Patent Publication Number: US-2023145447-A1

Title: Mouthpiece for a dental cleaning system and the dental cleaning system

Description:
FIELD OF THE INVENTION 
     This invention relates to dental cleaning systems, in particular to a dental cleaning system in the form of an automatic brush system based on an actuated mouthpiece. 
     BACKGROUND OF THE INVENTION 
     Automatic tooth brushing using cleaning mouthpieces has become an emerging technology. Several mouthpiece-based dental cleaning systems are in the development stage and claim in particular a short brushing time (e.g. 6-30 seconds). These systems hence have speed and ease of use as the main value drivers. 
     In this document, the term “mouthpiece” is used to refer to the part of a cleaning system which resides inside the mouth and is fitted to the teeth. Typically this is an arch to cover the teeth of a jaw or a pair of arches to cover the teeth of both jaws. The system will typically have other parts which remain external to the mouth, in use. Each arch of the mouthpiece for example has a base and side walls. 
     A dental cleaning system of this type for example comprises a mouthpiece which fits over the teeth of one or both jaws, with cleaning bristles facing the teeth. The mouthpiece or just the bristles are driven to move or vibrate relative to the teeth to provide a brushing action. 
     One issue that has been found is a lack of cleaning effectiveness, due to insufficient coverage/reach on the back molars and the gum line, lack of contour following of different jaw geometries, and due to limited kinetic energy transmitted to the teeth. 
     Difficulties are also found in providing sufficient energy transfer from an actuator to the bristles to enable sufficiently long bristle strokes and large amplitude needed to remove plaque. Vibrations/shaking of the jaw and head can also be a cause of discomfort. 
     By way of example, U.S. Pat. No. 8,636,677 discloses a dental cleaning system with an inner band along the inside surface of the teeth and an outer band along the outside surface of the teeth. The two bands and associated brush elements are moved towards and away from each other, vertically up/down or in small circular motions to clean the teeth. 
     There is a need for an improved dental cleaning system, for addressing some or all of the issues outlined above. 
     SUMMARY OF THE INVENTION 
     The invention is defined by the claims. 
     According to examples in accordance with an aspect of the invention, there is provided a mouthpiece for a dental cleaning system, comprising: 
     a base; 
     an inner arch for positioning adjacent an inner surface of the teeth of a jaw of the user; and 
     an outer arch for positioning adjacent an outer surface of the teeth of the jaw, 
     an actuator coupling for connection to an actuator for applying motion to the inner arch and/or the outer arch, relative to the base, 
     wherein the base, the inner arch and the outer arch are coupled by a coupling arrangement, wherein the coupling arrangement converts motion of one of the inner and outer arches in one direction relative to the base to motion in an opposite direction relative to the base of the other of the inner and outer arches. 
     This mouthpiece has inner and outer arches for brushing mainly the inner and outer surfaces of the teeth (wherein the inner surfaces are those facing inwardly into the mouth cavity i.e. proximal to the mouth cavity and the outer surface are those facing outwardly from the mouth cavity i.e. distal from the mouth cavity). Tooth cleaning bristles are for example attached to the arches. Angled bristles may be used to reach the occlusal tooth surfaces. The base forms a central stationary part. It for example has a tooth-contacting part for the biting surfaces of the teeth, and a cleaning element may be added to brush the occlusal tooth surfaces. The base is connected to the two arches. A coupling arrangement, for example formed of hinges or pivots, provides an anti-phase coupling mechanism between the movement of the inner and outer arches. This anti-phase coupling mechanism assists in providing reach to the rear molars, and also provides cancellation of vibrations and hence reduces the shaking of the device inside the mouth or shaking of the user&#39;s head. 
     Note that the actuator coupling may be fixed (so the mouthpiece is not detachable from the associated actuator) or it may be a detachable coupling, e.g. to allow cleaning of the mouthpiece separated from the actuator. 
     The coupling arrangement in particular couples to adjacent regions of the inner and outer arches, and converts motion of said region of one of the inner and outer arches in one direction relative to the base to motion in an opposite direction relative to the base of said region of the other of the inner and outer arches. 
