Making Acrylic Dentures – Impressions Stage 1 and 2

Making Acrylic Dentures

There are at least five main stages to making a denture. Each stage involves input from the dentist, patient and a dental technician.

  • Primary impressions
  • Secondary impressions
  • Bite recording
  • Try-in
  • Fit

Primary impressions

The first stage of making a denture involves the dentist taking upper and lower impressions of the patient’s palate, alveolar ridges and any existing teeth. Primary impressions are taken in stock impression trays, which are usually disposable, perforated arch shaped plastic trays, which are available in a number of sizes. The upper impression trays are ‘D’ shaped – to include the palate in the impression, and lower impression trays are ‘C’ shaped to fit over the teeth/alveolar ridges only. Impression trays are coated with a thin layer of fix before receiving the impression material, the fix helps to hold the impression to the tray once the impression material has set.

The most common type of impression material used for taking the primary impressions is alginate. Alginate is derived from seaweed, and comes in the form of a fine powder, which when mixed with the correct measure of water (ideally at room temperature) creates a soft, wet paste. The alginate paste is loaded into the impression tray, and the dentist places into the patient’s mouth, after a short period of time the alginate sets, and is removed from the patient’s mouth. Alginate, when set is an elastic, reasonably firm material, however, if the alginate impression is not kept moist after setting, the impression can distort or shrink, making it inaccurate.

Once these impressions have been taken, they must be washed and disinfected before being covered with damp gauze. The impressions are then bagged and a laboratory slip is filled out by the dentist. The laboratory slip includes;

  • dentists name
  • Patient’s name
  • prescription of work to be carried out by the dental technician
  • date the work is to be returned to the dentist by
  • Indication that the impressions have been disinfected

The disinfected impressions and laboratory slip are then sent to the dental technician who will carry out the work prescribed by the dentist, which at this stage is usually the casting of plaster models from the impressions and making ‘special trays’ for the secondary impressions.

Secondary impressions

Secondary impressions are taken at the next stage of making a denture. The impressions trays used for these impressions differ from the disposable trays used for primary impressions. Special trays are individually made for each patient, their shape and size accurately fit the patient’s arches, and therefore they allow for more accurate impressions to be taken. Special trays are usually made from either acrylic or shellac, so are sturdier than the plastic disposable type. Most special trays are perforated to allow excess impression material to disperse more evenly, a thin layer of fix is still (usually) applied to these trays to ensure that the impression material holds onto the impression tray rather than the patient’s teeth or alveolar ridges.

Alginate is the most common impression material of choice for this stage of denture making, however a dentist can choose to use a silicone based material (as used for crown and bridge impressions) instead if they desire.

The impressions are, as before, washed, disinfected and packaged, and a new prescription is written out for the dental technician. The prescription will ask the technician to provide stone models and wax rims for bite registration to take place at the next stage.

There is little input from the patient in these first two stages in the denture making process.

About the author

I’ve been a dental nurse for over 13 years, and have worked in various parts of the country in orthodontic practices, general dental practices, within the community dental services, for both NHS and private practices. Within that time I’ve seen quite a few changes, not only with the way services are provided, changes in laws and regulations but also with the use of new materials and more advanced treatments. The one thing that hasn’t changed at all in my time as a dental nurse is the importance of people receiving and understanding clear information about dentistry, treatments, regulations and jobs for example.

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