Method for creating a three-dimensional model of an object in an oral cavity using an intraoral 3D scanner and intraoral 3D scanner

Abstract

The invention relates to an intraoral 3D scanner (1) for capturing an object in the oral cavity, comprising a control and evaluation unit and an elongated base body (5) extending along an axis (A) on which an imaging sensor system is arranged, wherein the sensor system has at least two 3D sensors (6a, 6b), each of which is assigned a field of view. The object of the invention is to minimize the chaining error in images taken with an intraoral 3D scanner and to simplify operation. To this end, the invention proposes that the 3D sensors (6a, 6b) be arranged on the base body (5) such that the fields of view of at least two 3D sensors (6a, 6b) do not overlap and preferably the viewing directions of the 3D sensors (6a, 6b) are mirror-symmetrical with respect to a plane in which the axis (A) runs. Furthermore, the invention proposes a method for performing an intraoral 3D scan.

Description

[0001] The invention relates to an intraoral 3D scanner for capturing an object in the oral cavity, comprising a control and evaluation unit and an elongated base body extending along an axis on which an imaging sensor system is arranged, wherein the sensor system has at least two 3D sensors, each assigned a field of view. The invention further relates to a method for performing an intraoral 3D scan.

[0002] Such intraoral 3D scanners are known, for example, from the publication Park et al. (“Feasibility of using an intraoral scanner for a complete-arch digital scan”, THE JOURNAL OF PROSTHETIC DENTISTRY, December 2018; DOI: 10.1016 / j.prosdent.2018.07.014).

[0003] The 3D scanners described there capture an intraoral object to be measured only within a single, limited detection area. It is also known that sensor systems are used which contain several individual 3D sensors and capture an object to be scanned from slightly different directions, but the individual sensors share a common, overlapping, and limited detection area.

[0004] If a larger area or an entire dental arch of a patient is to be captured intraorally, the capture area of ​​the intraoral 3D scanner is moved step by step across the dental arch until all areas of the dental arch have been captured at least once. This process generates a large number of individual images, each of which depicts a different area of ​​the dental arch in three dimensions.

[0005] In order to obtain a three-dimensional overall model of the dental arch to be recorded, matching surface features in the overlap area are algorithmically sought in adjacent individual images, and the individual images at these overlap areas are combined to form a common model.

[0006] Errors can occur when combining individual images of the sub-areas. These errors increase proportionally with the number of images and, through error propagation, accumulate into a chaining error. When combining only a few individual images, the chaining error for known intraoral 3D scanners is in the single-digit to lower double-digit micrometer range.

[0007] The error depends not only on the number of individual images combined, but also on how many distinct surface features can be identified in the overlapping area of ​​the individual images. For example, molars with their fissures have many distinct surface features, while smooth anterior teeth have very few. This means that, in particular, when scanning the entire dental arch with individual images across the anterior teeth, which have only a few surface features, the error propagation and thus the chaining error increase significantly.

[0008] As a result, the overall accuracy of known intraoral 3D scanners drops into the three-digit micrometer range when scanning the entire dental arch. This inaccuracy is most noticeable in the relative position of the right and left molars, because only a relative spatial relationship can be established via the intervening teeth and individual scans with chaining errors. This represents the core problem of known intraoral 3D scanners and can lead to problems in the further processing and usability of the 3D data obtained from larger scanned intraoral areas or even an entire dental arch.

[0009] If teeth are absent in certain areas of the jaw, then, depending on the indication (e.g., if only very contourless gum tissue remains), few or no surface features may be identifiable in the individual images during composite reconstruction. In such cases, capturing the entire dental arch is either impossible or only possible to a very limited and inaccurate extent.

[0010] The final degree of chaining error also depends on the quality of the sensors used. The chaining errors of various intraoral 3D scanners were investigated in "Park et al." (so).

[0011] Furthermore, inaccuracies in the positioning of the intraoral 3D scanner during the alignment for the respective individual scans can lead to further errors.

[0012] Furthermore, US Patent 2020 / 0205942 A1 discloses an intraoral scanning system in which numerous individual images of small fields of view are created and stitched together to form a complete model. To reduce the resulting cumulative error, additional so-called "compound FOV (fields of view)" are provided, which capture several tooth regions in one image and serve for subsequent correction.

