FIELD OF THE INVENTION

The present invention relates generally to battery-powered dental handpieces.

BACKGROUND OF THE INVENTION

Common dental procedures involve the use of a manual drill known as a handpiece to which dental instruments such as endodontic files, also known as reamers, are releasably coupled. During use, different sizes of endodontic files are required to prepare and clean the root canal tissue residue and leave a clean conical cavity to allow rinsing with disinfecting and cleaning fluids and subsequent sealing with a rubber material rubber called "Gutta percha".

There are two main types of endodontic handpieces. A first type is connected to an external energy source such as electricity or compressed air, while a second type of wireless device is powered by a rechargeable battery. The present invention relates to battery-powered handpieces.

During use, the dental tool is inserted into the patient's mouth, thus requiring the handpiece to be sterilized between patients using an autoclave. During sterilization, a different handpiece is then required for the next patient or treatment must be delayed under sterilization is complete. This is not satisfactory. In addition, there is increasing concern among practitioners and patients alike that sterilization using an autoclave may not always be totally effective particularly when commercial pressures militate against protracted sterilization procedures. Furthermore, effective sterilization requires high temperatures which eventually damage the handpiece. There is therefore a requirement to avoid or reduce the need for sterilization and this has spurned interest in disposable handpieces for use with a single patient. Known handpieces of both types for use with endodontic files operate at a motor speed in the range of 20 to 30,000 rpm and have a body fixed to a metallic head that includes a speed reduction mechanism for reducing speed and increasing torque. Working speed is typically in the range 150 - 2,500 rpm Max. Both types of handpiece have a controller for controlling both the speed of rotation of the file and the torque transmitted thereto according to the size and purpose of the file.

Conventional endodontic files when connected to the handpiece rotate continuously in a single direction. The file includes a metal handle whose edge has a D-profile that ensures a decisive mechanical lock of the file in the head of the handpiece, so as to allow the required high torque to be transmitted to the file and thereby facilitate entry of the file into and expansion of the root canal.

There is another type of handpiece having a so-called "reciprocal" rotary mechanism, which rotate a partial forward rotation of about 2/3 of a revolution and then rotate in reverse about 1/3 revolution, and in this manner the file is advanced into the root canal. Some of these handpieces have a mechanism that can also grip a plastic handle of a manual endodontic file. Rotation speeds vary from 300 to 5,000 rpm when the movement is forward-reverse as described.

After use, the endodontic file is discarded and the complete handpiece must be sterilized giving rise to the same concerns as described previously.

IL 212101 discloses a disposable endodontic handpiece 10 as shown in Figs. 1 and 2. The handpiece 10 comprises a generally hollow body 11 configured at a first end 12 for accommodating a dental tool 13 and configured at a second end 14 opposite the first end for coupling to an adapter 15 that is configured for coupling to a micromotor 16 shown in Fig. 2. The dental handpiece 10 is disposable typically being formed of plastics so that after use it is discarded thereby obviating the need for sterilization. The adapter 15 is sufficiently remote from the working end of the handpiece and is held by the dentist so that it does not itself penetrate the oral cavity. The motor is typically part of a "low speed" handpiece operating at a maximum speed of 40,000 rpm to be used with reamers requiring higher torque.

US 2011/0275327 describes a wireless dental device having a circuit board that communicates by short range protocol such as ZigBee or Bluetooth to a computer so as to allow control parameters of the dental device to be set externally. US 2011/0065063 disclose an adapter for a dental prophylaxis handpiece. It is not used for an endodontic file.

US20090061384 discloses a sterile disposable dental handpiece for a dental drill constructed from two shells and a center core, the center core having a flow deflector on one end. The device is driven by compressed air and to this end includes at one end an impeller against which air is injected at high pressure. This is effective but since the complete handpiece is expendable is costly and wasteful.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a dedicated handpiece for an endo- dontic file.

According to the invention there is provided a dedicated dental handpiece having the features of claim 1.

In some embodiments, an adjustable stop is securely coupled to the head portion for mechanically limiting depth of penetration of the dental tool into a patient's root canal.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 is a pictorial representation showing a perspective view of a disposable prior art dental handpiece as shown in IL 212101;

Fig. 2 is a pictorial representation showing a perspective view of the prior art handpiece shown in Fig. 1 attached via an adapter to a micromotor;

Fig. 3 is a pictorial representation showing an exploded perspective view of a dental handpiece and disposable head portion according to a first embodiment of the invention;

Fig. 4 is a pictorial representation showing a detail of the head portion shown in

Fig. 1 ;

Fig. 5 is an exploded view of the handpiece and head portion shown in Fig. 1 ; Fig. 6 shows schematically a detail of the handpiece shown in Fig. 1 ; Figs. 7a and 7b show pictorially use of a mechanical stop securely attached to the handpiece for limiting depth of penetration of a dental tool into the dental root canal;

Fig. 8 shows pictorially an exploded view of a handpiece and disposable head portion according to a second embodiment of the invention;

Fig. 9 shows pictorially the handpiece and head portion shown in Fig. 6 when engaged;

Fig. 10 is an exploded view showing a side elevation of the handpiece and disposable head portion;

Fig. 11 is a block diagram showing functionally a motor control circuit within the dental handpiece.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description of some embodiments, identical components that appear in more than one figure or that share similar functionality will be referenced by identical reference symbols.

