Orthodontic device and method

Abstract

A dental appliance 20 for correcting jaw relationships, the dental appliance comprising a lower shell for fitting over the lower set of teeth, and an upper shell for fitting over the upper set of teet

Description

FIELD OF THE INVENTION The present invention relates to the field of orthodontics and more particularly to a dental appliance for correcting jaw relationships, and a method of doing the same. BACKGROUND TO THE INVENTION Malocclusion is a term used in orthodontics to refer to imperfect positioning of the teeth when the jaw is closed and thus to a non-ideal bite. Malocclusions can have several features, such as crowding, prominent teeth, deep bites, and jaw discrepancies, and encompass both skeletal jaw problems as well as individual dental problems within the jaws themselves. There are three types of malocclusions: a class I malocclusion refers to the upper teeth slightly overlapping the lower teeth; a class II malocclusion refers to a significant overlap of the lower teeth by the upper teeth (overbite); and a class III malocclusion refers to the lower jaw jutting forward such that the lower teeth overlap the upper teeth (underbite). In addition to an aesthetic undesirability, left untreated, Class II and Class III malocclusions can interfere with a person's ability to bite properly, and can cause significant pain, tooth erosion, gum disease and other oral health issues. One method for treating Class II and Class III malocclusions involves orthodontics and the use of a functional appliance to correct the jaw positioning. Functional appliance is a term used for orthodontic appliances which address the fundamental issue of a nonideal jaw relationship by utilising natural forces such as muscular activity during speech, chewing and / or swallowing to alter the position and alignment of the upper and lower jaws. Functional appliances can be fixed within a patient's jaw or may be removable. One of the most well-known types of functional appliance is the 'Twin Block' appliance, developed by Dr. William Clark. The Twin Block appliance comprises both acrylic and metal wire components to form two removable blocks or plates, one for the upper jaw and another for the lower jaw. The blocks have inclined acrylic surfaces which lead to movement and correction of the jaw position during bite closure. Traditional functional appliances like the Twin Block can be poorly tolerated and treatment is successful in approximately only 70% of cases in the UK O'Brien K et al. Effectiveness of treatment for Class II malocclusion with the Herbst or twin-block appliances: a randomized, controlled trial. Am J Orthod Dentofacial Orthop. 2003;124(2):128-137. doi:10.1016 / s0889-5406(03)00345-7 Clear aligners incorporating jaw repositioning features, without using any wire, have been developed. The aligners can be clear and flexible, and typically seek to replicate the mechanism of a traditional functional appliance whilst having an improved convenience and appearance. Aligners incorporating jaw repositioning elements can also have a dual function and simultaneously correct dental alignment. Aligners are often vacuum formed and / or 3D printed and / or injection moulded and use hollow jaw repositioning elements to replicate the mechanism of the 'Twin Block'. In addition to the traditional 'Twin Block' shape, aligners with elongated, buccally offset inclined planes or 'precision wings' are also known. Whilst being more aesthetically pleasing and therefore better accepted by the wearer, aligners incorporating jaw repositioning elements are known to have several challenges. The typical hollow nature of the jaw repositioning elements can cause the aligners to collapse under biting forces, making them ineffective. Additionally, the shape and size of the repositioning elements can result in cheek / lip soreness which can be exacerbated if the element becomes damaged or deformed. The shape of the dental appliance is therefore highly important to its effectiveness in addition to the wearer's comfort. There is therefore a requirement for a dental appliance which is both well accepted by the wearer, and effective in repositioning the jaw whilst causing minimum discomfort to the user. In particular, there is a need for an appliance in which the protrusive elements are carefully shaped and sufficiently rigid and robust to resist distortion. It is against this background that the present invention has arisen. SUMMARY OF THE INVENTION According to the present invention, there is provided a dental appliance for correcting jaw relationships, said dental appliance comprising: a lower shell for fitting over the lower set of teeth; and an upper shell for fitting over the upper set of teeth; wherein the lower shell comprises a mandibular alteration ridge configured to project occlusally on each side of the shell and the upper shell comprises a mandibular alteration ridge configured to project occlusally on each side of the shell; wherein each mandibular alteration ridge comprises at least one guide surface and one or more buttresses; and wherein a guide surface of a mandibular alteration ridge of the upper shell is configured to engage a guide surface of a mandibular alteration ridge of the lower shell to displace the mandible relative to the maxilla as the jaw closes. The present invention provides a dental appliance for correcting jaw relationships through the use of an upper and a lower shell each provided with mandibular alteration ridges (MARs) on either side of the shell. In contrast to prior art dental appliances, the mandibular alteration ridges have a distinctive shape, and each comprise a guide surface and at least one buttress. The upper and lower mandibular alteration ridges engage one another at the guide surfaces as the patient closes their jaw. Within the context of the present invention, the term 'engage' should be understood to mean interface, interact, and / or otherwise contact an opposing guide surface. The engagement of the guide surfaces displaces the lower shell relative to the upper shell and pushes the patient's mandible in an anterior or posterior direction, depending on the arrangement of the mandibular alteration ridges. Through guided movement of the lower jaw, muscles associated with movement of the lower jaw can be retrained to a new position or the lower jaw may be permitted to grow more fully if the patient has not fully developed skeletally. In contrast to repositioning