Field of the Invention

The invention relates to a device and methods to improve the accuracy of 3-D images of 3-D objects, particularly to dental or medical imaging. More particularly, the invention relates to improving the accuracy of 3-D images wherein a plurality of images are made and stitched together to represent a larger area. A verification gauge is provided with a visual and imigable scale (that is a scale that is able to be scanned) to correct discrepancies between the plurality of scans. At least one second scan is made including scanning the gauge, and the second scan is used to correct the discrepancies to the digital image made from the stitched first scans.

Many surgical procedures concern the temporary or permanent insertion, into the soft or bony tissue of a patient, of prosthetic and other artificial devices that are required to fit the anatomy of the patient to a very high degree of precision and accuracy. One such application concerns implant dentistry, in the course of which one or more often metallic implant anchors are surgically placed within the jawbone of a patient, to receive and support prosthetic components designed to simulate and replace one or more natural teeth lost by the patient. It is well known that, to be wholly successful, implant procedures must adhere to very strict placement, orientation and sizing requirements determined by existing bone structure and dentition, whereby the prosthetic components to be fitted onto surgically-placed implant anchors must preferably be designed, shaped and sized specifically to conform to the precise anatomical geometry of the patient, including the location, shape and size of adjoining teeth, and must transition to the precise orientation of the principal axis of the supporting implant anchor with a high degree of accuracy.

Conventional methods for meeting these rigorous requirements provide for the creation of a model of the patient's jaw and dentition, the making of said model comprising the taking of a so-called "impression" of the patient's dentition, using a malleable substance placed over and around the teeth in the patient's mouth comprising the entire dental arch. Where the placement of implants and restorative components is a factor, typically this impression is taken following the surgical insertion of the implant anchors. Typically, reference components called impression copings are affixed to the external extremity of the inserted implant anchors, and serve to reference the location and angular orientation of the anchors. Subsequently, a model made from a mold based on said impression will incorporate so-called "analog" anchors to model the anchors in the patient's jaw, and prosthetic devices for said anchors will be designed and manufactured based on the geometry of the model created as described.

In actual practice the conventional procedure described above is fraught with numerous difficulties and shortcomings. It has proven impossible for dental practitioners to make dental impressions, and thus models, that are consistently free of dimensional and positional errors; so rigorous are the geometrical requirements involved in such applications that even a sub-millimeter dimensioning error, or a 1 or 2 degree orientation error, will result in prosthetic placements that give rise to unacceptable stresses and conditions. In the dental arts, efforts have been made to employ image-based modeling techniques to address these well-known problems of conventional implant dentistry procedures. In these efforts, images are taken of the patient's mouth, and a three-dimensional model of the pertinent regions is recreated using so-called three-dimensional image processing techniques and software. In the art of 3- D imaging, it is often the case that a larger image is made by combining or stitching together overlapping images or "scans." An algorithm is often used to register identifiable points on the object to be scanned and or the surrounding area. By such registration, a plurality of scans can be stitched together to produce a digital representation of a larger area. For example, in the area of dentistry, a scanning device can be inserted into the oral cavity and a number of scan images can be obtained. Identifiable points in the oral cavity can be used to register the different scan images, such as points on a tooth or a dental appliance of some kind. While any dental appliance can be used, a useful one is commonly known as a scan flag.

It has been found that soft tissue, including the gums are not good choices for registering the different scans with respect to each other. Being soft, such surfaces can be easily moved such that a point I on scan may not be in the exact same location in a second scan. Also, minor movement of the patient during the scan can cause even fixed points in hard tissue to be slightly off between scan procedures. Hence, the stitched scan images are not always precisely located, meaning that the resulting stitched digital representation of the target is not suitably rendered. In some procedures such as in dental implant procedures, this is a particular concern as precise location of an implant is important for a number of reasons. This includes for example, the position of the restorative placed upon the implant and the avoidance of nerves and the like when an implant is placed. In short, it is advantageous for the resulting digital image to be as precise as possible so that subsequent procedures can be based upon such images with confidence.

