A tooth consists of a crown covered by very hard translucent enamel and a root covered by bone-like cement. The enamel covers an internal'structure comprising substantially dentine. The dentine contains an interior pulp cavity which typically extends into core of the root to form a pulp canal. The human jaw is formed with a plurality of sockets which accommodate rows of teeth. A periodontal ligament separates each root from the jaw socket. Fleshy gums surround the teeth and cover the neighbouring areas of jaw.

Tooth decay causes localised destruction of the enamel and rapid erosion of the internal dentine. In severe cases the pulp cavity is opened to reveal painful nerves in the interior of the tooth. Treatment of decayed teeth may involve filling, to replace decayed and eroded tooth material. In certain cases, for example where infection has set in, the tooth must be removed. Similarly orthodontal treatment of the arrangement and appearance of teeth may require removal of selected teeth. Recent

developments in prosthetic teeth involve removal of individual teeth and immediate replacement by individual prosthetic teeth.

Removal of a tooth is a time consuming and difficult procedure. A typical method involve the use of forceps to grip the crown of the tooth and pull the tooth from the jaw. This is an awkward technique which is may be uncomfortable for the patient whose tooth is being extracted, and difficult for the dentist who must exert relatively high levels of force to pull the tooth from its bed in the jaw. Frequently, when the tooth is decayed or otherwise damaged, the crown may be pulled off by the forceps, leaving the root behind and embedded in the jaw.

Removal of this remaining fragment of the tooth is very difficult because it is almost impossible to get any purchase on the embedded root. Because of this elevators may have to be wedged between the root and socket. The elevators are rocked to lever against the root and cause it to lift from the socket. Occasionally it is necessary to operate on the jaw to remove bone from around the socket in order to access, and permit clamping of the obscured root. This can be damaging to the jaw, and renders the adjacent teeth vulnerable. The above described complications increase the time taken for

extraction and greatly increases the pain, especially post-operatively, due to the extensive tissue damage.

Various attempts have been made to improve the process of tooth or tooth root removal. GB-A-2234679 discloses a device for extracting crowns in which calliper-like members are placed over the crown and two lever arms are pressed together to lift the crown away from the jaw.

GB-A-1168973 discloses forceps for removing teeth. This device again has calliper members 5 which grasp an outside surface of the tooth to be extracted. Levers are then pressed together to extract the tooth by drawing up of the callipers.

US-A-4,443,196 discloses a tooth root extractor having the general form of a pair of geometry compasses. There is a threaded tooth root screw which engages with the tooth root. Rotation of a knurled wheel causes two arms of the device to be splayed, one of which arms rests on a neighbouring tooth, and the other acts on the tooth root screw to withdraw the root.

US-A-4,230,454 discloses a tooth root extractor in which a tooth is grasped by means of a grip member. The grip

member includes a screw fitted tightening mechanism which tightens onto the side of the tooth. A lever arm is levered around a fulcrum 21 to draw the tooth from its socket.

US-A-3,579,834 discloses a crown and bridge remover in which calliper-like arms are engaged over a crown and a screw threaded displacement means draws the crown from the tooth.

US-A-2,210,349 discloses an instrument for extracting tooth roots which includes screw threaded engagement means. Rotation of a nut against an abutment draws the screw threaded engagement and root away from the socket.

US-A-1,666,860 discloses a tooth extractor which appears to work by calliper arms grasping either side of the head of the tooth. The callipers are tightened in position by a screw threaded wing nut. The tooth is drawn from the socket by relative motion of a lifting rod actuated by a further wing nut, the lifting rod acting against an abutment to draw the tooth from its socket.

DE-A-19646097 discloses a tooth extractor wherein a tooth head is grasped by a clamp which is screw tightened in

place. An abutment is made with teeth on either side of the tooth to be extracted. A wing nut is rotated to draw the clamped tooth from its socket.

DE-A-1013392 discloses a tooth extractor which includes a screw threaded tooth engagement. An abutment rests against a tooth adjacent the one to be extracted. A lever arm is used to draw the screw threaded engagement in a removal direction.

It is an object of the present invention to provide an improved apparatus and method of removing teeth from the jaw of an person or animal.

