The reaction of previously traumatized teeth to orthodontic force application was investigated. Four groups of children were examined: group T comprised 56 children who encountered trauma to their maxillary incisors; group O comprised 29 orthodontic patients with intact incisors; group TO comprised 28 previously traumatized orthodontic patients; and group C served as the control group (n = 26). Orthodontic treatment was restricted to tipping movement executed only by means of removable appliances. Groups T, O, and TO were followed up longitudinally by means of clinical and radiographic examinations. In most of the cases the reported trauma occurred to teeth with completed roots and affected the crown only. Group TO presented the highest, though relatively moderate, prevalence of root resorption (27.8 per cent) and was followed by groups O and T (6.7 and 7.8 per cent, respectively) while in the control group no resorption was observed. Electrical pulp testing revealed the highest prevalence of loss of tooth vitality in group TO (7.3 per cent) in which the highest prevalence of pulp obliteration was also found. It can be concluded that the combination of trauma with orthodontic tipping renders the teeth more susceptible to complications, especially to root resorption and loss of vitality.