WO2025244541A1 - Dental separator ring - Google Patents

Abstract

A separator ring for separating teeth in a dental restoration procedure in a mouth of a patient, the separator ring comprising a resilient body having a first end and an opposing second end with a gap provided therebetween, the first end and the second end each having a tooth engaging portion thereon. The first end is coupled to a first arm and the second end is coupled to a second arm and a central portion is coupled between the first arm and the second arm, wherein the central portion comprises at least one concave portion. The gap is configured to be expanded in use by pushing the first arm and second arm apart to facilitate engagement of the tooth engaging portions adjacent to a tooth to be restored. The at least one concave portion is configured to spread a stress force across the central portion when the gap is expanded.

Description

DENTAL SEPARATOR RING

CROSS REFERENCE TO RELATED APPLICATIONS

This application relates to and claims priority from New Zealand provisional applications No. 811302 filed 23 May 2024 and No. 813148 filed 20 July 2024, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to restorative dentistry, particularly to dental separators in the form of a matrix device. More specifically, the invention relates to a separator ring.

BACKGROUND OF INVENTION

Restorative dentistry involves the repair and restoration of teeth that have been damaged due to decay, trauma, or other factors. One of the critical components in restorative procedures is the use of separators or retainer rings. These devices are essential for ensuring proper isolation and stabilization of the tooth being restored, allowing for precise and effective dental work. Direct dental restorations typically involve using devices to separate the tooth being restored from the adjacent tooth to increase the interproximal space between the teeth and to secure a dental matrix against the tooth being restored. This is necessary so that when the matrix is removed, the adjacent teeth can move back together and create a tight contact, thereby preventing food packing between the teeth.

The mechanical separation force required to accomplish these tasks is typically provided by a retainer or separator ring and supplemented by a dental wedge to secure the matrix band to the tooth at the gingival margin. A dental separator ring is a specialized tool used in restorative dentistry, particularly where the restoration involves the proximal surfaces of posterior teeth (molars and premolars). Its primary function is to help recreate the natural contact point and contour between adjacent teeth when a portion of the tooth structure has been lost due to decay or damage. The separator ring is designed to exert gentle, consistent pressure to slightly separate adjacent teeth, creating space for the restorative material and ensuring a tight contact point once the material sets.

Separator rings commonly have two arms or tines that grip the tooth from the buccal (cheek) and lingual (tongue) sides. These tines may have silicone or plastic tips to improve grip and prevent damage to the tooth or gingiva. In dental restorations, several devices are commonly used to achieve optimal results including wedges, matrix bands, and separator rings. Wedges are small triangular pieces typically made from wood or plastic. They are inserted between teeth to create space and provide a tight seal at the gingival margin. Matrix bands are typically thin strips of metal or plastic that encircle a tooth to form a mold around which restorative material can be shaped. Separator rings, also known as matrix rings or retainer rings, are devices that apply pressure to hold matrix bands in place and ensure proper contouring of the restoration.

Matrix ring systems are widely used to assist in this process, with C-shaped separator rings being among the most common designs. However, this design introduces several mechanical and material limitations that affect performance and longevity. The C-shaped configuration inherently concentrates mechanical stress at the centre of the arc— specifically, the midpoint of the "C"— when the ring is expanded for placement. This region experiences the highest tensile load during opening, which can push the material closer to its yield point, especially with repeated use. Over time, this stress concentration can lead to material fatigue and eventual breakage, compromising the reliability of the device.

Material selection further influences the durability and cost-effectiveness of separator rings. Metal separator rings, typically made from stainless steel or nickel-titanium alloys, are durable and can withstand over 100 uses. However, they are expensive, and their rigidity can make them difficult to adapt to varying tooth anatomies. Plastic separator rings, while more affordable and easier to handle, often lack the mechanical strength to endure repeated expansion. Most plastic rings have a limited usage life of up to 5 to 10 cycles before they deform or fracture, making them less suitable for long-term or high-volume clinical use.

These limitations can result in inconsistent or inadequate tooth separation, poor matrix band adaptation, and an increased risk of restoration failure due to improper contact or contour. Additionally, they contribute to higher costs due to the frequent replacement of plastic rings or the need to invest in more expensive metal alternatives. The limitations associated with both metal and plastic separators highlight the need for an innovative solution that combines affordability with strength and durability.

