Field of the Invention

The present invention relates to a dental air abrasion tool and specifically to a removable and replaceable end portion for an air abrasion apparatus.

Background

Dental practitioners use an abrasive material to remove stains and the like from patients' teeth. The abrasive powder is normally delivered to the tooth my means of a handpiece the dentist can hold and control.

The abrasive material, normally in the form of a powder, is stored in a container and carried by means of a channel passing along the handpiece to a distal tip of the device. The powder is carried using compressed air along channels in a handpiece the practitioner can hold.

The abrasive powder not only cleans the teeth by removing stains and so forth but also in some cases de-sensitizes the teeth by blocking the tubules leading to the nerve endings within the tooth.

In order to minimise discomfort for the patient and to carry the powder away from the teeth a water channel is also provided in the handpiece to channel water to the distal tip where it is discharged into the patient's mouth proximate to the powder discharge channel.

In use, the dentist directs the powder at the relevant tooth and the water jet acts to carry debris and powder away from the tooth. Water is extracted from the mouth by means of a conventional vacuum system These conventional systems have proved popular with dentists, hygenists and patients and provide a means for the dentist to clean teeth with minimal discomfort for the patient. Powders used with conventional systems include bicarbonate of soda and aluminium oxide.

Although existing systems continue to be popular with dentists and the like the present invention aims to provide an improved tip for an abrasion blasting apparatus. Specifically the present invention aims to meet the needs of the practitioner in terms of functionality and to be efficient and cost effective to manufacture. The present invention further aims to provide an apparatus in which the tip lifetime is maximised thereby minimising operating costs for the practitioner.

Invention Summary

Viewed from a first aspect there is provided a discharge tip for a dental air abrasion device, said tip comprising a body having a first end adapted for connection to a dental air abrasion device and a second end comprising a discharge nozzle, said body comprising an first internal conduit arranged to communicate an abrasive powder from said first end to said discharge nozzle, wherein a portion of the conduit is formed from a ceramic material. Thus, according to an aspect of the present invention there is provided a discharge tip which is capable of being coupled to a dental air abrasion device and which communicates an abrasive powder to a distal tip under the control of the practitioner. Advantageously at least a portion of the conduit conveying the abrasive powder is formed from a ceramic material.

Conventional dental apparatuses of this type use stainless steel as a preferred material. Stainless steel is advantageously convenient to manufacture with and additionally allows the tip to be cleaned and sterilised for repeated use. In prior art devices the entire length of the conduit conveying the powder is formed from a stainless steel material thus the parts can be easily manufactured using conventional steel forming and machining processes.

According to the present invention a portion of the conduit is unconventionally formed from or provided with a ceramic surface against which the abrasive powder can pass. It will be recognised that at the time of the invention manufacturing a complex component such as a discharge tip from a ceramic material is inherently counterintuitive, not least because of the difficulties of manufacturing intricate parts with intersecting holes.

The conduit communicating the abrasive powder may advantageously comprise a first elongate portion extending along part of the length of the tip and a second portion arranged at an angle to said first portion and extending along the length of the discharge nozzle. Thus, the dentist or practitioner is able to access a greater proportion of the patient's teeth without discomfort to the patient when the apparatus is in the mouth. It is also easier and more comfortable for the practitioner using the apparatus.

The first and second portions may advantageously be substantially straight so as to minimise wear of the conduit by the abrasive powder travelling against the inner surface of the conduit. Aligning the conduit with the inlet from the powder delivery apparatus allows for laminar flow to occur within the conduit; this minimises the wear experienced by the conduit. The intersection between the first and second portions of the conduit defines the point within the conduit at which the abrasive powder changes direction. It is at this point that the abrasive powder is most likely to impact the inner surface of the conduit and to cause wear of the conduit itself. In use the powder travels along the first portion of the apparatus and then changes direction to travel along the second portion to the discharge nozzle.

