DENTAL ARTICULATORS

This invention relates to dental articulators.

When making a dental prosthesis for a patient, cast models of the

patient's upper and lower teeth are used to aid design of the prosthesis to

ensure that it will fit comfortably in the patient's mouth.

In particular, it is important to ensure that the prosthesis will not

disturb the normal bite relationship between the patient's upper and lower

teeth which could lead to discomfort or pain.

The cast models are made using impressions taken of the patient's

teeth using impression wax on a bite tray. The models are cast from the

impressions and conventionally are mounted in an articulator, by

attachment of a hinged linkage to the models, which holds the cast teeth

in the desired bite interrelationship whilst permitting movement of the

models towards and away from each other in simulation of normal jaw

movement. An arrangement of this kind is shown, by way of example, in

U.S. 5645425.

To facilitate correct location of the models in the articulator, it is

known to use a two-sided bite tray which takes impressions of the upper

and lower teeth at the same time, thereby retaining, on the tray, the

correct bite interrelationship. The tray is then used to cast the upper and

lower models in upper and lower moulding shells.

In accordance with conventional practice, this is done by pouring

casting material into one of the impressions which is uppermost and

allowing this to set, and then turning the tray over and repeating the

procedure with the other impression. One of the resulting tooth castings

which is lowermost is then placed onto more casting material in one of

the shells, and this is allowed to set to form a model in the shell. This

procedure is then repeated for the other tooth casting to form a further

model in the other shell. The two shells, with the models are then

attached to the hinged linkage of the articulator.

The use of a two-sided bite tray facilitates determination of the

correct positioning of the models relative to each other. However, in so

far as the placing of the tooth castings into the further casting material in

the shells is subject to variation, correct positioning requires exercise of

skill and judgement by experienced personnel, and a high level of

accuracy may be difficult or inconvenient to achieve.

Suitable two-sided bite trays are described in GB 2373448A and

GB 2373449A respectively for making impressions of anterior and

posterior teeth. In each case, in the practical embodiments described, the

bite tray comprises a gauze insert supported within an open frame having

an outwardly projecting handle. For convenience of use and to avoid or

minimise cleaning requirements, these bite trays may be wholly

disposable, or at least may have disposable gauze inserts.

An object of the present invention is to provide a dental articulator

with which accurate location of upper and lower cast models with a

desired bite interrelationship can be facilitated, whereby the need to

exercise skill and judgement to achieve such accurate location can be

minimised.

According to one aspect of the invention therefore there is provided

a dental articulator, for making opposed cast models of upper and lower

teeth, from impressions in impression material on a bite tray, comprising a

pair of opposed casting shells interconnected by an articulation joint,

characterised by the provision of a clamping device for clamping the bite

tray between the shells in fixed position relative thereto.

With this arrangement, the clamping device can act as a jig to hold

the impressions on the bite tray in fixed positions relative to the shells

whilst the cast models are formed whereby a desired bite relationship

between the cast models in the articulator can be readily, accurately

achieved and maintained, without undue reliance on skill and judgement

of expert personnel.

The arrangement can be such that the interconnected shells can be

readily turned over so that each shell can be filled in turn with casting

material whilst in the lowermost position. This can particularly facilitate

accurate casting of models conveniently and reliably with reduced skill

requirement.

Moreover, the shells, or even also the clamping device, can be

readily constructed to be conveniently disposable thereby avoiding or

minimising cleaning requirements.

Preferably the articulator also includes a base with a shell-locating

device, each shell being removably engageable with such device. With

this arrangement, the interconnected shells can be supported by or

mounted on the base in opposite upright orientations, i.e. each way up.

The shell-locating device may comprise a clip or a receptacle or

projection into or onto which the shell can be inserted e.g. to be

frictionally gripped or simply to be located without being positively

retained thereby. In one embodiment a friction-gripping device is used.

With regard to the clamping device, this may be removably or

permanently attachable to the bite tray and may be disposable or

reusable. The bite tray may be of the kind having an outwardly projecting

handle and the clamping device may be arranged to hold the bite tray by

clamping such handle.

The clamping device may be detachably engageable with the

aforesaid base, the base thereby acting to establish the positional

relationship between the clamping device and the shells.

The base may have at least one locating device for the clamping

device with which the clamping device is detachably engageable in

opposite upright orientations i.e. each way up. This may comprise a clip

or receptacle or projection into or onto which opposite ends of the

clamping device can be inserted or engaged e.g. to be frictionally gripped

or simply to be located without being positively retained thereby.

In the case where the bite tray is asymmetrical with regard to its

engagement with the clamping device, e.g. where the aforesaid handle

projects asymmetrically, the base may have two spaced apart locating

devices for the clamping device to accommodate the clamping device

each way up, whereby opposite ends of the clamping device are

engageable with different locating devices.

