Quick facts
- An impression tray is the rigid carrier that holds impression material against teeth or an edentulous ridge while the material sets.
- United States: the tray is a named device. 21 CFR 872.6880 covers a preformed impression tray in Class I, described as a metal or plastic device intended to hold impression material such as alginate.
- The material in the tray is classified differently. 21 CFR 872.3660 places impression material in Class II with special controls.
- Canada splits the pair by relationship, not by chemistry. Rule 3(b) of Schedule 1 to the Medical Devices Regulations, SOR/98-282 places all surgical or dental instruments in Class I, while Rule 3(a) places all denture materials and orthodontic appliances, and their accessories, in Class II.
- Canada no longer defines the term dental material. The definition was repealed by SOR/2002-190, so the class is read from the rules rather than from a definition.
- The purchase test is tray type, perforation and rigidity, plus which appliance the tray is supplied to support.
An impression tray is the least interesting object in a prosthetic workflow and the one that decides whether the model is usable. Both countries classify it, and the two systems divide responsibility between the tray and the material in opposite ways. This article sets out what the tray does, how each country classifies it, how the Canadian rules split a tray from its material, which formats exist, and what a clinic should verify on delivery.
What is a dental impression tray, and why does rigidity matter?
A tray is a carrier with a handle, a wall and a floor. It holds a measured volume of impression material in a fixed relationship to the arch, and it is removed once the material has set. Three properties decide the result:
- Rigidity. A tray that flexes as it is withdrawn distorts the set impression, and the distortion is not visible in the material.
- Retention. Perforations and a rim lock keep the set material attached to the tray. A material that separates from the tray on withdrawal pulls away from the sulcus.
- Fit. A stock tray that overlaps the sulcus or fails to cover the retromolar pad produces a short impression, which shows up later as a short denture border.
21 CFR 872.6880 identifies the article in a single sentence: "a metal or plastic device intended to hold impression material, such as alginate, to make an impression of a patient's teeth or alveolar process (bony tooth sockets) to reproduce the structure of a patient's teeth and gums". It is Class I, and the exemption in the section is subject to the limitations in § 872.9.
How do Canada and the United States classify a tray and its material differently?
| Item | Canada | United States |
|---|---|---|
| Named entry for a preformed tray | None; class derived by rule | 21 CFR 872.6880, preformed impression tray, Class I |
| Class of the tray | Class I under Rule 3(b), as a dental instrument | Class I (general controls) |
| Named entry for impression material | None; class derived by rule | 21 CFR 872.3660, impression material, Class II (special controls) |
| Class of impression material | Class II under Rule 3(a), as a denture material used to produce a prosthesis | Class II (special controls) |
| Named entry for custom tray resin | None; class derived by rule | 21 CFR 872.3670, resin impression tray material, Class I |
| Clause that can move a tray upward | Rule 3(a), where the tray is an accessory to a denture or orthodontic appliance | Not present in this shape |
| Premarket position | Licence only where the derived class requires one | Exempt from premarket notification, subject to § 872.9 |
The United States separates the two objects into two sections, and the sections do not agree. The tray is Class I; the material is Class II. That is why a clinic can buy a tray with a declaration of conformity and buy the material that goes into it against a different set of expectations, including the special controls attached to the material section.
Canada separates them by purpose instead. Rule 3(b) is broad — "all surgical or dental instruments are classified as Class I" — and a preformed tray used to carry material to the arch is a dental instrument. Rule 3(a) is the clause that captures the rest of the prosthetic workflow: all denture materials and orthodontic appliances, and their accessories, are Class II. A tray sold as part of a denture system, or supplied as an accessory to an orthodontic appliance, is caught by that broader clause rather than by Rule 3(b).
Do the two countries apply the same rule to a custom tray?
Almost, with one Canadian wrinkle worth knowing. A custom tray is made on a preliminary model from a resin material, and the United States has a section for exactly that: 21 CFR 872.3670 describes resin impression tray material as a device used "to form a custom impression tray for use in cases in which a preformed impression tray is not suitable, such as the fabrication of crowns, bridges, or full dentures", and places it in Class I.
In Canada the custom tray is read from Rule 3. If the tray is an instrument, Rule 3(b) applies and the class is Class I. If the tray is supplied as an accessory to a denture, Rule 3(a) applies and the class is Class II. The two readings sit a class apart, which is why the intended-use statement on the packaging, not the picture on the box, settles the question.
One more Canadian point is worth flagging, because it surprises suppliers. The Medical Devices Regulations once defined the term dental material, and that definition has been repealed — the interpretation section of the regulations now reads "dental material [Repealed, SOR/2002-190, s. 1]". Canada therefore classifies denture-related articles through Rule 3 rather than through a definition, and a supplier who quotes the old definition is quoting a provision that no longer exists.