Advantageously the ceramic material may be arranged at this portion of the conduit and in line with the flow of abrasive material. Thus, abrasive powder travelling towards the discharge tip makes contact with the inner surface of the conduit at this region. Not only is the ceramic material substantially chemically inert but also less prone to wear than conventional materials such as stainless steel. According to the present invention only a single change in direction of powder is provided. Thus, the regions of the conduit subject to excessive wear by the abrasive material can be minimised. Furthermore, an apparatus comprising a conduit arranged to change the direction of the powder only once advantageously allows the hand piece to have a smaller overall diameter i.e. the hand piece can be smaller. Thus allows the device to be more conveniently manipulated by the practitioner and reduces discomfort to the patient still further.

Any suitable ceramic material may be used having a hardness in excess of 5.5 Mohs Hardness (approximately 550 Hardness (Vickers))

Suitable ceramics include a combination of alumina (AI ₂ O ₃ ) and zirconia, such as zirconia toughened alumina. Alumina advantageously has a hardness of 3000HK. Other suitable materials include quartz and sapphire. In one arrangement a tungsten carbide or steel conduit may be provided with a thin ceramic coating along a portion of its length. Thus a composite conduit may be formed having a hard ceramic coating and a backing material with a lower hardness.

It has been established that the percentage of zirconia of < 15% by volume to alumina advantageously prevents break down of the ceramic during the autoclaving process. This thereby retains the part geometry whilst simultaneously allowing a part with the desired hardness to be manufactured. Additionally it has been established that the grain size of the powder used during the pre-forming mix of the zirconia and alumina should be 1 micron or less in diameter. This provides for a uniform and stabilised ceramic material not prone to water ingress.

Advantageously the substantially straight portions of the conduit may be formed from steel and a portion of the conduit at which the abrasive material turns formed of a ceramic. A conduit of composite materials is thereby defined optimising performance whilst allowing for convenient manufacturability. The apparatus may additionally comprise a second conduit to communicate a liquid, such as water, from the first end of the conduit to the discharge nozzle. The second conduit may be in the form of a conduit parallel with the conduit conveying the abrasive powder.

The discharge nozzle is advantageously adapted to discharge the abrasive powder and water in close proximity to the patient's tooth under the control of the practitioner.

In order to optimise the abrasive function of the powder and additionally the debris carrying function of the water the abrasive powder is arranged to be discharged within a shroud of water. The terms shroud is intended to mean a circumferentially extending flow of liquid extending around a centrally located flow of abrasive powder. Thus, the discharge nozzle may comprise a first outlet for the abrasive powder and a second outlet for the liquid. Advantageously the first and second outlets may be coaxial to each another and the first outlet disposed within the second outlet.

In effect the water is discharged as a shroud extending around the flow of abrasive powder. The abrasive powder itself may be carried by means of a compressed gas such as compressed air or the like.

A rib may be provided between the portion of the nozzle defining the first outlet and the portion of the nozzle defining the second outlet. The rib may be arranged so as to extend between the inner periphery of the second outlet to an outer periphery of the first outlet. This advantageously provides a support for the first outlet (located within the bore of the second outlet) during use and additionally during manufacture. Thus, a first outlet with a small diameter can be conveniently used and also reliably manufactured.

The discharge nozzle may be formed of any suitable material combination where at least a portion of the conduit in contact with the abrasive material is a ceramic material.

Advantageously the inventors have established that the entire portion of the body comprising the discharge nozzle may be formed from a single body of ceramic material. As stated above any suitable material may be used, including in particular those set out above.

Thus, the inlet and outlets may be defined within the single body during the manufacturing process. The process may for example be a ceramic injection moulding process permitting complex shapes and profiles to be formed.

The inventors have established that once the abrasive powder has passed the turning region of the conduit the flow within the conduit become significantly more turbulent. Because of the turbulent flow the abrasive powder contacts the inner surface of the conduit more in the second portion of its length than in the first where is travels in a straight line.