Accordingly, there is a need for an improved matrix ring system that addresses the issues of mechanical stress distribution, material durability, and cost-effectiveness, while maintaining ease of use and clinical reliability. It is an object of the present invention to provide a matrix ring designed to overcome the drawbacks of existing solutions. It is a further object of the invention to at least provide the public with a useful choice.

SUMMARY OF THE INVENTION

In a first aspect of the invention there is provided a separator ring for separating teeth in a dental restoration procedure in a mouth of a patient, the dental separator ring comprising a resilient body having a first end and an opposing second end with a gap provided therebetween, the first end and the second end each having a tooth engaging portion thereon, the first end is coupled to a first arm and the second end is coupled to a second arm; and a central portion coupled between the first arm and the second arm, the central portion comprising at least one concave portion, wherein the gap is configured to be expanded in use by pushing the first arm and second arms apart to facilitate engagement of the tooth engaging portions adjacent to a tooth to be restored, wherein the at least one concave portion of the central portion is configured to spread a stress force across the central portion when the gap is expanded.

Preferably the central portion further comprises a first convex portion and a second convex portion, the at least one concave portion being positioned between the first convex portion and the second convex portion.

Preferably the separator ring has an M-shaped design configured to increase a straight material length and spread stress forces across the central portion.

Preferably the central portion is configured to have an increased straight material length compared to the formed width length of the central portion to spread stress forces when the gap is expanded across the central portion.

Preferably each tooth engaging portion is configured in use to be located adjacent the gum in a patient's mouth between the tooth to be repaired and an adjacent tooth. More preferably each tooth engaging portion comprises a pair of prong-like extensions or tines with a channel provided therebetween

Preferably the pair of prong-like extensions are configured in use to act as contact points that rest against a buccal surface and a lingual surface of the gum in the patients mouth. More preferably in use the channel is configured to sit over the gum in the patients mouth between the tooth to be repaired and an adjacent tooth.

In some forms the first arm and the second arm of the separator ring each comprise a forceps notch or aperture configured to receive one end of a forceps. Preferably in use forceps are used to expand the gap by inserting one end of the forceps into the forceps notch or aperture provided on the first arm and second arm and spreading the forceps apart.

In some forms the separator ring is made from a plastic, a suitable steel alloy or a combination of plastic and steel alloy. Preferably the separator ring is made at least in part of acetal plastic. In some forms at least a portion of the first arm and the second arm are over-molded with a polymeric resin or silicone.

In some embodiments the separator ring has a width of between 15 mm to 25 mm. The separator ring may have a length of between 20 mm to 40 mm. The separator ring may have a thickness of between 3 mm to 8 mm. In some forms the width of the separator ring varies along the length. In some forms the separator ring further comprises small projections on the underside of the first arm and the second arm to help retain absorbent material such as cotton-wool rolls used in a dental restoration procedure.

In some embodiments the invention is a kit comprising a separator ring and a resetting instrument designed to compress the sides of the ring inwards to counteract fatigue and deformation.

Preferably the resetting instrument is made of a suitable plastic or steel alloy.

The present invention is a low cost plastic separator ring with the benefit of enabling a dentist to more easily separate adjacent teeth during a restorative procedure and support a dental matrix band for the same purpose.

The term "separator ring" is to be understood to include any form of dental ring retainer or matrix ring used in dental restoration procedures.

Further aspects of the invention, which should be considered in all its novel aspects, will become apparent to those skilled in the art upon reading of the following description which provides at least one example of a practical application of the invention.

BRIEF DESCRIPTION OF THE FIGURES

One or more embodiments of the invention will be described below by way of example only, and without intending to be limiting, with reference to the following drawings, in which:

Figure 1 shows an exemplary C-shaped separator ring applied to a tooth according to the prior art;

Figure 2 shows a drawing of a top perspective view of a separator ring according to an embodiment of the invention;

Figure 3 shows a drawing of a top view of the separator ring of Figure 2;

Figure 4 shows a drawing of a side view of the separator ring of Figures 2 to 3;

Figure 5 shows a drawing of a bottom view of the separator ring of Figures 2 to 4;

Figure 6 shows a front view of the separator ring of Figures 2 to 5;

Figure 7 shows a top perspective views of a separator ring according to an embodiment of the invention;

Figure 8 shows a bottom perspective views of a separator ring according to Figure 7; Figure 9 an exemplary separator ring of the invention applied to a tooth according to an embodiment of the invention;

Figure 10 shows ring forceps being applied to a separator ring of the invention;

Figure 11 an exemplary separator ring of the invention applied to a tooth according to an embodiment of the invention; and

Figure 12 an exemplary resetting instrument according to an embodiment of the invention.

