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Polyoxymethylene
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Polyoxymethylene (POM) is a material able to provide tooth-colored esthetics and that is suitable for fabrication of frameworks for removable dental prostheses. POM can be characterized as both polyethers (-C-O-) as well as polyacetals (-O-C-O-).

tooth wear bruxism dental restoration wear resin synthetic implant-supported removable partial dentures
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1. Introduction

Polyoxymethylene (POM) is a material able to provide tooth-colored esthetics and that is suitable for fabrication of frameworks for removable dental prostheses (RDPs). POM can be characterized as both polyethers (-C-O-) as well as polyacetals (-O-C-O-) [1]. Two formulations of POM are available: the polyoxymethylen homopolymer (POM-H) and copolymer (POM-C). POM-H can be fabricated either from formaldehyde monomers or from trioxane monomers [1]. POM-H is a highly crystalline thermoplastic material with a helical structure [1][2]. For the formulation of POM-C, small amounts of other cyclic ethers (-C-O-) featuring additional methylene groups are added (Figure 1) [3][4]. The additional methylene groups result in higher thermal and hydrolytic stability, which improves its resistancy against polymer chain degradation [5].

Figure 1. Structural formulas of POM-H, POM-C, and corresponding monomers, additional methylene groups (blue).

2. Application

Due to its excellent properties, POM is industrially used as a constructional material, e.g., for the manufacturing of gear wheels, housing parts, and bearings [2][5]. The favorable mechanical properties include high strength, stiffness, hardness, impact strength, low coefficient of friction, high wear resistance, and dimensional stability [2][5][6]. In addition, POM is featured by high chemical resistance, low water absorption, und high biocompatibility [7][8]. The melting point of POM ranges around 175 °C. For thermoplastic manufacturing techniques, injection moulding is the most frequently employed process [8]. By using subtractive manufacturing, artefacts due to smearing can arise due to excessive cutting temperature levels [9]. Additive manufacturing methods such as powder bed fusion have rarely been investigated [6]. Recent literature revealed that POM can also be processed via selective laser sintering [7]. Regarding the optical appearance, POM is characterized by even surfaces and an intrinsic whiteness. The latter is based on its crystallinity [6][7]; however, POM can also be colored [10]. All in all, favorable properties of POM are advantageous for medical application [3][7] and the CAD/CAM-techniques pave the way for application in dentistry (overview see Table 1).

Table 1. Advantages and Disadvantages of polyoxymethylene as material for removable dentures.

Advantages Disadvantages
Tooth-colored, available in different shades Opaque
Break-proof due to high impact strength Flexible
Smooth surface Low chemical interaction with other materials
Non known allergies Limited wear resistance
Color stability  
Customizable color  
 

References

  1. Uchida, T.; Tadokoro, H. Structural studies of polyethers. IV. Structure analysis of the polyoxymethylene molecule by three-dimensional fourier syntheses. J. Polym. Sci. A-2 Polym. Phys. 1967, 5, 63–81.
  2. Samyn, P.; van Driessche, I.; Schoukens, G. Thermal and spectroscopic analysis of worn polyoxymethylene surfaces and wear debris explaining degradation and polymerisation mechanisms. J. Polym. Res. 2007, 14, 411–422.
  3. Eschbach, L. Nonresorbable polymers in bone surgery. Injury 2000, 31, D22–D27.
  4. Klein, R.; Schüll, C.; Berger-Nicoletti, E.; Haubs, M.; Kurz, K.; Frey, H. ABA Triblock Copolymers Based on Linear Poly(oxymethylene) and Hyperbranched Poly(glycerol): Combining Polyacetals and Polyethers. Macromolecules 2013, 46, 8845–8852.
  5. Bergmann, W. Werkstofftechnik. Mit 4 Tabellen: Grundlagen, 7th ed.; Carl Hanser: Munich, Germany, 2013.
  6. Dechet, M.A.; Baumeister, I.; Schmidt, J. Development of Polyoxymethylene Particles via the Solution-Dissolution Process and Application to the Powder Bed Fusion of Polymers. Materials 2020, 13, 1535.
  7. Wendel, B.; Rietzel, D.; Kühnlein, F.; Feulner, R.; Hülder, G.; Schmachtenberg, E. Additive Processing of Polymers. Macromol. Mater. Eng. 2008, 293, 799–809.
  8. Domininghaus, H.; Elsner, P.; Eyerer, P.; Hirth, T. Kunststoffe. Eigenschaften und Anwendungen, 8th ed.; Springer: Berlin/Heidelberg, Germany, 2012; ISBN 9783642161728.
  9. Rubio, J.C.C.; Panzera, T.H.; Scarpa, F. Machining behaviour of three high-performance engineering plastics. Proc. Inst. Mech. Eng. Part B J. Eng. Manuf. 2015, 229, 28–37.
  10. Kaiser, W. Kunststoffchemie für Ingenieure. Von der Synthese bis zur Anwendung, 5th ed.; Carl Hanser: Munich, Germany, 2021.
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    Schierz, O. Polyoxymethylene. Encyclopedia. Available online: https://encyclopedia.pub/entry/9088 (accessed on 07 October 2022).
    Schierz O. Polyoxymethylene. Encyclopedia. Available at: https://encyclopedia.pub/entry/9088. Accessed October 07, 2022.
    Schierz, Oliver. "Polyoxymethylene," Encyclopedia, https://encyclopedia.pub/entry/9088 (accessed October 07, 2022).
    Schierz, O. (2021, April 27). Polyoxymethylene. In Encyclopedia. https://encyclopedia.pub/entry/9088
    Schierz, Oliver. ''Polyoxymethylene.'' Encyclopedia. Web. 27 April, 2021.
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