# Orthodontic Relapse after Fixed or Removable Retention Devices: A Systematic Review
## 4 Discussion
### Bonded Retainers versus Removable Retention Devices  
[PERSON] et al. [26] conducted a randomised controlled trial comparing three retention methods over two years. All methods effectively maintained orthodontic results, with minimal relapse in the lower anterior teeth. [PERSON] et al. [27] compared fixed upper and lower retainers to thermoformed mobile splints over 12 months. Both methods were equally effective in maintaining stability at the maxillary level, but the cemented retainer was more efficient in the mandibular arch. [PERSON] et al. [32] compared different types of retainers and found that all retainers had a similar rate of maintaining alignment. CAD/CAM retainers had a better fit. [PERSON] et al. [34] evaluated the significance of upper retainers in patients with impacted or unerupted maxillary incisors. They found no clinically significant differences in the maintenance of results between the group with no retainer and the group with a retainer. However, differences in lower incisor inclination were statistically significant. [PERSON] et al. [36] conducted a retrospective study and found that stability was good two years after orthodontic treatment, with less than 2% experiencing undesirable changes. [PERSON] et al. [1] found that fixed retainers were more effective than vacuum-formed retainers in maintaining mandibular anterior segment alignment at a 4-year follow-up. Periodonal health was similar between the two groups. [PERSON] et al. [40] evaluated different retention strategies and found improvements in various occlusal variables after one year of retention. However, some variables deteriorated over time. [PERSON] et al. [41] compared fixed lingual retainers to Essix-type retainers and found that Essix retainers were most effective in preventing extrusion of lower incisors. [PERSON] et al. [43] performed a randomised clinical trial over five years and found that all three retention methods were clinically valid. [PERSON] et al. [46] observed a significant recurrence of alignment and crowding after three years but stabilisation in the upper arch after 33 years. Prolonged use of retainers improved outcomes. [PERSON] et al. [52] followed up on patients with deep bites and found a recurrence of incisor position in 10% of cases, with causes unidentified. [PERSON] et al. [53] evaluated patients treated with fixed orthodontics and found higher recurrence with more significant initial tooth crowding. Oclusal stability decreased after ten years of retention. [PERSON] et al. [54] evaluated patients seven years after orthodontic therapy and found small, clinically insignificant changes, indicating the presence of recurrence regardless of retention methods. The findings suggest that retention methods can effectively maintain orthodontic results, but some relapse may occur over time, particularly in the mandibular arch. Fixed retainers tend to be more effective than removable ones, and prolonged use of retainers improves stability. [PERSON] et al., as a result of their analysis, suggested the use of a fixed retainer in the lower arch, bonded from canine to canine or from premolar to premolar [59]. However, suppose significant bodily movements of the teeth have been performed (distalization or mesialization). In that case, it is recommended to use a simultaneous lower thermoformedsplit that accommodates the space for the fixed retainer. A simple thermoformed splint is recommended for the upper arch, discouraging using a fixed retainer that could interfere with the patient's protrusive movements and potentially cause temporomandibular joint issues. The limitations of this study were related to the wide range of restraint devices on the market and the variables associated with the different types of treatment that can be adopted. The devices can be fixed or removable, or a combination of the two. The restraints can then be handmade, digitally designed and folded by machines. Articles were selected in which the cases treated were only fixed orthodontics in permanent dentition patients.