Objective To study the effect of weekly professional oral hygiene care on the proportion of micro‐organisms associated with good oral health, caries, and periodontal and soft tissue diseases in oral biofilms in dentate, dependent elderly residents.

Background Assisted oral hygiene care reduces the plaque score and number of micro‐organisms in the oral biofilms in elderly residents. Less is known about the effect on the quality/composition of the remaining oral flora.

Materials and methods Participants comprised 33 residents in the study and 35 in the control group. Dental status (≥10 natural teeth and no removable dentures to be included), plaque score, salivary secretion rate and prescription medicines were recorded. Duplicate samples, collected from supragingival plaque and tongue, were analysed using cultivation technique. Differences between and within groups were analysed using one‐way and two‐way ANOVA, respectively.

Results At the baseline, the number of teeth in the participants (mean age, 83.7 ± 7.4 years) was 22.0 ± 4.5. The number of prescription medicines was 9.4 ± 4.5. Seventy‐six per cent had low salivary secretion rate. Fifty per cent had “visible thick” supragingival plaque. At the 12‐month registration, “no visible” or “visible but thin” plaque was recorded in 92% in the study group. The proportions of bacteria associated with good oral health and periodontal diseases were decreased over time, while the frequency and proportions of micro‐organisms associated with caries and soft tissue infection were unaffected or increased.