Thus, providing a ceramic material at this region allows the lifetime of the tip to be maximise whilst allowing the remainder of the tip conduit to be formed of a steel material. This facilitates manufacture whilst optimising the product's useful life.

Additionally, forming the discharge tip from a single body of ceramic material simplifies the manufacture of the tip and allows the body to be optimised for strength to prevent brittle fracture of the nozzle or discharge outlets. It additionally advantageously aids cleanliness and the aesthetics of the product.

Viewed from another aspect there is provided a discharge tip for a dental abrasion device, said tip comprising a body having: a first portion adapted for connection to a dental abrasion device; a second elongate portion defining a region to be held by a user; and a ceramic distal portion coupled to said second elongate portion and defining a discharge nozzle, wherein the body comprises a first conduit adapted to communicate an abrasive powder from an inlet at said first portion to an outlet at said discharge nozzle.

Viewed from yet another aspect there is provided a ceramic discharge tip for an abrasive dental apparatus, said tip comprising a first inlet arranged in use to receive a mixture of a gas and an abrasive powder; a second inlet parallel to said first and arranged in use to receive a liquid; and a discharge nozzle arranged at an angle relative to the first and second parallel inlets and comprising a centrally located first outlet and second outlet surrounding said first outlet, wherein the ceramic tip further comprises a first channel connecting the first inlet to the first outlet and a second channel connecting the second inlet to the second outlet.

Viewed from yet another aspect there is provided a method of making a discharge tip as described herein wherein the method comprises the step of ceramic injection moulding the ceramic discharge nozzle. Viewed from still another aspect there is provided a single body ceramic discharge nozzle comprising a first inlet arranged to receive an abrasive powder and a second inlet arranged to receive a liquid, a first channel connecting the first inlet to a first outlet and a second channel connecting the second inlet to a second outlet. The single body ceramic discharge nozzle may advantageously be provided with a push fit coupling portion allowing the nozzle to be releasably coupled to a dental abrasive apparatus tip. This may for example be by means of an interference fit between a portion of the nozzle surrounding the first and second inlets. The coupling may for example define a male portion arranged to be inserted into a female portion of the discharge tip or vice-versa.

The nozzle may alternatively be coupled to the tip by means of a friction weld, adhesive or other mechanical coupling.

Brief Description of the Drawings

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

Figures 1A and IB show cross-sections of a first embodiment of an invention described herein;

Figure 2 shows an exterior view of a first embodiment of the present invention;

Figure 3 shows an end exterior view of a first embodiment of the present invention;

Figure 4 shows an exploded view of the components forming a first embodiment of the present invention;

Figures 5A and 5B show cross-sections of a second embodiment of the present invention;

Figure 6 shows an exterior view of a second embodiment of the present invention;

Figure 7 shows an end exterior view of a second embodiment of the present invention;

Figure 8 shows an exploded view of the components forming a second embodiment of the present invention;

Figure 9 shows a cross-section through a ceramic discharge nozzle according to an invention described herein;

Figure 10 shows an end view of a ceramic discharge nozzle according to an invention described herein;

Figure 11 show an exterior view of a ceramic discharge nozzle according to an invention described herein; Figure 12 shows an alternative exterior view of a ceramic discharge nozzle according to an invention described herein;

Figures 13 A, 13B and 13C show views of a clip arranged to couple a nozzle to a device;

Figure 14 shows a cross-section of a clip coupling arrangement; and Figure 15A and 15B show the clip in isolation.

While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood however that drawings and detailed description attached hereto are not intended to limit the invention to the particular form disclosed but rather the invention is to cover all modifications, equivalents and alternatives falling within the scope of the claimed invention.

Detailed Description

The invention will now be described with reference to three embodiments.

