WO1996034578A1

WO1996034578A1 - Apparatus for placement, condensation and curing of photopolymerizable dental material

Info

Publication number: WO1996034578A1
Application number: PCT/CA1996/000270
Authority: WO
Inventors: Nicholas Bekesch
Original assignee: Nicholas Bekesch
Priority date: 1995-05-02
Filing date: 1996-05-01
Publication date: 1996-11-07
Also published as: CA2148438A1; AU5394796A

Abstract

An apparatus for placing, condensing and curing photopolymerizable dental restorative material and photopolymerizable dental cement without substantially restricting the motion of the dentist. A first handpiece has a tip for use in condensing or plugging, as well as for the emission of ligth for curing. Visible light having a wavelength of about 400-500 nm. is emitted in short, high intensity bursts for rapid curing. In addition to the plugger, the end of the handpiece also has a blade that may be used for applying resin. Thus, the device need only be twisted, rather than flipped, to perform this function. The handpiece is an elongated member with a hexagonal cross section, and alternating sides of the tool have a conductive metal strip. The handpiece is only armed when all three strips are touched simultaneously. The handpiece is not armed when resting on a surface such as the chest of a patient, where at most two metal strips would receive contact. Emission of light from the handpiece can be controlled with a foot control. The handpiece may be detached from the fibre optic cable that connects it to a light source, and may be discarded or sterilized and replaced. A second handpiece has a forceps shape for placing around orthodontic brackets. Each prong of the forceps is equipped with a fibre optic bundle so that the firing of high intensity light bursts from the tips occurs simultaneously at two places on either side of the bracket. A light source module is connected to three handpieces by flexible fibre optic cables. There is mutual exclusion circuitry to prevent simultaneous firing of certain handpieces.

Description

APPARATUS FOR PLACEMENT, CONDENSATION AND CURING OF PHOTOPOLYMERIZABLE DENTAL RESTORATIVE MATERIAL

FIELD O F THE INVENTION

The present invention relates to apparatuses for placing, condensing and curing photopolymerizable dental material .

BACKGROUND OF THE INVENTION

In the past, dentists have primarily used gold and silver alloys, including silver-mercury amalgam, to fill or otherwise restore broken or decayed teeth . However, there has been a great deal of controversy about the safety of silver-mercury amalgam ever since its introduction, and both dentists and patients are increasingly avoiding its use .

In recent years, new dental materials for restoration and adhesion have been developed having the advantages of roughly matching the colour of a patient's teeth and of being highly durable. Typically, these new materials are composites of a photopolymerizable organic bonding agent and an inorganic filler material . The composite material or resin is applied to the tooth in thin layers and then cured by exposure to visible light, generally in the 400 to 500 nm ., or blue, range. The emission of light for curing from a dental handpiece can be continuous or pulsed. Known apparatuses for curing photopolymerizable dental materials typically include a lamp di sposed within a housing, a power supply, a transformer and timing circuits. Light ^■•^■emitted by the lamp is often conveyed to the proximity of the dental material by means of a flexible or rigid fibre optic wand. A filter for eliminating unwanted optical wavelengths is usually incorporated into the light path .

Conventional light units are generally powered by 75 to 150 W quartz halogen lamps. Light having a wavelength of 400-500 nm . is focused to a 6- 1 1 mm , fibre optic wand. Quartz halogen lamps have certain disadvantages: First, they produce a great deal of heat, both radiant and conductive . Second, the emission spectrum of the quartz halogen lamp is predominantly in the red and infrared part of the spectrum, with blue light comprising less than 1 0% of its output. As a result, the length of time required for curing of the photopolymerizable material is inconveniently long.

Typically, a dentist places dental material for restoration in a filling, condenses it with a plugging tool and uses a separate light-delivery handpiece for curing. To control shrinkage of the filling material during polymerization, the material should be cured every 1 - 1 .5 mm . Curing time is typically approximately 20 sec . per exposure . A moderately sized posterior filling requires 8 to 12 exposures, or approximately 3 - 4 minutes.

Long exposures contribute to the arm of the dentist or dental assistant performing the curing becoming fatigued and possibly oscillating or moving off target . The latter would, of course, necessitate even longer exposure time . Moreover any movem ent of the filling material during curing, especially when the initial set takes place (generally during the middle third of the exposure), could lead to restoration failure. This in turn would increase the risk of recurrence of decay at the site in the future. Composite filling failure is also known to occur when the filling material is under-cured, as is not uncommon in poorly accessible regions such as the gingival margin .

Usually, the light curing procedure i s completed by an assistant, especially when a long exposure time is required. Often, the assistant does not have first-hand knowledge of the internal form of the cavity preparation, and can frequently expose the wrong area of the tooth . In addition, the dentist wastes time waiting for the curing to be completed. In a typical day during which 20 fillings could easily be filled, this could add up to approximately 60 to 80 minutes of wasted, or down, time for the dentist .

Examples of stand alone light-delivery handpieces are shown in many patents, including U . S . Patents No . 4,888,489 to Bryan, No. 5 , 147,203 to Seidenberg, No . 5 , 147,204 to Patten et al . , No . 4,229,658 to Gonser, No . 4,309,617 to

Long, No . 4,450, 139 to Bussiere et al . , and No . 5 ,049,068 to Sterrett et al .

Some light delivery handpieces incorporate additional features, but still suffer from the problems discussed above or worse, given the additional restrictions provided by added weight and limitations on flexibility. U.S . Patent No. 5 ,007,837 to Werly discloses a device for two-step photopolymerization of dental restorative material . The disclosed tool can also transmit air and water through conduits. U . S . Patent No . 5 ,022,856 to Zimble discloses a dental probe including a tip that is used both to m easure the depth of a dental pocket and to transmit light. U . S . Patent No . 4,666,405 to Ericson discloses an adaptor for pressing the matrix band of a filling, while at the same time delivering light to cure the filling material .