     The separation of the base from the arches means the user can bite down on the base without affecting the anti-phase motion and therefore brushing performance. Biting on the mouthpiece will not cause an increased load on the motor, for example by ensuring that the coupling arrangement is at a different level to the tooth-contacting part of the base. The arches, on which bristles are for example formed, are separated from the (?) base which defines the mouthpiece body. 
     The mouthpiece also enables desired brushing motion along the tooth arch to be implemented with sufficient transfer of energy to remove plaque, stains or softer calculus. 
     The coupling arrangement may comprise a symmetric or asymmetric arrangement of coupling members such as flexible hinges. 
     The coupling arrangement for example comprises coupling members extending between the inner and outer arches, the coupling members connecting to the base at a location between the inner and outer arches. The coupling members for example function as hinges, with the pivot point of the hinges being defined where they connect to the base. The hinges thus rock about at least one pivot point in at least one dimension to provide the anti-phase relative movement between the inner and outer arches. Pivot points may be provided in different dimensions (axes) in space to provide more complex 2D or 3D motions such as circular motions, transverse motions (with tapping) or motions along more than just one axis. 
     The coupling arrangement is for example configured to provide actuation of the inner arch or the outer arch at a front of the mouthpiece: 
     along a single side-to-side axis; or 
     within a two dimensional side-to-side and up-down plane. 
     The front of the mouthpiece is the region positioned at the front teeth. 
     The arches may be driven to have lateral translational motion only, or else more complex motions can be generated such as up-down motion combined with lateral strokes, for example forming circular rotational motions. A more complex motion may for example be created by combining a 1D motion such as tapping (i.e. in a direction across rather than along the tooth) with a sliding motion or 2D circular motion along the tooth, which enhances the cleaning result. 
     In a first set of examples, the coupling arrangement comprises: 
     a first hinge at the back of a first lateral side (i.e. a left side or a right side) of the mouthpiece, which first hinge connects a back portion of the inner arch, a back portion of the outer arch and the base at said first lateral side; and 
     a second hinge at the back of a second lateral side of the mouthpiece, which second hinge connects a back portion of the inner arch, a back portion of the outer arch and the base at said second lateral side. 
     In this design, the coupling arrangement comprises hinges at the back of the arches, on both lateral sides (i.e. one at the left side and one at the right side of the mouthpiece). 
     In a second set of examples, the coupling arrangement comprises: 
     a first hinge along a first lateral side of the mouthpiece set forward from the back of the first lateral side, which first hinge connects the inner arch, the outer arch and the base at that first lateral side; and 
     a second hinge along a second lateral side of the mouthpiece set forward from the back of the second lateral side, which second hinge connects the inner arch, the outer arch and the base at that second lateral side. 
     In this design, the coupling arrangement comprises hinges set forward from the back of the arches, again with one on each side. 
     The coupling arrangement may then further comprise a first connector between the inner and outer arches at the back of the first lateral side and a second connector between the inner and outer arches at the back of the second lateral side. These connectors maintain the desired spacing between the inner and outer arches as well as permitting the anti-phase motion, but the anti-phase motion is generated/induced by the first and second hinges. 
     The first and second hinges in these designs for example each comprise: 
     a strut, rigidly coupled to the inner and outer arch with a pivot point symmetrically or asymmetrically located along the strut which is coupled to the base; or 
     a first U-bend or W-bend between the outer arch and at least one connecting node, and a second U-bend or W-bend between the connecting node and the inner arch, wherein the connecting node is coupled to the base. 
     Thus, different hinge designs are possible for generating the desired anti-phase coupling, with suitable elasticity. 
     The mouthpiece (base, coupling arrangement and arches) may be formed of a single material. However, in an example, the inner arch and outer arch are for example formed of a first material and the coupling arrangement, or portions of the coupling arrangement, are formed of a different material to the first material. The use of different materials enables the elastic coupling properties of the compliant system to be optimized. 
     The invention also provides a dental cleaning system comprising: 
     the mouthpiece as defined above; and 
     an actuator coupled to the coupling of the mouthpiece. 