SUMMARY OF THE INVENTION

According to the invention, a gauge to verify the accuracy of an image of at least a portion of the oral cavity which is formed from a plurality of intra-oral scans of the oral cavity of a patient. The gauge includes a bar of adjustable length and removably affixable between two points in the oral cavity. The bar has a first and a second end, and is scanable by the intra-oral scan. By "scanable" it is meant that it shows on a standard image scan. As such it may be made of a metal, plastic or other material that is subject to being scanned and showing up as a scanned image.

The relative position and/or measurement of the distance between the two points is thereby verified by the visual indicia and digitally by the scan of the bar. The bar is affixable at at least one of its ends to for example, the patient's dentition, a dental appliance, a dental implant component including the implant, its abutment, healing caps and the like without limitation. As used herein dental implant and dental implant component will be used interchangeably to refer to all such components. In addition, a method of improving the accuracy of a digital image the oral cavity of a patient includes making a plurality of first intraoral scans of the oral cavity. The data from the first intraoral scans is used to construct a digital image of at least a portion of the oral cavity. A gauge is provided having a bar of adjustable length and removably affixable between two points in the oral cavity. The bar has a first and a second end, such that it is removably secu red at its first end to one of the points in the oral cavity and the second end of the bar to the other point in the oral cavity. At least one second intraoral scan of the oral cavity is made, including scanning at least a portion of the bar. The data from the second scan is used to make correction adjustments to the digital image.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a gauge according to the present invention.

FIG. 2 is a perspective view of the gauge of FIG. 1 shown in use in the oral cavity of a patient. DETAILED DESCRIPTION

There is provided according to the present invention and as shown on the drawings, a gauge 10 made of a material as described hereinabove. According to the invention, gauge 10 is used to verify the accuracy of an image of at least a portion of the oral cavity which is formed from a plurality of intra-oral or other scans of the oral cavity of a patient. The gauge includes a bar 11 of adjustable length and removably affixable between two points 12, 13 in the oral cavity. The 11 bar has a first and a second end 14 and 15 respectively, and is scanable by an intra-oral scanner. The bar 11 preferably has a scale such as Vernier scale 21, or other suitable indicia, to show relative position or distance between ends 14, 15 and hence, the same between points 12, 13. The measurement of the distance between the two points 12, 13 is thereby verified by the visual indicia 21 and digitally by the scan of the bar 11. The bar 11 is affixable at at least one of its ends 14, 15 to for example, the patient's dentition, a dental appliance, a dental implant component including the implant 30 or its abutment 31, healing cap and the like without limitation. As used herein dental implant and dental implant component will be used interchangeably to refer to all such components.

Use of the present invention in inventive methods will be described in the following examples. Reference is made to IOFLO scan flags available from Dentsply Sirona, Inc. of York PA.

Method One:

This method is a complete intraoral scan with the scan flags placed in their respective implants. Here, a single scan would detect the gingival soft tissue along the maxillary or mandibular arch, along with the necessary features of the scan flag to enable detection of the implant locations and orientations from the resulting 3D scan file. In figure 1, the term IOFLO is used as a representation of a DENTSPLY SIRONA specific scan flag, but any generic scan flag can also be used in this method. Method Two:

Method two begins with an initial scan of the edentulous space to capture the soft tissue and the general shape of the arch. No scan flags are present in this initial scan. Subsequent scans are conducted with the scan flags placed into the implants. These scans may cover the entire clinically relevant area (as in the prior scan), or it may capture just the scan flags and the immediately surrounding edentulous space (e.g. within a 2-10mm radius of the scan flag). The auxiliary scan is processed using a detection algorithm to detect the location of the scan flags within the scan data, and thereby determine the implant location and orientation (Figure 2).

The implant locations obtained from the subsequent scan must be aligned and merged to the dental anatomy obtained in the initial scan. This alignment can take place before or after IOFLO detection, though if alignment occurs after IOFLO detection, the detected locations must be transformed according to the alignment results.

