As soon as possible. Losing your retainer is not a good feeling, but it happens to many patients. Once you are sure that your retainer is lost, it is time to contact your orthodontist. It can take time to make a new retainer. At times, your orthodontist may need to take new impressions. While admitting to losing your retainer may be a little embarrassing, it’s essential that you don’t put off getting in touch with your orthodontist. Ignoring your retainer can quickly undo the work that your braces did. Although a replacement retainer may be expensive, it’s certainly less expensive than another round of braces. Related Post: Tips for Taking Care of Retainers