This prospective clinical study aims to evaluate the effects of fixed lingual retainers placed after orthodontic treatment on periodontal soft and hard tissue parameters using ultrasonographic imaging. A total of 53 participants (636 anterior teeth) who had completed fixed orthodontic therapy were examined at baseline, 3 months, and 6 months after retainer placement. Ultrasonographic assessments were performed to measure gingival thickness, marginal bone level, and gingival level. Periodontal clinical parameters, including plaque index, gingival index, probing depth, bleeding on probing, and clinical attachment loss, were also recorded. The study seeks to determine whether fixed retainers induce measurable alterations in periodontal structures and to explore potential correlations between gingival phenotype and ultrasonographic findings.