A major dental problem confronting persons with mental retardation/developmental disabilities (MR/DD) is poor dental hygiene, which can result in an increased incidence of gingivitis and periodontal disease. Studies indicate that the most obvious reason for the poor oral hygiene of such persons is their inability to clean the oral cavity adequately. The objective of this study was to determine whether there was a difference in the oral health between a group of residents with MR/DD using the Interplak and a group using manual toothbrushes. Fifty-six residents from four Franklin County group homes completed the study. Each group home was divided into two study groups, one using the Interplak and the second using manual toothbrushes. Each subject was seen for initial recording based on the Gingival Index (Löe) and Simplified Oral Hygiene Index (Greene and Vermillion), followed by a thorough prophylaxis. These measurements were recorded again at three, six, and nine months, with a final recording at 12 months. At the conclusion of the study, analysis of the data indicated significant improvement in the Gingival Index over a 12-month period for the residents using the Interplak compared with a manual toothbrush.