Patent Application
20090254299
The present invention relates to using temporary dental prostheses, formed within the mouth of a patient, for deriving morphological information used in the fabrication of fixed dental prosthetic devices, such as crowns and bridges, for purposes of restorative dentistry.
Current practice in the field of restorative dentistry entails taking an impression in the mouth of a patient in order to provide an exact mold for a crown or a bridge. The dentist provides the impression to a dental lab where a template is cast that may then be digitized for fabrication of a permanent prosthesis using three-dimensional CAD/CAM techniques. The permanent prosthesis is then shipped to the dentist and installed in the patient's mouth. For the duration of this process, which may typically take a week or two, or even three, the patient is fitted with a temporary prosthesis fashioned by the dentist. Temporary (or interim) prostheses (generally referred to as “temporaries”) are typically made of an acrylic material and serve to protect dental surfaces that have been prepared to receive the final restoration and to prevent damage by food or microorganisms and sensitivity to hot or cold. The current process as heretofore described is, however, fraught with inconvenience, since it entails the physical shipment of an impression from the dentist's office to the dental lab, moreover, a loss of precision is inherent in the process of successive replication by taking an impression, casting a template, and then subsequent digitization. Improvements in precision and convenience are thus to be desired. Additional source imprecision is due to the retraction cord used in some cases to open the gingival sulcus prior to taking the impression.
Definitions: As used herein and in any appended claims, the terms “dental prosthesis” and “restorative” will be used in a general sense, to encompass crowns, or bridges, implants, veneers, or any other restorative structures of that class, as well as abutments employed to retain implants. Moreover, any use of any of the foregoing terms is to be understood as encompassing the entire class of dental prostheses, unless the context dictates otherwise.
In accordance with preferred embodiments of the present invention, systems and methods are provided for obtaining data requisite for fabrication of a dental restorative prosthesis. The method may have steps of:
In accordance with an alternative embodiment of the invention, the restorative dental prosthesis is fabrication on the basis of the three-dimensional data. Information may also be provided to a dentist at the site of patient treatment, where the information is based upon the three-dimensional digital data characterizing the temporary. Such information may include the thickness of the prosthesis in different portions of the prosthesis, prosthesis end-line quality, and the insertion axis of the prosthesis.
In accordance with other embodiments of the invention, the step of obtaining three-dimensional data includes measuring distances relative to at least one fiducial position of points on the exterior and interior surfaces of the temporary. Measuring distances may include measuring distances along paths collinear with an optical axis of a non-contact distance probe. The measurements may be performed intraorally. The temporary may be an interim prosthesis, and, more specifically, may be a crown or a bridge. The step of measuring distances may include measuring multiple sides of the temporary and co-registering data obtained on each side. Such registration may be done by external registration features on a holder. The method may also include measuring distances and the three dimensional shape of a pickup impression in which the temporary is embedded.
In accordance with another aspect of the present invention, a computer-implemented method is provided for supplying specifications for fabrication of a dental prosthesis. Such a method has steps of:
In accordance with further embodiments of the invention, a prosthesis is fabricated on the basis of the prosthesis design. Input may be received for editing the prosthesis design, and the computer-implemented method may further comprise editing the prosthesis design on the basis of the input received.
In accordance with yet another aspect of the invention, a computer program product is provided. The computer program product, for use on a computer system that supplies specifications for fabricating a dental prosthesis, has computer readable program code that includes:
The invention will more readily be understood by reference to the following description taken with the accompanying drawings which depict the used of impression scanning to characterize an implant in a patient's mouth. The drawings are intended to provide a better understanding of the present invention, but are in no way intended to limit the scope of the invention.
Preferred embodiments of the present invention are described in the following pages. Use of scanning and digitization, by whatever method, of dental structures or of impressions or templates, may be further appreciated by reference to the description provided in U.S. Pat. No. 7,375,827, issued May 20, 2008, entitled “Digitization of Undercut Surfaces Using Non-Contact Sensors,” and US Published Patent Application No. 2007/0293769, entitled “Double-Sided Measurement of Dental Objects Using an Optical Scanner,” published Dec. 20, 2007. Both of the foregoing publications are incorporated herein by reference in their entirety. Additionally, co-pending U.S. patent application Ser. No. 12/401,668, filed Mar. 11, 2009, entitled “Method and Apparatus for Intra-oral Digitization Scanning,” is incorporated herein in its entirety.
The customary course of restorative dentistry begins in the dentist's office. The first step entails taking a preliminary impression of a patient's mouth, typically before anesthesia is given, so as to ensure that the preliminary impression accords with the normal bite of the patient. Surfaces of teeth are prepared to receive the crown or veneer, etc., and then, either using the preliminary impression, or else directly inside the patient's mouth, the dentist forms a “temporary.”
Definition: As used herein and in any appended claims, a “temporary” is used broadly to encompass any provisional structure formed in the mouth of a patient, the inner surface of which conforms to the complementary structure in the mouth of the patient such as an underlying prepared tooth surface or abutment. A temporary thus includes an “interim prosthesis” or “temporary restoration” or any other dental prosthesis, either fixed or removable, that serves for a limited period of time, after which it is replaced by a definitive prosthesis that is designed for long-term use. It also refers to a mold or cube that acquires the interior shape conforming to the base upon which a definitive prosthesis will be cemented.
