Custom Bleaching Trays: Reservoirs, Gel Strength and Results That Last

A patient wants whiter teeth before a wedding, and you have three decisions to make: which gel strength, how the tray should be designed, and what to do about the old composite on #8 and the crown on #9. Get them wrong and you hear about sensitivity in week one and a shade mismatch for years.

Custom-tray bleaching has been studied since 1989, so most of these choices now have trial data behind them. Below: gel strength, reservoirs, tray borders, relapse, bonding, regulation, and the records to send for trays.

Quick Answer

Custom trays with 10% carbamide peroxide remain the best-studied at-home option: stronger gels reach about the same final shade but cause more sensitivity. Reservoirs and scalloped borders are optional: trials show no meaningful color benefit, and over-extended borders can irritate the gingiva. Results usually last years with some relapse. Restorations do not change color, so bleach first, wait before bonding, and match restorations to the new shade.

Why Is 10% Carbamide Peroxide the Reference Point?

Nightguard vital bleaching, introduced by Haywood and Heymann in 1989, used 10% carbamide peroxide in a custom-fitted tray; by 1997 Haywood described normal treatment time as one to two weeks, longer for difficult stains. According to the ADA, carbamide peroxide releases about one-third of its content as hydrogen peroxide, which can pass through enamel and dentin to the pulp within 15 minutes.

The ADA once accepted at-home bleaching agents: a 1997 JADA review recommended using an ADA-accepted at-home agent under a dentist's supervision. Today the ADA calls dentist-supplied whitening products professional products that are not eligible for the Seal. The Seal is now a voluntary program for over-the-counter products, and its first home-use bleaching Seals were awarded in 2017.

Long-term data on 10% carbamide peroxide are reassuring. In a University of North Carolina study, 98% of patients lightened and 82% kept the result at a mean of 47 months; 66% reported sensitivity or gingival irritation during treatment, none at the end. A follow-up 10 to 17 years later found no external cervical resorption, and 87% would whiten again.

Does a Stronger Gel Whiten More?

Not by the end of treatment: stronger gels can work faster in the first days, but final color is similar and sensitivity rises. The 2018 Cochrane review of 71 trials found sensitivity and oral irritation more common at higher concentrations, though mild and transient. The ADA says mild to moderate sensitivity can occur in up to two-thirds of users early in treatment.

CP is carbamide peroxide, HP hydrogen peroxide, RR relative risk. The 2025 review advises prescribing the strongest gels with care and closer supervision.

Do Reservoirs in Bleaching Trays Help?

Reservoirs are block-out spacers on the facial surfaces of the model, so the tray holds more gel. The evidence is mixed and mostly says they are optional:

A 2019 systematic review of 9 randomized trials found 4 with no color difference and 2 favoring reservoirs, and concluded there is no evidence that reservoirs improve color change. A 2026 review adds that more gel may mainly increase tissue exposure, cost and adverse effects.

Scalloped or Not, and How Far Should the Tray Extend?

Border shape

In a split-mouth trial of 120 patients using 10% hydrogen peroxide for 30 minutes a day, scalloped and non-scalloped borders were equivalent for gingival irritation and sensitivity, with color differences below the clinically noticeable threshold. The authors left scalloping to the clinician.

Border extension

How far the tray goes past the gingiva may matter more. In a 72-patient trial with 16% carbamide peroxide worn overnight, trays extended 3 mm past the gingival margin had more examiner-detected irritation than trays extended 1 mm, and more intense sensitivity, with no color difference; patient-reported irritation did not differ significantly. The ADA links gingival irritation mainly to poorly fitting trays or improper gel application.

We found little clinical research on tray thickness. One case report shows design can follow the patient: trimming a tray to the facial surfaces, incisal edges and buccal cusps restored tooth contact for a patient with TMJ pain, who then finished bleaching without symptoms.

How Long Do Results Last?

In the 92-patient Meireles trial, teeth were still lighter than baseline at 2 years, but more than 66% of patients in each group reported mild to moderate relapse, and the 16% gel did not outlast the 10% gel. In the UNC series, 43% perceived the shade as stable about 10 years later. Plan for touch-ups and tell patients to keep their trays.

How Long Should You Wait Before Bonding?

