Abstract:
Mandibular widening by symphyseal distraction osteogenesis is accomplished with the use of an appliance having first and second elongated support arms and an intervening displacement mechanism which, by rotation upon a horizontal axis, performs in the manner of a turnbuckle to force the arms apart. Lower apertures on the arms are attached to the mandibular bone, and upper apertures on the arms are attached to the teeth. Following a mid-symphyseal osteotomy and a latency period, the displacement mechanism is rotated according to a precise schedule to achieve widening of the lower jaw.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention concerns a mandibular distraction apparatus and its manner of use, and more particularly relates to an intraoral mandibular distraction apparatus for temporary attachment to the teeth and bone to produce osteogenesis by patient manipulation preparatory to an orthodontic remediation. 
     2. Description of the Prior Art 
     In a series of studies published by G. A. Ilizarov beginning in 1988, techniques were described for lengthening endochondral bones and the surrounding soft tissue matrix. In particular, it was shown that the genesis of new bone tissue between facing surfaces of a newly cut bone is dependent upon tension-stress effects associated with the rate and frequency of distraction, namely the forced separation of said facing surfaces. 
     In a series of studies published since 1997 by W. H. Bell and others, it was shown that the osteogenesis principles elucidated by Ilizarov can be facilitated with intraoral appliances to achieve mandibular widening by symphyseal distraction. Such technique has been found useful in facilitating orthodontic remediation of mandibular crowding and other conditions. The appliance employed by Bell, now marketed as DynaForm™ by Stryker Leibinger Gmb H of Freiburg, Germany, is comprised of two frames interconnected by an advancing screw rotatively held by a fixed yoke mounted upon paired slide posts. Each frame is comprised of a rigid bar base and superior and inferior elongated arms orthogonally emergent from said base and terminating in distal extremities directed away from said bases. The base of one of said frames functions a yoke moveable upon said screw and slide posts. The arms are bendable to match the patient&#39;s buccal mandibular contour, and securement forks or rings are crimped onto the distal extremities. When proper fitting has been achieved, the extremities of the upper arms are secured to mandibular teeth, and the lower extremities are secured to mandibular bone. 
     Following installation of the Bell appliance bridging the site of osteotomy, carefully controlled distraction to distances of 7 to 12 mm. is accomplished by an activation tool in the nature of a specialized screwdriver employed by the dentist to engage the horizontally directed head of the screw, and rotate the screw. 
     An intraoral palatal expansion device available from Orthodesign of Chicago, Ill. has been described by Liou, et. al. in the Journal of Craniofacial Surgery, Vol. 9, No. 6, pgs 564-71, Nov. 1998. The Orthodesign distractor is comprised of two laterally opposed arms and an intervening rotatable screw device in the nature of a turnbuckle having oppositely threaded screws telescopically interactive with a barrel-like body having a faceted central region. When emplaced, the arms attach to the bone of the mandible, and the screw device extends transmucosally within the vestibule of the mandible. Although the method of operation of the screw device is not disclosed by Liou, the distraction is presumably achieved by rotation of the barrel-like body of the turnbuckle, employing an open-ended hex wrench that engages the faceted central region. 
     It has been found, however, that bone-borne distraction appliances such as Liou&#39;s having only two attachment sites produce a V-shaped bone regenerate which is not as stable or desirable as a parallel regenerate, particularly in the case of symphyseal mandibular widening. It is further necessary that means be provided whereby the telescopic screw is caused to be parallel with the desired vector of distraction. 
     In order to achieve best osteogenesis results, a carefully prescribed rate of distraction is required, such as two 0.5 mm. increments/day. Such regimen is best achieved when the patient, parent or other caregiver can administer the prescribed rated of distraction at home. 
     It is accordingly an object of the present invention to provide an intraoral screw-activated appliance for mandibular widening by symphyseal distraction osteogenesis. 
     It is a further object of this invention to provide an appliance as in the foregoing object which will produce a substantially parallel bone regenerate. 
     It is another object of the present invention to provide an appliance of the aforesaid nature which can be patient-manipulated to achieve a carefully prescribed rate of distraction. 
     It is a still further object of this invention to provide an appliance of the aforesaid nature which allows for precise surgical placement such that the axis of screw rotation is parallel with the desired vector of distraction. 
