Abstract:
The present invention provides an improved adjustable chair headrest. Specifically, the present invention comprises a double articulating dental chair headrest apparatus which has a one-handed side pushbutton release and locking mechanism. When pressed, the pushbutton temporarily disengages a movable mating plate having splined perforations away from each of two corresponding rotatable splined pin assemblies to unlock each splined pin assembly. The unlocked splined pin assemblies each rotate independently. Each splined pin assembly is also fixedly attached to one of a headrest and a backrest via an attachment plate. The two splined pin assemblies are held in relation to each other, the movable mating plate having splined perforations, and the side pushbutton release and locking mechanism, by a housing component.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/730,276, filed Nov. 27, 2012. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to the field of adjustable headrests for chairs. Specifically, the present invention comprises a double articulating dental chair headrest apparatus which has a one-handed side pushbutton release and locking mechanism. When pressed, the pushbutton disengages a movable mating plate having splined perforations away from each of two corresponding rotatable splined pin assemblies to unlock each splined pin assembly. The unlocked splined pin assemblies each rotate independently. Each splined pin assembly is also fixedly attached to one of a headrest and a backrest via an attachment plate. The two splined pin assemblies are held in relation to each other, the movable mating plate having splined perforations, and the side pushbutton release and locking mechanism, by a housing component. 
         [0004]    2. Description of Related Art 
         [0005]    Many attempts have been made to produce a streamlined, comfortable, and easily adjustable headrest for chairs comprising a headrest that is a separate component from a chair backrest, but such attempts have failed to provide the range of adjustability, purity of form and function, comfort, and ease of use that may be desired. Specifically, improved adjustable headrests specific to the dental and medical fields are needed to provide comfort to the patient while at the same time facilitating the examination and work performed by the medical professional. 
         [0006]    Many conventional chair headrests are mounted on chair backrests by a mechanism that provides some degree of adjustability. However, conventional chair headrest adjustment often provides adjustment along only a singular axis, such as by using one hand to loosen and then re-tighten a screw-actuated mechanism while using the other hand to adjust the headrest and lock it into place. 
         [0007]    A more desirable mechanism would allow headrest adjustment by actuation of a single-handed release and/or lock mechanism. Further, an adjustment mechanism that would allow headrest adjustment along multiple axes by actuation of a single-handed release and/or lock mechanism would provide significant advantages to its user and the patient relative to conventionally available headrest adjustment apparatuses. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The present invention includes a double articulating dental chair headrest apparatus that overcomes disadvantages associated with prior adjustable headrests and imparts several new and distinct advantages. 
         [0009]    The present invention provides, for the first time, a simple design for the one-handed release and locking of double articulating members to permit adjustment of the dental chair headrest relative to the dental chair backrest. The splined mating surfaces incorporated in the double articulating dental chair headrest apparatus of the present invention permit fast, easy, secure, and finely tuned adjustment of the dental chair headrest relative to the dental chair backrest for maximum comfort by the user, and ease of use by the dental professional. The streamlined design of the present invention also provides an aesthetically pleasing form and results in eased manufacturing and maintenance due to the low number of component parts. The streamlined design of the present invention also provides for a strong and durable double articulating dental chair headrest apparatus due to the use of few component parts made of high quality materials and arranged in a straight-forward and intelligent manner that limits the introduction of problems via user error. The user need only use one hand to depress the pushbutton release and locking mechanism to permit adjustment of the headrest relative to the backrest of the dental chair. The ability to use only one hand to accomplish the release and locking of the adjustment mechanism reduces the work required on the part of the user to accomplish chair adjustment, results in less distracting and less time-consuming chair adjustment for both the user and the patient, and, optionally, frees the user&#39;s other hand to perform other tasks. 
         [0010]    Principle components of the present invention include two rotatable splined pin assemblies, a movable mating plate having splined perforations corresponding to each of the two rotatable splined pin assemblies, a pushbutton release and locking mechanism, and a housing component. 
         [0011]    An exemplary preferred embodiment is described in detail below, but should not be construed as limiting on the present invention as generally disclosed by this application. 
         [0012]    In a preferred embodiment, a spring mounted pushbutton release and locking mechanism is connected to a movable mating plate having two splined perforations that correspond to splined surfaces located on each of two rotatable splined pin assemblies. 
