original root three-dimensional surface structure data according to the original root three-dimensional surface data and the main root canal path alignment line data; combining the original root three-dimensional surface structure data with the enlarged main root canal diameter data to obtain a 3D printing research model of the root canal isthmus; the 3D printing research model of the root canal isthmus is a digital draft. Four types of root canal isthmuses distinguished by boundary features cover all possibilities of the root canal isthmus, and the method of layer-by-layer modeling using the original root canal data obtained by scanning in the present application can more accurately simulate the shape and size of the real root canal isthmus compared with the modular stacking method in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 Schematic flowchart of a method for constructing a 3D printing research model of a root canal isthmus provided by an embodiment of the present application;

[0022] Figure 2 Schematic diagram of four typical isthmus morphologies characterized by boundaries provided by an embodiment of the present application;

[0023] Figure 3 Schematic diagram of the construction of a 3D printing research model of a root canal isthmus provided by an embodiment of the present application;

[0024] Figure 4 Schematic diagram of the distribution of narrow diameter measurements of the isthmus of each type of digital model provided by an embodiment of the present application;

[0025] Figure 5 Color cloud map of the narrow diameter of each type of isthmus of the digital model provided by an embodiment of the present application;

[0026] Figure 6 Schematic diagram of the deviation between the digital model and the printed model provided by an embodiment of the present application;

[0027] Figure 7 Schematic diagram of the filling effect of hydrogel in various types of isthmus models provided by an embodiment of the present application;

[0028] Figure 8 Schematic diagram of the overall technical route of a method for constructing a 3D printed research model of root canal isthmus provided by another embodiment of the present application;

[0029] Fig. 9 Schematic diagram of the structure of a computer device provided by an embodiment of the present application. Detailed implementation manners

[0030] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0031] Based on the original root canal data obtained by micro-CT scanning, the present application successfully constructs and prints research models of various types of root canal isthmus after digital root canal shaping by applying medical imaging software and three-dimensional reverse engineering software. Through relevant measurements of the digital model and the printed model and 3D deviation analysis of their three-dimensional images, the results show that the Objet30 Pro three-dimensional resin printing system can accurately replicate the root canal and isthmus structures, providing a visual, homogeneous research model that is closer to the real root canal and isthmus system in terms of morphology and measurement values for subsequent research.

[0032] The purpose of the present application is to provide a method, device, medium and product for constructing a 3D printed research model of root canal isthmus, which can accurately simulate the shape and size of the real root canal isthmus. Based on the original root canal data obtained by micro-CT scanning, a 3D printed research model of root canal isthmus after digital root canal preparation and shaping is constructed by applying medical imaging software and three-dimensional reverse engineering software.

[0033] To make the above objects, features and advantages of the present application more obvious and understandable, the present application will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0034] In an exemplary embodiment, as Figure 1 shown, a method for constructing a 3D printed research model of root canal isthmus is provided, including the following steps S1 to S8. Among them:

[0035] S1. Obtain the original root canal data and the root canal data after preparation; the original root canal data is the scanning data including various typical morphologies of the root canal isthmus; the root canal data after preparation is the scanning data after the root canal is enlarged using dental instruments, which is the data obtained by scanning the tooth using a scanning device. Among them, the original root canal data includes the original scanning data of the molar root surface, root canal, and isthmus. Among them, the root canal data after preparation can also be understood as another selected molar sample after root canal preparation (one of the clinical root canal treatment steps), obtaining the main root canal scanning data after root canal preparation through a scanning device, and measuring the main root canal diameter numbers from the apex to the crown through a two-dimensional layer perpendicular to the root canal long axis.

[0036] In this embodiment, the original root canal data selected is micro-CT data. Based on the micro-CT data of the root canals of 187 molars with isthmuses, data with various typical morphologies of the root canal isthmus and each measured value close to its mean or median are selected. Among them, the typical morphology refers to four typical morphologies of the root canal isthmus distinguished by boundary features.

[0037] In this embodiment, through repeated observation and comparison of the isthmus and root canal system in the three-dimensional reconstructed micro-CT images of molars, according to the number and position characteristics of the isthmus boundaries of the root canal, the isthmus is divided into four types. Please refer to Figure 2 , Figure 2 : Type I: Coronal boundary type (with a top); Type II: Radicular boundary type (with a bottom); Type III: Double boundary type (band-shaped); Type IV, no boundary type; the blue arrow points to the isthmus boundary. Specifically as follows:

[0038] Type I, coronal boundary type (with a top): The isthmus between the two root canals has only a single coronal boundary, and the remaining directions are all connected to the main root canal or open at the apical foramen.

[0039] Type II, radicular boundary type (with a bottom): The isthmus between the two root canals has only a single radicular boundary, and the remaining directions are all connected to the main root canal or open into the pulp chamber.

[0040] Type III, double boundary type (band-shaped): The isthmus between the two root canals has boundaries both coronally and radicularly, connecting the two main root canals in a band-like shape.

