GUEST EDITORIAL The evolution and advancement of Dental Thermoplastics V. Kim Kutsch, DMD Joe Whitehouse, DDS Kris Schermerhorn, CDT Robert Bowers

hermoplastic materials for dental free monomer and these materials offer a prostheses, Valplast and Flexiplast, new safe treatment alternative for these Twere first introduced to dentistry in individuals. In addition, thermoplastic the 1950s. Both materials were similar materials have almost no porosity, which grades of Polyamides (nylon plastics). reduces biologic material build up, odors, Since their introduction, there has been a and stains and they also exhibit higher continued interest in thermoplastic dental dimension and color stability. All of these materials.1 factors become important when producing long-term provisional prostheses during Development History implant or complex restorative cases, or Rapid Injection Systems (currently known when used for permanent removable as The Flexite Company), originated in appliances. Typically the thermoplastic 1962. The company introduced the first resins are more flexible and stronger than Flexite thermoplastic which was a their traditional counterparts. Elastomeric flouropolymer (a Teflon-type of plastic). resins can be added to the resin polymer Valplast introduced a flexible semi- formulas to create greater flexibility, translucent thermoplastic resin to create which reduces fracturing. Thermoplastic flexible tissue-born partial dentures. Fig 1: Aesthetic Perfection Acetal resin materials and samples from Cosmetic resins can also be reinforced with glass While the material was not strong enough Dental Materials, Inc. filler or fibers to further enhance their to allow for conventional tooth born rest physical properties3,4. At the same time, seat, the flexibility added to patient com- DENTSPLY recently introduced the these restorations can be relined and fort in wearing the appliances. Success FRS, “flexible resin system” for repaired, by repressing the restoration. Flexite also was early into the dental mar- their Success denture press. The FRS sys- The thermoplastic resins can produce sin- ket with flexible thermoplastic acrylic tem utilizes a flexible tissue colored ther- gle cast or pressed restorations that are hybrid resin for removable appliances. moplastic resin for flexible partial dentures. strong, lightweight, flexible appliances in Acetal was first proposed as an unbreak- Currently Cosmetic Dental Materials, has tissue or tooth color matched materials able thermoplastic resin removable partial introduced Aesthetic PerfectionTM (patent that never need adjusting. These restora- denture material in 19712. It was during pending), a new line of thermoplastic tions display excellent esthetics and pro- this period that Rapid Injection Systems Acetal, Acrylic, and Polycarbonate mate- vide long-term comfortable use for the developed the first tooth-colored clasps rials that can be used in most thermoplas- patient. This provides excellent alterna- with a flouropolymer thermoplastic. tic presses, Fig. 1. These materials offer tive cosmetic restorations for esthetic- excellent esthetics combined with favor- conscious patients. Thermoplastic resins In 1986, Dental ‘D’ reintroduced tooth- have and are being used for a broad vari- colored clasps using Acetal resin. The able physical properties and easy process- ing characteristics. ety of applications from removable flexi- clasps were flexible, didn’t need periodic ble partial dentures, preformed partial adjusting to keep them tight, and the tooth Advantages of thermoplastic materials denture clasps, fiber reinforced fixed par- colored esthetics were appreciated by the Thermoplastic resins and co-polymers tial dentures5, temporary crowns and patients. Pressing Dental followed in the have many advantages over conventional bridges, provisional crowns and bridges, early 1990s with an acetal resin, (marketed powder or liquid resin systems. obturators and speech therapy appliances, in the U.S. by DENTSPLY Austenal), Thermoplastic resins tend to have pre- orthodontic retainers and brackets, which in addition to tooth colored clasps, dictable long-term performance. They are impression tray6 and border molding7 has been used for an entire partial denture stable and resist thermal polymer unzip- materials, occlusal splints, sleep apnea framework as well as other appliances. ping. They also exhibit high creep resist- appliances, and implant abutments. ance and high fatigue endurance as well as In 1992, The Flexite Company, developed Thermoplastic Acetal and patented the first pre-formed tooth- excellent wear characteristics and solvent resistance. Thermoplastic resins typically Acetal as a homo-polymer has good short- color clasps known as Clasp-Eze. This term mechanical properties, but as a co- product, made of a nylon material, is have very little or almost no free monomer in the material. A significant polymer, acetal has better long-term sta- available in pink and clear color shades bility. Acetal resin is very strong, resists and currently sold worldwide. percentage of the population is allergic to Continued on page 54

