The present invention relates to a dental tool for use in dental laminate restorations, also known as sandwich restorations. The invention further relates to a method of increasing a bonding surface area between glass ionomer cement and composite filling materials, a method of improving the cosmetic appearance of a tooth as well as increase the strength of restorations which cannot be entirely formed of composite due to moisture control issues and a tool head for use with a dental tool.

Dental laminate restorations, often termed sandwich restorations, are designed to improve the aesthetic appearance of a tooth as well as strengthen the restoration and in turn the tooth, should a totally composite or amalgam restoration not be appropriate, and are therefore common practice for both conservative and cosmetic dentists.

A sandwich restoration is typically achieved by providing a glass ionomer cement (GIC) or resin-modified GIC (RM-GIC) which can be directly applied to a tooth, to which a composite filling material is applied as a laminate veneer, to present the outwardly-facing surface of the restored tooth.

A common problem with such restorations is the delamination between the composite outer layer and the inner GIC or RM-GIC layer. At present, the methods by which the bonding is improved is by etching the surface of the set GIC or RM-GIC with 37% phosphoric acid to thereby provide a microscopically roughened surface upon which the application of a dental bonding agent creates micromechanical retention. Alternatively, RM-GIC can be co-cured with composite resin to create a chemical bond therebetween.

The co-curing process requires a GIC base to be applied to the tooth, and then an RM-GIC is used as an intermediary material between the GIC and the composite filling material. This allows for chemical bonding to occur between the GIC and RM-GIC. The composite can then be applied to the RM-GIC, and chemical bonding can occur, typically triggered as a photopolymerisation reaction between the RM-GIC and the composite.

There are disadvantages associated with each of these techniques. Acid roughening of the set GIC or RM-GIC should theoretically provide an improved seal to the composite; however, studies have shown this not to be the case. In particular, etching within 24 hours of placement of the GIC has been shown to be deleterious to the glass matrix thereof. Whilst co-curing has proven to have improved bond strengths, there is a greater propensity for material failure, rather than bonding failure in the restoration, due to the increased number of different material components.

It is therefore an object of the present invention to provide an improved means of increasing bond strength of a sandwich restoration, whilst obviating or limiting the above-mentioned problems. According to a first aspect of the invention, there is provided a dental tool for use in dental laminate restorations, the dental tool comprising: an elongate tool shaft; a tool head positioned at one end of the tool shaft; and a plurality of indentation elements on a surface of the tool head so as to extend outwardly therefrom, the indentation elements being impressable into a soft setting cementitious compound during a dental laminate restoration to leave a plurality of indentations therein.

By providing a dental tool having a tool head with indentation elements thereon, it becomes possible to provide a simple means of improving the bonding strength between a GIC or RM-GIC compound and a composite filling material or dental bonding agent in a dental laminate restoration process. The dental tool can be advantageously used to manipulate the GIC or RM-GIC during a soft setting phase thereof, so as to create an increased bonding surface area to which the composite filling material or dental bonding agent can attach. This significantly increases the survival rate of dental laminates affixed using such a tool.

Preferably, each of the indentation elements may be co-axially aligned with the other said indentation elements.

Coaxial alignment of the indentation elements of the tool beneficially allows for the indentations made in the GIC during the soft setting phase to be arranged in a regular manner, ensuring an even increase in the surface area of the GIC. This advantageously limits the risk of localised areas of weakness in the bonding to arise. The indentation elements may be provided so as to taper to a point in an outward direction from the surface of the tool head, in which case, they may be formed as conical or pyramidal spikes.

Tapering indentations elements beneficially improve the ease of entry and removal of the indentation elements into and out of the soft setting GIC. This ensures minimal disruption to the structure of the GIC layer on a tooth.

Preferably, each of the indentation elements may be less than or equal to 2mm in length, and more preferably may be less than or equal to 1mm in length.

The sizing of the indentation elements is such that the dental tool can mimic the natural etched structure of the interface between dentine and enamel in a tooth, which is a naturally strong bonding arrangement. This ensures that the laminate in the dental laminate restoration is bonded to a similar degree to the connection between natural dentine and enamel. The smaller the indentation elements, the greater the number which can be integrated onto the tool head, thereby increasing the packing density of the indentation elements.

