Method and Apparatus for Obturating the Coronal Canal of a Root Canal

This invention relates to the treatment of root canals and in particular the sealing of the coronal canal to prevent the passage of bacteria into the apical canal.

There are problems with existing obturating methods used in endodontic treatment of root canals. Solid material is forced into the root canal system, including the apical portion, which may have irregular fins, grooves and lateral canals. It is difficult to pack the entire volume successfully. If these parts of the root canal system contain infected material and communicate with periradicular tissues, then chronic to acute inflammation may result. It can be very difficult, if not impossible, to remove the hard packing material without causing permanent damage to the root canal system.

There is therefore a need for an obturating method and apparatus which allows the best possible treatment of the apical portion of the root canal system in a sealed environment and allows coronal restoration on the obturating means, while allowing subsequent access to the apical portion without causing permanent damage to the root canal system.

According to a first aspect of the present invention there is provided a method of sealing a coronal canal of a root canal, the method comprising the steps of: forming a bore in the coronal canal, the bore having a cylindrical section of substantially constant diameter extending from a first level in the root canal proximal the coronal opening of the root canal to a second level

in the root canal further from the coronal opening than the first level, thereby forming a constriction in the bore at the second level; applying a tool to a coronal opening of the root canal; operating the tool to place an obturating element in the cylindrical section to a depth such that the obturating element bears on the constriction; causing the obturating element to engage with the internal wall of the cylindrical section of the bore.

The cylindrical section and obturating element may generally be of circular cross-section. However if an appropriate tool is used to form the bore, the cylindrical section and obturating element may be of oval or other cross- section.

The obturating element can be placed by a dental surgeon using a prepackaged cartridge containing the obturating element. Placing the obturating element requires simple pre-drilling of the coronal canal using a dental drill of the required diameter, to a predetermined depth, which may be measured by means of an appropriate gauge. Since the coronal canal is narrower beyond the drilled cylindrical section, forming a constriction at the end of the cylindrical section, the obturating element, which is preferably of the same length as the cylindrical section, will sit against the constriction to ensure perfect positioning within the coronal canal.

Preferably the obturating element expands resiliently to engage against the internal wall of the cylindrical section of the bore. The element, or a portion thereof, may be made of a suitable resilient material.

Preferably the obturating element has an outer surface adapted to bond with the internal wall of the cylindrical section of the bore. The outer

surface of the obturating element, or the internal wall, or both may be provided with a cementitious coating.

The obturating element itself may seal against the internal wall of the cylindrical section of the bore.

Alternatively a sealing material may be applied to the obturating element to seal against the coronal canal. The obturating element is held in place in the canal by its own action, but it may serve as a convenient platform to use a suitable filling material to plug and seal the coronal canal.

Preferably the obturating element has a first end surface which is located at the first level when the obturating element is placed in the cylindrical section, a second end surface which is located at the second level when the obturating element is placed in the cylindrical section, and a soft core extending from the first end surface to the second end surface, the soft core being of material softer than the material of that portion of the obturating element surrounding the soft core.

Preferably the soft core is adapted to permit insertion of a needle from the first end surface to the second end surface and to seal itself after removal of the needle.

Preferably the soft core is adapted to permit drilling of a pilot hole in the soft core to create a bore extending from the first end surface to the second end surface.

Optionally, the method includes the step of inserting a needle into the soft core from the first end surface to the second end surface and injecting a liquid through the needle into the root canal beyond the second level.

Optionally, the method includes the step of removing the needle from the soft core and causing the soft core to reclose in a sealing manner.

The method may include the step of drilling a pilot hole in the soft core to create a bore extending from the first end surface to the second end surface.

The step of operating the tool may include causing a plunger to move relative to a sleeve in order to eject the obturating element from the sleeve.

In one embodiment, the obturating element comprises two portions, an expandable plug portion having a pin bore therethrough and an expander pin insertable in the pin bore to expand the plug portion. The expander pin may be removable to allow removal of the expandable plug portion from the cylindrical bore.

According to a second aspect of the present invention there is provided an obturating element for sealing a coronal canal of a root canal, the obturating element comprising a substantially cylindrical body of circular, oval or other cross-section having substantially planar first and second end surfaces; a soft core extending from the first end surface to the second end surface; and engaging means adapted to allow the obturating element to engage against the internal wall of a cylindrical section of a bore into which it is inserted.

Preferably the engaging means comprises a resilient portion of the obturating element which expands resiliently to cause the obturating element to engage against the internal wall of the cylindrical section of the bore.

Preferably the obturating element has an outer surface adapted to bond with the internal wall of the cylindrical section of the bore.

The obturating element may be adapted to seal against the internal wall of the cylindrical section of the bore.