Figs. 3 to 5 show a dental handpiece 20 comprising a generally hollow body 21 accommodating a motor (not shown) having an operating speed less than 50,000 rpm. A protruding bush 22 having a central bore constitutes a first mechanical transmission element that is coupled to a shaft of the motor within the body portion 21 proximate an end 23 thereof. The end 23 is configured for coupling to a disposable head portion 25 that accommodates a spindle 26 constituting a second mechanical transmission element adapted to frictionally engage the bush 22 when the head portion 25 is coupled to the body portion 21. The first end 27 of the head portion is recessed for accommodating the protruding bush 22, so that the head portion 25 fits snugly on to the handpiece 20. Alternatively, the motor shaft may protrude from the handpiece and engage a bush in the head portion 25.

The dental handpiece 20 does not itself come into contact with a patient's oral cavity and may therefore be formed of molded plastics there being no need for it to be sterilized and consequently no need to withstand the very high temperature of an autoclave. The handpiece 20 is a compact battery-operated device needing no external power connection. During use, only the head portion comes into contact with the oral cavity and its surroundings. The head portion 25 is used for only a single patient and discarded after use, thus avoiding the need for autoclaving and allowing it to be formed of an inexpensive plastic molding.

As shown in Figs. 6 and 7, the head portion 25 includes a connector 30 that constitutes a rotatable barrel for gripping a dental tool 31 disposed within the body at the first end of the handpiece, and a speed transmission 32 disposed within the body and connected to the connector for transferring rotation thereto, typically at a speed ratio of 1 : 1. In Fig. 6, the speed transmission is depicted schematically as a protruding shaft 33 that engages the bush 22 in the handpiece 20 constituting the first mechanical transmission element. Typically the speed transmission 32 includes a pair of intermeshing bevel gears 34, 35 that convert rotation of the shaft 32 to perpendicular rotation of the connector 30, so that when the dental tool 31 is inserted into the connector it is rotated at 90° to the shaft. The shaft 32, which is shown schematically in the figures, is gripped within the bush 22 in the handpiece 20 so that rotation of the motor within the handpiece 20 is conveyed to the connector 30. In the figure, the shaft 33 is shown as flexible so as to indicate that the opposing ends thereof are not necessarily collinear. However, in an alternative embodiment, the shaft 33 may be straight and rigid.

The connector 30 is adapted for coupling to the dental tool via friction alone as described in WO/2021/104705 entitled "Rotary Endodontic File with Frictional Grip" in the name of the present applicant. To this end, a dedicated endodontic file is used having at an end that fits into the connector an elastomeric grip serving to frictionally engage the connector. On insertion into the barrel, the elastomeric grip is squeezed by the connector and the endodontic file is supported therein by friction alone without any other locking means.

Owing to the superficial similarity between the appearance of the prior art arrangement of Fig. 2 and the invention shown in Fig. 3, it is instructive here to state the principal distinction of the invention over the arrangement disclosed in IL212101. Thus, in IL 212101 a handpiece 10 is coupled to a high-speed micrometer 16 via an adapter 15, which matches the speed of the micrometer 16 to the required rotational speed of the tool. In the present invention the handpiece is coupled directly to a dedicated low-speed micrometer so that neither speed matching nor an adapter is necessary. This in turn allows a custom handpiece to be utilized that is dedicated for use with the head portion and is ergonomically designed to be efficient for endodontic applications, specifically root canal treatment.

Figs. 7a and 7b show pictorially use of an adjustable stop 40 that may optionally be provided to limit depth of penetration. The adjustable stop 40 is threadably coupled to the first end of the body so as to be securely fixed thereto and incapable of voluntary movement during use. Fig. 5b shows how the stop 40 limits depth of penetration of the dental tool 23 into the dental root canal.