The clamping device may have two parts which snap fit or screw

fit or otherwise positively interengage e.g. to hold the aforesaid handle or

other part of the bite tray securely between such parts. Locating

structures may be provided to ensure a desired angular relationship is

maintained between the bite tray and the shells.

With regard to the shells, these may take any suitable form. Thus,

they may comprise open troughs having a bottom wall bounded by

upstanding side walls, and they may be identical or mirror images of each

other.

The shells may be of any suitable shape for example corresponding

to the shape of the bite tray. Thus, they may be generally rectangular or

segmental or otherwise shaped.

The articulation joint may take any suitable form and thus may

comprise two parts interconnected by a hinge joint.

These joint parts may be attached to the respective shells in any

suitable manner. In one embodiment the joint parts are located relative to

the shells e.g. by clipping or otherwise fitting over side walls of the shells,

and a locking element extends from each part into the respective shell, so

as to be keyed in position, thereby to lock the joint part to the shell, when

the model is cast in the shell. The elements may be perforated for

penetration of the model-forming material.

The articulator may be used with a bite tray of the kind described

in the aforesaid patent application GB 2373448A or GB 2373449A, that

is, with a bite tray of the kind having a frame which supports a bite tray

insert and to which the aforesaid handle is attached.

The articulator may be specially adapted for the respective anterior

and posterior bite trays described in the aforesaid patent applications

whereby two different said articulators are used for anterior and posterior

applications.

In accordance with a second aspect of the present invention there

is provided a method of forming cast models of a patient's upper and

lower teeth in an articulator so as to adopt a desired bite relationship

therebetween, wherein a bite tray having impressions of such upper and

lower teeth on opposite sides thereof is clamped between and in fixed

position relative to first and second shells arranged lowermost and

uppermost, said shells being interconnected by an articulation joint and

casting material being provided in the lowermost first shell in contact with

the lowermost impression on the bite tray, said casting material is allowed

to set to form a first model in the lowermost first shell, the bite tray and

shells are then turned over with the said fixed positional relationship

between the shells and the bite tray being maintained, further casting

material is provided in the lowermost second shell in contact with the

impression now lowermost on the bite tray, and said further casting

material is allowed to set to form a second model in the lowermost

second shell.

If desired, initial casting material may be inserted into the

impressions and allowed to set to form tooth castings therein prior to

formation of the models in the shells.

To ensure maintenance of the desired relationship between the

clamped bite tray and the shells in both orientations of the bite tray and

shells, the bite tray and shells may be engaged with locating devices on a

base or other structure.

The method of the second aspect of the invention may be

performed using the articulator of the first aspect of the invention.

The invention will now be described further by way of example

only and with reference to the accompanying drawings in which :-

Figure 1 is a plan view of one form of an articulator according

to the invention with a posterior bite tray mounted

therein;

Figure 2 is a sectional view on the line A-A of Figure 1 ;

Figure 3 is a sectional view on the line B-B of Figure 1 ;

Figures 4-5 are views respectively corresponding to Figures 1 -2 of

an alternative embodiment with an anterior bite tray;

Figure 6 is an end view of the arrangement of Figure 4;

Figures 7 & 8 are perspective views respectively of the posterior and

anterior embodiments of Figures 1 -6.

Figures 9 & 10 are perspective views of respectively posterior and

anterior bite trays used with articulators.

Referring to Figures 1 -3, 7 and 9 these show an articulator for use

with a posterior bite tray 1 .

The bite tray 1 , as shown in Figure 9, has a generally u-shaped

frame 2 with parallel support arms 3 linked by a cross-arm 4 at one end.

Opposite ends 5 of the arms are open. One arm 3 at the open end 5 has

an integral handle 6 which extends outwardly at an angle away from the

respective arm 3.

A bite tray insert 7 is fixed between the support arms 3. The insert

comprises two channel-section members 8 into which the support arms 3

can slide, and a gauze sheet 9 which is taut between the members 8

when engaged with the arms 3.

Further details are described in GB 2373449A.

The articulator comprises a flat base plate 10 which is generally of

trapezoidal shape.

The base plate 10 is moulded with an upstanding rectangular open-

topped receptacle 1 1 adjacent the narrow end of the base plate 10. The

longitudinal axis of the receptacle 1 1 lies on the longitudinal centre line of

the base plate 10.

Adjacent the opposite wider end of the base plate 10 there are

moulded two like circular shallow projections 12A, B. These projections

12 are disposed symmetrically on opposite sides of the centre line of the

base plate 10.

The articulator also includes two like interconnected open-topped

moulding shells 13A, B.

Each shell 13 is generally rectangular with a flat bottom wall and

four upstanding side walls of common height.

The shells 13 are interconnected by an articulation joint 14 so that

their open tops face each other and are mutually aligned.

The articulation joint 14 comprises two moulded parts each of

which has an outwardly projecting flange 15, an integral u-shaped

member 16, and a forwardly projecting perforated plate 17.