U.S . Patent No. 5 ,030,093 to Mitnick attempts to deal with these problem s by providing a device for delivering, condensing and curing photopolymerizable dental material. The device includes a fibre optic tool . The working end of the tool emits light both from its end and sides. The appropriate working end m ember for a job is selected so that it approximates the shape of the tooth on which work is being done. The device may alternatively be used for providing bleaching light for bleaching teeth with SUPEROXOL™

In order to illuminate the handpiece of the Mitnick patent, the handpiece is held by the dentist while an assistant brings a conventional curing light into optical proximity with the handpiece after placement of the dental m aterial . Such double holding of the instrument and light source immobilizes both the dentist and the assistant. The denti st cannot take a few seconds rest while the assistant cures the filling and the assistant cannot do any other task without risking moving the instrument and causing restoration failure,

Mitnick alternatively suggests having a battery operated light source in the handpiece; however, this could add significant weight and size to the handpiece .

Orthodontists also suffer through the drawbacks of stand¬ alone light delivery systems. Such system s cannot only be used for curing photopolymerizable dental material for restoration, but also for curing photopolymerizable dental material for adhesion, such as dental cement used for securing orthodontic brackets. Ordinarily, an orthodontist; Picks up a bracket with forceps or a haemostat, picks up photopolymerizable cement on the bracket, places the bracket on a tooth, cleans off excess cement, rem oves the forceps and picks up a light-delivery tool . During the change between the forceps and the light tool there can be vibration of the bracket, which can increase crevicular seepage. Even when the orthodontist continues to hold the bracket but allows an assistant to deliver curing light to the area, there is potential for vibration and associated curing problems.

A standard metal orthodontic bracket having a micro-m esh base which is held in place by photopolymerizable cement generally requires a minimum of 20 seconds curing from each of 4 directions. Usually, to ensure proper curing, this time is increased to 40 seconds per exposure . Thus, approximately 30 to 60 minutes of curing tim e are required for each patient. Other work cannot be done at the same time, as m ovement of the light tool may result in undercuring of the bonding cement or resin, thus making the bonding unpredictable.

S U MMARY OF TH E IN VENTION

In a first aspect, the present invention provides a dental system for use by a dentist, The system has a handpiece shaped for use in the application of dental restorative materials requiring curing by light. The handpiece has a fibre optic bundle directed to an area where curing will be required. The system has a source of light independently supported from the handpiece . A fibre optic cable is used for optical connection between the fibre optic bundle and the source during application of the material without substantially restricting the motion of the dentist.

In a second aspect, the invention provides a handpiece for use in the system of the first aspect. The handpiece has a body shaped for use in the application of dental restorative materials requiring curing by light. It has a fibre optic bundl e physically connected to the body and directed to an area where curing will be required, It also has a socket for connection to the fibre optic cable and the fibre optic bundle during application of the material Without substantially restricting the motion of the dentist. The body may have a length with the socket at a first end of the length . The fibre optic bundle extends from a second opposing end of the length to a tip for the delivery of curing light. The body has a blade extending from the second end. The blade and bundle are angled from one another to allow for separate use of the blade and bundle by the dentist.

The body may alternatively have a forceps shape with two prongs. The bundle extends into each prong to respective tips for the delivery of curing light. The forceps-shaped body may have prongs that are each at an angle pointing toward a midline drawn between the prongs through the handpiece . This aims the bundle at the tips toward an area where illuminating light is likely to be desired when the handpiece is in use .

In a third aspect, the invention provides a light source module for connection to a fibre optic cable used with a dental handpiece for light curing of dental material . The m odule has a light source for producing curing light, a switch, a timing block, an ignition block, and a charging block . The activation of the switch causes the timing block to time for a pre-determined time less than would overheat the light source, while remaining useful for curing the dental material . The ignition block triggers the illumination of the light source while the timing block is timing. The charging block provides illumination power to the light source when the light source is triggered .

In a fourth aspect, the invention provides a light source module for connection to a fibre optic cable used with a dental handpiece for light curing of dental material with a sensory area on the handpiece . The module has a light source for producing curing light, a sensing block connected to the fibre optic cable for sensing capacitive changes at the sensory area indicative of a dentist's hand, an ignition block, and a charging block. The sensing by the sensing block of capacitive changes at the sensory area indicative of a dentist's hand enables the ignition block to trigger the illumination of the light source. The charging block provides illumination power to the light source when the light source is triggered.

The module may have a first switch readily accessible to the dentist while using the handpiece. The first switch i s for activating the ignition block. The module may also have a second switch actuated by removal of the handpiece from the module and replacement of the handpiece . The second switch allows the activation of the ignition block when the handpiece is removed and prevents activation of the ignition block when, the handpiece is in place in the module .

In a fifth aspect, the invention provides a light source module similar to that of the fourth aspect, but also having a timing block, Sensing by the sensing block of capacitive changes indicative of a dentist's hand at the sensory area enables the timing block to become ready to time for a pre¬ determined time less than would overheat the light source, while remaining useful for curing the dental material . The ignition block triggers the illumination of the light source while the timer is timing. Final activation may be provided by a switch readily accessible to the dentist when using the handpiece .

In a sixth aspect, the invention provides a light source module similar to that of the fifth aspect; however, it acts with a handpiece having more than one sensory area. The timing block is made ready to time only when all of the areas are contacted simultaneously . Final activation may be provided by a switch readily accessible to the dentist when using the handpiece .