         [0013]    The release and locking action of the double articulating dental chair headrest apparatus is caused by a user&#39;s depression of the spring mounted pushbutton which modifies the contact between each of, the splined surfaces located on each of the two rotatable splined pin assemblies, and the movable mating plate having splined perforations. When the spring mounted pushbutton is not activated, i.e., not depressed, the movable mating plate having splined perforations that correspond to each of the two rotatable splined pin assemblies is locked in place by the interaction and contact between the splined surfaces located on each of the two rotatable splined pin assemblies and the corresponding splined perforations of the movable mating plate. Depression of the pushbutton pushes the movable mating plate away from and apart from each of the two rotatable splined pin assemblies, thus breaking the interaction and contact between the splined surfaces located on each of the two rotatable splined pin assemblies and the corresponding splined perforations of the movable mating plate and releasing each of the two rotatable splined pin assemblies to rotate about an axis. That is, once the mating plate is pushed away and apart from each of the rotatable splined pin assemblies, each of these assemblies is simultaneously released and permitted to rotate independently. Once adjustment of the headrest relative to the backrest of the dental chair is accomplished, the user discontinues application of pressure to the spring mounted pushbutton which, in turn, causes the movable mating plate to return to an apparatus locking position due to the contact and interaction between the two splined perforations on the movable mating plate and the splined surfaces located on each of the two rotatable splined pin assemblies. The density of the splined surfaces located on the movable mating plate and the rotatable splined pin assemblies permits fine-tuned dental chair adjustment. In a preferred embodiment, the splined surfaces located on each of the two rotatable splined pin assemblies are equipped with 48 teeth at a 0.721 inch diameter and have a class 7 fit. 
         [0014]    The movable mating plate having splined perforations can be fixedly attached to a bottom surface of a generally T-shaped pushbutton, although the pushbutton can comprise a variety of shapes. 
         [0015]    The two rotatable splined pin assemblies are held spaced apart and in relation to each other, the movable mating plate, and the pushbutton by a housing component. The housing component generally provides a protective shell for the movable mating plate having splined perforations and the corresponding splined mating parts of the two rotatable splined pin assemblies. As noted above, adjustment of the dental chair headrest is actuated by the application of pressure to a pushbutton release and locking mechanism. 
         [0016]    In a preferred embodiment, the housing component holds the two rotatable splined pin assemblies in parallel orientation to each other. Each of the two rotatable splined pin assemblies is oriented in the same direction, having a first splined end with a toothed surface area that corresponds to the movable mating plate having splined perforations and a second attachment end extending through and outwardly from the housing component. The first splined end of each of the two rotatable splined pin assemblies is held in place by a snap ring. The second attachment ends of each of the two rotatable splined pin assemblies extends through and outwardly from the housing component, and are used to connect with one of a headrest attachment plate and a backrest attachment plate. 
         [0017]    The housing component may comprise a variety of shapes. In a preferred embodiment, the housing component is generally oval-shaped. In a particularly preferred embodiment, the housing component also provides concave surfaces located generally in the middle of each of the two longest outermost surfaces without penetrations, thus, modifying the general oval-shape of the housing component to more of a dog bone-shape (for example, as generally depicted in  FIG. 1 ). A first side surface of the housing component is substantially flat and has three openings corresponding to parts of each of the two rotatable splined pin assemblies and the pushbutton. A second side surface of the housing component, which is opposite to the first side surface, is also substantially flat as defined by the outer peripheral edges of the housing component which surround an internal open space. The remaining surfaces of the housing component present a substantially flat, continuous, and uninterrupted smooth oval-shaped or dog bone-shaped exterior. 
         [0018]    It is an object of the invention to provide a housing component that permits the easy handling and adjustment of the headrest apparatus. Such handling and adjustment can be facilitated by providing a housing component that is easy to grip with one hand while optionally pressing, or otherwise activating, the pushbutton release and locking mechanism. Accordingly, the pushbutton and/or the housing component may be shaped to permit easy gripping, handling, and manipulation with one hand. 
