Invisible retainers
`
`Robert J. Ponitz, B.S., D.D.S., M.S.
`Ann Arbor, Mich.
`
`Methods of retention in orthodontic treatment seem to have under(cid:173)
`gone more drastic change than have many other aspects of practice. For this
`reason, the changes in retentive appliances will be reviewed briefly and experi(cid:173)
`ence with the invisible retainer will be presented.
`
`History
`
`Retainers used around 1914 by Hawley and others10 were basically fabri(cid:173)
`cated from gold wire and vulcanite. Since about 1937, steel wire and acrylic
`retainers have been used extensively. Many variations of the original design of
`the wire have been made through the years. The circumferential wire first was
`used by Paul Ponitz18 in 1946. Combinations of body wire, auxiliary wires, and
`elastics also have been used. Autopolymerizing methyl methacrylate was first
`used clinically by me in 1952. Cobalt wires first became available around 1955. 7
`Conventional premolar and second molar clasps and also ball-and-arrowhead
`clasps have been used.
`On July 21, 1923, Remensnyder1 introduced a rubber2 Flex-0-'l'ite "gum(cid:173)
`massaging appliance" which was first patented on Nov. 13, 1928. He described
`minor movements of teeth achieved with his first patented appliance. 3 Remen(cid:173)
`snyder's second patent6 used the term "orthodontic appliance"-a one-piece
`rubber device. 4
`Vulcanite positioning retainers were popularized by Kesling,5 Rocke, and
`others after 1943. Plastic finishing appliances have been used by others and
`myself for the past 10 years, but black vulcanite rubber is still preferred by
`many clinicians8 because of its special physical properties.
`Godwin,11 Tarbet, and others have pioneered in the fabrication, at modest
`cost, of large numbers of mouth guards for athletes.9 Shanks first showed mouth
`guards, transparent retainers, and a machine capable of producing them in
`1963. Cellulose acetate butyrate, polyurethane, polyvinylacetate-polyethylene
`polymer, polycarbonate-cycolac, and latex are the materials most frequently
`used in these applications. Special vacuum units that can be used to make
`plastic finishing appliances have been developed. Heating element capacity
`
`266
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`Volume 59
`Nurnber3
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`Invisible retainers 267
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`Fig. 1. Vacuum box with grid and tube.
`
`has been found to be insufficient for the present application in some commer(cid:173)
`cially available vacuum units.
`
`Fabrication of appliance
`The vacuum unit (Fig. 1) consists of a box, grid, and tube. A tank type of
`vacuum cleaner is used to provide the suction required. A frame (Fig. 2) is
`used to hold a plastic blank securely in place during heating over an electrical
`source of heat. A surface unit of 220 volts is more convenient, but two 110 volt
`units can be used satisfactorily. The second element is placed, heating down(cid:173)
`ward, about 9 inches above the first element, which is placed heating upward
`(Fig. 2). The temperature should be from 340 to 420° F., although the preferred
`range of temperature is 370 to 390° F.
`An impression of either arch is made by the method of one's choice. A model,
`without a base, is poured with improved stone or die stone. The model is placed
`with the anterior teeth toward the source of vacuum (Fig. 3). If protective
`packaging sheets are present, they are removed from the square of plastic to be
`used. The clear plastic, 5 inches square, is preheated in an oven for 15 minutes
`at 250° F. A sheet of preheated clear plastic is placed in the frame and heated
`over the electrical burner. The frame is kept moving in a horizontal pattern to
`avoid overheated spots which cause bubbles in the finished appliance. When the
`plastic slumps or begins to smoke, the vacuum device is turned on and the frame
`of heated plastic is placed immediately over the model on the vacuum unit (Fig.
`3) . An asbestos-gloved hand or a hot pad can be used to provide pressure in
`adapting plastic closely to the model. The speed of the motor will increase as
`the grid on the unit is sealed. A foot switch frees both hands for use in forming
`the appliance.
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`268 Ponitz
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`Am,·,· .J. Orthodont.
`Marr,h 1971
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`Fig. 2
`
`Fig. 3
`
`Fig. 2. Preheating oven at left. Twin 110 volt heating elements at right.
`Fig. 3. Invisible retainer formed.
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`Volume 59
`Number 3
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`Invisible retainers 269
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`Fig. 4. Invisible retainers ready for use.
