Patent Publication Number: US-2020289309-A1

Title: Oral appliance

Description:
TECHNICAL FIELD 
     The present invention relates to an oral appliance for preventing and treating sleep apnea. More particularly, the present invention relates to an oral appliance for treatment of snoring and sleep apnea which will effectively maintain the mandible in a preferred anterior position, but which will also allow a limited degree of forward or lateral excursion of the mandible relative to the upper jaw. 
     BACKGROUND 
     While people are asleep, the muscles relax causes the airways to close and vibrate as air is passed. This vibration causes the noise known as snoring. Also, the obstruction of the airways causes insufficient ventilation of the lungs, leading to disturbed sleep, and, potentially, to the person&#39;s breathing to stop for a moment (this being known as sleep apnea syndrome (SAS)). 
     SAS is a condition characterized by multiple episodes of cessation of respiration (apnea) during sleep, resulting from partial or complete obstruction of the airway by the root of the tongue and/or the soft palate falling down therein. As a result, sleep is disturbed and daytime sleepiness occurs. In recent years a large number of accidents have been attributable to this condition, including, for example, where the sufferer of the condition unknowingly drives a car while asleep. 
     The conventional method of treating SAS involves having the sufferer wear in his or her mouth while sleeping a mandibular advancement device, specifically an oral appliance, which applies pressure in such a manner to cause the lower jaw to be slightly drawn (pulled) forward from the normal occlusal position to forcibly maintain an airway, to prevent apnea during sleep. 
     More specifically, the oral appliance causes a slight forward movement of the mandible with respect to the upper maxillary bone, opening a bigger space at the back of the oral cavity, hence facilitating the passage of air from and to the pharynx. Thus, the mandibular advancement device can prevent the constriction of the airway, a breathing stop or low respiration during sleep. 
     However, conventional oral appliances are not easily adjustable by the SAS sufferer and do not allow for the natural movement of the jaws of the SAS sufferer while sleeping. 
     SUMMARY 
     The present invention provides an oral appliance that is easily adjustable by the SAS sufferer and allows for the natural movement of the jaws of the SAS sufferer while sleeping. 
     The present invention provides an oral appliance which includes a first jaw retainer piece, a second jaw retainer piece, and a holding member mounted on a front-facing portion of the first jaw retainer piece, wherein the holding member has an opening for receiving a rod. Further, the present invention provides that the leading (distal) end of the rod is slidably inserted into the opening of the holding member and a trailing end of the rod is mounted on a front-facing portion of the second jaw retainer piece. The oral appliance further includes a restrictor that restricts sliding of the rod relative to the holding member within the opening. 
     According to the present invention, the holding member can be a tubularly shaped or a ring shaped. Further, according to the present invention, the restrictor can be formed as part of the holding member to which the leading end of the rod abuts, thereby restricting the sliding of the rod relative to the holding member. Further still, according to the present invention, the restrictor can be a ring that encircles the rod and is position at the trailing end of the rod to which the holding member abuts, thereby restricting the sliding of the rod relative to the holding member. Moreover, according to the present invention, the restrictor can be an element that engages the leading end of the rod to which the holding member abuts, thereby restricting the sliding of the rod relative to the holding member. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description that follows, embodiments are described as illustrations only since various changes and modifications will become apparent to those skilled in the art from the following detailed description. The use of the same reference numbers in different figures indicates similar or identical items. 
         FIG. 1  shows an exemplary oral appliance after being assembled in accordance with at least some embodiments described herein; 
         FIG. 2  shows a top portion of an exemplary holding member mounted on a front-facing portion of a lower jaw retainer piece in accordance with at least some embodiments described herein; 
         FIG. 3  shows a top portion of an exemplary rod mounted on a front-facing portion of an upper jaw retainer piece in accordance with at least some embodiments described herein; 
         FIGS. 4A and 4B  show an exemplary holding member and rod in accordance with at least some embodiments described herein; 
         FIG. 5  shows an exemplary rod in accordance with at least some embodiments described herein; 
         FIGS. 6A and 6B  show an exemplary oral appliance while adjusting a lower jaw position in accordance with at least some embodiments described herein; 
         FIG. 7A and 7B  show a cross sectional view of an exemplary oral appliance while adjusting a lower jaw position in accordance with at least some embodiments described herein; 
         FIG. 8  shows a cross sectional view of an exemplary oral appliance in accordance with at least some embodiments described herein; 
         FIG. 9  shows a cross sectional view of an exemplary oral appliance in accordance with at least some embodiments described herein; 
         FIG. 10  shows an exemplary oral appliance after being assembled in accordance with at least some embodiments described herein; 
         FIG. 11A  shows a top portion of an exemplary holding member mounted on a front-facing portion of a lower jaw retainer piece in accordance with at least some embodiments described herein; 
         FIG. 11B  shows a front portion of an exemplary holding member mounted on a front-facing portion of a lower jaw retainer piece in accordance with at least some embodiments described herein; 
         FIG. 12A  shows a top portion of an exemplary rod mounted on a front-facing portion of an upper jaw retainer piece in accordance with at least some embodiments described herein; 
         FIG. 12B  shows a bottom portion of an exemplary rod mounted on a front-facing portion of an upper jaw retainer piece in accordance with at least some embodiments described herein; 
         FIGS. 13A and 13B  show an exemplary holding member and rod in accordance with at least some embodiments described herein; 
         FIG. 14  shows an exemplary rod and restrictor in accordance with at least some embodiments described herein; 
         FIGS. 15A and 15B  show an exemplary oral appliance while adjusting a lower jaw position in accordance with at least some embodiments described herein; 
         FIG. 16A  shows a cross sectional view of an exemplary oral appliance in accordance with at least some embodiments described herein; and 
         FIG. 16B  shows a cross sectional view of an exemplary oral appliance in accordance with at least some embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part of the description. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. Furthermore, unless otherwise noted, the description of each successive drawing may reference features from one or more of the previous drawings to provide clearer context and a more substantive explanation of the current example embodiment. Still, the example embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings, may be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     Described herein are related to an oral appliance intended to be placed in a user&#39;s mouth for preventing and treating sleep apnea syndrome. 
     In the present description, the following terms may be used, in addition to their accepted meaning, as follows: 
     “Forward” and “backward” directions may refer to respectively, a direction toward the front of a user wearing the oral appliance (a direction toward a mouth opening as viewed from a throat in the oral cavity) and a direction toward the rear (in a direction from the mouth opening to the throat in the oral cavity); the “right and left direction” or “rightward and leftward” refers to from the center of the upper jaw of the user wearing the oral appliance as a reference, to the right and left directions (a direction toward a right cheek and a direction toward a left cheek); and “upward and downward direction” refers to from the center of the upper jaw of the user wearing the oral appliance as a reference, to a direction towards upside (in a direction from the center of the upper jaw to a nose) and a direction towards downside (in a direction from the center of the upper jaw to the lower jaw). 
