Removable resilient orthodontic retainer

An orthodontic retainer which has an upper portion and a lower portion, with the upper defining an upper labial arch filament (20) positioned around anterior surfaces of a patient's teeth attached on each end to a pair of upper clasps (22). The clasps surround upper midregion teeth and are embedded into an upper lingual resilient thermoplastic bridge (32) that include a U-shaped posterior bridge integral with a palatal bridge leaving an open area (38) therebetween. The lower portion of the retainer utilizes a similar filament (40) and clasps (42) with the lower bridge (44) in horseshoe shape. The combined rigid clasps and resilient thermoplastic memory characteristics of the filament and bridges maintain a patient's tooth location and attitude. A second and third embodiment add resilient wire (46) at appropriate locations within the thermoplastic bridges (32) and (44) magnifying the memory characteristics of the retainer.

TECHNICAL FIELD 
The present invention relates to orthodontic retainers in general. More 
specifically to removable retainers having resilient bridges and labial 
arches for holding teeth in position after correction. 
BACKGROUND ART 
Previously, many types of retainers have been used in endeavoring to 
provide an effective means for retaining a patient's teeth after 
orthodontic corrections of malocclusions have been made. Most of the prior 
art utilizes the same basic approach as the orthodontic appliance used to 
make the original rectification, as in most cases, the appliance is rigid 
and designed to place pressure at specific points and areas. The prior 
retainers utilized a combination of steel wire, springs and elastic bands, 
along with a thermoset plastic bridge most commonly using a hard acrylic, 
such as methyl methacrylate. 
The Hawley retainer is well known in the art and has been in use for many 
years. This retainer consists of acrylic covering the full palate, along 
with the lingual mucosa area and is sometimes vented to expose selected 
palatal regions. While prior art has accomplished much using rigid 
materials, a search did not disclose any patents that rely upon resilient 
structure for retention, however, the following U.S. patents are 
considered related. 
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U.S. Pat. No. Inventor Issue Date 
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5,376,001 Tepper Dec. 27, 1994 
5,167,499 Arndt et al Dec. 1, 1992 
5,096,416 Hulsink Mar. 17, 1992 
4,976,614 Tepper Dec. 11, 1990 
4,468,196 Keller Aug. 28, 1984 
4,433,956 Witzig Feb. 28, 1984 
4,416,626 Bellavia Nov. 22, 1983 
4,028,808 Schwartz Jun. 14, 1977 
3,162,948 Gerber Dec. 29, 1964 
1,582,570 Brust Apr. 27, 1926 
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U.S. Pat. No. 5,376,001, issued to the present inventor, discloses a 
removable orthodontic appliance which utilizes a similar pair of clasps 
seated over midregion teeth connected to a labial arch wire. A pair of 
structural braces, either molded wings or connecting sections are attached 
to a radial loop of metal forming a palatial bridge. The loop preferably 
made of memory metal having the consistent tendency to return to its 
original state exerts persistent linear force in the opposite direction of 
deformation. The clasp is made of three pieces of tube and wire, and wings 
that are formed of rigid mono-methylate, which sets quickly under ultra 
violet light. 
Arndt et al, in U.S. Pat. No. 5,167,499, disclose a removable orthodontic 
palatial expansion arch in an "M" shape of nickel titanium wire attached 
to a metal band surrounding the upper first permanent molars. 
U.S. Pat. No. 5,096,416 of Hulsink teaches an orthodontic retainer made of 
hard non-moving acrylic sections interconnected by resilient wires. A 
spring arm made of acrylic covered wire engage the labial surfaces of the 
four front teeth. A pair of Adam's clasps supported by a rigid plate 
extend over the first molar assisting in clasping the retainer in place. 
It will be noted that all of the plates are rigid and the resiliency is 
provided by flexible wires. 
U.S. Pat. No. 4,976,614, also issued to the present inventor, utilizes 
midregion clasps and a label filament serving as a reference arch, along 
with a curved lingual spring filament urging the teeth against the 
reference. Synthetic resin filaments of transparent material hold the 
teeth to prevent relapse. A sinuous palatal arch wire, continuous in form, 
but having cyclic variations, extends across the patient's palate and 
provides a spreading force upon clasps attached to opposed pre-molar or 
bicuspid teeth. In another embodiment opposed facing palatal wings of hard 
material encompass the gingival region of a number of molars and include a 
wire arch device which extends back across the roof of the patient's 
mouth. 
Keller's U.S. Pat. No. 4,468,196 employs a method of treatment and an 
apparatus which includes bands around selected molars and an arch wire 
with springs that exert a specific force. A bracing wire is placed in 
contact with the buccal surfaces of the front teeth and is covered with a 
hardenable acrylic. 
