Patent Publication Number: US-2012040301-A1

Title: Mandibular advancement

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Australian Provisional Patent Application No 2009901240 filed on 23 Mar. 2009, the content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This description generally concerns mandibular advancement, that is bringing forward of the lower jaw. Aspects of the invention include various appliances, a method for advancing the mandible of a human subject, a shell, a method for personalising the frame from a blank frame using the shell, a dental device for mandibular advancement and a method for advancing the mandible of a human subject using the dental device. 
     BACKGROUND 
     Mandibular advancement is useful for treating a range of dental problems, for instance underdevelopment of the lower jaw. It is also useful for a number of medical problems, such as snoring obstructive sleep apnoea (OSA), which is a sleep disorder characterised by periodic reduction or cessation of breathing due to narrowing of the upper airway during sleep. 
     A range of oral appliances are currently available for mandibular advancement. These generally consist of respective ‘splints’ attached to each side of the maxilla (upper jaw) and each side of the mandible (lower jaw). The upper and lower splints interact with each other to draw the mandible forward. The interaction between the parts may rely on mechanical engagement, of for instance sloping surfaces of the opposed parts, springs, magnets or any combination of these things. 
     There are a number of disadvantages with using splints, such as restricting airflow, impeding speech and obstructing the tongue. A visit to the clinician is also generally necessary for adjustment. In addition, there will generally be some unwanted movement of the teeth caused by the reaction forces between the upper and lower jaw. 
     Maxillary advancement is also useful for a range of dental problems, particularly Class III malocclusions in children. This treatment typically makes use of a ‘facial mask’ that comprises a framework anchored to the forehead and chin, and a crossbar that is used to brace springs (elastic bands) attached to a pair of splints bonded to the teeth on respective sides of the upper jaw. 
     SUMMARY 
     In a first aspect, there is provided a personalised appliance for human mandibular advancement, comprising a frame having
         a first end adapted to be secured against a fixed part of the body of a subject,   a second end equipped with a pulling platform, and   an intervening length to present the pulling platform outside the mouth of the subject when the first end is mounted against the fixed part of the body of that subject. Wherein, at least part of the intervening length of the frame is shaped to match the contours of the subject&#39;s face so that when the first end is secured against the fixed part of the body, at least part of the intervening length lies against the matching contours of the subject&#39;s face.       

     Generally, the pulling platform is centred in front of the face and between the lips. In use, the pulling platform is attached to the subject&#39;s mandible by substantially inextensible means to pull it forward. Metal wires or cables (fishing line) may be suitable for this purpose. 
     Using this appliance to apply forward traction forces to a subject&#39;s mandible, no reciprocal force is exerted on the maxilla, thereby reducing unwanted side effects on the upper arch. Also, the bulk within the subject&#39;s mouth is reduced compared to ‘splints’ that are attached to each side of the maxilla (upper jaw) and each side of the mandible. Advantageously, this improves airflow and tongue posture, and reduces clockwise rotation of mandible and bite opening. The invention can be used to treat obstructive sleep apnoea, maxillary retrusion in skeletal Class III malocclusions, and potentially mandibular retrusion in the developing child to encourage mandibular translation or “bite jumping” and growth. 
     The first end of the frame may be secured against a fixed part of the skull, particularly by being strapped to the subject&#39;s forehead. 
     To assist in pulling the jaw forward, the pulling platform may include an adjustment mechanism that can be operated to vary the distance by which a subject&#39;s mandible is advanced. 
     The mechanism may be manual or motorised, in which case it may be computer controlled to vary the length of the attachment according to a preselected regime, or in response to stimuli. For instance, it may be programmed to pull the jaw further forward when snoring is detected, and to release after a period of quiet. 
     The attachment to the lower jaw may make use of temporary anchorage devices, such as orthodontic micro screws, or mini or micro implants that have no, or light, osseo-integration to bone. In this case, the temporary anchorage devices are implanted in the subject&#39;s lower jaw to provide skeletal anchorage for mandibular advancement. 
     Alternatively, the attachment to the jaw may be made to a dental prosthetic implant either directly or via an internal structure. In this case, the dental prosthetic implant also provides skeletal anchorage for mandibular advancement. 