     A “longitudinal direction” may refer to the axial direction of a rod or a holding member and back to front, and a “lateral direction” may refer to a side to side direction. 
     A “front-facing portion” of a first jaw retainer piece and a second jaw retainer piece may refer to, respectively, a front face portion of the first jaw retainer piece and a front face portion of the second jaw retainer. 
     In accordance with some embodiments, the oral appliance comprises a first jaw retainer piece; a second jaw retainer piece; a holding member mounted on a front-facing portion of the first jaw retainer piece, the holding member having an opening for receiving a rod; the rod having a leading end slidably inserted into the opening of the holding member and a trailing end mounted on a front-facing portion of the second jaw retainer piece; and a restrictor that restricts sliding of the rod relative to the holding member. 
     It is important to provide effective oral appliance in maintaining the mandible in a protruded position to improve airway patency, they often result in undesirable side effects. The need has therefore arisen for an oral appliance for treatment of snoring and sleep apnea which will effectively maintain the mandible in a preferred anterior position, but which will also allow a limited degree of forward or lateral excursion of the mandible relative to the upper jaw to avoid discomfort to the temporomandibular joint and related muscles and ligaments. The embodiments described herein improve user experience by allow a predetermined degree of lateral movement or forward movement of mandible in the protruded position, while still maintaining acceptable airway patency effectively by maintaining the mandible in a preferred position. 
       FIG. 1  shows an exemplary oral appliance after being assembled in accordance with at least some embodiments described herein. As illustrated in  FIG. 1 , the exemplary oral appliance  100  includes, at least a first jaw retainer piece, a second jaw retainer piece, a holding member  106 , and a rod  108 . The first jaw retainer piece may refer to a lower jaw retainer piece  102  and the second jaw retainer piece may refer to an upper jaw retainer piece  104 . The holding member  106  is mounted on a front-facing portion of the lower jaw retainer piece  102 , and has an opening  122  (as shown in  FIG. 2 ) for receiving a rod  108 . The holding member  106  may be tubularly shaped. The oral appliance  100  may include a restrictor  140  (as shown in  FIGS. 7A  and B) that restricts sliding of the rod  108  relative to the holding member  106 . The holding member  106  is mounted on or attached to the front-facing portion of the lower jaw retainer piece  102  via a first mounting unit  110 . The first mounting unit  110  includes a first plurality of through-holes  112  which allow for the infiltration of the material that forms the lower jaw retainer piece  102  for positional stability. The lower jaw retainer piece  102  includes a first fixing member  114  which is a dental wire (or a plurality of metallic dental wires) for fixing the user&#39;s teeth more firmly in place in the lower jaw retainer piece  102 . 
     One end of the rod  108  is mounted on a front-facing portion of the upper jaw retainer piece  104 , and the other end of the rod  108  is slidably inserted into the opening  122  of the holding member  106  along a longitudinal direction of the holding member  106 . The one end of the rod  108  is mounted on the front-facing portion of the upper jaw retainer piece  104  via a second mounting unit  116 . The second mounting unit  116  includes a second plurality of through-holes  118  which allow for the infiltration of the material that forms the upper jaw retainer piece  104  for positional stability. The upper jaw retainer piece  104  include a second fixing member  120  which is a dental wire (or a plurality of metallic dental wires) for fixing the user&#39;s teeth more firmly in place in the upper jaw retainer piece  104 . 
       FIG. 2  shows a top portion of an exemplary holding member mounted on a front-facing portion of a lower jaw retainer piece  102  in accordance with at least some embodiments described herein. A lower jaw retainer piece  102  is shaped and adapted to engage the mandibular dentition of the user, and the lower jaw retainer piece  102  is open towards a mandibular. The size and shape of the lower jaw retainer piece  102  can be customized to suit the anatomy of each user. The lower jaw retainer piece  102  may include a first fixing member  114  (as shown in  FIG. 1 ) which is a metallic (e.g. stainless steel) dental wire (or a plurality of metallic dental wires) to ensure that the lower jaw retainer piece  102  securely engages the user&#39;s teeth. 
     The holding member  106  may be an elongated hollow and tubularly shaped member which is longitudinally perpendicular to a front-facing portion of the lower jaw retainer piece  102 . The holding member  106  has a proximal end which is mounted on or attached to the front-facing portion of the lower jaw retainer piece  102  by the first mounting unit  110 , and a distal end extending along a longitudinal axis in a forward direction. The holding member  106  has an opening  122  for receiving the rod  108  at the proximal end and another opening at the distal end  132 . The opening  122  and the other opening are connected in a tubular shape body of the holding member  106  along the longitudinal axis. The opening  122  is adapted to receive the rod  108  from the front-facing portion of the lower jaw retainer piece  102  towards the distal end of the holding member along the longitudinal axis of the holding member  106 . 
       FIG. 3  shows a top portion of an exemplary rod mounted on a front-facing portion of an upper jaw retainer piece in accordance with at least some embodiments described herein. An upper jaw retainer piece  104  is shaped and adapted to engage the maxillary dentition of the user, and the upper jaw retainer piece  104  is open towards a maxillary. The size and shape of the upper jaw retainer piece  104  can be customized to suit the anatomy of each user. The upper jaw retainer piece  104  may include a second fixing member  120  which may be a metallic (e.g. stainless steel) dental wire (or a plurality of metallic dental wires) to ensure that the upper jaw retainer piece  104  securely engages the user&#39;s teeth. 
     The rod  108  is an elongated member that includes a trailing end  126  and a leading end  124 . The trailing end  126  of the rod  108  is mounted on or attached to the front-facing portion of the upper jaw retainer piece  104  by the second mounting unit  116 , and the leading end  124  is extending along a longitudinal axis in a forward direction. When the rod  108  is assembled with the holding member  106  in accordance with at least some embodiments described herein, the leading end  124  of the rod  108  may be slidably inserted into the opening  122  of the holding member  106  along the longitudinal axis of the holding member  106  in a forward direction. 