BRIE F DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made by way of example to the accompanying drawings, which show an apparatus according to the preferred embodim ent of the present invention and in which:

Figure 1 is a side elevational view of a dental handpiece according to a first preferred embodiment of the present invention; Figure 2 is a bottom plan view of the dental handpiece of Figure 1 ;

Figure 3 is an end view of the handpiece of Figure 1 . looking into the handpiece in the direction of arrow III: of Figure 1 ;

Figure 4 is a cross-sectional side view of the handpiece of Figure 1 taken along the line IV-IV of Figure 2 ;

Figure 5 is a cross-sectional side view of an end of a fibre optic cable for mating with the handpiece of Figure 1 ; Figure 6 is a diagramm atic side elevational view of a light source according to a preferred embodiment of the present invention;

Figure 7 is a top plan view of a dental handpiece according to a second preferred embodiment of the invention;

Figure 8 is a side elevational view of the handpiece of Figure 7 ;

Figure 9 is a cross-sectional side view of the handpiece of Figure 7 taken along lines IX - IX;

Figure 1 0 is a perspective view of an application and curing system according to a preferred embodiment of the invention;

Figure 1 1 is a block diagram of a single handpiece light source module according to a preferred embodiment of the invention;

Figure 12 is a block diagram of a dual handpiece light source module according to a preferred embodiment of the invention ; Figure 13a is the upper left quadrant of an electrical circuit diagram of a three handpiece light source module employing the m odules of Figure 1 1 and 12 and for incorporation in the system of Figure 1 0;

Figure 13b is the lower left quadrant of the electrical circuit diagram of Figure 1 3a;

Figure 13c is the upper right quadrant of the electrical circuit diagram of Figure 13 a;

Figure 13d is the lower right quadrant of the electrical circuit diagram of Figure 13a;

Figure 1 4 is a block diagram of an alternate embodiment of a three handpiece light source module for incorporation in the system of Figure 1 0;

Figure 15 is a side elevational view of a portion of the handpiece of Figure 7 in use with an orthodontic bracket and a tooth; and

Figure 16 is a cross-section of a cradle used in the system of Figure 10 showing the placement of a microswitch .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figures 1 through 4, a dental handpiece 10 according to a first preferred embodiment of the invention has a body 12 made of a rigid, light, opaque, temperature- resistant plastic or other material having similar characteristics that is safe for oral use, such as high temperature epoxy resin, or temperature-resistant composite resin . Temperature resistance may not be a primary consideration where the body 12 is disposable, rather than requiring high temperature sterilization for re-use . In this case, materials such as polystyrene, acrylic or epoxy resin, or epoxy- or polyester-bound composite material may be suitable . Preferably, the plastic is resistant to temperatures of 140 - 150 °C (typical autoclaving temperature) or more for cleaning and re-use. The body 12 can be suitably manufactured using inj ection moulding techniques.

As shown in Figure 3 , the body 12 has a hexagonal cross- section, which is preferably approximately 6-7 mm . in diam eter for most hands, similar to a pencil thickness. However, other shapes may also be used. Alternating longitudinal faces 13A, 13B , 13 C of the body are recessed and house respective corrosion-resistant conductive strips 14A, 14B, 14C . The recesses and the strips 14A- 14C are slightly narrower than the respective faces 13A- 13 C . The strips are conveniently of brass, stainless steel, copper or other similar conductive material that is resistant to corrosion or treated for resistance to corrosion . Each strip 1 4A- 14C is connected through the body 12 to a respective conductive wire 16A, 16B , 1 6C of an arming/disarming system . The body has a hollow core 1 7 partially filled by a fibre optic bundle 1 8.

The body 12 was previously described as opaque . It i s possible to make a body 12 from non-opaque material; however, this is not preferred, as transmission of light through fibre optic bundles is not perfect, especially if som e fibres are broken during manufacture or at a junction point of two fibre-optic bundles. When dealing with high intensity light, any leakage could result in a blinding flash radiating from the fibre optic bundle if it is not blocked by an opaque material .

As shown in Figures 1 , 2 and 4, the body 12 tapers inwardly at a first end 1 1 A of the handpiece 1 0 such that the fibre optic bundle 1 8 protrudes from the body 12. Just beyond the end 1 1 A, the bundle 1 8 has an elbow 20. The bundle 1 8 tapers inwardly after the elbow 20 to a rigid tip 22 that is preferably approxim ately 1 -1 .5 mm . in diameter in order to retain strength while being useful for m ost filling operations. The tip 22 and elbow 20 are made of fused or bonded fibre optic filaments, or possibly m ono-filament. The exact shape, dimensions and geometry of the tip 22 nay be varied to suit its use . The pointed nature of tip 22 is particularly useful for plugging or condensing dental material in deep recesses.

The bundle 1 8 could be formed from mono-filament to reduce costs; however, this may reduce the resistance of the tip 22 to being broken.

A blade 24 extends from the end 1 1 A opposite the elbow 20 and is angled away from the tip 22. The blade is particularly useful in Picking up dental material from storage and placing it where desired on a tooth . Referring to Figure 4, at the other end 11B of the body 12 is a socket portion 25. Here, the body 12 extends beyond the fibre optic bundle 18 at its core to form a receptacle 26 for receiving an end 28A of a fibre optic cable 28, shown in Figure 5 and discussed below. Referring again to Figure 4, the wires 16A-16C extend beyond the body 12 out the end 11B. Only wires 16B, 16C are visible in Figure 4 due to the cross- section. Being easily removable from the cable end 28A, the handpiece 10 is able to be sterilized by autoclaving.