DETAILED DESCRIPTION

Throughout the Figures, like references refer to like components.

Figure 1 shows a C-shaped separator ring 10 according to the prior art. The C-shaped separator ring 10 is designed to grip between the tooth 30 to be repaired from both the buccal 28b and lingual 281 sides of the mouth 28, applying lateral pressure to separate adjacent teeth 32 and secure a sectional matrix band 52. The matrix band 52 is adjusted via a body portion 54 that allows adjustment of the fit of the matrix band 52 around the tooth (tightening and loosening as required). The C-shaped separator ring 10 has a resilient body comprising a first arm 12 and second arm 14 that are connected by a central portion 16 at a first end. The central portion 16 having a curved shape or half circular shape. The second end of each arm 12, 14 comprises a pair of tines (not visible) that are a prong-like extensions that protrude from the ring 10 towards the gum of a patient's mouth 28 between the teeth 30, 32 to be separated. The tines are designed to rest firmly against the buccal and lingual surfaces to grip and separate adjacent teeth 30, 32. The tines assist in anchoring the separator ring in position to prevent movement during use. There is a gap or spacing 20 between the second end of the first arm 12 and second arm 14.

A separator ring 10 is made of a resilient material such as spring stainless steel or other expensive metals such as nickel titanium to allowed repeated stretching or expansion and then restoration to original state as required for application to and from teeth during restorative dentistry procedures. There are a few plastic-shaped separator rings on the market, but they lack sufficient strength to be effective for repeated use.

The first and second arms 12, 14 are configured to be pushed apart to increase the gap or spacing 20 therebetween the second ends. Generally dental ring forceps are used to apply a force to the ring 10 to expand the spacing 20 between the second end of the first arm 12 and second end of the second arm 14 to expand the ring 10 and facilitate insertion of the separator ring 10 over the teeth 30, 32. The separator ring 10 may include forceps notches 22 configured to receive the tips of a ring forceps. The curved central portion 16 of the separate ring 10 is configured to allow limited expansion of the first and second arms 12, 14. As the arms 12, 14 are expanded a stress force is provide in the curved central portion, particularly at the central point 46. Too much expansion may lead to breakage of the curved central portion 16 if the arms 12, 14 are expanded beyond a yield point.

The separator ring 110 of the current invention will now be described in further detail with reference to Figures 2 - 12. The separator ring 110 is designed to have increased resilience having a higher yield point allowing repeated expansion and restoration to original state (i.e. have elastic memory) and to prevent risk of breakage or distortion of the separator ring 110 in use. The separator ring 110 is designed to be used to separate teeth in a dental restoration procedure in a mouth of a patient.

The separator ring 110 of the invention has an increased straightened length compared to traditional C- shaped separator rings 10 to distribute opening force stress across a larger surface area. The separator ring 110 of the invention comprises a central portion 116 having at least one concave portion or dip portion 140 configured to increase the straightened length of the separator ring 110 compared to traditional C-shaped separator rings 10. In a preferred form the separator ring 110 has a M-shaped design. Preferably the side peaks of the M-shape have a rounded or smooth curved configuration. Preferably the central dip or concave portion 140 of the M shape has a rounded or smooth curved configuration. However, in other forms the central dip or concave portion 140 may have a sharper pointed configuration (not shown).

A first exemplary separator ring 110 having an M-shaped design is illustrated in figures 2 to 6 that show several views of the separator ring 110. Figures 7 and 8 show a further exemplary embodiment of a separator ring 110 formed of molded plastic.

As shown, the separator ring 110 has a resilient body that comprises a first arm 112 and second arm 114 that are connected at a first end to a central portion 116. The central portion 116 comprises at least one concave portion 140 arranged between first and second convex portions 142, 144. The first convex portion 142 is coupled to the first arm 112 and the second convex portion 144 is coupled to the second arm 114. The first and second convex portions 142, 144 and the at least one concave portion 140 are configured to increase the overall length of the material and/or surface areas of the central portion 116 to spread the opening force stress across the central portion 116 when the first arm 112 and second arm 114 are stretched apart.

