1. 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.
2. 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.
The presence of this intervening material, even though it may be quite thin, can prevent the required contact between the upper and lower teeth and thereby prevent an accurate impression and reproduction of the patient's bite registration. The thicker the intervening material, the less likely will be the reproduction of an accurate bite registration between maxilla and mandible.
An example of such prior art support material is a gauze or a meshed material which provides support for the impression material yet also allows the impression material to flow across and through it, preferably from the upper trough to the lower or bottom trough. Even though this mesh or gauze material is relatively thin, it still can prevent the upper and lower teeth from meeting.
One prior conventional approach to solving this problem has been to use mesh material having wide spacings between adjacent filaments or strands. This wide spacing allows the teeth to spread the filaments apart and thereby meet between the filaments. This in turn allows full penetration of the impression material and accurate bite registration.
Another approach to solving this problem relies on the use of a nonwoven fabric material to support the impression material. This nonwoven fabric material is formed of staple fibers having predetermined lengths. As such, it is generally thick and dense and must be penetrated and pierced by the teeth.
When this material is pierced and sheared, its cut ends, which are taut, can fold into the impression cavity adjacent and between the teeth. These ends then extend into the impression cavity after removal from the patient's mouth and act as foreign objects in the resulting mold. This can result in a defective, deformed or substandard prosthetic molding.
Accordingly, a need exists for a dental impression tray which includes a rigid structure resistant to deflection, deformation and twisting during and after the formation of a dental impression.
A further need exists for a dental multiple impression tray which is formed of a rigid material and which resists plastic deformation during the forming of dental impressions.
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.