Patent Application
20150059770
This invention relates generally to tools, devices and improved methods for providing intermaxillary fixation. The benefits of intermaxillary fixation, rigidly connecting the upper jaw to the lower jaw, are well known to promote healing of jaw fractures. Intermaxillary fixation is a common treatment to stabilize jaws for oral, plastic, maxillofacial, ENT and trauma surgeries. Further, intermaxillary fixation has been disclosed as a preferred stabilization method for the short term treatment of facial fractures in non-surgical settings, such as on the battlefield by military corpsmen.
The general process of fixing the upper and lower jaw together for medical purposes has been in place for decades. Early efforts for intermaxillary fixation were rudimentary, generally ineffective, often exacerbated patient discomfort, and often failed to achieve desired results. An early process for intermaxillary fixation included the steps of boring holes through the patient's upper and lower gums, passing a wire through the holes and then twisting the wire to join the upper jaw to the lower jaw. That process required boring several holes through the patient's gums. Later efforts have included a variety of apparatuses and processes that include drilling holes, placing bolts, screws or anchors in to the patient's gums, jaw bones and palate. Although such processes increase the possibility of patient discomfort, infection and long-term bone and tissue damage, they are sometimes necessary to effectively fix the patient's jaws together.
These methods have improved over the years including the device disclosed and described in U.S. Pat. No. 8,414,581 to Shah et al. Contemporary treatment methods tend to use non-invasive procedures when possible. The development of the Shah device was a significant advancement in the art in that it uses arch bars that fit adjacent to the outer surface of the patient's upper and lower teeth and are then fastened in place using a plurality of pliable zip or cable ties that connect the arch bars to individual teeth. Interarch receptacles provided on both the upper and lower arch bars can then be fastened together using reverse zip ties or double-ended flexible straps (described herein) thus holding the upper and lower jaw together. In many situations, this device eliminates the need for a physician to drill in to the patient's gum, palate or jaw to fix the upper and lower jaws together. The use of arch bars and zip tie connectors allows for easy and quick installation, removal and repair of the device.
However, the Shah device works best when patients have substantially all of their teeth. When patients present with substantial trauma to their jaw and teeth or have multiple teeth removed or missing, then the interarch bar may not have enough support on the remaining teeth to be an effective treatment. Likewise, for patients that have dentures or no teeth whatsoever, the Shah device may be ineffective as disclosed and described in the previously referenced Shah patent.
Accordingly, it is beneficial to provide a treatment that utilizes, to the extent possible, the noninvasive treatment disclosed in the previously referenced Shah patent, along with tools, devices and procedures that facilitate intermaxillary fixation when a patient has less than all of their teeth, dentures or no teeth at all. While the elimination of bone screws, drilling, boring and wire placement is a desirable goal, some of the historic techniques can be used in conjunction with more modern techniques and devices to substantially lessen the invasiveness of the intermaxillary fixation process.
The instant invention is intended to overcome certain limitations that are present in the noninvasive intermaxillary fixation devices, such as the Shah device. More specifically, the invention is intended to meet the needs of patients who do not have enough teeth for the intermaxillary fixation arch bar system to work effectively and in instances where the patient presents with dentures, partial teeth or no teeth at all. The inventive tools, devices and methods disclosed herein utilize the best features of arch bar fixation devices, such as that disclosed by Shah, with some traditional methods that can be effective in those circumstances described.
For example, a patient presenting with most of their teeth, but lacking teeth in one specific area of their mouth, a relatively common occurrence from trauma sustained in vehicle collisions or resulting from a sports injury, interarch bars can be used in those areas of the mouth where most of the teeth are present. However, in the area where teeth are not present, there would be insufficient stability to support an arch bar connected with an interarch receptacle and a strap with serrations.
