referring more specifically to fig1 there is shown a prior art method of separating gingival margin 1 from dentin 2 during a procedure in which the surface 3 of the tooth prior to preparation is removed in preparation for subsequent capping with an artificial material . removal of surface 3 and the pushing back of gingival margin 1 is accomplished by means of cutting surface 4 which is controlled by drill shank 5 . the prior art method , which is known in gingitage , has the disadvantage that it bruises margin 1 , often causing it to bleed and swell , making the subsequent taking of good impressions difficult . referring more specifically to fig2 and 4 there is shown another prior art method of pushing back gingival margin 1 from dentin 2 . as in fig1 dentin 2 has had tooth surface 3 removed in preparation for subsequent capping . retraction threads 6 of various sizes are used to separate gingival margin 1 from dentin 2 . fig3 shows in enlarged cross - section threads 6 , which may be impregnated with a vascularconstrictive chemical being pressed into the space between the gingival margin 1 and dentin 2 with dental instrument 7 . fig4 shows in enlarged cross section the condition of threads 6 after being pressed into place by instrument 7 . fig4 also shows a tip portion 8 of margin 1 which is beginning to curl or &# 34 ; rebound &# 34 ; in the direction of tooth base 2 . the extent of the rebound is shown by tip portion 8 in fig2 after threads 6 have been removed . the rebound of tip portion 8 after retraction threads 6 have been removed is a problem of this prior art method in that it makes subsequent treatments , such as the taking of impressions , difficult . referring more specifically to fig5 there is shown an embodiment of the present invention wherein foam material 9 has been formed over tooth 10 to separate tooth surface 11 from gingival margin 1 . the foam is held against tooth 10 and margin 1 by a downward force as shown by the arrow . the force may be applied by , for example , an opposing tooth or by a dental instrument . it can be seen in fig5 that gingival margins 1 are uniformly compressed and separated from tooth surface 11 . surprisingly , it has been observed that margin 1 retains its compressed shape and its separation from tooth surface 11 for a period of time sufficient to enable subsequent procedures such as the cleaning of portion 12 of surface 11 which is normally covered by margin 1 or the taking of an impression of the tooth using a dental impression material . it is further observed that there is no &# 34 ; rebound &# 34 ; effect shown by the tip of the gingival margin and that there is no accompanying swelling or pain when the present invention is used . cleaning portion 12 and the taking of impressions , both of which are facilitated by the present invention are procedures which will be well known to one of orindary technical skill in the dental art and need not be detailed here . foam composition 9 is developed from a system of components which , when mixed together and applied to the tooth and gum , will flow into the normal space between tooth surface 11 and margin 1 under only slight pressure applied by the dentist or by the dental patient . as the foam develops while being held in place by a suitable carrier , as is desribed in greater detail in connection with fig8 the portion of the system of components which flowed between margin 1 and surface 11 creates a foam which presses margin 1 away from surface 11 . foam 9 may be formed from any useful material . to be useful a material should be tissue compatible and non - toxic and the development of foam 9 from a system of components should not result in the evolution of a toxic or offensive gas . suitable materials are silicones , thicol rubbers , polyvinylethers , hydrocoloids and algenates . especially good results have been obtained using a silicone elastomer foam which is made from a system of components comprising silicone fluids , siliceous fillers , a crosslinker , a source of hydrogen and a catalyst . in order to be useful in the present invention these components must be combined in relative ratios such that the combined system of components has a paste - like consistency and so that the resulting elastomeric foam has sufficient resistance to compression to be useful . the surprising and unexpected results which provide the technical advantage for the present elastomeric foam over the elastomeric foams of the prior art ( such as the aforementioned dow corning silastic ® foam dressing ) are believed to result from the relative ratios of the components . for example said silicone elastomeric foam composition of the present invention has been found to display a useful paste - like consistency and to display a useful resistance to compression in the developed foam only when its components are combined in certain ratios . said silicone elastomeric foam is useful in the present invention when the system of components from which it is developed includes from about 190 to about 210 parts by weight of silicone fluids ; from about 85 to about 110 parts by weight of a siliceous filler ; from about 12 to about 16 parts by weight of a crosslinker ; from about 18 to about 22 parts by weight of a hydrogen source , and from about 45 to about 55 parts by weight of a catalyst . optionally , the system of components may contain colorants and flavorings . it has been observed that whenever the ratio of components varies from the above ratios in silicone elastomeric foam the usefulness of the material diminishes . such a variance results in the system of components losing its paste - like consistency and in the developed foam having a resistance to compression which is not useful in the desired applications . the resistance to compression of the composition of the present invention was measured by loading a force against the end of a foam cylinder measuring 2 . 5 cm in length and 3 . 5 cm in diameter . loading was increased until a 10 % deflection occurred . generally speaking , a 50 g . per square cm . loading is required to cause such a deflection in foams useful in the present invention . for comparison , an identically shaped sample of a foam composition made from dow corning silastic ® foam dressing , which is not sufficiently resistant to be used in the present invention , required only 10 g per square cm to obtain a 10 % deflection . foams which require less than 50 g . per square cm . to achieve a 10 % deflection in this test have a diminished usefulness in the present invention . the presently preferred embodiment , described below , requires an 80 g . per square cm . loading to achieve a 10 % deflection in this test . in order to be useful in this invention , a minimum expansion of about 150 % is required of a foam material in addition to the resistance to compression described above . the expansion , in accordance with the resistance , apparently enables the elastomeric foam to act as is described in fig5 - 10 . the volume expansion of foams is readily measured by placing the system of components in a graduated cylinder and calculating the volume of the starting material against the volume of the finished foam . foams , which show greater volume expansion than 150 % but do not