According to one aspect of the present invention there is provided an extraction device for removing a tooth, or root of a tooth, embedded in a patient's jaw, which device comprises tooth engaging means, abutment means to be placed around or adjacent to the tooth to be extracted and means for displacing said engaging means relative to the abutment means in a direction which draws the tooth from its bed.

The present invention has many advantages, but in particular it provides a controlled means of extraction

from the surrounding tissue. Because the abutment means may be placed on the surrounding teeth, jaw or gums, the drawing movement is braced and stabilised.

Preferably the engaging means comprises a screw cutting thread capable of being driven into the interior of a tooth or root of a tooth. An advantage of this is that the engaging means may engage with the relatively soft interior of the tooth, providing good mechanical keying and a sound mechanical connection, whatever the state of the crown. In addition, because the interior of the tooth is engaged, it is not necessary to remove the surrounding tissue from around the root. Thus the trauma suffered by the patient may be reduced.

In a preferred embodiment of the present invention the abutment means comprises a collar configured to fit around the tooth to be extracted, and abut the gums and jaw adjacent the tooth to be removed. The collar may be removably attached to the device, thereby permitting attachment of alternative collars.

The collars may be rendered removable by the provision of screw threaded attachment means operative between the device and an end of each collar. A plurality of

replacement collars may be provided, each configured for different tooth shapes and sizes.

In one embodiment, the means for displacing the engaging means comprises a rack and pinion mechanism. Preferably a rack is fixed for travel with the engaging means and a pinion is rotatably attached to the abutment means. The pinion may then be rotated to move the engaging means in a tooth-drawing direction, with the force reaction being directed in an opposite direction to brace the abutment means in position against the jaw. There may be two pinions, for example on one either side of a cylindrical rack. In one embodiment each pinion is provided with a lever which permits manual rotation of the pinion through an arc corresponding to drawing out of the engaged tooth.

The pinion lever may be provided with a handle portion.

In another aspect of the present invention the pinion forms a component of a gear train, which gear train provides a mechanical advantage.

The displacing means may comprise a powered mechanical mechanism. This is preferably a mechanism compatible with the electrically driven, hydraulically driven or compressed air driven power systems currently used for

dental tools.

In yet another aspect of the invention, the cutting screw is adapted to be replaceable. The screw may be provided on a bit, which bit may engage with the device by means of a bayonet mount or chuck engagement arrangement of a type common in the field of dental or other drilling tools. The replacement screws may be of varying thread pitch, wavelength, amplitude and length. In this way the optimum engagement with a particular tooth can be made.

In one aspect of the present invention the screw thread is rotated by a handle to effect engagement with a tooth.

In another aspect of the present invention the screw thread is rotated by a powered mechanical drive means.

Conveniently a dental power tool connection may be made to take advantage of known power drives, such as electrical, compressed air or hydraulic.

According to yet another aspect of the present invention, there is provided a method of extracting a tooth or root of a tooth from an animal or person comprising: providing an extraction device as hereinbefore described, causing the engagement means to engage with the tooth or root, causing the abutment means to abut a portion of the

gum or jaw or teeth surrounding the tooth or root to be removed, and operating the displacing means whereby the engaging means and engaged tooth or root are displaced relative to the abutment means, which abutment means is braced in position by the reaction of the abutment means against the displacing force, thereby to draw the tooth or root from its bed.

According to yet another aspect of the present invention there is provided a dental surgeon's tooth extraction kit comprising a tooth extraction device as hereinbefore described wherein the engaging means comprises a removable screw threaded cutting bit and the abutment means comprises a removable collar to be located around a tooth, and wherein the kit further comprises a plurality of replacement screw threaded cutting bits in a range of different configurations and a plurality of replacement collars in range of configurations.

Following is a description by way of example only and with reference to the drawings of a method of putting the present invention into effect.

In the drawings:-

Figure 1 is side elevation, partially in section, of an extraction device according to the present invention.

Figure 2 is a top elevation of the handle shown in figure 1.

Figure 3 is a side elevation of an extraction device according to the present invention.

Figure 4 shows the different possible sizes and shapes of the collar shown in figure 3.

Figure 5 shows a gear train located between the rack and pinion of an extraction device according to an alternative embodiment of the present invention.

