In traditional caries treatment the attacked tooth sub- stance is removed mechanically by means of a dentist's drill or a cutting excavator. Such a caries treatment is often a painful and unpleasant experience for the patient.

Some of the patients feel so uncomfortable with the treat- ment that they wait far too long before they visit a den- tist, which means that it is often too late to save the caries attacked teeth. Extraction of the teeth is then the only treatment method that is left.

However, there are other methods which are based on a chemical-mechanical treatment for the removal of the car- ies attacked substance. Such methods are described in SE 460258, SE 507437 and SE 98. 00025-0. According to these methods a preparation in the form of a two-component liq- uid is mixed and then immediately applied to the caries lesion. Functioning in a biological way, the liquid makes the caries attacked substance soft without causing any damage to the tooth or the soft tissue. After 10-15 sec- onds the dentist can start removing the carious substance by means of a scraping instrument. The scraping continues until all caries substance has been removed. Then the cav- ity is filled with a suitable filling material.

According to SE 460258 the two-component liquid consists of a sodium hypochlorite component and a nitrogen-contain- ing component. The nitrogen-containing component consists in this case of three nitrogen-containing compounds with different charge states in its side chain ; one neutral, one with a negative net charge and one with a positive net charge.

Unlike conventional mechanical caries treatment methods

the biological treatment method is usually not painful at all. Neither does it require any investments in expensive equipments. It only requires a scraping instrument to re- move softened carious dentine material.

Traditional excavator instruments, however, are not suita- ble for this purpose as they are cutting and not made for just scraping away already softened dentine material from different types of cavities and therefore could damage healthy dentine.

An instrument specifically made for removing softened car- ious dentine is previously disclosed in SE 96. 04626-3.

This instrument makes it possible to manually scrape in different directions and the scraping edges of the tool head of the instrument are adapted to all types of caries lesions. The instrument comprises a star-shaped tool head having four symmetrically arranged scraping edges with a curved, preferably spherical, outer contour (periphery) for scraping away softened carious substance.

The instrument can also be used to pick up drops of the liquid solution used for the chemical-mechanical treatment method and apply these drops to the caries lesion. This is possible because of the open, empty spaces which are formed between the scraping edges of the tool head of the instrument and this function of the instrument is facili- tated as the liquid solution which is used has a viscous, gel form.

So by using this type of scraping instrument which then also functions as a simple applicator for the gel used for the treatment, there is no need for the dentist to invest money in any expensive equipments for distribution and ap- plication of the liquid gel solution.

However, in cases where a relatively large amount of liq- uid is required for the treatment, it might be time-con-

suming to use any of said instruments as applicators as the instrument cannot pick up and carry so much volume of the liquid that would have been desired.

In SE 9700960-9 it is described a scraping instrument in which the tool head member has drop catching means in or- der to improve the ability to catch and carry liquid drops. The drop catching means can be made in the form of collars, flanges, surface enlargement portions, protru- sions, grooves, holes, channels or the like.

Both of these instruments are made for manually scraping softened, carious dentine, i e. the scraping motion is made by hand.

As the scraping motion should be carried out in different directions and repeated until all carious dentine has been removed, it might be a hard work for the dentist from an ergonomically point of view to fulfil the caries treat- ment. The dentist has to position the instrument as well as control the instrument with respect to the scraping di- rection. At the same time the scraping motion should not affect any of the healthy teeth. It should not be allowed to apply too heavy pressure from the instrument on the tooth.

It is an object of this invention to provide a scraping instrument which facilitates for the dentist to remove carious dentine. Specifically, it is an object to unload the specific scraping motion from the dentist so that he can concentrate on positioning the instrument. This means a more efficient treatment procedure.

A further object of this invention is to speed up the scraping operation so that each caries treatment procedure is shortened.

Also a further object of the invention is to provide a

scraping instrument with a more controlled scraping motion and a more steady scraping speed, which means that the scraping motion is independent of different users of the instrument, which in turn means a more predictable result from the treatment procedure.

According to the invention the scraping instrument is pow- er-driven, i. e. the instrument is equipped with, or con- nected to, for instance an electric motor for driving the tool head of the instrument according to a predetermined motion pattern. For instance it could be a rotating, low- speed motion, a reciprocating motion, a pendulating, wob- bling or oscillating motion.