     Alternatively again, the attachment to the jaw may be made to an appliance that is fixedly or removably secured to the teeth of the lower jaw. In this case, the appliance provides tooth-borne anchorage for mandibular advancement. 
     In a second aspect, there is provided an appliance for human mandibular or maxillary advancement, comprising a frame having
         a first end adapted to be secured against a fixed part of the body of a subject,   a second end equipped with a pulling platform, and   an intervening length to present the pulling platform outside the mouth of the subject when the first end is secured against the fixed part of the body of that subject. Wherein, the pulling platform comprises an entirely extra-oral adjustment mechanism to control the distance by which the jaw is advanced when, in use, the mechanism is attached to the subject&#39;s jaw.       

     Advantageously, the mechanism is able to advance the mandible or maxilla with precision. For instance, the mandible or maxilla can be advanced at a minimum of ⅙ mm at a time, up to 70% of a subject&#39;s maximum jaw protrusion. The amount of advancement can also be readjusted as required by a clinician or the subject herself. 
     In a third aspect, there is provided an appliance for human mandibular advancement, comprising a frame to present a pulling platform extra orally centred in front of the face and between the lips of a subject, wherein the pulling platform is attached to the lower jaw to pull it forward. 
     In a fourth aspect, there is provided an appliance for human mandibular or maxillary advancement, comprising a frame to present a pulling platform extra orally centred in front of the face and between the lips of a subject, wherein the pulling platform is attached to the jaw by substantially inextensible means to pull it forward. 
     In a fifth aspect, there is provided a method for advancing the mandible of a human subject, comprising the steps of:
         locating a pulling platform in a fixed position relative to the subject&#39;s head outside the subject&#39;s mouth and centred in front of the face and between the lips; and   attaching the pulling platform to the subject&#39;s mandible using substantially inextensible means.       

     The substantially inextensible means may be metal wires or cables (fishing line) extending from the pulling platform to the subject&#39;s mandible. 
     In a sixth aspect, there is provided a shell for forming a negative mould of a subject&#39;s face, comprising a plasticly deformable skeleton having multiple regions extending from a web that extends around a central breathing hole, all encapsulated within an elastic material such that, in use, the shell can be deformed into approximate conformity with the subject&#39;s face. 
     The skeleton may be made from metal mesh. The elastic material may be silicone. The shell may further comprise an integrated layer of impression material that can be activated and deactivated to make an impression of a subject&#39;s face. The integrated layer may be made of thermoplastic material, in which case activation is by way of heat. 
     In a seventh aspect, there is provided a method of personalising, from a blank frame, a frame that conforms to the contours of a subject&#39;s face, along at least part of its length, the method comprising:
         using a shell according to the sixth aspect to form a negative mould of the subject&#39;s face; and   matching at least part of the length of the blank frame to the contours of the subject&#39;s face using the negative mould, or a positive cast made from the negative mould.       

     In an eighth aspect, there is provided a dental device for human mandibular advancement, comprising:
         an elongated portion having first and second ends, the portion having a variable length and provided with a resilient member,   a locking mechanism to retain the elongated portion at a desired length, and   an attachment formation on each end of the elongated portion, each attachment formation being shaped and sized for connection with an anchorage device implantable in a subject&#39;s mandible or maxilla,   wherein, in use, the elongated portion is retained by the locking mechanism at a desired length and engaged with anchorage devices implanted in the subject&#39;s mandible and maxilla via the attachment formations such that the resilient member is operable to urge the subject&#39;s mandible forward relative to the maxilla.       

     The attachment formations may be shaped and sized for click connection with the anchorage device. 
     The attachment formations may be each provided with a ring surrounding a gripping portion for connection with a ring indentation and a head of the anchorage device respectively. 
     The elongated portion may comprise inner and outer telescopic members that are movable relative to each other and the locking mechanism is a screw that retains the members in a fixed relationship. 
     In a ninth aspect, there is provided a method for advancing the mandible of a human subject using the dental device according to the eighth aspect, the method comprising
         adjusting the length of the elongated portion and retaining the elongated portion at a desired length using the locking formation; and   connecting ends of the elongated portion to a respective anchorage device implanted on the subject&#39;s mandible or maxilla via the corresponding attachment formation.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of non-limiting examples with reference to the accompanying drawings, in which: 
         FIG. 1  is a frontal view of a first example of an appliance exemplifying the invention. 
