*2.1. Design of the Experiment*

In this work, an attempt was made to analyze the influence of the geometric configuration and the thickness of the interlayer on the deformation behavior of the elements of the dentition. The peculiarity of the models is the use of data on the geometry of teeth for a real clinical case. To fully evaluate the effectiveness of a multilayer mouthguard with an A-silicone interlayer, the contact of a pair of antagonist teeth was simulated for a clinical case (Figure 1) with and without the multilayer EVA of an individual protective mouthguard. In this work, an attempt was made to analyze the influence of the geometric configuration and the thickness of the interlayer on the deformation behavior of the elements of the dentition. The peculiarity of the models is the use of data on the geometry of teeth for a real clinical case. To fully evaluate the effectiveness of a multilayer mouthguard with an A-silicone interlayer, the contact of a pair of antagonist teeth was simulated for a clinical case (Figure 1) with and without the multilayer EVA of an individual protective mouthguard.

Five numerical models of the contact of a pair of teeth, with and without protective mouthguards of different geometries (Figure 2), were analyzed. Five numerical models of the contact of a pair of teeth, with and without protective mouthguards of different geometries (Figure 2), were analyzed.

**Figure 2.** Numerical scheme of the contact between upper (1) and lower (2) teeth with and without a mouthguard: (**a**) case a without mouthguard; (**b**) case b with a multilayer EVA (3) mouthguard; (**c**) case c with a multilayer EVA (3) mouthguard with an A-silicone interlayer (4) of different geometries and thicknesses (**A**–**C**). ( *S*σ is the boundary where the loading is applied; *SK* is the boundary where the contact occurs (for multilayered mouthguards ∪ *KK K 1 2 S =S S* ); *SU* is the boundary where displacements are set). **Figure 2.** Numerical scheme of the contact between upper (1) and lower (2) teeth with and without a mouthguard: (**a**) case a without mouthguard; (**b**) case b with a multilayer EVA (3) mouthguard; (**c**) case c with a multilayer EVA (3) mouthguard with an A-silicone interlayer (4) of different geometries and thicknesses (**A**–**C**). (*S<sup>σ</sup>* is the boundary where the loading is applied; *S<sup>K</sup>* is the boundary where the contact occurs (for multilayered mouthguards *SK*= *SK*<sup>1</sup> ∪ *SK*<sup>2</sup> ); S*U*is the boundary where displacements are set).

The geometric configuration of the teeth was based on clinical case data (Figure 1). Mouthguard fit of the teeth geometry and frictional contact were considered. In case a, frictional contact was taken into account in the area of teeth-antagonists occlusion. In cases b, c-A, c-B, c-C, antagonist teeth were in contact with mouthguards.

The maximum thickness of multilayer mouthguards in the area of teeth occlusion was about 7 mm. All multilayer mouthguards were based on EVA layers. Contact interaction between EVA layers was not considered (modeled as a solid). Multilayer mouthguards with a layer of A-silicone were modeled within the framework of the frictional contact between the layers of EVA and A-silicone.

To analyze the influence of mouthguard on the teeth deformation under contact, three variants of the A-silicone interlayer were considered (Figure 2):


For the first two variants of the geometric configuration of the A-silicone interlayer, a slight change in thickness in the occlusion region of 10–15% is characteristic. The third variant of the interlayer has a more significant change in thickness in the occlusion region (more than 30%). It should also be noted that the interlayer thickness was adjusted to the teeth geometry: for the area where the tooth has a smaller contact area, the interlayer was selected to be the thinnest and vice versa.