         [0019]    On the outside surface of the housing component, each of the two rotatable splined pin assemblies provides rotatable attachment via second attachment ends of each of the two rotatable splined pin assemblies which extend through and outwardly from the housing component to one of a headrest attachment plate and a backrest attachment plate. The range of rotation provided to the headrest attachment plate and the backrest attachment plate can be limited by the shape of the attachment plates, the housing component, and the external surface of the pushbutton. Each of the two rotatable splined pin assemblies can be locked at any of a variety of angles within a range of rotation about its fixed axis, limited only by the density of the splined teeth on each of the two rotatable splined pin assemblies and the two splined perforations on the movable mating plate, and the physical interruption of movement, if any, provided by one or more of the shape of the attachment plates, the housing component, and the external surface of the pushbutton. In a particularly preferred embodiment, the headrest attachment plate has a maximum of about 180 degrees of rotation relative to the housing component, and the backrest attachment plate has a maximum of about 270 degrees of rotation relative to the housing component. 
         [0020]    In one embodiment, the housing component can provide a uniformly smooth outer surface. In another embodiment, the housing component can provide a surface that facilitates gripping the adjustment apparatus. Any grip surface provided on the housing component of the present invention may either be formed integrally as part of the housing component, or provided as a separate component. For example, a separate gripping surface may be additionally be adhered to the outside of the housing component and provided as part of the invention. 
         [0021]    Various fastening means are also contemplated as part of the present invention. For example, screws or welding or other means can be used to fixedly attach any of the movable mating plate having splined perforations to a bottom surface of a pushbutton, the headrest attachment plate to a first rotatable splined pin assembly, the backrest attachment plate to a second rotatable splined pin assembly, and an optional cover plate to one of the movable mating plate having splined perforations or the outer peripheral edges of the external second side surface of the housing component. 
         [0022]    The various components of the present invention may comprise different materials. For example, the housing component may be made of any grade of steel or aluminum. Either or both of two rotatable splined pin assemblies may be formed from any grade of steel or aluminum. The pushbutton may be made of any grade of steel, aluminum, or plastic. The movable mating plate may be made of any grade of steel or aluminum. The headrest attachment plate and the backrest attachment plate may be made of any grade of steel or aluminum. The splined surfaces may be treated with plating and grease. Washers included as part of the invention may be made of any grade of steel, aluminum, or plastic. Snap rings included as part of the invention may be made of any grade of steel. 
         [0023]    In a particularly preferred embodiment, the housing component is aluminum, the rotatable splined pin assemblies are steel, the pushbutton is a hard plastic (preferably DELRIN®), the movable mating plate is steel, the headrest attachment plate and the backrest attachment plate are steel, the splined surfaces are treated with electroless nickel plating, the washers are plastic, and the snap rings are steel. 
         [0024]    Various lubricants may be used as part of the present invention, including general purpose grease or lubricant. In a particularly preferred embodiment, the lubricant is lithium grease. 
         [0025]    It is also contemplated that the present invention may include rotatable splined pin assemblies that are integrally formed with at least one of the headrest attachment plate and the backrest attachment plate. 
         [0026]    Although this invention has been described with reference to dental chairs, it is also applicable to other chairs, for example, other patient and medical chairs and beds, massage chairs and beds, automobile seats, plane seats, train seats, lounge chairs, office and home furniture, and anywhere where the benefits of the present invention can be enjoyed. 
         [0027]    While preferred embodiments have been shown and described, those skilled in the art will recognize that changes and modifications may be made to the foregoing examples without departing from the scope and spirit of the invention. In particular, it is noted that the external appearance of the present invention may vary considerably from the appearance of the specific embodiments disclosed herein without departing from the scope and spirit of the invention. It is thus intended to claim all such changes and modifications that fall within the scope and spirit of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0028]    The accompanying Figures, which are incorporated in and constitute a part of this specification, illustrate various exemplary embodiments. 
           [0029]      FIG. 1  provides an exploded perspective view of the component parts and assembly of a double articulating dental chair headrest apparatus. 
           [0030]      FIG. 2  provides a side view of a folded and partially dis-assembled double articulating dental chair headrest apparatus, with the pushbutton assembly and springs removed. 