The first embodiment is a dental tip arranged to couple to an air abrasion device manufactured by Electro Medical Systems S.A of Switzerland and suitable for use with SYLC (registered trademark) abrasive powder manufactured by OSspray Limited (a UK based company). The device may equally be used with other suitable abrasive powders such as Alumina, Sodium Bicarbonate, Glycene based powders and combinations thereof.

The second embodiment is a dental tip arranged to couple to an air abrasion device manufactured by Dentsply and again suitable for use with SYLC abrasive powder.

The final embodiment is a single body ceramic discharge nozzle as shown in each of the above referenced embodiments. It will be recognised from the following discussion that the same discharge nozzle can be employed in each embodiment and further may be used in any other abrasive dental device.

Figure 1 A shows a cross-section through a first embodiment of an invention described herein. The tip shown in figure 1A is adapted for coupling to a dental blasting abrasion apparatus device manufactured by Electro Medical Systems. The tip 1 is arranged to connect to the shaft of the EMS delivery system 2. The tip 1 comprises O ring seals 3, 4 to seal the internal conduits discussed below.

The tip 1 comprises a plastic injection moulded sleeve 5 which may be formed for example of glass-filled nylon or other suitable plastic. It may alternatively be formed of stainless steel. The tip 1 defines a first end for connection to the EMS device and a second distal end comprising a nozzle 6.

The nozzle is described in more detail below but is formed of a zirconia toughened alumina ceramic material. The tip comprises a centrally located conduit 7 which is in alignment with the supply conduit 8 of the EMS system (Figure IB). This conduit conveys a mixture of abrasive powder and compresses air. The air acts as a carrier for the abrasive powder.

Any suitable abrasive powder may be used. Advantageously SYLC™ powder may be used with the devices described herein.

The alignment of the conduits 7 and 8 allows the abrasive powder to travel in a substantially straight path minimising contact of the powder against the inner surfaces of the conduits 7 and 8. This minimises wear and prolongs the life of the tip. It additionally reduces turbulence within the conduits and restrictions in powder flow.

The conduit 7 is formed of a stainless steel tube having a hardness of at least 600 Knoop Hardness.

Conduit 7 is coupled to conduit 8 by means of an elastomeric seal 9 located on the end of the EMS device. A portion of the stainless steel conduit 7 penetrates the seal 9 to prevent egress of powder from the conduit. The distal end of the conduit 7 is coupled to the ceramic nozzle 6 by means of FEP (fluorinated ethylene propylene) heat shrink seals 10.

The EMS device additionally provides a supply of water which is also communicated to the discharge nozzle. Water is supplied via supply conduit 11 which is arranged parallel to the powder supply conduit 8 in the EMS device. Water is communicated from channel 11 along channel 12 towards the distal part of the device.

Returning to Figures 1 A and IB, water is released from conduit 11 of the EMS device and passes along conduit 12. The O ring seals prevent water loss or water mixing with the powder within the device. The distal end of the channel 12 is in fluid communication with a further angled channel 14. The channel 14 provides a flow path between the slot 12 and a second stainless steel tube 15. The second tube 15 is parallel to the first powder carrying stainless steel tube 7. Tube 15 communicates water from the channel 14 to the discharge nozzle 6. The tubes 7, 15 are at a first end connected to the ceramic discharge nozzle by means of a fluorinated ethylene propylene seal which advantageously allows the stainless steel tubes to be coupled to ceramic material forming the discharge nozzle 6.

The ends of the tube 7, 15 proximate the EMS device are connected to a turned stainless steel insert 16 which supports the ends of the tubes for alignment with the EMS powder supply conduit 8 and water supply 11. Thus, each end of the tube 7, 15 is securely located in position within the tip body 5.

A plastic moulded insert 17 is arranged within the tip body between the insert 16 and the end portion of the tip body which couples to the EMS device. A proximate portion of this insert 18 is arranged to cooperate with O ring seals 18 to provide a seal around the distal portion of the EMS device.

