GB2297940A - Dental mould - Google Patents

Abstract

There is provided a mould 110 to facilitate efficient manufacture of denture impressions and replicas which is adapted to be complementary with a standard dental impression tray 100 and to form a substantially closed mould when aligned therewith. Generally the mould of the invention is substantially horseshoe-shaped and of U-shaped cross-section. It may optionally have an opening to permit entry of casting material.

Description

"Dental Mould" This invention relates to moulds, and relates more particularly but not exclusively to impression trays for use in dentistry.

Impression trays (also known as "dental trays") are deep-rimmed horseshoe-shaped trays which are used as open-topped moulds to obtain a negative mould of teeth by partially filling the tray with a plastic material (eg a silicone putty), impressing the teeth into the plastic material (eg by biting), and causing or allowing the plastic material to cure so as to retain an impression of the teeth.

A denture is a multi-tooth dental prosthetic substituting for part or all of the set of natural teeth of an upper jaw or a lower jaw. A denture may incorporate a plate, eg a palate plate in an upper denture. The formation of a negative mould of the denture requires an impression of the top and bottom of the dentures and is normally obtained by pressing the dentures into a dental tray filled with moulding material, such as silicone putty. Silicone putty is then spread over the exposed area of the dentures (optionally the dentures are first covered with a layer of emulsion to aid separation) and a second tray is then pressed over the putty-covered dentures (see Fig.

6).

Once the negative mould has been produced, the dentures are removed by careful cutting through the putty and the negative mould is then realigned before being filled with a molten casting, such as wax at 1000C, to provide a positive replica of the dentures. For the positive replica to be accurately produced, it is essential that the two halves of negative mould are exactly aligned.

However, conventional dental trays have rims whose free edges are contoured for physiological compatibility with the mouth so that a pair of such trays have substantial and irregular gaps between the nominally adjacent edges when aligned (see Fig. 6). Consequently the correct mutual alignment of a pair of conventional dental trays requires considerable manipulative skill, and must be undertaken by a technician or dentist to ensure that correct alignment is obtained. Moreover, the trays never provide positive confinement of the putty or other material(s) held within them because of the back-to-back gaps.

It is an object of the invention to provide a mould which is adaptable for use as a dental impression tray, and which obviates or mitigates the above-described disadvantages of the prior art.

The present invention thus provides a mould adapted to be substantially complementary to a dental tray. The mould and dental tray fit closely together to form a closed mould suitable for forming impressions or replicas of dentures.

Desirably the mould according to the invention may be adapted to be substantially complementary to either a dental tray for taking impressions of the upper jaw or to a dental tray for taking impressions of the lower jaw.

The mould according to the present invention may conveniently be substantially horseshoe-shaped. The term "horseshoe-shaped" is used herein to refer to an item where the two legs of the horseshoe are separated by a space between them ("open" horseshoe) and also to an item having the outline of a "U" and including the area spanning widthways ("closed" horseshoe). Thus, for example, the mould may be of an "open" horseshoe shape of the general type illustrated in Figures 9, or 11 to 17 or alternatively may be of a "closed" horseshoe-shape of the general type illustrated in Figures 25 and 26.

Optionally the cross-section of the mould may be substantially "U"-shaped.

The mould may advantageously possess an opening to permit entry of casting material. The exact location and size of this opening is not critical, although for convenience particular positions and sizes may be preferred.

In one embodiment the legs (optionally including the area spanning between the legs) of the horseshoe-shaped mould may be closed by an end wall. Preferably however the end wall may have an opening, such as a hole or slit, to permit introduction of molten wax or other suitable casting material for production of a positive copy of the dentures or teeth from the negative impression.

According to one aspect of the present invention the mould may be a closure for use with an open tray (for example a tray capable of independent use as an impression tray), the closure having bounding edge(s) shaped and dimensioned to be substantially complementary to a bounding edge or edges of the tray whereby the closure is usable conjointly with the tray to produce a closed mould therewith. Thus, use of the closure will convert the otherwise open tray to a substantially closed mould when the tray and the closure are mutually conjoined with the respective bounding edges of the tray and of the closure mutually aligned edge-to-edge.

