IMPRESSION TRAY

Luca Martinelli

Basics on dental impression tray

Publication nr. 52 – 29th December 2014

Foreword

Take the impression of the patient’s mouth is not a trivial operation. To the doctor’s office, a wrong impression may represent a loss of time, extensions of the patient stey in the chair, waste of expensive materials, misunderstanding with the dental laboratory, new dates which are a damage to the patient and to the dentist, with a tarnished image itself of the dental office.

Over the years from dental impressions detected using wax, in the Seventeenth Century, we moved to the plaster and then to the gutta percha. Around 1925 we can find hydrocolloids, later alginates, curing silicons and polyether. From 1976 on we find addition silicon and many others will come.

Trays have remained essentially the same from their first invention up to now. Perhaps that’s the reason why they have always been considered the “Cinderella” of manual dental devices yet they are of fundamental importance to get a corretc impression. The kind of impression material and skill of operator are not the only requirements to get a correct dental impression.

With the use of new technologies such as laser light, particularly effective in the detection of impressions,  mentioning the traditional impression tray is a bit “anachronistic”. On the other hand, in the vast majority of dental offices around the world, is even massive the use of traditional tray and it is therefore still interesting an overview on them.

Prof. Enrico Gherlone about fingerprint says: "The fingerprint is an innovation that is revolutionizing the traditional dental impression methods because it allows you to transfer images to your computer the mouth through the use of a tiny camera ".

The impression

European statistical reports says that almost 50% of cases detected impressions are not accurate enough, so are unusable or otherwise that may cause incorrect work. In particular the impressions needed to build fixed prosthesis show a defect precisely at the expense of the preparation margins; not least the antagonist should be precise, even in this case has been detected a frequent shallowness in the accuracy of these.

In this publication we will go neither in clinical appearance, nor in the aspect of choosing the most suitable type of tray for each type of different impression but only in appearance constructive-normative. For in-depth knowledge we recommend the excellent book by Prof. own Gherlone "The impression denture" (Publisher ELSEVIER - MASSON), which in the updated version devotes ample space to the new technologies.

Signs on digital impression

The digital impression, detected by laser light scanner, it is particularly suitable for fixed prostheses. It is also used in orthodontics, at all stages of the treatment.

We recall that more than 6% of the “child” population is subjected to orthodontic treatment, it is therefore easily understood that the use of a not-invasively impression detection system, without that for this lost in precision, becomes a particularly pleasing from the doctor and the patient, too.

The instrument that allows the digital detection now represents the near future impression. It is substantially a scanner (oral Scanners - Fig. 1) that detects, captures and processes in 3D the image of the mouth, creating an accurate virtual reconstruction of it.

1

Scanner in the patient’s mouth

On the market we can find a remarkable variety in the photos below (Fig. 2, 3, 4, 5, 6) a few examples by way of example only.

         

            

Various types of impression trays

There are different types of impression tray, perforated, non-perforated, with border, without border, for edentulous, partially edentulous, for orthodontics, implantology, for reversible hydrocolloid. There are also a number of trays that actually should not be used for clinical technical reasons as the partial impression trays, the impression trays to take simultaneously arch, or upper and lower hemi arch, and also the impression tray for the control of the bite. The complete impression tray itself (upper and lower full arch) is already a loophole - understandable for costs reasons and time - to the individual impression tray that it is actually the only real “accurate” impression tray.

Construction materials

The impression trays can be built with different materials, depending on the use and the cost that these must have. Most of them are steel manufactured, but we find many also in aluminum, teflon coated aluminum, coated aluminum Rislan, nickel-plated or chrome-plated brass (although today the use of chrome stainless steel (usually steel of the AISI 304 series) is prohibited almost everywhere), polycarbonate, teflon and polypropylene sulphide, as regards the reusable impression trays. Polystyrene and in some cases aluminum (Ex. Impression tray for implantology) as regards instead the disposable impression trays.

Trays for edentulous type Schreinemakers

A impression trays coming out of the standard is to Josephus Schreinemakers. Usually made of steel, it has the edges with special millimetrature, drilled laterally and not only on the top (American patent of 1979 presented a few years before in Holland 1975).

                           

The classification of the impression tray

The trays are regulated by a standard, in this case it is an American standard, and more precisely the ANSI / ADA 1995 Specification 87  - raffirmed 2014.

Like all technical standards are voluntary adaptation, in this case it is not a European standard. However, as in all cases in which there is a national or European standard reference, these still represent state of the art.

This standard indicates:

-Classification

-Definitions

-Requirements such as biocompatibility

-Security Of form and surface finish

-Shapes and sizes

Operating instructions packaging and marking

-Functionality And water seal for PI for reversible hydrocolloids

-Corrosion and resistance

-Sampling for test methods

And more.

Let's see in detail at least the three main aspects

1-Classification;

2-Measurement and exposure to the user of the measures;

3-Labelling.

Classification

The impression trays are divided into:

Type 1: metal tray, perforated reusable;

Class 1: Cooled water;

Class 2: "Normal" is not water-cooled.

Type 2: metal impression tray, smooth reusable (non-perforated);

Class 1: Cooled water;

Class 2: "Normal" is not water-cooled.

Type 3: disposable impression tray perforated

Type 4: smooth disposable impression tray (not drilled).

Measures and outline measures

The measurement of the impression tray and the exposure to the catalog of its measures should take place as in figure 7.

Most of the time the catalogs of the various manufacturers only show the D1 and D2 extent, rarely the D3 even if it would be desirable, especially for the choice of the impression tray for orthodontics, that there are measures with major and minor edge, or impression tray which have necessarily the high board, to get them to take well the fornix area.

The right impression tray – very brief.

As we wrote in the introduction we won’t tell anything about the impression argument, that is, what is the way and the best way to keep an impression; However, we do a very brief including but not limited to some schools of thought just to give a general indication of the use of different impression tray.

Precise impression can not be separated from the use of a rigid metal tray.

The impression tray in plastic material does not have sufficient rigidity to ensure the accuracy of the impression material, particularly when using silicones dual-phase (to be relined), the finger pressure is enough to deform the impression trays and the same impression.

A slightly rigid impression trays makes impressions with dimensional changes that, especially for fixed prosthesis, are unacceptable.

The deformation of the plastic impression tray during impression taking implies, after its removal from the mouth, it returns to its original geometry consequently the models developed by this imprint will be affected from the actual sizes of the elements and the arch .

The use of a perforated impression tray rather than unperforated can, for example, cause dimensional alterations impression depending on the impression material used;

-If you use a polyether monophasic will be important to choose an impression tray without holes so that they may contain the material without it is extended and therefore allow for a sufficient build up of pressure against the walls of the impression tray which will retain positioned the same material;

-If You use an alginate or elastomer two-phase perforated impression tray allows a better retention of the impression material without major compromises.

Both may have a retentive edge, solid ones with the retentive board were equipped with mostly edge to their users using alginate.

It goes without saying that the impression tray for reversible hydrocolloid, as little used today, are solid (Fig. 14).

Conclusions

Still employed at full capacity the traditional impression trays are different in form, material of construction and prices.

The impression materials have undergone transformations over time for the composition, type of use and final precision.

It is not always clear the construction material, the classification, the type and the use of the impression tray. While remaining unchanged in time, it should in fact be the accessory that supports the most recent impression materials created.

The advent of new technologies, which allow greater precision, greater savings in time and money, is starting faster and faster to "retire" the traditional impression tray.