[0041] Type IV, no boundary type: The two root canals are connected by an isthmus from the root canal orifice to the apical foramen or to the confluence of the two root canals.

[0042] S2. Obtain the main root canal diameter data after enlargement according to the root canal data after preparation.

[0043] Among them, the post-preparation root canal data includes: data obtained by scanning the mandibular first molar after root canal preparation. In this embodiment, first, a cross-sectional view of the root canal of the mandibular first molar after root canal preparation is obtained according to the post-preparation root canal data; then, according to the cross-sectional view of the root canal, starting from the position of the apical foramen to the position of the root canal orifice, the main root canal diameter is measured every 1 mm, and the diameter data of the main root canal related to the root position of the cross-section is obtained, that is, the enlarged main root canal diameter data.

[0044] In this embodiment, when obtaining the post-preparation root canal data, another 3 extracted mandibular first molars with relatively narrow and thin mesial root canals and mild to moderate curvature from the middle to the apical region of the root are selected. The ProTaper Next system is used for root canal preparation, and the final file is F3. The extracted teeth after preparation are scanned with a SkyScan 1172 desktop X-ray microtomography scanner. The scanning conditions are: spatial resolution 12.85 μm, voltage 80 kV, current 100 μA. Pixel 1024×1280, exposure 4840 ms, angular increment 0.34° (rotation step 2), 360° rotational scanning. The NRecon software is used to convert the data to generate a cross-sectional view of the root canal. The CTAn software is used to measure the diameter of the main root canal of the cross-section, with the apical foramen as the 0 mm position point, and measured every 1 mm until the position of the root canal orifice. When the cross-section of the root canal is oval, the shorter diameter value is used.

[0045] S3. According to the original root canal data, three-dimensional reconstruction is performed by the threshold segmentation method to obtain the original three-dimensional surface data of the root. The original three-dimensional surface data includes: the original three-dimensional surface data of the root, root canal, and isthmus.

[0046] First, determine the length data from the crown tip to the anatomic apex in the original root canal data; then determine the length data of the three-dimensional model according to the length data from the crown tip to the anatomic apex; then, according to the length data and the original root canal data, the three-dimensional model of the root canal is reconstructed by the threshold segmentation method to obtain the original three-dimensional surface data of the root.

[0047] S4. Horizontally cut the original three-dimensional surface data of the root perpendicular to the long axis of the root canal to obtain two-dimensional layer data.

[0048] S5. Mark the center points of the main root canal on the two-dimensional layer data in sequence from the apex to the root crown to obtain the data of the walking line of the main root canal pathway.

[0049] S6. Taking the data of the walking line of the main root canal pathway as the center, import the enlarged main root canal diameter data to form the main root canal surface data that fits the walking line of the root canal pathway.

[0050] In this embodiment, the micro-CT data (original root canal data) of the molar teeth screened out is imported into the medical imaging software Mimics, and the three-dimensional model of the root canal is reconstructed by the threshold segmentation method. The CTAn software is used to measure the length from the top of the tooth crown to the anatomical root tip in the micro-CT data, so as to define the size of the three-dimensional reconstruction model in Mimics, and finally the three-dimensional surface data of the original tooth root is generated. After setting an axial direction, the three-dimensional surface data of the original tooth root is horizontally cut to obtain two-dimensional layer data (two-dimensional CT layer), and then the main root canal pathway is marked and drawn on the two-dimensional CT layer in sequence from the root tip area to the root crown part. According to the enlarged main root canal diameter data, the diameter of the main root canal of the printed model is set to complete the digital preparation and shaping of the root canal, and the data of the main root canal pathway trace is generated.

[0051] Then, the three-dimensional surface data of the original tooth root and the data of the main root canal pathway trace are imported into the Geomagic Studio2012 software, the three-dimensional surface structure data of the original tooth root is extracted, the tooth crown, redundant tooth roots and the outer surface data of the tooth root are removed, and only the original root canal structure containing the isthmus is retained.

[0052] S7. Perform a Boolean addition on the main root canal surface data and the original root canal data to obtain a 3D printing research model of the root canal isthmus after the main root canal is enlarged; the 3D printing research model of the root canal isthmus is a digital draft.

[0053] First, combine the main root canal surface data and the original root canal data through a Boolean addition operation to obtain combined data; then remove the anatomical variations in the combined data to obtain variation-removed data; the anatomical variations include: lateral accessory root canals and apical delta areas; then remove the sharp protrusions on the inner wall of the root canal in the variation-removed data to obtain protrusion-removed data; finally, encapsulate the protrusion-removed data with a cuboid to obtain a 3D printing research model of the root canal isthmus.