Witzig, in U.S. Pat. No. 4,433,956, employs acrylic anterior segments over 
the front teeth in conjunction with an expandable screw, connecting a 
similar posterior segment over the mid-range teeth. The appliance is 
adjusted in stages to correct lower jaw movements. 
U.S. Pat. No. 4,416,626, issued to Bellavia, teaches a method and apparatus 
which utilizes acrylic wings with caps that cover screw adjusting 
mechanisms and alignment pins. 
For background purposes and as indicative of the art to which the invention 
is related, reference may be made to the patents issued to Schwartz, 
Gerber and Brust. 
DISCLOSURE OF THE INVENTION 
The field of orthodontic appliances and retainers is replete with structure 
using wires, bands, clasps, springs, screw adjustments, bridges, and the 
like, for holding teeth and creating movement. In some cases, the 
appliance is attached to the patient's teeth directly and stays in place 
until the malocclusion is corrected. Other appliances are removable and 
adjustments are made over periods of time to complete the correction. In 
order to prevent relapse when the orthodontic treatment is concluded, a 
retainer is worn by the patient. As previously discussed, retainers 
include a lingual portion that is custom fit to generally engage the 
undercuts of the teeth, and wire members are embedded to coact with the 
teeth for securement. The most widely used appliance of this type is known 
as the Hawley retainer and, along with it, variations are constructed of a 
hard unyielding acrylic and act as a rigid barrier. It has been known that 
this popular retainer has had some asperity in fabrication, as removal 
from the model has proven difficult due to the hard nature of the acrylic. 
It is, therefore, a primary object of the invention to, not only overcome 
this difficulty in fabrication, but to add an entirely new aspect to 
retainers in general. The present invention utilizes an injection molded 
thermoplastic as the material for the bridge structure. This novel 
approach now creates an appliance that actually exerts a gentle but 
constant force on only the teeth that have the tendency to revert from 
their final corrected position. A labial arch filament that is registered 
around the anterior teeth provides the limit position and a bridge of 
resilient thermoplastic is in intimate contact with the undercuts of all 
of the representative teeth providing control that has infinite memory 
and, yet, is flexible enough to be comfortable and utilitarian. Clasps of 
a memory metal apply tension on the labial arch filament, which by itself 
is a flexible thermoplastic. The retainer, or positioner, now places 
pressure only where required and may be worn with ease for long periods of 
time, including eating meals. 
An important object of the invention is the ability to make minor tooth 
movements including rotations and even bodily movements by simply 
correcting the inaugural plaster cast by removing and resetting the image 
to the desired position and recasting the mold. This flexibility permits a 
broad spectrum of corrections to be made with little effort and the memory 
characteristics of the resilient thermoplastic provides the needed 
constant force. 
Another object of the invention is directed to the labial arch filament, 
which may be transparent and hardly visible at a distance. This cosmetic 
effect has a desired appeal for many, or on the other hand, the arch 
filament may be colored brightly for those desiring novelty. 
Still another object of the invention is the open palatal area of the upper 
portion of the retainer. By having the roof of the patient's mouth open, 
proper proprioceptive tongue posture is realized. Further, wearing the 
retainer during eating is not only possible, but tongue function is 
enhanced due to the complete lack of obstruction to the palatal rugae 
region and minimal contact with the mucosal tissue. 
Yet another object of the invention is the lack of physical weight of the 
appliance, as it is thin and formed of relative light components, 
therefore, the combined device has little weight which adds considerably 
to the comfort of the patient when wearing the device. 
A further object of the invention has to do with the basic materials, which 
individually are not toxic and are allergy free. All materials used in the 
invention have already been cleared by the Food and Drug Administration 
for similar applications. 
A final object of the invention is the use of a two-piece clasp bracket 
that is unique and novel in its own right. The clasp is made of only two 
pieces of wire that are brazed together with cadmium free silver solder. 
This clasp consists of an omega loop wire and a marginal ridge wire with 
the loop flattened on one end. The marginal ridge wire is rectangularly 
formed with the exposed ends opposed and may be used as clamps or levers. 
The clasp is fabricated in the flat and the dental technician may then 
individually form the assembly into the configuration required, right or 
left hand, including rolling the flattened end of the loop into a filament 
receiving circular ring. This construction technique simplifies 
fabrication of the appliance, as clasps may be mass produced on wire 
forming equipment, thus reducing the labor content of the dental 
practitioner and overall expense. 