The second plastic insert advantageously reduces the volume of the cavity within the tip body which would otherwise be filled with water. This prevents water spillage when the tip is de-coupled from the EMS device. In use the tip is aligned by the practitioner with the distal end of the EMS device and pushed axially into place. Simultaneously the O ring seals 18 seal the tip to the EMS device and the elastomeric seal 9 seals the powder supply conduit 8 to the elongate conduit 7. The EMS device is actuated and compressed gas carrying an abrasive powder is conveyed along the conduit 8, 7 and to the ceramic discharge nozzle 6. As discussed above the path of the powder is substantially straight until the powder reaches the discharge nozzle. The function of the nozzle is described below. Water is conveyed from the EMS water supply conduit 11 along the channels 12, 14 and into the tube 15. Water can thereby be supplied to the discharge nozzle 6. The overall diameter of the device is maintained at a diameter which is ergonomic for the user. Aligning the channels in this way facilitates an ergonomic design. Thus, the practitioner is able to use the EMS delivery system with an improved tip according to the present invention. The EMS delivery system operates in a normal way. Figures 2 and 3 show outer views of the first embodiment of the present invention. The figures illustrate the contours of the device which are selected to optimise the ergonomic performance of the tip.

Figure 4 shows an exploded view of the component parts of the tip. Here the EMS delivery system is not shown.

Figure 4 shows the plastic moulded insert 17, stainless steel insert 16 and stainless steel tubes 7, 15. The figure shows tubes 7, 15 bonded to the insert 16. This connection may be by any suitable means including welding or brazing. The first moulded plastic insert 17 can then be located around the tubes 7, 15 and finally the tip body 5 can slide over the entire assembly. The ceramic discharge nozzle can then be coupled to the end of the tip as described further below.

The second embodiment will now be described with reference to figure 5 A to 8.

Figures 5A and 5B show cross-sections through the second embodiment of an invention described herein. The tip shown in figures 5A and 5B is adapted for coupling to a dental blasting abrasion apparatus device manufactured by Dentsply of the USA.

In much the same way as the EMS delivery system the Dentsply delivery system also provides a supply of abrasive powder in a flow of compressed air and a water supply. Figure 5A show the tip in isolation and Figure 5B shows the tip together with the Dentsply device. The Dentsply device comprises a first supply conduit 19 for supplying abrasive powder and a second supply conduit 20 for supplying water (see Figure 6B).

The tip according to the second embodiment of the invention comprises a stainless steel tip body 21 arranged for abutment with the Dentsply device. The tip body 21 comprises a first end arranged to receive a ceramic discharge tip 6 corresponding to that shown in the first embodiment and described further below. The tip body 21 contains a pair of elongate holes arranged to receive first and second stainless steel tubes 22, 23. The first stainless steel tube 22 is arranged so as to align with the conduit 19 of the Dentsply device and to communicate abrasive powder from conduit 19 to the ceramic discharge nozzle 6. The conduit 22 is in alignment with the conduit 19 so as to minimise wear caused by contact of the abrasive powder against the inner surfaces of the conduits.

The second stainless steel tube 23 is arranged to communicate water to the discharge nozzle 6. In order to minimise the diameter of the tip body and to thereby facilitate its use an angled channel 24 is provided permitting fluid communication between a stainless steel insert member 25 and the tube 23.

The stainless steel insert member 25 comprises a central channel 26 allowing water to flow from the Dentsply water supply conduit 20 to the channel 24. The member 25 is adapted so as to fit into the water supply conduit of the Dentsply device. The member 25 is further provided with a pair of O ring seals 27 to prevent egress of water out of the device or tip.

At a first end the tube 22 is provided with a seal portion 28 to prevent egress of abrasive powder from the device or tip body. At the opposing end the tube 22 is provided with FEP heat shrink seals 30 sealing the tube to the ceramic discharge nozzle. The same seal is additionally provided on the second stainless steel tube 23.