The surface of the tool head may be or substantially be circular, in which case, the diameter of the surface may preferably be 3mm. The indentation elements may be concentrically arranged on the surface.

The size and shape of the surface of the tool head is designed to appropriately contact and engage with a standard human tooth, and therefore is capable of modifying the surface of GIC attached thereto in as straightforward a manner as possible.

Preferably, the indentation elements may be provided in a close-packed arrangement on the surface of the tool head. A separation between outermost ends of the indentation elements may optionally be 0.5mm. Again, the spacing of the indentation elements is such that the indentations eventually formed using the dental tool in the GIC closely match those formed between dentine and enamel in a natural tooth.

In one preferred embodiment, nineteen indentation elements may be provided. An optimum arrangement of indentation elements has found to be nineteen, which keeps an accurate spacing and depth of indentations so as to best match the etching between dentine and enamel without significantly increasing the manufacturing complexity of the tool. The tool shaft may be formed as a 150mm ISO dimension handle, and there may further comprise a shank which connects the tool head and tool shaft. An axis of the shank may be positioned at an angle to an axis of the tool shaft, and additionally the said axis of the shank may be positioned at an angle to an axis of the tool head. Said shank may preferably be 35mm in length. The dental tool is beneficially formed so as to be readily usable inside the mouth of a person undergoing dental laminate construction, and the dimensions above are sized for an average adult, and correspond with the sizes of existing dental tools.

The indentation elements may be formed from a rigid material, may be at least in part non-compressible along a longitudinal axis thereof,. and/or may be integrally formed with the tool head. This may advantageously improve the ease of construction of the dental tool, in addition to the ability of the indentation elements to insert into the soft setting cement without deformation.

According to a second aspect of the invention, there is provided a method of increasing a bonding surface area between glass ionomer cement and composite filling materials for dental laminate restorations, the method comprising the steps of: a] providing a dental tool, preferably in accordance with the first aspect of the invention; b] pressing the indentation elements of the dental tool into a glass ionomer cement during a soft setting phase thereof to provide a plurality of indentations into the glass ionomer cement; and c] applying a composite filling material to the glass ionomer cement, such that an interface between the composite filling material and glass ionomer cement includes at least one of the plurality of indentations, thereby increasing a bonding surface area between the composite filling material and glass ionomer cement.

Preferably, the plurality of indentations may be formed so as to mimic an etched surface between dentine and enamel in a tooth. By increasing a surface area of a GIC compound used during a sandwich restoration, the bonding strength of any compound attached thereto is advantageously also increased. This significantly increases the survival rate of the dental laminate when compared with acid etching based processes. According to a third aspect of the invention, there is provided a method of improving the cosmetic appearance of a tooth, the method comprising the steps of: a] applying a glass ionomer cement to the said tooth; b] during a soft setting phase of the glass ionomer cement, forming indentations in an exposed surface of the glass ionomer cement using a dental tool, preferably in accordance with the first aspect of the invention; c] applying a dental bonding agent to the upper exposed surface of the glass ionomer cement; and d] applying a dental laminate to the dental bonding agent to improve the cosmetic appearance of the tooth.

According to a fourth aspect of the invention, there is provided a tool head for use with a dental tool, the tool head comprising a head surface having a plurality of indentation elements outwardly extending therefrom.

It may be possible to provide a dental tool head which is separate to the dental tool, and can be releasably engaged with a plurality of different dental tools. This may reduce the equipment costs for a dentist.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a perspective representation of one embodiment of a dental tool in accordance with the first aspect of the invention;

Figure 2 shows a side view of the dental tool of Figure 1;

Figure 3 a shows a bottom plan view of the dental tool of Figure 1; Figure 3b shows a magnified plan view of the head of the dental tool shown in

Figure 3 a;

Figure 4 shows a perspective representation of the head of the dental of Figure i ;

Figure 5a shows a side diagrammatic representation of a tooth undergoing a laminate restoration utilising the dental tool of Figure 1, the tooth having a GIC layer applied thereto; Figure 5b shows a side diagrammatic representation of the tooth and dental tool of Figure 5a, the dental tool contacting the GIC layer; and

Figure 5c shows a side diagrammatic representation of the tooth and dental tool of Figure 5 a, following extraction of the dental tool from the GIC layer.