Method One-A

This method is a complete intraoral scan where the scan flags and/or the digital verification gauges are placed in the oral cavity. The single scan would detect the gingival soft tissue along the mandibular arch, along with the necessary indicators to measure the critical features of an implant orientation. In this embodiment, the gauge can either be used in conjunction with existing scan flags, or extra implant identifying features can be integrated into the gauge that replicate the function of a scan flag. If the gauge and the scan flags are to be used together, the two devices would attach either actively or passively with each other and the location to the implant will be preserved though the coupling to the two devices. Information from each of the scans can be used to stitch together an accurate representation of the underlying edentulous space.

In this method, the single scan can be repeated multiple times depending on the number of implants in the edentulous restoration. For example, if there are 4 implants, one to six total individual scans may be required. This can be from one implant to implant location, or up to every possible implant to implant combination. For example, if the implants are number 1, 2, 3, and 4, the possible combinations include: 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4. Not all multiples may be required, and only the implant to implant distances representing the longest lengthwise distance may be necessary. The maximum critical number of scans be quantified as, [(n*(n-l)]/2, where n represents the number of implants in a single arch. (Figure 3)

Method One-B

This method begins with an initial scan of the edentulous space to capture the soft tissue and the general shape of the arch. The second scan would capture the critical implant features and distances. This can be a combination of using existing scan flags and the digital verification gauge together, or an embodiment of the gauge with integrated scan flag features as also described previously.

The scan, in this scenario can also be repeated multiple times (as depicted in Figure 4) according to the protocol as defined above in the "one scan method" section.

Method Two-A:

The three scan method also begins with an initial scan of the edentulous space. The second scan is taken with the scan flag in place, and can be repeated for each implant location. The third scan will feature the digital verification gauge, capturing the implant to implant location. This scan can also be repeated up to the maximum number of unique implant to implant positions as described above (as depicted in Figure 5).

Additional image method:

The scan methods described previously only utilize a single scanning source, in this case an intra oral scanning system. Flowever, the digital verification gauge can also be used with auxiliary inputs, either in a form of an optical camera or manual recording of the gauge system in place. In using an optical camera, various photogrammetry techniques can be utilized to automatically detect key distances from a two-dimensional image. The optical image can also be interpreted manually as part of the restoration workflow.

Technical Details:

The use of the digital verification gauge during an edentulous scan accomplish two primary tasks. The first is that the gauge can incorporate defining features along the length of the device to aid in the scanning and stitching of the multiple images required to create a full three-dimensional scan.

These defining features can be protruding shapes, space out a different distance intervals, and be between 50 microns to 1 centimeter in length.

The second task of the gauge is to serve as a calibration device and allow for additional data points for post processing of the raw scan file. The post processing can be completed either in real time during the scan or at a later point after the scan, either locally or offsite at a remote location or server. Methods of secondary analysis include a scale factor to augment the original scan based on the measurements gathered from the gauge and also fixing localized stitching errors captured in the frame scan.

The scale factor method is highlighted in figure 6, where known distances from the gages can be used to scale and "calibrate" the scan in a non-uniform manner. Flere, the entire scan file is augmented in each of the known orientations from the various scans with the gage in place. As error can be introduced in a non-linear method, the augmentation of the scan can also vary along each axis.

Alternatively, scans with the gage in place can be used to better inform the frame by frame image stitching process used by the scanning systems. Each image, or series of images, captured by the scanner is overlaid on top of the prior using a best fit algorithm. If not enough unique detail is present in each scan, additional error may be introduced during the stitching process. The known accuracy provided by the gages can help better inform these stitching algorithms to produce a final scan result that better represents the physical scanning surface. This essentially acts as a real-time offset or coefficient to modify the process during scanning.

It will be appreciated that a gauge and methods of using the gauge as described herein provide a valuable contribution to the art of verifying and improving the accu racy of 3D scans, in particu lar those used in dental arts. Alternatives to the invention as described are within the scope of the invention and will only be limited by the attached claims.