elements known in the art, the guide surface and buttresses of the present invention provide a rigid and robust protrusion which works to correct the jaw relationship whilst resisting distortion. The mandibular alteration ridges are minimally intrusive and considerably less bulky compared to other dental appliances, maximising convenience for the wearer whilst minimising discomfort. In some embodiments, the dental appliance may only correct the jaw relationship. In some embodiments, the dental appliance may be an aligner, and may correct the alignment of the teeth whilst simultaneously correcting jaw relationship. In some embodiments, the dental appliance may be fixed in place within the jaw of the wearer. In some embodiments, the dental appliance may be removable. Within the context of the present invention, the term 'rear teeth' should be understood to refer to premolar and / or molar teeth. In some embodiments, when the dental appliance is applied to correct the positioning of an adult jaw, the mandibular alteration ridges may be configured to project above / below the premolar and / or molar teeth. In some embodiments, when the dental appliance is applied to correct the positioning of an adolescent jaw, the mandibular alteration ridges may be configured to project above / below the molar teeth or the premolar teeth if present. In some embodiments, the dental appliance may be applied to deciduous teeth. In some embodiments, the MARs of the lower shell and the upper shell may be configured to be directly above / below one another. In some embodiments, the MARs of the lower shell and the upper shell may be configured to be offset from one another. In some embodiments, the exact placement and size of the mandibular alteration ridges may be dependent on the patient's jaw and the class of the malocclusion to be corrected. In some embodiments, each mandibular alteration ridge may be located substantially on the occlusal face of the shell. In contrast to some existing jaw repositioning elements which are provided to the side of a shell, by providing the mandibular alteration ridge on the occlusal face of the shell, the dental appliance has an improved comfort for the wearer by minimising contact between the protruding elements and the lips and / or cheek. In some embodiments, the mandibular alteration ridges may be configured such that the dental appliance of the present invention can be used to treat a Class II or a Class III malocclusion. In some embodiments, the dental appliance of the present invention may be configured such that the mandible is displaced anteriorly relative to the maxilla as the jaw closes. In some embodiments, the dental appliance of the present invention may be configured such that the lower mandibular alteration ridge is held in front or anterior to the upper mandibular alteration ridge. In some embodiments, the guide surfaces of the lower shell engage the guide surfaces of the upper shell as the wearer closes their jaw, pushing the mandible forwards and preventing the mandible from moving posteriorly. In some embodiments, such a configuration may be used to correct a Class II malocclusion of a patient's jaw. In some embodiments, the dental appliance of the present invention may be configured such that the mandible is displaced posteriorly relative to the maxilla as the jaw closes. In some embodiments, the dental appliance of the present invention may be configured such that the lower mandibular alteration ridge is held behind or posterior to the upper mandibular alteration ridge, and the guide surfaces of the lower shell engage the guide surfaces of the upper shell as the jaw closes, pushing the mandible backwards and preventing the mandible from moving anteriorly. In some embodiments, such a configuration may be used to correct a Class III malocclusion of a patient's jaw. In some embodiments, the upper and lower shells of the dental appliance are configured such that they fit to the upper and lower jaws of the wearer respectively by fitting over the wearer's upper and lower teeth. In some embodiments, the dental appliance may include an upper shell, which may have one or more teeth-receiving cavities for receiving teeth of an upper jaw, and a lower shell, which may have one or more teeth-receiving cavities for receiving teeth of a lower jaw. In some embodiments, the upper and lower shells of the dental appliance may comprise a plurality of cavities therein configured to receive teeth. In some embodiments, the upper and lower shells may be moulded to fit the teeth of the wearer. In some embodiments, each cavity may be shaped to mate with a particular tooth. For example, the cavity can be shaped to mate with three surfaces of a corresponding tooth to be received therein: inner surface (lingual or palatal), outer surface (buccal) and biting surface (occlusal). In some embodiments, the plurality of cavities may receive one or more teeth without applying repositioning force to the teeth. In some embodiments, the plurality of cavities may apply force to reposition one or more teeth of a jaw from one teeth arrangement to a successive teeth arrangement. In some embodiments, the cavities may be configured to anticipate the eruptive position of an adult tooth, thereby promoting eruption in a favourable position. Each mandibular alteration ridge comprises a guide surface and one or more buttresses. Within the context of the present invention, the term "buttress" should be understood to include any suitable structure configured to provide support for the guide block and / or guide surface and to prevent collapse of the guide block and / or guide surface when the upper guide surface and the lower guide surface meet and a bite force is applied. In some embodiments, the one or more buttresses extend away from the guide surface and extend along the occlusal surface of the shell. In some embodiments, each buttress may extend away from the guide surface at an angle between 100 and 30 degrees. In some embodiments, the arrangement of each buttress extending away from the guide surface provides the mandibular alteration ridge with stability and robustness such that it can withstand deformation. In some embodiments, each buttress may extend from the guide surface substantially perpendicularly. Within the context of the present invention, the term 'substantially perpendicularly' should be understood to mean approximately perpendicularly and may include some slight deviation from perpendicular. In some