The cable 28 shown in Figure 5 is approximately the same diameter (1/8-3/16 in is typical) as an encased fibreoptic bundle 29 surrounded by sheathing 30. Three thin leads 31A,

31B and 31C (31C is not visible in Figure 5 because of the cross-section) are coaxial to the cable 28 and also enclosed in the sheathing 30. For example, polyvinyl chloride flexible hose could be used. The cable 28 could be replaced by another non-coaxial cable 28 serving similar functions to those described herein. The relatively small diameter of the cable 28 permits it to be quite light and flexible.

As shown in Figure 5, the cable 28 terminates in a plug

32 that is conveniently made of a moulded rubber or rubber¬ like material. The plug 32 includes three cavities 34A, 34B, 34C (34A.34B are visible in Figure 5) for receiving the protruding wires 16A, 16B, 16C, respectively, and connecting them to respective leads )31A, 31B, 31C. The end 28A protrudes beyond the plug 32 for mating with the receptacle 26. The plug 32 can be attached to and detached from the socket 25 easily. The flexibility of the cable 28 allows the handpiece 10 to be manipulated quite easily and for a relatively long period of time in terms of the application and curing of dental material .

Referring to Figure 6, a light source 36 has a socket 38 for mating with a plug, not shown, on the opposite end, not shown, of the fibre optic cable 28 to that shown in Figure 5. The socket 38 includes a receptacle 40 for receiving the end of the fibre opti c cable 28.

The light source 36 includes a compact, high power xenon gas discharge tube 42 encased in a housing 44 with a reflective interior. The housing interior can be coated with a highly reflective titanium oxide paint suitable for exposure to high temperatures. The housing 44 exterior may be ribbed, not shown, to facilitate heat dissipation . Base 46 of the light source 36 is preferably made of ceramic material, for electrical insulative and heat resistance properties, that may be white in colour for reflectivity . Electrical connections 48 are provided to the tube 42.

The light source 36 may include a lens 50 between the tube 42 and the socket 38 for tight focusing of the light discharge directed to the cable 28, which has a relatively small diameter. The use of a lens 50 is not essential; however, it may reduce the power requirement of the gas discharge tube 42. The lens could be similar in construction to a very wide aperture, short focus telescope, not shown, consisting of a large converging front element and a small diverging rear element. The desired result in m ost cases is to bring as much as possible of the direct rays with an angle of entry of less than 30° (i .e. , +/- 15⁰ from the axis of the fibre optic cable) into the fibre optic cable 28. The lens 50 can also be reflex with the converging and/or diverging elements being replaced by spherical or, preferably, parabolic reflectors. It is possible to facet a highly refractive glass (e.g., high lead glass or synthetic crystal, such as synthetic rutile or cubic zirconium) to collect light rays, internally reflect them and permit them to emerge through a designated facet.

A filter 52 may be positioned after the lens to allow the passage only of light of the curing wavelength for the dental material used in a particular application, usually wavelength 400-500 nm . The necessity and type of the filter 52 are determined by the output spectrum of the light source 36 and the desired spectrum for optimal cure, including molecular interlinking and strength. A blue filter 52 is dictated by the emission spectrum of the xenon tube 42 , which produces almost a complete spectrum ranging from infrared to ultraviolet, with principal emission in the blue portion of the spectrum . As an example, if an argon gas laser, not shown, is used for the light source, then it might be necessary to filter out the yellow and green light components. Figures 7, 8, and 9 show a dental handpiece 60 according to a second preferred embodiment of the invention. The handpiece 60 is shaped in the form of forceps with prongs 61 and a body 62 made of the same material as the handpiece 10. An inner surface 62A of the prongs 61 is lined with conductive strips 63 made from the same m aterial as strips 14A- 14C, although possibly a little bit heavier due to the possibility of wear. The strips 63 extend from the inner surface 62A and wrap about side surfaces 62B of the Prongs 61 ,

Each of top and bottom surfaces 64 of the handpiece 60 has a recess 65 that houses strips 66 of a similar material to strips 14, both the recesses and the strips 66 being slightly narrower than the surfaces 64. Connected to the conductive strips 63 , 66 are wires 67A, 67B , 67C extending through the body 62 and similar to wires 16A, 16B, 16C of the handpiece 10. Only three wires 67 are necessary, as one wire 67A connects to the top strip 66, one wire 67B connects to the bottom strip 66, and one wire 67C connects to one of the strips 63, which are in turn connected to one another at the juncture 68 of the prongs 61 .

The body 62 has a hollow core 69 that extends into each of the prong 61 . A fibre optic bundle 70 fills the core 69 from beneath a socket 71 , similar to socket 38, through respective tips 72 of the prongs 61 . The bundle 70 can be flattened out to take the shape of tips 72. Each tip 72 is preferably angled so that light from the bundle 70 leaves the handpiece 60 at an angle of about 45° to the midline of the forceps, as shown in Figures 8 and 9. Attached to the inner surface 62A of each prong 61 is an adjustable leaf spring 73.

The spring 73 preferably terminates about 0 ^~5 mm . short of the respective tip 72. This will provide a good hold on, for example, an orthodontic bracket (later described as component 1 80) and will permit the tips 72 to emit curing light on each side of the base of the bracket 180.

Referring to Figure 1 0, an application and curing system 75 has a three handpiece light source module 76, three handpieces 10, 60, 77, and an air-actuated, on-off foot switch device 78. The handpieces 10, 60 are those described previously, while the handpiece 77 is an assistant's handpiece 77.

The assi stant's handpiece 77 is simply a light delivery tool and does not incorporate features for the application of restorative material . The assistant's handpiece 77 has a button 79 on it for triggering its activation . The assistant's handpiece 77 could have a wide angle light spreading tool for use in curing a wide area. Although it could incorporate conductive strips, not shown, such as the strips 14 , 66 of the handpieces 10, 60 (the function of which will be described later), this would not be required for most assistant applications.

