Description

Electrically Operated Heating Tool

The present invention relates to an electrically operated heating tool suitable for melting, cutting and cauterising primarily in the dental, medical and veterinary fields, to a method of manufacture of such a tool and to its use in dental, medical, veterinary and general commercial fields. For use in dentistry, the heating tool when used to melt and cut wax avoids the risk of burning associated with the current use of a metal knife heated in bunsen flame when latex gloves are worn. The heating tool has additional advantages because in battery-powered form it is fully portable and can be used away from gas or mains electricity, and also provides a more controllable heat means for softening, shaping and moulding wax.

For use in the medical field or for surgery in dental and veterinary situations, the cauterising effect of the heating tool, when used at appropriate temperatures, achieves haemostasis by denaturation of protein. This results in coagulation in areas of tissue. Modern diathermy machines have evolved to provide electrical currents in interrupted bursts to give haemostasis and in pure sine waves for cutting. There are hazards

associated with such machines including earthing to produce a therrao electrical burn. In addition there are disadvantages which include lack of portability, because of the need for expensive and complicated circuitry, and difficulties with sterilization. The cauterising heating tool - particularly when battery-powered - avoids these disadvantages and finds wide application in every day surgical procedures, key-hole surgery and dental surgery work to arrest gingival bleeding.

Disclosure of Invention

In accordance with the present invention there is provided an electrically operated heating tool for melting, cutting and cauterisation for use in dental, medical, veterinary and general commercial fields in which there is provided a projecting heating means for melting, cutting and cauterising, having an electrically conducting heating path associated with a temperature-change detecting means, means for controlling the functions of the projecting means, and power source.

The electrically operated heating tool at certain lower temperatures functions to melt the substrate with which it is in contact and thereby achieves a cutting effect, for example, when used in the dental field at a suitable temperature to melt

and "cut" dental wax (melting point around 70°C). However when used in the medical field, the temperatures are preset to those necessary to cut and cauterise tissue and is useful in surgery when the flow of blood is to be arrested after tissue severance. Similarly when the tool is used as a thermal scalpel, the temperature control setting is such that the temperature increase assists cutting. There may also be a further blade set at a temperature to cauterise, to be used in conjunction with the blade warmed to effect better cutting.

As just described, the tool according to the invention finds use in various technical fields, including general commercial such as sail making, hobbying, jewellery working and electronics assembly.

One form of the heating tool which is envisaged is tubular comprising an outer casing housing all components, preferably with a control switch and either or both fitted with a source of electrical power eg. batteries or connected to an alternative power source, such as mains electricity. In this tubular form, the tool is ideal for use in the dental wax-melting technical area. This form is illustrated in Fig. 10.

Alternatively, the tool may comprise the heating means, suitably housed to facilitate

handling and the power means and function controlling means conveniently remotely sited therefrom. In this form, the tool may suitably be used in dental laboratories and in medical applications, such as key-hole surgery.

In all forms, for all applications, the heating means of the tool comprises a substrate which may be non-metallic, metallic, preferably coated in whole or in part with insulating material or a laminate of one or more metals and/or one or more non-metals.

The non-metallic support material used may be ceramic and/or polymeric and may suitably be a laminate or a ceramic partly or wholly encapsulated in a polymeric protective material which is stable at temperatures achieved on the heating means. The non-metallic heating means may optionally be in association with a metallic or non-metallic support material.

When metallic substrates are used as heating means, the metal is insulated from the electrical conducting track and is preferably wholly or partly coated with or encapsulated in an insulating material for example polymeric material.

The heating means may be of any convenient size or shape. For certain purposes, for example, dental surgery work with wax blocks, the means is

preferably in the form of a blade as illustrated in Fig. 1 although other shapes are envisaged. For dental laboratory use, the means may suitably be in the form of a bar or tube, and for cautery means may be other shapes as illustrated in Fig.2. For medical use the means may be in the form of a blade, such as a scalpel blade or a loop, suitable for key¬ hole surgery work, as illustrated in Figs. 5, 7 and 8 respectively.