embodiments, a configuration in which each buttress extends from the guide surface substantially perpendicularly may be biomechanically optimal for correcting jaw relationships. In some embodiments, the one or more buttresses of the mandibular alteration ridges of the lower shell may extend anteriorly. In some embodiments, the one or more buttresses of the mandibular alteration ridges of the lower shell may extend away from the guide surface towards the front of the jaw. In some embodiments, the one or more buttresses of the mandibular alteration ridges of the upper shell may extend posteriorly. In some embodiments, the one or more buttresses of the mandibular alteration ridges of the upper shell may extend away from the guide surface towards the back of the jaw. In some embodiments, the dental appliance may comprise such a configuration when used to treat a Class II malocclusion. In some embodiments, the one or more buttresses of the mandibular alteration ridges of the lower shell may extend posteriorly. In some embodiments, the one or more buttresses of the mandibular alteration ridges of the lower shell may extend away from the guide surface towards the back of the jaw. In some embodiments, the one or more buttresses of the mandibular alteration ridges of the upper shell may extend anteriorly. In some embodiments, the one or more buttresses of the mandibular alteration ridges of the upper shell may extend away from the guide surface towards the front of the jaw. In some embodiments, the dental appliance may comprise such a configuration when used to treat a Class III malocclusion. In some embodiments, the length of one or more of the buttresses may be 5 mm to 20 mm. In some embodiments, the length of one or more of the buttresses may be more than 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19 mm. In some embodiments, the length of one or more of the buttresses may be less than 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7 or 6 mm. In some embodiments, the buttresses may have a constant width along the entire length of the buttress. In some embodiments, buttresses may have a constant width along the height of the buttress. In some embodiments, the buttresses may have a width of 0.5 to 5 mm. In some embodiments, the occlusal surface of each buttress may have the same width as the base of the buttress in contact with the shell. In some embodiments, the occlusal surface of each buttress may have the same length as the base of the buttress in contact with the shell. In some embodiments, this contrasts some known jaw positioning elements such as those with a block shape which are characterised by a wider base to provide stability and robustness. In some embodiments, the constant width of the buttresses of the present invention reduces the bulkiness of the jaw repositioning element and reduces discomfort to the wearer. In some embodiments, each mandibular alteration ridge may comprise a guide block comprising the guide surface. In some embodiments, the guide block may be 5 mm to 10 mm in width. In some embodiments, the guide block may be more than 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0 or 9.5 mm in width. In some embodiments, the guide block may be less than 10.0, 9.5, 9.0, 8.5, 8.0, 7.7, 7.0, 6.5, 6.0 or 5.5 mm in width. In some embodiments, when the guide block is provided to the lower shell, the guide block may be arranged such that it extends in a buccal-lingual direction. In some embodiments, when the guide block is provided to the upper shell, the guide block may be arranged such that it extends in a buccal-palatal direction. In some embodiments, one or more buttresses extend from the guide block along the occlusal surface in a mesial-distal direction. In some embodiments, the one or more buttresses extend substantially from the centre of the guide block. In some embodiments, the guide block and the one or more buttresses form a T shaped configuration. In some embodiments, the one or more buttresses may extend from the guide block substantially perpendicularly. Within the context of the present invention, the term "guide block" should be understood to refer to any suitable structure extending substantially transversely across a tooth, comprising at least one guide surface which engages with another guide surface to provide a jaw repositioning action. In some embodiments, each guide block and each buttress may have a height of 5 mm to 10 mm. In some embodiments, the guide block and each buttress may be equal in height. In some embodiments, each guide block and each buttress may have a height of more than 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2, 6.4, 6.6, 6.8, 7.0, 7.2, 7.4, 7.6, 7.8, 8.0, 8.2, 8.4, 8.6, 8.8, 9.0, 9.2, 9.4, 9.6 or 9.8 mm. In some embodiments, each guide block and each buttress may have a height of less than 10.0, 9.8, 9.6, 9.4, 9.2, 9.0, 8.8, 8.6, 8.4, 8.2, 8.0, 7.8, 7.6, 7.4, 7.2, 7.0, 6.8, 6.6, 6.4, 6.2, 6.0, 5.8, 5.6, 5.4, or 5.2 mm. In some embodiments, the height of the guide block and the one or more buttresses may be determined by the biomechanics of an individual wearer's jaw, and the optimal angle of the guide surface for correcting the jaw relationship. In some embodiments, the guide blocks and buttresses may be solid. In some embodiments, the guide block and buttresses may be hollow. In some embodiments, the guide blocks and buttresses may be substantially solid. Within the context of the present invention, the term "substantially solid" should be understood to include a guide block and buttress which is mainly of solid construction but may comprise small gaps or micro-spaces between the walls of each side of the buttress and guide block. In some embodiments, the substantial solidity and shape of the mandibular alteration ridges of the present invention provide the dental appliance with an increased robustness and an increased ability to withstand deformation. The shape and height of the guide blocks and buttresses is important to ensure the comfort of the appliance for the wearer. In some embodiments, each mandibular alteration ridge may comprise a plurality of buttresses. In some embodiments, providing one or more additional buttresses to each guide block may increase the stability of the mandibular alteration ridge and increase the ability of the ridge to resist deformation. In some embodiments, in which each mandibular alteration ridge comprises a plurality of buttresses, the plurality of buttresses may be substantially