The switch device 78 can be a separate hard-wired, foot- operated, momentary single pole single throw (spst), normally off switch, or it can be an air-actuated momentary spst switch, hard-wired into the tool 79 and connected to the electrical circuit of the module 76 by a low voltage lead, not shown . Another alternative is to mount the air-operated spst switch inside casing 83 and connect it to the tool 79, either air line or to a spare handpiece via a dummy handpiece connector, not shown, built into the casing 83 . A further alternative is to use a built-in infrared receiver in the casing that receives transmission from the foot device 78, or a separate infrared receiver hard-wired to the electrical circuit of the module 76.

Each of the handpieces 10 and 60 are connected to the m odule 76 by respective fibre optic cables 28, as described previously . The assistant's handpiece 77 is similarly connected to the module 76 by a fibre optic cable 81 similar to fibre optic cable 28, but without the co-axial leads 3 1 .

The module 76 has the casing 83 with a system on-off switch 85 , two handpiece m anual override switches 86A, 86B for the handpieces 1 0 and 60 respectively, and three cradles 87A, 87B , 87C for holding the handpieces 10, 60, 77 respectively. In the cradles 87A and 87B are respective microswitches 89A (see Figure 16 for detail) and 89B . Each microswitch 89A, 89B is opened when its respective handpiece 1 0, 60 is in the cradle and closed when the -handpiece 1 0, 60 is removed from the cradle .

The detailed operation of the system will be described further below with reference to the internal structure of the module 76 ; however, the basic principle is to turn on the module 76 at switch 85. As an example, handpiece 1 0 is required by a dentist, and it is removed from its cradle 87A. Microswitch A closes to indicate that the handpiece 1 0 has been removed. When the dentist grasps the handpiece 1 0 in his/her fingers, the handpiece is armed and ready to be fired. The dentist applies restorative material to the patient's teeth using the blade 24. When the application process is complete, the handpiece 1 0 is simply twisted in the dentist's fingers to aim the tip 22 at the applied material for condensation . When condensation is complete, the device 78 is depressed to activate the module 76 to provide curing light at the tip 22. When curing is complete, the dentist releases the device 78 and light at the tip 22 is extinguished.

Since electronics can malfunction or drift out of adjustment, if the touch-sensitive strips 14A, 14B , 14C fail to actuate the handpiece 10, they can be overridden by actuating the manual override switch 86A, which may be mounted either on the casing 83 or the cradle 87A. The switch 86A could be a toggle switch, rocker switch, or the like . The handpiece 1 0 selection/arming will then be carried out by switch 89A. That is, as soon as the handpiece 10 is removed from the cradle 87A, it will be ready to fire whether or not it is being held by the dentist. The manual override switch 86B works similarly for the handpiece 60. Switch 78 will continue to carry out the light activation/extinguishing function .

It would not be uncommon to have both handpieces 10, 60 out of their cradles 87A, 87B at the same time, or to put one handpiece 10 or 60 into the wrong cradle 87B or 87A, respectively. The requirement to have each strip 14 in contact with the dentist's hand prevents the handpiece 10 or 60 from being illuminated when it is not in use. The handpiece 10 could be left on a patient's chest, which is not uncommon, and would not illuminate, as at most two strips 14 would sense contact.

Normally, open switch 78 prevents illumination of handpiece 1 0, even when it is lifted from cradle 87 A and grasped on all three strips 14A, 14B , 14C . Switch A prevents illumination of handpiece 10 when it is in its cradle 87A.

In this way, a number of applications can be done very quickly without requiring an assistant to work separately with the light source, as has been previously done . When the dentist is finished applying and curing material for one patient, the handpiece may simply be removed from the fibre optic cable 28 and sterilized in an autoclave or other sterilizing device, not shown . Alternatively, the use of cost-effective materials, such as high density polyethylene or another material of light weight and sufficient strength for the body 12, and monofilament optical fibre for the bundle 28, together with manufacturing techniques such as injection moulding for the body 12 and vacuum deposition of the strips 14, would result in a disposable handpiece 10 that would be preferable for most dentists.

The operation of the handpiece 60 is similar to the operation of the handpiece 10. The extent to which they differ is described later with reference to Figure 15.

The operation of the assistant's handpiece 77 is much simpler than the other handpieces 10, 60. The handpiece 77 is removed from the cradle 87C and brought to the desired location of curing light. The button 79 is depressed to activate the module to provide curing light at tip 91 . The assistant's handpiece 77 may be used in all situations where a conventional curing light would be used, but at higher speed, due to the button 79 being within easy access, the light spreading tool 91 , and the high power, high efficiency light source 36. It is particularly useful when doing final cures on large multi-surface posterior fillings and anterior veneers where a large expanse of filling material is to be cured simultaneously.

Referring to Figure 1 1 , a single handpiece light source module 1 00 for providing curing light to an assistant's handpiece 77 has a switch 102 , timing block 104, ignition block 106, charging block 1 08 and light source 36 (see Figure 6) .