         FIG. 2  is a side view of the appliance shown in  FIG. 1 . 
         FIG. 3  is a pictorial view of a substantially inextensible means. 
         FIG. 4(   a ) is a pictorial view of the substantially inextensible means in  FIG. 3  when attached to a subject&#39;s mandible using temporary anchorage devices. 
         FIG. 4(   b ) is a side view of a temporary anchorage device. 
         FIG. 4(   c ) is a pictorial view of the substantially inextensible means in  FIG. 3  when attached to a subject&#39;s mandible using dental prosthetic implants. 
         FIG. 4(   d ) is a pictorial view of the substantially inextensible means in  FIG. 3  when attached to a subject&#39;s mandible using an appliance attached to the teeth of the lower jaw. 
         FIG. 5  is a flowchart of a method of advancing the mandible of a human subject. 
         FIG. 6  is a flowchart of a method of fabricating a frame that conforms to the contours of a subjects face. 
         FIG. 7  is an exploded view of a shell. 
         FIG. 8(   a ) is a pictorial view of a cast for fabricating a shell. 
         FIG. 8(   b ) is a pictorial view of the cast in  FIG. 8(   a ), after a layer of silicone is poured onto a skeleton. 
         FIG. 8(   c ) is a pictorial view of a shell fabricated using the cast in  FIG. 8(   a ). 
         FIG. 9(   a ) is a pictorial view of a shell, with a layer of impression material applied onto its inner surface. 
         FIG. 9(   b ) is a pictorial view of a subject using the shell in  FIG. 9(   a ). 
         FIG. 9(   c ) is a pictorial view of the shell in  FIG. 9(   b ) after a negative mould of the subject&#39;s face is made. 
         FIG. 10(   a ) is a pictorial view of the shell in  FIG. 9(   c ), after dental stone is poured into the shell to make a positive cast. 
         FIG. 10(   b ) is a pictorial view of positive cast created in  FIG. 10(   a ). 
         FIG. 10(   c ) is a pictorial view of the shell in  FIG. 10(   a ), after the positive cast and negative mould are removed. 
         FIG. 11(   a ) is a frontal view of a second example of the appliance in  FIG. 1 . 
         FIG. 11(   b ) is a frontal view of a third example of the appliance in  FIG. 1 . 
         FIG. 12(   a ) is a pictorial view of a dental device for mandibular advancement when attached to a subject&#39;s maxilla and mandible via two anchorage devices. 
         FIG. 12(   b ) is a pictorial view of the dental device. 
         FIG. 12(   c ) is a cross-sectional pictorial view of the anchorage device in  FIG. 12(   a ) when engaged with the dental device in  FIG. 12(   b ). 
     
    
    
     BEST MODES OF THE INVENTION 
     Referring first to  FIG. 1 , the appliance  10  exemplifying the invention is shown worn by a subject  20  requiring mandibular or maxillary advancement. The appliance  10  comprises two identical frames  30 , each having:
         A first end  32  to be secured against a fixed part of the body of a subject  20 , specifically against the upper part of the subject&#39;s skull.   A second end  34  equipped with a pulling platform  40 . And,   An intervening length  36  extending from the first end  32  to the second end  34  to present the pulling platform  40  outside the mouth of the subject  20  when the first end  32  is secured against the upper part of that subject&#39;s  20  skull.       

     The appliance  10  is a laboratory-fabricated device that is personalised for each subject  20 . In particular, at least part of the intervening length  36  of the frame  30  is shaped to match the contours of the subject&#39;s  20  face so that when the first end is secured against the fixed part of the body, at least part of the intervening length  36  lies against the matching contours of the subject&#39;s  20  face. 
     In the example shown in  FIG. 1 , the intervening length  36  is shaped to match the contours of the subject&#39;s face along the right hand side of the subject&#39;s forehead, cheekbone and cheek so as to present the pulling platform  40  outside the centre of the mouth. A zygomatic pad  37  is placed below one section of the intervening length  36  to make the appliance  10  more comfortable. 