parallel to each other and substantially perpendicular to the guide surface. Within the context of the present invention, the term 'substantially parallel' should be understood to mean approximately parallel and may include some slight deviation from parallel. In some embodiments, a configuration in which each buttress extends from the guide surface substantially perpendicularly and extends substantially parallel to the other buttresses may be biomechanically optimal for correcting jaw relationships. In some embodiments, the arrangement of each buttress substantially parallel to one another and extending away from the guide surface provides the mandibular alteration ridge with stability and robustness such that it can withstand deformation. In some embodiments, the plurality of buttresses may be evenly spaced along the width of the guide block. In some embodiments, in which each mandibular alteration ridge comprises a plurality of buttresses, the plurality of buttresses may be arranged in a cross-linked design. In some embodiments, the buttresses may be transversely joined, in some embodiments, the buttresses of a MAR are cross linked by braces that extend between the buttresses. The braces can extend from top to bottom of the buttress at that point in some embodiments, cross-linked buttresses may increase the stability of the mandibular alignment ridge and reduce deformation from occlusal pressures. In some embodiments, where a plurality of buttresses are present they may be arranged in a crosslinked or interlinking configuration. In some embodiment buttresses may be cross braced, they may be cross linked by braces that extend between them. In some embodiments the braces are the same height as the buttress. In some embodiments the braces may be in a crossed formation, whilst in other embodiments the braces may be arranged in parallel, in a ladder formation. In some embodiments, the one or more buttresses may be inclined. In some embodiments, the buttresses may comprise an inclined surface extending along the occlusal surface of the shell. In some embodiments, an engaging pair of mandibular alteration ridges provided to one side of a dental appliance (i.e. the upper right and lower right mandibular alignment ridges) may comprise buttresses which are inclined at opposing angles. In some embodiments, one of the engaging guide surfaces is positioned at an acute angle to the occlusal surface. In some embodiments, the mandibular alignment ridges of the lower shell may comprise one or more buttresses with a rear inclined face. In some embodiments, the mandibular alignment ridges of the upper shell may comprise one or more buttresses with a forward inclined face. In some embodiments, such an arrangement may be used to hold the lower jaw forward and treat a Class II malocclusion. Within the context of the present invention the term 'rear inclined' should be understood to refer to a configuration in which the 'highest point' of the buttress or the point on the buttress which is furthest from the shell vertically is further towards the posterior of the jaw than the anterior of the jaw. In some embodiments, such an arrangement may be referred to as inclined distally or distally inclined. Within the context of the present invention, the term 'forward inclined' should be understood to refer to a configuration in which the 'highest point' of the buttress or the point on the buttress which is furthest from the shell vertically is further towards the anterior of the jaw than the posterior of the jaw. In some embodiments, such an arrangement may be referred to as inclined mesially or mesially inclined. In some embodiments, the mandibular alignment ridges of the lower shell may comprise one or more buttresses with a forward inclined face. In some embodiments, the mandibular alteration ridges of the upper shell may comprise one or more buttresses with a rear inclined face. In some embodiments, such an arrangement may be used to hold the lower jaw backwards and treat a Class III malocclusion. In some embodiments, the guide surfaces of the upper and lower shells may engage substantially parallel to one another. In some embodiments, the guide surfaces may be inclined with respect to the occlusal surface so that each guide surface faces the other at an angle. In some embodiments, the guide surface provided to the lower shell may slant forwards. Similarly to above, when referring to the guide surfaces, within the context of the present invention, the term 'slant forwards' or 'forward inclined' should be understood to mean that the 'highest point' of the guide surface or the point on the guide surface which is furthest away from the shell vertically is further towards the anterior of the jaw, whilst the part of the guide surface closest to the shell is further towards the posterior of the jaw. In some embodiments, such an arrangement may be referred to as slanting mesially or mesially slanted. In some embodiments, the guide surface provided to the upper shell may slant backwards. Similarly to above, when referring to the guide surfaces, within the context of the present invention, the term 'slant backwards' or 'rear inclined' should be understood to mean that the 'highest point' of the guide surface or the point on the guide surface which is furthest away from the shell vertically is further towards the posterior of the jaw, whilst the part of the guide surface closest to the shell is further towards the anterior of the jaw. In some embodiments, such an arrangement may be referred to as slanting distally or distally slanted. In some embodiments, such an arrangement may be used to hold the lower jaw forward and treat a Class II malocclusion. In some embodiments, the guide surface provided to the lower shell may slant backwards. In some embodiments, the guide surface provided to the upper shell may slant forwards. In some embodiments, such an arrangement may be used to hold the lower jaw backwards and treat a Class III malocclusion. In some embodiments, the guide surfaces may be inclined to the occlusal surface at an angle of approximately 90 to approximately 45 degrees. In some embodiments the guide surfaces may be inclined to the occlusal surface at an angle of approximately 70 degrees. In some embodiments, the shells of the dental appliance may be made of a clear material. In some embodiments, the shells of the dental appliance may be made of a substantially clear material which may be slightly opaque. In some embodiments, the