Physical and biologic properties of different splint materials in orthodontics: A narrative review

Objective: To compare the physical and biologic properties of plastics for oral splints made using subtractive or additive methods with conventional materials. For additively manufactured splints, only studies involving resin-based systems were considered.
Materials and methods: The literature search was conducted according to PRISMA guidelines, with an electronic search in the MEDLINE database (via PubMed) from February 14, 2025, to March 25, 2025.
Results: When comparing different materials used for oral splints, subtractively manufactured splints exhibit the highest mechanical properties, characterized by greater hardness and initially higher flexural strength. In both subtractive and additive manufacturing techniques, flexible material subgroups have become available in addition to conventional materials. These flexible materials demonstrate distinct mechanical characteristics and contribute to the heterogeneity of results—particularly among 3D-printed materials. Flexible 3D-printed materials show the highest wear when compared to conventionally and subtractively processed materials. Conventional 3D-printed materials exhibit similar abrasion resistance to that of conventionally and subtractively produced splints. The elution of monomers into water is higher in 3D-printed splints than in conventional or subtractive counterparts; however, subsequent surface polishing can improve biocompatibility. Additionally, both the 3D printing direction and postprocessing steps such as washing and curing influence the outcome and can be further optimized through postcuring in a nitrogen atmosphere.
Conclusions: Additional clinical studies are necessary to make well-founded statements about the clinical suitability of these materials. Keywords: splints, orthodontics, 3D printing, CAD/CAM, mechanical properties