Is it normal for retainers to change shape after a few months of use?

Hi, Each invisalign retainer (Vivera retainer) usually last between 6-18 months. In order not to change the shape of retainers, you need to always wash them with cold water as hot water can distort the plastic. Another important factor is your parafunction habits, if you grind your teeth at night ( bruxism) or clench your teeth together , you are more likely to damage your retainers even making holes in them. Please contact your invisalign provider dentist if you think your teeth have moved already, they can order the retainers based on teeth position when you finish your invisalign treatment, even refine it for you. Dr Sara Amini,  

There are so many factors that affect retainer self-life. it's my advice to upload a photo of the retainer, so I can guide you better. But as you said 3 sets have changed their shape within one year, so one of the reasons is heavy occlusal forces OR the habit of clenching at night. If you see any frosty surface on your retainer, then heavy forces is the reason.

Certainly! Retainers can undergo slight changes in shape over time, especially if they are subject to regular wear. This is a normal occurrence due to factors like the natural shifting of teeth, jaw movements, and the materials used in the retainer itself. However, significant changes or discomfort might indicate a need for adjustment or replacement. I always advise my patients to schedule regular check-ups to ensure their retainers fit properly and continue to support their beautiful smiles effectively. If you're experiencing noticeable changes or discomfort, it's best to reach out for an evaluation to ensure your retainer continues to do its job effectively.