The duration of the investigation must be long enough to permit detection of effects, which vary according to the purpose of the study. In order to gain its Seal of Acceptance, the Council on Scientific Affairs of the American Dental Association requires that clinical trials be at least six months long for chemotherapeutic products to control gingivitis. However, the association requires only thirty to ninety days for testing manual or powered toothbrushes.8 For dental caries trials, where the development of disease is a more lengthy process, a duration of several years is needed. For studying the durability of restorative material or implants, investigators may be interested in longer term results, such as eight years or more. Once again, the duration of the experiment should be clearly stated in the Methods section.
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