In operation, the switch 102 is closed by pushing button 79. This activates the timing block 1 04, which in turn activates the ignition block 1 06. The ignition block 1 06 allows the source 36 to accept a charge from the charging block 1 08 and provide curing light. When a pre-determined time has passed, the timing block 104 times out and shuts down the ignition circuit, which deactivates the source 36. The pre-determined time is a function of the advisable length of time the source should be illuminated and the normal amount of time required to cure restorative material . The maximum tim e must be less than the source can take, while the minimum tim e must be sufficient for curing to take place. This will depend on the charging rate of the charging unit 1 08 and the efficiency of the source 36. The actual time will depend on the particular set-up and components used in the m odule 1 00 and the characteristics of the restorative material used. The timing block is not essential, as manual counting may be performed; however, that is not nearly as convenient. Referring to Figure 12 , a dual handpiece light source module 120 has a sensing block 122 , an exclusion block 124, a timing block 126, an ignition block 128, a charging block 130 and light sources 132A and 132B (the same as light source 36). The sensing block 122 has inputs 134A, 134B, 134C for the leads 31 A, 31 B , 31 C from the fibre optic cable 28 for handpiece 1 0 and inputs 136A, 136B , 1 36C for the leads from the fibre optic cable 28 for the handpiece 60. The sensing block 122 also comprises the switches 86A, 86B and the switches 89A, 89B . The timing block 126 has an input for the device 78.

In operation, as an example, the switch A closes when the handpiece 10 is removed from cradle 87A. This is sensed by the switch A in the sensing block 122. When all three strips 14A, 14B and 14C on the handpiece 10 are touched at the same time this is transmitted to the sensing block 122 at the inputs 1 34A, 134B and 1 34C . When these conditions occur at the sam e time, the exclusion block 124 is activated and the handpiece 60 is locked out. The timing block 126 is in turn activated. The device 78 is switched on and the ignition block 128 allows the light source 132A to draw charge from the charging block 1 30 and illuminate .

When the timing block 126 times out, the ignition block 128 is deactivated and the light source 132A is extinguished. The handpiece 60 is illuminated in a similar manner, provided the handpiece 10 has been replaced in its cradle 87A.

Referring to Figures 13 a- 13d, the three handpiece light source module 76 combines the modules 100 and 120, so similar reference numerals will be used where applicable . Power is applied to the module from a 1 1 5 VAC source . DC power is provided to the module through a transformer T l , rectifying bridge B l and voltage regulator VR set using potentiometer PI and smoothed through capacitor C l , all in a known manner, to produce ground and positive voltage references VO and V+ . T l is a step down transformer T l to about 8 VAC, producing a V+ of approximately 9 V .

A delay circuit 1 51 is engaged on the closure of switch 85. The circuit 1 5 1 prevents the charging blocks 1 08 and 130 from charging for a few seconds before the sensing and timing blocks 122 , 1 04, 126 have stabilized.

Considering the assistant portion of module 76, when switch 85 closes, and the module 76 is powered to V+, RE2 is normally closed. Thyristor TH 1 draws current from a rectifying bridge B2 and transformer T2 to provide charging to capacitor C2. T3 is a 220-330 VAC step up transformer for the type of tube 42 used in the preferred embodiment. However, this may have to be adapted when other tubes 42 are used. When the assistant depresses button 79 and moves switch 102 , this activates the timing block 104 by closing relay RE3. The timing block 104 employs a 555 timer Ti l which, when grounded, drives an optical coupler 01 to switch on a relay driver comprising NPN transistors N I , N2 and resistors R l , R2 to open RE2 and close relay RE4.

For safety reasons, it is preferable to have RE2 and RE4 as one double throw relay to ensure that they move simultaneously .

The closing of RE4 activates the ignition block 1 06 by turning on thyristor TH2 and short circuiting the capacitor C3 across transformer T3 and putting a high voltage across a high voltage trigger HVTA of the light source 36. Capacitors C2, C3 are high voltage electrolytic capacitors, the value of which needs to be matched to the particular light source 36 used; in the preferred embodiment, they are 0.1 microfarad 450 V capacitors.

When Ti l times out, RE4 opens and RE closes, the light source 36 is extinguished and charging recommences. During charging, the light source 36 has a chance to cool down after firing to below conductive threshold. This prevents m elting of the electrodes, not shown, inside the tube 42 due to remaining on. This process continues until the button 79 is released.

Referring to the dentist portion of the module 76, the timing block 126, ignition block 128 and charging block 130 operate in a similar manner to timing block 1 04, ignition block 106 and charging block 108. However, the timing block 126 is activated not only by the foot-activated device 78, but also by the sensing block 122 through the exclusion block 124.

The sensing block 122 is symmetrical about an oscillator OS I , so only the left portion having input from the handpiece 10 through inputs 134A, 1 34B, 1 34C will be discussed in detail . Each input 134A, 134B, 1 34C is connected to identical capacitive change detectors CD 1 , CD2, CD3. The operation of one detector CD 1 will be discussed in detail; the operation of the other detectors is similar. OS I outputs an AC voltage Vosc that is divided by two voltage dividers, one made up of resistors R5, R6 and the other P2, and input into operational amplifier OA1, A capacitor C5 is connected to input 134A and one input I I of OA1. When strip 14A is touched by the dentist, the voltage at I I will drop and the operational amplifier will activate optical coupler 03. As 03 is connected in series with optical couplers 04 and 05 , they form an AND gate . Only when all three inputs 1 34A, 134B , 124C are touched by the dentist will the opticouplers 03 , 04, 05 conduct. When they do (or switch 86A is closed) and when switch A is closed (i .e. the handpiece 1 0 is lifted off the cradle 87A) current will be allowed to flow into the exclusion block 124 through NPN transistor N3. Switch 86A bypasses the opticouplers 03 , 04, 05 , so that if switch 86A and switch 89A are closed, current will be allowed to flow into exclusion block 124.

The frequency of the oscillator OS I must be set sufficiently low to avoid random triggering by obj ects in proximity of the handpiece 1 0, and sufficiently high to be sensitive to touch by a hand through a latex glove. This will depend on the particular set-up and components used in the module 76.

