After completion of orthodontic treatment, a retention phase is required to prevent relapse of tooth malposition. Fixed retention in the mandibular anterior region is commonly used. This type of retainer is bonded to the lingual surfaces of the canines and incisors and may hinder oral hygiene, thereby promoting bacterial plaque accumulation and gingival inflammation.
Currently, probably due to the increasing use of clear aligner therapy, clear removable Essix-type retainers are becoming more widely used. Since these retainers can be removed by the patient, they may facilitate oral hygiene. However, studies assessing gingival health and the composition of the subgingival microbiota in patients wearing orthodontic retainers remain scarce.
Therefore, the aim of this study will be to assess the composition of the gingival sulcus microbiota and gingival health in patients wearing fixed or removable orthodontic retainers.
Ten adult patients who have completed orthodontic treatment will be recruited and divided into two groups:
1. Fixed retention group. 2. Removable retention group.
Periodontal parameters will be assessed, and bacterial plaque samples will be collected from the gingival sulcus at five time points:
T0: Bracket removal and dental scaling appointment. Periodontal parameters will be assessed, and plaque samples will be collected before bracket debonding and dental scaling.
T1: Retainer placement appointment, three days after T0. Periodontal parameters will be assessed, and plaque samples will be collected before retainer placement.
T2: One month after retainer placement.
T3: Three months after retainer placement.
T4: Six months after retainer placement.
Treatment involving both dental arches
Permanent dentition with at least 24 teeth
Treatment duration longer than 12 months
Treatment using the Versatile MBT system with a 0.022-inch slot
Patients with systemic disease or taking medications that may affect periodontal health
Inadequate restorations or active carious lesions
iodontal disease
Plaque index greater than 20% before placement of the retainer or during the study
Parallel
Fixed Orthodontic Retainer
DeviceA fixed lingual orthodontic retainer bonded to the mandibular anterior teeth, extending from tooth 33 to tooth 43
Removable Essix-Type Orthodontic Retainer
DeviceA clear removable Essix-type orthodontic retainer prescribed for 22 hours of daily wear
Longitudinal change in subgingival microbial community composition assessed using Bray-Curtis dissimilarity
Subgingival plaque samples collected from the mandibular anterior teeth will be analyzed using 16S rRNA gene sequencing. Overall microbial community composition will be assessed using the Bray-Curtis dissimilarity index. Longitudinal differences in microbial community composition will be evaluated between participants receiving fixed orthodontic retainers and those receiving removable Essix retainers, considering the effect of study group, assessment time point, and their interaction.
Longitudinal change in bleeding on probing
Bleeding on probing will be recorded as present or absent at six sites per tooth in the mandibular anterior region following gentle periodontal probing. The outcome will be calculated as the percentage of examined sites showing bleeding for each participant. Longitudinal changes in bleeding on probing will be compared between participants receiving fixed orthodontic retainers and those receiving removable Essix retainers, considering the effect of study group, assessment time point, and their interaction.
Longitudinal change in subgingival microbial alpha diversity assessed using the Shannon diversity index
Subgingival plaque samples collected from the mandibular anterior teeth will be analyzed using 16S rRNA gene sequencing. Alpha diversity will be quantified using the Shannon diversity index for each sample. Higher values indicate greater microbial diversity within the sample. Longitudinal changes will be compared between participants receiving fixed orthodontic retainers and those receiving removable Essix retainers, considering study group, assessment time point, and their interaction. Time Frame
Longitudinal change in subgingival microbial evenness assessed using Pielou's evenness index
Microbial community evenness will be quantified using Pielou's evenness index calculated from the 16S rRNA gene sequencing data. The index ranges from 0 to 1, with higher values indicating a more even distribution of bacterial taxa within the microbial community. Longitudinal changes will be compared between the fixed-retainer and removable-retainer groups across all study visits.
Longitudinal change in subgingival microbial dominance assessed using the Simpson dominance index
Microbial dominance will be quantified using the Simpson dominance index calculated from the 16S rRNA gene sequencing data. Higher index values indicate greater dominance of the microbial community by a limited number of bacterial taxa. Longitudinal changes will be compared between participants receiving fixed orthodontic retainers and those receiving removable Essix retainers across all study visits.
Longitudinal change in subgingival microbial taxonomic composition
The relative abundance of bacterial taxa identified by 16S rRNA gene sequencing will be calculated as the percentage of sequencing reads assigned to each taxon. Taxonomic composition will be evaluated at the phylum, family, and genus levels and, where technically feasible, at the species level. Longitudinal changes will be compared between participants receiving fixed orthodontic retainers and those receiving removable Essix retainers.
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