     The first end  32  of each frame  30  is secured against the upper part of the subject&#39;s skull by being strapped to the subject&#39;s forehead using strap  39 . The first end  32  is attached to a laboratory-fabricated frontal plate  38  that has been shaped to match contours of the subject&#39;s forehead so as to better secure the frame  30  against the subject&#39;s forehead. The frontal plate  38  is made acrylic, but other suitable material such as plastics may be used. Strap  39  is elastic to allow stretching to fit around the subject&#39;s head. Alternatively, strap  39  may be inelastic and fastened using hook and loop fasteners such as Velcro™. 
     Pulling Platform  40   
     Referring also to  FIG. 2 , the second end  34  of the frames  30  is equipped with the pulling platform  40 , which is centred in front of the subject&#39;s face and between the lips when the first end  32  is strapped to the subject&#39;s head. 
     The pulling platform  40  comprises an entirely extra-oral adjustment mechanism  42  which can be operated to vary the distance by which a subject&#39;s mandible  22  is advanced. The adjustment mechanism shown  42  is in the form of a manually operatable screw (also  42 ) having a turning knob  44 . The screw  42  is attached to the subject&#39;s mandible  22  using a substantially inextensible means  50 . In use, the substantially inextensible means  50  is attached to the subject&#39;s mandible  22  using anchorage devices  60  and  62 . 
     When the turning knob  44  is rotated in a specified direction, the screw  42  will move away from the subject&#39;s face, pulling the attached substantially inextensible means  50 , and therefore the subject&#39;s mandible  22 , towards the forward direction (labelled ‘F’). The screw  42  may be chosen such that one full turn of the knob  44  advances the subject&#39;s mandible  22  by at a minimum of, for instance, 1 mm. The length of the screw  42  may be also chosen such that the subject&#39;s mandible can only be advanced up to a certain percentage of the subject&#39;s maximum mandibular protrusion. In practice, the maximum displacement is generally 70% of the subject&#39;s maximum protrusion. 
     Advantageously, the extra-oral adjustment mechanism  42  allows a clinician to vary the mandible displacement of a subject, for instance during a polysomnographic study to determine an effective mandibular displacement to treat obstructive sleep apnoea. Further self-readjustments can be made by the subject whenever the displacement set by the clinician is no longer effective, for instance due to muscle relaxation or adaptation after prolonged use. 
     Although not shown, the adjustment mechanism  42  may also be motorised. In this case, the mechanism  42  may be computer-controlled to displace a subject&#39;s mandible  22  to a preselected regime, or in response to stimuli detected by a sensor. For instance, it may be programmed to pull the mandible  22  forward when snoring is detected by the sensor, and to release after a period of quiet. Further, the motorised adjustment mechanism  42  may comprise a remote control operable to send a radio signal to the adjustment mechanism  42  to increase or decrease the displacement. 
     Substantially Inextensible Means  50   
     Referring now to  FIG. 3 , the substantially inextensible means  50  attaches the extra-oral pulling platform  40  centred outside the subject&#39;s mouth to the subject&#39;s (intra-oral) mandible  22  for mandibular advancement. The substantially inextensible means  50  may be made of metal wires, cables or plastics such as fishing lines. Unlike elastomeric banding devices, the substantially inextensible means  50  do not degrade with oral fluids. 
     The substantially inextensible means  50  comprises two arms  52  and  53 , to which hooks  56  and  58  are attached. A hoop  54  is formed on the opposite end of the substantially inextensible means  50 . The hooks  56  and  58  are attached to the elongated member  52  using crimping or welding at  59 . In use, the hooks  56  and  58  are each attached to a corresponding intra-oral anchorage devices  60  ( 62 ) held in fixed relationship to the subject&#39;s mandible. On the opposite end, the hoop  54  is attached to an extra-oral pulling platform  40 , such as to a hook (not shown) extending from the pulling platform  40 . 
     The substantially inextensible means  50  is adaptable in order to connect the extra-oral pulling platform  40  to a variety of intra-oral anchorage devices  60  and  62 . Referring now to  FIGS. 4(   a ),  4 ( b ),  4 ( c ) and  4 ( d ), the substantially inextensible means  50  is designed to be attached to one or more of the following anchorage devices: 
     (a) Temporary anchorage devices. 
     (b) Dental prosthetic implants. 
     (c) An appliance that is fixedly or removably secured to the teeth on the mandible  22 . 
