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What is Karlstad studies were held in: and explain in detail?
Since artiﬁcial ﬂuoridation is not permitted in Sweden a number of other initiatives were introduced in 1971 as part of the "Karlstad studies" to evaluate the separate and combined eﬀects of diﬀerent plaque control programs. 
The eﬃcacy of professional tooth cleaning was extensively investigated for the ﬁrst time in the so-called Karlstad studies.