           [0031]      FIG. 3  provides a partial side view of a folded and partially dis-assembled double articulating dental chair headrest apparatus according to the present invention, with the movable mating plate and fastening means removed. 
           [0032]      FIG. 4  provides a partial side view of a folded double articulating dental chair headrest apparatus according to the present invention, without the optional cover plate. 
           [0033]      FIG. 5  provides a perspective view of a folded double articulating dental chair headrest apparatus according to the present invention in a locked position. 
           [0034]      FIG. 6  provides a view of a fully extended double articulating dental chair headrest apparatus according to the present invention in a locked position. 
           [0035]      FIG. 7  provides a view of a fully extended double articulating dental chair headrest apparatus with a pushbutton assembly according to the present invention in a locked position. 
           [0036]      FIG. 8  provides a three-quarters view of a fully extended double articulating dental chair headrest apparatus with a pushbutton assembly according to the present invention in a locked position. 
           [0037]      FIG. 9  provides a side view of a maximally folded double articulating dental chair headrest apparatus with a pushbutton assembly according to the present invention in a locked position. 
           [0038]      FIG. 10  provides a top and end view of a folded double articulating dental chair headrest apparatus according to the present invention in a locked position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structures. Elements common between Figures may retain the same numerical designation. 
         [0040]      FIG. 1  provides an exploded perspective view of the component parts and assembly of the double articulating dental chair headrest apparatus. As depicted, the primary components of the headrest include a first rotatable splined pin assembly  20 , a second rotatable splined pin assembly  96 , a housing component  52 , a movable mating plate  62  having splined perforations  68  and  80 , and a pushbutton assembly  40 . 
         [0041]    The headrest attachment plate  10  is generally rectangular in shape with rounded edges. The headrest attachment plate  10  has openings  12  to permit connection of the headrest attachment plate  10  to a headrest. The headrest attachment plate  10  has openings  14  to permit connection of the headrest attachment plate  10  to the first rotatable splined pin assembly  20 , for example, by fastening means  16 . 
         [0042]    The first rotatable splined pin assembly  20  comprises an outer head portion  22 , which has a generally triangular-shaped outer side surface  28 , a flat plate attachment surface  24 , and fastening openings  26  to permit connection of the headrest attachment plate  10 . The first rotatable splined pin assembly  20  also comprises a first splined pin axle  30 , which has a reduced circumference ring area  32  where the snap ring  60  attaches, a circumferentially toothed spline portion  34 , and a flat circular end surface  36 . 
         [0043]    The pushbutton assembly  40  is generally T-shaped, with the outer pushbutton surface having a generally oval shape corresponding to the top of the T-shape. The pushbutton assembly  40  comprises an extended shaft  44  having fastening openings  48  in a flat surface  46 , corresponding to the bottom of the T-shape, for connection to the movable mating plate  62  having splined perforations  68  and  80  via fastening openings  70  and fastening means  72 . As assembled, two springs  50  are located on either side of the extended shaft  44  and between the bottom surface of the top of the T-shape of the pushbutton assembly  40  and the pushbutton surface  114  (not shown and not indicated) of a first outer surface  122  (not shown and not indicated) of housing component  52  and on either side of opening  118  (not shown and not indicated) located on the pushbutton surface  114  of a first outer surface  122  of housing component  52 . 
         [0044]    The second rotatable splined pin assembly  96  includes an outer head portion  98 . The outer head portion  98  has a generally circular-shaped outer side surface  100 , an (optional) attachment surface  102  (not shown and not indicated), and one or more optional fastening openings  104  (not shown and not indicated) to permit connection of the second rotatable splined pin assembly  96  to the backrest attachment plate  110 . Alternatively, the second rotatable splined pin assembly  96  and the backrest attachment plate  110  may be integrally formed as one unit. The second rotatable splined pin assembly  96  also comprises a second splined pin axle  94 , which has a reduced circumference ring area  92  where the snap ring  82  attaches, a circumferentially toothed splined portion  90 , and a flat circular end surface  88 . 
