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.
The objectives of this study are: 1. To compare the gingival sulcus microbiota in patients wearing fixed versus removable orthodontic retainers. 2. To compare periodontal health in patients wearing fixed versus removable orthodontic retainers. This prospective interventional comparative study will evaluate changes in gingival health and in the subgingival microbiota of adult patients following completion of orthodontic treatment with fixed multibracket appliances. Ten participants attending the University Dental Clinic will be assigned to one of two retention groups: a fixed mandibular retainer group or a removable Essix-type retainer group. Participants in the fixed retention group will receive a lingual retainer bonded from the mandibular left canine to the mandibular right canine, corresponding to teeth 33 to 43 according to the FDI tooth-numbering system. The same type of wire and bonding material will be used for all participants in this group. Participants in the removable retention group will receive a clear Essix-type retainer manufactured using the same material and by the same dental technician. Participants will be instructed to wear the retainer for 22 hours per day. To standardize oral hygiene procedures, all participants will receive the same oral hygiene instructions and an oral hygiene kit for use throughout the study period. Clinical periodontal assessments and subgingival plaque sampling will be performed at five study visits: T0: On the day of bracket removal and dental scaling. Periodontal assessments and plaque sampling will be performed before bracket debonding and scaling. T1: Three days after T0, immediately before retainer placement. T2: One month after retainer placement. T3: Three months after retainer placement. T4: Six months after retainer placement. At each visit, periodontal health will be evaluated using plaque accumulation, bleeding on probing, probing pocket depth, clinical attachment level, and gingival recession. Subgingival plaque samples will be collected from the mandibular anterior region using sterile paper points. Sampling will be performed at the mesial surface of each mandibular canine and at the mesial and distal surfaces of each mandibular incisor. The gingival tissue will be gently displaced to allow insertion of the paper point into the gingival sulcus without bending or contaminating the sample. After collection, the portion of the paper point inserted into the gingival sulcus will be placed in an Eppendorf tube containing sterile phosphate-buffered saline. Samples will be stored at -22 °C until microbiological analysis. The bacterial composition of the samples will be assessed using 16S ribosomal RNA gene sequencing. Changes in microbiota composition and periodontal parameters over time will be compared between the fixed and removable retention groups. Participants will be instructed not to eat, drink, brush their teeth, or use mouthwash for at least two hours before each plaque-sampling visit.
Study Type
INTERVENTIONAL
Allocation
NON_RANDOMIZED
Purpose
OTHER
Masking
SINGLE
Enrollment
10
A fixed lingual orthodontic retainer bonded to the mandibular anterior teeth, extending from tooth 33 to tooth 43
A clear removable Essix-type orthodontic retainer prescribed for 22 hours of daily wear
University Dental Clinic
Murcia, Spain
RECRUITINGLongitudinal 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.
Time frame: T0: pre-debonding; T1: pre-retainer baseline, 3 days after T0; T2: 1 month post-retainer; T3: 3 months post-retainer; T4: 6 months post-retainer.
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.
Time frame: T0: pre-debonding; T1: pre-retainer baseline, 3 days after T0; T2: 1 month post-retainer; T3: 3 months post-retainer; T4: 6 months post-retainer.
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
Time frame: T0: pre-debonding; T1: pre-retainer baseline, 3 days after T0; T2: 1 month post-retainer; T3: 3 months post-retainer; T4: 6 months post-retainer.
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.
Time frame: T0: pre-debonding; T1: pre-retainer baseline, 3 days after T0; T2: 1 month post-retainer; T3: 3 months post-retainer; T4: 6 months post-retainer.
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.
Time frame: T0: pre-debonding; T1: pre-retainer baseline, 3 days after T0; T2: 1 month post-retainer; T3: 3 months post-retainer; T4: 6 months post-retainer.
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.
Time frame: T0: pre-debonding; T1: pre-retainer baseline, 3 days after T0; T2: 1 month post-retainer; T3: 3 months post-retainer; T4: 6 months post-retainer.
Differential abundance of subgingival bacterial taxa
Differential abundance analysis will be performed using 16S rRNA gene sequencing data to identify bacterial taxa whose abundance differs between participants receiving fixed orthodontic retainers and those receiving removable Essix retainers, as well as taxa showing changes over time within each group. Correction for multiple comparisons will be applied.
Time frame: T0: pre-debonding; T1: pre-retainer baseline, 3 days after T0; T2: 1 month post-retainer; T3: 3 months post-retainer; T4: 6 months post-retainer.
Longitudinal change in plaque index
The presence or absence of dental plaque will be recorded at six surfaces per tooth in the mandibular anterior region: three buccal surfaces and three lingual surfaces. The plaque index will be calculated for each participant as the percentage of examined surfaces showing detectable plaque. Longitudinal changes will be compared between participants receiving fixed orthodontic retainers and those receiving removable Essix retainers.
Time frame: T0: pre-debonding; T1: pre-retainer baseline, 3 days after T0; T2: 1 month post-retainer; T3: 3 months post-retainer; T4: 6 months post-retainer.
Longitudinal change in periodontal probing depth
Periodontal probing depth will be measured in millimeters from the gingival margin to the base of the gingival sulcus or periodontal pocket using a periodontal probe. Measurements will be recorded at six sites per tooth in the mandibular anterior region. The mean probing depth will be calculated for each participant, and longitudinal changes will be compared between study groups.
Time frame: T0: pre-debonding; T1: pre-retainer baseline, 3 days after T0; T2: 1 month post-retainer; T3: 3 months post-retainer; T4: 6 months post-retainer.
Longitudinal change in clinical attachment level
Clinical attachment level will be measured in millimeters from the cementoenamel junction to the base of the gingival sulcus or periodontal pocket. Measurements will be recorded at six sites per tooth in the mandibular anterior region. The mean clinical attachment level will be calculated for each participant, and longitudinal changes will be compared between study groups.
Time frame: T0: pre-debonding; T1: pre-retainer baseline, 3 days after T0; T2: 1 month post-retainer; T3: 3 months post-retainer; T4: 6 months post-retainer.
Longitudinal change in gingival recession
Gingival recession will be measured in millimeters from the cementoenamel junction to the gingival margin when the gingival margin is located apical to the cementoenamel junction. Measurements will be recorded at six sites per tooth in the mandibular anterior region. The mean gingival recession will be calculated for each participant, and longitudinal changes will be compared between study groups.
Time frame: T0: pre-debonding; T1: pre-retainer baseline, 3 days after T0; T2: 1 month post-retainer; T3: 3 months post-retainer; T4: 6 months post-retainer.
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