The exclusion block 124 is two double throw relays RE7, RE8 interconnected so that when one relay, for example RE7 , is closed, one end of the other relay RE8 floats so that it cannot be activated. When N3 conducts sufficiently, RE7 closes. If the device 78 i s closed, then relay RE9 closes and the timing block 126 is activated. This closes relay RE 1 0. The closing of RE7 (activated by closing microswitch A to apply power to RE7) also connects the charging block 1 30 to transformer T5 of the ignition block 128. This triggers the trigger input HVT2 of the light source 1 32A and illuminates the handpiece 1 0.

After the timing block 126 times out, the light source 1 32A is extinguished. Referring to Figure 14, a three handpiece light source module 1 60 perform s similar functions to that of module 76, and like components are given the same reference numerals. The module 1 60 operates under control of a microprocessor 162, such as a Z80, connected to a databus 164. Also connected to the bus are random access .memory (RAM) 1 66. read only m em ory (KUMj l όS, an programmabl e input/output integrated circuit 170.

When the m odule 1 60 is switched on, it loads a program from ROM 168, whi&h-fras instructions required for operation of the microprocessor 162. Calculations are performed by the microprocessor 162 using RAM 1 66 to store temporary information . The microprocessor 162 obtains from the sensing block 122 through the circuit 1 70 information about which handpiece 10, 60 is in use and is being grasped by the dentist. The microprocessor 1 62 also obtains from the circuit 170 information about whether or not the assistant has pushed the button 79 and whether or not the dentist has activated the device 78.

From the obtained information, the microprocessor 162 performs the exclusion functions described for the module 76 and activates one of timing blocks 1 72 and 1 74 and, if desired, timing block 1 04, depending on which of the handpieces 10, 60, 77 is/are selected. The timing blocks 172, 174 together perform the same function as the timing block 126. They have been divided for simplicity of addressing by the microprocessor 162. Similarly, separate ignition blocks 176, 178 together perform the functions previously described for the ignition block 128 in causing the appropriate light source 132A, 132B to illuminate .

Module 160 allows for additional functions to be added, beyond those for the m odule 76. For example, sequencing of handpieces 10, 60 is possible when more than one handpiece 10, 60 is in use . This might occur in a particularly complicated procedure, where the assistant or a second dentist is required to use the second handpiece 1 0, 60.

Alternatively, the module 160 could be used in a situation where two dentists are working on two different patients.

In other embodiments of the invention, timing could be controlled by measuring the accumulated light output of the lamp . In still other embodiments, not shown, the device is adapted to receive and monitor light reflected from the restorative material . When the ratio of the intensities of preselected wavelengths of reflected light is consistent with free monomer no longer remaining in the vicinity of the light probe/plugger, the light unit ceases emission . These measuring systems would require a microprocessor and the use of a m odule such as module 160.

Referring to Figure 1 5 , in the case of orthodontic brackets 1 80, the dentist uses the handpiece 60 as a forceps to place a bracket 180 with photopolymerizable cem ent 1 82 on a tooth 184. The leaf springs 73 are used to grip wings 186 of the bracket 180 to aid in seating on the tooth 1 84. The tips 72 are positioned to be flush with a metal base 1 88 of the bracket 1 80.

When the bracket 1 80 is correctly placed, the dentist depresses the device 78 to activate light delivery, thereby illuminating the cem ent 1 82 from two sides simultaneously. The flush placement of the angled fibre optic tips 72 against the tooth 1 84 provides for light delivery directly into the thin cement layer 1 82 under the bracket 1 80 and for delivery into the translucent tooth structure 1 84. The structure 192, which is indicated by hatched lines is the micromesh layer which covers most of the metal base of the bracket 1 80. The structure 192 leads to back-scattering of light, which further aids in curing the cement 1 82, Next, the dentist turns the handpiece 60 at right angles and illuminates the remainder of the cement 1 82 around the bracket 1 80.

All of the light emitted from the handpiece 60 is concentrated precisely where it is needed, immediately next to the bracket 1 80. The light enters the tooth 1 84 enamel at an advantageous angle, approximately 45° toward the midline of the handpiece 60. These factors, combined with simultaneous light delivery on both sides of the bracket 1 80, result in improved adhesion of the bracket 1 80, more efficient curing and time saved for the orthodontist and patient. The curing tim e per bracket 1 80 can .be greatly reduced. The time saving is significant when accumulated over the whole mouth and summed for numerous patients.

The handpiece 60 provides for particularly efficient m ounting of m etal-based brackets 1 80, which, unlike plastic brackets 180, are not easily mounted using conventional quartz halogen curing lights. In addition, the concentration of emitted light from the handpiece 60 can reduce backflash into the orthodontist's eyes.

A number of modifications to the embodiments of the invention described above could be made without deviating from its spirit and scope. For instance, it is possible to construct a single handpiece light source module, not shown, for use with the handpieces 1 0 or 60, instead of the three handpiece modules 76, 1 60. Such a single handpiece module would not require an exclusion block 124. It could have the three-conductive strip 14 arming/disarming feature, the cradle microswitch 89 arming/disarming feature, or both .

The switch device 78 described above requires hard-wiring and, possibly, a service call . In an alternative embodiment, not shown, a clip-on or stick-on pressure-sensitive infrared transducer could be part of the device 78. A receiver or sensor could be attached to the light source m odule used. This would allow light delivery to be activated without hard¬ wired connections and switches. Such an infrared transducer/receiver system could be adapted to permit foot- controlled activation of other dental tools, such as a cavitron or electrocautery unit, providing the system has additional ports for these devices. In offices using infrared computer communication, such a system would have to be adapted not to interfere with the computers.

In some embodiments of the invention, not shown, each xenon flash tube 42 is replaced by a pair of xenon flash tubes using two 330 V, 1 100 mF electrolytic charging capacitors. Such configurations will depend on the particular tubes used and the intensity and efficiency of illumination required. Where a handpiece receives light from two or more flash tubes, those tubes will likely need to be illuminated simultaneously for the desired combined effect and control of that effect.