The tip is coupled to the Dentsply device by means of pressure applied by O ring seals preventing the tip from accidental release from the Dentply device.

In use the Dentsply device is activated and abrasive powder is supplied in a compressed gas stream to the conduit 22. This is in turn communicated to the ceramic discharge nozzle. Simultaneously water is supplied to the second tube 23 via the member 25 and channel 24. Thus water is also communicated to the ceramic discharge nozzle.

It can be seen that in each embodiment the abrasive powder is only required to change direction once from its source in the EMS or Dentsply device respectively. This advantageously reduces the pressures and or flow rate of gas needed to convey the abrasive powder to the discharge nozzle but also minimise wear between the abrasive powder and the inner surface of the respective conduit. This maximises tip life. Figures 6 and 7 show the outer view of the second embodiment of the present invention and illustrate the ergonomic profile of the tip body 21.

Figure 8 shows an exploded view of the second embodiment of the present invention. As shown the insert 25 comprises a pair of O ring seals 27 together with the subcomponents. Figure 8 (and also figure 4 discussed above) also shows the nozzle 6 and its coupling arrangement. This is described below.

The ceramic discharge nozzle will now be described with reference to figures 9 to 12. Figure 9 shows a cross-section of the ceramic discharge nozzle 6.

The ceramic nozzle is formed of a zirconia toughened alumina material by means of ceramic injection moulding followed by kiln curing. The ceramic tip comprises a first inlet 31 arranged to receive an abrasive powder carried in a flow of compresses gas and a second inlet 32 arranged to receive a flow of water.

The first and second inlets are formed in a first portion 33 of the nozzle which is adapted to be located in the distal portion of the tip bodies described above. Portion 33 comprises a collar and recess providing a snap fit connection for coupling the nozzle to the respective tip on insertion into the respective orifice. A second portion 35 of the nozzle defines the outlets from the nozzle. The nozzle comprises a first outlet 36 arranged to discharge abrasive powder carried in a flow of compresses gas and a second outlet 37 arranged to discharge water. The outlets 36, 37 are connected to the respective inlets by means of two internally formed conduits 38 and 39. Conduit 38 communicates abrasive powder and conduit 29 communicates water.

As can be seen in the cross-section of figure 9 the conduits can be divided into a first portion in alignment with the inlets and a second portion in alignment with the outlets. The intersection between these two portions defines the region at which the flow of powder and flow of water change direction.

Of particular relevance is the portion of intersection of the inlet and outlet channels communicating the abrasive powder. This is the region of highest wear within the apparatus since the abrasive powder collides with the end of the hole defining the first inlet. Conventional tips are prone to significant wear in these regions, sometimes resulting in complete penetration of the nozzle wall. However, the hardness of the ceramic material is sufficient to allow for long term operation of the discharge nozzle without significant wear. This is even the case with modern material such as SYLC glass powder technology.

In use the ceramic discharge nozzle is coupled onto the end of the respective tip and the device activated. Compressed air carrying abrasive powder enters the inlet 31 and is communicated to the outlet 36. Simultaneously water is supplied to inlet 32 and is communicated to outlet 37.

The tip is held by the practitioner and used to bring the outlet portion 35 of the nozzle into propinquity with the tooth or teeth to be treated. The tooth or teeth can then be accurately and conveniently cleaned.

The outlet will now be described in more detail. As partially visible in figure 9 the outlet for the abrasive powder is centrally located with respect to the outlet for the water. Thus, water and abrasive powder are discharged from the ceramic nozzle simultaneously and in such a way that the water creates a shroud or curtain extending around the periphery of the powder flow.

Figure 10 shows an end view of the outlets of the ceramic nozzle. As shown in figure 10 the powder outlet 36 is centrally located with respect to the water outlet.