     The dental cleaning system for example comprises a frame which carries the actuator, wherein the frame is rigidly coupled to the base. Thus, the base and the frame are static parts of the system. The user can bite on the static base, and the motor is fixed on the frame, which is also fixed relative to the base. Thus, all movements are performed by the mouthpiece only, in particular the arches, which ensure that most of the vibration energy goes into the mouth for cleaning and minimizes losses of vibration energy in the handle. 
     The actuator is for example arranged in front of the mouthpiece (i.e. outside of, and in front of the mouth of the user) and couples to the outer arch at the front of the mouthpiece. The frame and actuator for example form a handle of the cleaning system. 
     The frame for example couples to the outer arch with a connection which allows rotation of the outer arch relative to the frame about a rotation axis behind the front of the mouthpiece. This rotation axis is for example a vertical axis, allowing side-to-side rotation. The frame thus has a rigid connection to the base and a flexible connection to the outer arch, so that the outer arch can move relative to the base. 
     In all examples, the actuator may comprise a motor with an eccentric coupling element which connects to the outer arch. The eccentric coupling convers a rotational motor output to the desired 1D, 2D or 3D motion pattern to be applied to one of the arches. An eccentric motor may for example be integrated in the handle of the cleaning system to actuate the outer arch with suitable frequencies in the range of 0.5-300 Hz and strokes of about 0.5-10 mm to obtain a large range of reach towards the back teeth. 
     In another set of examples, instead of forming the actuator outside of and in front of the mouthpiece, the actuator may be arranged in a space partially surrounded by the inner arch. Thus, it may be for positioning inside the user&#39;s mouth. This may enable a more compact device. 
     The coupling arrangement may then comprise first and second swash plates at the output of the actuator, wherein: 
     the first swash plate connects to a back of opposite lateral sides of the inner arch, and the second swash plate connects to a back of opposite lateral sides of the outer arch; or 
     the first swash plate connects to a back of one same lateral side of the inner and outer arches, and the second swash plate connects to a back of the other same lateral side of the inner and outer arches. 
     These swash plate designs enables the desired anti-phase motion to be generated directly at the output of the actuator, e.g. motor 
     In all examples, the dental cleaning system may further comprise cleaning elements (silicone bristles, nylon bristles, etc.) on the inner arch and the outer arch, as well as on the base to be able to brush the occlusal tooth surfaces. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: 
         FIG.  1    shows a first example of a dental cleaning system; 
         FIG.  2    shows the design of  FIG.  1    from above; 
         FIG.  3    shows more clearly that the design of  FIG.  1    has two U-shaped channels back to back, to enable cleaning of the teeth of both jaws at the same time; 
         FIG.  4    shows one unit which is an assembly of one U-shaped channel of the mouthpiece and one frame; 
         FIG.  5    shows an exploded view of the design of  FIGS.  1  to  4   ; 
         FIG.  6    shows the shape of the mouthpiece and the part of the frame which connects to the outer arch of the mouthpiece; 
         FIG.  7    shows how the anti-phase motion is induced using the design of the mouthpiece shown in  FIG.  6   ; 
         FIG.  8    shows the shape of the mouthpiece and the part of the frame which connects to the outer arch of the mouthpiece for an alternative design; 
         FIG.  9    shows a further alternative design of the coupling members; 
         FIGS.  10 A to  10 C  show how different materials may be used in the designs of  FIGS.  6  and  8   ; 
         FIG.  11    shows a modification of the frame to create an additional degree of freedom; 
         FIG.  12    shows a first alternative actuator design; and 
         FIG.  13    shows a second alternative actuator design. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The invention will be described with reference to the Figures. 
     It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts. 
     The invention provides a mouthpiece for a dental cleaning system and the dental cleaning system itself. The mouthpiece has a base and inner and outer arches. An actuator is used for applying motion (i.e. movement) to the inner arch and/or the outer arch, relative to the base. A coupling arrangement converts motion of one of the inner and outer arches in one direction relative to the base to motion in an opposite direction relative to the base of the other of the inner and outer arches. By forming the mouthpiece as a central stationary base enveloped by two contour-following and moving arches (coupled via the coupling arrangement), an anti-phase brushing motion at opposite tooth sites along the tooth arch is enabled, giving increased reach toward the molars as well as a reduction head shaking or device shaking inside the mouth. 