[0054] In this embodiment, after obtaining the original root canal structure containing the isthmus, the three-dimensional surface data of the main root canal is opened in the Geomagic Studio 2012 software. Because in the same coordinate system, the two surface structure files will automatically appear at the same position, and the three-dimensional surface data of the main root canal and the original root canal structure containing the isthmus are combined through a Boolean addition operation. Then remove other anatomical variations such as lateral accessory root canals and apical delta areas. Then repair the mesh in the data through the "Mesh Doctor" function in the software to remove the sharp protrusions on the inner wall of the root canal. To facilitate model fixation, a cuboid of appropriate size is designed to encapsulate the root canal, and the coronal plane of the root canal isthmus is kept parallel to the surface of the cuboid as much as possible. Small cuboid structures are added at the root canal orifice and the apical foramen to lead to the model surface to simulate the pulp cavity and keep the root canal orifice and the apical foramen have unobstructed channels. Finally, it is saved as an.stl file for printing. For reference, see Figure 3 , Figure 3 In (a), a three-dimensional image of the root canal is reconstructed in Mimics software, and the original three-dimensional surface data of the root canal is generated; Figure 3 In (b), the position of the main root canal is marked and drawn in Mimics, the diameter of the root canal after preparation is set, and digital root canal preparation is completed; Figure 3 In (c), first open the original three-dimensional surface data of the root canal in Geomagic, remove the root canal shell, leaving only the root canal, open the surface data of the main root canal in (b), combine them, complete the Boolean operation, encapsulate them in a designed rectangular body, and keep the root canal orifice and the apical foramen unobstructed. Figure 3 In (a), a three-dimensional image of the root canal is reconstructed in Mimics software, and the original three-dimensional surface data of the root canal is generated; Figure 3 In (b), the position of the main root canal is marked and drawn in Mimics, the diameter of the root canal after preparation is set, and digital root canal preparation is completed; Figure 3 In (c), first open the original three-dimensional surface data of the root canal in Geomagic, remove the root canal shell, leaving only the root canal, open the surface data of the main root canal in (b), combine them, complete the Boolean operation, encapsulate them in a designed rectangular body, and keep the root canal orifice and the apical foramen unobstructed.

[0055] This embodiment may further include the following steps:

[0056] Adjust the narrow diameter of the isthmus of the digital model:

[0057] When the isthmus of the printed model is still blocked (liquid cannot flow) after post-processing, use Geomagic Studio 2012 software, and gradually increase the value of the narrow diameter of the isthmus of the digital model with a carving tool, reprint and perform post-processing until the isthmus area of the printed model is unobstructed and a satisfactory filling effect can be obtained. It is found in this embodiment that the median of the shortest diameter (d min ) of the cross-section of the isthmus root canal is within the range of 0.050 mm to 0.080 mm except for type IV isthmus. Although it is several times the nominal printing accuracy (16 μm) of the 3D printer, problems of unclogging the isthmus are encountered when printing type II and type III isthmus with the original isthmus data. Therefore, the narrow diameter of the isthmus of the digital model is adjusted through software, and adjusted to 0.070 mm to 0.080 mm and 0.100 mm to 0.110 mm respectively. Tests find that when the narrow diameter of type II and type III isthmus is adjusted to about 0.100 mm to 0.110 mm, a more satisfactory hydrogel filling effect of the isthmus can be obtained.

[0058] 3D printing: Import the constructed digital model.stl file into the Objet30 Pro three-dimensional resin printer. The printing accuracy is 16 μm. Place it in a position where the root canal isthmus structure is parallel to the horizontal plane. The printing material is transparent resin material (VeroClear, RGD810). Select the support mode type as Lite and the surface effect type of the printed model as smooth surface.

[0059] Post-printing processing: After printing, remove the model from the printing substrate with a special spatula. Use instruments such as a cement filling instrument to remove the support material on the surface of the printed model, in the simulated pulp chamber and at the apical opening. Use a No. 20 H-file to remove most of the support material in the main root canal. Immerse the model in the prepared alkaline solution (the preparation method is shown in Table 1 in detail), place it on a T09-1S constant temperature magnetic stirrer, keep the liquid temperature at 40 °C, soak and clean for 1 to 3 days, and replace the alkaline solution regularly. During this period, clean the root canal isthmus 2 to 3 times by adding PUI to the alkaline solution until the support material in the isthmus is removed and the liquid can flow smoothly.

[0060] Since there will be more reflected light spots on the surface of the printed model under direct microscope light, use an MP-2B grinding and polishing machine to polish the model surface at a speed of 500 revolutions per minute, using sandpaper with 400 mesh, 600 mesh, 1000 mesh, 1500 mesh, and 2000 mesh in sequence. After drying, spray the surface with transparent hand-cranked automatic paint and use it after natural drying.

[0061] Table 1 Preparation table of alkaline solution

[0062] Element Molecular formula Quality Ratio factory Origin Sodium hydroxide NaOH 2％ Zhiyuan Chemical Reagent Co., Ltd. Tianjin Sodium silicate Na2SiO3·5H2O 1％ Zhiyuan Chemical Reagent Co., Ltd. Tianjin Deionized water H2O 97％ Central laboratory --

[0063] Preparation of hydrogel: Refer to the method of Macedo et al. Dissolve 3 g of gelatin and 0.06 g of sodium hyaluronate in 45 mL of deionized water in a 50 °C water bath, and add 0.5 mL of red food coloring. Since the hydrogel will convert to a solid gel state at room temperature, before injecting it into the printed model, it can be restored to the liquid sol state in a 50 °C water bath and then injected.