         [0045]    The first rotatable splined pin assembly  20  and the second rotatable splined pin assembly  96  are inserted into circular-shaped splined pin assembly openings  112  (not shown and not indicated) on the first outer surface  122  (not shown and not indicated) of housing component  52 , which, as shown here, is generally oval-shaped, and also provides concave surfaces located generally in the middle of each of the two longest outermost surfaces without penetrations, thus, modifying the general oval-shape of the housing component to more of a dog bone-shape. Mounted onto each of the first splined pin axle  30  and the second splined pin axle  94  are nylon washer  38  and nylon washer  86 , respectively. As assembled, the nylon washer  38  is located between the first outer surface  122  (not shown and not indicated) of housing component  52  and the interior surface of the outer head portion  22  of the first rotatable splined pin assembly  20  and around the first splined pin axle  30 . Also, as assembled, the nylon washer  86  is located between the first outer surface  122  (not shown and not indicated) of housing component  52  and the interior surface of the outer head portion  98  of the second rotatable splined pin assembly  96  and around the second splined pin axle  94 . 
         [0046]    The housing component  52  comprises a bottom internal surface  120  (not shown and not indicated) which is opposite to the substantially flat first outer surface  122  (not shown and not indicated) that has two similarly sized splined pin assembly openings  112  (not shown and not indicated) to accommodate, on one end, passage of the first splined pin axle  30  of the first rotatable splined pin assembly  20 , and on another end, passage of the second splined pin axle  94  of the second rotatable splined pin assembly  96 . The pushbutton surface  114  (not shown and not indicated) of a first outer surface  122  (not shown and not indicated) of housing component  52  also includes an opening  118  (not shown and not indicated) to accommodate passage of the extended shaft  44  of the T-shaped pushbutton assembly  40 . The T-shaped pushbutton assembly  40  is located between the first rotatable splined pin assembly  20  and the second rotatable splined pin assembly  96 . The housing component  52  has a uniformly smooth outer surface  56 , and an interior cavity  54 . The interior cavity  54  of the housing component  52  defines an internal open space that accommodates the extended shaft  44  of the pushbutton assembly  40 , the first splined pin axle  30 , the second splined pin axle  94 , and the movable mating plate  62  having splined perforations  68  and  80 . The plane occupied by the second side surface of the housing component  52 , which is opposite to the first substantially flat outer surface  122  (not shown and not indicated), is also substantially flat as defined by the outer peripheral edges of the housing component  52  which surround interior cavity  54 . 
         [0047]    The movable mating plate  62  having splined perforations  68  and  80  includes, at a first end portion  64 , a first splined perforation  68  with a splined surface  66  corresponding to the circumferentially toothed splined portion  34  of the first rotatable splined pin assembly  20 . The movable mating plate  62  having splined perforations  68  and  80  further includes, at a second end portion  76 , a second splined perforation  80  with a splined surface  78  corresponding to the circumferentially toothed splined portion  90  of the second rotatable splined pin assembly  96 . Also included on the movable mating plate  62  having splined perforations  68  and  80  are fastening openings  70  to permit connection of the movable mating plate  62  to the pushbutton assembly  40  via fastening openings  48  in flat surface  46  on the bottom of the pushbutton assembly  40 . Optionally, a cover plate  74  may be used to cover the outer surface area defined by the movable mating plate  62  having splined perforations  68  and  80  and the interior cavity  54  of the housing component  52 . 
         [0048]    As assembled, the nylon washer  58  and snap ring  60  are located between the bottom internal surface  120  (not shown and not indicated) opposite to the first outer surface  122  (not shown and not indicated) of the housing component  52  and the interior surface the first end portion  64  of the movable mating plate  62  having splined perforations  68  and  80  and around the first splined pin axle  30 . Specifically, the snap ring  60  is located on reduced circumference ring area  32  of the first splined pin axle  30 . Also, as assembled, the nylon washer  84  and snap ring  82  are located between the bottom internal surface  120  (not shown and not indicated) opposite to the first outer surface  122  (not shown and not indicated) of the housing component  52  and the interior surface the second end portion  76  of the movable mating plate  62  having splined perforations  68  and  80  and around the second splined pin axle  94 . Specifically, the snap ring  82  is located on reduced circumference ring area  92  of the second splined pin axle  94 . 