The heating means carries an electrically conducting heating path connected to a source of power, such as batteries or mains electricity. The path is suitably constructed of conducting material eg. metallic, metallic oxides and salts to form a track connected to the power source.

Alternatively there may be deposited on the non-metallic heating means a carbon film and electrically-conducting metal-impregnated resin, for example, silver impregnated resin. In this particular alternative, it is advantageous to construct the projecting heating means such that at a required temperature, the heat generated is equal to the heat dissipated. To achieve this, the non- metallic support, for example, ceramic material, polymeric material or carbon fibres, which are coated in part with a conducting material eg. silver or silver-impregnated resin and in part with a

carbon - or carbon-containing material, for example, a thin carbon film. It is necessary for both silver-containing material and carbon film to be attached firmly, or bonded, to the non-metallic substrate. The carbon film preferably contains additives, suitably metallic compounds, for example, of barium, preferably barium titanate, which varies the electrical conductivity of the film using its temperature-variable electrical resistance property.

It is a result of the invention that the projecting means possesses rapid heat-up and rapid cool-down. This property is achieved using the non- metallic substrate, metallic conducting means such as the silver-impregnated resin coated over a part of the substrate and carbon film material coated also over part of the substrate.

The projecting heating means may suitably be in the form of a blade coated with the silver-loaded epoxy resin on the shaft of the blade and a silver- loaded epoxy resin to which five to ten percent nickel chrome powder had been mixed, to coat the blade area. This increased the resistance of the epoxy resin and produced a positive temperature coe ficient.

The power source used to generate the heat may be any electrical means, but it has been found that the use of batteries, preferably rechargeable

batteries, enables the device to be used in many different locations. The rechargeable batteries are preferably those of the longer life, high powered type eg. Nicad batteries. These batteries are housed in an outer casing which is preferably fitted with a control switch. The heating tool may be capable of being connected to the mains electricity or other suitable electrical source such as a car cigarette lighter socket, in such a way that the batteries are recharged readily, frequently or continuously.

It is also a feature of the invention that the battery and other inner components may be easily removable, suitably on a slide-out holder, to permit sterilization of the casing by autoclaving or other means. This is illustrated in Fig. 10.

It is also a further feature of the present invention to provide a cover for the projecting means which is also designed to immobilise the operating switch. In this way the dangers involved in accidentally switching on the heater during transit are avoided. A further embodiment includes the provision of light means included in the casing to illuminate working areas, particularly in the mouth or during in vivo operations.

The batteries may be recharged through a suitably designed stand or holder, this stand/holder

being preferably connected to the mains electricity in such a way and at such recharging points in the outer casing, that the batteries are recharged readily, frequently or continuously when the heating tool is on the stand.

The electronic controls are preferably, but not essentially, adjustable in such a way that the heating means is heated to the appropriate temperature for wax work, cautery work and/or electro surgery.

The projecting heating means may be constructed to any suitable size or shape for its purpose and certain shapes are illustrated in Fig. 2.

It has now been found that when the projecting heating means consists of, comprises or contains non-metallic e.g.ceramic, material, the temperature control of the projecting means may suitably be achieved using electronic means which comprises one or more of each of switch, transistor, dual comparator, thermistor, resistor, all on or connected to the projecting means.

Maximum temperature control is achieved by locating the thermistor close to the heating element and feeding back to the comparator, the temperature of the projecting means as a change in resistance. By comparing the voltage so derived with one set via a preset control (temperature adjuster) the output

of the comparator changes state when the preset temperature is reached, thereby completely turning off the switching transistor. When the temperature of the projecting means falls by a few degrees, the comparator again changes state and turns the element on again to maintain the preset temperature, the duty cycle changing to meet demand, so conserving power.