When described herein the female end of a zip or cable tie may be referred to as ratchet head, or as an interarch receptacle. Both terms refer to the case having a port through it for receiving a flexible strap. A flexible retention member or pawl is disposed inside the port of the ratchet head or interarch receptacle, as is commonly found with the female end of a zip or cable tie. The male end of a zip or cable tie may be referred to as a flexible strap. The flexible straps are provided with ratchet teeth or serrations. Some embodiments of the flexible strap are attached at one end to a ratchet head forming the common cable or zip tie. Some embodiments of the flexible straps are attached at one end to an inventive washer described in relation to the figures. Some embodiments of the flexible straps have two male ends, each with a section of ratchet teeth oriented in opposing directions, which may be referred to as a double-ended flexible strap. Each end of the double-ended flexible strap may be inserted into opposing interarch receptacles to fix the patient's jaws together, as is described in more detail in relation to the figures. The various embodiments of the flexible straps are inserted through the port on the ratchet head, thereby engaging the ratchet teeth on the flexible strap with the pawl and allowing insertion of the flexible strap but not its removal from the port. In some embodiments the flexible straps are flexible along their length, in one or both axes perpendicular to the longitudinal axis of the strap, so that they may be bent, curved or twisted in simple or compound curves as necessary. In some embodiments the flexible straps have limited extensibility or compressibility parallel to their longitudinal axis.
In another embodiment of the invention, a unique hanger assembly provides a ratchet head, similar to those found on the Shah arch bar assembly, which can be connected to a screw fastened in to the patient's jaw bone. As shown in
For example, if the patient presented with no teeth on the left upper jaw but with teeth on the lower left jaw, an arch bar, similar to the Shah device, can be fastened to the lower teeth. At least one bone screw would be mounted into the upper left jaw bone of the patient opposite each arch bar receptacle provided on the arch bar fastened to the left lower teeth. An inventive washer assembly, an embodiment of which is depicted in
In situations where multiple teeth are missing from both the upper and lower jaw of the patient, it may be necessary to use multiple bone screws on both the upper and lower jaw to present enough ratchet heads or interarch receptacles so that the patient's jaws are maintained in the preferred rigid closed position by the flexible straps.
In another embodiment of an intermaxillary fixation accessory, the innovative washer for fastening to a bone screw may also be attached to a flexible strap, an embodiment of which is shown in
In some embodiments the bone screw must be inserted through the washer prior to placing the bone screw in the jaw. In other embodiments, the washer component is a slotted washer that has one end of its slot large enough to pass over the head of the bone screw and the other end of the slot small enough that it will not pass over the head of the bone screw. This allows the bone screw to be placed in the jaw and then the washer passed over the screw head and then manipulated so that the narrow portion of the slot underlies the head of the screw such that it cannot be removed without loosening or removing the bone screw. This also allows the washer assembly to be removed from the bone screw without fully removing the screw, in instances where the fastening assembly must be adjusted or replaced. Substantial care must be taken when applying washers with bone screws to not unduly compress gum tissue as doing so can cause permanent damage to the patient's gums.
Another novel tool for intermaxillary fixation is a flexible strap-compatible bone screw. As shown in
The inventive screw is installed in a traditional manner by driving the threaded portion of the shaft in to the bone of the patient. In an embodiment with the ratchet head incorporated into the head of the bone screw, the openings of the ratchet head are aligned as needed for clamping the jaws together, and are often oriented in an up and down orientation, with respect to the jawline of the patient. A flexible strap is inserted into the ratchet head. When the bone screw is mounted in the lower jaw, the orientation of the ratchet head and flexible strap is reversed.
In another embodiment the ratchet head is not integrally formed with the bone screw and must be inserted into the cavity in the head of the bone screw. When this embodiment of the bone screw is installed in the jaw of a patient, the openings of the cavity and the optional retaining ledge are oriented generally toward the opposite jaw. The ratchet head is then installed into the cavity. Any protrusions on the ratchet head are disposed away from the opposing jaw so that the pulling force exerted by the flexible strap will pull the ratchet head farther into the cavity in the bone screw. In some circumstances, bone screws are presented in both the upper and lower jaw and are substantially aligned. A double-ended flexible strap may be provided and inserted into the ratchet heads on both bone screws. Thus, as the double-ended flexible strap is pulled upward through the ratchet head in the top bone screw and downward through the ratchet head in the lower bone screw, the patient's jaws are forced together.
For those instances where a patient presents with upper, lower or both upper and lower dentures, the full interarch bar fixation assembly may not be effective because the dentures do not afford the stability necessary for good intermaxillary fixation. It is desirable, however, to fix the jaw in place with the dentures inserted so that as jaw bones heal they are healed in the configuration, orientation and spacing necessary to accommodate post-procedure denture usage that is appropriate and patient friendly. Fixing the jaws together without the dentures in place would likely result in improper post-procedure denture fit because the bone alignment would be different from the bone alignment at the time the dentures are originally fitted.