     The rod  108  may comprise two segments including an inner segment and outer segment. The inner segment of the rod  108  may be a screw portion  128  that extends from the upper jaw retainer piece  104  and the outer segment of the rod  108  may be a screw-adjustable portion  138  that engages with the screw portion  128  to move in forward and backward directions. As per  FIGS. 7A and 7B , the screw-adjustable portion  138  (the outer segment) may be a hollow cylindrical shape and holds the screw portion  128  (the inner segment) therein. The screw-adjustable portion  138  has an open end at the leading end  124  and another open end at opposite side, and the open end and another open end form an elongated opening through rod  108  along its longitudinal axis. One end of the screw portion  128  is mounted on or attached to the front-facing portion of the upper jaw retainer piece  104  by the second mounting unit  116  and is the trailing end  126  of the rod  108 . Another end of the screw portion  128  is positioned inside the screw-adjustable portion  138  and is extended towards the leading end  124  of the rod  108 . The screw portion  128  has external threads thereon, which are male threads. The another end of the screw-adjustable portion  138  is formed to receive a shaft of a screwdriver which can be used to adjust the positioning of the screw-adjustable portion  138  relative to the trailing end  126  of the screw portion  128 . The inner surface of the screw-adjustable portion  138  includes a set of internal threads  138   a  (shown in  FIGS. 7A and 7B ) which are female threads, and threadingly engaged with the screw portion  128 . 
     The screw-adjustable portion  138  is movable longitudinally relative to the screw portion  128  between a retracted position and an extended position so as to effect telescopic transition of the screw-adjustable portion  138  with respect to the screw portion  128 . When the screw-adjustable portion  138  is screwed by the screw driver, the screw-adjustable portion  138  is moving forward relative to the trailing end  126  of the screw portion  128 , and the screw-adjustable portion  138  moves to the extended position. The screw portion  128 , which was previously positioned inside of the screw-adjustable portion  138 , is coming out from the screw-adjustable portion  138 , and a total length of the rod  108  is extended and getting longer. When the screw-adjustable portion  138  is screwed by the screw driver, the set of internal threads  138   a  in the inner surface of the screw-adjustable portion  138  threadingly engages with the screw portion  128  to move in a forward direction. Since one end (a trailing end  126 ) of the screw portion  128  is mounted on or attached to the front-facing portion of the upper jaw retainer piece  104 , as the screw portion  128  is coming out from the screw-adjustable portion  138 , a position of the screw-adjustable portion  138  moves in the forward direction. 
     When the screw-adjustable portion  138  is unscrewed (or reverse screwed) by the screw driver, the screw-adjustable portion  138  is moving backward relative to the trailing end  126  of the screw portion  128 , and the screw-adjustable portion  138  moves towards the retracted position. The screw portion  128 , which was previously positioned outside of the screw-adjustable portion  138 , is coming back to the screw-adjustable portion  138 , and the extended total length of the rod  108  is retracted and shortened. Accordingly, a relative position of the screw-adjustable portion  138  moves in a backward direction. The total length of the rod  108  or a relative position of the screw-adjustable portion  138  is adjustable by screwing or unscrewing the screw-adjustable portion  138 . The screw-adjustable portion  138  may have a larger outer diameter at the leading end  124  side than opposite end side thereof. 
     In accordance with some implementations, the lower jaw retainer piece  102  and the upper jaw retainer piece  104  may be made of, but not limited to, for example, acrylic resin. The lower jaw retainer piece  102  and the upper jaw retainer piece  104  are preferably made of a single hard material having a flexural modulus of 2,000 MPa or more and 3,000 MPa or less, or combination of a soft material having a flexural modulus of 10 MPa or more and 300 MPa or lower and a hard material having a flexural modulus of 1,000 MPa or more and 3,000 MPa or less. 
     The lower jaw retainer piece  102  and the upper jaw retainer piece  104  may also be made of relatively soft material having a tensile strength of 150 N or more and less than 2,000 N, particularly 150 N or more and 500 N or less. The lower jaw retainer piece  102  and the upper jaw retainer piece  104  made of the aforementioned materials have high conformity to the teeth when they are worn by the user. The tensile strength refers to the strength at which an oral appliance (3-mm thick) fabricated with a Nissin standard model tears in a tensile testing conducted in the molar direction (backward on the row of teeth) with a hole 1.5 mm in diameter bored at the sixth tooth in the lower jaw retainer piece and the upper jaw retainer piece of the oral appliance. 
     Materials having a tensile strength of 150 N or more and less than 2,000 N include, for example, olefin-based resin, polyester-based resin, urethane-based resin, polyamide-based resin, or acrylic rubber resin, where the olefin-based resin is preferable inter alia. The olefin-based resin is a polymer made by homopolymerization of olefin or a copolymer of olefin and another monomer. Olefin with a carbon number of 2 to 6 containing ethylene, propylene, butene, methylpentene, and hexene is preferred. The another monomer may be for example, vinyl acetate. 
     Preferably, the olefin-based resin is polyethylene (PE), polyethylene-based resin, polypropylene (PP), polypropylene-based resin, and ethylene-vinyl acetate copolymer (EVA), for example, and more preferably, is polyethylene (PE), polyethylene-based resin, polypropylene (PP), or polypropylene-based resin. 
     Polyester-based resin is a polycondensate of polyvalent carboxylic acid (dicarboxylic acid) and polyalcohol (diol), for example, polyethyleneterephthalate (PET). Urethane-based resin is a polycondensate of a compound having an isocyanate group and a compound having a hydroxy group, for example, is thermoplastic polyurethane (TPU). 
     Polyamide-based resin is a polymer formed by binding of many monomers by amide bond, for example, nylon, para-amide, and meta-amide. Acrylic rubber resin consists mainly of acrylic rubber, for example, is a block copolymer of methyl methacrylate and butyl acrylate. 
     Material having a tensile strength of 150 N or more and less than 2,000 N may be a commercially available material, for example, F327, a polypropylene resin manufactured by Prime Polymer Co., Ltd. 
     In accordance with some implementations, the rod  108  and the holding member  106  may be made of, but not limited to, titan, or alloys containing titan, iron or steel such as stainless gold, silver, platinum, cobalt or chromium, and a hard material having a flexural modulus of 2,000 MPa or more and 3,000 MPa (such as polycarbonate). 
       FIG. 4A  shows an exemplary holding member and  FIG. 4B  shows an exemplary rod in accordance with at least some embodiments described herein. The holding member  106  has a proximal end  130  which is to be mounted on or attached to the front-facing portion of the lower jaw retainer piece  102  by the first mounting unit  110 , and a distal end  132  extending along a longitudinal axis in a forward direction. The proximal end  130  of the holding member  106  is attached to the first mounting unit  110  that is adapted to be mounted on or attached to the front-facing portion of the lower jaw retainer piece  102 . The first mounting unit  110  is a thin plate-like member that may be made of material which may be used for forming the rod  108  or the holding member  106 . The first mounting unit  110  may be formed in a curved shape along the shape of a front-facing portion of the lower jaw retainer piece  102 . The first mounting unit  110  may have a first plurality of through-holes  112  for facilitating the fixation of the first mounting unit  110  to the lower jaw retainer piece  102 . The first mounting unit  110  may be mounted on the front-facing portion of the lower jaw retainer piece  102  using a resin material which may be used for forming the lower jaw retainer piece  102 . The resin material may pass through the first plurality of through-holes  112  and attaching or fixing the position of the first mounting unit  110  to the lower jaw retainer piece  102  to enhance the fixing strength each other. 