     First in  FIG. 4(   a ), the temporary anchorage devices  60   a  and  62   a  are orthodontic micro screws, or mini or micro implants that provide skeletal anchorage to the mandible  22 . These temporary mini-implants have no, or light, osseo-integration and therefore are easily implanted and removed. Generally, insertion of these temporary anchorage devices  60   a  and  62   a  takes only a few minutes. Their removal can, generally, be performed with relative ease and little discomfort to the patient. They are considerable smaller in diameter compared to conventional dental implants and can be placed in between roots of teeth and in edentulous spans where there are no teeth. 
     To provide skeletal anchorage, one temporary anchorage device  60   a  ( 62   a ) is implanted on each side of the subject&#39;s mandible  22 . The temporary anchorage devices  60   a  and  62   a  are shaped and sized to engage with the substantially inextensible means  50 . As shown more clearly in  FIG. 4(   b ), each temporary anchorage device  60  ( 62 ) has a mushroom-shaped head  63  for engagement with a hook  56  ( 58 ) of the substantially inextensible means  50 , and a threaded shaft  64  for implantation into the subject&#39;s mandible  22 . The elongated arms  52  and  53  of the substantially inextensible means  50  extend along the side of the teeth on the mandible  22  to meet at the hoop  54  for attachment to a pulling platform  40 . 
     With reference to  FIG. 4(   c ), dental implants  60   b  and  62   b  are designed to be osseo-integrated to the subject&#39;s bone and therefore are immobile and resistant to movement. As such, the anchorage to the subject&#39;s mandible  22  provided by the osseo-integrated dental implants is also a form of skeletal anchorage. In use, the substantially inextensible means  50  is attached to the dental implants  60   b  and  62   b  via hooks  56  and  58  respectively to provide an anterior pulling force for mandibular advancement. 
     The process of placing an osseo-integrated implant is much more involved than that of a temporary anchorage device. Typically, a healing period is recommended and once the implants are osseo-integrated (stage 1). Then, a prosthetic stage (stage 2) is implemented where a tooth coloured crown/bridge is attached to the implants in stage 1. For patients who are completely edentulous (no teeth) on the lower arch, a lower denture is fabricated to give the patient “teeth” in the lower jaw. This denture is only supported by soft tissue and the denture tends to move and “float” between the tongue and cheek muscles. 
     To provide better stability, sometimes, two dental prosthetic implants are placed in the bone in the lower jaw. To these two dental osseo-integrated implants, a super structure called an abutment arising from the implant above the gum tissue is often fixed. These abutments connect to the denture to provide increase stability and retention for a lower denture (overdenture). These dental implants can provide support and retention for an overdenture during the day, and can be connected to the pulling platform  40  for mandibular advancement after the denture is removed at night. 
     Referring now to  FIG. 4(   d ), the substantially inextensible means  60  can also be connected to lower appliances  60   c  and  62   c  that are fixedly or removably secured to the teeth on the mandible  22  to provide tooth-borne anchorage. Unlike attachment via temporary anchorage devices ( 60   a,    62   a ) and dental prosthetic implants ( 60   b,    62   b ), the lower appliances  60   c  and  62   c  are not suitable for edentulous patients because they usually require a minimum usually of 6 to 10 teeth to be present. 
     The appliances  60   c  and  62   c  can be made of a combination of metal and acrylic. In use, the hooks  56  and  58  of the substantially inextensible means  50  are each engaged with a corresponding attachment member  61 , also in the form of a hook, of the appliances  60   c  and  62   c.    
     Method for Mandibular Advancement Using Appliance  10   
     Referring to  FIG. 5 , a method for advancing the mandible of a human subject using the appliance  10  will now be described. The process typically starts with a subject  20  going to a clinician for treatment of, for instance, obstructive sleep apnoea. 
     In step  110 , a personalised appliance  10  having a frame  30  that conforms to the contours of the subject&#39;s face is fabricated using the method outlined in  FIG. 6 . Personalising the frame  30  allows the appliance  10  to be worn more comfortably by the subject  20 , taking into account the subject&#39;s face contours and sleeping habits. If the subject  20  does not have any existing intra-oral anchorage devices ( 60  and  62 ) that can provide anchorage to the subject&#39;s mandible  22 , these anchorage devices need to be implanted or fitted in step  120 . 
