Dentistry – Prosthodontics – Preliminary casting – model – or trial denture
Reexamination Certificate
2000-12-22
2003-06-17
Lewis, Ralph A. (Department: 3732)
Dentistry
Prosthodontics
Preliminary casting, model, or trial denture
C433S049000
Reexamination Certificate
active
06579095
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to scanning of complex geometries. More particularly, the invention relates to methods to achieve bite registration of scanned images of dental study casts. The methods also have application in verifying the accuracy of mating parts, such as housings for electronic devices including cellular telephones and electronic organizers, and other housings of complex geometry such as a pacemaker housing.
BACKGROUND OF THE INVENTION
Dental study casts are an integral part of a dentist's understanding of how a patient's teeth and bite function in a static relationship. This static relationship serves three important functions. The primary function is one of a diagnostic function for interpretation of any discrepancies or problems that exist within the bite relationship. The second function is educational. For example, the study casts provide better communication as a concrete model while helping the patient understand any discrepancies that may exist in the way their teeth function in that static relationship. Third, the dental study casts serve an important medical/legal function in defining the pre-existing static bite relationship prior to the performance of any work. This work can be defined either from an oral surgical standpoint, prosthetic standpoint or orthodontic/periodontal standpoint.
Significant complications are associated with study casts, however, since the casts need to be stored for an extended period (generally seven years). For example, the storage of the study casts requires large amounts of space in humidity controlled environments, as well as extensive laboratory procedures involving OSHA guidelines and space utilization for the study casts to be constructed. In addition, a significant amount of turn-around time is required for the curing process of the plastic study casts to occur. In light of these significant constraints as well as the importance associated with having an accurate recording of the pre-existing bite relationship, there arises a need for an apparatus (or system) and method in which electronic image data can be collected from an impression to circumvent the need for storage of physical study casts.
As noted above, in order to study dental work to be performed on a patient's teeth, a working model of the teeth constructed of a plaster study cast is created. The plaster cast is based on a series of impressions taken to obtain the geometry of the teeth. To take an impression, alginate impression material is poured into a tray (i.e., an impression tray) which is then introduced into the patient's mouth for a period of time (typically one to two minutes). The impression material sets about the teeth and soft tissues forming a negative impression. The patient also bites into a soft material for registering a simultaneous imprint of the upper and lower set of teeth which records the relationship of the teeth in the upper and lower jaws respectively in three planes of space.
Once the impressions have set, they are sent to a lab to be processed into an upper and lower plaster study cast. The study casts are articulated together via the bite registration material to reproduce the bite of the patient. After construction, the study casts are returned to the dentist/orthodontist as a working study cast.
Formation of the study casts are governed by guidelines set by the American Board of Orthodontics (ABO). As illustrated in
FIGS. 1A
,
1
B, the upper and lower study casts
1
,
2
each comprise a base
3
,
3
′ and a positive impression of the patient's teeth
4
,
4
′. Each base
3
,
3
′ includes a rear surface
5
,
5
′ and a bottom surface
6
,
6
′. The bases
3
,
3
′ of the upper and lower casts
1
,
2
are machined to a precise geometry illustrated in
FIGS. 2A
,
2
B. The total height h of the two casts
1
,
2
, measured from the bottom surface
6
of the cast
1
to the bottom surface
6
′ of the other cast
2
, is about 70 mm, and machining begins a distance d of about 13 mm from the bottom surfaces
6
,
6
′ of each cast. Further, as illustrated in
FIGS. 2A and 2B
, the study casts include angled surfaces
7
,
7
′ and
8
,
8
′ that connect the rear surfaces
5
,
5
′ to the side surfaces of the casts
1
,
2
. The angled surfaces have a length l of about 13 mm. A schematic illustration of the geometry of the casts is provided at the right hand side of
FIGS. 2A and 2B
, in which the angle &agr; between each side surface and the rear surface
5
is about 70 degrees for the upper cast
1
, while the angle &bgr; between each side surface and the rear surface
5
′ is about 65 degrees for the lower cast
2
.
A serious drawback of this method is the number of labor intensive steps required to produce the study casts, the space and legal storage requirements of the study casts, and the inability to interface the study casts interactively with other diagnosis information (e.g., photographs and radiographs). Accordingly, if additional work is required, the cast fails in some way or is damaged, and/or the cast is lost, then an additional impression series must be taken. The development of a set of electronic data from the series of dental impressions wherein only a single impression need be taken for multiple interactive functions would be beneficial.
In the past, several devices have been designed for the electronic imaging of teeth. Also, other devices are known which utilize numerical data to create prototype devices. While known examples of such systems and devices follow, generally such systems do not provide the accuracy required for orthodontic work. Instead, such systems are generally useful only for crowns, fillings, etc.
U.S. Pat. No. 4,182,312 generally discloses a dental probe having a stylus which is connected through a rod to a three position transducer. Three signals are produced for indicating the position of the probe at any point to which the probe is applied. The transducers are mounted on an index tray which is adapted to be fastened to the jaw of the patient. Thus the patient's jaw becomes the origin against which all measurements are made. Contact between the tip of the stylus and the patient's tissue completes a circuit to turn on a recording mechanism which receives the transducer's outputs.
U.S. Pat. No. 4,611,288 generally discloses a method of automatically producing dental prostheses (e.g., crowns, inlays, dentures and the like) using an optical impression taken of the oral region with nontraumatic radiation. The reflected waves are transformed into numerical data which is used to operate a numerically controlled machine in the fabrication process.
U.S. Pat. No. 4,752,964 generally discloses an apparatus for producing, from an object having a three-dimensional shape, a shape equivalent or analogous to the three-dimensional shape. Here, light is irradiated to the object in an optical cutting plane. The light is picked up by an image pick-up device, and two-dimensional positions of the light are obtained in a direction perpendicular to the optical cutting plane to determine its three dimensional shape.
U.S. Pat. No. 4,935,635 generally discloses a three-dimensional point measuring system which includes a laser diode for projecting a triangulating beam at a surface to be mapped, with the beam scanned repeatedly across the surface. Photodetectors detect the position of the beam as reflected from the mapped surface, given by triangulation Z-axis or depth information. Correlation of a particular point with the position of the scanner along the scan line gives Y-axis information, or information in a width direction. The scanner and diode are mounted on a slide or platform device which moves perpendicularly to the Y axis in the direction in and out of the mouth, driven by a stepper motor, and the monitored position of the stepper motor is coordinated with the other information on each spot to yield X-axis information.
U.S. Pat. No. 5,198,877 generally discloses
Hultgren Bruce W.
Marshall Michael C.
Vadnais Timothy W.
Geodigm Corporation
Lewis Ralph A.
Merchant & Gould P.C.
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