As in prior art separator rings 10, the separator ring 110 of the invention comprises a pair of tines 118a, 118b, being prong-like extensions or protrusions, that protrude from the second or free end of each of the first arm 112 and the second arm 114. The tines 118 may be referred to as tooth engaging portions. Each tine 118 comprise a pair of protrusions 118a, 118b separated by a channel 119 on the under surface (see Figures 6 to 8) of the separator ring 110. The protrusions 118a, 118b are configured to act as contact points that rest firmly against the buccal and lingual surfaces of the adjacent teeth in use. The channel 119 sits on the gum between the adjacent teeth. The tines 118 help to anchor the separator ring 110 in place and prevent it from slipping or rotating during a procedure.

Figure 9 illustrates an exemplary arrangement for a dental restoration procedure. A separator ring 110 is applied to provide a force to the tooth 30 to be repaired/restored and the adjacent tooth 32, being the tooth adjacent to the repair region 34 of the tooth 30 to be repaired. A matrix band 52 is applied around the tooth 30 to be repaired. The matrix band 52 acts as a barrier around the tooth and as a mold for the wall of the tooth 30 to be repaired allowing the clinician to shape the inserted restorative material and ensure proper tooth alignment. The matrix band 52 is adjusted via a body portion 54 that allows adjustment of the fit of the matrix band 52 around the tooth (tightening and loosening as required). A wedge 50 presses the matrix band 52 tightly against the tooth at the gum line, preventing restorative material from leaking out and forming an overhang. The wedge 50 may also stabilise the matrix band 52, separate the teeth 30, 32 and protects the gingiva from injury or irritation.

The separator ring 110 provides a separation between the teeth 30, 32 to compensate for the thickness of the matrix band 52. The separator ring 110 is also configured to retain the matrix band 52 against the tooth 30 being restored. To be able to place the separator ring 110 between the teeth 30, 32 for the restoration the gap or spacing 120 between the tines 118 on each of the first arm 112 and the second arm 114 of the separator ring 110 need to be opened or expanded to clear the matrix band 52. The distance between the gap 120 needs to also be wide enough for a clear field of view for the clinician to ensure the edges of the Matrix band 52 don't get damaged by the tines 118 of the separator ring 110 and the separator ring 110 is positioned correctly. Dental instruments such as Ring Forceps are typically used to achieve this.

For the separator ring 110 to have sufficient separation force the separator ring 110 needs to perform as a spring and retain a memory. In traditional separator rings when the gap or spacing 20 are opened wide enough to achieve the above, it can put large stress on the central portion of the separator ring, especially with repeated uses and leads to breakage failure or yield failure. Advantageously, the design of the central portion 116 of the separator ring 110 of the invention having an increased straightened length of material, formed into a first convex portion 142, at least one concave portion 140 and a second convex portion 144 or M-like shape, spreads the opening forces or stress across the central portion 116 rather than in a concentrated area or point as in the prior art. Thus the effective increased material length spreads the stress forces across a larger portion of its length.

In alternative forms (not shown) the separator ring 110 may comprise a plurality of concave portions across the central portion 116 to further increase the straight length of the central portion to spread the opening force stress across a larger surface area. In use the second ends of the first and second arms 112, 114 of the separator ring 110 are configured to be pushed apart to increase the gap or spacing 120 therebetween to facilitate insertion or removal from the teeth 30, 32. Dental ring forceps 56 are used to apply a force to the separator ring 110 to expand the spacing 120 between the second end of the first arm 112 and second end of the second arm 114 to expand the separator ring 110 and facilitate insertion of the separator ring 110 over the teeth 30, 32 in use (see Figures 9 to 11). The separator ring 110 preferably includes forceps notches 122 configured to receive the tips of a ring forceps 56. The arms of the forceps 56 are used to pull apart the second ends of the first arm 112 and the second arm 114 to increase the gap or spacing 120 therebetween.