       FIG.  1    shows a first example of a dental cleaning system. The system comprises a mouthpiece  10  for insertion in the mouth of the user and an external part  50  for positioning outside the mouth of the user, in front of the user&#39;s mouth. The external part  50  for example functions as a handle of the system. 
     The mouthpiece comprises a first U-shaped channel for receiving the teeth of one jaw, and a second U-shaped channel for receiving the teeth of the other jaw. The mouthpiece is bitten onto by the user with their teeth in the two channels. The system may instead have only one channel, in which case the cleaning may be performed one jaw at a time. 
     In  FIG.  1   , the features of one of the U-shaped channels can be seen (facing upwardly). The opposite, downward facing, U-shaped channel may be the same. The features of one of the U-shaped channels will be described. 
     For the shown U-shaped channel, the mouthpiece  10  comprises a base  12 , an inner arch  14  for positioning adjacent an inner surface of the teeth of a jaw of the user and an outer arch  16  for positioning adjacent an outer surface of the teeth of the jaw. 
     The U-shaped channel of the mouthpiece fits over the teeth of the jaw with the inner and outer arches  14 ,  16  positioned against the inner and outer surfaces of the teeth. The user can bite on the base  12  (or an insert with cleaning elements mounted on the base; not shown in  FIG.  1   ) because it is intended to be static in use, whereas the inner and outer arches  14 ,  16  are designed to move against the surface of the teeth, in the manner explained further below. 
     It is noted that in  FIG.  1    and several other figures, cleaning bristles are omitted for the sake of clarity, because the focus of the invention relates to motion generation and reach. Bristles or tufts may be provided at various angles, length, packing density etc. on various parts of the mouthpiece: the inner arch, the outer arch and the stationary base. 
     There may be bristles on the base for the biting surfaces of the teeth or bristles may reach across from the sides to contact the biting surfaces. It is preferred that a tooth-contacting part with cleaning elements (bristles) is added on top of the base to enable brushing the occlusal tooth surfaces. 
     The external part  50  has an actuator  52  for applying movement to the inner arch and/or the outer arch, relative to the base. For a system with two U-shaped channels, a shared actuator is used. In this example, the actuator  52  is in front of the mouthpiece and therefore connects most simply with the outer arch  16 , as shown. It could however connect to the inner arch  14 . Similarly, in other examples where the actuator is inside the user&#39;s mouth within the U-shaped space formed by the inner arch, it may most easily connect to the inner arch instead of the outer arch. 
     The base  12 , the inner arch  14  and the outer arch  16  are coupled by a coupling arrangement  18 ,  20 . The coupling arrangement  18 ,  20  converts movement of one of the inner and outer arches in one direction relative to the base to movement in an opposite direction relative to the base of the other of the inner and outer arches. In particular, each coupling arrangement connects between adjacent regions of the inner and outer arches. These regions are adjacent, in that they are located at the same angular position around the jaw. The coupling arrangement connects between those adjacent regions. The coupling arrangements for example perform a pivot function. 
     Thus, in the example shown in  FIG.  1   , the actuator  52  imparts movement to the outer arch  16 , and the coupling arrangement  18 ,  20  converts this movement to an anti-phase movement (i.e. in an opposite direction) of the inner arch. 
     By “opposite direction” is not necessarily meant a perfectly opposite movement vector. Instead, one direction is generally across the edge surfaces of the teeth from one side of the jaw to the other (e.g. right to left), and the opposite direction is generally across the edge surfaces of the teeth from the other side of the jaw to the one side of the jaw (e.g. from left to right). 
     The coupling arrangement  18 ,  20  is not clamped when the user bites down, but is free to move. This may be enabled be providing the coupling arrangement at a different level to the tooth-contacting part of the base  12 . 
     The cleaning system thus has inner and outer arches for brushing the inner and outer surfaces of the teeth. The base is a central stationary part. The anti-phase coupling assists in providing reach to the rear molars and also provides cancellation of vibrations and hence reduces the shaking of the device inside the mouth. 