The obturating element may include a soft core extending from the first end surface to the second end surface, the soft core being of material softer than the material of a portion of the obturating element surrounding the soft core. The soft core may be adapted to permit insertion of a needle from the first end surface to the second end surface and to seal itself after removal of the needle. The soft core may be adapted to permit drilling of a pilot hole in the soft core to create a bore extending from the first end surface to the second end surface.

The obturating element may comprise two portions, an expandable plug portion having a pin bore therethrough and an expander pin insertable in the pin bore to expand the plug portion. The expander pin may be removable to allow removal of the expandable plug portion from the cylindrical bore.

In one embodiment, the obturating element carries a medicament on the second end surface, ie. the surface which is to face the apical canal. The medicament can be selected from antimicrobial agents, antibiotic agents, tissue solvents, chelating agents, anti-inflammatory agents, steroids, cell growth media, growth enhancing agents, tissue guidance agents, bacterial treatments and pharmaceutical preparations, or a combination thereof and can be in the form of a liquid, gel or dissolvable solid.

According to a third aspect of the present invention there is provided a system for sealing a coronal canal of a root canal, the system comprising an obturating element and a tool for placing the obturating element, wherein the obturating element comprises: a substantially cylindrical body of circular, oval or other cross-section having substantially planar first and second end surfaces; engaging means adapted to allow the obturating element to engage against the internal wall of a cylindrical section of a bore into which it is inserted; and wherein the tool comprises: a sleeve containing the obturating element; and a plunger operable to move relative to the sleeve in order to eject the obturating element from the sleeve.

Preferably the engaging means comprises a resilient portion of the obturating element which expands resiliently to cause the obturating element engage against the internal wall of the cylindrical section of the bore. The obturating element may be held in a compressed state in the sleeve and may expand resiliently to engage against the internal wall of the cylindrical section of the bore once it is released from the sleeve.

The obturating element may have an outer surface adapted to bond with the internal wall of the cylindrical section of the bore. Both or either of the outer surface and the internal wall may be coated with an adhesive or bonding agent, such as a cementitious product.

The obturating element may be adapted to seal against the internal wall of the cylindrical section of the bore.

The obturating element may include a soft core extending from the first end surface to the second end surface, the soft core being of material softer than the material of that portion of the obturating element surrounding the soft core.

The tool may include a handle adapted to operate the plunger to move relative to the sleeve.

The obturating element may comprise two portions, an expandable plug portion having a pin bore therethrough and an expander pin insertable in the pin bore to expand the plug portion. The expander pin may be removable to allow removal of the expandable plug portion from the cylindrical bore.

According to a fourth aspect of the present invention there is provided a method of endodontically treating a tooth having a root canal, the method comprising the steps of: applying a medicament to an apical portion of the root canal; forming a cylindrical bore in a coronal canal of the root canal; and plugging the cylindrical bore with an obturating element.

Preferably the cylindrical bore is formed to have a cylindrical section of substantially constant diameter extending from a first level in the root canal proximal a coronal opening of the root canal to a second level in the root canal further from the coronal opening than the first level, thereby forming a constriction in the bore at the second level.

The cylindrical section and obturating element may generally be of circular cross-section. However if an appropriate tool is used to form the bore, the

cylindrical section and obturating element may be of oval or other cross- section.

In one embodiment, the medicament is applied to the apical portion of the root canal prior to formation of the cylindrical bore. Alternatively, it may be more convenient to apply the medicament following formation of the bore. The medicament can be applied as a separate composition or could be located on the second end surface of the obturating element and be applied by the insertion of the obturating element into the cylindrical section.

Preferably the medicament is selected from antimicrobial agents, antibiotic agents, tissue solvents, chelating agents, anti-inflammatory agents, steroids, cell growth media, growth enhancing agents, tissue guidance agents, bacterial treatments and pharmaceutical preparations, or a combination thereof.

Preferably the medicament is applied in the form of a liquid, gel or dissolved solid.

Preferably the obturating element is an obturating element according to the second aspect.

The cylindrical bore may be sealed with the obturating element. Alternatively a sealant may be applied to the obturating element to seal the coronal canal.

The invention will now be described further with reference to the drawings in which:

Fig 1 is a schematic sectional view through the root canal system of a tooth including obturating elements of the invention; Fig 2 is a schematic sectional view through a root canal showing a bore in the coronal canal for receiving an obturating element of the invention; Fig 3 shows an obturating element of the invention;

Fig 4 shows an application tool for applying a obturating element of the invention;

Fig 5 is a partial enlarged view of Fig 4 with an obturating element of the invention prepared for application; Fig 6 shows a further application tool for applying a obturating element of the invention; and

Fig 7 shows an application tool and obturating element according to another embodiment of the invention.