Some current methods for intermaxillary fixation when a patient has dentures involve an elaborate process of wiring the dentures in place. For the lower dentures, a hole is generally made between the patient's gum and cheek tissue oriented downward and passing along the patient's jaw, exiting under the chin. A second hole is then bored upward through the floor of the patient's mouth adjacent the inner edge of the jaw and gums. This bore is generally made with a pointed or sharp instrument such as an awl or trochar. The dentures are then placed over the patient's gums and a wire is inserted through the hole between the patient's cheek and gum, passed downward below the patient's chin and then back upward and through the bore that is interior the patient's jaw bone. The wire is passed over the dentures and twisted or otherwise secured to itself so that the dentures are pulled downward on to the patient's gum and retained rigidly in place. A plurality of these circum-mandibular wires may be necessary to rigidly fix the lower dentures in place. In some cases this requires two sets of holes on either side of the patient's mouth, and in practice as many as four to six sets of holes may be used.
For dentures on the upper jaw, multiple bone screws through the patient's hard palate can be used to secure the dentures in place. In the alternative, holes can be bored in the upper gum to allow wires to pass through these holes in the piriform aperture adjacent to the nose, and these wires are then tied around the circum-mandibular wires (wires around the lower jaw). Another alternative is to fix screws into the patient's upper jaw and then fastening wires to the screws which are then secured to bone screws in the lower jaw bone or, in some instances, to additional wires passed through holes drilled in the gum line (circummandibular wires).
The use of wires to tie the dentures in place is not desirable because of the difficulty in positioning the wires, the propensity of the wires to cause sores within the patient's mouth and for the ends of the wires to gouge patient's jaws, cheek, tongue and the like. Moreover, as is well known, the use of wires in a patient's mouth often results in injuries to the physician, orthodontist and other medical staff during placement, adjustment and removal. One of the inventive devices that overcomes many of these limitations and drawbacks is an improved zip tie assembly that can be substituted for the wires in the process described above. In one instance, shown in
In practice, the dissection tip of the flexible strap is used in a similar manner to an awl or trochar for creating tissue access for wire placement. The flexible strap is pushed, passed or guided through the tissue adjacent the gum and then passed through a small incision made below the patient's chin and then back up through the tissue thereby encircling the lower jaw and any associated dentures or dental blocks. Likewise, for application on an upper jaw of a patient, bores through the patient's gum, such as commonly used for that application are formed. A flexible strap can then be positioned through the bore around the jaw and fastened to a ratchet head on the other end of the flexible strap to hold the upper dentures in place. Multiple bores with multiple fasteners may be necessary to firmly secure dentures to the patient's upper gums. Once the dentures are fastened in place, the upper and lower jaws can be fixed together by traditional means, or by fastening interarch bars to the upper and lower teeth, whether natural or dentures, and then using an interarch bar attachment assembly such as that disclosed in the Shah patent. Alternatively, the innovative washer attachment system described herein may be utilized for intermaxillary fixation once the dentures are secured in place.
In those instances when a patient presents with no teeth whatsoever and dentures are not provided or otherwise available, another embodiment of the invention may be used to securely fix the patient's jaws. As described above, it is not desirable to fix the patient's upper and lower jaws together for bone healing when there are no teeth or dentures present. Doing so results in improper jaw bone alignment during the healing process and may make it difficult, if not impossible, for subsequent use of dental implants or dentures. In other embodiments of the invention, as shown in
As shown in
Another inventive tool is a unique trochar or awl that is provided with a unique retention member at or substantially near the blade or dissection tip of the awl. The retention member is configured to engage and frictionally retain a knob provided on another embodiment of the flexible strap which may be used as a circum-mandibular strap. In some embodiments, a slot may be presented in the blade of the awl to engage a pin attached to the circum-mandibular strap being placed through tissue contemporaneously with advancement of the awl through the tissue. The awl is used in a manner similar to a trochar or awl would be used to form a path around the patient's jaw for securement of dentures or a dental block as described above. Once the circum-mandibular cable has been placed around the patient's jaw as described, the cable is disconnected from the awl by simply disengaging the pin on the strap from the retention member.
Referring now generally to the drawings, the instant invention relates to devices to improve intermaxillary fixation for patients who do not have all, or any, of their teeth. The inventive devices and methods disclosed herein may be utilized separately or in conjunction with arch bar fixation devices described in the Shah patent to provide intermaxillary fixation for patients missing some or all of their teeth.
