Abstract: Proposed is a flexible dental mask having sides that adhere closely to the wearer's cheeks, in which both sides of a rectangular mask body are bonded so that a predetermined length of a lower end of a pleated portion is not bonded, thus forming a non-bonded portion, and only the remaining part excluding the non-bonded portion is bonded, so the non-bonded portion is folded to flexibly cope with shape deformation when the mask is worn, enabling the both sides of the mask body to closely adhere to the wearer's cheeks when the mask is worn.

Abstract: The present invention also relates to a fluid processing device using material pieces, which is usable for processing liquid and gas. The hexagon nut shaped material pieces of stainless steel and the like are heat-treated and oriented such that the material pieces form up into a kind of concentric circles and make single plane, with drawing lines linked the center points of the hexagonal nut shaped material pieces positioned the outermost circumferentially periphery of the concentric arrangement forming up into an equilateral hexagon and such arrangement is retained. Also, a fluid processing device comprises a hollow container that such field converter is positioned in.