We compared the effects of four oral hygiene methods (manual tooth-brushing, power toothbrushing, manual toothbrushing plus irrigation, and power toothbrushing plus irrigation) on plaque and periodontal disease. These methods were tested both when used alone and when used in conjunction with professional mechanical oral hygiene. 108 subjects were clinically assessed for plaque, stain, gingival inflammation, bleeding to probing, probing depth and attachment loss, and randomly assigned to one of the 4 oral hygiene groups. Subjects were carefully instructed in the use of their assigned method and asked to discontinue all other forms of oral hygiene. After 3-months, subjects returned for re-examination and full-month professional mechanical oral hygiene care. 3 months later, subjects returned for a final oral examination. All subjects kept a diary of use of their assigned method and were called every 2 weeks to monitor discomfort, provide reinforcement and answer questions. Results showed that all the oral hygiene methods were equally effective in reducing plaque and stain accumulation, gingival bleeding, bleeding to probing ratio and the % of pockets 4 mm or deeper. None of the oral hygiene methods was associated with injury to soft or hard tissues.