The effects of fixed and removable orthodontic retainers: a systematic review

Progress in Orthodontics

Table 6 Excluded studies with reasons for exclusion (n = 36)

Reason for exclusion	Studies
Irrelative outcome to the systematic review	[42–63]
Cross sectional study	[64–67]
Follow-up less than 6 months	[68–70]
Subjects did not undergo orthodontic treatment	[71, 72]
Retrospective study	[73–76]
No control group	[77]