Metal Impression Trays: Perforated vs Unperforated, Ehricke Pattern, Sizing and Open-Tray Implant Impressions

Every crown, bridge, denture and implant restoration starts with an impression, and every impression starts with the tray. A tray that flexes, lets the material pull away on removal, or is a size too small will undo careful preparation work before the case reaches the lab. This guide covers the stainless steel dental impression trays made by Helmut Zepf: perforated versus unperforated, the Ehricke pattern, how to pick the figure size for upper and lower arches, and what the 28.640 implantology tray adds for open-tray implant impressions.

Which dental impression tray should I use?

Use a perforated metal tray (Ehricke 28.601 or standard 28.606) for alginate and most silicone impressions, where the holes lock the material mechanically into the tray. Use an unperforated tray (INF B 28.636) when the material is bonded with tray adhesive and you want a smooth, closed tray wall. For open-tray implant impressions, use the implantology tray 28.640, whose opening lets the impression posts protrude through the tray. In every case the tray should cover all the teeth with a few millimeters of space for material.

Perforated vs unperforated trays: how the material stays put

Perforated trays have holes in the floor and walls. Alginate and elastomeric materials flow through the perforations and set on the outside, giving mechanical retention so the impression stays seated in the tray during removal. This is the everyday choice for alginate study models, opposing-arch impressions and most silicone work. Both the Ehricke model (28.601) and the standard series (28.606) are perforated.

Unperforated trays have a smooth, closed wall. Retention comes from a tray adhesive applied before loading. The closed wall gives an even surface behind the material and lets it flow more smoothly, which is why many clinicians prefer it for polyether and silicone work. Helmut Zepf's unperforated tray is the INF B (28.636) lower-arch series.

The Ehricke model and the standard series

Helmut Zepf offers two perforated full-arch families, both in figure sizes 0 to 4. The Ehricke model (28.601) is the named perforated pattern; the standard perforated tray (28.606) is the series for everyday full-arch impressions. Both are rigid, autoclavable stainless steel with a rim that follows the dental arch to support the material and cover the vestibule. If your practice already works with Ehricke-pattern trays, stay with 28.601 so sizes and handling carry over; if you are building a set from scratch, the 28.606 series is the straightforward starting point.

Upper vs lower, and how to choose the size

Zepf labels its trays by arch: SUP for the upper jaw and INF for the lower. The implantology trays in this collection are SUP, upper-jaw trays; the unperforated INF B trays are lower-jaw trays. Figure sizes run from Fig. 0 (smallest) to Fig. 4 (largest).

Size selection follows the same general principle regardless of brand. Try the empty tray in the mouth before loading it. It should seat without pressing on the teeth, cover every tooth, and leave the collection's rule of thumb of 2–3 mm of clearance all round for a uniform thickness of material. On the upper arch, confirm the tray reaches back to the tuberosity; on the lower arch, check that it reaches the retromolar pad. A tray that is too small forces the material thin over the distal teeth; one that is too large is harder to seat evenly. Keeping all five figure sizes on hand is the simplest way to avoid compromising on fit.

Border molding, shaping the impression periphery to the functional depth of the vestibule, is normally done on a custom tray for complete dentures. The stock tray still matters, because the preliminary impression taken in it is what the custom tray is built on: a rigid rim that follows the arch captures the full sulcus without flexing at the flanges, and saves adjustments later.

Open-tray vs closed-tray implant impressions

Implant impressions transfer the position of the fixture, not a tooth, to the working model, and the two techniques differ in how the impression coping leaves the mouth. In a closed-tray impression, the coping stays on the implant when the tray is removed; it is then unscrewed, attached to an analog and re-seated into the impression, using a standard full-arch tray. In an open-tray (pick-up) impression, the coping is held by a long guide screw that protrudes through an opening in the tray. Once the material has set, the screw is loosened from above and the coping comes out embedded in the impression, which is why the technique is favoured for multiple implants and wherever a passive fit of the final restoration matters most.

The Helmut Zepf implantology tray (28.640) is built for the open-tray technique. Its window is covered with wax or foil while the tray is loaded, then opened over the impression copings so the guide screws can be unscrewed before the tray is removed. Because the tray is rigid stainless steel, it holds the copings in their exact position while the material sets, which protects the passive fit downstream. It comes in SUP sizes, with SUP 1 and SUP 4 in the current range. For the surrounding armamentarium, see our must-have implantology instrument list and the Dental Implantology Instrument Collection.

Why stainless steel instead of plastic?

Stainless steel does not flex under the pressure of heavy-body materials, so the impression keeps its dimensions from mouth to model. A disposable plastic tray can bend as the impression is pulled over the undercuts of the teeth, and a tray that springs back after removal has already distorted the material it carries. For crown and bridge work, where margins are being recorded, and for implant impressions, where coping position is everything, that rigidity is the case for metal. Reuse is the second argument: a metal tray is cleaned in the washer-disinfector and steam sterilized again and again, which lowers the cost per impression and removes a stream of plastic waste from the practice.

Helmut Zepf impression trays at a glance

Cleaning and sterilizing metal impression trays

Rinse the tray as soon as the impression has been separated so that alginate or silicone residue does not dry into the perforations, then run it through the normal washer-disinfector and steam sterilization cycle. The step-by-step process, cycle parameters and inspection points are in our Dental Hand Instrument Reprocessing & Sterilization Guide for Helmut Zepf instruments, and each product page links to the manufacturer's reprocessing instructions. Blocked perforations no longer give the mechanical retention the tray depends on, so a tray with residue in the holes goes back through cleaning.

Building a tray set for the practice

For most general practices the starting point is a full run of perforated trays in Fig. 0 to 4, either the Ehricke model or the standard series, so every patient can be fitted at the chair. Add the INF B unperforated lower trays when you routinely take adhesive-retained elastomer impressions for crown and bridge work; our crown preparation margin guide covers the bur side of that workflow. Practices placing or restoring implants should add the 28.640 implantology trays so open-tray impressions are not improvised with a modified stock tray. Every tray in the range is made in Germany from stainless steel and ships from DeutscheDT.com; browse the complete Dental Impression Trays by Helmut Zepf collection to put the set together.

Frequently asked questions

What is the difference between perforated and unperforated impression trays? Perforated trays retain the material mechanically: it flows through the holes and sets on the outside, locking the impression in, which is what alginate needs. Unperforated trays rely on a tray adhesive and give a smooth, closed wall for the material to flow against.

What is an open-tray implant impression? A technique in which the impression copings protrude through an opening in the tray. After the material sets, the guide screws are loosened from above and the copings come out embedded in the impression.

Open tray vs closed tray impression: which is better? Closed-tray is simpler and uses a standard tray; open-tray avoids re-seating the coping and is generally preferred for several implants or when passive fit is critical. The 28.640 implantology tray is designed for the open-tray method.

How do I choose the size of a dental impression tray? Try the empty tray in the mouth first. It should cover all the teeth, reach the tuberosity (upper) or retromolar pad (lower), and leave 2–3 mm of space all round for material. Sizes run from Fig. 0 (smallest) to Fig. 4 (largest).

Can metal impression trays be autoclaved? Yes. Helmut Zepf trays are stainless steel and are suited to washer-disinfector cycles and steam sterilization, which is the main advantage over disposable plastic trays.

This article is intended as an educational reference for dental professionals and does not replace clinical judgment or manufacturer instructions for use.