     The separation of the base from the arches means the user can bite down on the base without affecting the brushing performance. Biting on the mouthpiece will not cause an increased load on the motor, and hence will not dampen the driven vibrations. The system enables the desired brushing motion along the tooth arch to be implemented with sufficient transfer of energy to remove plaque and stains. 
     The coupling arrangement comprises coupling members  18 ,  20  each extending between the inner and outer aches  14 ,  16 . The coupling members  18 ,  20  each connect to the base  12  at a location  22  between the inner and outer arches, via a flexible strut or web. The coupling members  18 ,  20  and flexible struts function as hinges, with a main pivot point of the hinges being defined at some point on a flexible connecting member which extends between the base  12  and the location  22  where the coupling members connect to the base. The hinges thus rock about the pivot point to provide the anti-phase movement of the inner and outer arches. Some pivoting at the connections between the ends of the coupling members and the inner and outer arches allows the overall arrangement to have the required flexibility. 
       FIG.  1    shows that the actuator  52  is mounted in a frame  54 . The frame  54  is rigidly coupled to the base  12  by a support plate  55  (shown more clearly in other figures) so that the base and the frame are static parts of the system. 
     The frame  54  also connects to the outer arch  16  by limbs  56 . These limbs  56  provide a movable coupling between the main body of the frame and the outer arch  16 . In particular, the limbs  56  allow rotation of the outer arch relative to the frame  54  about a rotation axis  58  behind the front of the mouthpiece. This movement is shown by arrow  60 . 
     In the example of  FIG.  1   , the coupling arrangement comprises a first coupling member in the form of a hinge  18  along a first lateral side of the mouthpiece (the left side of the user&#39;s jaw) set forward from the back of the first lateral side. This first hinge  18  connects the inner arch, the outer arch and the base at that first lateral side. A second hinge  20  is along the other lateral side of the mouthpiece (the right side of the user&#39;s jaw) set forward from the back of the other lateral side. The second hinge  20  connects the inner arch, the outer arch and the base at that second lateral side. The coupling arrangement thus comprises hinges set forward from the back of the arches. 
     The coupling arrangement additionally has a first connector  24  between the inner and outer arches  14 ,  16  at the back of the first lateral side and a second connector  26  between the inner and outer arches at the back of the second lateral side. These connectors  24 ,  26  maintain the desired spacing between the inner and outer arches and allow a transfer of the anti-phase movement, but the anti-phase motion is initially generated by the first and second hinges  18 ,  20 . 
     The actuator  52  in this example comprises a motor, with a rotating output shaft. An eccentric coupling  57  converts the rotation into a desired movement of the outer arch  16 . This desired movement may be a simple lateral oscillation (i.e. left to right), or it may be a more complex motion, such as a motion in a 2D plane (i.e. left to right and up-down, i.e. in a vertical plane in a normal orientation of the device) such as a circular motion. It may even be a 3D motion, with a component in the 2D plane (the vertical plane) as well a component parallel to the output shaft axis. This may be used to provide an additional tapping effect. 
     Thus, in a most basic example, the actuator applies a lateral 1 dimensional translational motion, thus providing movement of the arch along a single side-to-side axis. More complex motions are however possible. A combination of a tapping motion (i.e. in a direction across rather than along the tooth) and a sliding motion may enhance the cleaning result. 
     An eccentric motor may for example be integrated in the handle of the mouthpiece to actuate the outer arch with suitable frequencies in the range of 0.5-300 Hz and strokes of about 0.5-10 mm to obtain a large range of reach towards the back teeth. 
       FIG.  2    shows the design of  FIG.  1    from above. 
       FIG.  3    shows more clearly that the design of  FIG.  1    has two U-shaped channels  10   a ,  10   b  back to back, to enable cleaning of the teeth of both jaws at the same time. and with cleaning elements such as bristles  70  projecting inwardly (towards the teeth) from the inner and outer arches. 
     There is a single shared actuator  52 , two back to back U-shaped channels  10   a ,  10   b  and two separate frames  54   a ,  54   b.    
