Orthodonic Device

Abstract

A jig for the fabrication of orthodonic casts which comprises first and second plates separated by several vertical posts that maintain a fixed vertical spacing between the plates. The plates support model molds in opposed relationship. An alignment bracket is also provided for vertical alignment of the first model. The jig is used by placing plaster in one mold, embedding the first of a set of maxillary and mandibular models, preferably the mandibular, of a patient's teeth in the plaster and aligning the model with the alignment bracket to insure that the occulusion plane lies about midway between the finished casts. The mold on the second plate is then filled with plaster, the second model, preferably the maxillary, is temporarily attached to the model in the hardened cast and the assembly is inverted and placed over the plate with the soft plaster by engaging the vertical posts between the plates. This presses the second model into the soft plaster to a uniform depth and insures the preparation of precisely shaped casts.

Description

DESCRIPTION OF THE INVENTION

Orthodonic casts are commonly used in dental offices as permanent records of a patient's teeth. The casts are often displayed in the office and accordingly, there is a need for the preparation of uniformly shaped and neatly appearing casts. The casts are prepared by first forming plaster models of the pathient's teeth from an impression mold that has been formed on the patient. For strength and ease of storage, these models are then generally cast in a plaster base to prepare the final orthodonic cast. Presently, models are hand formed into the cast which is trimmed into final shape by sawing or grinding. The hand labor is tedious and is not precise so that variations occur in the shape and size of the casts.

Some attempts have been made to introduce uniformity by jigs for holding molds for the casts; however, these prior approaches have not been widely accepted because the jig structure has been too cumbersome and unwieldy, In U.S. Pat. No. 2,545,249 a jig is described having top and bottom plates, vertical posts with adjustable sliding clamps and a vertical back plate that aligns the plates and offers attachment for the cast molds. Although uniformly shaped casts can be made with the jig, the back plate obstructs access to the molds and renders it difficult to make minor adjustments in the models or to remove excess plaster during the casting operation. The use of adjustment clamps on the vertical posts also needlessly complicates the setting of the jig for the casting operation.

It is an object of this invention to provide a simple and direct method for forming orthodonic casts.

It is also an object of this invention to provide an apparatus for use in the method.

It is a further object of this invention to provide said method and apparatus with the facility to prepare uniformly shaped casts.

Other and related objects will be apparent from the following description of the invention.

The preceding objects are achieved by the apparatus and use thereof of this invention. The apparatus comprises first and second generally flat plates each of which support, in a substantially centric position, a dental base mold having a generally flat-bottomed, cup configuration with a flat base and upright walls defining an enclosure for surrounding a dental model; a plurality of posts orthogonal to said plates supported on one of said plates and bores in the other of said plates to receive the free ends of the posts with fixed vertical indexing means carried by one of said plates and said posts to index the plates at a fixed and predetermined vertical separation. Also included in the device is a bracket having a crosspiece supported at a fixed vertical height above the base molds.

The apparatus is used by forming the usual models of the patient's teeth and then filling one of the base molds with plaster and centrically placing a model in the soft plaster. The alignement bracket is then passed over the model to force it to the correct vertical position in the soft plaster. Plaster is then placed in the other mold, the remaining model is temporarily secured to the first model and the vertical posts are placed between the plates while inverting the assembly of hardened cast and models over the mold containing the soft plaster. This embeds the remaining model to the correct depth in the soft plaster and results in precisely shaped casts which can be removed from the molds after the plaster has hardened. The molds can be cleaned for reuse or, in one embodiment, can be discarded.

The invention will now be described by reference to the FIGS. of which:

FIG. 1 shows the jig of the invention;

FIG. 2 shows the first steps in the method of forming the casts with the jig;

FIG. 3 shows the final steps in the method of forming the casts;

FIG. 4 shows an alternate alignment bracket; and

FIG. 5 shows an alternate, disposable plate and cast mold for use in the invention.

Referring now to FIG. 1, the jig comprises a first plate 10 and a second similar plate 12 from which depend upright posts 14. The plates support cast molds 16 and 17 which are generally flat-bottomed, cup-shaped molds having a flat base 18 with upright walls defining a polygon with diverging sidewalls 23 and 25, converging rear walls 27 and a posterior wall 20 perpendicular to a longitudinal axis passing through the central front edge 21. The particular shape of the cast mold is not critical and any similarly shaped mold can be used; however, the particularly illustrated mold is preferred because it readily accommodates most dental models and results in a neatly appearing cast. The molds 16 and 17 are conventional in construction and are formed from a flexible plastic, e.g., soft rubber, polyethylene, etc.

The molds 16 and 17 are secured to the base plates 10 and 12 by cutting a polygon cavity in the center of the plates as shown at 24. The cavity 24 is sized to conform to the periphery of the base of the molds so that the molds can be slipped into the cavity in a snug fit where they are retained until forcibly ejected.

The jig is used in the fabrication of uniform casts in the manner shown in FIGS. 2 and 3. Conventional wax impressions of the patient's teeth are made using an impression tray and plaster models 30 and 40 of the patient's mandibular and maxillary teeth are prepared. Preferably, the models are formed with a thin base but still retaining some peripheral tissue roll 31. After the plaster has hardened, the models are removed from the impression mold and the buccal and labial surfaces of the models are covered with a protective strip of adhesive tape 33. The bottom of the models can then be scored and, prior to use, can be moistened to facilitate adhesion of the model to the cast.

