There is famous saying among the athletes that it is easy to because a champion but it is not easy to remain a champion. From the early days of orthodontic science, relapse of the results of treatment over time has been one of the main themes for discussion and retention and preservation of the results have been the main concern of orthodontists. Different reasons have been reported for the relapse and the necessity for retention, including re-organization of gingival and periodontal tissues after tooth movements, moving the teeth to an unstable position and the continuation of growth.
Continuation of skeletal growth not only affects the occlusal relationships but also can change the position of teeth. For example, if the mandible moves forwards or rotates downwards, the lower incisors will move toward the lip, resulting in a force that will give rise to distal tipping of these teeth. This problem is particularly evident in patients with Cl III malocclusion and skeletal open bite. In most cases it is recommended that retention should continue until the eruption of the wisdom teeth, although the theory of the effect of the pressure of the developing wisdom tooth on the crowding of lower incisors does not appear to be correct. Nonetheless, it seems logical to continue retention until the eruption or extraction of wisdom teeth, which occurs during the late stages of the second decade.
In the majority of adults, both those who have undergone orthodontic treatment and those who have had correctly aligned teeth from the beginning and have never received orthodontic treatment, a slight crowding is normally expected with aging, and such a problem is observed even in those who have extracted their premolars during orthodontic treatment. It appears the delayed growth of the mandible is the most important factor involved in the tendency to create crowding. Therefore, it is important to preserve the alignment of lower incisors until the growth of the mandible decreases to the base level observed in adults.
Various appliances, techniques and protocols have been introduced for retention. Generally, removable and fixed appliances can be used for retention. Hawley retainer is the most common removable retainer, which was introduced in 1920 as an active removable appliance. Fixed bonded retainers are used in cases in which here is intra-arch instability and long-term retention is considered. FSW is one of the most commonly used fixed retainers. To this end, usually a flexible wire is bonded in the lower incisor area to the lingual aspects of 6 anterior teeth. However, in cases in which the first premolars have been extracted, the wire can be extended up to the second premolars (extended FSW) to prevent re-opening of the extraction space.
Little et al. evaluated changes in anterior teeth and preservation of their alignment after the retention period and concluded that the arch compression trend that is effective in the crowding of anterior teeth continues after the completion of active growth. Therefore, clear changes are seen after the retention period (
14). Sinclair et al. reported in a study entitled ‘Development and Maturation of Normal Untreated Occlusion’ that there is a continuous inclination for decreasing the arch length from the mixed dentition period until adulthood ( 15).
In the present study, two different types of retention were evaluated. In the first group, the extended fixed retainer (from the second premolar on one side to the second premolar on the other side) was used. In the second group, FSW retainer (from the canine tooth on one side to the canine tooth on the other side) in association with overnight wearing of Hawley plaque was used.
Statistical analyses showed that both groups exhibited homogenous distributions of age, gender, crowding severity and the type of postero-anterior and vertical malocclusion and had proper matching. In addition, at baseline (the bonding day) there were no differences in interdental spaces of second premolars and first molars between the two groups. Therefore, the two groups were identical at baseline and could be compared, which made the results of the 2- and 6-month intervals highly valid.
Comparison of the results showed that the interdental spaces decreased from the debonding day until the 2-month interval after debonding. Although the decrease in FSW + Hawley group was higher, the differences between the two groups were not clinically significant. In addition, the changes from the 2-month interval to the 6-month interval and from the debonding day to the 6-month interval were not clinically significant.
Overall, the interdental spaces decreased from the debonding day up to the 6-month interval in both groups, which might be attributed to the possible inclinations of teeth to move mesially and compress and decrease the arch length from the mixed dentition period to adulthood, consistent with the results of studies by Little et al. (
14) and Sinclair and Little ( 15).
All these findings show the success of both retainers in preventing re-opening of spaces. On the other hand, since the aim of retainers is to preserve the alignment of teeth and prevent re-opening of interdental spaces, it can be concluded that both retainers were very successful in preventing re-opening of interdental spaces.
• The interdental spaces decreased from the debonding day to the 6-month interval after debonding, which was not significant statistically and clinically. The majority of changes in space occurred during the first two months after debonding,
• Both extended fixed retainer and fixed retainers in association with the overnight use of Hawley plaque were successful in preserving the closed space of extracted mandibular first premolar during the retention phase of fixed orthodontic patients during the first 6 months.