The handpiece 20 is a dedicated device that operates at low speed less than 50,000 rpm and most typically 7,000 rpm ± 10%, this being very significantly lower than state of the art devices, which can operate at 300,000 rpm or more. The lower speed is such that lubricating gel or fluid can be applied locally without requiring external irrigation. Furthermore, it is adapted to operate by depressing a pushbutton 41, upon release of which the handpiece 20 stops instantaneously. Alternatively, depressing the pushbutton 41 may be adapted to operate the handpiece 26 in burst mode for a preset time interval of 3-8 seconds. The time interval may be set by a dial or selector switch (not shown). Alternatively, a USB socket 42 (constituting a communications port) may be provided for allowing connection of the handpiece 20 to an external computer such as a PC allowing the time interval to be set externally. Instead of a USB socket 42, there may be provided a short range wireless transceiver such as BlueTooth™ or ZigBee that effects short range wireless communication with a PC. The dedicated handpiece 20 is particularly adapted to operate with endodontic files formed of stainless steel of the kind described in WO/2022/143928 and entitled "Endodontic File and Brush". Rotation of stainless steel files can be interrupted even while the file remains inside the root canal, something that cannot be done with files formed of nickel-titanium alloy (Ni-Ti), owing to the difficulty in subsequent activation and rotation of the file.

Figs. 8 to 10 show pictorially constructional details of a handpiece 20 and disposable head portion 25 both formed of plastics according to a second embodiment of the invention. The motor shaft in the handpiece 20 is coupled to a rotating bush 22, which constitutes the first mechanical transmission element and protrudes from the end 23 of the handpiece. The handpiece 20 has a single direction of rotation and a single fixed speed which decreases automatically in accordance with the file resistance under workload. The maximum speed of the motor under no-load conditions is 9 to 20,000 rpm. The typical motor speed under load conditions is 6,000-8,000 rpm.

As best seen in Figs. 9 and 10, the handpiece 20 is shaped so that when attached to the head portion 25, the upper surface of the handpiece is beveled where it engages the head portion. The pushbutton 41 is ergonomically mounted in the beveled surface so as to be ideally located for operation by the dentist's forefinger, which is easily held on the pushbutton so as to maintain it depressed, while allowing momentary dislocation whereupon the motor instantaneously stops rotating. The bush has on an outer wall 22 an axial rib that serves as key 45 and engages a corresponding slot (not shown) in the head portion 25, thus facilitating correct engagement and ensuring that the pushbutton 41 is uppermost and properly aligned with the tool 31. The pushbutton 41 reacts instantaneously to finger pressure and serves only to switch the motor on and off. A lamp or bar display (not shown) may be mounted in the handpiece to provide a visual indication of the battery status.

The internal construction of the head portion 20 may be similar to that described above with reference to Fig. 6. In any event, the connector 30 is mechanically coupled to a spindle in the head portion 20, typically via a pair of meshed gears, so that rotation of the spindle induces rotation of the connector 30. Preferably, the tool 31 is retained within the connector 30 by friction alone as described in WO/2021/104705 without any other locking means. Thus, the endodontic file is retained within the head portion by friction only between the rubber handle of the file and the plastic seating of the connector 30, which is coupled to the gear train. This manner of retaining the file creates a friction clutch that slips on undue and sudden load and thereby protects the file from fracturing and avoids damage to the root canal caused by excessive power. All parts of the head are formed of plastic including the shaft which transmits rotation of the motor. The motor shaft is coupled to the rotating spindle in the head portion by means of a plastic clutch that locks the spindle in the head portion by friction. There is no contact with metal parts.

The body of the handpiece is formed entirely of plastic and contains the battery, a single-speed motor connected for rotation in a clockwise direction, an electronic actuation and control circuit 50 (shown in Fig. 11) mounted on a small PCB on which the pushbutton 41 is also mounted. The electronic control circuit 50 is adapted to stop the motor automatically if the file rotates for longer than several seconds under no load: this ensures idle mode when working in or out of the root canal at no load. Likewise, the electronic control circuit preferably includes a time interval controller 51 adapted to control the motor speed as a function of load and resistance applied by the root canal through the endodontic file to the motor. The handpiece may be optimized to co-operate with custom endodontic files manufactured by the present Applicant. In this case, dimensions of the handle of the custom files are incompatible with conventional endodontic files, which are thus unable to operate with the handpiece 20 according to the invention.

It will also be appreciated that while the dental handpiece in the described embodiment is formed of plastics, it may be formed of any other material suitable for one-time use.

It should also be noted that the stop according to the invention differs from known devices in that it is both adjustable and also capable of being securely attached to the head of the handpiece, so as to prevent voluntary movement during use. While in the embodiment shown in Fig. 1, it is threadably attached to the head potion, it will be understood that the manner of its attachment and securement is not critical as long as it fulfills these requirements. Thus, the stop could be provided with a ratchet or knurled locking grub screw which, when tightened, prevents axial sliding of the stop or any other suitable securement means.

It will also be appreciated that features described with reference to only one of the embodiments may also be used with the other embodiment. It should also be noted that the appended claims form an integral part of the description.