According to another aspect of the present invention there is provided a mould comprising a first mould part and a second mould part, the first mould part may be capable of independent use as an impression tray or other open mould, the second mould part having a bounding edge(s) shaped and dimensioned to be substantially complementary to a bounding edge or edges of the first mould part whereby the second mould part is usable conjointly with the first mould part to form a substantially closed mould when the two mould parts are mutually conjoined with the respective bounding edges of the two mould parts mutually aligned edge-toedge. Optionally, the two mould parts may be hinged together and in this embodiment it may not be convenient to use the first mould part alone as an impression tray.

In this embodiment, the second mould part may be a deep-rimmed horseshoe-shaped mould, as described above.

The tray or first mould part may have a bounding edge or edges, which are irregular and/or non-planar. The tray or first mould part may be a conventional dental tray for taking impressions of the teeth from either the upper or lower jaw.

The mould of the present invention may preferably be particularly adapted for use with conventionally-shaped dental impression trays.

In both aspects of the present invention, one or more clips or other closing means may be provided for use with the closed mould to hold the mould closed. Any form of retaining the two trays in alignment together may be used.

Desirably the mould or mould parts according to the present invention may be provided with means to retain the putty therein. Suitable retaining means include internal ridges, rims or indentations within the closure or mould part or alternatively a number of aperatures may be present through which small amounts of putty are pressed thus retaining the putty within the mould or mould part.

Any size, shape or number of retaining means may be used provided that the putty is sufficiently retained within the mould or mould part.

As will be apparent to the skilled practioner the size, shape, thickness and weight of the mould or mould part of the present invention may be varied as required and as a matter of routine selection. The colour of the material forming the mould and mould part is simply a matter of personal preference.

According to another aspect of the present invention there is provided a cooling arrangement for use with a closed mould provided by the present invention, the cooling arrangement comprising an open-top container having resilient means disposed therein, the resilient means being such as to hold the closed mould at least partially submerged in liquid coolant held in the container. The resilient means preferably comprises a plurality of resilient fringes each secured at one end to one or other of two opposite edges of the container and extending towards the respective opposite edge such that a mould inserted into the container will be held between free ends of at least some of the resilient strips.

In a further embodiment the present invention provides a method of producing an impression of dentures, said method comprising: a) obtaining a dental impression tray and at least partially filling said tray with moulding material; b) at least partially filling a mould as described above with moulding material; c) locating said dentures in one of said tray and said mould and aligning the other of said tray and said mould therewith; d) pressing said tray and said mould together edge to-edge to completely surround said dentures with moulding material; e) allowing said moulding material to cure; and f) cutting through said cured moulding material to remove said dentures and removing said dentures.

To form a replica of the dentures the following additional steps may be carried out: a) re-aligning said tray and said mould and introducing casting material into the volume previously described by said dentures; b) allowing said casting material to cure to form a denture replica; and c) removing said denture replica.