[0013] It is therefore the object of the invention to minimize the chaining error in images from an intraoral 3D scanner and to simplify operation. To solve this problem, the invention proposes a method for creating a three-dimensional model of an object in the oral cavity using an intraoral 3D scanner (1) with a control and evaluation unit and an elongated base body (5) which extends along an axis (A) and on which an imaging sensor system is arranged, wherein the sensor system has at least two 3D sensors (6a, 6b), each of which is assigned a field of view, wherein - the at least two 3D sensors (6a, 6b) are calibrated together so that their relative spatial position to each other is known and all 3D data recorded by them are immediately captured in a common coordinate system, - the sensor system is inserted into the patient's oral cavity, - the 3D sensors (6a, 6b) synchronously create first images of at least one first and one second section of the dental arch, - the 3D scanner (1) is pivoted in the oral cavity so that the 3D sensors (6a, 6b) synchronously create further images of further sections of the dental arch, whereby the images of the sections of the respective 3D sensor partially overlap with previous images of this 3D sensor, - and the synchronously recorded 3D data are directly available in a common coordinate system due to the known spatial position of the sensors (6a,6b) and can be assembled into a sufficient model of the dental arch.

[0014] The problem is also solved by an intraoral scanner with the features of claim 3.

[0015] In a preferred embodiment of the invention, the viewing directions of at least two 3D sensors are mirror-symmetrical with respect to a plane in which the longitudinal axis of the base body runs.

[0016] In the concept of an intraoral 3D scanner according to the invention, the 3D data of an intraoral object to be scanned is acquired synchronously from at least two or more surfaces of the object in separate acquisition areas, ideally at maximum distance from each other. The sensor system is arranged on the base body in such a way that it can be inserted intraorally into a patient's mouth to acquire the 3D data. The acquisition of data from all 3D sensors of the sensor system is synchronous. Through this synchronous acquisition and through a joint calibration of all 3D sensors, the respective spatial position of the sensors relative to each other is known, and thus also the respective relative spatial position of the 3D data acquired synchronously by each 3D sensor.

[0017] This known spatial orientation allows the 3D data acquired by the respective 3D sensors to be directly captured in a common coordinate system, without having to merge them by identifying surface features and overlaps within the capture area. Depending on the orientation of the 3D sensors, this enables, for example, the synchronous capture of the left and right molars from above or from a slightly lingual or palatal angle when using at least two sensors. This allows 3D data of the right and left molars to be directly captured in a single coordinate system. Compared to conventional intraoral 3D scanners, this offers the advantage that the molars are captured directly in one coordinate system without having to take individual images of all the intervening teeth and then combine them, thus avoiding the resulting merging error.For this purpose, the 3D sensors are preferably arranged such that the viewing directions of at least two 3D sensors are mirror-symmetrical with respect to a plane in which the longitudinal axis of the base body runs.

[0018] To capture additional areas of the dental arch beyond the previously described molars, the detection ranges of the individual 3D sensors of the sensor system can be gradually shifted mesially across the molars towards the canines. Using at least two 3D sensors of the sensor system, at least pairs of 3D data can be acquired from the right and left regions of the dental arch. These paired 3D data can be considered a single scan because, as previously described, the 3D data are captured directly in a common coordinate system.

[0019] To combine these individual images into a common model of the object, algorithmic searches for similarities in surface features within the overlap area can be used, as in the prior art, and the individual images at these overlap areas can be successively assembled into a common model. However, unlike the prior art, the overlap areas do not extend to a limited detection area on one side of the dental arch, and in extreme cases, to a single tooth, but rather to the overlaps of the detection areas on both sides of the dental arch of all synchronously recording 3D sensors.

[0020] This results in at least twice as many surface features being present in the respective overlapping areas. Furthermore, the 3D data originates from different, widely separated surfaces of the object being scanned, which counteracts any angular errors that may occur when stitching together the individual images.

[0021] This, along with the larger number of usable surface features, significantly reduces the chaining error in the composition of the individual images thus obtained. Furthermore, additional images capturing at least pairs of different areas of the dental arch are conceivable using at least two 3D sensors from the sensor system.

[0022] The sensors can be positioned so that anterior and posterior teeth are captured directly in a common coordinate system from above or from a slightly lingual or palatal angle. The resulting combined scan of the anterior and posterior teeth can then be merged with the remaining 3D data using surface features of the fissures in the posterior region. This ensures that the few surface features of the anterior teeth do not negatively impact the overall accuracy due to chaining errors during the merging process. This is a further advantage over conventional intraoral 3D scanners.

[0023] If a sufficient number of areas of the dental arch have been captured, a precise model of the dental arch can be created from this data, with the chaining error being significantly minimized, as described above.