`
`The flash is trimmed away with coarse tin snips. A Vulcarbo, Joe Dandy, or
`knife-edge disk in a mandrel is used to carve the approximate periphery of the
`retainer. At this point, the retainer is lifted off the model with the large end of
`an inverted No. 7 wax spatula and trimmed with curved, nonserrated crown(cid:173)
`and-bridge scissors. Finally, the edges are polished with an Indianhead pear(cid:173)
`shaped stone. The patient's name can be carved in the flange with a small half(cid:173)
`round bur or a vibrating stylus instrument of the type usually used to mark
`metal objects.
`Teeth can be moved and repositioned in pink baseplate wax on the master
`model before the appliance is formed. The patient's teeth then can be moved to
`reasonable new positions by means of the retainer (Fig. 5). Bite planes can be
`formed on the model with asbestos material, and retainers can be formed over
`the asbestos with or without acrylic between the retainer and the patient's tissue.
`Acrylic bite planes can be formed over or under the clear plastic and bounded
`to the plastic with self-curing acrylic liquid. Denture teeth can be attached in
`edentulous areas in the same way. Plastic denture teeth usually are chosen for
`convenience. They bond to the appliance if covered with a drop of self-curing
`liquid just before the appliance is formed. Vinyl1 7 is customarily used to form
`mouth guards and appliances for the correction of bruxism. This type of ma(cid:173)
`terial is readily available from supply houses and can be used to gain greater
`changes in the position of teeth than the harder and clearer invisible material
`for the retainer will permit.
`Final finishing, positioning appliances can also be made from vinyl blanks
`or wafers. Some blanks are heated in boiling water, while others are softened
`with dry heat. The heated wafer then is placed over the model, and a squared
`coffee can with a petrolatum-lubricated rubber dam banded to place is quickly
`placed over the plastic to form it on the vacuum unit.
`·when both surfaces of the clear plastic sheet are smooth, either side may be
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`270 Ponitz
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`•lmcr. J. Ort/wclont
`Mnrch 1971
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`Fig. 5. Invisible retainers being worn.
`
`placed up or down in forming the appliance. If one surface is a matte or has a
`dull finish, the matte should be placed toward the model when the invisible re(cid:173)
`tainer is formed. Should the plastic sheets be packaged with a protective poly(cid:173)
`ethylene thin-film wrapping or interlining, the protective sheets should be re(cid:173)
`moved before preheating, as mentioned previously.
`
`Additional implications
`
`At the present time, invisible retainers usually last many months to a few
`years. The standard appliances made of wire and acrylic or of rubber usually
`last many years. As materials improve, comparable life expectancies may he
`anticipated in the future. Today's challenges for plastics seem to result in to(cid:173)
`morrow's accomplishments.
`Invisible retainers fit as accurately as the impression and model permit.
`Usually, no adjustment is needed. Occasionally, the periphery will require
`reduction for the attachments of muscles. Heat guns can be used to join cracks,
`separations, or split areas in the plastic. Usually it is preferable to make a new
`appliance after considerable wear has occurred. The ease of fabrication, the
`speed of insertion, and the almost complete lack of need for adjustment have
`amazed all who have used these appliances. It is usually easier to remake than
`to repair an invisible retainer.
`Periodontists12 have found invisible retainers valuable for keeping surgical
`packs in place with maximum comfort for the patient. These appliances have
`been used successfully as splints to stabilize traumatic and surgical fractures of
`the maxilla, premaxilla, and mandible until the bony fragments heal. Tempo(cid:173)
`rary partial dentures15 have been made and used with excellent acceptance. These
`appliances also have been used as splints for the treatment of bruxism,19 trau(cid:173)
`matized teeth, and the correction of oral habits. A maxillary and a mandibular
`retainer can be fused to make a surgical splint or a finishing appliance.
`·webbing or folding of the appliance upon itself is a common problem en(cid:173)
`counttired in the use of thermoformed materials. Usually this fault comes from
`excessive temperature when the appliance is being formed. Leaving an extended
`base on the model, insufficient vacuum or pressure, delay between heating and
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`Volume 59
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`Invisible retainers 271
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`Fig. 6. Maxillary and mandibular invisible retainers used as a surgical splint. Note
`acrylic bead on superior portion of the maxillary retainer. Two invisible retainers-one
`maxillary and one mandibular-are fused on an articulator, with a bead of acrylic added
`to the superior border of the upper retainer. The maxillary portion of the appliance thus
`formed is wired to the skull from below the bead. The bead is added to prevent the
`wire from being pulled through the appliance. The mandibular portion of the appliance
`is wired around the mandible in two places. In this manner, the previously determined
`jaw sections are secured until healing has taken place.
`
`forming, or any other failure in technique during formation of the appliance
`can cause undesirable webbing.