     Once custom-made, the subject  20  can then use the appliance for mandibular advancement. Specifically in step  130 , the pulling platform  40  at the second end  34  of the frame  30  is located in a fixed position relative to the subject&#39;s head and outside the subject&#39;s mouth and centred in front of the face and between the lips. This is achieved by first placing the frontal plate  38  of the frame  30  against the subject&#39;s forehead and then fastening the strap  39  extending from the frontal plate  38  around the subject&#39;s head. 
     The pulling platform  40  is then attached to the subject&#39;s mandible using the substantially inextensible means  50 ; see step  140 . This is achieved by first engaging the hooks  56  and  58  of the substantially inextensible means  50  with the corresponding anchorage devices  60  and  62  that are held in fixed position relative to the subject&#39;s mandible  22 . The hoop end  54  of the substantially inextensible means  50  is then connected to adjustment mechanism  42  of the pulling platform  40 . 
     The distance (“D” in  FIG. 1 ) by which the subject&#39;s mandible  22  is displaced (in the forward direction “F” in  FIG. 1 ) is pre-set by a clinician. However, due to muscle relaxation over time, the distance required may need re-adjusted. In that case, the subject or a third person can vary the distance from time to time using the adjustment mechanism  42 . 
     Method of Fabricating Frame  30   
     Referring now to  FIG. 6 , a method of fabricating a frame  30  that conforms to the contours of the subject&#39;s face will now be described. 
     A facial moulding shell  70  is first used to create a negative mould of a subject&#39;s face; see  FIG. 111 . As shown in the exploded view in  FIG. 7 , the shell  70  comprises a plasticly deformable skeleton  72  encapsulated in a silicone body having inner  74  and outer  78  layers. The skeleton  72  is in the form of a piece metal mesh having multiple regions with a web  73  that extends around a central breathing hole  76 , such that, in use, the shell  70  is deformable into approximate conformity with a subject&#39;s face. 
     The process of making the shell  70  using a shell mould  80  is illustrated in  FIGS. 8(   a ), ( b ) and ( c ). Specifically, a skeleton  72  is first placed on the shell mould  80 , which in this case, is a positive face cast of a person (not of the subject  20 ); see  FIG. 8(   a ). The body of the shell mould  80  is generally made of dental stone while its periphery is made of clay that is shaped to form a receptacle to hold the skeleton  72  and silicone forming the body. Of course, other plastic material such as Plaster of Paris may be used to make the shell mould  80 . 
     Then, in  FIG. 8(   b ), a first layer of liquid silicone is poured onto the skeleton  72  on the shell mould  80  to form the inner surface  74 . After the first layer sets, more silicone is poured onto the first layer. This step of silicone pouring is repeated until the skeleton  72  is fully encapsulated within the silicone. 
     The product of this process is the shell  70  shown in  FIG. 8(   c ). The shell  70  has an inner surface  74  that follows the shape of the mould  80 , an outer surface  78  having rough texture due to the layers of silicone encapsulating the skeleton  72 , and a central breathing hole  76 . The facial moulding shell  70  fabricated using this process is deformable, and therefore reusable to take an impression of the face of a plurality of subjects. 
     To use the shell  70  to make a negative mould of a subject&#39;s face, an impression material  84  is applied onto the inner surface  74  of the shell  70 , carefully avoiding the central breathing hole  76 ; see step  112  in  FIG. 7  and  FIG. 9(   a ). For instance, the impression material  84  may be a dental alginate mixture prepared by mixing water with alginate powder. Then, while the impression material  84  is still plastic, the inner surface  74  of the shell  70  is pressed against the subject&#39;s face, and held in this position until the impression material  84  sets; see step  113  in  FIG. 7  and  FIG. 9(   b ). The subject&#39;s face, especially areas with facial hair, could first be given a light covering of petroleum jelly to ease removal of impression material  84 . As impression material  84  such as dental alginate usually sets within  2  to  3  minutes, this method allows a negative mould of a subject&#39;s face to be taken quickly at a clinic. 