In order to cool tubes 42, it may be desirable to enclosed them in a liquid cooling medium, not shown . Pulsed xenon light sources 36 could be replaced by continuous xenon arc light or by an argon laser or by other light sources providing illumination of the desired frequency and intensity.

Employing the principles described herein, it is evident that the invention is not restricted to specific dental restorations, for example class II restoration, but can be used in all classes of restoration . The handpieces may also be used to spot tack porcelain veneers. Handpiece 1 0 is ideally suited to deliver light to cure the gingival margins of class II, ceramic inlays. This area is a serious problem for conventional light curing equipment since the margin is frequently below the gum level and is tucked away between the teeth.

Handpiece 10 can also be used for other dental light cured materials, such as pulp protection cements, for example, light cured DYCAL™, and light cured intermediate materials and temporary cements, for example, RMO™ cement. It can also be used in the construction and repair of orthodontic appliances, removable prostheses and temporary crowns and bridges using photochemically activated resins. Other applications include try-ins of precision attachment prostheses including crown based precision attachments and attachments on intraosseous implants. Usually the framework is placed in the mouth; then the small precision attachments are placed on their mating counterparts and are luted to the framework with some form of acrylic-based cement. Simuitaneous delivery, placement and quick spot luting using the handpiece 1 0 is extremely helpful .

This description is made with reference to the preferred embodiments of the invention . However, it is possible to m ake other embodiments that employ the principles of the invention and that fall within its spirit and scope as defined by the following claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1 . A dental system for use by a dentist, comprising: a handpiece shaped for use in the application of dental restorative materials requiring curing by light, the handpiece having at least one fibre optic bundle directed to an area where curing will be required; a source of light independently supported from the handpiece; and a fibre optic cable for optical connection to the at least one fibre optic bundle and the source during application of the material without substantially restricting the motion of the dentist.

2. A dental handpiece for use by a dentist with an independently supported source of light connected to a fibre optic cable, comprising: a body shaped for use in the application of dental restorative materials requiring curing by light; a fibre optic bundle physically connected to the body and directed to an area where curing will be required; and a socket for connection to the fibre optic cable and the fibre optic bundle during application of the material without substantially restricting the motion of the dentist.

3. The dental handpiece of claim 2 , wherein the body has a length and the socket is at a first end of the length, the fibre optic bundle extends from a second opposing end of the length to a tip for the delivery of curing light, and the body has a blade extending from the second end, the blade and the bundle being angled from one another to allow for separate use of the blade and the bundle by the dentist.

4. The dental handpiece of claim 2 , wherein the body has a forceps shape with two prongs, and the bundle extends into each prong to respective tips for the delivery of curing light,

5. The dental handpiece of claim 4, wherein the prongs are each at an angle pointing toward a midline drawn between the prongs through the handpiece to aim the bundle at the tips toward an area where illuminating light is likely to be desired when the handpiece is in use.

6. A light source module for connection to a fibre opti c cable used with a dental handpiece for light curing of dental material, the module comprising: a light source for producing curing light; a switch; a timing block; an ignition block; and a charging block; wherein activation of the switch causes the timing block to tim e for a pre-determined time less than would overheat the light source, while remaining useful for curing the dental material; wherein the ignition block triggers the illumination of the light source while the timing block is timing; and wherein the charging block provides illumination power to the light source when the light source i s triggered.

7. A light source module for connection to a fibre optic cable used with a dental handpiece for light curing of dental material with a sensory area on the handpiece, the module comprising: a light source for producing curing light; a sensing block connected to the fibre optic cable for sensing capacitive changes at the sensory area indicative of a dentist's hand; an ignition block; and a charging block; wherein sensing by the sensing block of capacitive changes at the sensory area indicative of a dentist's hand allows the ignition block to trigger the illumination of the light source; and wherein the charging block provides illumination power to the light source when the light source is triggered.

8. The module of claim 7 , further comprising a first switch readily accessible to the dentist while using the handpiece, the first switch for activating the ignition block.

9. The module of claim 8, further comprising a second switch actuated by removal of the handpiece from the module and replacement of the handpiece, the second switch allowing activation of the ignition block when the handpiece is removed and preventing activation of the ignition block when the handpiece is in place in the module.

10. A light source module for connection to a fibre optic cable used with a dental handpiece for light curing of dental material with a sensory area on the handpiece, the m odule comprising: a light source for producing curing light; a sensing block connected to the fibre optic cable for sensing capacitive changes at the sensory area indicative of a dentist's hand; a timing block; an ignition block; and a charging block; wherein sensing by the sensing block of capacitive changes indicative of a dentist's hand at the sensory area enables the timing block to time for a pre-determined time less than would overheat the light source, while remaining useful for curing the dental material ; wherein the ignition block triggers the illumination of the light source while the timing block is timing; and wherein the charging block provides illumination power to the light source when the light source is triggered.

1 1 . A light source module for connection to a fibre optic cable used with a dental handpiece for light curing of dental material with at least two spaced apart sensory areas on the handpiece, the module comprising: a light source for producing curing light; a sensing block connected to the fibre optic cable for sensing capacitive changes at the sensory areas indicative of a dentist's hand; a timing block; an ignition block; and a charging block; wherein sensing by the sensing block of capacitive changes indicative of a dentist's hand, simultaneously at each sensory area enables the timing block to time for a pre¬ determined time less than would overheat the light source, while remaining useful for curing the dental material ; wherein the ignition block triggers the illumination of the light source while the timing block is timing; and wherein the charging block provides illumination power to the light source when the light source is triggered.