The temporary may be formed from any of a variety of plastic reshapable materials, which vary in the advantages they provide under differing sets of circumstances. Some typical temporary materials, provided here by way of example and without limitation, include the distinct classes of polymethyl methacrylate (PMMA) and polyethyl methacrylate (PEMA) acrylics that polymerize to form reasonably strong structures that are readily smoothed and polished. Additionally, bis-acryl resin composites may be used as temporary materials, and, like any material used in the formation of temporary prostheses, are within the scope of the present invention.
The material used for a temporary is typically formed by mixing powder and liquid, and the material is allowed to cure until it achieves a putty consistency, at which time the dentist inserts it into the patient's mouth over the tooth that has been prepared to receive it. The raw material for formation of a temporary may also be supplied to the dentist preformed into one of a number of starting shapes, to facilitate the process of forming a finished interim prosthesis.
Definition: As used herein and in any appended claims, the word “fashion,” in its various grammatical forms, refers to the process of advancing an object towards its final shape. Thus, the dentist may be said to be “fashioning” a temporary when he advances its formation relative to a starting shape.
The dentist carefully shapes the temporary, using a variety of trimming and polishing techniques suitable to the material employed. Shaping is critical so as to conform the interior surface of the temporary to the underlying prepared tooth, and so as to conform the exterior surfaces of the temporary to the closure opposite, i.e., to achieve proper occlusal contact with the surface of the opposing tooth. Additionally, margins of the temporary are trimmed to allow proper spacing relative to neighboring dental and maxillofacial surfaces.
It is sometimes the case (such as in situations involving more than few teeth are involved or for aesthetic zone treatment) that a temporary is preliminarily fabricated by a dental lab before the dental appointment where the patient's teeth are trimmed. Typically, on the basis of a preliminary impression, the lab prepares a temporary prosthetic that is like a shell, with the inner part empty and ready to be relined. Lab temporaries may be more finely detailed, stronger, and longer lasting than temporaries fashioned by the dentist in situ, and are typically of higher aesthetic quality. That said, the scope of the present invention encompasses temporaries formed in this manner or any other, and interim prosthetics that are relined in order to provide precisely detailed margin line and surfaces.
Under certain circumstances, an impression may be taken of the patient jaw with the temporary in place on its retaining tooth (or teeth, as in the case of a bridge). This impression serves as a “pickup impression” in that the impression is removed from the patient mouth with the temporary retained in the impression.
In accordance with preferred embodiments of the present invention, instead of taking an impression for use as an intermediary for fine detailed three-dimensional information of the prepared tooth, the temporary itself is optically scanned, at the very location where the dental patient is being treated, in order to derive high-quality three-dimensional digital data from which a definitive prosthesis is fabricated using standard techniques.
Moreover, in accordance with further embodiments of the present invention, the pickup impression itself may also serve as a basis for deriving three-dimensional data by optical scanning at the dentist's office, both with the temporary embedded in the pickup impression, and with the temporary removed, in order to acquire the complementary surface structure with high fidelity and resolution.
Scanning of the temporary may be performed, within the scope of the present invention, using any sort of contact or non-contact surface characterizing equipment. However, it is to be noted that use of a collinear probe, such as a conoscopic probe, is desirable, and, in some cases, essential, because of the sharp angles, vertical surfaces and undercuts and deep cavities inherent in the morphology of crowns, particularly their recessed interior surfaces that envelop prepared underlying teeth. This feature is particularly prominent with respect to front teeth, and requires that the scanning sensor allow for the measurement of deep ‘pits.’
One limitation imposed by existing coordinate measuring machines (CMMs) is due to the fact that even the most versatile optical sensors are unable to digitize on vertical or very steep angles measured with respect to the optical axis (or ‘line of sight’) of the probe. ‘Vertical’, in this case, refers to the surface of the scanned body lying parallel to the optical axis of the probe. An ‘undercut’ refers to a negative angle relative to the line of sight.
Surfaces characterized by steep angles, such as prevalent in interim prostheses, may be advantageously mapped by means of a conoscopic scanning system of the sort provided by the Optimet Dental Scanner of Optimet (Optical Metrology) Corporation. Such a system is described in detail in U.S. Pat. No. 7,375,827 (Sanilevici, et al.), and one embodiment is now described with reference to
A distance probe 1 is typically characterized by an optical axis or line of sight, designated, in
Line of sight 14, and the laser beam coaligned with it, is bent by one or more folding mirrors 3 so that the line of sight impinges upon the surface of scanned body 6. It is to be understood that the optical path shown is described for purposes of convenience and that more complex optical paths, entailing any other optical elements, are within the scope of the present invention and described herein and as claimed in any appended claims.