Mold 17 is then filled with plaster 32 and model 30 is placed centrically in the mold. Some excess plaster will ooze from the top of the mold during this operation and it can be readily removed from the mold and the plate. The vertical alignment of the model in the cast is then made with the alignment bracket which has upright posts 34 of a predetermined length. The bracket is placed on the work table with the posts resting on the table and the crossbar 36 straddling the cast as shown in FIG. 2. The bracket is then carefully moved across the model which gently presses the model into the soft plaster so that bar 36 clears the top of the model. In this fashion, an exact vertical alignment of the model 30 in mold 17 can be obtained.

The height of posts 34 of the bracket is approximately half the height of posts 14 of the casting jig so that the occusal plane of the models will be cast midway between plates 10 and 12 in the final casting operation.

After the plaster in mold 17 has hardened, tape 33 is stripped off the cast and any excess plaster not previously removed is carefully broken off the cast. The remaining model, e.g., the maxillary model 40 is then temporarily secured to the hardened cast. The correct or centric positioning of the maxillary is insured by the use of wax bite guides 41 which are placed between the models which are then occluded as shown in FIG. 3. To retain the occlusion, rubber bands 42 and 43 are placed about the model and the mandibular cast.

Mold 16 is then placed in plate 10 and filled with plaster 44. The assembly of the mandibular cast, maxillary model 40 and mold 17 in plate 12 is inverted over plate 10 and posts 14 are guided into engagement with bores 22 in plate 10 to rest on the work surface. This forces model 40 into the correct vertical and horizontal alignment in mold 16. After the plaster 44 has hardened, bands 42 and 43 can be cut and removed and the casts can be removed from the molds which are then cleaned for reuse. The bands can be slipped between the base of the mold and plate 17, or attachment means such as hooks 47 can be provided as shown in FIG. 2.

FIG. 4 illustrates an alternative alignment bracket which can be used with plate 12 and its upright posts 14 in the method shown in FIG. 2. In use of this bracket, sleeve 62 is slid over the anterior post 14 so that the end of the sleeve 62 rests on plate 12. Crossbar 64 can then be swung over model 30 while gently forcing the model into the soft plaster 32 until the bar 64 clears the top of the model. A handle 66 can be fastened to bar 64 with rivet 68 to provide a grip on the bar while it is moved across the model. As with bracket 36, the crossbar 64 is secured to the sleeve 63 at a predetermined height so that model 30 is positioned in mold 17 at approximately half the distance between molds 16 and 17 in the assembled jig.

FIG. 5 illustrates an alternative plate having an integral mold formed with base 54 and walls 52 which are substantially of the same configuration as previously described with regard to FIG. 1. Plate 50 and the mold are preferably formed of a cellular or foamed plastic such as polystyrene foam or expanded polystyrene beads. Other foamed plastics such as foamed polyurethanes or foamed polyolefins can also be used. Of these, the expanded polystyrene beads are preferred for their low cost, strength and ease of separation from the plaster casts. Polystyrene foams having densities from 1 to about 2 pounds per cubic foot, preferably of about 1.5 pounds per cubic foot are particularly useful. The plate 50 is formed by conventional molding of the polystyrene beads by expanding the beads against a metal die to form the mold and plate 50 in a single operation. Preferably, the die has bosses which provide the alignment bores 56 in the plate 50 to receive the ends of the vertical alignment posts 58. A flange or washer 60 can be placed on each end of these posts as shown so that the flange surface bears against the surface of plate 50 when the posts are inserted in the bores 56. The low cost of the foamed plastics permits the plate 50 to be discarded after its use or, if desired, the plates 50 can be retained as protective covers for the casts.

The invention has been described with reference to illustrated modes of practice which presently constitute the best mode of practice contemplated. It is of course apparent that various changes in the shape and structure of the invention can be made without departing from the scope of the invention which is defined by the following claims.

Claims

I claim:

1. A device for the fabrication of precisely uniform orthodonic casts comprising first and second generally flat plates, a pair of dental base molds positioned substantially centrically, one of each of said plates with their bases engaged on said plates, said molds having a generally flat-bottomed cup configuration with a flat base and upright walls defining an enclosure for surrounding a dental model; a plurality of posts orthogonal to said plates and supported on at least one of said plates, means carried by the other of said plates to engage the free ends of said posts whereby to precisely orient said other of said plates to the plate supporting said posts in both vertical and horizontal planes and thereby precisely orient said molds to each other.

2. The device of claim 1 wherein said molds are removably secured to said plates.

3. The device of claim 1 wherein said plates are triangular in shape and are separated by a post positioned at each apex of the triangular plates.

4. The device of claim 1 in combination with an alignment bracket comprising a crossbar and an upright crossbar support post secured thereto to position said crossbar approximately midway between said first and second plates.

5. The device of claim 1 wherein said plates are formed of a rigid foamed plastic.

6. The device of claim 5 wherein said foamed plastic comprises expanded polystyrene beads.

7. The method of forming orthodonic casts that comprises: placing a dental model in unobstructed open view in soft plaster maintained in a cast mold affixed to a first generally flat plate, embedding said model in said plaster at a predetermined height by passing the crossbar of a bracket having at least one leg corresponding to said predetermined height over the model while pressing said model into said plaster to permit said bar to clear the top of said model, occluding the opposite model to the aforesaid model by positioning wax bites between the models and bringing said models into occlusion, temporarily securing said models in said occlusion, inverting the assembly of said first plate and said occluded models above a second, generally flat plate bearing a second mold filled with soft plaster and forcing said opposite model into the soft plaster in said second mold while positioning vertical posts of predetermined height between said first and second plates to align the horizontal and vertical positions of said models in said molds.