     It is yet another object of the present invention to provide an appliance of the aforesaid nature having a low profile which results in greater comfort to the patient. 
     It is an additional object of this invention to provide an appliance of the aforesaid nature which is durable, reliable, and amenable to low cost manufacture. 
     It is a further object of the present invention to provide a method for mandibular widening employing the appliance of the aforesaid nature. 
     These objects and other objects and advantages of the invention will be apparent from the following description. 
     SUMMARY OF THE INVENTION 
     The above and other beneficial objects and advantages are accomplished in accordance with one aspect of the present invention by an intraoral appliance for mandibular widening by symphyseal distraction osteogenesis comprising: 
     a) first and second elongated support arms of substantially equal length disposed in facing opposition, each arm comprised of upper and lower aperture-equipped extremities, and a central portion, and 
     b) a displacement mechanism disposed between the central portions of said arms and interactive therewith, said mechanism comprising: 
     1) a turning barrel elongated upon an axis of rotation between first and second end walls, and having a substantially circular cylindrical exterior surface provided with an annular gripping zone comprised of six flat facets in hexagonal array, said facets having instructive indicia, 
     2) a machine screw having a proximal extremity attached to said first arm at said central portion and extending in threaded engagement with an axially centered threaded aperture in said first end wall, and terminating in a distal extremity located within said barrel, and 
     3) a measuring tube slideably emergent from said second end wall upon said axis and extending to a proximal extremity attached to said second arm at said central portion, the distance of emergence of said rod being dependent upon the degree of rotational movement of said barrel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing forming a part of this specification and in which similar numerals of reference indicate corresponding parts in all the figures of the drawing: 
     FIG. 1 is an enlarged vertical front sectional view of an embodiment of the distraction appliance of the present invention, shown in its starting position. 
     FIG. 2 is a view similar to FIG. 1 showing the appliance in its expanded, functional position. 
     FIG. 3 is a top view of the embodiment of FIG. 2 following customized modification to fit a patient. 
     FIG. 4 is a right end view of the embodiment of FIG.  2 . 
     FIG. 5 is a front view of the embodiment of FIG. 2 following a distraction procedure and still installed on an orthodontic patient. 
     FIG. 6 is a front view of the embodiment of FIG. 5 provided with a removable index for establishing precise surgical placement of the appliance. 
     FIG. 7 is a sectional view taken in the direction of the arrows upon the line  7 — 7  of FIG.  6 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1-7, an embodiment of the mandibular widening appliance  10  of the present invention is shown comprised of first and second elongated support arms  11  and  12 , respectively, and intervening displacement mechanism  13 . 
     Said support arms are of rigid but bendable metal construction, preferably fabricated as monolithic structures from metals such as stainless steel. The arms are of substantially equal length and mirror-image contour, having a central portion  14  and upper and lower portions  15  and  16 , respectively, provided with apertures  17 . The arms may be fabricated from wire stock, or may be otherwise fabricated to be of strong, thin construction. Apertures  17  may be fabricated by the bending of wire stock or by the drilling of ribbon stock or a molded piece. Apertures  17  may be either of full circular configuration, or of keyhole configuration having a partial circular configuration providing forklike access to the partial circle. 
     The support arms are configured such that lower portions  16  are substantially straight, and upper portions  15  are divergently directed by virtue of bending. The lengths of the upper and lower portions of each arm are substantially equal. 
     The exemplified embodiment of the displacement mechanism is comprised of a hollow turning barrel  18  elongated upon an axis of rotation  19  between first and second end walls  20  and  21 , respectively. Barrel  18  has a substantially circular cylindrical exterior surface  22  provided with an annular gripping zone  23  having six flat facets  24  in a hexagonal array centered upon axis  19 . The hexagonal configuration permits gripping by an open-headed hex wrench. The facets are provided with instructional indicia such as an arrow which indicates direction of rotation, and dots or numerals indicating extent of rotation. 
     A machine screw  25  having a proximal extremity  26  attached to the center portion of first arm  11  extends in threaded engagement with an axially centered threaded aperture  27  in first end wall  20 , and terminates in a distal extremity  28  located within said barrel. 