upper and lower shell may be a lightweight, and / or thin and / or flexible and / or transparent material to provide a dental appliance which is aesthetically pleasing, comfortable and accepted by the wearer. In some embodiments, suitable materials for the shells of the dental appliance include, but are not limited to, polymeric materials such as polycarbonate or polyacrylates including grades of polymethylmethacrylate. In some embodiments, the shells of the dental appliance may be made of a 3D printable material. In some embodiments, the shells of the dental appliance may be produced by pressure formation to a plastic blank which is then drawn over a 3D model of teeth and the mandibular alteration ridges. In some embodiments, the 3D model is based on data representing a user's teeth. In some embodiments, the shells of the dental appliance may be produced through positive pressure formation. In some embodiments, the shells of the dental appliance may be produced through negative pressure formation. In some embodiments, other processes including, but not limited to, thermoforming, casting, injection moulding and / or 3D printing may be used to form the upper and lower shells of the dental appliance. In some embodiments, the shells and the mandibular alteration ridges may be made from the same material. In some embodiments, the mandibular alteration ridges may be made from the same polymeric material as the upper and lower shells. In some embodiments, the mandibular alteration ridges may be formed separately from the upper and lower shells and may be bonded onto the upper and lower shells at the appropriate positions. In some embodiments, the shells and mandibular alteration ridges may be monolithic. In some embodiments, the mandibular alteration ridges may be formed at the same time as the upper and lower shells of the appliance. In some embodiments, the upper shell and the mandibular alteration ridges on either side of the upper shell may be one piece. In some embodiments, the lower shell and the mandibular alteration ridges on either side of the lower shell may be one piece. In some embodiments, the mandibular alteration ridges may be incorporated during the manufacturing of the shells. In some embodiments, the mandibular alteration ridges may be integrally moulded within the upper and lower shells. In some embodiments, the guide surface and the buttresses may be made from the same material. In some embodiments, a dental appliance in which the mandibular alteration ridges are integrally moulded within the shells provides a shell with increased stability and robustness. Compared to the original Twin Block design in which wire and acrylic components were used, providing a monolithic shell and mandibular alteration ridges increases comfort and aesthetics for the user, whilst providing a reliable and robust jaw repositioning action. In some embodiments, there is provided a method of correcting a Class II or Class III malocclusion wherein the dental appliance as described herein is used. In some embodiments, there is provided a method of correcting a Class II or Class III malocclusion, the method comprising: applying the device described herein to the jaw of a patient for a sufficient time to correct the jaw relationship. In some embodiments, one or more dental appliances of the present invention may be used to correct the jaw relationship of a patient. In some embodiments, a plurality of dental appliances of the present 5 invention may be used as part of a sequential treatment plan, for example where each of the plurality of dental appliances is configured to adjust a malalignment partially and sequentially. In some embodiments, the position of a wearer's jaw may be monitored over a period of time, and successive dental appliances may be prescribed with progressive optimised mandibular alteration ridge shape and placement, to gradually correct the wearer's jaw position as required. In some embodiments, a 10 treatment plan incorporating the dental appliance of the present invention can have an improved reliability over treatment plans using other appliances which are more easily deformed. The optimised shape of the dental appliance of the present invention ensures the treatment plan minimises discomfort for the wearer and therefore has an improved acceptance rate. In some embodiments, there is provided a kit comprising a plurality of dental appliances as described 15 herein. In some embodiments, a kit comprising a number of dental appliances may be provided for use in the sequential adjustment of a misaligned jaw. In some embodiments, when successive appliances of the present invention are used to adjust jaw alignment sequentially, additional scans or impressions of the wearers jaw may be taken. FIGURES The present invention will now be described, by way of example only, with reference to the accompanying figures in which: Figure 1A shows a side view of a prior art dental appliance; Figure IB shows an upper jaw fitted with a prior art dental appliance; Figure IC shows a lower jaw fitted with a prior art dental appliance; Figure 2A shows a side view of the dental appliance of the present invention; Figure 2B shows a side view of an alternative embodiment of the dental appliance of the present invention; Figure 2C shows a side view of an alternative embodiment of the dental appliance of the present invention; Figure 3A shows an upper jaw fitted with the dental appliance of the present invention; Figure 3B shows a lower jaw fitted with the dental appliance of the present invention; Figure 4A shows an upper jaw fitted with an alternative embodiment of the dental appliance of the present invention; Figure 4B shows a lower jaw fitted with an alternative embodiment of the dental appliance of the present invention; Figure 5A shows an upper jaw fitted with an alternative embodiment of the dental appliance of the present invention; and Figure 5B shows a lower jaw fitted with an alternative embodiment of the dental appliance of the present invention. Figure 6A shows an upper jaw fitted with a further alternative embodiment of the dental appliance of the present invention; and Figure 6B shows a lower jaw fitted with a further alternative embodiment of the dental appliance of the present invention. DETAILED DESCRIPTION The present invention provides a dental appliance 20, 30 for correcting jaw relationships. The dental appliance includes an upper and lower shell which interface with the upper and lower teeth of a