     Finally, after the impression material  84  in  FIG. 9(   a ) sets to form a negative mould  85  of the subject&#39;s face, the shell  70 , together with the negative mould  85 , is then carefully removed from the subject&#39;s face; see step  114  in  FIG. 7 . As shown in  FIG. 9(   c ), the negative mould  85  registers the contours of the subject&#39;s face. The negative mould  85  can then be used to create a positive face cast. This involves pouring casting material  86  such as dental stone or Plaster of Paris into the shell  70 ; see step  115  in  FIG. 7  and  FIG. 10(   a ). Once dried, the casting material  86  is removed to obtain the positive cast  90  in  FIG. 10(   b ). 
     Next, frames  30  that conform to the contours of both sides of the subject&#39;s face, as captured by the positive cast  90 , can be formed from a blank, unshaped frame (not shown); step  116  in  FIG. 7  and  FIG. 10(   b ). The blank frame may be made of material such as plastics or metal wires that can be matched, at least part of its length, to the contours of the subject&#39;s face. Also, the blank frame may be fabricated by a clinician or pre-fabricated elsewhere. This method of personalising the frames  30  takes into account of the shape of the subject&#39;s forehead, cheekbone and cheek, as well as the position of the subject&#39;s mouth. Where appropriate, a zygomatic pad  37  can be placed under one section of the intervening length  36  of the frames  30  to improve comfort. 
     Then in step  117  in  FIG. 7 , a frontal plate  38  is fabricated to conform to the contours of the subject&#39;s forehead and connected to the first end  32  of the frame  30  and strap  39 . The frontal plate  38  may be made of plastics or acrylic. Once formed, the pulling platform  40  should be positioned outside the mouth of the subject  20  when the first end  32  is secured against the upper part of that subject&#39;s  20  skull. After the positive cast  90  and negative mould  85  are removed, the facial moulding shell can be reused to make a positive cast of another subject; see step  118  in  FIG. 7  and  FIG. 10(   c ). 
     Alternatively, the frame  30  can be formed to match the contours of the subject&#39;s face without forming the positive cast ( 90 ). Instead, the negative mould  85  of the subject&#39;s face in  FIG. 9  is used for this purpose. Specifically, like in steps  116  and  117  in  FIG. 7 , this involves bending at least part of the intervening length  36  of the frame  30  to match the contours registered by the negative mould  85 . One or more zygomatic pads  37  can be placed under a section of the intervening length  36  to improve comfort. 
     Although the invention has been described with reference to a particular example, it will be appreciated by the appropriately skilled person that many modifications and additions are possible. For instance, the appliance  10  can also be used for maxillary advancement by connecting the pulling platform  40  to the subject&#39;s maxilla. In this case, anchorage devices  60  and  62  also need to be on the maxilla. 
     Also, while the frames  30  have been shown in  FIG. 1  to extend from the subject&#39;s forehead to both the left and right hand sides of the subject&#39;s face, the appliance  10  may be modified to only have one frame that extends from either the right or the left hand side of the subject&#39;s face; see  FIG. 10(   a ). Alternatively, the appliance  10  may have one frame that extends from the subject&#39;s forehead to the middle of the face (i.e. mid-sagittal plane); see  FIG. 10(   b ). This allows subjects to sleep on their preferred left or right side. 
     Also, it is envisaged that the facial moulding shell  70  can be modified to include an integrated layer of impression material that can be activated and deactivated to make an impression of a subject&#39;s face. The impression material may be made of thermoplastic material, in which case activation is by way of heat. This way, step  112  in  FIG. 7  (i.e. applying a layer on the inner surface of the shell  70 ) can be skipped. 
     Outside of the field of dentistry, it is envisaged that the facial moulding shell  70  could be used in the following fields: 
     (a) Medical field, to create a full or partial face cast for prosthetic surgery 
     (b) Optometry, to create a personalised pair of spectacles or eye mask; 
     (c) Forensics, to create a face cast of a crime victim; 
     (d) Fabrication of breathing apparatus such as customised CPAP masks, diver breathing apparatus and full face masks. 
     (e) Cosmetic and beauty industry, such as to create personalised beauty masks. 
     Also, the negative mould  85  removed from the shell  70  in step  118  in  FIG. 7  can be used for other purposes. For instance, the negative mould can be used as a face mask, onto which special effects make-up can be applied. 
     Although not illustrated, the appliance  10  may have an integrated continuous positive airway pressure (CPAP) mask. The subject is connected to a positive pressure air supply via a nose mask or nasal prong that is integrated with the appliance  10 . In use, the combination of mandibular advancement using the appliance  10  and provision of a positive pressure air supply using a CPAP mask keeps the subject&#39;s upper airway open during sleep to reduce the likelihood of upper airway occlusions. 