Referring to figure 10, the M-like shape of the separator ring 110 spreads the opening forces, so the stresses generated are typically shared across the three areas and not concentrated in one. When the gap or spacing 120 between the first arm 112 and second arm 114 starts to open there is a stress generated at point 141. As the gaps or spacing 120 increases further and the stress at point 141 increases then the stresses are transferred to points 143 and 145. The spreading of these stresses generated by the opening forces across these three points 141, 143, 145, lowers the level of stress in one given point providing the separator ring 110 with a reduced risk or probability of reaching the yield or failure point of the design at the necessary opening distances. If the stress at one given point is lower than the design yield point there is a higher probability that the separator ring 110 will retain memory, relating to separator force, for a longer period of time.

The separator ring 110 may be formed of any suitable material as used in the prior art, such as a metal, stainless steel or nickel titanium or a plastic material. Preferably, the separator ring 110 is made from Acetal, also known as polyoxymethylene, which is an engineering plastic known for its elasticity and strength. Other suitable plashes or steel alloys may also be used. Preferably the separator ring 110 is formed by molding.

Advantageously the increased length of the central portion 116 facilitates the use of lower cost plastic materials, such as acetal, to make the separator ring 110. Such plastic formed M-like shaped separator rings 110 are durable and can withstand more cycles of use, such as greater than 20 uses, more preferably greater than 50 uses and most preferably 80 to 100 uses or more.

In some forms the separator ring 110 or portions thereof, such as the arms 112, 114 or portion thereof and/or tines 118 may be over-molded with a polymeric resin (such as Polyether Ether Ketone (PEEK) or nylon) or silicone to improve grip, durability, biocompatibility and prevent damage to the tooth or gingiva.

The separator ring 110 may vary in size depending on the teeth or mouth size of a patient. An exemplary separator ring 110 has a width of between 15 mm to 25 mm, a length of between 20 mm to 40 mm and thickness of between 3 mm to 8 mm. In some forms the width of the separator ring 110 may vary along the length. It is to be understood that other dimensions may be used. Preferably an M-shaped separator ring 110 of the invention has a straightened length that is at least 2 mm, preferably 3 mm, or 4 mm or 5 mm or longer than a C-shaped separator ring that has a similar folded length and/or dimension to the M-shaped separator ring 110.

The overall straight length of the separator ring 110 is an important determinator of the physical properties of a separator ring 10, 110, especially C-shaped separator rings 10. A shorter length separator ring, when opened widely, will reach its yield point earlier than a longer length separator ring. This is particularly an issue when the separator ring is formed of plastic, due to plastic having less strength than metal. Thus, a separator ring formed of plastic is generally bulkier to achieve a similar spring strength. Plastic also reaches its yield point if the separator ring is relatively short and may break or become deformed. By designing the separator ring 110 with at least one concave portion within the central portion or in an M-shape, the length of a plastic separator ring 110 is increased without making the overall size bulkier, while maintaining a high separating force.

Some matrix rings are autoclavable and reusable, while others are designed for single-use to maintain sterility and reduce cross-contamination. Cleaning and reusing multiple use dental separator rings is a standard practice in clinical settings.

All separator rings in the market may be prone to fatigue after multiple uses or over extension by the user, which leaves the separator ring slightly open and not in an optimal functional state. In some optional forms of the invention a specially designed resetting instrument 200 (see Figure 12) may be used to compress the sides of the separator ring 110 inwards. The resetting instrument 200 is configured to counteract the tendency of some separator rings 110 to fatigue and gradually lose its strength due to gradual deformation of the plastic, such as the Acetal plastic. The resetting instrument 200 may be made of a suitable plastic or steel alloy or any other material that is suitable for autoclaving.

After use, most dental instruments are cleaned and then autoclaved at around 134C. Some plastic separator rings 110 may become distorted with repeated autoclaving. To increase the life of the separator ring 110 and subject to the plastic materials used the M-shaped separator ring 110 may be constrained for cleaning by placing it in a resetting instrument 200 shaped to receive the separator ring 110. The resetting instrument 200 comprises a base portion 202 and a ring constraining portion 204 that is configured to receive a separator ring 110 thereon, as seen in Figure 12. The shape of the constraining portion 204 is configures to complement the shape of the separator ring 110. Additionally, the underside of the separator ring 110 may optionally comprise small projections 106 that function to help retain any cotton-wool rolls that the dentist might use during the restoration procedure.