patient respectively. The dental appliance 20, 30 can correct a jaw relationship without applying force to correct the positioning of teeth or may be provided as an aligner to simultaneously correct the alignment of teeth and the relationship of the jaw. The dental appliance 20, 30 may be fixed in place within the jaw of the wearer or may be removable. Dental appliances for correcting jaw relationships are known in the art. Figure 1 depicts a prior art dental appliance 10 comprising a bulky block 12 projecting below the rear teeth of a patient's upper jaw 18 (Figure IB) and a bulky block 14 projecting above the rear teeth of a patient's lower jaw 16 (Figure IC). As can be seen in Figure 1A the prior art dental appliance 10 also comprises additional features 22, 24 which facilitate efficient tooth movement, through the attachment of elastic bands. Although present in Figure 1, these are not always present in prior art devices. The design of the dental appliance 10 is similar to the traditional 'Twin Block' appliance design, well known in the field, however utilises hollow blocks as opposed to the traditional solid acrylic blocks. The hollow blocks 12, 14 may lack rigidity and collapse under biting forces, making them ineffective. Although not shown in Figure 1, the blocks 12,14 and additional features 22, 24 are part of an aligner design that follows the tooth surfaces, inside and out. Referring to Figure 2, the present invention provides a dental appliance 20,30 comprising a lower shell for fitting over the lower set of teeth of the mandible 26; and an upper shell for fitting over the upper set of teeth of the maxilla 28. Although not visible in Figures 2, 3,4 and 5, it should be understood that the upper and lower shell are present and follow the tooth surfaces inside and out. The upper shell has at least one teeth-receiving cavity for receiving teeth of the maxilla 28. The lower shell has at least one teeth-receiving cavity for receiving teeth of the mandible 26. The upper and lower shells of the dental appliance 20, 30 may comprise a plurality of cavities therein configured to receive teeth. The upper and lower shells can be moulded to fit the teeth of the wearer. Each of the upper and lower shells comprise two mandibular alteration ridges 42, 44. It should be understood that although the figures depict the mandibular alteration ridges 42, 44 provided above / below certain molar and premolar teeth, the appliance is not limited to such an arrangement and the exact positioning of the ridges will depend on the individual patient's jaw, and the Class of malocclusion to be corrected. Each mandibular alteration ridge 42, 44 comprises a guide surface 32, 36 and one or more buttresses 34, 38. The mandibular alteration ridges of the lower shell 44 are configured to project occlusally on each side of the shell and the upper shell comprises mandibular alteration ridges 42 configured to project occlusally on each side of the shell. The guide surface 32 of a mandibular alteration ridge of the upper shell 42 is configured to engage a guide surface 36 of a mandibular alteration ridge of the lower shell 44 to displace the mandible 26 relative to the maxilla 28 as the jaw closes. As shown in Figures 2, 3, 4 and 5, each mandibular alteration ridge 42, 44 is located substantially on the occlusal face of the shell. This contrasts known jaw repositioning elements which are provided to the side of a shell. Referring to Figures 2A, 2B, 3, 4 and 5, a dental appliance 20 for treating a Class II malocclusion is shown. The dental appliance 20 is configured such that when worn, a wearer's mandible 26 is displaced anteriorly relative to the maxilla 28. Figures 2A and 2B show the lower mandibular alteration ridge 44 being held in front or anterior to the upper mandibular alteration ridge 42 through engagement of the guide surfaces 36, 32 as the wearer closes their jaw. The engagement of the guide surfaces 36, 32 prevents the mandible 26 from moving posteriorly and the angle of inclination of the guide surfaces 36, 32 and buttresses 38, 34 pushes the mandible 26 forwards. Referring to Figure 2C, a dental appliance 30 for treating a Class III malocclusion is shown. The dental appliance 30 is configured such that when worn, a wearer's mandible 26 is displaced posteriorly relative to the maxilla 28. Figure 2C shows the lower mandibular alteration ridge 44 being held behind or posterior to the upper mandibular alteration ridge 42 through engagement of the guide surfaces 36, 32 as the wearer closes their jaw. The engagement of the guide surfaces 36, 32 prevents the mandible 26 from moving anteriorly and the angle of inclination of the guide surfaces 36, 32 and buttresses 38, 34 pushes the mandible 26 backwards. As shown in Figure 2, the buttresses 34, 38 of each mandibular alteration ridge 42,44 are inclined with respect to the occlusal plane. As shown in Figures 2A and 2B, the dental appliance 20 for treating Class II malocclusion may comprise lower mandibular alteration ridges 44 comprising buttresses 38 with a rear or distally inclined face. The dental appliance 20 may comprise upper mandibular alteration ridges 42 comprising buttresses 34 with a forward or mesially inclined face. As shown in Figure 2C, the dental appliance 30 for treating Class III malocclusion may comprise lower mandibular alteration ridges 44 comprising buttresses 38 with a forward or mesially inclined face. The dental appliance 30 may comprise upper mandibular alteration ridges 42 comprising buttresses 34 with a rear or distally inclined face. Referring to Figure 2, the guide surfaces 32, 36 of the upper and lower shells engage substantially parallel to one another. The guide surfaces 32, 36 are inclined to the occlusal surface so that each guide surface 32, 36 faces the other at an angle. As shown in Figures 2B and 2C, the guide surfaces 32, 36 may be inclined, for example at approximately 70 degrees. Referring to Figure 2B the guide surface 36 provided to the lower shell slants forwards or mesially whilst the guide surface 32 provided to the upper shell slants backwards or distally. Such an arrangement can be used to hold the mandible 26 forward and treat a Class II malocclusion. Referring to Figure 2C, the guide surface 36 provided to the lower shell slants backwards or distally whilst the guide surface 32 provided to the upper shell slants forwards or mesially. Such an arrangement can be used to hold the mandible 26 backwards and treat a Class III malocclusion. As