The aim of this study will be to evaluate the biological reaction of direct three dimensional printed retainers.

Primary objective is to evaluate bacterial growth and color stability between different thicknesses of 3d printed material used as a retainer .

Secondary objective is to determine the optimal thickness for use in clear aligner fabrication based on biological performance.

Retainers are routinely fitted at the end of active orthodontic treatment to allow the teeth to adjust to their new positions The growing demand has led to constant improvements in materials and technologies offered by a rising number of different companies.

In recent years, major technological innovations in 3D printing, especially related to computer-aided design, biomaterials and manufacturing techniques, have enabled the production of in-office direct printed Retainers (DPRs) - representing an innovation compared to the traditional thermoformed Retainers.

Insufficient cleaning will lead to microbe's growth in retainers. The mostly found microbes are candida and staphylococcus that may include MRSA strains. Once the biofilms are formed in the retainer it's quite difficult to remove that biofilm which shows resistance to antimicrobials and difficult to clear.

orthodontic retainers hinder the sterilizing effect of saliva, which further promotes the rapid division, reproduction, and growth of colonized bacteria.

Staphylococcus aureus is most commonly found on the retainers and tends to cause bloodstream infections which can lead to serious other infections.

While several studies have assessed tooth movement, and biomechanical and clinical effects according to the design of attachments, studies investigating the thickness of the CAs are limited

Inclusion Criteria:

• -Finished fixed orthodontic therapy and seeking for retention as a part of their original treatment plan.
• Good oral hygiene.
• No habits (e.g., smoking)

Exclusion Criteria:

• Medication affecting saliva.

  • intrinsic tooth discoloration.
  • Uncooperative patients.
  • Patient with periodontitis.
  • Learning difficulties and inability to read written instructions.