There are many different treatments and prosthetics that require a dental impression. One way to create an accurate dental impression is to utilize the correct materials and trays. To help you select the materials and trays best fit for your dental practice, we’ve created this simple overview.
Dental Impression Trays
Trays are fabricated with different types of materials, which allows dentists to adapt them to the needs of their patients. Plastic and metal trays are most common with stock trays, while custom trays are typically made from acrylic or shellac. Metal trays are the most accurate option because they are less prone to expansion issues once the impression sets.
Types of Dental Impression Trays
- Plastic (most common)
- Metal (most common)
- Light-curing acrylic
- Self-curing acrylic
When selecting an impression tray, there are typically 2 main types available:
- Stock Trays – Mass manufactured in a wide range of sizes and shapes. Stock trays can be fabricated from plastic or metal and can typically be perforated to allow impression material to run through the holes and increase the bond to the tray when it sets.
- Custom Trays – These special trays are made to fit a specific patient’s mouth. Talk with you dental lab about requesting a custom tray for patients.
The type of impression tray that best suits your practice will also depend on your specialty.
- Dental Prostheses
Tip: After evaluating a patient’s dental arches, first select and try on an impression tray without any material. This allows you to assess any modifications that may be needed, which lower stock trays can often require.
The importance of a good tray system should not be underestimated. A tray that does not support the impression material well will distort and can rebound out of shape when it is removed from the mouth. Just because an impression looks good does not mean it’s accurate. Your laboratory’s work will only be as good as the accuracy of your impression. No matter what impression material you use, investing in a reliable tray system is the foundation of your accuracy. PRO-Craft recommends the Quad Tray system from Clinicians Choice. Many of our clients use it. It is comfortable for the patient and will not rebound.
Countless types of impression materials have become available over the years. Each of these can serve a specific purpose, but the proper impression material should include these qualities:
Quality of Impression Material
- Fidelity – The material’s ability to record the finest details.
- Stability – The material should be able to maintain its exact shape for a certain amount of time.
- Elasticity – Material should keep the fidelity of an impression when it’s removed from a patient’s mouth.
- Setting Time
- Sensory Pleasing – The taste, smell, and color should be pleasant to the patient.
- Non-Irritant – Should not be toxic or irritate the mouth.
- Consistent manufacturer quality control.
First impressions are for orthodontic appliances, custom trays for partials or dentures, diagnostic models, opposing models, and temporary coverage for crowns and bridges commonly use alginate. Alginate is typically available in two different settings:
- Normal Set - Working time of 2 minutes and a setting time of 4 ½ minutes
- Fast Set - Working time of 1 ½ minutes and a setting time of 2 minutes.
The most common challenges in getting a quality impression are adequate tissue retraction and sufficient moisture control. Dr. Dan Fischer, president and CEO of Ultradent Products, Inc. often says, “There is nothing one can do well, in a quality sense, when it comes to operative dentistry in the presence of bleeding.”
Retraction cord, helps to enhance tissue management techniques by delivering the ferric sulfate solutions sub gingivally for optimum sulcular fluid control. Ideal tissue displacement occurs within one to three minutes after cord placement. Packing cord placement technique also plays an important role in achieving quality, predictable tissue management.
Expasyl from Acteron is an alternative to retraction cord. It is a viscous, rigid paste for gingival retraction that not only opens the sulcus, but also leaves the field dry and ready for impression taking, cementation or digital scanning. It is extruded directly into the sulcus where it holds its rigidity to create space between the tooth and the tissue. It can be used for all procedures requiring gingival retraction including impressions, seating of restorations, fitting rubber dams, restoring class II, III and V cavities.
The laboratories ability to to see the margin as opposed to just trimming to the bottom of the sulcus (not recommended) requires the clinician's impression material to fill the sulcus and go slightly past the margin. The techniques mentioned here will assist in the effort.
Final impressions used for restorations will need to show precise details of the tissue and tooth structure. Materials used for a final impression are typically supplied in three different forms:
- Fluid (Light) – Consistency is very cord “runny” when placed inside of an impression tray but hardens as it sets. The fluidity of this impression material makes it the most accurate in capturing fine details. Polysulfide and fluid silicones are some of the materials in this category.
- Elastic (Regular) – This is slightly thicker than the fluid form. Material is initially soft in consistency when placed inside impression trays and as it sets it will harden and become elastic. Alginate is one example of elastic impression material.
- Rigid (Heavy) – This impression material is the thickest of the three forms. Its base has a putty-like consistency. Unlike the other two forms, once this material sets it becomes hard and rigid. One benefit to using this type of impression material is for its excellent stability. Plaster, waxes, and hard silicones are examples of rigid materials.
- Paying particular attention to the material expiration dates, and material instructions especially the set times and room temperature.
When choosing the right impression material, select the one with the qualities that allow you to obtain the most accurate reproduction. Here at Pro-Craft we have monitored our remakes and adjustments for many years. We have found that the materials with the most consistency and lowest remake factor are Aquasil from Dentsply and Impergum from 3M. We believe they have the most consistent quality control.
In the end, the tools you choose to work with should benefit you and provide a successful restoration. Being selective and paying attention to the types of trays, the viscosity of impression material, tissue management along with strict adherence to set times and manufacture instructions will ensure a successful outcome. As always patient satisfaction and the growth of your practice as they share their experience to their friends and families is the ultimate goal.