BACKGROUND OF THE INVENTION Field of the Invention The present invention relates in general to an apparatus for forming impressions of a patient's teeth, gums and oral cavity and particularly relates to a dental tray having a rigid frame supporting a thin mesh or membrane for simultaneously making accurate impressions of a patient's upper and lower teeth as well as the bite registration therebetween. Description of Prior Developments

Dental impression trays have long been used by dentists to form impressions of various portions of a patient's mouth and teeth. Such impressions are typically used to produce dental replacement components and dental assemblies such as crowns, teeth, bridgework, dentures and other oral prostheses.

One common type of dental impression tray is used to take an impression of either an upper or lower portion of the teeth and mouth by pressing a tray filled with impression material against that area of the mouth requiring repair or reconstruction.

Another type of dental impression tray, referred to herein as a multiple impression tray, is used to take impressions of both upper and lower portions of a patient's teeth and mouth and to concurrently provide an impression of the relative positions of the upper and lower teeth during a bite. The upper impression corresponds to an impression section of maxilla, the lower impression corresponds to a complimentary section of mandible and the two complimentary impressions jointly provide an impression of the bite relationship of mandible to maxilla. A typical multiple impression tray includes an upper trough and a bottom trough, each filled with impression material such as a setable rubber base material. The tray is placed in a patient ' s mouth and the patient is instructed to bite into the impression material until the patient ' s upper and lower teeth substantially abut one another. During this procedure, the impression material is displaced and extruded between portions of the tray and the patient's teeth and gums.

The forces developed during this displacement and extrusion of the impression material have resulted in the formation of

inaccurate and distorted impressions. That is, as the impression material is pressurized during biting, it presses against the frame of the multiple impression tray causing it to flex, bend and distort in shape. If the frame does not fully recover or if it takes a permanent set, for instance during manipulation for removal from mouth or in lab production (preparation and stone moldings) an inaccurate impression will likely result. This problem is particularly noticeable with those multiple impression trays formed of highly flexible material such as plastic or thin wire.

When a dental impression is taken with such a prior art impression tray, the bending and flexing of the frame can be further exacerbated as the tray is removed from the patient ' s mouth. Due to the forces required to free the patient's teeth from the impression material, the tray is again flexed and often spread open and twisted causing deformation and distortion of the impressions.

Even after an impression has been made, it may be subject to additional distortion in the laboratory. As a technician manipulates the impression tray while producing a mold, the tray is often again flexed or bent thereby causing the movement and relative displacement of the impression material.

Although some dental impression trays have been made of metal, the particular metal used has been in the form of easily deformed wire or easily flexed sheets which provide minimal rigidity against deformation and flexing. Moreover, such trays have been known to take a permanent set once they have been bent out of shape and therefore fail to return to their original shape. In this case, the impressions taken tend to be held in a deformed condition thereby yielding unsuitable impressions. Another problem particularly applicable to multiple impression trays is the inability, in some cases, of the patient to bring the upper and lower teeth into full abutting contact due to the presence of an intervening layer of material which defines upper and lower troughs for receiving impression material. This intervening layer or membrane is required to support and hold the impression material in the upper and lower troughs of the impression tray.

A further need exists for a dental multiple impression tray which adequately supports a layer of impression material in both its upper and lower troughs, yet allows substantially free abutting contact between a patient's upper and lower teeth during the formation of a dental impression.

Still a further need exists for a dental multiple impression tray which substantially eliminates the need for piercing an intervening layer of material which supports impression material in the upper and lower troughs of the tray. Yet a further need exists for a dental multiple impression tray which eliminates the presence of sheared filaments or strands extending into a dental impression cavity carried by the tray.

SUMMARY OF THE INVENTION The present invention has been developed to fulfill the needs noted above and therefore has as an object the provision of a dental tray formed of a rigid material which resists deflection, deformation, flexing, bending and twisting during the formation of a dental impression. Another object of the invention is the provision of a dental impression tray which resists bending, flexing and deformation during its removal from a patient's mouth and during subsequent handling during laboratory work.

Another object of the invention is the provision of a dental impression tray having a rigid frame which resists flexure and which also resists plastic deformation.

Another object of the invention is the provision of a dental impression tray which adequately supports a layer of impression material in its upper and lower troughs, yet which also allows virtually free unobstructed contact between a patient's upper and lower teeth.

Still another object of the invention is the provision of a dental impression tray which substantially eliminates the need for the piercing or shearing of an intervening layer of material during the formation of a bite registration impression.

Yet another object of the invention is the provision of a dental impression tray which provides accurate dental impressions free from deformities caused by flexure, twisting or bending of the frame which supports the impression material.

fibers having a typical length of about 1 to 2-1/2 inches.

Staple fibers include natural fibers, synthetic fibers and blends of the two. Woven materials are not preferred for membrane 30.

Grooves provided for anchoring the impression material within the multiple impression tray are formed in such a manner that they do not extend across the full height of the sidewalls.

Rather, the grooves extend toward the rigid core from the top and bottom portions of the sidewalls and end short of the core so as to define a plastic reinforcing rib surrounding the rigid core. This rib can extend partially or completely around the rigid core to resist flexure and twisting of the tray.

The aforementioned objects, features and advantages of the invention will, in part, be pointed out with particularity, and will, in part, become obvious from the following more detailed description of the invention, taken in conjunction with the accompanying drawings, which form an integral part thereof .