         [0049]      FIG. 2  provides a partial side view of a folded and partially dis-assembled double articulating dental chair headrest apparatus according to the present invention, with the pushbutton assembly  40  and springs  50  removed. As depicted, the housing component  52  is generally oval-shaped and comprises a pushbutton surface  114  that is generally oval in shape and includes an opening  118  to accommodate passage of the extended shaft  44  of the pushbutton assembly  40 . Also shown is the first rotatable splined pin assembly  20  comprising an outer head portion  22 , which has a generally triangular-shaped outer side surface  28 , a flat plate attachment surface  24 , and fastening openings  26  (not shown) to permit connection of the headrest attachment plate  10 . Here the second rotatable splined pin assembly  96  includes an outer head portion  98  that has a generally circular-shaped outer side surface  100  and is integrally formed as one unit to include backrest attachment plate  110 . Both the first rotatable splined pin assembly  20  and the second rotatable splined pin assembly  96  are mounted on the first outer surface  122  of the housing component  52 . 
         [0050]      FIG. 3  provides a side view of a folded and partially dis-assembled double articulating dental chair headrest apparatus according to the present invention, with the optional cover plate  74  (not shown), movable mating plate  62  having splined perforations  68  and  80 , and fastening means  72  removed. The splined surface  66  of the first splined perforation  68  corresponds to the circumferentially toothed splined portion  34  of the first rotatable splined pin assembly  20 . The splined surface  78  of the second splined perforation  80  corresponds to the circumferentially toothed splined portion  90  of the second rotatable splined pin assembly  96 . 
         [0051]    As depicted, the housing component  52  is generally oval-shaped and comprises a bottom internal surface  120  opposite to the first outer surface  122  (not shown) of the housing component  52 . Three openings are provided in the bottom internal surface  120  which extend through to the first outer surface  122  (not shown). Opening  118  (not visible due to occupation by the extended shaft  44  of the pushbutton assembly  40 ) accommodates passage of the extended shaft  44  (not indicated) of the pushbutton assembly  40  (not indicated). The extended shaft  44  (not indicated) has fastening openings  48  in a flat surface  46 , corresponding to the bottom of the pushbutton assembly, for connection to the movable mating plate  62  via fastening means  72 . 
         [0052]    Openings  112  (not visible due to occupation by either of the first rotatable splined pin assembly  20  and the second rotatable splined pin assembly  96 ) accommodate, on one end, passage of the first splined pin axle  30  (not indicated) of the first rotatable splined pin assembly  20 , and on another end, passage of the second splined pin axle  94  (not indicated) of the second rotatable splined pin assembly  96 . As depicted, the snap ring  60  which is attached to reduced circumference ring area  32  (not indicated) of the first splined pin axle  30  (not indicated) of the first rotatable splined pin assembly  20  is visible. Also, the circumferentially toothed spline portion  34  and a flat circular end surface  36  of the first rotatable splined pin assembly  20  are visible. Nylon washer  58  and snap ring  60  are also located around the first splined pin axle  30  (not indicated) and, as assembled, between the bottom internal surface  120  of the housing component  52  and the interior surface of the first end portion  64  of the movable mating plate  62  having splined perforations  68  and  80 . Also as depicted, the snap ring  82  which is attached to reduced circumference ring area  92  (not indicated) of the second splined pin axle  94  (not indicated) of the second rotatable splined pin assembly  96  is visible. The circumferentially toothed spline portion  90  and a flat circular end surface  88  of the second rotatable splined pin assembly  96  are visible. The nylon washer  84  and snap ring  82  are located around the second splined pin axle  94  (not indicated) and, as assembled, between the bottom internal surface  120  and the interior surface the second end portion  76  of the movable mating plate  62  having splined perforations  68  and  80 . 
         [0053]      FIG. 4  provides a partial side view of a folded double articulating dental chair headrest apparatus according to the present invention in a locked position, without the optional cover plate  74  (not shown). The circumferentially toothed splined portion  34 , and a flat circular end surface  36  of the first splined pin axle  30  (not indicated) of the first rotatable splined pin assembly  20  (not indicated) is shown. The splined surface  66  of the first splined perforation  68  (not indicated) at a first end portion  64  of movable mating plate  62  is shown to complement and match the circumferentially toothed splined portion  34  of the first rotatable splined pin assembly  20  (not indicated). The circumferentially toothed splined portion  90 , and a flat circular end surface  88  of the second splined pin axle  94  (not indicated) of the second splined pin assembly  96  (not indicated) is shown. The splined surface  78  of the second splined perforation  80  (not indicated) at a second end portion  76  of movable mating plate  62  is shown to complement and match the circumferentially toothed splined portion  90  of the second rotatable splined pin assembly  96  (not indicated). 
