Table 1.

Outcomes of studies of fixed and removable appliances.

Authors	Year of Publication	Parameters	Outcome Measures
Liu et al. [75] (clinical study)	2011	PLI, GI, PD	PLI, GI, and PD increased significantly in the first 3 months following appliance insertion but decreased significantly in the first 6 months after appliance removal.
Madariaga et al. [76] (prospective clinical study)	2020	PLI, GI, GBI, PD	According to the linear regression models, appliance type did not affect periodontal variables. Thus, fixed appliance and clear aligner orthodontic patients had similar gingival health statuses.
Wu Y. et al. [77] (meta-analysis)	2020	PLI, GI, PD	Removable appliances had significantly lower PLIs than fixed equipment. At 6 months, removable appliances reduced GI, but they did not do so at 3 months. At 3 months, mobile devices had lower PDs than fixed appliances.
Li W. et al. [78] (clinical study)	2017	PLI, GI, PD, GBI	After 3 months, Invisalign therapy lowered GBI and PD levels compared to fixed treatment (p < 0.05); however, there was no significant difference after 6 months (p > 0.05).
Eroglu et al. [27] (clinical study)	2019	PLI, GI, PD, GBI	The authors found no significant differences in the plaque index, gingival index, bleeding on probing, or probing depth (p > 0.05).
Sun et al. [79] (prospective clinical study)	2018	PLI, GI, PD, GBI	Before and three months after treatment, the two patient groups had similar periodontal indicators.

GI = gingival index; PLI = plaque index; PD = probing depth; GBI = gingival bleeding index.