I had my teeth whitened about six years ago and wanted to touch them up before my wedding, but it looks like I’ve lost my trays. I’ve seen websites where you get an impression kit and go from there but I still have my stone molds – can I get trays made from these at a lower cost than the whole impression route?
If your impressions and study casts were taken 6 years ago, your bite will almost definitely have changed.
If you have had any restorations (fillings crowns bridges) these can change your bite…Your bite is continually changing without any restorations, just with wear and tear on your dentition.
If you went to a dental laboratory, they may be able to make them in there, but in the UK, they require a prescription from your dentist as trays, crowns, dentures etc are classed as medical devices.
If your tray does not fit correctly, you may find that your teeth do not bleach evenly, and you may cause damage to your gums, either with the trays causing to much pressure, or the bleach itself causing chemical burns…
My advice…bite the bullit and pay for new impressions at the dentists….sorry 
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If your impressions and study casts were taken 6 years ago, your bite will almost definitely have changed.
If you have had any restorations (fillings crowns bridges) these can change your bite…Your bite is continually changing without any restorations, just with wear and tear on your dentition.
If you went to a dental laboratory, they may be able to make them in there, but in the UK, they require a prescription from your dentist as trays, crowns, dentures etc are classed as medical devices.
If your tray does not fit correctly, you may find that your teeth do not bleach evenly, and you may cause damage to your gums, either with the trays causing to much pressure, or the bleach itself causing chemical burns…
My advice…bite the bullit and pay for new impressions at the dentists….sorry
References :
im a dental nurse and dental student