A second comparator may be used in conjunction with a Zenner diode and LED to give an indication of low battery power and the need to recharge - in that form of apparatus which uses battery power rather than mains electricity.

Although the electronics may be located on or in close proximity to the projecting means, they may be conveniently sited remote from the projecting means via wires or other connecting means which carry the power to the cutting or melting means e.g. blade, and carrying back the temperature - sensing feedback, as illustrated in Figs.7 and 8.

In a preferred modification the projecting heating means may suitably comprise a ceramic or other suitable support means for carrying the heating track and thermistor while in intimate or remote connection with it is a further means which comprises, for example, a PC board on or in which are located those other electronic and electrical

co ponents necessary to effect the required heating, temperature control and where appropriate, movement, of the projecting means. Movement of the projecting means may be desirable in application of cautery e.g. key-hole surgery and this movement can be controlled using the remotely sited PC board or other electrical means.

This heating tool is suitable for use in many fields where delicate control of temperature is required, in association with large or extremely minute size of "cutting" area. These include hobbying, jewellery making, electronics assembly, sail making, as well as dental, medical and veterinary applications.

It is a further advantage and feature of the present invention, particularly where most of the electronic components can be remotely situated from the heating (cutting) means, that the temperature and other controls located on, for example, a PC board, can be situated in an area which is convenient for operation. This is of particular importance in key-hole surgery where the cutting, heating and cauterising means is remotely separated from the power and controlling electronic means, the latter being near the VDU which monitors visually the progress of the operation. Digital read-out means may be incorporated on the PC board.

Furthermore, the power source, when batteries are used, may also be remotely situated, thereby permitting the projecting heating means to be carried in a light weight, slim support. The apparatus may optionally be fitted with illuminating means to illuminate the area of "cutting".

It is also envisaged that the range of temperatures over which the apparatus can be operated and within which range the temperature can be finely controlled, may be varied using a control device in association with the electronics situated, for example, on the PC board. The electrically operated heating tool of the invention is now illustrated and further exemplified using the illustrations set out as Figs. 1 to 10. In Fig.l 1 represents the carbon film

2 represents the silver-containing resin. Fig.2 represents various suitable shapes of projecting heating means.

Fig.3 illustrates the tool with the casing for the batteries exposed.

Fig.4 illustrates suitable circuitry for use in the heating tool illustrated in Fig.5 Mode of operation in Fig.4 and Fig.5

When the press switch (1) is closed 2.4v is applied to the bias network comprising resistor (8) and thermistor (4). 29/30ths of this is presented

to the gate of the mosfet (3) turning it on. (Vd - Vs being 0.2 - 0.3volts initially.) As the ceramic blade (5) heats up a decreasing proportion of the battery voltage is applied to the gate due to the action of the thermistor (4). At 110-120°C the mosfet (3) is backed off sufficiently to prevent any further rise in blade (5) temperature. Some overshoot in blade temperature is present in this model due to the thermistor (4) being positioned at the rear of the blade. This position was chosen initially to keep the thermistor cooler as it is being operated close to its maximum temperature rating. When heat is taken from the blade (5) the thermistor (4) increases in resistance allowing more bias to transistor (3) thereby increasing the power supplied to the blade (5) in order to maintain the set temperature. Blade Details:

The blade resistance was approximately 1.6 ohms at 25°C. Operating at 3.5 - 4w the dissipation to maintain 110-120°C was approximately 1.5w.

The blade was a ceramic material partly coated with silver-loaded epoxy in which 5-10% nickel chrome powder was mixed, to coat the blade area.