     The rod  108  is an elongated member that includes a trailing end  126  and a leading end  124 . The trailing end  126  of the rod  108  is to be mounted on or attached to the front-facing portion of the upper jaw retainer piece  104  by the second mounting unit  116 , and the leading end  124  is extending along a longitudinal axis in a forward direction. The trailing end  126  of the rod  108  is attached to the second mounting unit  116  that is adapted to be mounted on or attached to the front-facing portion of the upper jaw retainer piece  104 . The second mounting unit  116  is a thin plate-like member that may be made of material which may be used for forming the rod  108  or the holding member  106 . The second mounting unit  116  may be formed in a curved shape along the shape of a front-facing portion of the upper jaw retainer piece  104 . The second mounting unit  116  may have a second plurality of through-holes  118  for facilitating the fixation of the second mounting unit  116  to the upper jaw retainer piece  104 . The second mounting unit  116  may be mounted on or attached to the front-facing portion of the upper jaw retainer piece  104  using a resin material which may be used for forming the upper jaw retainer piece  104 . The resin material may pass through the second plurality of through-holes  118  and attach or fix the position of the second mounting unit  116  to the upper jaw retainer piece  104  and enhance the fixing strength each other. 
       FIG. 5  shows an exemplary rod in accordance with at least some embodiments described herein. In  FIG. 5 , the rod  108  may optionally include a protective cover  136  that covers at least a part of the rod  108 . The protective cover  136  may have a substantially hollow semi-cylindrical shape defining a rounded inner surface. One end of the protective cover  136  is mounted on the second mounting unit  116  and located above the rod  108 , and the other end of the protective cover  136  is extended along a longitudinal axis of the rod  108  and parallel to the rod  108 . The rounded inner surface of the protective cover  136  faces the rod  108 , and a gap exists between the protective cover  136  and the rod  108 . After the rod  108  is slidably inserted into the opening  122  of the holding member  106  and assembled with the holding member  106 , the holding member  106  is positioned at the gap between the protective cover  136  and the rod  108 , and the protective cover  136  covers at least a part of the holding member  106  in which the rod  108  is inserted. Therefore, after assembly of the rod  108  and the holding member  106 , the rounded inner surface of the protective cover  136  faces the holding member  106 . 
       FIGS. 6A and 6B  show an exemplary oral appliance while adjusting a lower jaw position in accordance with at least some embodiments described herein. The assembled oral appliance  100  worn by the user is illustrated in  FIGS. 6A and 6B . To assemble the oral appliance  100 , as described above, the leading end  124  of the rod  108  is slidably inserted into the opening  122  of the holding member  106  from the front-facing portion of the lower jaw retainer piece  102  towards a forward direction along a longitudinal axis of the holding member  106 . The trailing end  126  of the rod  108  is mounted on the front-facing portion of the upper jaw retainer piece  104  via the second mounting unit  116 . The lower jaw position of the user may be adjusted after or before the user wears the assembled oral appliance. 
       FIG. 6A  shows that the position of the lower jaw retainer piece  102  and the position of the upper jaw retainer piece  104  are initially same, and the lower jaw retainer piece  102  has not moved forward yet relative to the upper jaw retainer piece  104 . The position of the screw-adjustable portion  138  of the rod  108  is adjusted in forward and backward directions to adjust an abutment position of the rod  108  relative to a restrictor (as shown in  FIG. 7 ). As described above, a relative position of the screw-adjustable portion  138  of the rod  108  is adjusted by screwing or unscrewing the screw-adjustable portion  138 . The rod  108  comprises the screw portion  128  that extends from the upper jaw retainer piece  104  and the screw-adjustable portion  138  that engages with the screw portion  128  to move in forward and backward directions. In  FIG. 6A , the screw-adjustable portion  138  is at a fully retracted position and the screw portion  128  is located within the screw-adjustable portion  138 . 
     As described above regarding  FIG. 3 , the screw-adjustable portion  138  (the outer segment) may be a hollow cylindrical shape and engages the screw portion  128  (the inner segment) therein. The screw-adjustable portion  138  has an open end at the leading end  124  and another open end at opposite side, and the open end and another open end form an elongated opening along a longitudinal axis of the screw-adjustable portion  138 . One end of the screw portion  128  is mounted on or attached to the front-facing portion of the upper jaw retainer piece  104  and is the trailing end  126  of the rod  108 . Another end of the screw portion  128  is positioned inside the screw-adjustable portion  138  and extended towards the leading end  124  of the rod  108 . The another end of the screw-adjustable portion  138  is formed to receive a shaft of a screwdriver  144  which can be used to adjust the positioning of the screw-adjustable portion  138  relative to the trailing end  126  of the screw portion  128 . The inner surface of the screw-adjustable portion  138  includes a set of internal threads  138   a  which is female threads, and threadingly engages with the screw portion  128 . As shown in  FIG. 2 , the holding member  106  has an opening  122  for receiving the rod  108  at the proximal end  130  and another opening at the distal end  132 . The opening  122  and the another opening are connected through a tubular shape body of the holding member  106  along its longitudinal axis. The opening  122  is adapted to receive the rod  108  from the front-facing portion of the lower jaw retainer piece  102  towards the distal end  132  of the holding member  106  along its longitudinal axis. Thus, after the rod  108  is inserted into and assembled with the holding member  106 , the screwdriver  144  may be inserted into the another opening at the distal end  132  of the holding member  106 . Then, the another end of the screw-adjustable portion  138  receives a shaft of a screwdriver  144  which can be used to adjust the positioning of the screw-adjustable portion  138  relative to the trailing end  126  of the screw portion  128 . 