[0024] Gaps in this model can then be filled with further individual images of the dental arch taken by at least one of the sensors, allowing a complete model to be created. While these individual images must then be combined with the previously acquired model, the merging error is significantly reduced because only gaps in the captured object are filled.

[0025] Furthermore, with the intraoral 3D scanner according to the invention it is also possible to capture intraoral areas which, depending on the indication, have only a few surface features, e.g., when only very contourless gum tissue is present in individual areas.

[0026] The sensor system can be positioned so that, using at least two 3D sensors, areas of intact teeth with many surface features, such as the molars, and an indication with few surface features, such as the gums, are synchronously captured within a single coordinate system. The resulting individual scans of the indication and the molars can then be combined with the remaining 3D data via surface features of the fissures in the molar region. This ensures that the few surface features of the contourless indication do not negatively impact the overall accuracy due to chaining errors during the merging process. This is a further advantage over existing intraoral 3D scanners.

[0027] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. The drawings show: Fig. 1: schematically a 3D view of an intraoral 3D scanner according to the invention and a first dental arch; Fig. 2: Schematic top view of the intraoral 3D scanner and the dental arch Fig. 1 (left) and a top view of the dental arch with marked detection areas (right); Fig. 3: Schematic top view of the intraoral 3D scanner Fig. 2 in a different orientation and of the first dental arch Fig. 2 (left) and a top view of the first dental arch with marked detection areas (right); Fig. 4: Schematic top view of the intraoral 3D scanner Fig. 2 in a further orientation and of the first dental arch Fig. 2 (left) and a top view of the first dental arch with marked sections (right); Fig. 5: Schematic top view of the intraoral 3D scanner Fig. 2 and a second dental arch (left) as well as a top view of the second dental arch with marked capture areas (right); Fig. 6: Schematic top view of the intraoral 3D scanner Fig. 2 and a third dental arch (left) as well as a top view of the third dental arch with marked detection areas (right);

[0028] Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5 to Fig. Figure 6 schematically shows an intraoral 3D scanner 1 according to the invention, set up to carry out the method according to the invention, when scanning different dental arches 2a, 2b, 2c.

[0029] Fig. 1 and Fig. Figure 2 specifically shows an embodiment for recording a first dental arch 2a with left and right molars 3, 4. The intraoral 3D scanner 1 has an elongated, essentially cylindrical base body 5 extending along an axis A. A sensor system with two imaging 3D sensors 6a, 6b is arranged on the base body 5. The 3D sensors 6a, 6b are positioned opposite each other with respect to the axis A of the base body 5, so that the viewing directions of the 3D sensors 6a, 6b are mirror-symmetrical with respect to a plane in which the axis A runs. The 3D sensors 6a, 6b communicate with a control and evaluation unit (not shown here).

[0030] Using the intraoral 3D scanner 1 and its 3D sensors 6a, 6b, 3D data in the form of images of two sections of the dental arch 2a, which here comprise the molars 3, 4, can be recorded from above in a lingual direction in two separate, non-overlapping recording areas 7a, 7b.

[0031] Through a joint calibration of the 3D sensors 6a, 6b, their respective spatial positions relative to each other are known, and thus also the respective relative spatial position of the 3D data synchronously acquired by each 3D sensor 6a, 6b. Due to the known spatial position of the 3D sensors 6a, 6b on the base body 5, the acquired 3D data can be directly recorded in a common coordinate system. In order to capture further areas of the dental arch 2a in addition to the previously described molars 3, 4, the detection areas of the individual sensors 6a, 6b are gradually shifted mesially across the molars towards the canines 8, 9 of the dental arch 2a. Thus, 3D data can be recorded in further acquisition areas 10a, 10b, 11a, 11b, whereby the 3D data from the respective acquisition areas (7a, 7b and 10a, 10b as well as 11a, 11b) are each recorded in a common coordinate system and are to be regarded as individual recordings.

[0032] To combine these individual recordings into a common model of the object, algorithmic matching of surface features in the overlap area of ​​the adjacent recording areas (7a to 10a, 10a to 11a as well as 7b to 10b, 10b to 11b) can be sought and the individual recordings at these overlap areas can be combined into a common model.

[0033] Furthermore, additional images capturing at least paired different areas of the dental arch 2a are conceivable in this embodiment. As in Fig. As shown in Figure 3, the intraoral 3D scanner 1 according to the invention can be positioned so that the sensors capture front teeth 12, 13 and molar teeth 3, 4 from above in a lingual direction in the further detection areas 14a, 14b, 15a, 15b.

