Ruby Perez Aldana
September 5, 2018
Even though there may be many classifications of impressions, or bite registrations, one of the most common and more used is the preliminary impressions.
Preliminary impressions are impressions used to create a reproduction of the teeth and the surrounding tissues CITATION Bir181 l 1033 (Bird and Robinson). Both the dentist and the dental assistant are able to take these impressions. There are many reasons why either the dentist or the dental assistant would do this procedure on a patient. Some of the reasons include for pretreatment and posttreatment records, provisional coverage, and orthodontic appliances CITATION Bir181 l 1033 (Bird and Robinson). There are many types of hydrocolloid materials used to take these impressions, but one of the most common and popular hydrocolloid is the irreversible hydrocolloid.
An irreversible hydrocolloid, or also known as alginate, is exactly what its name states; a hydrocolloid that is unable to return to its original state once it becomes a gel. Alginate is used mainly for preliminary impressions because it is faster, easier to mix, and because of its low cost. The main components of alginate include potassium alginate, calcium sulfate, trisodium phosphate, diatomaceous earth, zinc oxide, and potassium titanium fluoride CITATION Bir181 l 1033 (Bird and Robinson). Just like anything, alginate has some pros and cons. Some of the pros include that it is low cost and very easy to use. While some cons can include that it sets really fast and if not properly distributed, it could go to the back of the patient’s throat when taking the impression. Mixing alginate can be very tricky especially if you have never done it before.
When mixing alginate, you should have in mind what type of setting your irreversible hydrocolloid is. That is because it is available in two types of settings: normal set and fast set. Normal-set alginate has a working time of 2 minutes and a setting time of 4 ½ minutes after mixing. Fast-set alginate has a working time of 1 ¼ minutes and a setting time of 1 to 2 minutes. Working time is the time for mixing the alginate, loading, and positioning the tray in the patient’s mouth. And the setting time is the time required for the chemical reaction to be completed CITATION Bir181 l 1033 (Bird and Robinson). That is why you should have in mind what types of setting your alginate is. Not only does the type of set effect your alginate, water temperature and water content also alters the setting time. When using warmer water, the alginate tends to set much faster than using cold water. Water content is also a huge factor when mixing alginate. If you add too much water than it will be too runny and if you don’t add enough it will be too dry. It has to be an equal ratio of both alginate and water.
When taking preliminary impressions with alginate the best kind of tray to use is the perforated surface tray. That is because when using a perforated tray, adhesive is not required due to the fact that the material oozes through the holes of the tray, letting the material lock in place. Even though the best kind of tray to use for alginate is the perforated tray, it is not the only one available. There is also a smooth surface tray. When using a smooth surface tray, you would need to have in mind that an adhesive is going to be required. That is because it does not lock the material in place leading to a big mess if not properly operated. When adding adhesive to the tray, it is important for the adhesive to be dry prior to adding the material. Both a perforated and a smooth surface tray are classified as stock trays. Stock trays come in different sizing, depending on the region you would like to take the impression of: quadrant trays, section trays, and full-arch trays. If necessary, the length of the tray can be extended by adding utility wax.
Even though taking an impression is very common, the field of digital impressions is growing rapidly. There are two types of digital impression technology currently available for dentists to use. One type captures the images as digital photographs, providing dentists and dental laboratories with a series of images; the other type captures images as digital video CITATION Con182 l 1033 (Consumer Guide to Dentistry ). There are some advantages and disadvantages for using digital impressions. Some advantages are that it’s faster, more accurate, and more comfortable. The main disadvantage is that it would cost more. In the future, more and more dental offices will provide digital impressions instead of traditional ones.
BIBLIOGRAPHY Bird, Doni L. and Debbie S. Robinson. Modern Dental Assisting. St. Louis, 2018.
Consumer Guide to Dentistry . 5 September 2018