Fig 1 shows a schematic arrangement of a tooth comprising a root 10 and a crown 12. Located within the root 10 are three root canals each having an apical canal 16 extending from the apical opening 18 and a coronal canal 20 extending from the coronal opening 22. An access cavity 24 is located in the crown 12, to allow access to the root canals 14.

According to the invention an obturating element 30, shown in more detail in Fig 3, is provided in the coronal canal 20 to form a hermetic seal in the root canal 14. This allows a variety of treatments to be carried out in the lower part of the root canal 14, in particular the apical canal 16. The apical canal 16, including any other portions of the root canal system in communication with the apical canal 16, may contain solid or non-solid obturating materials. The obturating element 30 may be used to provide a temporary hermetic seal, for example for a period of six months or so, for endodontic medicaments to be contained in the apical portion of the root canal 14. The obturating element 30 is removable by first drilling a pilot

hole through the obturating element 30, and then drilling the cylindrical section 32 of the bore in the coronal canal 20 to remove the obturating element 30.

The formation of the cylindrical section 32 is shown more clearly in Fig 2. The internal wall of the root canal 14 before drilling is shown by dotted line 34. The cylindrical section 32 extends from a first level 36 in the root canal 14 proximal coronal opening 22 of the root canal 14 to a second level 38 in the root canal 14 further from the coronal opening 22 than the first level 36. This forms a constriction 40 in the bore at the second level 38. The obturating element 30 may be then placed in the bore of cylindrical section 32 and urged along the root canal 14 until one end of the obturating element 30 engages with the constriction 40.

The obturating element 30 is shown in more detail at Fig 3. It is of generally cylindrical form, having a length L of typically between 3 and 5 mm, and a diameter D typically in the range from 0.5 mm to 1.5 mm, to correspond to the diameter of conventional dental drills. The obturating element 30 includes a main body 50 of relatively stiff material surrounding a soft core 52 of material softer than the material of the main body 50. The core 52 may be of a natural or synthetic rubber or other self-sealing material which allows the insertion of a needle through the soft core 52 to allow a liquid to be injected through the obturating element 30 to the apical canal 16 from the coronal opening 22.

The soft core 52 also allows a pilot hole to be readily drilled through the soft core 52 to relieve pressure in the apical portion of the root canal 14, prior to and during removal of the obturating element 30 by drilling.

The obturating element 30 may have a softer outer layer 54 adapted to resiliency engage with the internal wall of the cylindrical section 32. Alternatively the main body 50 of the obturating element 30 may have sufficient resilience to engage resiliently with the internal wall.

In one variation, the obturating element 30 may be provided with a slight taper from the first end surface 56 to the second end surface 58. In another variation the bored cylindrical section 32 of substantially constant diameter may be shorter than the length L of the obturating element 30, so that the obturating element extends into the pulp chamber 25 to assist with mechanical retention or bonding of coronal restoration material which may be applied after insertion of the obturating element 30.

Figs 4 and 5 show schematically a tool 70 which may be used to apply the obturating element 30 to the coronal canal 20. The tool 70 comprises a body 72 to which is flexibly mounted a plunger 74. A sleeve 76 is mounted on the lever of a handle 78, which is pivotally connected to the body 72. Operation of the handle 78 causes the plunger 74 to move axially relative to the sleeve 76, thereby urging an obturating element 30 from the sleeve 76 into the coronal canal 20. It will be clear that the dimensions and shape of the sleeve 76 and plunger 74 may be selected as appropriate to allow the tool to be placed adjacent to the bore of cylindrical section 32 in the coronal canal 20. The tool 70 need not be limited to a lever-type operation, but may instead include a spring loaded or air assisted plunger which delivers the obturating element 30 to the selected canal position. For example it may be placed at or below the pulpal floor in posterior teeth. Anterior teeth may require a different applicator tool or a different shape and size of sleeve 76 to deliver the obturating element 30 to below the depth of a post, typically 10 to 15 mm below the access opening.

An alternative applicator portion of a tool according to the present invention is shown in Fig 6. The plunger 74' includes a flange 75 which engages with a corresponding flange 77 on the sleeve 76' to control the extent to which the obturating element 30 is ejected. An arm 80 on the sleeve 76' is provided with an internally threaded hole which engages with a threaded adjusting screw 82. The screw 82 has a foot portion 84 which engages with the pulpal floor in use to control the level at which the obturating element 30 is placed. Typically the tool may be used so that the bottom of the sleeve 76' is 1 to 2 mm below the pulpal floor.

The obturating element 30 may be supplied in cartridge form such that it can be fed in a compressed state into the applicator sleeve 76, and then allowed to resiliently expand once placed in the coronal canal 20 so as to securely engage in the cylindrical section 32. Either or both of the cylindrical section 32 and the outer cylindrical surface 60 of the obturating element 30 may be provided with a sealing agent, for example a cementitious material.