         [0054]    As depicted, the circumferentially toothed splined portion  34  of first rotatable splined pin assembly  20  (not indicated) and the circumferentially toothed splined portion  90  of the second rotatable splined pin assembly  96  (not indicated) are shown fully mated, and locked, with the splined surfaces  66  and  78 , respectively, of the movable mating plate  62 . 
         [0055]    Defining one outer portion of the interior cavity  54  of the housing component  52  is a variable distance interior wall space  124  between the outer surface of the movable mating plate  62  and the outer peripheral edges of the housing component  52  which surround interior cavity  54  and define a second side surface of the housing component  52 , which is opposite to the first substantially flat outer surface  122  (not shown and not indicated). 
         [0056]    As depicted, the pushbutton assembly  40  is not depressed. When the pushbutton assembly  40  is depressed, however, the movable mating plate  62  having a splined perforation  68  with a splined surface  66 , and a splined perforation  80  with a splined surface  78 , is simultaneously unlocked from each of the circumferentially toothed splined portion  34  of the first rotatable splined pin assembly  20  and the circumferentially toothed splined portion  90  of the second rotatable splined pin assembly  96 , respectively, and pushed out towards the outer peripheral edges of the housing component  52  which surround interior cavity  54  and define a second side surface of the housing component  52 . Accordingly, the amount of variable interior wall space  124  between the outer surface of the movable mating plate  62  and the outer peripheral edges of the housing component  52  which surround interior cavity  54  and define a second side surface of the housing component  52  is reduced when the pushbutton is pressed and the double articulating dental chair headrest apparatus is in an unlocked position. The variable distance interior wall space  124  between the outer surface of the movable mating plate  62  and the outer peripheral edges of the housing component  52  which surround interior cavity  54  and define a second side surface of the housing component  52  is at its maximum distance when the pushbutton assembly  40  is not depressed and the double articulating dental chair headrest apparatus is in its locked condition. 
         [0057]      FIG. 5  provides a perspective view of a folded double articulating dental chair headrest apparatus with a movable mating plate  62  according to the present invention in a locked position. 
         [0058]      FIG. 6  provides a view of a fully extended double articulating dental chair headrest apparatus according to the present invention in a locked position. 
         [0059]      FIG. 7  provides a view of a fully extended double articulating dental chair headrest apparatus with a pushbutton assembly according to the present invention in a locked position. 
         [0060]      FIG. 8  provides a three-quarters view of a fully extended double articulating dental chair headrest apparatus with a pushbutton assembly according to the present invention in a locked position. 
         [0061]      FIG. 9  provides a side view of a maximally folded double articulating dental chair headrest apparatus with a pushbutton assembly according to the present invention in a locked position. As depicted, the headrest attachment plate  10  is generally rectangular in shape. The headrest attachment plate  10  is shown oriented with its headrest attachment surface facing downwards towards the backrest attachment plate  110 . As shown, the outer head portion  22  of the first rotatable splined pin assembly  20  is in contact with the pushbutton assembly  40 . Additionally, the outer head portion  98  of the second rotatable splined pin assembly  96  is in contact with the pushbutton assembly  40 . In the embodiment shown, the pushbutton assembly  40  blocks both the further rotation of the outer head portion  22  of the first rotatable splined pin assembly  20  and the further rotation of the outer head portion  98  of the second rotatable splined pin assembly  96 . 
         [0062]      FIG. 10  provides a top and end view of a folded double articulating dental chair headrest apparatus according to the present invention in a locked position. As depicted, the headrest attachment plate  10  is oriented with the headrest attachment surface facing downwards. In this orientation, the headrest attachment plate  10  provides a resting surface upon which the housing component  52  rests. The backrest attachment plate  110  is similarly positioned with respect to the pushbutton assembly  40  as described above in connection with  FIG. 9 .