This study aims to evaluate the clinical effectiveness of CAD/CAM 3D printed Chrome Cobalt fixed retainer in maintaining mandibular anterior teeth stability.

The Research Question; "Does the Cobalt-Chromium CAD/CAM designed customized lingual retainer better than Stainless steel lingual retainer in improving tooth stability after orthodontic treatment?" The null hypothesis "There is no differences between the fixed CAD/CAM 3D printed Chrome Cobalt customized retainer and the multi-stranded stainless-steel fixed retainer in maintaining mandibular anterior teeth stability."

A multicenter, single-blinded, randomized controlled trial will be consist of three main parts:

1. Questionnaire Survey - A cross-sectional survey will be distributed to orthodontists to assess their experience and perception of CAD/CAM retainers.
2. In Vitro Study - Laboratory tests will be performed on different diameters of CAD/CAM cobalt-chromium retainers to evaluate their mechanical properties, including tensile strength, load deflection, and shear bond strength.
3. Clinical trial to to evaluate the effectiveness of CAD/CAM retainer group in minimizing the 6month post-orthodontic treatment change in term of a Little's Irregularity Index (LII).

42 Patients will be enrolled; at the last appointment of orthodontic treatment before debonding, subjects will be assessed for the presence of good gingival health parameters using the BPE. Then the patients will have supra gingival debridement followed by an intraoral scan for lower arch; Intraoral scans will be taken for all the participants and STL files will be generated. In addition, a stone model will be made for the lower arch of the control group.

Group 1 (CAD/CAM retainers): STL files will be sent to lab. Group 2 (conventional retainers): The retainer wire will be shaped to adapt passively to the lingual surfaces of lower anterior teeth on the stone model. A silicone transfer key will be prepared to facilitate the positioning of the retainers Laboratory work: CAD/CAM Chrome cobalt retainers; will be digitally designed by the dental technician using EXOCAD software. Then, they will be 3D printed by metal 3D printer and then will be polished. Also, a projection like extensions will be added at the ends of the retainers to avoid slippage in addition to gingivally directed V notch shaped bend in the retainer to increase the retention in the anterior region.

Bonding procedures: The operators will first check the fitting and adaptation of the retainers on the teeth. After cleaning the teeth and isolate them by placement the rubber dam; 35% phosphoric acid etchant gel will be applied. Bonding agent, as the manufacturer's recommendations will be used, After completing the bonding procedure, the patient will be recalled after one week to measure the parameters of gingival health to exclude the plaque retentive fixed appliance effect. The patient will be given oral hygiene instructions and encouraged to use the interdental brush and will be advised to contact the clinician as soon as possible if they have any concerns or problems.

Inclusion Criteria:

• Completion of a course of fixed appliance therapy.
• with a satisfactory correction of malocclusion and dental alignment.
• Class I canine relationship based on Andrew's criteria for finishing.
• Patients with a history of constant oral hygiene measures daily.
• Good general health.
• Subjects had a full and normal complement of teeth in the lower labial segments.
• Teeth within the labial segments should be regularly sized and shaped.
• Subjects willing to consent to the trial.

Exclusion Criteria:

• Patients with a deep overbite
• Patients with traumatic parafunctional habits such as bruxism and clenching.
• Patients with carious, restored, fractured, or missing lower anterior teeth.
• Patients with medical health problems that may influence gingival health, like uncontrolled type II diabetic patients.
• patients under systemic drug administration that affects oral health.
• Smokers