     A hollow measuring tube  29  having a proximal extremity  37  attached to the center portion of second arm  12  extends to a distal extremity  50  in threaded engagement with internal threading  30  within barrel  18 , and is slideably emergent from hole  38  in second end wall  21 . The direction of threaded engagement of said measuring tube with barrel  18  is opposite to the direction of threaded engagement of machine screw  25  with said barrel. Accordingly, rotation of barrel  18  upon axis  19  produces a turnbuckle effect wherein rotation of the barrel in one direction will bring the moveable threaded members together, and rotation in the opposite direction will drive said members apart. A series of millimeter rulings  36  are disposed upon the cylindrical outer wall  40  of said measuring tube. 
     The diameter of machine screw  25  is sufficiently narrow to enter the hollow region  39  of measuring tube  29 . By virtue of such manner of construction, the appliance of this invention has a very small overall length in its starting state, as shown in FIG. 1, and is capable of achieving distraction distances between 5 and 18 millimeters with accurate control by observation of the rulings  36  on measuring tube  29 . The displacement mechanism  13  is generally similar to an orthodontic device disclosed in U.S. Pat. No. 5,564,920 for expanding the upper jaw. 
     The configuration of the divergent upper portions  15  of the arms with respect to the corresponding lower portions is such that said upper portions are bent at an angle A with respect to the lower portion. The value of angle A is between 90 and 115 degrees. The length of the laterally directed segment  41  of said upper portion, measured between the center of upper aperture  17  and the site of bending  42 , is smaller than the length of the corresponding lower portion  16  measured between the center of the lower aperture and axis  19 . 
     A lower segment  43  of each upper portion  15 , will generally remain in straight alignment with the corresponding lower portion  16  of the arm. The length of said lower segment  43  will generally be shorter than the length of the corresponding laterally directed segment  41 . 
     The appliance is employed in a multi-step treatment protocol involving the following phases: 
     1) Pre-surgical orthodontics 
     2) A mid-symphyseal osteotomy 
     3) A latency period 
     4) A distraction period 
     5) A consolidation period 
     6) Post-surgical orthodontics. 
     The first phase of pre-surgical orthodontics is similar to preparing a patient for conventional orthognathic surgery. If needed, the maxilla is expanded via rapid palatal expansion to its ideal width and arch form. It is advisable to diverge the roots of the teeth adjacent to the surgical site (usually the mandibular central incisors). However, a step-osteotomy may be performed between the central and lateral incisors, or even the lateral incisors and the canines. The surgery can be performed without opening space between the crowns in the surgery site. 
     The appliance is then custom fitted in a dental laboratory to a model based upon a lateral cephalometric x-ray, a P-A cephalometric x-ray and a mandibular alginate or PVS impression with a deep vestibular reflection in the anterior region. A submental vertex x-ray is also preferably provided. Such customization, achieved by accurate bending of arms  11  and  12 , particularly the upper portions thereof, and positioning of apertures  17 , causes the appliance to have a low profile with attendant greater comfort to the patient. 
     Said customization is also intended to ensure that axis  19 , which represents the direction of extension of the appliance, will be aligned parallel to the desired vector of distraction, namely parallel to the mandibular transverse occlusal plane. Said alignment is achieved by fitting the appliance, shaped by the precise bending of arms  11  and  12 , to the model. When the correct position on the model is verified, a light body P.V.S. (polyvinyl siloxane) or equivalent removable molding composition is applied over the anterior teeth and further extended and shaped laterally to span and embrace the upper portions  15  of said arms. The cured, shaped spanning composition molded onto the appliance represents an “index”, designated by numeral  45  in FIG. 6, which defines the precise positioning of the customized appliance. The index is further characterized in having a trough-like portion  46  adapted to fit precisely upon the anterior teeth  47 . 
     A maxillary impression is taken to construct a bite plane, to be utilized during the distraction phase. To determine the amount of distraction needed, a diagnostic setup may be utilized. This may be necessary to determine arch width discrepancies or, to more precisely calculate the amount of crowding and/or protrusion. 