Referring firstly to Figures 1, 2 and 3a, there is illustrated a dental tool, indicated globally at 10, intended in particular for use with dental laminate restorations, also known as sandwich restorations.

The dental tool 10 comprises an elongate tool shaft 12, preferably in accordance with ISO regulations, and a tool head 14 at one end of the tool shaft 12. The tool head 14, as illustrated, may preferably be connected to the tool shaft 12 via a, preferably angled, shank 16. Typically, the dental tool 10 will be formed from a hard-wearing, non-toxic and resistant material, such as stainless steel.

The tool head 14 includes a plurality of indentation elements 18, which are here formed as elongate spikes engaged with a, preferably circular, engagement or mounting surface 20 on the tool head 14. In the depicted embodiment, the indentation elements 18 are formed so as to extend away from the surface 20 coaxially and/or in parallel with one another, the spikes of each of the indentation elements 18 tapering from the surface 20 into a sharp or relatively sharp tip or point 22. These spiked indentation elements 18 can be seen in detail in Figures 3b and 4; here, the indentation elements 18 are substantially conical or pyramidal; however, truncated cones or spikes could feasibly be provided. As with the rest of the dental tool 10, the indentation elements 18 may be preferably formed from stainless steel, but any appropriate material with sufficient rigidity so as to leave an indentation in soft setting GIC or RM-GIC could feasibly be provided.

It is noted that the indentation elements 18 are designed to be urged into soft-setting cementitious material, and therefore must be rigid or at least in part rigid. The indentation element 18 may be formed from a rigid metal material such as steel, but could alternatively be formed from a semi-rigid material such as a pliable elastomer. Bristled arrangements, such as those found on a toothbrush, are not suitable for this task, as they will deform under the application of axial pressure. Preferably, the indentation elements 18 may therefore be at least in part, and more preferably completely, non-compressible along a longitudinal axis thereof, that is, in the direction of extension of the indentation element 18 away from the tool head surface 20.

The arrangement of the points 22 of the indentation elements 18 is designed so as to as closely mimic the natural etching arrangement of a dentine surface of a tooth to which a dentine bonding agent is applicable. In the depicted embodiment, this consists of nineteen indentation elements 18, which are preferably arranged in a concentric configuration on the circular surface 20 of the tool head 14. An ideal point-to-point separation of indentation elements 18 may be 0.5mm, although various factors may affect the arrangement, not least ease of manufacture and closeness of the arrangement to the natural etched dentine surface of a tooth. In order to mount the indentation elements 18 in such an arrangement, the surface 20 may have a diameter of around 3mm, as in the illustrated embodiment.

Each of the indentation elements 18 in the illustrated embodiment is formed such that the length of the spike is 2mm, measured from the point 22 to the surface 20 of the head. This is the simplest arrangement from a manufacturing perspective. However, in order to create the best bonding surface possible, shorter indentation elements 18 may be preferable, for instance, indentation elements 18 which have a length of less than lmm. This in turn will result in a greater number of indentation elements 18 being packed onto the surface 20 of the tool head 14, resulting in an optimal packing density.

The tool shaft 12 is an elongate element, here having a hexagonal profile, and is 150mm in length, this being a suitable length to be held in a user's hand. At one end 24 thereof, the shank 16 is connected, and as shown, may preferably be provided such that an axis of the shank 16 is at an angle to an axis of the tool shaft 12. The shank 16 as shown is here 35mm in length. Furthermore, an axis of the tool head 14 may then be positioned at an angle to the shank 16, so as to give the overall dental tool 10 a partially sigmoidal profile. This beneficially facilitates ready insertion of the dental tool 10 into the mouth of a patient, which is consistent with commonplace dental tools such as dental mirror or periodontal scaler.

Figures 5a to 5c illustrate the intended usage of the dental tool 10 in a dental laminate or sandwich restoration. A tooth 26 requiring restoration is illustrated free from the mouth of a patient for clarity, but it will be apparent that such a dental laminate restoration process would be performed in vivo.