These and other objects and advantages of the present invention will become 
apparent from the subsequent detailed description of the preferred and 
other embodiments, also the appended claims, further taken in conjunction 
with the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
The best mode for carrying out the invention is presented in terms of a 
preferred, second and a third embodiment. All three embodiments are 
primarily designed alike, except the second and third have added structure 
to the basic preferred embodiment. 
The preferred embodiment, as shown in FIGS. 1 through 8, comprises an 
orthodontic retainer for both the upper and lower dental arches to be used 
in concert, or singly if the occasion arises. The upper portion of the 
retainer is illustrated in FIGS. 1, 3, 5 and 6 and consists of an upper 
labial arch filament 20 that is contiguous with the labial surfaces of the 
patient's upper anterior teeth for creating a limiting position. The 
filament 20 is made of a thermoplastic material having a relative high 
tensile yield strength. While any thermoplastic filament having the 
requisite characteristics may be used, it has been found that a nylon 
formulated of hexametylenediamine and dodecanedioic acid, as manufactured 
by DuPont under the designation nylon 612 and registered tradename TYNEX 
is ideal. The nylon filament 20 may be utilized in this invention in its 
transparent form or may be colored a variety of bright hues, which may be 
attractive to the younger patient wearing the retainer. 
A pair of upper clasps 22 secure the filament 20 at each end. These clasps 
22 removably engage the upper midregion teeth on opposite sides, as shown 
in FIGS. 1, 3 and 5. The exact attaching tooth may vary as to the 
individual patient's requirements, however, the drawings illustrate the 
second bicuspids. The clasp 22 in this combination is unique in and of 
itself, as it may be mass produced in the flat and formed into shape by 
the dental practitioner at the time of fabrication. It will be noted that 
the present inventor has already applied for a separate design patent for 
the clasp in the flat and it is presently pending under Ser. No. 
29/043,770. The clasp 22 is shown in the flat in FIG. 7 and formed into 
the final usable shape in FIG. 8. Each clasp 22 consists of a marginal 
ridge wire 24 that is formed into a rectangular shape with upper end 
segments bent angularly inward until they almost touch and then sharply 
bent outwardly in opposed directions, thus forming a T-shape on top. An 
omega loop wire 26 is formed in a "U" like loop shape described as having 
a first end and a second end for clarity. The first end is depicted on the 
left and has a right angle step downward. The second end also distends 
downwardly from the loop and is flattened 28 on the terminating end. The 
two elements are aligned, with the second end of the loop 26 disposed 
contiguously between the inwardly bent portions of the marginal ridge wire 
24. The intersecting joint is brazed with cadmium free silver solder 30, 
preferably 45/30/25 alloy per Federal standard QQ-B-654. The above wires 
24 and 26 are preferably stainless steel, however, other wire materials 
may be substituted with equal ease. 
FIG. 8 depicts one configuration of the clasp 22 with the flattened end 28 
of the loop wire 26 rolled into a cylindrical shape to receive the labial 
arch filament 20. The clasp is bent to surround the appropriate tooth with 
the rectangular end of the ridge wire 24 conforming to the slope of the 
patient's adjacent mucosal tissue. It should be noted that the final shape 
will differ considerably, as each clasp must be custom fit to accommodate 
the patient's oral configuration. 
The upper clasps 22 are joined together with upper lingual resilient 
thermoplastic bridge means 32, which comprise a U-shaped posterior bridge 
34 from lingual surfaces of a patient's mucosal tissue and teeth up to and 
including second molars, when present. This bridge 34 is formed integrally 
with a posterior palatal bridge 36 that spans the patient's palatal arch 
region. An open area 38, surrounded by these bridges 34 and 36, 
circumvents the patient's palatal regae region allowing proper 
proprioceptive tongue position relative to the rugae. The open area 38 
also permits greater lateral and longitudinal flexibility of the retainer. 
The configuration and attaching points of the clasps 22 embedded into the 
bridge means 32 maintain the patient's tooth location and attitude by the 
combined effort of the rigidly attached clasps 22 and the memory 
characteristics of the resilient thermoplastic bridge means 32, as 
previously discussed. In order to achieve the most notable results, the 
resilient thermoplastic must have substantial memory and structural 
integrity to accomplish the retaining ability and minor rotations and 
bodily movement built into the appliance. There are many resilient 
thermoplastic materials that meet the design criteria, such as a 
formulation of polybisphenol-A carbonate, manufactured by General Electric 
under its tradename LEXAN, or Mobay Chemicals under its tradename MERLON, 
which has been found to be the forerunner material. Hexametylenediamin and 
dodecanedioic acid manufactured by DuPont et al under the generic name 
nylon is also acceptable, along with a proprietary material manufactured 
by, and designated, VALPLAST. Other materials include a combination of 
polybisphenol-A carbonate and hexametylenediamine with dodecanedioic acid 
(nylon) and also a natural based thermoplastic of vulcanized rubber. Still 
other resilient thermoplastics include solid polyurethane elastomers 
produced by numerous manufacturers, such as Stevens Molded Products, under 
their registered trademark HI-TUFF and many others. 