In various embodiments of the devices disclosed herein, various ratchet components and straps with ratchet teeth are described. In the depicted embodiments, the straps are provided on one surface with a gear rack section provided with a plurality of ratchet teeth or serrations. A first or male end of the strap may have a narrowing or pointed end or a blunt end. The strap itself may be a flat tape, have a circular cross-section, or other similar shapes. The strap is preferably formed from a flexible but strong material. In some embodiments, a second end of the strap is provided with a ratchet head with a port through the head. Inside the port, a pawl is provided to engage ratchet teeth disposed on the strap. When the first end of the strap is inserted through the port in the ratchet head, the ratchet teeth engage the pawl to allow the strap to be pulled through the port but not to be retracted from the port.
For clarity, the second end with the ratchet head, sometimes referred to as the female end, of a zip tie or strap may be referred to herein as an interarch receptacle and the first or male end may be referred to as a flexible strap provided with ratchet serrations or teeth. It should be understood that the interarch receptacle includes a port and a flexible retention member, or pawl, as is commonly found with the ratchet head, or female end, of a cable or zip tie.
Some embodiments of the flexible straps are attached at one end to an inventive washer described in relation to the figures. Some embodiments of the flexible straps have two male ends, each with a section of ratchet teeth oriented in opposing directions, which may be referred to as a double-ended flexible strap. Each end of the double-ended flexible strap may be inserted into opposing interarch receptacles or ratchet heads to fix the patient's jaws together, as is described in more detail in relation to the figures. The various embodiments of the flexible straps are inserted through the port on the ratchet head, thereby engaging the ratchet teeth on the flexible strap with the pawl and allowing insertion of the flexible strap but not its removal from the port. In some embodiments the flexible straps are flexible along their length in one or both axes perpendicular to the longitudinal axis of the strap, so that they may be bent, curved or twisted in simple or compound curves as necessary. In some embodiments the flexible straps have limited extensibility or compressibility parallel to their longitudinal axis.
As best shown in
When installed in a patient's mouth, the bone screw 104 is fastened into the jaw bone of the patient in a location where one or more teeth are missing. The installed hanger assembly 100 disposes the ratchet head 102 adjacent to the areas of missing teeth so that an interarch receptacle on an arch bar may be secured to the ratchet head 102 and thus to the jaw. In some embodiments, bone screw 104 may be provided with a bearing area 103 disposed on the shaft 105 of the bone screw 104 adjacent to the head 107. The bearing area provides a surface for contact with the washer 106 to allow the washer to rotate smoothly. The surface of bearing area 103 may be flat, concave, convex or textured as desired.
As shown in the previously referenced Shah patent, interarch receptacles are positioned along the arch bar for the receipt and retention of a flexible strap or the male end of a zip tie. In use, the inventive receptacle hanger 101 is positioned on the patient's jaw opposite an interarch receptacle, or zip tie receptacle, mounted on the arch bar or ratchet head attached to another bone screw 104 on the opposing jaw of the patient.
For example, if the patient presented with no teeth on the left upper jaw but has teeth on the lower left jaw, an arch bar may be fastened to the lower teeth. A bone screw 104 could be mounted in to the upper left jaw bone of the patient opposite the interarch receptacles presented on the arch bar fastened to the left lower teeth. In some embodiments the washer 106 of the receptacle hanger 101 may be placed over the threaded shaft 105 on the screw 104 and simultaneously mounted with the bone screw 104. In other embodiments the slotted or wide portion of the washer 106 may be slipped over the driving head 107 of the bone screw 104 after it has been secured in the patient's jaw bone. The interarch receptacle 102 is generally oriented so that a zip tie or flexible strap having reversed teeth at opposite ends can be inserted in to both the interarch receptacle and the opposed ratchet head 102 so that when the patient's jaws are closed together the zip tie or flexible strap holds the opposing arch bar receptacle and ratchet head 102 and associated arch bar (on the lower teeth) in place.
In situations where multiple teeth are missing from both the upper and lower jaw of the patient, it may be necessary to use multiple bone screws 104 and receptacle hangers 101 on both the upper and lower jaw to present enough ratchet heads so that the jaws are maintained in the preferred rigid closed position by the flexible straps.
