Howard asked: “Why are whitening trays made of flexible material?  Wouldn’t a rigid whitening tray work better?”

Thanks for the question, Howard.

I get that question frequently.  The good thing about a rigid whitening tray would be the stability of the tray on the teeth.  But that is only one of the properties we need from a whitening tray.

Sealing at the cervical area of the tooth is of paramount importance, and a rigid whitening tray simply will not provide an excellent seal.  Let me use a refrigerator door as an analogy.  If you look at your refrigerator door, you will see a sealing gasket around the perimeter of the door.  Is that gasket hard or soft?  It’s soft because that is what will create an excellent seal.  

So when determining the specific EVA material we use for KöR Whitening trays, I had to determine at what point the compromise should be made.  The material needed to be stiff enough to be stable on the teeth, yet soft enough to allow the creation of an excellent seal of the tray against the cervical margins of the teeth.

The entire goal of a whitening tray is to keep the whitening gel inside and to prevent saliva and sulcular fluid from getting under and into the tray, contaminating the whitening gel.  If you have a tray that’s too flexible, it will not stay in place and will allow the rapid ingress of saliva under the tray.

But on the other hand, if the tray material is too rigid, it will not create a proper seal, and again you’ll have saliva and sulcular fluid getting under and inside the whitening tray.

So why is the cervical seal of the whitening tray so important?  Conventional whitening trays do not create a cervical seal.  You’ve no doubt read or heard about the multiple studies that show whitening gel in conventional trays only stays “active” for 20-35 minutes.  The reason for the short period of activity is that saliva and sulcular fluid seep under and into the whitening tray.  This saliva and sulcular fluid destroy whitening gel ON CONTACT.

Both saliva and sulcular fluid are heavily concentrated with the natural antioxidant enzyme glutathione peroxidase.  The sole job of this enzyme is to destroy peroxide and force it to break down to only molecular oxygen and water instantly.  The fact is, sulcular fluid is even more highly concentrated with this antioxidant than saliva.

As I’m sure you have heard, I created KöR-Seal whitening trays to provide a seal at the cervical margin of the trays, helping to seal out saliva and sulcular fluid.  This is precisely why KöR whitening gels stay active inside the KöR-Seal trays for a full 6+ HOURS, with some activity out to ten hours.  Huge difference in effectiveness between 20-35 minutes and 6+ hours.

I hope I’ve adequately answered your question, Howard.

Very best regards,


Dr. Rod Kurthy

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