Summary How bruxism develops from adolescence to early adulthood remains unclear. A previous database was revisited to evaluate the natural course of self-reported tooth grinding and clenching among young Finns aged 14–23 using four assessments. Overall, the self-reported frequencies of both grinding and clenching increased during the examination period: from 13·7% to 21·7% and from 9·2% to 14·8%, respectively. There were significant increases (without a statistically significant difference between genders) in both grinding (P = 0·002) and clenching (P = 0·015) between 15 and 23 years. A significant rise in grinding between 18 and 23 years was also found (P = 0·011). It is concluded that self-reported bruxism increases from adolescence to young adulthood. Moreover, there are large differences between individuals, and fluctuations may occur in the natural course of bruxism.