     After the rod  108  is inserted into the holding member  106  and assembled, the holding member  106  holds the screw-adjustable portion  138 . The screw-adjustable portion  138  is the outer segment of the rod  108 , and engages the screw portion  128  (the inner segment) therein. As the screw-adjustable portion  138  is screwed by the screw driver, the screw-adjustable portion  138  is moving forward relative to the trailing end  126  of the screw portion  128 , and the screw-adjustable portion  138  moves to the extended position. The set of internal threads  138   a  in the inner surface of the screw-adjustable portion  138  threadingly engages with the screw portion  128  and the screw-adjustable portion  138  moves in a forward direction. Therefore, a total length of the rod  108  is extended and getting longer. As the position of the screw-adjustable portion  138  moves in a forward direction, the position of the holding member  106  that holds the screw-adjustable portion  138  of the rod  108  also moves in the forward direction. Accordingly, the position of the lower jaw retainer piece  102  which is attached to the holding member  106  also moves in the forward direction. On the other hand, as one end of the screw portion  128  (i.e. the trailing end  126  of the rod  108 ) is mounted on the front-facing portion of the upper jaw retainer piece  104 , the position of the upper jaw retainer piece  104  which is attached to the rod  108  maintains same position. Thereby, the lower jaw retainer piece  102  is positioned forward relative to the upper jaw retainer piece  104 . In particular,  FIG. 6B  shows that the position of the lower jaw retainer piece  102  and the position of the upper jaw retainer piece  104  are different after screwing, and the lower jaw retainer piece  102  has moved in a forward direction relative to the upper jaw retainer piece  104 . In  FIG. 6B , the screw-adjustable portion  138  is at an extended position and a portion of the screw portion  128  is located outside of the screw-adjustable portion  138 . 
     When the screw-adjustable portion  138  is unscrewed (or reverse screwed) by the screwdriver  144 , the screw-adjustable portion  138  is moving backward relative to the trailing end  126  of the screw portion  128 , and the screw-adjustable portion  138  moves towards the retracted position. The screw portion  128 , which was previously positioned outside of the screw-adjustable portion  138 , is coming back to the screw-adjustable portion  138 , and the extended total length of the rod  108  is retracted. Accordingly, the position of the screw-adjustable portion  138  moves in a backward direction relative to the previous position. As the position of the screw-adjustable portion  138  moves in a backward direction, the position of the holding member  106  that holds the screw-adjustable portion  138  of the rod  108  also moves in a backward direction. Accordingly, the position of the lower jaw retainer piece  102  which is attached to the holding member  106  also moves in a backward direction. 
     By positioning the lower jaw retainer piece  102  forward relative to the upper jaw retainer piece  104 , the oral appliance  100  can restrict the displacement of the lower jaw of the user to the backward direction, thereby preventing the constriction of the airway, a breathing stop or low respiration during sleep. As the oral appliance  100  adjusts the amount of advancement of the lower jaw retainer piece  102  relative to the upper jaw retainer piece  104 , the lower jaw moves forward relative to the upper jaw by the adjusted amount of the advancement. Therefore, it is possible to make the user&#39;s airway less likely to be narrowed. 
       FIGS. 7A and 7B  show a cross sectional view of an exemplary oral appliance while adjusting a lower jaw position in accordance with at least some embodiments described herein. In  FIG. 7A , the holding member  106 , which is tubularly shaped, includes a restrictor  140  that restricts sliding of the rod  108  relative to the holding member  106 . The holding member  106  has a proximal end  130 , a distal end  132 , and a middle portion located between the proximal end  130  and the distal end  132 . For example, the restrictor  140  is a ring-shaped protrusion portion provided on an inner circumference of the holding member  106  at a distal end  132 , and is a cylindrical portion with a smaller inner diameter. The inner diameter of the restrictor  140  is smaller than the inner diameter of the proximal end  130  or the middle portion of the holding member  106 . Accordingly, the restrictor  140  makes a diameter of the another opening at the distal end  132  smaller than a diameter of the opening  122  at the proximal end  130  or the middle portion of the holding member  106 . 
     Further, the screw-adjustable portion  138 , which is a hollow cylindrical shape that engages the screw portion  128  therein, may have an outer diameter at the leading end  124  side larger than an outer diameter at the opposite end side. The inner diameter of the restrictor  140  (i.e. a diameter of the another opening at the distal end  132 ) may be large enough to receive a screwdriver  144  but may be smaller than an outer diameter of the screw-adjustable portion  138  at the leading end  124  side. Therefore, even after setting an abutment position of the rod  108  relative to the restrictor  140  via screwing (i.e. a position of the lower jaw retainer piece  102  relative to a position of the upper jaw retainer piece  104 ), the leading end  124  of the rod  108  can slide forward and backward within the holding member  106 . However, the leading end  124  of the rod  108  cannot pass beyond the restrictor  140  in a forward direction, and the restrictor  140  restricts sliding of the rod relative within the holding member. Similarly, the distal end  132  of the holding member  106  can move in a forward and backward directions relative to the rod  108  but cannot pass over the leading end  124  of the rod  108  in a backward direction.  FIG. 7B  shows a partial cross sectional view of an exemplary oral appliance in accordance with at least some embodiments described herein. In particular,  FIG. 7B  illustrates the inner surface of the screw-adjustable portion  138   a  which includes a set of threads which are female threads. 
       FIG. 8  shows a cross sectional view of an exemplary oral appliance in accordance with at least some embodiments described herein. In  FIG. 8 , the restrictor  140  abuts against the rod  108  and restricts a forward movement of the rod  108  within the holding member  106 . Further, the restrictor  140  restricts a backward movement of the holding member  106  relative to the rod  108 . Therefore, the restrictor  140  prevents the rod  108  from sliding too much in a forward direction within the holding member  106 , and further prevents the holding member  106  from sliding in a backward direction relative to the rod  108 . Still, the holding member  106  can move in a forward direction. If the holding member  106  does not have the restrictor  140 , the rod  108  further moves to a forward direction, and the holding member  106  moves backward, and therefore, the upper jaw retainer piece  104  attached to the rod  108  moves to a forward direction and the lower jaw retainer piece  102  attached to the holding member  106  moves can move backward. The restrictor  140  restricts the displacement of the lower jaw of the user to the backward direction during sleeping and therefore an oral appliance  100  allows the user to maintain the position of the lower jaw forward relative to the upper jaw. At the same time, the restrictor  140  does not restrict the user to move the lower jaw forward relative to the upper jaw when the oral appliance  100  is worn by the user during sleeping. Therefore, the restrictor  140  sets a predetermined degree of a forward and backward movement of mandible within the protruded position, while still maintaining acceptable airway patency effectively by maintaining the mandible in a preferred protruded position. Therefore, the oral appliance  100  allows the user to move the lower jaw forward within a predetermined degree during sleeping, and provides more flexibility, comfortable use, and ease of use of the oral appliance  100  to the user who worn the oral appliance. Thereby, the oral appliance  100  provides great user experience without detriment the effectiveness and function of mandibular advancement. 
