the physical structure of dental appliances may be appreciated by reviewing fig1 through 4 . in fig1 the standard non - custom mouthguard 10 generally includes a horseshoe or u - shaped base or occlusal pad 11 with a lingual wall 12 and a labial wall 13 . in fig2 the custom mouthguard or dental appliance 20 may have a base 21 , a lingual wall 22 , and a labial wall 23 . typically , the custom mouthguard 20 is placed in boiling water to soften and then fitted to the mouth for a sure - grip fit to the wearer . [ 0019 ] fig3 and 4 show a typical dental appliance 30 other than a protective mouthguard 10 or 20 . the appliance 30 typically includes occlusal posterior pads 31 appropriately connected by an arch 32 to assure that the appliance 30 is not swallowed by the wearer . the arch may also extend along the outside or inside of the anterior teeth . the appliances , 10 , 20 and 30 of the present invention are made of low - density polyethylene . a suitable material is exact ® 4023 from exxon mobile chemical company of houston , tex . 77253 - 3272 . after molding into an appliance , the user simply places the appliance 10 , 20 or 30 into hot water 100 ° to 150 ° for a few seconds . thereafter , the appliance 10 , 20 or 30 is removed and fitted to the user &# 39 ; s mouth , teeth and gums just like an eva appliance as is well known . it is also well known that illness , infection , tooth decay and / or periodontal disease is caused by bacteria , fungus , yeast , and virus . these microbials can grow and multiply on dental appliances when the appliances are being stored between uses as well as when the appliance is actually being worn or used . antimicrobial substances which are non - toxic and free of heavy metal or resisting the growth of the microbials may include chlorinated phenol ( e . g . 5 - chloro - 2 -( 2 ,- 4 - dichlorophenoxy ) phenol ), polyhexamethylene biguanide hydrochloride ( phmb ), doxycycline , chlorhexidine , metronidazole , thymol , eucalypol and methyl salycilate . triclosan ® from siba giegy of switzerland is also available . incorporating an antimicrobial agent into the low - density polyethylene during the manufacture of the dental appliance 10 , 20 or 30 is achieved by incorporating the agent into the synthetic polymeric master batch . the antimicrobial agent is suitably placed into the batch in a concentration as high as 10 % which will permit a let - down ratio resulting in the final concentration of the antimicrobial agent and the dental appliance of about 0 . 005 to about 2 % by weight . by encapsulating the antimicrobial agent into the polymer batch mix , the agents survive molten temperatures approximately or above 350 ° f . and thus the antimicrobial agent loses none of its biocidal properties in the formation of the dental appliance 10 , 20 or 30 . it is to be understood that the foregoing description and specific embodiments are merely illustrative of the best mode of the invention and the principles thereof . various modifications and additions may be made to the present invention by those skilled in the art without departing from the spirit and scope of this invention which is to be limited only by the scope of the appended claims .