`Heat and pressure have provided the best methods found for producing
`appliances of acrylic and rubber that are dense. Heat, vacuum, and pressure have
`been used in fabricating invisible retainers. The thicker the plastic sheet and
`the more sophisticated the composition of the plastic, the greater the porosity
`that develops.
`Preheating of the clear plastic sheets for about 15 minutes at 250° F., plus
`or minus 10 degrees, has been recommended for the material currently available.
`The preheating removes moisture from the plastic and thereby eliminates the
`bubbles that cause porosity in the finished appliance. Since it is impractical to
`store the material in an airtight environment, preheating is desirable before
`any group of appliances is fabricated. A sealed container with an adequate
`dehydrating agent might be developed and used. :F'uture development of ma(cid:173)
`terial may require modifications of present methods, but most plastics are not
`available for experimentation in these developmental stages.
`
`Summary
`A review of the literature provided surprisingly little historical information
`of value on retainers. This dearth of material in the literature indicates that,
`although many innovations have been made by persons in the profession, few
`busy practitioners find time, encouragement, or facilities to publish them. As a
`result, the present article reports in detail the findings of earlier investigators
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`272 Ponitz
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`Anwr. J. Ortlwdunt.
`Ma.roh l9il
`
`and describes the technique used in the production of invisible retainer:-.. Whm1
`an orthodontist or other specialist perfects this method, he will find i1 a 1·ewa1·d.
`ing·, time-saving and valuable addition to his treatment procedures.
`
`REFERENCES
`1. Remensnyder, Orrin: A gum-massaging appliance in the treatment of pyorrhea, Dent.
`Cosmos 48: 381-384, 1926.
`2. Burchard, H. H., and Inglis, 0. E.: Textbook of dental pathology and therapeutics,
`Philadelphia, 1926, Lea & }'ebiger, p. 738.
`3. Remensnyder, Orrin: United States Patent 1,691,785, dental massage device., Nov. 13,
`1928.
`4. Remensnyder, Orrin: Treatment of pyorrhea, Dent. Econ. 1: 32-35, 1929.
`5. Kesling, H. D.: The philosophy of the tooth positioning appliance, AMF!R. :r. ORTHOJ)ON'l'.
`ORAL SURG. 31: 297-304, 1943.
`6. Rcmensnyder, Orrin: United States Patent 2,479,780, orthodontic appliance, Aug. 23, 1949.
`, . Ponitz, R. J.: Tensile properties of heat-manipulated stainless steel orthodontic wires,
`Thesis, University of Michigan, School of Dentistry, Ann Arbor, Mich., 1955.
`8. Kesling, P. C.: Practical application of the Kesling tooth positioner, Thesis, Westville,
`Ind., 1964.
`9. Craig, R. G., and Godwin, W. C.: Physical properties of materials for custom-made mouth
`protectors, ,J. Mich. Dent. Ass. 49: 34-40, 1967.
`10. Shepard, E. E.: Address presented at American Association of Orthodontists' Golden
`Anniversary Luncheon, St. Louis, Mo., April 24, 1967.
`11. Godwin, W. C.: Simplified mouth protector technic, .T. Mich. Dent. Ass. 44: 132-133, 1962.
`12. Horii, A. A., and Keyes, P. H.: A vinyl applicator for assessing drugs in the treatment
`of caries and periodontal diseases in the hamster, J. Dent. Res. 43: 152, 1964.
`13. Blackburn, M. M.: One-year evaluation of twelve mouth protectors for Edmonton hockey
`players, J. Canad. Dent. Ass. 30: 560-564, H!64.
`14. Nahoum, H. I.: The vacuum-formed dental contour applianee, New York J. Dent. 30:
`385-390, 1964.
`15. Michnick, B. T., Demauro, James, and Reinhart, Ellen: A simplified temporary bridge
`technique, New York J. Dent. 32: 73-75, 196(l.
`16. Fiasconaro, ,T. E., and Sherman, Harold: Vacuum-formed prostheses. 1. A temporary fixed
`bridge or splint, J. Amer. Dent. Ass. 76: 74-78, 1968.
`17. Goodman, S. F.: Plastic guard held to cushion effects of bmxism, clenching, Dent. Times
`11: 2, 1968.
`18. Ponitz, P. V.: Personal communication, Feb. 15, 1946.
`19. Godwin, \V. C.: A simplified mouth protection technic. Part II, J. Mich. Dent. Ass. 44:
`227-234, 1962.
`20. Cottingham, L. L.: Gnathologic clear plastic positioner, Amer. ,T. Orthodont. 55: 23-31,
`1969.
`
`425 E. 'Jflllshington St.
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`ClearCorrect Exhibit 1049, Page 7 of 7
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