According to a preferred embodiment the instrument has a star-shaped tool head and a shaft for connecting the in- strument to a rotating machine (power tool).

Also other tool heads could be used, such as brush type tool heads. According to a further preferred embodiment a set of different instruments, i. e. instruments with dif- ferent tool heads but easy connectable to the rotating ma- chine, could be used.

In the following some examples of instruments according to the invention will be described more in detail with refer- ence to the accompanying drawings, wherein figure 1 is an overall view of an instrument, figure 2 illustrates a star-shaped tool head with scraping edges more in detail, figure 3 illustrates a star-shaped tool head with four scraping edges, figure 4 illustrates a tool-head in the form of a"brush",

figure 5 illustrates a further embodiment of a brush-type tool head, figure 6 and 7 illustrate a tool head having a geometry adapted to an axial oscillating motion and an elliptical motion, respectively, and figure 8 illustrates schematically a torque controller for the instrument.

As illustrated in figure 1 the instrument comprises a tool head 1 having a spherical outer contour. The tool head is intended to be used for scraping a tooth cavity after a biochemical caries treatment. The tool head has in this case a star-shaped geometry formed by three symmetrically arranged scraping edges 2 having a circular periphery. The scraping edges 2 are extending radially outwards in three different directions and thanks to the circular periphery both the bottom and the sides of the cavity can be scraped with one and the same star-shaped tool head.

The tool head itself could have the same form as in the instrument illustrated in SE 9604626-3, but in which the scraping motions are carried out completely by hand. Simi- lar to the previously known instrument, of course also this instrument could have more or less than three symmet- rically arranged scraping edges. In figure 3 it is illus- trated as an example a tool head having four scraping edg- es 2. However, a common feature for these embodiments is the form of the scraping edges 2 : a substantially circular or curved periphery to permit scraping of the bottom as well as the sides of a tooth cavity.

In contrast to the previously known hand instrument, in which two tool members are arranged with a hand grip mem- ber therebetween for handling the instrument entirely by hand, the instrument according to the present invention has a bent connecting part (shaft) 3 to a driving tool or

similar rotating machine 4, preferably an electric driving motor. In this way a rotary motion, preferably a reversi- ble motion, is applied to the tool head. However, this mo- tion should not be compared with the motion of the high speed dentist's drill.

According to the chemical-mechanical treatment method it is the softened caries tooth substance that should be re- moved by the instrument. The rotary speed for the tool head is then approximately 10-1000 rpm, which should be compared with 20. 000-40. 000 rpm for a conventional dentist's drill, and even 200. 000-600. 000 rpm for a con- ventional high speed turbine for dental use.

In case an ordinary driving motor for a dentist's drill is used as a driving tool in our application, then the motor speed must be reduced to approximately 10-1000 rpm, which also could be arranged by means of a speed reduction gear or adaptor connected to the output of the driving motor.

As the scraping instrument concurrently should be used as an uncomplicated applicator for the caries dissolving liq- uid gel, i e the instrument should be able to carry drops of the liquid to the caries lesion, then it is important that the dentist can control the rotary speed from zero and upwards in a simple way. Unintentional high rotary speeds could otherwise easily throw off the gel drops from the tool head and cause unnecessary spillage.

The driving motor could be connected to the electric power supply or for practical reasons having rechargeable bat- teries.

In figure 4 it is illustrated a tool head in the form of a brush 5 made of a metallic, polymer or other similar fibre material. The bristles could be directed either in the ax- ial or in the radial direction or in all directions (a spherical brush) from a substantially spherical main body

6. By means of the brush structure the transformation of the gel liquid in the caries lesion interface is acceler- ated. By making the bristles more stiff some mechanical abrasion could be achieved.

In figure 5 it is illustrated a further embodiment of a brush-formed tool head. In this case the bristles 5 are directed in the axial direction from a main body 7 with a substantially planar end surface 8.

In figures 6 and 7 it is illustrated a tool head having a geometrical shape adapted for another type of motion, in this case an axially oscillating motion (figure 6) or a motion having an elliptical pattern (figure 7). The scrap- ing edges 9 have a circular symmetrical contour in a plane perpendicular to the longitudinal axis 10 of the tool head, i e in contrast to the previously in figures 2 and 3 described tool heads with substantially longitudinally ar- ranged scraping edges 2.