52 DentalTown Magazine February 2003 GUEST EDITORIAL Dental Thermoplastics Continued from page 52 wear and fracturing, and is quite flexible. Fig 2 (left): Unilateral sin- These characteristics make it an ideal gle cast, single tooth material for pre-formed clasps for partial replacement acetal partial dentures, single pressed unilateral partial denture. dentures, partial denture frameworks, pro- Fig 3 (below): Acetal visional bridges, occlusal splints, and resin mandibular partial even implant abutments. Acetal resins denture framework with resist occlusal wear and are well suited for acrylic saddles and den- maintaining vertical dimension during ture teeth processed to the framework. provisional restorative therapy. While stronger, acetal does not have the natural translucency and vitality of ther- moplastic acrylic and polycarbonate, and gival colors, and has both translucency these materials might offer better results and vitality, providing excellent esthetics. for short term temporary restorations. Like most thermoplastic resins, acrylic Thermoplastic Polycarbonate resin is also strong, resists fracturing, and Polycarbonate is a polymer chain of is flexible. However, acrylic does not bisphenol-A carbonate. It is a popular wear as well as acetal during occlusal material and has been used in dentistry for forces and consequently will not maintain a long time as preformed temporary vertical dimension over long periods of crown shells. Like acetal resin, polycar- time. strength is 16000 psi. Nylon is a little bonate resin is also very strong, resists Flexite M.P.—a thermoplastic acrylic, is a more difficult to adjust and polish, but the fracturing, and is quite flexible. However, special blend of polymers and has the resin can be semi-translucent and provides polycarbonate does not wear as well as highest impact rating of any acrylic. You excellent esthetics for flexible tissue born acetal during occlusal force and conse- can bounce a Flexite M.P. denture off the partial dentures. quently will not maintain vertical dimen- floor without cracking the base. Flexite Applications for Thermoplastic Resins sion as long. Polycarbonate is ideally suited M.P. has a surface hardness of 55-65, Applications for thermoplastics resins for provisional crowns and bridges but not making it popular for bruxism appliances originally involved flexible tooth born suitable for partial denture frameworks. as well as dentures. partial dentures. Currently dental applica- The material has a natural translucency Thermoplastic Nylon tions include: preformed partial denture and finishes very well, yielding excellent Nylon is a resin derived from diamine and clasp, flexible tooth born partial denture esthetics. Temporary and provisional framework, single cast partial dentures, restorations with thermoplastic polycar- dibasic acid monomers. From an engi- neering standpoint, nylon is a versatile temporary crowns and bridges, provisional bonate provide patients with excellent crowns and bridges, occlusal appliances, short or mid-term function and esthetics. material with a depth of characteristics making it suitable for a broad range of implant abutments, orthodontic and sleep Thermoplastic Acrylic applications. Nylon exhibits high physical apnea appliances, many of which have Acrylic is better known as polymethyl strength, heat resistance and chemical been described previously. However, with methacrylate or PMMA. This material has resistance. It can easily be modified to the development of new elastomers and been used in dentistry for many years in increase stiffness and wear resistance. copolymer alloys, there are certain to be the form of temporary crowns and thermal Because of its excellent balance of many new clinical applications for ther- polymerized as baseplate material for par- strength, ductility and heat resistance, moplastic resins in dentistry. tial and complete dentures. Thermal poly- nylon is an outstanding candidate for Clinical Examples merized PMMA demonstrates high poros- metal replacement applications. However, The first clinical example is a single cast ity, high water absorption, volumetric in dentistry, because of its inherent flexi- partial denture. The unilateral appliance is 8 changes and residual monomer . These bility, it is used primarily for flexible tis- injected in one process with acetal resin, properties lead to many of the problems sue born partial dentures. It does not have tooth color matched by standard Vita associated with thermally polymerized enough strength to use for occlusal rest shades, Fig 2. The clasp, rest seats and acrylic versus the thermoplastic version. seats, and won’t maintain vertical dimen- pontic are all injected as a uniform piece Thermoplastic acrylic has poor impact sion when used in direct occlusal forces. of acetal resin. The clasps provide excel- resistance, but has adequate tensile and Thermoplastic nylon is injected at temper- lent retention, are esthetic and the restora- flexural strength for a variety of applica- atures from 274 to 293 C and has a spe- tion supplies proper occlusal function and tions. The material is easy to adjust, han- cific gravity of 1.14. Mold shrinkage maintains vertical dimension. dle and polish. It is relineable and amounts to 0.014 in/in. The tensile repairable chairside. Thermoplastic strength is 11000 psi and the flexural Acetal resin is also ideally suited to acrylic is available in both tooth and gin- Continued on page 56