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings :

Fig. 1 is a top plan view of a posterior dental impression tray according to the invention;

Fig. 2 is a view in partial section taken along line 2-2 of

Fig. 1;

Fig. 3 is a view in section taken along line 3-3 of Fig. 1;

Fig. 4 is a right side elevation view of Fig. 1; Fig. 5 is a left side elevation view of Fig. 1;

Fig. 6 is a view in partial section taken along line 6-6 of

Fig. 1;

Fig. 7 is a view in partial section taken along line 7-7 of

Fig. 1; Figs. 8(a), 8(b), 8(c), 8(d), 8(e) and 8(f) are views in cross section through various embodiments of a core rod according to the invention;

Fig. 9 is a view similar to Fig. 2 showing an alternate embodiment of the invention; Fig. 10 is a top plan view of another embodiment of the invention in the form of a full arch multiple impression tray;

Fig. 11 is a perspective view of an alternate embodiment of the invention; and

invention. Handle 28 may be molded with a pair of opposed recesses 32,34 as shown in Fig. 3 so as to provide a convenient grip between a dentist's thumb and index finger.

Frame 22 and membrane 30 define an upper trough 36 and a lower trough 38 for receiving and containing dental impression material 40 as shown in phantom in Fig. 2. The impression material 40 is coated over first and second opposed sidewalls 42,44 and membrane 30. Sidewalls are also molded from the plastic material 26 during the molding of frame 22. Although sidewalls are generally preferred, they are not always required for carrying out the invention.

Each sidewall 42,44 respectively includes an inner face 46,48 having a plurality of cavities or recesses 50 formed therein. For the particular posterior form of simultaneous impression tray shown in Figs. 1 through 7, and as best seen in Figs. 4, 5 and 6, the first or inner sidewall 42 is both shorter in its length L and its height H than the corresponding length and height of the second or outer sidewall 44.

The first or inner sidewall 42 is bordered along its upper edge by a generally arcuate top wall 52 and along its lower edge by a generally arcuate bottom wall 54. In a similar fashion, the second or outer sidewall 44 is bordered along its upper edge by a generally arcuate top wall 56 and along its lower edge by a generally arcuate bottom wall 58. Walls 52 and 54 of sidewall 42 are disposed generally symmetrically about core 24 as are walls 56 and 58 of sidewall 44.

A series of longitudinally spaced cavities or recesses 50 extends from top wall 52 of inner sidewall 42 along its inner face 46 and from bottom wall 54 of inner sidewall 42 along its inner face 46 in general mutual alignment toward core 24. In similar fashion, a series of cavities 50 extends from top wall 56 of outer sidewall 44 along its inner face 48 and from bottom wall 58 of outer sidewall 44 along its inner face 48 in general mutual alignment. As seen in Fig. 2, cavities 50 do not extend completely across the respective sidewall inner faces 46,48 but rather terminate before reaching the central core 24. In this manner, a first longitudinally extending rib 60 is defined along inner face

of titanium and aluminum may be used for core 24. Moreover, core 24 may be fabricated from reinforced fiber materials such as carbon-carbon and aramid fibers.

In order to provide even greater rigidity and structural integrity to the impression tray, the cross section of core 24 is designed to provide the greatest resistance to bending and flexure in the plane defined by membrane 30. That is, core 24 is designed in such a manner so as to resist the relative movement of sidewalls 42 and 44 toward and away from one another so as to prevent distortion of the impression material during the formation of an impression. This in turn minimizes the flexure of the frame 22 toward and partially away from the sides of a patient's teeth during bite registration.

Referring again to Fig. 2, as well as to Figs. 6 and 7, and particularly to Fig. 8(a) , core 24 may be formed with a rectangular cross section having its major dimension or largest pair of sides extending generally parallel to a plane defined by the intersection of membrane 30 with frame 22. Stated another way, the major dimension of core 24 extends transverse to the sidewalls in a direction generally parallel and coplanar with a plane which separates the upper trough 36 from the lower trough 38 symmetrically with respect to frame 22 and core 24. The minor dimension of core 24 extends generally transverse to the plane of the membrane between the upper and lower troughs. In this manner, the minor dimension or shortest sides of core 24 face one another across the gap between sidewalls 42,44 which define the sides of troughs 36,38. This orientation of the short sides or minor dimension extends generally transverse to the above-noted plane and membrane. This orientation of core 24 provides the greatest resistance to transverse bending of frame 22 toward and away from the sides of a patient ' s teeth during bite registration and reduces the chance of forming an inaccurate or distorted dental impression.

Alternate cross sections for core 24 taken for example through arcuate end portion 25, are shown in Figs. 8(b) , 8(c) , 8(d) , 8(e) and 8(f) . Fig. 8(b) depicts a rectangular core 24 with chamfered edges. Fig. 8(c) depicts an oval or elliptical core 24 and Fig. 8(d) depicts a core with flat upper and lower surfaces interconnected by semi-circular sides. Other sections

tray 20(b) virtually identical to tray 20 of Fig. 1. Fig. 12 provides additional details of trays 20 and 20(b).

There has been disclosed heretofore the best embodiment of the invention presently contemplated. However, it is to be understood that various changes and modifications may be made thereto without departing from the spirit of the invention.