[0064] Gelation time: It is measured by the test tube pouring method. Add 1 mL of hydrogel solution to a 4 mL centrifuge tube with a diameter of 10 mm, start timing at room temperature, tilt or invert the centrifuge tube every 1 minute, observe the change of the hydrogel, and determine that the hydrogel has gelled when the centrifuge tube is inverted for 30 s and the hydrogel does not flow. This time is used as the gelation time.

[0065] Measurement of the narrow diameter of the isthmus in the digital model: Since the isthmus of the type II and type III isthmus models was blocked when the models were constructed and printed according to the selected micro-CT data of the premolars, the narrow diameter of the isthmus was adjusted according to step 4.2.5.3. To clarify the range of the narrow diameter of the modified isthmus, the final digital model was imported into Geomagic Studio 2012 software. The outer wall of the model was cut off, and the complete root canal structure was separated. Then, the main root canal and the isthmus boundary were removed to form two opposite thin slice-like three-dimensional images. By flipping the normal vector and repairing the mesh, it was saved as a new.stl file. The file was imported into Dragonfly software, and the "Compute Ray-Tracing Thickness" function was applied to measure the distance from any plane on the thin slice to the opposite side.

[0066] Measurement of the narrow diameter of the isthmus in the printed model: The printed model was scanned with Inveon MMCT (micro-CT). The scanning conditions were: spatial resolution 8.9 μm, voltage 80 kV, current 500 μA, and exposure 1500 ms. The scanned file was exported in DICOM format. The root canals in the model were marked and three-dimensionally reconstructed using the threshold segmentation method in Dragonfly software to generate root canal surface data. The file was imported into Geomagic Studio software to remove the main root canal and the isthmus boundary, and two opposite thin slice-like three-dimensional images at the isthmus position of the root canal were retained. The "Mesh Doctor" function was applied to repair the mesh, remove the sharp protrusions on the inner wall of the root canal, flip the normal vector, and save it as an.stl file; then it was imported into Dragonfly software, and the "Compute Ray-Tracing Thickness" function was applied to measure the distance from any plane on the thin slice to the opposite side.

[0067] 3D deviation measurement of the digital model and the printed model: The digital model file and the file after scanning and reconstruction of the printed model were opened in Geomagic Studio 2012 software. After registration of the two, the main root canal was cropped and removed, and the isthmus area was retained. Taking the digital model as a reference, the 3D deviation between the three-dimensional image of the printed model after micro-CT scanning and the three-dimensional image of the digital model was measured.

[0068] Measurement of the angle of the main root canal in the printed model and inspection of the isthmus liquid filling condition: Hydrogel was injected into the isthmus model, and the curvature of the main root canal of the printed model was observed and measured under a stereomicroscope, and the hydrogel filling condition of the isthmus was observed.

[0069] Screening of micro-CT data: After screening the micro-CT data of 187 molars with isthmus structures, 1 sample data was finally selected for each type to construct the root canal isthmus model. The basic information is shown in Table 2.

[0070] Table 2 Basic information table of the selected samples

[0071]

[0072]

[0073] Measured values of root canal diameter after root canal preparation (three-dimensional surface data of the main root canal):

[0074] After the mesial root canal of the molar was prepared with ProTaper Next, the measured values of the root canal diameter at different distances from the apical foramen are shown in Table 3:

[0075] Table 3 Measured values of root canal diameter after ProTaper Next preparation (mm)

[0076]

[0077] Among them, MB: mesial buccal root canal; ML: mesial lingual root canal.

[0078] Recheck measurement of the root canal isthmus model:

[0079] Measurement of the narrow diameter of the isthmus of the digital model: For the narrow diameter of the isthmus of type I-IV digital models, 7611, 3898, 5552, and 46605 measurement values were obtained respectively due to different isthmus areas. The minimum values were 0.071 mm, 0.049 mm, 0.098 mm, and 0.115 mm respectively. The numerical distribution is shown in Figure 4 and Figure 5 . Figure 4 The solid line position in the figure represents the median, and the upper and lower dotted lines represent the Q1 (25%) position and the Q3 (75%) position.

[0080] Measurement of the narrow diameter of the isthmus of the printed model: The minimum values of the narrow diameter of the isthmus of the three-dimensional reconstruction data of the micro-CT scan of type I-IV printed models were 0.050 mm, 0.027 mm, 0.109 mm, and 0.066 mm respectively. Table 4 lists the measured values of the narrow diameter of the isthmus of the digital model and the printed model.

[0081] Table 4 Measured values of the narrow diameter of the isthmus of the digital model and the printed model (mm)

[0082]

[0083] Deviation measurement between the digital model and the printed model: The 3D average deviation distance between each type of printed model and the digital model ranges from 0.003 mm to 0.025 mm. See Table 5 and Figure 6 . Figure 6 (a) in the figure is the distance map of "deviation analysis" between the digital model and the printed model in Geomagic software (left), and the distance map of "deviation analysis" of the local isthmus (right); Figure 6In (b), it is the matching diagram of digital model data and printed model scanning data in Dragonfly software.

