Opinions about the proper design for the bleaching tray used with tray-based teeth whitening have changed since this method was first introduced over ten years ago. The bleaching tray, as originally described the dental literature, was a stiff plastic tray created from dental molds of a person's teeth. The edges of the tray overlapped onto the person's gums about one-sixteenth of an inch or so.
Now days the standard for teeth bleaching tray design is typically referred to as a "custom" bleaching tray. Custom bleaching trays are fabricated on dental molds of a person's teeth. In most cases the tray is created from a thin, soft plastic that is clear in color. The edges of the tray are trimmed in a scalloped fashion so that they end right at a person's gum line.
As an alternative to a custom bleaching tray like that which a dentist fabricates, most over-the-counter teeth whitening kits make use of what is commonly referred to as a stock "boil and bite" tray. These trays are placed in warm water so they become softened. While still soft the trays are placed onto and then pushed over the person's teeth so to be molded by their shape.
Some over-the-counter whitening kits seem to offer the availability of a custom tray. This would imply that the user takes an impression of their teeth (using materials supplied in the kit) that is then returned to the manufacturer. This impression is used to create dental molds of the person and a custom tray is then fabricated on these molds and subsequently returned to the user.
Stock bleaching trays are typically thicker and more bulky than custom fabricated trays. The thickness of stock trays in some instances can:
Compared to custom trays that are typically made out of a thinner plastic, a stock bleaching tray may be more visible or may interfere with activities such as speaking. Either of these problems might limit the number of opportunities you have to perform your whitening activities, thus prolonging the whitening process.
The edges of a stock bleaching tray will extend onto the user's gums, possibly placing the user at greater risk for developing treatment side effects. Custom trays are typically shaped so that their edges end right at a person's gum line. This design makes it less likely that the bleaching process will irritate the person's gums, either by way of rubbing against them or holding whitening gel in contact with them.