54 DentalTown Magazine February 2003 GUEST EDITORIAL Dental Thermoplastics Continued from page 54 replace chromium in the fabrication of a acetal resin clasps virtually never need Dr. Kim Kutsch received his tooth born partial denture. In this exam- adjustment, they can be adjusted with a DMD degree from the ple, the lingual apron major connector and heated set of 3-prong pliers. University of Oregon School clasps and framework are all pressed as a of Dentistry in 1979. Conclusion Currently he serves as Chief single and continuous piece of acetal Thermoplastic resins have been used in Executive Office and Chief Technical resin. Then the partial denture is completed dentistry for over 50 years. During that Officer of Cosmetic Dental Materials, a by traditional methods, with denture teeth time the applications have continued to manufacturer of various cosmetic related and acrylic baseplate resin, Fig 3. In the grow, and the interest in these materials by dental materials. Dr. Kutsch maintains a mouth, the partial denture is functional, both the profession and the public have cosmetic dental practice in Albany, esthetic, and the flexibility and light- Oregon. Contact Kim at increased. The materials have superior [email protected]. properties and characteristics and provide excellent esthetic and biocompatible treat- ment options. With the development of Joe Whitehouse, DDS, new properties, elastomers and copolymer maintains a private practice focused on cosmetic restora- alloys, there are certain to be additional tive dentistry in Castro Valley new applications for thermoplastic resins California. He is a member 9 in the future , to help patients with dam- of the AACD and is a Diplomat of the aged or missing teeth. World Congress of Microdentistry.

Kris E. Schermerhorn, CDT, is manager for Northern Fig 4: Clinical photo of the acetal Virginia Dental Laboratory mandibular partial denture. and consultant in product development for Cosmetic Dental Materials Inc. Kris has 6 years hands-on experience with acetal resins.

Robert J. Bowers Bachelor of Science in Management Information Systems and Fig 6: Acetal resin unilateral single cast Economics From Oregon partial denture, clinical photo after. State University Operations and Manufacturing Manager for Cosmetic Dental Materials, Inc. Fig 5: Traditional metal cast unilateral partial denture, clinical photo. References weight make the restoration very comfort- 1. Kutsch VK. DentalTown April 2002. able to wear, Fig 4. Patients really appre- 2. Eid DM el-S. A new material for partial dentures: an unbreakable thermoplastic resin ciate the tooth colored esthetics. paraformaldehyde and its co-polymers. Egypt Dent J January 1971. 17(1):1-22. Acetal resin can be used for a variety of 3. Amin AE. The effect of poly-aramid fiber reinforcement on the transverse strength of a provi- applications in restorative appliances. The sional crown and bridge resin. Egypt Dent J July 1995. 41(3):1299-1304. inert, bio-compatible properties, strength 4. John J, Gangadhar SA, Shah I. Flexural strength of heat-polymerized polymethyl methacry- and esthetics make it suitable for provi- late denture resin reinforced with glass, aramid or nylon fibers. J Prosthet Dent October 2001. 86(4):424-7. sional bridges, occlusal splints, partial dentures and a number of additional 5. Altieri JV, Burstone CJ, Goldberg AJ, Patel AP. Longitudinal clinical evaluation of fiber-rein- forced composite fixed partial dentures: a pilot study. J Prosthet Dent January 1994. 71(1):16- restorations. The esthetics and comfort are 22. two advantages most appreciated by 6. Dimashkieh MR, Morgano SM. A procedure for making fixed prosthodontic impressions with patients. A traditional unilateral partial the use of preformed crown shells. J Prosthet Dent January 1995. 73(1):95-6. denture with cast metal framework is 7. Heath JR, Boru TK, Grant AA. The stability of temporary prosthetic base materials. J Oral rigid, uncomfortable and unesthetic, Fig Rehabil July 1993. 20(4):363-72. 5. An acetal single cast partial denture 8. Hiromori K, Fugii K, Inoue K. Viscoelastic properties of denture base resins obtained by that is color matched for the patient is underwater test. J Oral Rehabil June 2000. 27(6):522-31. both esthetic and the flexibility aids in 9. Price CA. A history of dental polymers. Aust Prosthodont J 1994. 8:47-54. retention and comfort, Fig 6. While the

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