     In accordance with some implementations, the opening  122  of the holding member  108  has an ellipse shape, an oval shape, an egg shape, a rectangle shape, or any oblong shape. The term “oblong” may include a structure having a dimension, especially one of two perpendicular dimensions, such as, for example, width or length, that is greater than another and includes shapes such as rectangles, ovals, ellipses, and any other elongated shapes. In particular, the opening  122  has an oblong shape having a width along the right and left directions, and the width is larger than a length of the oblong shape that is perpendicular to the width. The larger width of the opening  122  enables more free movement of the rod  108  along the right and left directions within the holding member  106 , and more free movement of the holding member  106  rightward and leftward relative to the rod  108 . For example, the opening  122  has an ellipse shape having a major axis and a minor axis. The major axis, which is the longest diameter of an ellipse shape is along the right and left directions, and the minor axis, which is the shortest diameter of the ellipse is along the upward and downward directions. Therefore, the rod  108  is allowed to more freely move rightward and leftward along the major axis of the ellipse shaped opening  122  within the holding member  106 , and the holding member  106  is also allowed to move rightward and leftward relative to the rod  108 . Therefore, the oral appliance  100  allows the user to move the lower jaw or upper jaw rightward and leftward relative to each other during sleeping. The embodiments described herein improve user experience by allow a predetermined degree of lateral movement of mandible and provide more flexibility, comfortable use, and ease of use of the oral appliance  100  to the user who wears the oral appliance. Accordingly, the oral appliance  100  provides great user experience without detriment the effectiveness and function of mandibular advancement. 
       FIG. 9  shows a cross sectional view of an exemplary oral appliance in accordance with at least some embodiments described herein. In  FIG. 9 , the oral appliance  100  includes another restrictor  142  at opposite side of the restrictor  140 . The another restrictor  142  prevents the rod  108  from being fully withdrawn from the holding member  106 . The holding member  106  has a proximal end  130 , a distal end  132 , and a middle portion located between the proximal end  130  and the distal end  132 . For example, the another restrictor  142  is a ring-shaped protrusion portion provided on an inner circumference of the holding member  106  at the proximal end  130 , and is a cylindrical portion with a smaller inner diameter. The inner diameter of the another restrictor  142  is smaller than the inner diameter of the middle portion of the holding member  106 . The inner diameter of the another restrictor  142  may be substantially same as the inner diameter of the restrictor  140 . The another restrictor  142  abuts against the rod  108  and restricts the rod  108  from being fully withdrawn from the holding member  106  in a backward direction. Further, the another restrictor  142  restricts the holding member  106  from being fully withdrawn from the rod  108  in a forward direction. 
     The another restrictor  142  may be manufactured as a ring-shaped protrusion portion provided on an inner circumference of the holding member  106  at the proximal end  130 , or alternatively, may be a separate supporting member. The separate supporting member may be inserted after assembly of the rod  108  and holding member  106  (i.e. after the rod  108  is inserted into the opening  122  of the holding member  106 ) and fixed to the inside of the holding member  106  at the proximal end  130  to prevent the rod  108  from being fully withdrawn from the rod  108 . 
       FIG. 10  shows an exemplary oral appliance after being assembled in accordance with at least some embodiments described herein. As depicted, another exemplary oral appliance  200  includes, at least a first jaw retainer piece, a second jaw retainer piece, a holding member  206 , and a rod  208 . The first jaw retainer piece may refer to a lower jaw retainer piece  202  and the second jaw retainer piece may refer to an upper jaw retainer piece  204 . The holding member  206  is mounted on the front-facing portion of the lower jaw retainer piece  202 , and has an opening  222  (as shown in  FIG. 11A ) for receiving a rod  208 . The holding member  206  may have a ring shape. The oral appliance  200  may include a restrictor  240 , or another restrictor  242  (as shown in  FIG. 14 ), that restricts sliding of the rod  208  relative to the holding member  206 . The holding member  206  may be mounted on or attached to a front-facing portion of the lower jaw retainer piece  202  via a first mounting unit  210 . The first mounting unit  210  includes a first plurality of through-holes  212  which allow for the infiltration of the material that forms the lower jaw retainer piece  202  for positional stability. The lower jaw retainer piece  202  includes a first fixing member  214  which is a metallic (e.g. stainless steel) dental wire (or a plurality of metallic dental wires) for fixing the teeth more firmly in place in the lower jaw retainer piece  202 . 
     One end of the rod  208  is mounted on the front-facing portion of the upper jaw retainer piece  204 , and the other end of the rod  208  is slidably inserted into the opening  222  of the holding member  206  in a forward direction. The one end of the rod  208  is mounted on the front-facing portion of the upper jaw retainer piece  204  via a second mounting unit  216 . The second mounting unit  216  includes a second plurality of through-holes  218  which allow for the infiltration of the material that forms the upper jaw retainer piece  204  for positional stability. The upper jaw retainer piece include a second fixing member  220  which is a metallic (e.g. stainless steel) dental wire (or a plurality of metallic dental wires) for fixing the teeth more firmly in place in the upper jaw retainer piece  204 . 
       FIG. 11A  shows a top portion of an exemplary holding member mounted on a front-facing portion of a lower jaw retainer piece in accordance with at least some embodiments described herein. A lower jaw retainer piece  202  is shaped and adapted to engage the mandibular dentition of a user, and the lower jaw retainer piece  202  is open towards a mandibular. The size and shape of the lower jaw retainer piece  202  can be customized to suit the anatomy of each user. The lower jaw retainer piece  202  may include a first fixing member  214  (as shown in  FIG. 10 ) which may be a metallic (e.g. stainless steel) dental wire to ensure that the lower jaw retainer piece  202  securely engages the user&#39;s teeth. 
     The holding member  206  is mounted on the front-facing portion of the lower jaw retainer piece  202  by the first mounting unit  210 , and has an opening  222  for receiving a rod  208 . The holding member  206  may have a ring shape and be longitudinally perpendicular to a front-facing portion of the lower jaw retainer piece  202 . The opening  222  is adapted to receive the rod  208  from the front-facing portion of the lower jaw retainer piece  202  towards the forward direction along the longitudinal axis. 
       FIG. 11B  shows a front portion of an exemplary holding member mounted on a front-facing portion of a lower jaw retainer piece in accordance with at least some embodiments described herein. The holding member  206  may be mounted on or attached to the front-facing portion of the lower jaw retainer piece  202  via a first mounting unit  210 . The first mounting unit  210  may be placed into the front-facing portion of the lower jaw retainer piece  202 . The rod  208  may be slidably inserted into the opening  222  in  FIG. 11B  from a backward to a forward direction. 
       FIG. 12A  shows a top portion of an exemplary rod mounted on a front-facing portion of an upper jaw retainer piece in accordance with at least some embodiments described herein. An upper jaw retainer piece  204  is shaped and adapted to engage the maxillary dentition of the user, and the upper jaw retainer piece  204  is open towards a maxillary. The size and shape of the upper jaw retainer piece  204  can be customized to suit the anatomy of each user. The upper jaw retainer piece  204  may include a second fixing member  220  which may be a metallic (e.g. stainless steel) dental wire to ensure that the upper jaw retainer piece  204  securely engages the user&#39;s teeth. 