In accordance with preferred embodiments of the invention, a plurality of folding mirrors 3 are mounted on a multi-position actuator 2 in such a way to allow laser beam bending in different directions. Multi-position actuator 2 may be a carousel supporting multiple mirrors that is rotated about a central axis 16. More particularly, mirrors 3 may be mounted on a polygon, such as the pentagon shown in
Measurements of distances to the surface of body 6 along line of sight 14 are collected and processed separately for each of the mirrors 3, thus forming a distinct ‘cloud’ of points attributable to that mirror. Merger (or ‘stitching’) of the respective clouds of points to form a single consistent image is discussed below.
In the case where mirrors 3 are disposed at preset angles, after assembly an accurate measurement of each bending angle is performed for each position of the actuator. The measured angle values are transferred to the software and used for the coordinate transformation from a coordinate system based on motion of the scanning system 7 to an orthogonal coordinate system. Since the line of sight is incident onto the surface of the object at an angle that is specific to each mirror position, a separate coordinate system attaches to each position of the mirror until coordinates are transformed to an orthogonal system.
Desired bending angles may be calculated for a particular application in order to cover the desired undercut angle and leave enough working range. Mirrors 3 may then be set accordingly. High bending angles will reduce the actual working range relative to vertical position and require larger travel for the moving stages.
It is to be noted that the main scanning movement (typically X-Y) may be performed either by the measured object and reference samples fixed on a mounting table or, as a matter of design choice, by the sensor mounted together with the folding mirrors on a common support. Both equivalent motions are within the scope of the present invention.
Data from the measurements described herein are advantageously gathered and processed automatically and without human intervention. In order to increase accuracy of measurement, a fixed reference object (sphere 4, V prism 5) may be scanned before the part is scanned, enabling an accurate calibration of the beam position relative to the X-Y scanning system 7.
All the gathered data for each mirror position is processed first by applying the angular correction for the profiles to orthogonal coordinates and then an origin shift, using the spherical fit to translate the local coordinates to the same origin in a frame of reference fixed with respect to the body. Since the measured object 6 remains fixed (relative to the mounting device, carriage 12) for the entire measurement cycle, the actual X, Y coordinates of each point are the same for all beam positions, thus simple robust mathematical methods are advantageously employed for data processing in a totally automatic cycle.
Using the foregoing, or another, scanning modality, two sides of the temporary are scanned and registered to form a complete set of three-dimensional data from which a definitive prosthesis may be fashioned at a dental laboratory. Registration may be performed using external registration features on a holder which may also be scanned. Two-sided measurement and subsequent registration is described in U.S. patent application Ser. No. 11/829,471, which is incorporated herein by reference.
In accordance with other embodiments of the present invention, characterization of the three-dimensional structure of the temporary may be performed intraorally, such as by means of an intraoral 3-D camera.
Referring to
In the manufacture of the definitive prosthesis, data provided by the dentist on the basis of scanning either the temporary or the pickup impression (or both) may be supplemented to include more detailed morphologies, on the basis of data obtained from an analog tooth (on the opposite side of the patient's jaw) or from a library of tooth anatomy. Moreover, account may be taken of a spacing required for interposition of bonding material and for connection to adjacent teeth in the case of bridges, etc. All such modification and enhancement may be performed using CAD-type software.
It is to be understood that, within the scope of the present invention, other information may be obtained in the mouth of the patient and scanned to provide further data for fabrication of a precise prosthetic at a remote site. For example, a mold or cube conforming to the prepared underlying tooth or abutment may be scanned, using technology capable of scanning steep vertical angles, as described above, in order to enable remote fabrication of a prosthesis.
One or more of the following advantages may be realized due to practice of methods in accordance with the present invention:
In alternative embodiments of the present invention, the disclosed methods for deriving data for the fabrication of a dental prosthesis may be implemented as a computer program product for use with a computer system. Such implementations may include a series of computer instructions fixed either on a tangible medium, such as a computer readable medium (e.g., a diskette, CD-ROM, ROM, or fixed disk) or transmittable to a computer system, via a modem or other interface device, such as a communications adapter connected to a network over a medium. The medium may be either a tangible medium (e.g., optical or analog communications lines) or a medium implemented with wireless techniques (e.g., microwave, infrared or other transmission techniques). The series of computer instructions embodies all or part of the functionality previously described herein with respect to the system. Those skilled in the art should appreciate that such computer instructions can be written in a number of programming languages for use with many computer architectures or operating systems. Furthermore, such instructions may be stored in any memory device, such as semiconductor, magnetic, optical or other memory devices, and may be transmitted using any communications technology, such as optical, infrared, microwave, or other transmission technologies. It is expected that such a computer program product may be distributed as a removable medium with accompanying printed or electronic documentation (e.g., shrink wrapped software), preloaded with a computer system (e.g., on system ROM or fixed disk), or distributed from a server or electronic bulletin board over the network (e.g., the Internet or World Wide Web). Of course, some embodiments of the invention may be implemented as a combination of both software (e.g., a computer program product) and hardware. Still other embodiments of the invention are implemented as entirely hardware, or entirely software (e.g., a computer program product).
The described embodiments of the inventions are intended to be merely exemplary and numerous variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims.
The present invention claims the priority of U.S. Provisional Patent Application 61/042,425, filed Apr. 4, 2008, and incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61042425 | Apr 2008 | US |