       FIG.  4    shows one unit which is an assembly of one U-shaped channel  10   a  of the mouthpiece  10  and one frame  54   a  (which connects to the outer arch) and excluding the support plate  55 , which is a separate part. 
       FIG.  5    shows an exploded view of the design of  FIGS.  1  to  4   . 
     The support plate  55  carries the actuator  52 , and it is sandwiched between the first and second frames  54   a ,  54   b . The support plate has a mounting region  80  to which the bases  12   a ,  12   b  of the two U-shaped channels  10   a ,  10   b  of the mouthpiece  10  connect. The two bases and the mounting region are for example clamped together with bolts or screws. 
       FIG.  6    shows the shape of the mouthpiece  10  and the part of the frame  54  which connects to the outer arch of the mouthpiece, and how the anti-phase motion is induced by pairs of arrows pointing in different directions along the arches. The motion of the solid arrows takes place at one time, and the motion of the dashed arrows takes place at a subsequent time. This is provided to enable comparison with an alternative example which is shown in  FIG.  8   . 
       FIG.  7    shows how the anti-phase motion is induced using the design of the mouthpiece shown in  FIG.  6   . 
     The actuator induces lateral movement as shown by the pair of arrows  90 . The coupling member  20  has the main hinge pivot point defined at some point on the flexible connect between the base  12  and the location  22 . The hinge point is in this example asymmetrically positioned between the inner and outer arches (although a symmetric arrangement is also possible, shown below). Thus, the movement of the outer arch is amplified (based on the ratio between the distances  92   a ,  92   b ). This compensates for a loss of motion causes by losses in the flexible hinge structure. 
     Thus, the asymmetrical hinge design provides improved transfer of motion between the outer arch and the inner arch. 
     As a general indication of the approximate range of movement which may be used, the anti-phase motion amplitude may be of the order of 1 mm to 5 mm. For example, the actuation amplitude may be around ±1.2 mm with an actuation input of ±1.5 mm. A larger actuation amplitude may be used, e.g. around 3-4 mm (half the width of a molar), for example using geared motors. 
     In the example of  FIGS.  1  to  7   , the hinges of the coupling arrangement are set forward from the back of the mouthpiece as explained above, and there are additional connectors  24 ,  26 . An advantage of the example of  FIGS.  1  to  7    is that the coupling members transfer motion from the outer arch to the inner arch close to the actuator. This minimizes motion loss and allows the molar section to conform to the teeth. 
       FIG.  8    shows an alternative design, in which the coupling arrangement comprises a first hinge  18  at the back of a first lateral side (the left side) of the mouthpiece. This first hinge  18  connects the back of the inner arch  14 , the back of the outer arch  16  and the back of the base  12  at said first lateral side. A second hinge  20  is at the back of the opposite lateral side (the right side) of the mouthpiece. The second hinge connects the back of the inner arch  14 , the back of the outer arch  16  and the back of the base  12  at that opposite lateral side. This structure has fewer intricate parts. 
     The hinges are shown as symmetrical in this example, with the main pivot point mid-way between the inner and outer arches. Thus, it can be seen that different hinge designs are possible with symmetric or asymmetric positioning of the main hinge. 
     The examples above make use of coupling members formed as a first U-shaped coupling between the outer arch and the location  22  (where there is a strut connecting to the base), and a second U-shaped coupling between the location  22  and the inner arch. An alternative design makes use of first and second W-shaped couplings. 
       FIG.  9    shows a further alternative design of the coupling members  18 ,  20 . A rigid strut  100  extends between the inner and outer arches, and a pivot or rocker bearing  102  provides the connection to the base  12 . There is thus a T-shaped connector with a pivot point at the interconnection of the three limbs of the strut. 
     The mouthpiece (base, coupling arrangement and arches) may be formed of a single material. However, in an example, the inner arch and outer arch are for example formed of a first material and the coupling arrangement, or portions of the coupling arrangement, are formed of a different material to the first material. The use of different materials enables the elastic coupling properties to be optimized. 
       FIG.  10 A  shows the design of  FIG.  8    and shows regions A which may be formed of a different material (material A) to the remainder of the structure. 