In the illustrated example there are three such parallell scraping edges 9 with the central one having the larger radius. By means of the rounded spacings 9'between the scraping edges, also in this case drops of the liquid gel, which is used for the chemical-mechanical caries treatment method, can be more easily picked up and carried by the instrument.

In the previous examples the tool head makes either a "single"rotary motion or a more complicated motion pat- tern such as a reciprocating motion, oscillating motion, wobbling motion, elliptic motion or the like, which is in- dicated in the figures.

A reciprocating motion can be achieved by means of an an- gle gear which transforms the rotary motion of the motor axis to a reciprocating motion on the tool head 1. Such gears are known per se and will therefore not be described

in any detail here. A similar arrangement is used for an angle piece in connection with endodontic teeth treatment methods in which an axial or rotating oscillating motion is used. The oscillating motion could also be provided by means of the motor operating voltage. Compare electrical adjusting means for numerically controlled machines. Fur- ther alternatives for providing the driving motion to the tool head is to use for instance linear motors or so- called voice-coil technique which is used today in loud- speakers and in computer disc memories to position the reading head.

In Swedish patent application 96. 04626-3 it is mentioned that one of the objects of the scraping instrument design is to scrape away the loosened caries, but as far as pos- sible without affecting healthy dentine. This should be the same also for a machine instrument and this can be achieved, like in the hand instruments, by designing the cutting angles in such a way that the risk for cutting in- to healthy dentine is reduced.

In the hand-held scraping instruments the cutting angles are then made less cutting, i e the cutting angles are less acute, in order to prevent any abrasion of healthy dentine material. However, healthy dentine might be dam- aged even with an instrument like the one described in said patent 96. 04626-3 if too much pressure is applied on the scraping motion.

In the same way a machine instrument might damage healthy dentine if too much pressure is applied against the sur- face when the tool head is rotating or moved in any of the pattern that has been described above. It is therefore an object to limit this possibility. This can be achieved by providing the machine with means for sensing the pressure against the instrument directly or indirectly by measuring the torque for rotating the instrument. By measuring the torque continuously and comparing it with a set limit val-

ue determined experimentally for a specific tool head ge- ometry the machine can be alarmed or stopped as soon as this value has been reached so that the risk for damaging healthy tooth dentine is reduced.

The surface of a caries lesion can be more or less hard, see for instance Swedish patent application 98. 03057-0.

Therefore a relatively high torque for the instrument is sometimes required. However, the instrument must be han- dled very gently when working close to the tooth pulp to avoid any risks to go through the dentine separating the caries from the pulp. In such a case a lower torque limit is choosen which reduces the possibility for the instru- ment to cut into healthy dentine but which also forces the dentist to work more gently.

In one example of an instrument torque control the torque is measured by measuring the input current to the electric motor driving the tool. As soon as the current exceeds a predetermined value the machine is shut-off. In order not to manually have to reset and restart the machine again after a stop, and once the pressure on the tool head has been reduced, the motor current could be limited to a val- ue corresponding to the actual torque. Another practical solution is to limit the motor current to a much less val- ue when the torque limit has been reached. Then the ma- chine starts rotating again as soon as the instrument has been unloaded. When the motor is rotating again this can easily be detected by measuring the electromotive force of the motor. As soon as the rotational speed has been re- turned the machine also returns to its predetermined value with the higher motor current and corresponding higher torque.

Figure 8 shows by means of a block diagram how such a torque control could be accomplished. An electrical driv- ing motor 4 is connected to the tool head 1 by means of a connector shaft. The motor current can be easily measured

as the voltage over a resistor R in series with the driv- ing motor 4. This signal is submitted to a comparator K via a differential amplifier D for comparing the signal from the differential amplifier D with a reference value or transformed to a digital signal for a computer chip controlling the machine. When the signal from the diffe- rential amplifier D exceeds the reference voltage then the status of the output signal is changed to an electronic control circuit S, to limit the motor current or shut-off the motor current as soon as the predetermined limit value has been reached. By means of a switch B a plurality of preset torque values could be selected.

The invention is not limited to the examples which have been illustrated here but can be varied within the scope of the accompanying claims. For instance the invention could also include a set of different instruments in which the tool heads are different but the connecting shafts the same so that each of them can be connected to one and the same driving tool.