Referring now to
Referring now to
In some embodiments, the driving head 202 includes a cavity 206 for receiving a removable ratchet head 208. The cavity 206 is an opening laterally through the elongated driving head 202 of the bone screw 200 in to which a ratchet head 208 may be inserted. The ratchet head 208 may be frictionally retained, adhered or otherwise secured in cavity 206. The cavity 206 may include a small ledge or other retention member along one edge 211 of the cavity 206 to further engage and retain the ratchet head 208 in place. In some embodiments, the ratchet head 208 may be formed with at least one lip or protrusion 210 that engages the driving head 202 adjacent the cavity 206 to prevent the ratchet head 208 from passing through the cavity 206. In some embodiments, ratchet head 208 may also be provided with slots or flanges 212 to engage the edge 211 of cavity 206 to engage and retain the ratchet head 208 in cavity 206.
The bone screw 200 is installed by driving the threaded shaft 204 into the bone of the patient. The openings of the cavity 206 are preferably oriented in a vertical position with respect to the jawline of the patient. When the screw 200 is installed in the jaw of a patient, the ratchet head 208 is disposed in cavity 206 with protrusion 210 disposed generally on the side of driving head 202 away from the opposite jaw. A flexible strap such as 110 is then installed into the ratchet head 208 by passing one end of the flexible strap through the ratchet head 208. When the other end of the flexible strap is attached to another interarch receptacle, ratchet head, or bone screw and tightened to hold the jaws of the patient together, the flexible strap will pull interarch receptacle 208 into cavity 206 maintaining protrusion 210 securely against the edge of cavity 206. The protrusion 210 engages a portion of the driving head 202 adjacent to the cavity 206 such as edges 211 and prevents the ratchet head 208 from passing through the cavity 206. Where opposing screws are presented in both the upper and lower jaw, a reversing zip tie or double-ended flexible strap, where the teeth on one end of the flexible strap are reversed from the teeth on the other end, is provided. The teeth disposed in opposite directions allow each end of the double-ended flexible strap to be inserted into opposing interarch receptacles or ratchet heads for securing the opposite jaws together. This double-ended flexible strap is positioned within and manipulated through the ratchet head 208 and secured by the ratchet inside the ratchet head 208 engaging the teeth on the flexible strap. As the reversing zip tie or double-ended flexible strap is pulled through the ratchet head 208 and through the opposed interarch receptacle or ratchet head, the patient's jaws are forced together and secured in a closed position.
In those instances when a patient presents with no teeth whatsoever on one or both jaws, and dentures are not provided or are otherwise not available, a different problem must be overcome. It is not desirable for bone healing to fix the patient's upper and lower jaws together when there are no teeth or dentures present. Doing so results in improper jaw bone alignment during the healing process and may make subsequent use of dental implants or dentures difficult, if not impossible. To overcome this problem, an inventive set of dental blocks (sometimes referred to as dental splints) 300 has been designed and developed, an embodiment of which is depicted in
An upper dental block 302, shown in
Blocks 302 and 304 may be provided in various sizes to fit different patient's bites. When in place, the dental blocks 302 and 304 hold the upper and lower jaws apart a sufficient distance such that when the jaw bones heal, suitable space has been provided between the jaw bones for proper placement of dental implants or dentures. If a patient has teeth on one jaw but not on the other, only one of blocks 302 and 304 may be necessary.
In some embodiments, each dental block 302 and 304 is provided with multiple receptacles or ratchet heads for receiving the male end of a zip tie or a flexible strap. In some embodiments, the ratchet heads or receptacles may be fixedly or pivotally attached directly to the blocks 302 and 304 at various locations around the outside plate 301 of each block 302 and 304. In the embodiment shown in
Rail 303 provides a means of attaching a plurality of ratchet heads or receptacles 310 to the rail for attaching the dental blocks 302 and 304 to a patient's jaws and to the other dental block. In the depicted embodiment, bores, holes or indentations 307 are provided at numerous locations along the length of rail 303. If indentations that do not extend completely through rail 303 are provided at locations 307, a corresponding indentation may be provided on the inside surface of rail 303 facing the outside plate 301. In some embodiments holes 307 will extend completely through rail 303. In some embodiments, receptacles 310 may be provided with screws or locking pins for inserting into holes 307. In other embodiments, such as that shown in
The upper edge 309 of the outside plate 301 of lower dental block 304 may be provided with various undulations, lower portions, higher portions, raised portions, or indentations along the length of the outside plate 301. Similar undulations, raised portions or indentations may be provided on lower edge 311 of upper dental block 302. The varying shape of the upper edge 309 and lower edge 311 may be designed to interact with the patient's teeth and the other dental block to create and maintain space for the patient's tongue and passageways between the dental blocks for airways, tubes, circum-mandibular straps, and other medical devices when the two blocks are in contact at the outside plates.