     The treatment of sleep apnoea can also be enhanced using a dental device  100  for mandibular advancement, such as when the appliance  10  is not in use. As shown in  FIG. 12(   a ), the dental device  100  is attached to two anchorage devices  130  respectively implanted in the subject&#39;s maxilla  21  and mandible  22  to urge the mandible  22  forward. Although only the right side of the mouth is shown in  FIG. 12(   a ) for simplicity, an identical dental device  100  is also placed on the left side. 
     Referring also to  FIG. 12(   b ), the dental device  100  comprises an elongated portion  120  having a variable length, a locking mechanism  128  to retain the elongated portion  120  at a desired length, and an attachment formation  110  on each end of the elongated portion  120  for attachment with a respective anchorage device  130 . 
     The length of the elongated portion  120  is adjustable by moving an inner telescopic member  122  within an outer telescopic member  124 . To fix the elongated portion at a desired length, the inner  122  and outer  124  telescopic members are retained in a fixed relationship relative to each other using the locking mechanism  128 . 
     The locking mechanism  128  is in the form of a hex screw housed within the outer  124  telescopic member, but its head is accessible externally via an opening  129  in the member  124  for easy manipulation. The tip of the hex screw  128  engages the inner telescopic member  122  in a friction fit engagement to prevent movement of the outer telescopic member  124  with respect to the inner telescopic member  122 . The resilient member  126  within the outer telescopic member  124  helps retain this engagement while exerting a forward force onto the subject&#39;s mandible  22  to urge it forward relative to the maxilla  21 . 
     The attachment formations  110  are each shaped and sized for attachment with an anchorage device  130  implanted in the subject&#39;s mandible  22  or maxilla  21 . Each attachment formation  110  comprises a continuous ring  112  surrounding a central gripping portion  116 . As shown more clearly in  FIG. 12(   c ), the gripping portion  116  has a small protrusion that is designed for gripping by a subject while locating an anchoring device  130  within the subject&#39;s mouth. 
     The anchorage device  130  is generally in the form of a micro screw, mini screw or dental prosthetic implant. The anchorage device  130  comprises a mushroom-shaped head  132  that is shaped and sized for a “snap” or “click” connection with the attachment formation  110 , and a threaded shaft  134  for implantation in the subject&#39;s maxilla  21  and mandible  22 . The mushroom-shaped head  132  is formed with a ring indentation  136  for retaining the continuous ring  112  of the attachment formation  110 . 
     When in use, the length of the elongated portion  120  is determined and adjusted by a clinician by moving the inner telescopic member  122  within the outer telescopic member  124  until a desired length is achieved. The telescopic members  122   124  are then retained by screwing the hex screw  128  into the inner telescopic member  122  through the opening in the outer telescopic member  124 . The suitable length depends on the amount of mandibular advancement required by the subject. 
     To attach the attachment formations  110  to the anchorage device  130 , the gripping portion  116  at one end of the device  100  is first held by one or two fingers and then “clicked” onto the mushroom-shaped head  132  of an anchorage device  130  within the subject&#39;s mouth. When connected, the continuous ring  112  of the attachment formation  110  is fitted within a corresponding ring indentation  136  in the mushroom-shaped head  132 ; see  FIG. 12(   c ). 
     The process is repeated for the other attachment formation  110  of the dental device  100  such that both formations  110  are connected to a respective anchorage device  130  implanted in the subject&#39;s mandible  22  or maxilla  21 . The same is repeated for the other side of the subject&#39;s mouth such that two dental devices  100  are used at the same time. 
     The use of a dental devices  100  on both sides of the subject&#39;s mouth helps to advance the subject&#39;s mandible forward and keep the subject&#39;s upper airway open during sleep. This reduces the likelihood of upper airway occlusions and therefore sleep apnoea. The attachment formations  110  and telescopic members  122  and  124  can be made of suitable material such as silicon. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 
     For example, the ring  112  of the attachment formation  110  may not be continuous at all. A hook-like design can be used for the ring  112 , as long as engagement with the corresponding indentation  136  in the anchorage device  130  can be achieved.