Embodiments of the invention will now be described by way of example, with reference t@ the accompanying drawings wherein: Fig. 1 is a plan view of a conventional dental tray adapted for taking impressions of the teeth in the lower jaw; Fig. 2 is a front elevation of the tray of Fig. 1; Fig. 3 is a perspective view, from above and to the right, of the tray of Fig. 1; Fig. 4 is another perspective view, from above and to the front, of the tray of Fig. 1; Fig. 5 is a further perspective view, from above and to the left, of the tray of Fig. 1; Fig. 6 depicts how two conventional dental trays are brought together; Fig. 7 is a left side view of a closed mould in accordance with one aspect of the invention;; Fig. 8 is a right side elevation of one form of complementary mould in accordance with another aspect of the present invention; Fig. 9 is a perspective view, from above and to the right, of the complementary mould of Fig. 8; Fig. 10 is a fragmentary detail showing a modification of the complementary mould of Fig. 9; Fig. 11 is a perspective view, from above and to the front right, of another form of complementary mould in accordance with the invention; Fig. 12 is another perspective view, from above and to the rear left, of the complementary mould of Fig. 11; Fig. 13 is a further perspective view, from above and to the right, of the complementary mould of Fig. 11; Figs. 14A, 14B and 14C show successive stages in assembling a closed mould in accordance with the invention; Fig. 15 is a perspective view, from beneath and to one side, of the closed mould shown in Fig. 14C;; Fig. 16 is a perspective view, from the same direction as in Fig. 15, of the mould closure in accordance with the invention; Fig. 17 is a perspective view, in a direction corresponding to Fig. 16, of another form of mould closure in accordance with the invention; Fig. 18 is a perspective view of a clip suitable for use with the closed mould of the present invention; Fig. 19 is a perspective view of a ladle suitable for use with the invention; Fig. 20 is a perspective view of a cooling arrangement forming an auxiliary aspect of the present invention; Fig. 21 is a transverse section of the cooling arrangement of Fig. 20 in use; Fig. 22 is a perspective view of another form of clip suitable for use with the invention; Fig. 23 is a perspective view of another form of ladle suitable for use with the invention;; Fig. 24 is a perspective view of another form of cooling arrangement forming an auxiliary aspect of the present invention; Fig. 25A is a perspective view of a conventional dental tray adapting for taking impressions of teeth in the upper jaw; Fig. 25B is a perspective view of one form of complementary mould in accordance with the invention; Fig. 26A is a perspective view of a complementary mould in accordance with the invention; Referring first to Figs. 1-5, these show various views of a conventional dental impression tray 100 in the form of a deep-rimmed horseshoe-shaped tray intended for filling with moulding material such as silicone putty followed by insertion in a patient's mouth to obtain an impression of the teeth in the lower jaw of the patient. In this respect, the dental tray 100 functions as an independent open-topped mould.The bounding edges 102 of the tray 100 are contoured to fit comfortably within a patient's mouth.

When it is intended to take an impression of a denture, it is necessary to use a closed mould so as to take a simultaneous impression of all parts of the denture.

Hitherto for lower jaw dentures it has been customary to utilise a pair of conventional (lower jaw) dental trays 100 aligned as shown in Fig. 6. Fig. 6 clearly shows the gross mis-match between the respective bounding edges 102 of the two trays 100, which results in a large, irregular gap around the nominally closed mould, thus obviating a properly closed mould of the kind which is desirable or essential for certain subsequent procedures. Moreover, the lack of any form of "fit" or mutual keying between the two trays 100 prevents their positive registration when mutually assembled; mutual alignment of the two trays 100 becomes dependent on the haphazard application of the operator's manipulative skills.

Retaining means 101 are present in the conventional trays 100 of Figs. 1-6 and in the mould according to the invention (see Figs. 7-9). The retaining means may be small aperatures, slits, ridges or the like into or around which moulding material is pressed so that retention of the moulding material in the tray or mould is enhanced. The size, type and number of retaining means may vary from that illustrated.

Once a negative mould of the denture is produced from cured silicone putty it is generally desirable to obtain a positive copy of the denture by introducing melted wax (or other such casting material) into the negative moulding. Before introducing the melted wax the two halves of the mould must be separated (usually by careful cutting between the layers of putty), the dentures removed and the two halves of the moulds exactly realigned. The process of realignment is crucial to obtain an accurate copy of the dentures, but using conventional techniques is currently timeconsuming and a matter of skill.

Fig. 7 shows one form of the present invention, in which a single conventional dental tray 100 is converted to a closed mould by being fitted with a mould closure 110 (shown separately in Figs. 8, 9, 11, 12 and 13). In plan view, the closure 110 has approximately the same horseshoe-shaped outline and overall size as the conventional tray 100, but in other respects the closure 110 has a radically different shape, basically by being complementary to the tray 100. In particular, the shapes of the bounding edges 112 of the closure 110 are exactly complementary to the shapes of the bounding edges 102 of the conventional dental tray 100, such that when the closure 110 is fitted on to the tray 100 as shown in Fig. 7, the two mould parts meet edge-to-edge without a gap (contrast with the excessive gaps in the Fig. 6 mould).Details of the shape of the mould closure 110 in general and its bounding edges 112 in particular can be ascertained from Figs. 7-13 (and contrasted with the details shown in Figs. 1-6).

