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-).
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-) . 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 . POM-H is a highly crystalline thermoplastic material with a helical structure . For the formulation of POM-C, small amounts of other cyclic ethers (-C-O-) featuring additional methylene groups are added (Figure 1) . The additional methylene groups result in higher thermal and hydrolytic stability, which improves its resistancy against polymer chain degradation .
Figure 1. Structural formulas of POM-H, POM-C, and corresponding monomers, additional methylene groups (blue).
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 . The favorable mechanical properties include high strength, stiffness, hardness, impact strength, low coefficient of friction, high wear resistance, and dimensional stability . In addition, POM is featured by high chemical resistance, low water absorption, und high biocompatibility . The melting point of POM ranges around 175 °C. For thermoplastic manufacturing techniques, injection moulding is the most frequently employed process . By using subtractive manufacturing, artefacts due to smearing can arise due to excessive cutting temperature levels . Additive manufacturing methods such as powder bed fusion have rarely been investigated . Recent literature revealed that POM can also be processed via selective laser sintering . Regarding the optical appearance, POM is characterized by even surfaces and an intrinsic whiteness. The latter is based on its crystallinity ; however, POM can also be colored . All in all, favorable properties of POM are advantageous for medical application  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.
|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|