Which tray format fits which impression?
| Tray format | What it suits | What a buyer should confirm |
|---|---|---|
| Perforated stock tray | Alginate impressions of a dentate arch | Perforation pattern, size range, rigidity |
| Rim-lock stock tray | Materials that need mechanical retention at the border | Rim lock profile, material compatibility |
| Triple tray | Simultaneous upper and lower registration on a bite | Frame stiffness, bite registration clearance |
| Sectional tray | Quadrant work and implant-level impressions | Coverage, stability under withdrawal |
| Edentulous tray | Full arch impressions of a ridge | Border extension, handle position |
| Custom tray | Cases where a stock tray does not fit | Resin compatibility, spacer clearance |
The format decision interacts with the material decision, and both are affected by the class split. A triple tray that also carries bite registration material is doing two jobs at once, so the clinic is buying a tray, an impression material and a registration material in one package, and each part has its own intended use.
What should a clinic verify on delivery?
Four checks keep an impression tray line from producing unexplained remakes:
- Rigidity and batch consistency. Test a tray from the new lot against the material the clinic uses; a flexible tray is a remake.
- Intended-use statement. Read whether the tray is sold as an instrument or as an accessory to a denture or orthodontic system, because that is the input the Canadian class rules need.
- Cleaning and disinfection instructions. A tray that has been in the mouth and then sent to a laboratory is subject to the infection control guidance the Royal College of Dental Surgeons of Ontario publishes, and to the Canadian Dental Association material on laboratory work.
- Traceability of the lot. Impressions are remade because of a defect in the tray, the material or the technique, and the lot number is what allows the first two to be excluded.
Which consumables does an impression workflow go through?
An impression workflow restocks trays, alginate or elastomer, mixing supplies, cotton rolls, isolation items, bibs and disinfectant in the same cycle. For practices buying at case level, the wholesale ordering page sets out account and case pricing, and the B2B wholesale collection lists the lines held for institutional buyers. The alginate impression material, one pound canister is the line we hold for impression work, and practices that also run an in-house sterilizer can start with the biological indicator 5-pack trial and read the sterilization monitoring collection for the monitoring lines.
Sources
- 21 CFR 872.6880, preformed impression tray
- 21 CFR 872.3660, impression material
- 21 CFR 872.3670, resin impression tray material
- Medical Devices Regulations, SOR/98-282, full text, Schedule 1, Rule 3
- Royal College of Dental Surgeons of Ontario, standards, guidelines and resources
- Canadian Dental Association
- Canadian Dental Hygienists Association
- American Dental Association, infection control and sterilization
- Health Canada, medical devices
- openFDA device classification database
- FDA device classification database search
- ISO 10993-1:2018, biological evaluation of medical devices
- ISO 11609:2017, dentistry, dentifrices
- Public Health Ontario, infectious diseases
- CCOHS, osh answers
- World Health Organization, oral health fact sheet
- Ontario Ministry of Health
- Clinical and Laboratory Standards Institute
- CCOHS, personal protective equipment
- US Department of Labor, OSHA bloodborne pathogens standard, 29 CFR 1910.1030
Related reading
- Dental impression materials in Canada vs the US: which class
- Denture clinic supplies: impressions and the prosthetic workflow
- Dental lab disinfection: cleaning impressions without damage
- Dental dams in Canada vs the US: materials and isolation
CliniEco Medical supplies eye care, laboratory and clinic consumables of the kind described in this article. Health Canada MDEL #35334. This article is written for clinic, laboratory and procurement professionals and is not clinical guidance; tray selection for a patient and impression technique belong to the treating dentist or denturist.
Frequently Asked Questions
What class is a preformed impression tray in the United States?
Class I. 21 CFR 872.6880 describes a preformed impression tray as a metal or plastic device intended to hold impression material, such as alginate, to make an impression of teeth or the alveolar process, and places it in Class I with the exemption subject to § 872.9.
Why is impression material a different class from the tray in the United States?
Because the two are separate entries. The tray sits in 21 CFR 872.6880 in Class I, while 21 CFR 872.3660 places impression material in Class II with special controls. The tray is a carrier; the material becomes part of the model from which a prosthesis is made.
How does Canada classify an impression tray?
Through Rule 3 of Schedule 1 to the Medical Devices Regulations. Rule 3(b) places all surgical or dental instruments in Class I, which covers a tray used as an instrument. Rule 3(a) places all denture materials and orthodontic appliances, and their accessories, in Class II, which can catch the same tray when it is supplied as an accessory to a denture or orthodontic system.
Does Canada still define the term dental material?
No. The interpretation section of the Medical Devices Regulations now reads "dental material [Repealed, SOR/2002-190, s. 1]". Classification of denture-related articles therefore follows Rule 3 rather than a definition, and a supplier quoting the old definition is quoting a repealed provision.
Is a custom tray classified the same way as a stock tray?
In the United States the custom route has its own section, 21 CFR 872.3670, which covers resin impression tray material in Class I. In Canada the class depends on the intended use: an instrument reading gives Class I under Rule 3(b), while an accessory-to-a-denture reading gives Class II under Rule 3(a).
What should a clinic check when a tray delivery arrives?
Rigidity across the lot, the intended-use statement that decides the Canadian class reading, the cleaning and disinfection instructions, and the lot number. Impression remakes are traced by lot, and a tray that flexes on withdrawal will produce a remake that no material change can fix.
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