Well-aligned anterior teeth are the major reason for the patients seeking orthodontic treatment, and keeping teeth aligned and stable afterwards is a goal for the orthodontist and the patient. Relapse after treatment is a common problem, and it is defined as when teeth go back to their previous positions. Removable or fixed retainers have been used to avoid relapse after treatment. It has been common practice to use removable retention to retain anterior teeth in the maxilla. However, in recent decades, it has become increasingly common to retain with bonded retainers.

Almost all previous studies on retention devices in the maxilla were based on removable retainers. Consequently, there existed knowledge gaps and lack of short-term and long-term studies on the capability to maintain the stability of the maxillary anterior teeth with bonded retainers. Hence, the reason for the papers in this study. In addition, it is not known if retentionis needed in all orthodontic patients or if there are patients, based on their initial malocclusion and individual variations, who may not need retention after treatment.

The research questions addressed in this thesis thus originate from knowledgegaps and clinical needs concerning retention strategies after orthodontic treatments. To provide strong clinical evidence, randomised controlled trials (RCT) as well as intention to treat (ITT) methodology has been assessed. The results are expected to be beneficial for the patients who will be offered the most effective retention strategy for maxillary anterior teeth based on patients’ preferences.

In Paper I and II, 45 and 27 adolescents’ patients were collected from the Orthodontic Clinic in Mariestad, Sweden. At the time when Paper Iand II were conducted, there were no studies that had evaluated the longterm effect of bonded retainers in the maxilla. In two RCTs, Paper III and IV, 90 and 63 adolescents’ patients were collected from the Orthodontic Clinic in Växjö, Region Kronoberg, Sweden.

Paper I: The aim was to investigate the amount and pattern of relapse of maxillary anterior teeth previously retained with a bonded retainer.

Paper II: The aim was to investigate the amount and pattern of changes of maxillary anterior teeth seven years post-retention, which previously were retained with a bonded retainer.

Paper III: The aim was to evaluate post-treatment changes in the irregularity of the maxillary six anterior teeth and single tooth Contact Point Discrepancy (CPD) of three different retention methods.

Paper IV: The aim was to evaluate whether retention is needed after orthodontic treatment for impacted maxillary canines and with moderate pre-treatment irregularity in the maxilla.

Key findings in Paper I

• The contact relationship between the laterals and the centrals is the most unstable   contact. Canines are the most stable teeth.

• There was no difference in the relapse pattern between rotational displacements and labiolingual displacement.

Key findings in Paper II

• There was a strong correlation between irregularity at one- and seven-years post-retention. Stable cases one-year post-retention were stable and unstable cases deteriorated with time.

Key findings in Paper III

• All three retention methods showed equally effective retention capacity and all the changes found in the three groups were small and considered clinically insignificant. Thus, the null hypothesis was confirmed. All three methods can be recommended.

Key findings in Paper IV

• Changes between the retention and the non-retention group were statistically but not clinically significant. Since satisfactory clinical results one-year post-treatment were found in the non-retention group, retention does not appear always to be needed.

• Most of the changes occur within the first 10-week period after treatment with no retention.

Key conclusions and clinical implications

Both removable and bonded retainers are effective for holding teeth inposition and can be used for preventing the relapse. It can be enough toretain with bonded retainer 12-22 instead of 13-23. It might be possibleto avoid retention in selected cases in the short-term, but a longer evaluationperiod is needed.