Do You Really Need to Use a Custom Tray?
Every year, I get repeated questions about the significance of using custom trays. At the dental school, for removable cases, fixed cases and even implant cases, the students are required to fabricate custom trays for the final impression procedures.
Unfortunately, there is a learning curve to making a good custom tray. Many of the custom trays are way too bulky and not properly extended. As a result, the students may not get the clinical outcome they hope for.
For me, I continue to use a lot of custom trays after dental school and graduate school. Putting aside the extra time and cost, I always thought why wouldn’t I? It makes my life easier. So what are my reasons of using them?
Why I use Them?
1/Theoretically, the custom tray provides an even layer of space for the impression material. Most elastomeric impression material has a certain amount of polymerization shrinkage…so by having an even layer of impression material, the amount of shrinkage will likely be more even all across. Now some people may argue that this is not clinically significant because we are working now with very accurate impression materials. But this is one theoretical background of why we started using custom trays….
2/Using custom trays mean the shape of the tray is customized to each individual arch. WE are all shaped differently with various arch form and occlusal plane. With stock trays, you may end up capturing some areas with too little impression material…some areas with too much material or even worse failure to capture the critical areas like the hard palate or the hamular notch for removable cases.
3/If you like to use open tray impression technique, you will know the critical moment is to be able to position the tray such that you can access the impression screw so you can loosen it after the set. If I use a stock tray , the extra bulkiness may not give me a lot of interocclusal space to access the screw. If I have a custom tray, it can be customized so that I have more interocclusal space to reach for the screw. Sometimes for patients with limited mouth opening on posterior sites, it does make all the difference to create a more tolerable experience for the patient.
How I use Them?
Some pearls on using custom trays. Even for me, the custom trays I get from the lab often will require further customization by flange adjustment and border moulding. Some requires minimal work. Some requires further work.
For the open implant impression technique, I often find the opening created by the lab is often too small. The lab has no knowledge about the patient’s arc of opening and often will create a very conservative opening for where the implant impression coping will be. So before I take the actual impression and applying the adhesive, I practice putting the tray in and out to appreciate the patient’s arc of opening and the angulation of the other teeth. I make a mental note of how the tray should rotate into the mouth without banging it on the other teeth and how to manipulate the lips and soft tissue so they don’t get in the way of taking the impression
A note on printed Custom Trays
Beware of digitally printed trays. I once got these printed trays that look more like printed stock tray then a printed custom tray. I feel I get better customization of the tray by fabricating it the old way then designing it than from a computer software. The technician has to be knowledgeable about the design criteria. For printed trays, I find that I also need mechanical retention as the adhesive does not seem to work the same way on these new printed materials.
Taking a good impression is the first step in making a good prosthesis. I really do think that taking the time to make a custom tray will help towards this goal. Thanks for reading!