     One end (i.e. a trailing end  226 ) of the rod  208  is mounted on the front-facing portion of the upper jaw retainer piece  204  by the second mounting unit  216 , and another end (i.e. a leading end  224 ) is extending along a longitudinal axis in a forward direction. When the rod  208  is assembled with the holding member  206  in accordance with at least some embodiments described herein, the leading end  224  of the rod  208  may be slidably inserted into the opening  222  of the holding member  206  along a longitudinal axis in a forward direction. The oral appliance  200  may optionally include a protective cover  236  that covers at least a part of the rod  208 . The protective cover  236  may have a substantially hollow semi-cylindrical shape defining a rounded inner surface. One end of the protective cover  236  is mounted on the front-facing portion of the upper jaw retainer piece  204  via the second mounting unit  216  and above the rod  208  and the other end of the protective cover  236  is extended along a longitudinal axis and parallel to the rod  208 . The rounded inner surface of the protective cover  236  faces the rod  208 , and a gap exists between the protective cover  236  and the rod  208 .  FIG. 12B  shows a bottom portion of an exemplary rod mounted on a front-facing portion of an upper jaw retainer piece in accordance with at least some embodiments described herein. 
     In accordance with some implementations, the lower jaw retainer piece  202  and the upper jaw retainer piece  204  may be made of same material as that of the lower jaw retainer piece  102  and the upper jaw retainer piece  104  as mentioned above. Further, the rod  208  and the holding member  206  may be made of aforementioned same material used for forming the rod  108  and the holding member  106 . 
       FIG. 13A  shows an exemplary holding member  206  and  FIG. 13B  shows an exemplary rod  208  in accordance with at least some embodiments described herein. One end of the holding member  206  is attached to a first mounting unit  210  that is adapted to be mounted on the front-facing portion of the lower jaw retainer piece  202 . The first mounting unit  210  is a thin plate-like member that may be made of same material with the holding member  206 . The first mounting unit  210  may be formed in a curved shape along the shape of a front-facing portion of the lower jaw retainer piece  202 . The first mounting unit  210  may have a first plurality of through-holes  212  for facilitating the fixation of the first mounting unit  210  to the lower jaw retainer piece  202 . The first mounting unit  210  may be mounted on or attached to the front-facing portion of the lower jaw retainer piece  202  using a resin material which may be used for forming the lower jaw retainer piece  202 . The resin material may pass through the first plurality of through-holes  212  and attach or fix the first mounting unit  210  to the lower jaw retainer piece  202  and enhance the fixing strength each other. One end of the holding member  206  may be mounted on the front-facing portion of the lower jaw retainer piece  202  via the first mounting unit  210 . 
     The rod  208  is an elongated member that includes a trailing end  226  and a leading end  224 . The trailing end  226  of the rod  108  is to be mounted on or attached to the front-facing portion of the upper jaw retainer piece  204 , and the leading end  224  is extending along a longitudinal axis in a forward direction. The trailing end  226  of the rod  208  is attached to a second mounting unit  216  that is adapted to be mounted on or attached to the front-facing portion of the upper jaw retainer piece  204 . The second mounting unit  216  is a thin plate-like member that may be made of material which may be used for forming the rod  208  or the holding member  206 . The second mounting unit  216  may be formed in a curved shape along the shape of a front-facing portion of the upper jaw retainer piece  204 . The second mounting unit  216  may have a second plurality of through-holes  218  for facilitating the fixation of the second mounting unit  216  to the upper jaw retainer piece  204 . The second mounting unit  216  may be mounted on or attached to the front-facing portion of the upper jaw retainer piece  204  using a resin material which may be used for forming the upper jaw retainer piece  204 . The resin material may pass through the second plurality of through-holes  218  and attach or fix the second mounting unit  216  to the upper jaw retainer piece  204  and enhance the fixing strength each other. 
     The oral appliance  200  may include a protective cover  236  that covers at least a part of the rod  208  as described in the above and shown in  FIG. 12A . Further, the leading end  224  of the rod  208  comprises a set of threads  224   a  which are male threads, and adapted to threadingly engage with another restrictor (as shown in  FIG. 14 ). 
       FIG. 14  shows an exemplary rod and a restrictor in accordance with at least some embodiments described herein. More particularly,  FIG. 14  shows that the rod  208  is inserted into the holding member  206 . The leading end  224  of the rod  208  is slidably inserted into the holding member  206 , and the rod  208  moves in the forward and backward directions relative to the holding member  206 . When the oral appliance  200  includes a protective cover  236  that covers at least a part of the rod  208 , the rod  208  is slidably inserted into the holding member  206 , and the holding member is located at the gap between the rod  208  and the protective cover  236 . Therefore, the protective cover  236  covers and protects both of the holding member  206  and the rod  208 . The oral appliance  200  may include a restrictor  240  that restricts sliding of the rod  208  relative within the holding member  206 . The restrictor  240  may be a plurality of restrictors, for example, four restrictors  240   a - 240   d  as shown in  FIG. 14 . The restrictor  240  may be a restrictor ring, and the leading end  224  of the rod  208  is slidably inserted into the restrictor  240  (i.e. a restrictor ring). Then, the leading end  224  of the rod  208  is slidably inserted into the holding member  206 , and the restrictor  240  may be located between the holding member  206  and the upper jaw retainer piece  204  along a longitudinal axis of the rod  208 . By adjusting the number of the restrictor  240 , an amount of movement of the holding member  206  relative to the rod  208  in the forward direction can be adjusted. By increasing the number of the restrictor  240  between the holding member  206  and the upper jaw retainer piece  204  along the longitudinal axis of the rod  208 , an advancement position of the holding member  206  in a forward direction relative to the rod  208  is getting increased. Thereby, an abutment position of the rod  208  relative to the restrictor  240  can be adjusted. 
     Further, the oral appliance  200  may include another restrictor  242 . The leading end  224  of the rod  208  comprises a set of threads  224   a  which are male threads, and adapted to threadingly engage with the another restrictor  242 . The another restrictor  242  prevents the rod  208  from being fully withdrawn from the holding member  206 , and prevents the holding member  206  from being fully withdrawn from the rod  208 . The another restrictor  242  may be a restrictor cap having a female threaded portion inside which allows the cap to be removably attached to the leading end  224  of the rod  208  having the set of threads thereon. The another restrictor  242  has a diameter that is larger than a diameter of a ring opening of the holding member  206  so as to prevent the holding member  206  being fully withdrawn from the rod  208 . 