[0034] Here, the 3D data from acquisition areas 14a, 14b and 15a, 15b are each acquired in a common coordinate system and are to be considered as individual images. The resulting combined individual images of the anterior teeth 12, 13 and molars 3, 4 can then be combined with the remaining previously acquired 3D data to form a model using surface features of the fissures in the molar region.

[0035] Gaps in this model can then be filled with further individual images of the dental arch 2a with at least one 3D sensor 6a, 6b of the sensor system and a complete model can thus be created.

[0036] This is done as described in Fig. Figure 4 schematically illustrates that only one 3D sensor 6a of the intraoral 3D scanner 1 is used for data acquisition. Individual images of the dental arch 2a are then created with the 3D sensor 6a in further acquisition areas 16, 17, 18, 19, 20, 21, 22, 23, 24 to fill gaps in the previously created sufficient model and to obtain a complete model of the dental arch 2a to be scanned. In addition to the use of only one 3D sensor 6a, as schematically illustrated in this embodiment, a further embodiment also allows for the mechanical exchange of the sensor for creating the individual images. In this case, before capturing the entire dental arch to create the complete model, the sensor of the intraoral 3D scanner would be replaced with a sensor system containing only one 3D sensor, and the individual images for completing the sufficient model would be created with this sensor.

[0037] Furthermore, with the intraoral 3D scanner 1 according to the invention, it is also possible, depending on the indication, to capture areas that have few surface features, e.g., when in individual areas of a dental arch 2b only very contourless gingiva remains, as in Fig. Figure 5 shows that the intraoral 3D scanner 1 can be positioned so that the 3D sensors 6a, 6b capture areas of intact teeth, here the molars 3, and of gums 25 with few surface features with the respective detection areas 26a, 26b in a coordinate system.

[0038] The resulting individual image of the gum 25 and the molars 3 can then be combined with the remaining 3D data of the sufficient model via surface features of the fissures in the molar region, without the few surface features of the gums having a negative impact on the overall accuracy due to chaining errors during the merging process.

[0039] In addition to the previously schematically illustrated and described recording of gum tissue 25 together with areas of intact teeth, here the molars 3, the recording of other contourless areas, e.g. as in Fig. 6 shown with included implants 27, or the inclusion of further contourless indications is conceivable. Reference symbol list: 1 intraoral 3D scanner 2 dental arches 3rd and 4th molars 5 basic shapes 6 3D sensor 7. Detection area 8, 9 canine 10, 11 Recording area 12, 13 front tooth 15-24, 26 coverage area 25 gums 27 implant

Claims

[1] Method for creating a 3D scan of an object in an oral cavity using an intraoral 3D scanner (1) with a control and evaluation unit and an elongated base body (5) which extends along an axis (A) and on which an imaging sensor system is arranged, wherein the sensor system has at least two 3D sensors (6a, 6b) to which a field of view is assigned, wherein - the at least two 3D sensors (6a, 6b) are calibrated together so that their relative spatial position to each other is known and all 3D data recorded by them are immediately captured in a common coordinate system, - the sensor system is inserted into the oral cavity of a patient, - the 3D sensors (6a, 6b) synchronously create first images of at least one first and one second section of a dental arch, - the 3D scanner (1) is pivoted in the oral cavity so that the 3D sensors (6a, 6b) synchronously create further images of further sections of the dental arch, whereby the images of the sections of the respective 3D sensor partially overlap with previous images of this 3D sensor, - and the synchronously recorded 3D data are directly available in a common coordinate system due to the known spatial position of the sensors (6a,6b) and can be assembled into a sufficient model of the dental arch. [2] Method according to claim 1, characterized by , that subsequently additional further recordings of overlapping subsections are taken using only one of the 3D sensors (6a, 6b) of the sensor system. [3] Intraoral 3D scanner (1) for carrying out the method according to one of the preceding claims, comprising a control and evaluation unit and an elongated base body (5) which extends along an axis (A) and on which an imaging sensor system is arranged, wherein the sensor system has at least two 3D sensors (6a, 6b) to which a field of view is assigned, wherein the 3D sensors (6a, 6b) are arranged offset on the base body (5) such that the fields of view of at least two 3D sensors (6a, 6b) do not overlap, wherein the control and evaluation unit is configured to calibrate the at least two 3D sensors (6a, 6b) together so that their relative spatial position to each other is known and all 3D data recorded by them are directly captured in a common coordinate system.

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