Should we always agree with peer-reviewed published research?

When I was in practice patients frequently asked my advice as to whether or not they should buy an electric toothbrush. My answer was always that the most important aspect of tooth cleaning was that every surface of every tooth must be methodically and systematically brushed. If the patient was doing this with a manual toothbrush then, I said, they did not need an electric one, and if they were not following such a regime then an electric brush would be no more effective. I still think this is basically correct but, following personal practice, clinical observation, and from reading research reports, I have learned that an electric toothbrush, properly used, does indeed result in cleaner teeth! Having given these as presents to most of my family and friends and recommended them to patients I have been able to undertake a wide range of observations.

Imagine my surprise, therefore, when I read this paper in which the plaque-scores of three groups of 15 patients were followed over a two-week period. Two groups were allocated different branded manual toothbrushes and the third an electric brush. The research concluded that there was no statistically significant difference in plaque control over the study period. Why, I wondered, did this result not conform to my own clinical observations?