The mould closure 110 can optionally be provided with a suitable handle 114 as shown in Figs. 8 and 9. The handle 114 may be a detachable handle temporarily secured to the closure 110 by being plugged into suitable apertures (not shown) which may be similar to the handle-attaching slots 104 (Figs. 1 and 2) in the conventional tray 100.

End parts 116 of the rim of the mould closure 110 are preferably provided with apertures 118 (Figs. 9 and 11-13) to enable a casting material (eg molten wax) to be poured into the closed mould, as will be subsequently described in detail. The apertures 118 may optionally be modified to the form of slots 120, as shown in Fig. 10. The use of slots may be beneficial to enable easy removal of a small portion of the cured putty to permit entry of the casting material. The small portion of putty may be removed by any suitable means, for example by using a scalpel. The mould 110 may be manufactured of the same material as the conventional dental impression tray 100.

Figs. 14A, 14B and 14C show successive stages in the process of fitting the mould closure 110 onto the dental tray 100 to provide the closed mould shown in Figs. 14C and 15. The relationship of the mould closure 110 to the dental tray 100 may be seen by comparing Fig. 16 with Fig. 15.

A slightly modified form of mould closure 130 is shown in Fig. 17.

When a closed mould is provided by the mutual assembly of a dental tray 100 with a mould closure 110 (or 130), these two mould parts can be mutually secured by any suitable means, for example by the use of one or more of the resilient C-form clips 140 shown in Fig. 18.

When the mould containing the impression or negative mould formed from moulding material is closed and secured, wax or another suitable casting material is introduced. The wax may be melted by any convenient means, for example the solid wax may be placed in an aluminium/copper ladle 150 (Fig. 19) (forming an accessory for use with the invention) and melted by holding the ladle 150 over a gas flame 152 or other suitable heat source. The molten wax is poured into the mould through the apertures 118 in the ends 116 of the closure 110. A portion of the impression will have been removed to enable entry of the casting material into the volume previously described by the dentures.

The mould is cooled after casting to solidify the wax with convenient speed, by placing the still-closed mould in a cooling tank 160 (Figs. 20 and 21). The tank 160 is formed of a suitable material, such as an unplasticised acrylic polymer, capable of holding a suitable liquid coolant, eg cold domestic tap water.

To ensure that the mould remains submerged during cooling, the cooling tank 160 is provided with an array of resilient fringes 162 disposed along each long edge of the rim of the tank. The fringes 162 extend inwards from the respective edge towards the respective opposite edge, and slope downwards. The fringes 162 grip a closed mould between them as shown in Fig. 21 in order to hold the mould submerged in the cooling water 164, thus to prevent the mould from floating. The tank 160 is preferably made long enough to hold two or three moulds at any one time.

Fig. 22 shows an alternative form of mould securing clip 170, which dimensionally differs slightly from the functionally equivalent clip 140 of Fig. 18.

Fig. 23 shows an alternative form of ladle 180 for the melting of wax or other casting material, and which is dimensionally slightly different from the functionally equivalent ladle 150 of Fig. 19.

Fig. 24 shows an alternative form of cooling tank 190, having four resilient fringes 192 along each edge (only the fringe set at one side being visible in Fig. 24), as compared to three fringes 162 per side in the cooling tank 160 of Figs. 20 and 21. The cooling tank 190 functions in the same manner as the cooling tank 160 (see Fig. 21 and the related description).

Fig. 25A shows a conventional dental impression tray 105 in the form of a deep-rimmed horseshoe-shaped tray intended for filling with a silicone putty followed by insertion in a patient's mouth to obtain an impression of the teeth in the upper jaw of a patient. In this respect, dental tray 105 functions as an independent open-topped mould. Retaining means 101 are illustrated as small aperatures. The bounding edges 102 of the tray 105 are contoured to fit comfortably within a patient's mouth.