       FIGS. 15A and 15B  show an exemplary oral appliance while adjusting a lower jaw position in accordance with at least some embodiments described herein. In particular, the assembled oral appliance  200  worn by the user is illustrated in  FIGS. 15A and 15B . To assemble the oral appliance  200 , as described above, the leading end  224  of the rod  208  may be slidably inserted into the restrictor  240 , and then, the leading end  224  may be further slidably inserted into the opening the holding member  206  (a ring shape) from the front-facing portion of the lower jaw retainer piece  202  to a forward direction the along a longitudinal axis. The trailing end  226  of the rod  208  is mounted on the front-facing portion of the upper jaw retainer piece  204 . After assembly, the lower jaw position of the user may be adjusted after or before the user wears the oral appliance. 
       FIG. 15A  shows that the position of the lower jaw retainer piece  202  and the position of the upper jaw retainer piece  204  are initially same, and the lower jaw retainer piece  202  has not moved forward yet relative to the upper jaw retainer piece  204 . The position of the holding member  206  is adjusted in the forward and backward directions to adjust an abutment position of the rod  208  relative to the restrictor  240  (as shown in  FIG. 16A ). The position of the holding member  206  relative to the rod  208  is adjusted by the number of the restrictor  240 . 
     As the position of the holding member  206  moves in a forward direction along the rod  208 , the position of the lower jaw retainer piece  202  which is attached to the holding member  206  also moves in a forward direction. On the other hand, the position of the upper jaw retainer piece  204  which is attached to the rod  208  maintains same position. Therefore, the lower jaw retainer piece  202  is positioned forward relative to the upper jaw retainer piece  204 .  FIG. 15B  shows that the position of the lower jaw retainer piece  202  and the position of the upper jaw retainer piece  204  are different after sliding and adjustment, and the lower jaw retainer piece  202  has moved in a forward direction relative to the upper jaw retainer piece  204 . 
     By positioning the lower jaw retainer piece  202  forward relative to the upper jaw retainer piece  204 , the oral appliance  200  restricts the displacement of the lower jaw of the user to the backward direction, thereby preventing the constriction of the airway, a breathing stop or low respiration during sleep. As the oral appliance  200  adjusts the amount of advancement of the lower jaw retainer piece  202  relative to the upper jaw retainer piece  204 , the lower jaw moves forward relative to the upper jaw by the adjusted amount of the advancement. Therefore, it is possible to make the user&#39;s airway less likely to be narrowed. 
       FIG. 16A  shows a cross sectional view of an exemplary oral appliance in accordance with at least some embodiments described herein. The oral appliance  200  may include a restrictor  240  that restricts sliding of the rod  208  relative within the holding member  206 . For example, the restrictor  240  may be a restrictor ring, and the restrictor  240  is located between the holding member  206  and the upper jaw retainer piece  204  along a longitudinal axis of the rod  208 . 
     An abutment position of the holding member  206  relative to the restrictor  240  is set by sliding the holding member  206  (i.e. a position of the lower jaw retainer piece  202  relative to a position of the upper jaw retainer piece  204 ). Even after the setting of the abutment position, the holding member  206  can slide forward and backward directions along the rod  208 . However, the holding member  206  cannot pass over the restrictor  240  in a backward direction, and the restrictor  240  abuts against the rod  208  and restricts sliding of the holding member  206  in a backward direction relative to the rod  208 . Similarly, the rod  208  can move in forward and backward directions relative to the holding member  206  but cannot pass over the holding member  206  in a forward direction because the restrictor  240  abuts against the holding member  206  and restricts a forward movement of the rod  208  relative to the holding member  206 .  FIG. 16B  shows a cross sectional view of an exemplary oral appliance in accordance with at least some embodiments described herein. In particular, a restrictor  240  that abuts against the rod  208  is illustrated in  FIG. 16B . 
     If the oral appliance  200  does not have the restrictor  240 , the rod  208  moves in a forward direction, and the holding member  206  moves in a backward direction, and thus, the upper jaw retainer piece  204  attached to the rod  208  can move to a forward direction and the lower jaw retainer piece  202  attached to the holding member  206  can move backward. If the oral appliance  200  does not have the restrictor  240 , the lower jaw position of the user who worn the oral appliance  200  during sleeping would not be effectively maintained. The restrictor  240  restricts the displacement of the lower jaw of the user to the backward direction during sleeping and therefore an oral appliance  200  allows the user to maintain the position of the lower jaw forward relative to the upper jaw. At the same time, the restrictor  240  does not restrict the user to move the lower jaw forward relative to the upper jaw when the oral appliance  200  is worn by the user during sleeping. Therefore, the restrictor  240  sets a predetermined degree of a forward and backward movement of mandible within the preferred protruded position, while still maintaining acceptable airway patency effectively by maintaining the mandible in a preferred protruded position. Therefore, the oral appliance  200  allows the user to move the lower jaw forward within a predetermined degree during sleeping, and provides more flexibility, comfortable use, and ease of use of the oral appliance  200  to the user who wears the oral appliance. Thereby, the oral appliance  200  provides great user experience without detriment the effectiveness and function of mandibular advancement. 
     In accordance with some embodiments, the oral appliance  200  includes another restrictor  242  (as shown in  FIG. 14 ) at opposite side to the restrictor  240 . The another restrictor  242  prevents the rod  208  from being fully withdrawn from the holding member  206 , and prevents the holding member  206  from being fully withdrawn from the rod  208 . The rod  208  has a leading end  224  and a trailing end  226 . The leading end  224  of the rod  208  comprises a set of threads  224   a  which are male threads, and adapted to threadingly engage with the another restrictor  242 . The another restrictor  242  may be a restrictor cap having a female threaded portion inside which allows the cap to be removably attached to the leading end  224  of the rod  208  having the set of threads. The another restrictor  242  has a diameter that is larger than a diameter of a ring opening of the holding member  206  so as to prevent the holding member  206  from moving too much in a forward direction and being fully withdrawn from the rod  208 . The another restrictor  242  prevents the rod  208  from moving too much in a backward direction and from being fully withdrawn from the holding member  206 . 
     In accordance with some embodiments, the opening  222  of the holding member  208  has an ellipse shape, an oval shape, an egg shape, a rectangle shape, or any oblong shape. Therefore, in the same manner as described above with respect to the opening  122  of the oral appliance  100 , the oral appliance  200  further allows the user to move the lower jaw or upper jaw rightward and leftward relative to each other during sleeping. The embodiments described herein improve user experience by allow a predetermined degree of lateral movement of mandible and provide more flexibility, comfortable use, and ease of use of the oral appliance  200  to the user who wears the oral appliance. Accordingly, the oral appliance  200  provides great user experience without detriment the effectiveness and function of mandibular advancement. 
     From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the following claims.