shown in Figures 3, 4 and 5, the guide surfaces 32, 36 extend in the buccal-lingual direction for the mandible 26 and in the buccal-palatal direction for the maxilla 28. The buttresses 34,48 extend in the mesial-distal direction. As shown in Figure 3, the guide surfaces 32, 36 and buttresses 34,48 may form a 'T'-shaped configuration. The buttresses 34, 38 extend away from the guide surface 32, 36 and extend along the occlusal surface of the shell. The buttresses 34, 38 may extend away from the guide surface 32 at an angle between 100 and 30 degrees. As shown in Figures 3A and 3B each buttress 34, 38 may extend away from the guide surface 32, 36 substantially perpendicularly. The guide surfaces 32, 36 may form part of a guide block 46, 48. The guide block may be 5 mm to 10 mm in width. The buttresses 34, 38 may be 5 mm to 20 mm in length. The buttresses may have a constant width. Each guide block 46, 48 and each buttress 34, 38 may have a height of 5 mm to 10 mm. The guide blocks 46,48 and buttresses are substantially solid, although it is to be understood that small spaces may exist within these depending on the manufacturing approach chosen. As shown in Figures 3 and 4, the buttresses 38 of the mandibular alteration ridges of the lower shell 44a, 44b extend anteriorly from the guide surface 36 towards the front of the jaw. The buttresses 34 of the mandibular alteration ridges of the upper shell 42a, 42b may extend posteriorly from the guide surface 32 towards the back of the jaw. Such a configuration can be used to treat a Class II malocclusion. Although not shown, when used to treat a Class III malocclusion, buttresses 38 of the mandibular alteration ridges of the lower shell 44a, 44b extend posteriorly from the guide surface 36 towards the back of the jaw. The buttresses of the mandibular alteration ridges of the upper shell 42a, 42b extend anteriorly from the guide surface 32 towards the front of the jaw. Referring to Figure 4A, each mandibular alteration ridge 42a, 42b of the maxilla 28 can comprise a plurality of buttresses 34a, 34b. Referring to Figure 4B, each mandibular alteration ridge 44a, 44b of the mandible 26 can comprise a plurality of buttresses 38a, 38b. This can increase the stability of the mandibular alteration ridge and increase the ability of the ridge to resist deformation. Similarly to the buttress arrangement shown in Figure 3, the plurality of buttresses 34a, 34b, 38a, 38b may extend in the mesial-distal direction along the occlusal surface of the shell, whilst the guide surfaces 32, 36 extend in a buccal-lingual direction for the mandible 26 and in the buccal-palatal direction for the maxilla 28. The plurality of buttresses 34a, 34b, 38a, 38b may extend away from the guide surfaces 32, 36 at an angle between 100 and 30 degrees. As shown in Figures 4A and 4B each of the plurality of buttresses 34a, 34b, 38a, 38b may extend from the guide block 46, 48 substantially perpendicularly and can be substantially parallel to each other. Figure 5 shows the plurality of buttresses 34a, 34b, 38a, 38b arranged in a cross-linked or interlinking configuration. As can be seen in Figure 5, the plurality of buttresses 34a, 34b, 38a, 38b extend away from the guide blocks 46, 48 at an angle and are joined transversely at points 52, 54, 56, 58. Figure 6 shows the plurality of buttresses 34a, 34b, 38a, 38b arranged in a further cross-linked or interlinking configuration. The plurality of buttresses 34a, 34b, 38a, 38b extend away from the guide blocks 46, 48, and the buttresses of each MAR are cross linked by braces 60, that extend between the buttresses. The braces can extend from top to bottom of the buttress at that point. It should be appreciated that although Figures 4 and 5 show the plurality of buttresses 34a, 34b, 38a, 38b in an arrangement for correcting a Class II malocclusion, they may also be configured in an arrangement for correcting a Class III malocclusion, as discussed above for Figure 3. The upper and lower shells of the dental appliance 20, 30 are preferably a lightweight, and / or thin and / or flexible and / or transparent material to provide a dental appliance 20, 30 which is aesthetically pleasing, comfortable and accepted by the wearer. Suitable materials for the shells of the dental appliance 20, 30 include, but are not limited to, polymeric materials such as polycarbonate or polyacrylates including grades of polymethylmethacrylate. The shells of the dental appliance 20, 30 may be made from 3D printable materials. The shells and the mandibular alteration ridges 42, 44 are preferably made from the same material although the mandibular alteration ridges 42, 44 may be formed separately from the upper and lower shells and may be bonded onto the upper and lower shells at the appropriate positions. The shells and the mandibular alteration ridges 42, 44 may be monolithic. The mandibular alteration ridges 42, 44 may be formed at the same time as the upper and lower shells of the appliance. The upper shell and the mandibular alteration ridges 42a, 42b on either side of the upper shell may be one piece. The lower shell and the mandibular alteration ridges 44a, 44b on either side of the lower shell may be one piece. The mandibular alteration ridges 42, 44 may be incorporated during the manufacturing of the shells. The mandibular alteration ridges 42, 44 may be integrally moulded within the upper and lower shells. The dental appliance 20, 30 can be used in a method of correcting a Class II or Class III malocclusion. The method may comprise applying the device described herein to the jaw of a patient for a sufficient time to correct the jaw relationship. One or more dental appliances 20, 30 of the present invention may be used to correct the jaw relationship of a patient. A plurality of dental appliances 20, 30 of the present invention may be used as part of a sequential treatment plan. Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure. "and / or" where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example "A and / or B" is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein. The term "approximately" when used herein, as applied to a numerical value, should be understood to mean + / -15% of that value, particularly + / -5% of that value. Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described. It will further be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments. It is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined in the appended claims.