[0084] Table 5 3D Deviation between Digital Model and Printed Model (mm)

[0085] Isthmus type Average deviation distance Standard Deviation RMSEstimate Type I -0.006(+0.033 / -0.041) 0.045 0.045 Type II -0.010(+0.023 / -0.030) 0.033 0.035 Type III 0.003(+0.021 / -0.016) 0.026 0.026 Type IV 0.025(+0.022 / -0.040) 0.050 0.055

[0086] Gel time: The hydrogel used in this example showed a slowdown in flow 20 minutes after being taken out of a 50°C water bath, and completed the sol-gel transition in 26 - 28 minutes. When placed in a 4°C refrigerator at 20 minutes, the sol-gel transition was completed within 2 minutes. After gelation and placed at room temperature, the gel state did not change.

[0087] Measurement of the bending angle of the main root canal of the printed model and the filling condition of the hydrogel: After measurement, the buccolingual bending angles of the main root canal of the type I isthmus model were 23.1° and 26.9° respectively, and the mesiodistal main root canal bending was mainly located in the apical region below the isthmus structure, which was 26.3°; the buccolingual bending angles of the main root canal of the type III isthmus model were 14.4° and 16.4° respectively, and the mesiodistal bending angle was 21.7°; the main root canals of the type II and type IV isthmus models were basically straight root canals in the buccolingual direction, and the bending angles in the mesiodistal direction were 17.9° and 19.4° respectively.

[0088] After injecting the hydrogel into each type of isthmus model, a satisfactory filling effect can be obtained in the root canal isthmus, as shown in Figure 7 .

[0089] 3D printing is a technology that uses digital model files as the basis, adopts discrete materials, and manufactures solid parts through the principle of layer-by-layer stacking and accumulation. In recent years, 3D printing technology has made rapid progress in the application of stomatology. In endodontics, extensive attempts and applications have been made in teaching, assisting laboratory research, and digital guides for clinical root canal and apical localization.

[0090] Selection of 3D printing system: Different transparent materials were selected for 3D printing in this embodiment. In the preliminary experiment of printing the type I isthmus model, VisiJet Crystal transparent resin was once selected, and a ProJet MJP3600 (3D System, USA) printer was used to print the transparent model. The forming accuracy was 16 μm, and the support material was paraffin. The printed type I isthmus model could well reproduce the root canal and isthmus morphology. Good hydrogel filling effect could also be obtained after the isthmus was treated with hot oil flushing, PUI, etc. However, the transparent resin model would show a frosted glass-like change when soaked in hot oil (about 50 °C - 60 °C) and alcohol (it would gradually return to transparency after being removed from the influence of heat and alcohol), which affected the observation of the removal degree of the support material. Therefore, in the subsequent research, the Objet30 Pro printing system was selected. Its printing accuracy was also 16 μm, and the support material was an acrylic mixture, which presented as a wet sand-like mass on the outer surface of the model. The large mass of the support material could be scraped off with instruments, and the support materials inside and outside the model could be further dissolved under the action of an alkaline liquid.

[0091] Influence of the diameter of the root canal and the narrow diameter of the isthmus on the patency of the model root canal system: Song Ying et al. found that the apical foramen was closed in the tooth model of VisiJet Crystal after printing the root canal with three materials, namely Wic300a, E-Dent, and VisiJet Crystal, and blockages occurred in the apical 1 / 3 segment of the other two materials. Therefore, the digital model needed to be modified before the tooth model could be printed. In this embodiment, the steps of digital preparation and shaping of the main root canal were pre-designed. In addition to preventing problems such as apical foramen closure and blockage of the lower root canal during printing, the most important purpose was to reduce the chance of material debris generated during the subsequent preparation of the main root canal from entering or blocking the isthmus structure. Practice has proved that the pre-digital preparation and shaping of the main root canal can not only keep the root canal patent but also reduce the difficulty of removing the support material, making it easier for the alkaline solution to enter the root canal system to dissolve the support material.

[0092] In this embodiment, it was found that the median of the shortest diameter (dmin) of the cross-section of the isthmus root canal was within the range of 0.050 mm - 0.080 mm except for the type IV isthmus. Although it was several times the nominal printing accuracy (16 μm) of the 3D printer, problems of unclogged isthmus occurred when printing the type II and type III isthmus with the original isthmus data. Therefore, the narrow diameter of the isthmus of the digital model was adjusted through software, adjusted to 0.070 mm - 0.080 mm and 0.100 mm - 0.110 mm respectively. Tests found that when the narrow diameter of the type II and type III isthmus was adjusted to about 0.100 mm - 0.110 mm, a more satisfactory hydrogel filling effect of the isthmus could be obtained.