In Figure 5a, the tooth 26 is pre-prepared having a glass ionomer cement (GIC) layer 28 affixed to prepared cavity 30 of the tooth 26, and the GIC layer 28 has entered a soft setting phase in which the GIC layer 28 is at least partially malleable. Whilst a GIC material is referenced hereafter as being the material utilised in the GIC layer 28, it will be appreciated that various types of soft setting or curable materials are available and known in the preparation of dental laminate restorations, and the term GIC layer 28 is not intended to restrict solely to pure glass ionomer cements. In particular, it should be noted that resin-modified GIC (RM-GIC) compounds are also commonly used, and the present technique is equally applicable to such compounds.

In use, the dental tool 10 is brought into close proximity with the GIC layer 28 affixed to the tooth 26, such that the points 22 of the indentation elements 18 are presented so as to face the GIC layer 26, as illustrated in Figure 5 a. As shown in Figure 5b, the tool head 14 is moved towards the GIC layer 28 such that at least a portion of the indentation elements 18 enter into the soft setting GIC layer 28, displacing at least a portion of the GIC.

The dental tool 10 can then be extracted, as illustrated in Figure 5c, thus leaving a plurality of indentations 32 in the GIC layer 28 which correspond to the indentation elements 18 of the tool head 14. This has the advantage of greatly increasing a surface area of an upper exposed surface 34 of the GIC layer 28.

Once this upper exposed surface 34 has been indented to a satisfactory degree, the GIC layer 28 can be allowed to set and/or harden, such that the indentations 32 are permanently fixed into the GIC layer 28. Following setting, a dental bonding agent or composite filling material can be applied to the upper exposed surface 34 of the GIC layer 28, seeping into the indentations 32 so as to improve the surface contact between the GIC layer 28 and the dental bonding agent or composite filling material. The laminate can then be affixed to the dental bonding agent or composite filling material to complete the dental laminate restoration.

The increased surface area of the upper exposed surface 34 of the GIC layer 28 as a result of the indentations 32 greatly increases the strength of the bond between the GIC layer 28 and any composite filling material or dental bonding agent applied thereto, upon which the dental laminate is to be mounted. In doing so, the risk of dislodging of the dental laminate is significantly reduced.

The dental tool 10 is formed so as to facilitate this bonding; the indentation elements 18 on the tool head 14 are formed such that the corresponding indentations 32 closely match or mimic the natural etching between dentine and enamel in a tooth. This is the reason that the preference for the indentation element 18 length is sub-millimetre, since this is closer to the etching pattern of dentine. However, from a manufacturing perspective, it may be more challenging to produce indentation elements 18 which are less than 1mm long.

It will be appreciated that although the dental tool as described above is intended for use in the context of assisting dental laminate restorations so as to improve the GIC bonding strength, the tool could more generally be provided as a means to increase a surface area of any malleable substance, and could therefore be used in, for example, craft or hobby modelling contexts with modelling putty.

Additionally, whilst the dental tool has been described above as having the tool head affixed to the tool shaft, it is possible that the tool head could be provided so as to be releasably engagable with the tool shaft. In such a scenario, it may be feasible that the tool head could be provided separately of the tool shaft, so as to be interchangeably engagable with dental tool shafts, or potentially with motorised toolings. Similarly, whilst the indentation elements are illustrated as being integrally formed with the tool head in the embodiment described above, it will be appreciated that this is primarily due to ease of manufacture of the dental tool. It is thus possible that the indentation elements could be formed separately to the tool head.

Whilst the dimensions provided for the tool shaft, shank and tool head above are typical for dental instruments, there is not intended to be any specific restriction to particular dimensions for any part of the tool in the present invention. It will be appreciated that, at the very least, there may be a difference in scale between tools suitable for use with children and adults, for example.

It is therefore possible to provide a dental tool which can be used to increase the bonding characteristics in the context of a dental laminate or sandwich restoration. This is achieved by provided a dental tool having a tool head which has a plurality of indentation elements thereon which can be pressed into a soft setting GIC compound affixed to a tooth, to thereby increase the surface area of the GIC compound to which a laminate bonding agent can be affixed. This tool has significant strength benefits when compared with acid etching of a GIC compound after the soft setting phase of the GIC compound. The words 'comprises/comprising' and the words 'having/including' when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention herein described and defined.