Mixtures of conjugates in which each conjugate in the mixture comprises a growth hormone drug coupled to an oligomer that includes a polyalkylene glycol moiety wherein the mixtures have a molecular weight distribution with a standard deviation of less than about 22 Daltons are disclosed. Regular use of such a floss will therefore provide not only a significant improvement in the interproximal and subgingival whiteness of teeth but also provide all other benefits normally associated with flossing. A back face of the bracket can include a first opening that communicates with a cavity. An optically blocking structure may be placed in close proximity directly over the reference pixels.