# Fixed Flexible Spiral Wire Retainers and Unwanted Tooth Movements: A Case Report
## 4 Discussion  
This case report illustrates an adverse effect in orthodontics. This concerned unwanted tooth movement during the retention phase, probably due to the fixed retainer in the upper jaw. Even though fixed retainers are effective in preventing relapse, previous research has shown that fixed FSWs may also lead to unwanted effects and can complicate oral hygiene, with negative consequences for the periodontion [9; 16; 28; 29; 30]. [PERSON] et al. described two possible effects of fixed FSWs during the retention phase: (1) the X-effect, a torque difference between two adjacent mandibular incisors, and (2) the twist-effect, an increase in the buccal inclination of the canine [16]. The X-effect or twist effect was observed in 2.7% (6/221) of the evaluated patients during a retention period of 5 years [9]. Recently, [PERSON] described a case in which a combination of the X-effect and twist-effect was present, leading to the avulsion of the canine [20]. These reported 'twist-effects' are similar to the tooth movements described in this case report. However, in the current case report, the fixed FSW retainer was located in the upper jaw, while previous studies investigated fixed FSWs in the lower jaw [9; 16; 20; 28]. It is hypothesized that the forces that contribute to the etiology of these unwanted tooth movements might be generated in three ways: (1) by the untwisting of the round flexible spiral wires (tooth movements generated by these forces might also be the reason for the observed root resorption localized at the 12, 11, and 21 on the panoramic radiograph from July 2017 (Figure 3D) [31]), (2) the mechanical deformation of the wire as a result of masticatory forces, and (3) the elastic deflection of the wire due to an inadequate passive bonding procedure [25]. One or more of the aforementioned etiologic factors might explain the situation described in this case report. To prevent a recurrence of these unwanted tooth movements, BRWs were bonded to the upper and lower jaws after the second orthodontic treatment. Fiber-reinforced composite or polyethylene splints could represent a viable alternative to conventional metallic bonded retention [32]. However, these materials have been shown to be less clinically reliable over time than stainless steel retainers [33]. A rectangular chain retainer could also have been a good alternative for the fixed retention in the upper and lower jaws. However, according to [PERSON] et al., BRWs achieve higher torque control [25]. Therefore, we chose to apply BRWs. Due to occlusal interferences with the lower canine, the retainer in the upper jaw was bonded to the incisors alone. However, it has been shown that significantly fewer rotational changes occur when fixed retainers are bonded from 13 to 23 compared to fixed retainers bonded from 12 to 22 [34]. Therefore, a VFR was prescribed to prevent rotational changes of the 13 and 23. According to a systematic review conducted by [PERSON] et al., fixed retainers and VFRs in the upper jaw are equally effective in maintaining the end result of an orthodontic treatment (with a moderate level of certainty) [14]. Hence, a VFR placed in the upper jaw should stabilize the cuspids adequately. It has been shown that the failure of fixed orthodontic retainers occurs more frequently in the upper jaw compared to the lower jaw [10]. Therefore, if the fixed retainer fails from 12 to 22, the VFR will stabilize the alignment until the retainer can be repaired. The limitations of this case report include (1) the delay of the first follow-up appointment, which was eventually scheduled after 28 months due to the patient's departure abroad and the COVID-19 pandemic. Fortunately, the fixed retainers did not fail in this period. However, the first follow-up appointment should have been scheduled earlier, since most failures of fixed retention occur in the first 6 months after the bonding of fixed retainers. In addition, failure is more frequent in the upper jaw [10].