For taking impressions of an upper jaw denture, it is necessary to use a closed mould in order to obtain a complete impression of the denture. Previously such a closed mould was formed by use of two trays 105 aligned in a manner similar to that illustrated in Fig. 6.

However, this results in gross mis-match analogous to that shown in Fig. 6 for a lower jaw. The procedure for taking an impression of an upper denture is identical in every respect for that described above for a lower jaw.

Figure 25B shows one form of the mould closure 115.

Closure 115 has approximately the same horseshoe-shaped outline and overall size as tray 105 and is complementary thereto. In particular the bounding edges 117 of the closures 115 are shaped to be exactly complementary to the bounding edges of conventional tray 105. Thus when closures 115 is fitted onto tray 105 the two parts may be aligned edge-to-edge without any substantial gap. Mould 115 is provided with retaining means 107.

Similarly to the mould closure 110 of Figs. 8 and 9, closure 115 may optionally be provided with a handle 114, for example via suitable apertures.

End parts 116 of the rim of closure 115 are preferably provided with apertures 118 to enable a casting material (such as molten wax) to be poured into the closed mould as described above. Apertures 118 may optionally be in the form of slots 120, as shown.

Figure 26A shows a mould closure 115 adapted for use with either a conventional dental tray 105 for an upper jaw (as shown in Fig. 26B) and also for a conventional dental tray 100 for a lower jaw (as shown in Fig. 26C).

While certain modifications and variations have been described above, the invention is not restricted thereto, and other modifications and variations can be adopted without departing from the scope of the invention. For example, the mould cover could be shaped and dimensioned to be complementary to a nonstandard dental tray, such that the mould parts could only be used together.

Claims (14)

1. A mould adapted to form a substantially closed mould with a dental impression tray.

2. A mould as claimed in Claim 1 wherein said tray is adapted for taking impressions of teeth in the lower jaw.

3. A mould as claimed in Claim 1 wherein said tray is adapted for taking impressions of teeth in the upper jaw.

4. A mould as claimed in any one of Claims 1 to 3 which is substantially horseshoe-shaped.

5. A mould as claimed in any one of Claims 1 to 4 having a subs'anzi2ilv U-sh2p2d cross-section.

6. A mould as claimed in any one of Claims 1 to 5 having an opening to permit entry of casting material.

7. A mould as claimed in any one of Claims 4 to 6 wherein the legs of the horseshoe are closed by an end wall.

8. A mould as claimed in any one of Claims 1 to 7 being provided with closing means to keep the mould aligned with said tray during curing.

9. A mould as claimed in any one of Claims 1 to 8 having means to retain moulding material therein.

10. A mould as claimed in Claim 9 wherein said retaining means include internal ridges, rims or indentations or aperatures or a mixture thereof.

11. A closed mould comprising a first mould part and a second mould part, wherein said first mould part is functionally equivalent to a dental impression tray and said second mould part is a mould as claimed in any one of Claims 1 to 10.

12. A closed mould as claimed in Claim 11 wherein said first and second mould parts are hinged together.

13. A method of producing an impression of dentures, said method comprising: a) obtaining a dental impression tray and at least partially filling said tray with moulding material; b) at least partially filling a mould as claimed in any one of Claims 1 to 10 with moulding material; c) locating said dentures in one of said tray and said mould and aligning the other of said tray and said mould therewith; d) pressing said tray and said mould together to completely surround said dentures with moulding material; e) allowing said moulding material to cure; and f) cutting through said cured moulding material to remove said dentures and removing said dentures.

14. A method of producing a replica of dentures, said method comprising the method as claimed in Claim 13 and including the following steps: a) re-aligning said tray and said mould containing cured moulding material and introducing casting material into the volume described by said dentures; b) allowing said casting material to cure to form a denture replica; and c) removing said denture replica.