Claims

1. A dental appliance for correcting jaw relationships, said dental appliance comprising:a lower shell for fitting over the lower set of teeth; andan upper shell for fitting over the upper set of teeth;wherein the lower shell comprises a mandibular alteration ridge configured to project occlusally on each side of the shell and the upper shell comprises a mandibular alteration ridge configured to project occlusally on each side of the shell;wherein each mandibular alteration ridge comprises at least one guide surface and one or more buttresses; andwherein a guide surface of a mandibular alteration ridge of the upper shell is configured to engage a guide surface of a mandibular alteration ridge of the lower shell to displace the mandible relative to the maxilla as the jaw closes.

2. The dental appliance of claim 1, wherein each mandibular alteration ridge is located substantially on the occlusal face of the shell.

3. The dental appliance of any preceding claim, configured such that the mandible is displaced anteriorly relative to the maxilla as the jaw closes.

4. The dental appliance of either of claim 1 or claim 2, configured such that the mandible is displaced posteriorly relative to the maxilla as the jaw closes.

5. The dental appliance of any of the preceding claims, wherein the upper and lower shells comprise a plurality of cavities therein configured to receive teeth.

6. The dental appliance of any of the preceding claims, wherein each buttress extends from the guide surface substantially perpendicularly.

7. The dental appliance according to any of the preceding claims, wherein the one or more buttresses of the mandibular alteration ridges of the lower shell extend anteriorly.

8. The dental appliance according to any of the preceding claims, wherein the one or more buttresses of the mandibular alteration ridges of the upper shell extend posteriorly.

9. The dental appliance according to any of the preceding claims, wherein the buttress is 5 mm to 20 mm in length.

10. The dental appliance of any of the preceding claims, wherein each mandibular alteration ridge comprises a guide block comprising the guide surface.

11. The dental appliance according to claim 10, wherein the guide block is 5mm to 10mm in length.

12. The dental appliance according to claims 10 or 11, wherein the guide block and the buttress have a height of 5 mm to 10 mm.

13. The dental appliance according to any of the preceding claims, wherein each mandibular alteration ridge comprises a plurality of buttresses.

14. The dental appliance according to claim 13, wherein the plurality of buttresses are substantially parallel to each other and substantially perpendicular to the guide surface.

15. The dental appliance according to any of the preceding claims, wherein the one or more buttresses are inclined.

16. The dental appliance according to any of the preceding claims, wherein the guide surfaces of the upper and lower shells engage substantially parallel to one another.

17. The dental appliance according to any of the preceding claims, wherein the shells are made of a clear material.

18. The dental appliance according to any of the preceding claims, wherein the shells and mandibular alteration ridges are made from the same material.

19. The dental appliance according to any of the preceding claims, wherein the shells and5 mandibular alteration ridges are monolithic.

20. The dental appliance according to any of the preceding claims, wherein the guide surface and buttresses are made from the same material.10 21. A method of correcting a Class II or Class III malocclusion wherein the dental appliance asclaimed in any of claims 1 to 20 is used.

22. A method of correcting a Class II or Class III malocclusion, the method comprising:applying the device of any of claims 1 to 20 to the jaw of a patient for a sufficient time to15 correct the jaw relationship.

23. A kit comprising a plurality of dental appliances, as claimed in any of claims 1 to 20.s

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