[0093] Recheck measurement of the root canal isthmus model: Since the narrow diameters of the isthmus in type II and type III digital models were adjusted, and due to software limitations, only the longest diameter of the cross-section of the isthmus root canal and the shortest diameter of the same cross-sectional layer were measured. Therefore, in order to obtain more clear information on the narrow diameter of the isthmus, based on software updates, the new function "ComputeRay-TracingThickness" of Dragonfly software was applied in this embodiment to attempt to measure the narrow diameter of the isthmus of the designed digital model. "Ray-Tracing" is also known as "NormalRay Tracing", which measures the distance that a ray perpendicular to a selected plane reaches the opposite surface when generated on any plane within the selected range. Since the surface morphology of the isthmus region is not smooth and not parallel to each other, the rays perpendicular to each small plane are not all projected at the angles desired by the research. Therefore, the distribution of this measurement value does not fully represent the distribution of the narrow diameter of the model isthmus, but the minimum value among the large number of obtained numerical values can, to a certain extent, represent the minimum value of the narrow diameter of the model isthmus.

[0094] After measurement, the minimum narrow diameters of the isthmus of type I-IV digital models are 0.071 mm, 0.049 mm, 0.098 mm, and 0.115 mm respectively. Compared with the medians of the shortest diameters (dmin) of the cross-sections of the isthmus root canals of each type measured in the previous chapter, which are 0.067 mm (0.045 mm, 0.113 mm), 0.073 mm (0.053 mm, 0.141 mm), 0.065 mm (0.046 mm, 0.077 mm), and 0.153 mm (0.070 mm, 0.248 mm), the value of type II is smaller, which may be related to the different measurement cross-section positions in the previous chapter's research (the longest diameter of the cross-section of the isthmus root canal is generally more crownward); while the value of type III isthmus is larger, probably because the selected type III isthmus is located in the apical region, the distance between the two root canals is larger (d max = 2.655 mm), and the length of the isthmus extending in the tooth long axis direction is short (L i = 1.801 mm), which increases the difficulty of alkaline liquid entering during post-processing. In order to completely remove the support material, only by increasing the narrow diameter value of the isthmus, thus causing deviation.

[0095] Some studies have shown that 3D printing technology can provide high-precision dental replicas. By comparing the micro-CT scan data of extracted teeth and printed models in terms of the pulp cavity morphology, the mean and standard deviation of the deviation values between the two are 0.045±0.102 mm (Wic300a material, printing accuracy 25 μm). This deviation value range can be negligible for the overall tooth or pulp cavity morphology, but it is too broad for the size of the root canal isthmus. The ink droplet size of the Objet30 Pro three-dimensional resin printer used in this study is 12 picoliters; in the XY direction, the printer's accuracy is 1200×600 DPI, that is, there are 1200×600 ink droplets per square inch; in the Z direction, the height of each layer is 16 μm - 32 μm. At the isthmus or the edge of the root canal inner wall, the printer sprays ink centered on the data edge points, so the radial distance between the two inner walls will theoretically narrow. Coupled with the fact that the support material may not be completely removed, the narrow diameter of the isthmus of the actual printed model should theoretically be smaller than that of the digital model and closer to the actual situation of the root canal isthmus.

[0096] To verify the printed model, in this embodiment, micro-CT was used to obtain the three-dimensional reconstruction data of the printed model. After measuring the narrow diameter value of the isthmus of the printed model and registering it with the digital model data, 3D deviation analysis was carried out. It can be seen from the results that except for type III, the minimum value of the isthmus narrow diameter has decreased; but it can also be seen from the results that except for type IV, the number of measured values after the reconstruction of the printed model has increased significantly. This is mainly because a large number of small protrusions appear on the surface of the root canal and isthmus after the scan and reconstruction of the printed model, resulting in a significant increase in the number of small planes. And these protrusions will generate hundreds of extremely small values when using "ComputeRay-Tracing Thickness" for measurement, disturbing the judgment of the minimum value of the isthmus narrow diameter; therefore, the three-dimensional image of the isthmus surface of the printed model needs to be smoothed to a strong degree before subsequent measurement, and the smoothing operation will make the protrusions and depressions on the same surface approach the central plane of the two, and will also change the value of the isthmus narrow diameter; and during the three-dimensional reconstruction process, the setting of the threshold and the accuracy of the delineation are also influencing factors. Thus, it can be seen that the measurement of the isthmus narrow diameter of the printed model in this section of the study is affected by scanning accuracy, threshold setting, smoothing processing and algorithms, and is for reference only. It needs to be verified using different software and algorithms in terms of science.

