Impression flaws is an umbrella term referring to all unwanted complications that may arise while and after taking dental impressions. An impression is the basis for any dental prosthesis; mistakes that occur during this step of the procedure will inevitably lead to an ill-fitting prosthesis. Here you see a brief summary of the steps involved after the impression has been taken. The impression is removed from the patient’s mouth and sent to the dental technician, who pours plaster into the impression and prepares a replica of the patient’s mouth; this replica is called a plaster model. The dental technician uses this model to fabricate the prosthesis. So the dental impression is an important step in the creation of your replacement teeth – your dentist will certainly not bother you with this. For a better understanding we’d like to explain few points.
One of the most common errors in dental impressions is the presence of air bubbles. By using a fine syringe—as seen here—most air bubbles are avoided. Distributing the impression material with the aid of an air blower further decreases the presence of air bubbles. Another important issue is well-defined margins, which are created during tooth cutting for crown placement. These preparation margins refer to the point where the uncut tooth transitions into the cut tooth. This preparation margin should be clearly visualized in the impression. If not, the dental technician will not be able to identify where he should place the crown margins. In many cases, blood, saliva, or the gums themselves obscure the preparation margins. Thus, an impression taken without the appropriate preliminary work and/or inadequate coverage of the preparation margins by the impression material will result in a dental impression with missing borders. That’s why dentists prepare the cut tooth carefully before taking the impression.
Furthermore, distortion of the impression can also result in an ill-fitting prosthesis. This can happen if the material has exceeded its shelf-life, if the processing times are not observed, or if the impression material is handled incorrectly. In this example, because of the occlusion of the teeth, the impression of the upper jaw should be pulled from the opposite side of the cut teeth first (shown in blue). This way, the impression is pulled off in a longitudinal direction from the cut tooth and is less likely to become deformed. The teeth in the lower jaw are leaning inwards; therefore, the impression in the lower jaw should be prepared and pulled from the side of the cut teeth first. If the impression tray is removed on the wrong side, the impression material is more likely to become distorted. Your dentist takes such details into consideration to prevent this from happening.
Why does the dentist take impressions with full trays – wouldn’t partial trays be more comfortable? Impressions should always be taken with full trays, illustrated to the left of the image. As a rule, partial trays—as seen on the right—are not precise because then the plaster models cannot be precisely aligned with one another. With a partial tray, the dental technician obtains partial models; these can be swiveled and thus improperly positioned. This leads to the fabrication of an inaccurate dental prosthesis (shown in blue here). A full impression yields complete jaw models, thus forming a so-called three-point contact. Moreover, the models cannot be swiveled, and the technician can produce an exact-fitting dental prosthesis.
A pre-impression prevents teeth from touching the impression tray (push through). If the metallic tray is exposed through the impression because of the push through, the impression must be repeated (note the two arrows marking the areas where the teeth pushed through). In the event of push through, the respective tooth is slightly deflected, resulting in an inaccurate impression. The dental technician would then inevitably fabricate an ill-fitting dental prosthesis; a long cutting process and/or leaking crown margins would be the consequence. Finally, let’s consider the faults that may occur during transportation of the impression; e.g., transport routes that are too long, less than perfect packaging of the impression, and improper handling at the dental technician’s office. Fortunately, all these faults can be avoided with good cooperation between doctors, technicians, and dental assistants!
Maybe now you can understand better why your dentist puts in so much effort in order to obtain a perfect dental impression – it’s for your replacement teeth! A possible remedy to this method could be digital dental impressions. Whilst these are ready for the market, the machines are still extremely expensive and one mustn’t forget: at the end of the day it’s you who pays for all this investment.dental Impression Flaws