Effectiveness of Gold Fixed Retainers Compared to Conventional Stainless Steel Retainers

Little's Irregularity Index (LII) is a quantitative scale of mandibular anterior alignment, calculated as the sum of the linear displacements (in mm) of the contact points of the six mandibular anterior teeth. Scores range from 0 mm (perfect alignment, no irregularity) to ≥10 mm (very severe irregularity); higher scores indicate greater crowding and therefore a worse outcome.

LII will be measured for the mandibular anterior teeth (canine-to-canine) at baseline (T0, before fixed-retainer placement) and at follow-up visits (T1 = 1 month, T2 = 3 months, T3 = 6 months). The primary endpoint is the change in LII (follow-up LII minus baseline LII), comparing gold-plated versus stainless-steel fixed-retainer groups.

Time (days) from fixed retainer bonding to the first failure event requiring repair/rebonding/replacement. Failures will be recorded and classified (e.g., adhesive-enamel debond, wire-composite debond, wire fracture, partial/complete loosening) and compared between groups.

Silness-Löe Plaque Index is a 4-point scale (0-3) that scores plaque accumulation on tooth surfaces adjacent to the gingival margin. Scores range from 0 (no plaque) to 3 (abundant soft deposits); higher scores indicate poorer oral hygiene and a worse periodontal condition. The mean Plaque Index will be recorded for the mandibular anterior teeth adjacent to the fixed retainer at baseline (T0, before retainer placement) and at 1 month (T1), 3 months (T2), and 6 months (T3) after retainer placement, and compared between the gold-plated and stainless-steel fixed-retainer groups.

Biofilm will be collected using a sterile swab moved along interdental spaces over the exposed retainer, then placed in transport medium and sent for cultivation. After incubation on agar, the total number of bacterial colonies (colony-forming units, CFU) will be counted for each sample. Higher CFU counts indicate greater plaque accumulation and a worse periodontal outcome. Samples will be collected at 1 month (T1), 3 months (T2), and 6 months (T3) after retainer placement and compared between the gold-plated and stainless-steel fixed-retainer groups.

Mandibular inter-canine width (mm) will be measured on study casts/impressions as the linear distance between the cusp tips of the right and left mandibular canines. Measurements will be taken at baseline (T0, before fixed-retainer placement) and at 1 month (T1), 3 months (T2), and 6 months (T3) after retainer placement. The outcome is the change in inter-canine width from baseline at each follow-up visit; larger absolute changes indicate greater relapse and worse post-treatment occlusal stability. Changes will be compared between the gold-plated and stainless-steel fixed-retainer groups.

Gingival condition will be assessed using the Löe-Silness Gingival Index, a 4-point scale (0-3) where 0 = normal gingiva, 1 = mild inflammation, 2 = moderate inflammation, and 3 = severe inflammation with ulceration and/or spontaneous bleeding. Higher scores indicate more severe gingival inflammation and a worse periodontal outcome. The mean Gingival Index will be recorded for the mandibular anterior teeth adjacent to the fixed retainer at baseline (T0) and at 1 month (T1), 3 months (T2), and 6 months (T3) after retainer placement, and compared between the two retainer groups.

Probing pocket depth (PPD) in millimeters will be measured at specified sites around the mandibular anterior teeth using a calibrated periodontal probe. Higher values indicate deeper pockets and a worse periodontal outcome. Mean PPD will be calculated for the mandibular anterior region at baseline (T0) and at 1 month (T1), 3 months (T2), and 6 months (T3) after retainer placement, and compared between the two fixed-retainer groups.

Mandibular arch length (mm) will be measured on study casts as the linear distance from the mesial surface of the right mandibular first permanent molar to the mesial surface of the left mandibular first permanent molar, parallel to the occlusal plane. Measurements will be taken at baseline (T0, before fixed-retainer placement) and at 1 month (T1), 3 months (T2), and 6 months (T3) after retainer placement. The outcome is the change in arch length from baseline at each follow-up visit; larger absolute changes indicate greater relapse and worse post-treatment occlusal stability. Changes will be compared between the gold-plated and stainless-steel fixed-retainer groups.

Overjet (mm) will be measured as the horizontal distance between the labial surface of the most prominent mandibular incisor and the palatal surface of the corresponding maxillary incisor, measured on study casts and/or intraoral records. Measurements will be taken at baseline (T0, before fixed-retainer placement) and at 1 month (T1), 3 months (T2), and 6 months (T3) after retainer placement. The outcome is the change in overjet from baseline at each follow-up visit; larger absolute changes indicate greater relapse and worse post-treatment occlusal stability. Changes will be compared between the gold-plated and stainless-steel fixed-retainer groups.

Overbite (mm) will be measured as the vertical overlap of the maxillary incisors over the mandibular incisors, using study casts and/or intraoral records. Measurements will be taken at baseline (T0, before fixed-retainer placement) and at 1 month (T1), 3 months (T2), and 6 months (T3) after retainer placement. The outcome is the change in overbite from baseline at each follow-up visit; larger absolute changes indicate greater relapse and worse post-treatment occlusal stability. Changes will be compared between the gold-plated and stainless-steel fixed-retainer groups.