The purpose of the nickel chrome:

(a) to increase the resistance of the epoxy

(b) to produce a positive temperature

coefficient thereby giving a "positor" effect. When Vg = 0, Id = >10 to 8 amps Electronic Parts List

Key Switch R.S. 320-871

Mosfet BUK555-60B R.S. 658-299

NiCads 700mAH H.D. AA's R.S. 594-656

Thermistor MEC CITEC 3157-303-55006

Resistor IKohms 5% 1/lOw

Two part silver loaded epoxy R.S. 567-604

Fig 6 illustrates suitable circuitry for use in the heating tool illustrated in Figs. 7 and 8 Mode of Operation in Fig. 6, 7 and 8 When press switch (1) is closed, +4.8v or as appropriate is applied to the control electronics. Provided the voltage supplied by potential divider comprising resistor (2) and thermistor (4) on pin 5 of dual comparator (7) is above that on pin 6 the output on pin 7 will be non conducting, keeping the gate of the mosfet transistor at supply potential vis resistor (8) thereby turning mosfet transistor (3) on, and completing the circuit to the blade element (5). Thermistor (4) responds to the rapidly increasing blade temperature, making pin 5 of comparator (7) progressively less positive until it is below the voltage at pin 6 which is derived from the set temperature control (6). At this point the

output of the comparator (7) changes, removing the bias from transistor (3), turning it off. As the blade cools the potential on pin 5 of the comparator (7) increases due to the action of the thermistor (4). Comparator (7) again changes state, turning the blade element on so closely maintaining the preset temperature, the cycle being repeated on a supply and demand basis. The temperature of the blade is determined by the set temperature control (6) precise control being achieved by placing the thermistor close to the heating element. The spare comparator in (7) is used to indicate low battery level, temperature etc. as desired.

With tinned track to heater, the blade is giving approximately lOw. When the switch is released there is effectively a 50k ohms path from gate (3) to Ov. Fig 7 and Fig 8

Fig.7, the heating means used for dental wax work, illustrates the temperature - controlling circuitry detached from the heating means. However the blade and electronics may be in one piece. In the Fig.7 the numbers represent parts described under Mode of Operation above. A & D indicate blade element connections. B & C indicate thermistor connections.

Fig 8, the heating means used for key-hole

surgery work, illustrates the temperature - controlling circuitry detached from the heating means. In the Fig.8 the numbers represent parts described under Mode of Operation above.

Fig.9 illustrates a typical design of thermal scalpel which is suitable for cauterising, for use in dental, medical and veterinary fields. The scalpel, which is heated to a temperature such that haemostasis occurs on cutting, comprises a handle containing the means for controlling the functions on the blade, and power means; and a blade which is metallic, non-metallic preferably ceramic and may be wholly or partly coated with thermally conductive electrically insulating material, and carrying an electrically conducting heating path together with a temperature-change detecting means, ie. thermistor in the form of a chip or as an ink type material printed on the blade.

The scalpel blade is suitable for sterilization and heats to the required controlled temperature at precisely the moment required by the surgeon, by touching or pressing a switch on the handle or blade to initiate the power derived from batteries in the handle or remotely sited, or from the mains.

In the Fig 9 (5) represents the heating element, (4) represents the thermistor and (9) represents the electronics.

Fig.10 illustrates a typical electrically operated heating tool in which there is a projecting heating means (1) having an electrically conducting heating path (2) associated with a temperature- change detecting device (3) means (4) for controlling the functions of the projecting heating means (1) and a power source in the form of batteries (5) or mains electricity (6).

The invention also includes a process for the manufacture of a heating tool for melting, cutting and cauterising, for use in dental, medical, veterinary and general commercial fields which comprises the use of a projecting heating means for melting, cutting and cauterising, carrying an electrically conducting heating path, associated with a temperature-change detecting means joined intimately or remotely to a means for controlling the functions of the projecting heating means, the tool being powered by electricity in the form of batteries or mains electricity.

The invention also covers the use of the electrically operated heating tool for wax melting/cutting, for cutting and cauterising, in association with surgery control equipment for key¬ hole surgery work in dentistry medicine and veterinary and hobbying, sail making, jewellery and electronic component manufacture.