An alternative embodiment of an obturating element 130 is shown in Fig 7. The obturating element 130 is of resilient material and has an axial bore 132. An insert 134 is partly engaged with the axial bore 132. The head 136 of the insert 134 is provided with engagement means (not shown) which can engage with a screwdriver tool 138. The insert 134 may be tapered and/or threaded. The shaft 140 of the tool 138 extends through a tubular sleeve 142 which fits on a ledge 144 on the outer wall of the obturating element 130. In use the obturating element 130 is placed at the correct depth in the bore of cylindrical section 32 by means of the tubular sleeve 142, which may be provided with a handle or other positioning means (not shown). A handle 144 or other operating means of the screwdriver tool 138 is operated to turn the head 136 of the insert 134 and

cause the insert 134 to enter the axial bore 132, thus expanding the obturating element 130. The obturating element 130 thus engages resiliently with the internal wall of the cylindrical section 32 of the bore.

The material of the obturating element 30, 130 may be any material suitable for medical device use which provides the required combination of resilience and rigidity. For example, the material may be a silicone, a natural rubber or polypropylene. The obturating element acts as a cork, so the resilient expansion must be controlled to avoid fracturing the root canal. Preferably the obturating element 30, 130 is radiopaque, of similar radiopacity to existing root filling materials such as gutta percha, to allow its identification on a dental radiograph. The obturating element 30, 130 may be supplied colour coded, so that the correct diameter of obturating element 30, 130 is used with the correct diameter of drilled cylindrical section 32. Ideally the obturating element 30, 130 should be placed at or below gingival attachment level to limit coronal leakage.

The obturating element 30, 130 may be used to seal the coronal canal on its own, or a further sealant material 31 may be applied on top of the obturating element 30, 130 which serves as a platform for supporting the sealant material 31. This is shown in the right hand canal 14 of Fig 1.

The obturating element 30, 130 may be used as part of a method of treatment of a root canal. A medicament may be applied to an apical portion of the root canal 14 without having to fill and seal the entire root canal. The medicament is applied before insertion of the obturating element 30, which then forms a seal and allows the treatment of the apical portion to continue. Alternatively, or in addition, the obturating element 30, 130 may carry a medicament on its second end surface, the surface facing the apical canal.

Coronal restoration can then take place in the region of the access cavity 24. Restorative materials for coronal restoration are well known, and are not described further here. The use of an obturating element 30, 130 allows easy re-entry to the apical canal 16. A dental surgeon will recognise the distinctive colour of the obturating element 30, 130 and it will have a hardness different to dentine.

The present invention provides advantages for the dental surgeon. The obturating element 30, 130 is easy to prepare and place, allows easy re- entry, and provides a precision fit in an easily drilled and/or milled part of the canal system. It utilises a technique similar to the familiar technique of post preparation and placement. It provides a predictable, secure coronal seal. It can be installed by general dental practitioners as well as specialists. It allows long-term medication of recalcitrant cases with easy access to the apical portion of the root canal for re-medication. Acute problems can be controlled with canal medicaments and a predictable coronal seal, which is easy to open for drainage if required. An endodontic medicament below the obturating element 30, 130 may continue to carry out its work between dental appointments. The system is compatible with existing canal preparation techniques and existing restorative techniques.

Use of the obturating element 30, 130 allows an apical management system which can provide a range of specific materials for placement in the apical canal 16 to deal with specific canal conditions. The materials can be selected to provide a variety of properties either separately or together and they can be incorporated in various endodontic medicaments. The materials used as medicaments may include antimicrobial agents, antibiotic agents, tissue solvents, chelating agents, anti-inflammatory agents, steroids, cell growth media, growth enhancing

agents, tissue guidance agents, bacterial treatments and pharmaceutical treatments, or a combination thereof. Because the apical portion of the root canal 14 is not plugged, the medicaments may be effective in any branch passages which connect with the apical route canal 16.

The obturating method and apparatus of the present invention allows the best possible treatment of the apical portion of the root canal system in a sealed environment and allows coronal restoration on the obturating means, while allowing subsequent access to the apical portion without causing permanent damage to the root canal system. Instead of sealing within the apical region, the only hermetic seal is provided in the coronal region. The introduction of hard packing material to the apical region is avoided. Instead appropriate medicaments may be applied to the apical region to encourage recovery of infected areas. If it is necessary to gain subsequent access to the apical region, the obturating element 30, 130 may be removed by drilling and replaced by a new obturating element 30, 130 after any subsequent treatment of the apical area, without causing any additional damage to the apical region or the coronal canal.

Many modifications and other embodiments of the invention will be apparent to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing description and the associated drawings. It is to be understood that the invention is not limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purpose of limitation.