The upper bridge means 32 is constructed using the well known and popular 
injection molding process applying the so-called last wax procedure for 
developing the mold. The thermoplastic, in granular form, is heated to 
plasticity in a cylinder, then forced through sprues and runners into a 
controlled temperature mold, forming the bridge with the clasps 22 
embedded at the appropriate location. This procedure leaves the bridge 
finished with no polishing or trimming necessary. As previously mentioned, 
easy modifications in the original plaster cast permit the final 
configuration to include the corrections needed to apply pressure from the 
resilient material to straighten or move teeth, as required. 
The lower portion of the orthodontic retainer is depicted in FIGS. 2, 4 
through 6, and is basically the same as the upper portion. A lower labial 
arch filament 40 is of the same material and is registered about the lower 
labial anterior teeth surfaces in the same manner. Each lower clasp 42 is 
identical to start with, in the flat, as shown in FIG. 7, however, it is 
bent into a reverse image for the lower connection to the teeth and 
bridge. The lower lingual resilient thermoplastic bridge 44 is joined to 
the lower clasps 42 and is in a horseshoe shape. As with the bridge means 
32, the lower bridge 44 proceeds around the lingual surfaces of the 
patient's mucosal tissue and teeth up to and including the second molars, 
when present. The materials of both the lower filament 40 and lower bridge 
44 are the same as their corresponding elements 20 and 32. 
The second embodiment is depicted in FIGS. 9 and 10 and differs only in the 
addition of at least one resilient wire 46 embedded in the upper and lower 
portion of the retainer. Specifically, the upper portion illustrated in 
FIG. 9, preferably includes three separate straight wire segments 48, a 
pair of segments 48 parallel the patient's teeth on each side and an 
arched segment across the palatial bridge. While these are designated 
"straight", they may be arched to follow the contour of the bridge and, 
yet, are straight in one plane, as shown. The lower portion, likewise, 
includes a pair of straight segments 48 embedded on opposed sides between 
the patient's second molars and up to cuspids. 
The third embodiment is depicted in FIGS. 11 and 12 and basically includes 
at least one resilient wire 46 embedded in each upper and lower portion of 
the retainer. The upper portion, shown in FIG. 11, employs a single wire 
segment 50 bent to follow the contour of the patient's teeth and arch 
across the palatal bridge 36. While the single wire segment 50 is shown 
terminating by overlapping on the bridge 36, the joint may be at any 
convenient location and either overlap, butt, or be spaced apart, as 
desired. The lower retainer includes a U-shaped segment 52, depicted in 
FIG. 12, that follows the patient's lower teeth contour. 
In each case the wire 46 is embedded completely into the bridge 32 or 44 
and may be positioned underneath the clasps 22 and 42, as shown in FIGS. 9 
and 10, or on top of the clasps, illustrated in FIGS. 11 and 12, or any 
combination thereof with equal ease. 
The wire 46, in all its variations, is added to the upper and lower 
retainer portions for augmenting the propensity of each bridge to return 
to its original posture, or memory, thus maintaining a patient's tooth 
location and attitude by combining the resilient thermoplastic memory 
characteristics of the bridge structure 32 and 44 with the stiffness or 
resiliency of the wire 46. 
The wire 46, in all of its different segments 48, 50 and 52, may be made of 
a variety of different materials, all functioning properly, but each 
having slight variations in its flexing characteristics. Stainless steel, 
so-called "KANGAROO" steel, ferrous metal and nickel titanium in a 
diameter of from 0.010 inch (0.254 mm) to 0.050 inch (1.27 mm) are all 
acceptable wire materials and sizes. It has been found, however, that 
nickel titanium wire of 0.028 inch (0.71 mm) to 0.036 inch (0.91 mm) in 
diameter is the preferred selection for most common applications. 
While the invention has been described in complete detail and pictorially 
shown in the accompanying drawings, it is not to be limited to such 
details, since many changes and modifications may be made in the invention 
without departing from the spirit and scope thereof. Hence, it is 
described to cover any and all modifications and forms which may come 
within the language and scope of the appended claims.