develop the necessary resistance to compression , are not useful in the present invention . another aspect in which the above - described silicone elastomeric foam demonstrates a surprising and unexpected technical advance over the prior art is in the mixing and curing time . for example , the preferred embodiment , described below , provides a curing time of about four minutes between mixing and curing which gives the dental practitioner an appropriate time to position the system of components after mixing . a preferred embodiment of the above - described silicone elastomeric foam is made from a system of components which comprises a first component formed from 95 to 105 parts by weight of a -- oh terminated polydimethylsiloxane polymer ; from 52 to 63 parts by weight of a siliceous filler ; from 9 to 11 parts by weight of an -- sih functional silicone fluid , from 9 to 11 parts by weight of a low - viscosity hydroxyfunctional polydimethylsiloxane fluid ; from 9 to 11 parts by weight of diphenylmethylsilanol ; from 3 to 5 parts by weight of normal propylorthosilicate , and from 7 - 9 parts by weight of a white pigment . the second component is formed from 95 to 105 parts by weight of a trimethyl terminated polydimethyl siloxane fluid having a viscosity of about 12 , 500 centistokes ; from about 35 to about 45 parts by weight of a siliceous filler ; from about 45 to about 55 parts by weight stannous octoate ; from about 1 . 5 to about 2 . 5 parts by weight of a pink pigment , and from about 0 . 1 to about 0 . 2 parts by weight of a flavoring . the first and second components are prepared separately and stored in tubes . the orifices of the tubes are adjusted in size so that equal length strips of the first and second components may be extruded onto a mixing surface while maintaining the correct relative ratio of components . the strips are then combined , as by a spatula , and immediately placed into position for foam development . in the preferred embodiment the colored pigment is placed only in one component . the dental practitioner or patient may then understand from a uniformly colored mixture that the components are evenly dispersed . uniform blending of the two components is important to obtain a uniformly textured foam composition . referring more specifically to fig6 there is shown dental appliance 13 mounted on gum 14 and having foam material 9 acting as a cushion therebetween . in this embodiment of the invention , foam material 9 is formed by first placing a system of components onto the side of appliance 13 which would normally contact gum 14 . appliance 13 is then mounted on gum 14 while foam 9 is allowed to develop . this application of the present invention is especially suitable when gum 14 is sore or irritated . referring more specifically to fig7 there is shown mouth 15 of a dental subject having open wound 6 resulting from an extraction on the lower jaw . syringe 17 is being used to place system of components 18 in extraction wound 16 . system of components 18 has a paste - like consistency which enables it to fill the shape of open wound 16 without danger of flowing into respiratory passageway 19 of the dental patient . system of components 18 , when it cures to an elastomeric foam material will act as a dressing and will also keep the normal extraction blood clot in place to prevent the &# 34 ; dry socket &# 34 ; condition which results whenever an extraction blood clot comes out of place . it has been observed that system of components 18 develops into a foam material which operates as a wound dressing to promote healing . the wound is maintained in a clean condition , protected from direct contact with the atmosphere or the mouth while the porous nature of the foam draws secretions away from the wound . the foam wound dressing has the added advantage that it can be removed , cleaned and replaced by the dental subject . as the wound heals and changes shape subsequent foam dressings may be applied by the patient without the intervention of a dental professional . syringe 17 is shown as a convenient device for applying system of components 18 to locations in the back of the mouth . alternatively , system of components 18 could be applied by means of a dental spatula after the base component and the catalyst component had first been mixed together on a plate . referring more specifically to fig8 there is shown mouth 15 of a dental patient in which carrier 20 is being held in place by finger 21 while a system of components under carrier 20 develops into a foam material while being held against the dental subjects upper teeth and gums . carrier 20 may be of any useful size or shape and can be made of any suitable material to contain the system of components against the desired surface in mouth 15 . for example , a dental instrument may be used for small locations or a spoon can be used . referring more specifically to fig9 there is shown mouth 15 of a dental subject with foam material 9 covering the upper teeth and gums . foam material 9 of fig9 is of the shape which would have been produced by carrier 20 of fig8 . foam material 9 of fig9 may be held in place under pressure by lower jaw and teeth 22 for a time sufficient to accomplish the separation of the gingival margin from the tooth surface as is shown in fig5 . experience has shown that such separation can be accomplished by maintaining said pressure for a period of from about 5 to about 10 minutes for the average dental patient . foam material 9 is then removed to facilitate subsequent procedures . alternatively the foam material 9 of fig9 may be moved relative to the surface of the teeth with which it is in contact to accomplish cleaning of said surface . only small , repeated relative movements are necessary . such movements can be accomplished by manual manipulation of the foam or , as is shown in fig9 by the arrows , by a chewing action of the lower jaw and teeth 22 against foam material 9 . referring more specifically to fig1 there is shown a portion 23 of the lower teeth and jaws of a dental patient wherein wound 25 is present resulting , for example , from a tissue grafting procedure . elastomeric foam composition 24 is shown in use as a pressure pack on wound 25 . pressure pack 24 is applied by placing the system of components of the present invention into contact with wound 25 . upon curing to an elastomer the pressure pack is held against wound 25 by the pressure of the patient &# 39 ; s lip . unlike the pressure packs of the prior art , pressure pack 24 remains resilient even when wet and distributes pressure uniformly against wound 25 . pressure pack 24 can be removed , cleaned and reinserted and can be replaced , if necessary , by a new foam structure if the shape of the wound changes significantly . the present invention has been disclosed in the above teachings and drawings with sufficient clarity and conciseness to enable one skilled in the art to make and use the invention , to know the best mode for carrying out the invention and to distinguish it from other inventions and from what is old . many variations and obvious adaptations of the invention will readily come to mind , and these are intended to be contained within the scope of the invention as claimed below .