Figure 10 also shows a rib 40 which extends between the inner surface of outlet 37 and the outer surface of the tube 41 defining outlet 36. The rib defines a rigid connection between the ceramic material defining tube 41 and the portion of the nozzle 6 defining the outlet 37.

The rib 40 advantageously service two purposes. First, the rib supports the inner tube 41 allowing the tube to be smaller in diameter than would normally be the case. As discussed above ceramic materials are brittle and prone to fracture. Introducing the rib supports the tube enhancing its strength thereby allowing a tube with a smaller diameter to be manufactured. Additionally the rib allows the outlet holes to be formed more reliably during the ceramic injection moulding process.

The rib may be formed as a small portion at the distal end of the outlets. Advantageously though the rib may extend along the full length of the tube, as shown in the cross-section of figure 9 (where it location of the rib is illustrated by the dashed lines).

Figure 11 and 12 show other views of the ceramic discharge nozzle. As shown in figure 11 the rib is arranged to terminate prior to the end of the outlets. This advantageously allows for water flow around the entire circumference of the outlet thereby retaining the desired shroud of water leaving the discharge nozzle. Forming the rib to the very end of the outlet creates a discontinuity in the shroud which degrades performance and comfort for the patient.

A ceramic discharge nozzle according to an invention described herein advantageously enhances the operational life of abrasion tips using abrasive powders and then like. The replaceable nature of the ceramic tip additionally allows the tip to be conveniently replaced and used with a variety of dental apparatuses. The size of the conduits is advantageously optimised for the given supply pressure of the dental apparatus i.e. the water and air pressure. Advantageously the powder outlet may have a diameter of between 0.1mm and 2mm and the water outlet of 0.1mm to 4.0 mm. The powder outlet is located inside the water outlet, hence a water outlet diameter of 4mm will define an area between the inner surface of the water outlet and the outer diameter of the portion defining the powder outlet.

It will be recognised that the ceramic nozzle 6 is common to both the EMS and Dentsply arrangement s. The ceramic nozzle 6 is coupled to either tip by means of a locking clip as described below with reference to Figures 14A to 16B.

It is essential that the nozzle is safely secured to the tip and cannot be accidentally released during use. A locking mechanism is therefore used which secures the nozzle in place whilst conveniently allowing the nozzle to be coupled to the tip during manufacture.

Referring to Figures 13A to 13C the locking mechanism can be seen. The nozzle 6 is formed so as to have an elongate male portion 42 for insertion into the respective bodies of the EMS or Dentsply tips as illustrated in figures 4 and 8. The elongate male portion 42 comprises a recess 43 arranged on either side of the male portion 42 (only one side being visible in Figures 13A to 13C).

The locking mechanism comprises a spring steel clip 44 which can be located and clipped onto the male portion 42. Location of the clip 43 is shown in figure 13B.

The clip is shown in more detail in figures 15A and 15B. The clip is formed of a suitable spring steel sufficiently flexible to be compressed during manufacture. The clip comprises two end or wing portions 45 a and 45b which can be brought together by forces in the F and F' directions shown in figure 15A. Figure 15B shows an alternative view of the clip.

Returning to Figure 14C the clip can be seen during assembly where the wing portions 45 a and 45b have been compressed sufficiently to allow the clip and the male portion 42 to pass into the end of the EMS or Dentsply tip. Figures 4 and 8 show exploded views of the assembly.

Figure 14 shows a cross-section through the recess 43 shown in figure 13A when the clip is in situ. This corresponds to cross-section A-A' in figures 4 and 8.

As shown in figure 14 the Dentsply or EMS body portions 5, 21 comprise a recess 46a and 46b arranged to receive the wing portions 45a and 45b of the clip. Thus, once inserted into the body portions 5, 21 of the respective tip the wing portions are urged into the respective recess by virtue of the release of the compression forces F, F'. The nozzle portion is thereby axially locked into position. It is not possible to access the wing portions 45a and 45b to release the nozzle. A permanent and convenient fixing is thereby provided.