[0097] The 3D deviation analysis between the printed model and the digital model was carried out without smoothing the three-dimensional reconstruction image of the printed model. The 3D average deviation distances between various types of printed models and digital models ranged from 0.003 mm to 0.025 mm, and the standard deviations were from 0.026 mm to 0.050 mm; the RMS showed the root mean square error of all comparison points, and the smaller its value, the smaller the deviation (0.026 mm to 0.056 mm); at the same time, it could be seen that after the digital model and the printed model data were registered, the average deviation distance in the main root canal area was extremely small, and the main deviation changes existed in the isthmus area; most of the red lines outlined by the printed model were within the green lines of the digital model. These results indicate that the Objet30 Pro three-dimensional resin printing system can print the root canal isthmus model constructed in this study relatively accurately, and is closer to the real root canal isthmus structure not only in terms of morphology but also in terms of the measured values of the isthmus compared with the models used in previous studies.

[0098] Selection of root canal contents: In previous studies, bovine dental pulp tissue powder, hydrogel, temporary filling paste, etc. were placed into the root canal model, or bacterial biofilms were colonized in the model to carry out related research. In the early stage of this chapter's research, an attempt was made to prepare bovine dental pulp tissue powder, but the process was relatively complex and the final obtained amount was small, so it was not adopted; while the temporary filling paste may not be completely removed from the root canal isthmus under the action of the existing clinical root canal irrigation methods, which will affect the repeated use of the root canal isthmus model. Therefore, the hydrogel reported by Mecedo et al. was adopted in this chapter's research. Except for not adding 10-μm hollow glass beads, it was basically prepared according to the literature. From the perspective of the gelation time and the filling results of the model isthmus, the hydrogel prepared in this chapter's research has good fluidity, sufficient operation time, simple preparation and good homogeneity.

[0099] Based on the original root canal data obtained by micro-CT scanning in this embodiment, various types of root canal isthmus research models after digital root canal shaping were successfully constructed and printed using medical imaging software and three-dimensional reverse engineering software. Through the relevant measurements of the digital model and the printed model and the 3D deviation analysis of their three-dimensional images, the results show that the Objet30 Pro three-dimensional resin printing system can accurately replicate the root canal and isthmus structures, providing a visual, homogeneous research model that is closer to the real root canal and isthmus system in terms of morphology and measured values for subsequent research.

[0100] The overall technical route of this embodiment is as Figure 8As shown in the figure. First, the micro-CT data were screened according to the characteristics of each type of isthmus, and the surface morphology data of the root canal and isthmus were extracted by Mimics software. Then, the main root canal pathway was traced, and the main root canal pathway was widened with the data of the root canal diameter after preparation to obtain the surface morphology data of the main root canal. The two sets of data were combined and encapsulated in Geomagic software to generate a digital model of the root canal isthmus. When the isthmus of the printed model was blocked, Geomagic software was used to adjust the narrow diameter of the isthmus and then print again. After that, the narrow diameter of the isthmus of the digital model and the printed model was re-measured, and a 3D deviation analysis was performed on the three-dimensional images of the two. The prepared hydrogel was used as the root canal content and injected into the isthmus model to observe the filling condition of the isthmus.

[0101] The experimental instruments, devices and reagents used in this embodiment are shown in Table 6 below:

[0102] Table 6 Experimental Instruments, Devices and Reagents

[0103]

[0104]

[0105] The software used in this embodiment is shown in Table 7 below:

[0106] Table 7 Software Used in the Experiment

[0107] name Version factory Origin NRecon 1.6.9.18 Bruker Germany CTAn 1.10.1.0 Bruker Germany Mimics 23.0 Materialise Belgium Geomagic Studio 2012 RaindropGeomagic USA Dragonfly 2021.3 ORS Canada

[0108] In an exemplary embodiment, a computer device is provided. The computer device can be a server or a terminal, and its internal structural diagram can be as Fig. 9 shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, abbreviated as I / O), and a communication interface. Among them, the processor, the memory, and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The input / output interface of the computer device is used to exchange information between the processor and external devices. The communication interface of the computer device is used to communicate with external terminals through a network connection. When the computer program is executed by the processor, it realizes a method for constructing a 3D printed research model of the root canal isthmus.

[0109] Those skilled in the art can understand, Fig. 9The structure shown is only a block diagram of some structures related to the solution of this application, and does not constitute a limitation on the computer device to which the solution of this application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine some components, or have different component arrangements.

[0110] In an exemplary embodiment, a computer device is further provided, including a memory and a processor. A computer program is stored in the memory, and when the processor executes the computer program, the steps in the above method embodiments are implemented.

[0111] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0112] In an exemplary embodiment, a computer program product is provided, including a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0113] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use, and processing of relevant data need to comply with relevant regulations.

[0114] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, database, or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memories. Non-volatile memories can include read-only memory (ROM), magnetic tapes, floppy disks, flash memories, optical memories, high-density embedded non-volatile memories, resistive random access memories (ReRAM), magnetoresistive random access memories (MRAM), ferroelectric random access memories (FRAM), phase change memories (PCM), graphene memories, etc. Volatile memories can include random access memory (RAM) or external cache memories, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0115] The databases involved in the embodiments provided in the present application can include at least one of relational databases and non-relational databases. Non-relational databases can include distributed databases based on blockchain, etc., without limitation. The processors involved in the embodiments provided in the present application can be general-purpose processors, central processors, graphics processors, digital signal processors, programmable logics, data processing logics based on quantum computing, etc., without limitation.