In figure 1 a screw head 11 comprises a bit formed with a sharp cutting thread 12 sufficient for cutting into a tooth or root of a tooth. The screw head is selected from a plurality of screw heads of differing sizes to suit the dimension of the tooth or root being removed. The plurality of screw heads typically all have a length of less than 25 millimetres and a diameter of between 2 and 4 millimetres at the top and tapering to a point at the bottom. The plurality of screw heads may be made from

stainless steel or tungsten-carbide. It may be necessary to specify a tool grade steel, or another high performance material, in order to maintain cutting performance and confer sufficient strength to permit tooth extraction.

The screw head is attached at a base end thereof to a generally cylindrical shaft 13. The attachment is by means of a bayonet mount 14 (detail not shown) of conventional construction. The bayonet mount permits screw head detachment and replacement with another screw head of a different configuration.

The shaft is formed from stainless steel and is formed with a plurality of axially spaced annular rings 21. An extension 22 of the shaft is provided at a lower end thereof with a rectilinear handle 23. The handle is fixed to the shaft by suitable means, for example a grub screw engagement. An upper end of the shaft extension is formed with a flat 24. This permits drivable engagement with a mechanical power drive (not illustrated) of a type conventional in the art. The handle 23 is preferably removed when the power drive is attached. The handle is formed from stainless steel and is about 40 millimetres in length. The handle has a rectangular groove 27

intruding from each end face of the handle. The overall length of the shaft and extension is about 100 millimetres.

The shaft is accommodated in a sleeve 30 formed from stainless steel. The shaft is not attached to the sleeve and thus is free to rotate within the sleeve. The sleeve has a generally cylindrical configuration. A mid region of the sleeve is formed with two radially extending arms 31. An end region of each arm is provided with a rotatably mounted pinion gear 32. Each pinion is provided with an elongate lever portion 33 which extends radially from the pinion. When the handles are perpendicularly, that is fully extended, the total width is about 80 millimetres or less. Elongate slots (not shown) are formed longitudinally of the sleeve, on opposite sides thereof and adjacent each arm. The pinion teeth are entered into the slots to engage with the annular rings on the shaft 21.

A lower end region of the sleeve is formed with an internal threaded portion 40. A generally tubular abutment collar 41 is provided at an upper end thereof with a screw threaded external portion 42. This engages with the threaded portion 40 of the sleeve, as shown in

figure 1. The collar accommodates the screw threaded cutting bit 11.

The collar may be replaced by a range of differently sized collars 45, examples of which are shown in figure 4. One of the collars 46 has a generally oval section and flares outwardly at a base end 47 thereof. Another of the collars tapers 48 inwardly at a base end 49 thereof. The cross section of the lower end regions of the collars is not limited to round or oval. The configurations available are dictated by the likely tooth shapes encountered. The primary concern is that the collar should surround the tooth to be extracted and provide sufficient clearance for the tooth to be raised within the collar.

In an alternative embodiment a gear train 50 is inserted between the pinion and the rack. The incorporation of a gear train advantageously provides a mechanical advantage and thus less downward pressure is required to raise the shaft.

In use, the dentist first has to attach the bit to the tooth. In the case of decayed teeth or damaged teeth direct access to the pulp interior of the tooth may be

possible. In cases where the tooth is structurally sound and the crown is intact it may be necessary to provide an initial access bore by drilling into the interior of the tooth. This initial boring may be performed by conventional dentists drilling equipment.

The screw threaded cutting bit is then placed against a top end surface of the tooth. The bit is manually turned by the handle 23. It cuts into the interior of the tooth, preferably into at least the upper end region of a root canal of the tooth. As the cutting continues the collar is drawn down around the tooth and against the gums.

Eventually the collar will abut the bone of the jaw surrounding the tooth to provide a solid bracing of the collar.

The tooth removal process involves depressing the lever arms 33. This rocks the pinions which act upon the annular rings to lift the shaft within the sleeve. The cutting bit is lifted along with the shaft. The collar directs a reaction to the lifting forces onto the jaw bone surrounding the tooth, and maintains stable bracing of the device. The tooth is gradually and controllably drawn from its socket.

The present invention allows the controlled and safe removal of teeth from the jaw. A particular advantage is the ability to remove root portions of damaged teeth, even in the absence of a crown portion. This is done without the removal of surrounding bone, and therefore results in considerably less damage to the patient. For the dentist, the device is considerably easier and less time consuming to use.