       FIG.  10 B  shows the design of  FIG.  6    and shows regions B and C which may be formed of a different material to the remainder of the structure. Regions B and C may be of the same material (material B), or they may be two different materials (materials B, C), both different to the main structure. 
       FIG.  10 C  shows the design of  FIG.  6    and shows regions D which may be formed of a different material (material D) to the remainder of the structure. These regions formed of a different material are the joints between the coupling members and the arches and the joints between the coupling members and the base. 
     Materials A to D have for example a (relatively) low hardness and low Young&#39;s modulus to add flexibility and deformity to the hinges. 
     The material of the remainder of the structure has for example a (relatively) medium or high hardness and medium or high Young&#39;s modulus. 
     By way of example, the main material may be polyethylene (with elastic modulus 1.1 GPa and Poisson&#39;s ratio 0.42. While this is one option of food grade material for parts with flexure design (living hinges), there are also other materials such as polyamides (e.g. Nylon) and a thermoplastic elastomer that can be used for this application. 
     The hinges are designed for low stress, long life and minimal loss of energy in the system. The parts may be made by 3D printing or by injection molding, for example. 
     The overall system can be described as a compliant spring system. The system may for example be driven at its resonance frequency, reducing the power needs of the system. The frequency may also be tuned individually to the resonance frequency, using feedback of the amplitude, since damping on the teeth may vary from person to person, and also parts of the system may be customized for better fitting. 
     As explained above, a 1-dimensional reciprocating brushing motion may be used.  FIG.  11    shows a modification in which the limbs  56  are made thinner and have a cut-out  110  to create an additional degree of freedom in their movement. This can be used to generate a 3D motion from a 2D eccentric drive. For example, by actuating with a circular trajectory, a more complex (2D) circular brushing motion is generated. By adding another pivot point, a complex 3D motion can be generated, e.g. circular motion superimposed by a tapping motion. 
     In the example above, the actuator is in front of the mouthpiece, i.e. outside the mouth. In another set of examples, instead of forming the actuator outside of and in front of the mouthpiece, the actuator may be arranged in a space partially surrounded by the inner arch. Thus, it may be for positioning inside the user&#39;s mouth. This may enable a more compact device. 
     One option is to use a similar actuator to that shown above, for example for driving the inner arch (which is then closer to the actuator). 
       FIG.  12    instead shows an alternative actuator design. 
     The actuator comprises a dual shaft motor  120  with swash plates at the output shafts. A first swash plate  122  connects to a back of one same lateral side of the inner and outer arches  14 ,  16 , and a second swash plate  124  connects to a back of the other same lateral side of the inner and outer arches. Thus, each swash plate ensures opposite motion of a common end of the inner and outer arches. The two shafts for example rotate in the same direction. 
       FIG.  13    shows a further alternative actuator design. 
     The actuator comprises a dual shaft motor  130 , with two swash plates at the output shafts. A first swash plate  132  driven by one shaft connects to a back of opposite lateral sides of the inner arch  14 , and a second swash plate  134  driven by the other shaft connects to a back of opposite lateral sides of the outer arch  16 . Thus, each swash plate ensures opposite motion of the two ends of a respective one of the inner and outer arches, and the two swash plates operate in anti-phase with each other. They may for example rotate in opposite directions. 
     The benefits of anti-phase brushing motion in combination with larger reach can be achieved in this way. 
     In  FIGS.  12  and  13   , the swash plates function as the coupling arrangement. The overall swash plate design again connects between adjacent regions (the ends in these examples) of the inner and outer arches, and the adjacent ends are made to move in opposite directions by the overall swash plate design. 
     The U-shaped channels of the mouthpiece allow occlusal bristles to be added on the stationary base. The incisors bite on the front base part to hold the stationary part stationary. This stationary part may be covered with a (tooth-contacting) cleaning structure (e.g. rough surface or short 0.5-1 mm bristles to have some cleaning of the top incisors). The thickness of this stationary part can be increased to make room for occlusal bristles on the molar-premolar areas. 
     Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. 
     The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 
     If the term “adapted to” is used in the claims or description, it is noted the term “adapted to” is intended to be equivalent to the term “configured to”. 
     Any reference signs in the claims should not be construed as limiting the scope.