How to Avoid Voids in Your Dental Impressions
Voids in dental impressions can lead to all kinds of troubles with restorations. Fine-tuning your technique and using the right materials are key to avoiding this.
Why first impressions are so important
The process of fabricating an indirect restoration takes careful attention to detail at every step because there are many opportunities for error.
The most critical step is the first impression as this is what every step that follows hinges on.
Despite this, lab technicians can sometimes be asked to create flawless restorations based on flawed or incomplete impressions.
Technicians cannot accurately add detail that the impression itself lacks. Only the dentist can provide the information necessary for an error-free reproduction.
This is why the use of careful, proper technique is essential to avoiding troublesome voids and creating a quality impression.
Critical areas, critical consequences
Critical areas require exact duplication of detail, such as margins (especially subgingival) and the fine details of tooth preparations for crowns, veneers, onlays or inlays. It’s not easy to compensate for any voids or errors in the first impression and any flaws can even be compounded throughout the rest of the procedure.
Gingival displacement and accurate impressioning still pose some of the greatest challenges in dentistry, despite the use of modern impressioning materials.
Though today’s materials may be more forgiving than their predecessors, they can’t fully compensate for shortcomings in the procedure.
A recent evaluation conducted within a commercial dental laboratory determined that 86% of crown-and-bridge impressions contained at least one detectable error and 55% contained a critical error related to the finish line.
Soft and hard tissue anatomy, gingival displacement, moisture management and the behaviour of impressioning materials are all part of the equation.
Troubleshooting voids
Here are a few top tips for remediating common issues with technique, material, or both:
Issue:
- Voids on margin and preparation
Causes:
- Blood and saliva contamination around preparation
- Improper syringe technique
- Working time exceeded, flowability already impaired
- Air bubbles in elastomer syringe or intra-oral syringe
- Tray not seated properly
- Storage at elevated temperature
Solutions:
- Rinse and dry the prepared area properly and stop any bleeding by using appropriate retraction / haemostatic agents.
- When syringing wash material, it is important to always let the material “lead” by advancing the tip forward while keeping it fully submerged in wash material.
- Select material with sufficient working time (i.e. regular set instead of fast set). Do not exceed working times given in the instructions for use
- Bleed cartridge prior to loading syringe. Keep flow of material consistent. Do not stop and start while loading the syringe.
- Slowly insert the loaded tray into the mouth parallel to the long axes of the prepared teeth and hold it in place without applying pressure.
- Store impression material at room temperature. Polyether and VPS usually require different storage temperatures to ensure sufficient working time, and it’s important to refer to each manufacturers’ instructions for use for best practices. Once cured, recommended storage temperatures and conditions will change. Keep in mind that higher temperatures can reduce material working time, while lower temperatures may increase intra-oral setting times.
Choosing the right materials
Always choose appropriate tray and wash impression material viscosities and material class according to the impression technique and indication to be carried out.
In the impression taking procedure, several different materials and techniques are available. Elastomers are the best materials to comply with the requirements needed for indirect restorations.
Polyether, for example, produces highly accurate results in a single step using one or two different viscosity materials (monophase or one-step) and is arguably the most forgiving when moisture control is difficult as it is inherently hydrophilic from the beginning.
Implants, dentures, complex multi-unit cases and cases where moisture control is a challenge are all ideal applications for polyether.
According to its manufacturer, 3M Impregum Penta Polyether Impression Material is still the only true polyether impression manufactured in the world and is considered “the gold standard” for the most challenging of cases. More detail on the advantages of Impregum Penta can be found here.
Another option is vinyl polysiloxane (VPS or A-Silicone), which is the most widely used material for one or two-step impression techniques.
3M Imprint 4 VPS impression material has been on the market for over a decade and has won several industry awards and accolades thanks to its intrinsic hydrophilicity. Imprint 4 reproduces fine details even in moist environments, so you can work quickly and confidently.
To learn more about 3M products click here or hit the link below to browse 3M other impression materials.