The flanges 15 are linked by a hinge joint 18.

The u-shaped members 16 fit tightly over end walls of the shells 13

so that the hinge joint 18 is centred between the shells 13A, B, and the

plates 17 project in parallel disposition slightly above the bottom walls of

the shells 13.

The articulator also includes a clamping device 19 comprising two

posts 2OA, B each having a circular recessed end cap 21 A, B of common

size and shape at one end and a shaped transverse flat flange 22A, B at

the other end.

At such other ends there are projections 23 engaging with holes

23a in the bite tray handle 6, and recesses by means of which the posts

20 can snap or otherwise fit together coaxially with the flanges 22A, B

confronting each other.

Each circular end cap 21 can fit securely yet removably over each

of the circular projections 12. This may be a frictional or snap fit or

simply a location with limited sideways movement restrained by abutment

with the projection 12.

Each shell 13 can fit securely yet removably in the rectangular

receptacle 1 1 , and again this may be a frictional or snap fit or simply a

location. The side walls of the rectangular receptacle 1 1 are outwardly

inclined to accommodate readily each shell 13.

In use, the bite tray insert 7 is charged with impression wax on

both sides and is inserted into the patient's mouth to take an impression

of the patient's upper and lower posterior teeth in their bite

interrelationship.

The bite tray handle 6 is then securely mounted into the clamping

device 19 between the flanges 22A, B and liquid casting material poured

into one side of the bite tray impression. The articulator shell 13A is then

fitted into the receptacle 1 1 and is filled with liquid casting material.

The clamping device 19 is mounted on the articulator base plate 10

by fitting one end cap 21 A onto one of the circular projections 12A. The

bite tray insert 7 is thus held in correct position aligned with the lower

shell 1 3A with the lower impression wax and casting material on the bite

tray insert 7 projecting into the casting material in the shell 13A.

Correct positioning is attained due to the projections 23 of the

posts 20 engaging holes in the bite tray handle 6, and due to engagement

of a locating recess 24a on the respective end cap 21 with a locating pin

24 on the base plate 10 alongside the projection 12A.

The casting material is then allowed to set and harden in the

shell 13A.

The entire interconnected assembly of the shells 13, the bite tray 1

and the clamping device 19, is removed from the articulator base plate 10

and turned over so that the other shell 13B is now fitted into the

rectangular receptacle 1 1 .

This shell 13B is now filled with casting material, the other end cap

21 B of the clamping device 19 is fitted onto the other circular projection

12B and the casting material is allowed to set and harden with the

impression wax on the opposite side of the bite tray 7 within this

material.

The bite tray 1 and clamping device 19 can now be removed to

give models of upper and lower posterior teeth in correct bite

interrelationship.

The shells 13 with the articulation joint 14 are disposable. New

shells 1 3 and an articulation joint 14 are used to produce further models,

with the same base plate 10, which enhances convenience and avoids or

minimises cleansing requirements.

The clamping device 1 9 may be disposable or reusable, as also may

be the bite tray 1.

Figures 4-6, 8 and 10 show a similar arrangement for use with an

anterior bite tray of the kind described in GB 2373448A, and the same

reference numerals are used for corresponding parts.

As shown in Figure 10, the anterior bite tray 25 has a curved

support frame 26 with free ends 27 defining an opening therebetween. A

handle 28 projects outwardly from the frame in symmetrical disposition.

The frame 26 has upper and lower frame members which snap-fit

together.

The bite tray has an insert 29 comprising a segmental shaped

gauze sheet 30 with a mounting element fixed around its curved

periphery. This element is clamped between the frame members with the

straight periphery of the gauze sheet extending tautly between the free

ends 27 of the frame 26.

The trapezoidal base plate 10 has the shell receptacle 1 1 moulded

centrally adjacent the wider end and a single clamping device projection

1 2 moulded centrally adjacent the narrower end.

The shells 13A, 13B have a bottom wall bounded by upstanding

side walls but are segmental shaped, corresponding to the shape of the

bite tray insert 29.

The arrangement of Figures 4-6 is used in like manner to the

articulator of Figures 1 -3 except that the same locating projection 12 is

used for the clamping device 1 9 each way up, since the handle 28

projects symmetrically for the anterior bite tray 25.

With the embodiments described above cast models can be readily

constructed in a particularly simple, convenient and reliable manner. In

particular, the embodiments enable use of a standardised procedure

ensuring common location and positional accuracy of cast models

avoiding inaccuracies due to human error, with reduced skill requirement.

It is of course to be understood that the invention is not intended

to be restricted to the details of the above embodiment which are

described by way of example only. Thus, for example, it is to be

understood that casting material may be introduced into, and allowed to

set within, the impressions, to form tooth castings, before presentation of

the impressions to casting material in the shells, to form the upper and

lower models.