120 b 120 c 120 d and 120 e have less desirable or even unacceptable endrounding characteristics these bristle filaments are less desirable or are unacceptable because they have sharp pointed or jagged edges for additional information on generally acceptable end rounding see e g silverstone l m amp featherstone m j 1988 a scanning electron microscope study of the end rounding of bristles in eight toothbrush types journal quintessence international volume 19 no 2 pp 87 107 reiter c amp wetzel w e 1991 abteilung kinderzahnheilkunde zentrum f u00fcr zahn mund und kieferheilkunde giessen the finishing of the bristle ends in interdental brushes schweiz monatsschr zahnmed volume 104 no 4 pp 431 437 the illustrations in fig1 of generally acceptable endrounding or less desirable or even unacceptable endrounding are merely for illustrative purposes only there may be instances where bristle filaments having characteristics that appear to be less desirable based on fig1 are nonetheless acceptable or good endrounding characteristics for a particular purpose accordingly the illustrations of fig1 should not be construed to limit the scope of or define what is acceptable end rounding because there are often hundreds of bristle filaments in a toothbrush head and some of the bristles may have an acceptable endrounding and others may not methods have been established to determine the u201c levels u201d of endrounding on a toothbrush to determine the level of endrounding on a toothbrush the endrounding of all of the bristle filaments on a toothbrush head are conventionally examined microscopically each of.