Referring now to
The dental blocks 302 and 304 are held in place using methods described herein for securing dentures in place, some of which are depicted in
Unique circum-mandibular straps 314 may be used to secure the lower dental block 304 in place. The circum-mandibular straps 314 are placed by methods similar to known methods of wiring lower dentures in place for intermaxillary fixation procedures. For securing the lower dental block 304 with circum-mandibular straps 314, as best shown in
Two perspective views of a similar embodiment of the dental block 302 is depicted in
Referring now to
Once the dental blocks are fixed in place, reverse zip ties or double-ended flexible straps 313 can be used in the receptacles 310 on the opposing dental blocks or opposing teeth to fasten the upper and lower jaws together. The edge 311 of upper block 302 may include an upper arcuate opening 315 and the lower block 304 may include a substantially similar, but opposing lower arcuate opening 316 so that when the dental blocks are in place, an annular opening is formed for access to the patient's mouth for cleaning, suction and the like, or in some instances, the placement of a breathing tube.
Referring now to
One of the inventive intermaxillary fixation accessories that can be used to place circum-mandibular straps 314 is an improved zip tie assembly or strap, one embodiment of which is shown in
In some embodiments, the male end 401 of strap 400 may have one or more sections 404 with a thinner profile or smaller cross-section than other portions of the strap 400 to ease insertion of the strap 400 through the patient's tissue. Between the sections 404 of the strap 400, some embodiments incorporate sloping sections 406 gradually narrowing the thickness or cross-section of strap 400 as it approaches the dissection tip 402.
Strap 400 is provided on one surface with a gear rack section 408 provided with a plurality of ratchet teeth 410. The second end of strap 400 is provided with ratchet head 412 with a port 414 through the head 412. Inside the port 414 a pawl 416 is provided to engage ratchet teeth 410. In some embodiments, the other ratchet heads described herein contain similar elements. As with the other straps used in the depicted embodiments of the invention, when the first end 401 of strap 400 is inserted through the port 414 in the ratchet head 412, the ratchet teeth 410 engage pawl 416 to allow the strap to be pulled through port 414 but not to be retracted from the port 414.
In practice, the dissection tip 402 of the strap 400 is used like an awl or trochar for wire placement. The strap 400 may be pushed through the tissue adjacent the gum and then passed below the patient's chin, creating a small loop and then back up through the tissue so the strap 400 encircles the jaw and any associated dentures or dental block. As the strap 400 is pushed through the tissue, dissection tip 402 cuts the tissue sufficiently to allow the strap 400 through the tissue.
Another inventive tool, as shown in
Referring now to
The general shape of the block 600 is semi-arcuate when viewed from above. In some embodiments the block comprises a substantially semi-circular front portion with substantially linear wings extending substantially tangentially to the circumference of the semi-circular portion. In some embodiments the plate 602 is substantially flat and extends perpendicularly to the outside plate 608. In some embodiments the inside plates 618 and 620 are provided adjacent to the inside edge of plate 602 and substantially perpendicular to the plate 602. The inside plates 618 and 620 and outside plate 608 generally run around the inner and outer periphery, respectively, of the patient's gums.
In some embodiments, a port 616 may be provided through the dental block 602. The port 616 may be used to suction the patient's mouth, insert tubes for air, nutrition or other needs, or other similar purposes.
As shown in
Many different arrangements of the various components depicted, as well as components not shown, are possible without departing from the spirit and scope of the present invention. Embodiments of the present invention have been described with the intent to be illustrative rather than restrictive. Alternative embodiments will become apparent to those skilled in the art that do not depart from its scope. A skilled artisan may develop alternative means of implementing the aforementioned improvements without departing from the scope of the present invention.
It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations and are contemplated within the scope of the claims. Not all steps listed in the various figures need be carried out in the specific order described.
This application claims the benefit of U.S. Patent Application Ser. No. 61/871,456 filed Aug. 29, 2013, the disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61871456 | Aug 2013 | US |