Cvitko et al. found that 10% carbamide peroxide reduced the shear bond strength of composite to etched enamel, and that removing surface enamel restored it. A 2021 meta-analysis of 24 lab studies confirmed that at-home bleaching lowers immediate bond strength; antioxidants improved it, in studies at medium to high risk of bias. Ceramic is not exempt: in a 2023 lab study, e.max Press discs bonded 14 days after 15% carbamide peroxide, even after 0.5 mm of enamel reduction, had the lowest bond strength of all groups (5.39 MPa vs 15.71 MPa unbleached).

These are lab findings: they set a direction, not an exact day count. For the bonding steps, see our cementation and bonding guide.

Why Does Shade Planning Matter With Existing Restorations?

The ADA states that only natural teeth can be whitened, not tooth-colored restorations, and advises documenting existing restorations before bleaching and warning patients about the mismatch. That sets the sequence: bleach first, then make new restorations to the bleached shade.

For shade tab photos and stump shade, see Shade Matching: Photos and Stump Shade. If veneers will follow, our veneers guide compares e.max, zirconia and feldspathic options.

How Are Whitening Products Regulated?

United States

In 1991 FDA sent warning letters calling peroxide tooth whiteners unapproved new drugs. Den-Mat sued, then withdrew its case in 1992 after FDA agreed to review new information, and FDA says it has issued no determination on that product since. In 2014 FDA denied an ADA citizen petition asking for a classification, saying data were insufficient to decide whether peroxide whiteners as a group meet the definition of a drug. ADA policy holds that only licensed dentists or their supervised auxiliaries should make impressions for whitening trays.

European Union

Commission Regulation (EU) No 344/2013 carried the same rule into the EU Cosmetics Regulation from 11 July 2013: no use under age 18, and the hydrogen peroxide percentage on the label. By the ADA's one-third rule, 6% hydrogen peroxide equals roughly 18% carbamide peroxide, so much of the 10% to 38% range the ADA describes for US at-home systems sits above the EU limit.

What Records Should You Send for Bleaching Trays?

• Arches: a complete scan or impression of every arch to be bleached, with clean gingival margins, since the border is trimmed to them (see How to Send a Scan to a Dental Lab).
• Rx: arch, border shape and extension, reservoirs or none, teeth to leave uncovered (see How to Fill Out a Dental Lab Rx).
• Restorations: note crowns, veneers and large composites that will not change color.
• Notes: sensitivity history, TMJ symptoms, planned restorations.

Bleaching Trays at Elegant Dental Laboratory

• Bleaching trays are part of our orthodontic appliances line, made in house in Brooklyn by more than 35 technicians, with no outsourcing.
• Digital scans are reviewed before production; we accept STL and PLY files from all major intraoral scanners (submit a digital case), or you can send a case by impression.
• When restorations follow the bleaching, we make IPS e.max veneers from 0.3 mm, crowns and onlays, plus zirconia and PFM.
• Our own drivers pick up and deliver free every business day during lab hours in all five New York City boroughs and 13 northern New Jersey counties; practices elsewhere can print a UPS label. Call 877-335-5221.

FAQ

Is 10% carbamide peroxide still the standard for tray bleaching?

It is the best-studied concentration; stronger carbamide gels reach a similar final shade with more sensitivity.

Do reservoirs make bleaching faster or better?

Not meaningfully. A systematic review of 9 trials found no evidence that they improve color change, and one trial linked them to more gingival inflammation.

How long should I wait to bond after bleaching?

Lab studies show reduced bond strength right after bleaching; in one, it recovered after three weeks.

Will bleaching change the color of crowns or veneers?

No. Only natural teeth whiten, so bleach first and make restorations to the new shade.

Can teenagers use whitening trays?

In the EU, products above 0.1% hydrogen peroxide are barred under 18. The American Academy of Pediatric Dentistry discourages full-arch cosmetic bleaching in the primary and mixed dentition.

Has FDA approved whitening gels?

FDA has issued no classification for peroxide whiteners as a group. In 2014 it denied the ADA's petition to set one, saying the data were insufficient.

Reviewed by Gary Fingerman, founder and CEO of Elegant Dental Laboratory, Brooklyn, New York (founded 2007). Last reviewed: October 1, 2026. Study values are from published research and regulatory documents; follow the instructions for use of the whitening gel you prescribe.