     The patient is placed in a semi-reclining position. Intravenous general anesthesia is given. Local anesthesia is administered for hemostasis and postoperative pain control. A horizontal incision is made with a #15 blade in the oral mucosa of the lower lip approximately 8 mm. from the mucogingival reflection extending from the right canine tooth to the left canine tooth. The incision is carried through mucosa, submucosa, muscle, and periosteum. A full thickness subperiosteal flap is elevated inferiorly and the symphysis is completely degloved including the inferior border. 
     The custom designed distraction appliance with attached index is taken to the mouth and seated onto the anterior teeth. The appliance is attached to the bone of the symphysis with two 2.0 millimeter×10millimeter bicortical bone screws  48  through the apertures  17  of the lower (inferior) portions  16 . The index is then cut and peeled away from the appliance. Correct positioning of the appliance is checked for the apertures of superior extremities  15 . The appliance is then attached to the canine (or other designated tooth) on either side of the planned osteotomy with circumdental 24-gauge stainless steel wire and light-cured resin. A flowable composite, such as Kerr Revolution or Transbond LR, will work well. Superiorly, a tunnel is developed in the midline beneath the attached gingiva up to the gingival margin. A bone bur is used to score the midline of the mandible in a vertical direction. A reciprocating bone saw is then used to create a vertical midline osteotomy  35  out from the inferior border of the mandible up to the apices of the incisor teeth. A narrow osteotome and mallet are used to complete the cut between the roots of the central incisor teeth (or teeth indicated, if a step osteotomy is being performed). The two halves of the mandible are then mobilized. The appliance is activated 2.0 millimeters to ensure adequate separation and mobilization of the osteotomized segments. 
     The appliance is deactivated after separation and mobilization is confirmed. The wound should be thoroughly irrigated with normal saline solution. Incision closure can be made with multiple interrupted sutures of 4-0 Vicryl material. A pressure dressing is then applied. A 0.12% chlorhexidine oral rinse is prescribed to the patient for 1 week post-operatively. 
     After a seven-day latency period, the patient is scheduled in the surgeon&#39;s office to start the distraction period. Patients are requested to make two 0.5-millimeter activations per day. This is easy for the patient, especially when one complete revolution of barrel  18  yields one millimeter of distraction, corresponding to a one millimeter extrusion of measuring tube  29  from said barrel. For this reason, an arrow which shows direction of rotation appears on one facet  24 , and a dot or other indicia appears on an opposite facet, indicating the extent of barrel rotation. 
     During this phase, it is advisable to see patients every two to three days. Not only will the surgeon ensure that the appliance is being activated, but the total amount of distraction can be determined by inspection of the incremental markings on tube  29 . Activation continues in said manner until the desired amount of distraction is achieved. 
     Once distraction is complete, the anterior portion of the arch wire is cut so that a sectional arch wire can be placed. The purpose of this wire is to support the placement of a pre-selected denture tooth. This will improve cosmetics, as well as, support the dentition, during the consolidation phase. 
     Following distraction, a flowable bonding compound is applied to machine screw  25  and measuring tube  29  to ensure against any retractive motion of either component. Although there is very little, if any relapse, it is preferable that a slight over-distraction be employed. 
     The consolidation period will generally vary from eight to twelve weeks. During said period it is preferable to monitor the regenerate through occlusal and periapical x-rays every three to four weeks. The appliance is not removed until bony bridging of the adjacent sides of the osteotomy is seen completed. It is further preferable to see radiographic evidence of the mineralization of the inferior cortex before removal. The removal of the appliance is easily made with local anesthesia and stab incisions. 
     As seen from P-A cephalometric x-ray, the appliance of this invention produces a parallel regenerate. Thus, there is a proportionate widening of the dento-osseous segments. With basal bone being expanded proportional to the alveolar bone, it is considered that this type of expansion provides greater stability than tooth-borne appliances of the prior art which produce a V-shaped regenerate. 
     Following the consolidation period of 8 to 12 weeks, the appliance is removed, and post-distraction orthodontic treatment may begin. It is preferred that movement of single rooted teeth into the regenerate should not be initiated for at least 8-12 weeks following distraction. Tooth movement through regenerate bone has been found to occur at a faster rate than through the normal host bone. 
     While particular examples of the present invention have been shown and described, it is apparent that changes and modifications may be made therein without departing from the invention in its broadest aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall within the true spirit and scope of the invention.