Abstract: There is disclosed a .Iadd.novel .Iaddend.process and a .[.material.]. .Iadd.composition .Iaddend.for brightening teeth.Iadd., together with a novel use of old compositions for brightening teeth. .Iaddend.The .Iadd.novel .Iaddend.process .Iadd.and use each comprises .Iaddend..[.comprises.]. the .[.construction.]. .Iadd.placing .Iaddend.of a splint around the tooth or teeth to be brightened, .[.followed by the insertion within the splint of.]. .Iadd.with .Iaddend.a brightening agent .[.selected from one of many peroxide groups.]. .Iadd.comprising a composition capable of sustained nascent oxygen release.Iaddend.. The splint is constructed so that the splint is relatively liquid tight .[.to the gingiva.].. .Iadd.Preferably, .Iaddend.the brightening agent is periodically renewed .Iadd.during the day .Iaddend.and can be mixed with various other agents to increase the nascent oxygen release .[.aerating factors.].. In one embodiment, the .[.perioxide.]. .Iadd.peroxide .Iaddend.