the above described drawing figures illustrate the described apparatus and its method of use in at least one of its preferred , best mode embodiment , which is further defined in detail in the following description . those having ordinary skill in the art may be able to make alterations and modifications to what is described herein without departing from its spirit and scope . therefore , it must be understood that what is illustrated is set forth only for the purposes of example and that it should not be taken as a limitation in the scope of the present apparatus and method of use . described now in detail is a mouthpiece apparatus with a relatively rigid substrate portion and an overlay portion of a soft , low - friction material . fig1 and 2 illustrate the various aspects of the inventive mouthpiece herein described . therefore , now referring to these figures , the present invention comprises a substrate portion 10 and an overlay portion 20 where the overlay portion 20 is attached to the substrate portion 10 by thermal bonding , polymer welding , adhesive bonding or any other prior art technique that results in an intimate and monolithic formation of the two portions so that they are inseparable . the substrate portion 10 of the present invention is u - shaped as shown in fig1 and also has a u - shaped cross section as shown in fig2 . the prior art teaches this substrate portion in great detail including the shape and material that such a substrate portion may be comprised of . please refer to jacobs , u . s . pat . no . 3 , 312 , 218 which is hereby incorporated by reference into this disclosure . the overlay portion 20 is a polymer with the characteristics of : high adhesion to the substrate during the assembly process , and a soft and compliant texture with a low - friction or slippery surface . this overlay portion 20 is preferably produced by making at least a portion of an outer surface of the substrate chemically reactive by affixing reactive chemical functional groups to it . next , the treated substrate is coated with a first coating 22 comprising a hydrophilic prepolymer intermediate , which is capable of forming a polyurethane - polyurea hydrogel - forming polymer , and which contains terminal isocyanate groups , such that at least a portion of said terminal isocyanate groups are covalently bonded to the surface of said substrate , forming covalent polyurea bonds and thereby resulting in the formation of a tie coat of a polyurethane - polyurea hydrogel - forming polymer , that adheres to the surface of the substrate , and wherein at least a portion of the terminal isocyanate groups of said polyurethane - urea prepolymer intermediate are present in the polyurethane - polyurea hydrogel - forming polymer , such that they remain free to react with other species . finally , the overlay portion 20 is coated with a second coating 24 comprising a moisture - containing hydrogel - forming compound , further containing isocyanate - reactive chemical functional groups , such that a barrier coat of a hydrogel is formed upon the application of the second coating to the tie coat of the first coating . if the second coating is foamed , i . e ., aerated , the resultant is a slippery surface that is soft and compliant . the overlay process is taken in part from hostettler et al , u . s . pat . no . 6 , 265 , 016 which is hereby incorporated herein by reference . as shown in the figures , the assembly of the mouthpiece results in the overlay portion 20 being placed on the convex surfaces of the substrate portion 10 . in use , the substrate portion 10 may be heated to a point of softening such that an interior surface 12 may be impressed by the teeth of a person that will wear the apparatus . this process of customizing a mouthpiece for a particular person is very well known in the art . in use , the upper and - or the lower teeth of a user are covered by one of the described apparatus . the apparatus , as worn , is able to cushion the gums of the user against painful contact from the opposing dental formations when speaking and chewing . the apparatus is also able to provide safe and pleasurable oral sex activity . the enablements described in detail above are considered novel over the prior art of record and are considered critical to the operation of at least one aspect of the apparatus and its method of use and to the achievement of the above described objectives . the words used in this specification to describe the instant embodiments are to be understood not only in the sense of their commonly defined meanings , but to include by special definition in this specification : structure , material or acts beyond the scope of the commonly defined meanings . thus if an element can be understood in the context of this specification as including more than one meaning , then its use must be understood as being generic to all possible meanings supported by the specification and by the word or words describing the element . the definitions of the words or drawing elements described herein are meant to include not only the combination of elements which are literally set forth , but all equivalent structure , material or acts for performing substantially the same function in substantially the same way to obtain substantially the same result . in this sense it is therefore contemplated that an equivalent substitution of two or more elements may be made for any one of the elements described and its various embodiments or that a single element may be substituted for two or more elements in a claim . changes from the claimed subject matter as viewed by a person with ordinary skill in the art , now known or later devised , are expressly contemplated as being equivalents within the scope intended and its various embodiments . therefore , obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements . this disclosure is thus meant to be understood to include what is specifically illustrated and described above , what is conceptually equivalent , what can be obviously substituted , and also what incorporates the essential ideas . the scope of this description is to be interpreted only in conjunction with the appended claims and it is made clear , here , that each named inventor believes that the claimed subject matter is what is intended to be patented .
a mouthpiece made of a relatively rigid thermoplastic substrate having a shape generally complementary to the wearer &# 39 ; s dental arch ; a layer of compliant , slippery material overlaid on the outer surface of the mouthpiece .