[0116] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0117] In this article, specific examples are used to elaborate on the principles and implementation manners of the present application. The descriptions of the above embodiments are only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A method for constructing a 3D printing research model of a root canal isthmus, characterized in that: include: Acquire original root canal data and prepared root canal data; the original root canal data is scanned data containing various typical forms of the isthmus of the root canal; The prepared root canal data is scanned data after the root canal is enlarged by dental instruments; data obtained by scanning the teeth using a scanning device; According to the prepared root canal data, obtaining the diameter data of the main root canal after enlargement; According to the original root canal data, three-dimensional reconstruction is performed by threshold segmentation method to obtain original root three-dimensional surface data; The original three-dimensional surface data includes: original root, root canal and isthmus three-dimensional surface data; The original tooth root three-dimensional surface data is horizontally cut in a direction perpendicular to the long axis of the root canal to obtain two-dimensional layer data; Marking the center point of the main root canal from the root apex to the root crown on the two-dimensional layer data in sequence to obtain the main root canal path shape line data; Taking the main root canal path shape line data as the center, importing the enlarged main root canal diameter data, and forming main root canal surface data that matches the root canal path shape; The main root canal surface data and the root canal original data are Boolean added to obtain a 3D printing research model of the root canal isthmus after the main root canal is enlarged; the 3D printing research model of the root canal isthmus is a digital draft.

2. The method for constructing a 3D printing research model of the root canal isthmus according to claim 1, characterized in that: The root canal raw data include four types of data with typical morphology of the root canal isthmus; The first type is the coronal boundary type; the coronal boundary type is that the isthmus between the two root canals has only a single coronal boundary, and the remaining directions are connected to the main root canal or open to the apical foramen; The second type is the root square boundary type; the root square boundary type is that the isthmus between the two root canals has only a single root square boundary, and the remaining directions are connected to the main root canal or open to the medullary cavity; The third type is the double-boundary type; the double-boundary type is that the isthmus between the two root canals has boundaries on the coronal and radicular sides, and is shaped like a belt connecting the two main root canals; The fourth type is: borderless type; the borderless type means that the two canals are connected by an isthmus from the root canal orifice to the apical foramen or to the confluence of the two canals.

3. The method for constructing a 3D printing research model of the root canal isthmus according to claim 1, characterized in that: According to the original root canal data, three-dimensional reconstruction is performed by threshold segmentation method to obtain original root three-dimensional surface data, specifically including: Determine the length data from the crown top to the anatomical root apex in the root canal original data; Determine the length data of the three-dimensional model according to the length data from the top of the crown to the anatomical root apex; According to the length data and the original root canal data, a three-dimensional model of the root canal is reconstructed by a threshold segmentation method to obtain original three-dimensional surface data of the tooth root.

4. The method for constructing a 3D printing research model of the root canal isthmus according to claim 1, characterized in that: According to the prepared root canal data, obtaining the diameter data of the enlarged main root canal includes: Acquire a root canal cross-sectional image of the prepared root canal of the mandibular first molar according to the prepared root canal data; According to the root canal cross-sectional view, the main root canal diameter is measured every 1 mm from the position of the apical foramen to the position of the root canal orifice to obtain the main root canal diameter data after expansion.

5. The method for constructing a 3D printing research model of the root canal isthmus according to claim 1, characterized in that: The main root canal surface data and the root canal original data are Boolean-added to obtain a 3D printing research model of the root canal isthmus after the main root canal is enlarged, specifically including: Combining the main root canal surface data with the root canal original data by Boolean addition operation to obtain combined data; Removing anatomical variations from the combined data to obtain variation-removed data; the anatomical variations include: lateral root canals and apical triangles; removing sharp protrusions on the inner wall of the root canal in the variation removal data to obtain protrusion removal data; The protrusion removal data is encapsulated by using a cuboid to obtain a 3D printing research model of the root canal isthmus.

6. The method for constructing a 3D printing research model of the root canal isthmus according to claim 1, characterized in that: The root canal isthmus 3D printing research model is an stl file.

7. The method for constructing a 3D printing research model of the root canal isthmus according to claim 1, characterized in that: After performing Boolean addition on the main root canal surface data and the root canal original data to obtain a 3D printing research model of the root canal isthmus after the main root canal is enlarged, the method further includes: After 3D printing is performed according to the root canal isthmus 3D printing research model, determining whether the isthmus of the printed isthmus model is atresia; When the isthmus of the printed isthmus model is closed, the value of the isthmus narrow diameter in the root canal isthmus 3D printing research model is increased, and reprinting is performed until the isthmus area of ​​the printed isthmus model is unobstructed.

8. A computer device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method for constructing a 3D printed research model of the root canal isthmus according to any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for constructing a 3D printing research model of the root canal isthmus described in any one of claims 1 to 7 is implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method for constructing a 3D printing research model of the root canal isthmus described in any one of claims 1 to 7 is implemented.

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