The heat of the autoclave may reset the shape of the separator ring 110 back to its original conformation. This may be repeated many times and the strength of the separator ring 110 is returned to its original strength. Giving the user confidence in the separator ring 110 being in its optimal functional state and increasing longevity. It is to be understood that the use of a resetting instrument is optional, the separator ring 110 may be autoclaved without use of the resetting instrument 200.

In some forms a M-like shaped separator ring system or kit is provided comprising a resetting instrument 200 and a M-like shaped separator ring 110, thus a kit comprising two parts.

While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Further, the above embodiments may be implemented individually, or may be combined where compatible. Additional advantages and modifications, including combinations of the above embodiments, will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of the Applicant's general inventive concept.

Claims

1. A separator ring for separating teeth in a dental restoration procedure in a mouth of a patient, the dental separator ring comprising a resilient body having: a first end and an opposing second end with a gap provided therebetween, the first end and the second end each having a tooth engaging portion thereon; the first end is coupled to a first arm and the second end is coupled to a second arm; and a central portion is coupled between the first arm and the second arm, wherein the central portion comprises at least one concave portion, the gap is configured to be expanded in use by pushing the first arm and second arm apart to facilitate engagement of the tooth engaging portions adjacent to a tooth to be restored, wherein the at least one concave portion of the central portion is configured to spread a stress force across the central portion when the gap is expanded.

2. The separator ring according to claim 1 wherein the central portion further comprises a first convex portion and a second convex portion, the at least one concave portion being positioned between the first convex portion and the second convex portion.

3. The separator ring according to any one of claims 1 to 2, wherein the separator ring has an reshaped design.

4. The separator ring according to any one of claim 1 to 3, wherein the central portion is configured to have an increased straight material length compared to the formed width length of the central portion to spread stress forces when the gap is expanded across the central portion.

5. The separator ring according to any one of claims 1 to 4, wherein each tooth engaging portion is configured in use to be located adjacent the gum in a patient's mouth between the tooth to be repaired and an adjacent tooth.

6. The separator ring according to any one of claims 1 to 5, wherein each tooth engaging portion comprises a pair of prong-like extensions or tines with a channel provided therebetween.

7. The separator ring according to claim 6, wherein the pair of prong-like extensions are configured in use to act as contact points that rest against a buccal surface and a lingual surface of the gum in the patients mouth.

8. The separator ring according to any one of claims 6 or 1, wherein in use the channel is configured to sit over the gum in the patients mouth between the tooth to be repaired and an adjacent tooth.

9. The separator ring of any one of claims 1 to 8, wherein the first arm and the second arm each comprise a forceps notch or aperture configured to receive one end of a forceps.

10. The separator ring of claim 9, wherein in use forceps are used to expand the gap by inserting one end of the forceps into the forceps notch or aperture provided on the first arm and second arm and spreading the forceps apart.

11. The separator ring of any one of claims 1 to 10, wherein the separator ring is made from a plastic, a suitable steel alloy or a combination of plastic and steel alloy.

12. The separator ring of claim 11, wherein at least a portion of the separator ring is made of acetal plastic.

13. The separator ring of any one of claims 10 to 11, wherein at least a portion of the first arm and the second arm are over-molded with a polymeric resin or silicone.

14. The separator ring of any one of claims 1 to 13, wherein the separator ring has a width of between 15 mm to 25 mm.

15. The separator ring of any one of claims 1 to 14, wherein the separator ring has a length of between 20 mm to 40 mm.

16. The separator ring of any one of claims 1 to 15, wherein the separator ring has a thickness of between 3 mm to 8 mm.

17. The separator ring of any one of claims 1 to 16, wherein the width of the separator ring varies along the length.

18. The separator ring of any one of claims 1 to 11, further comprising small projections on the underside of the first arm and the second arm to help retain absorbent material used in a dental restoration procedure.

19. The separator ring of any one of claims 1 to 17, wherein the separator ring is configured to be autoclaved and reused for at least 20 cycles.

20. A kit comprising a separator ring of any one of claims 1 to 17 and a resetting instrument designed to compress the sides of the separator ring inwards to counteract fatigue and deformation.

21. The kit according to claim 20, wherein the resetting instrument is made of a suitable plastic or steel alloy.