When I Forgot To Bleed The Core Build Up Dental Material

Written & Reviewed by Dr David Chen

We were taught to bleed all dental materials that require mixing prior to using them. The core build up dental material is no exception since it comes in a cartridge that requires mixing.

core paste unopened

Do you know what happens if you forget to bleed it before using it? Well I do because I completely forgot to do it one time while I was trying to do a core build up procedure.

This is the recount of the day that I forgot to bleed it and what I learned from it.

The Story

The patient finished their root canal and returned to me, their restorative dentist to complete the next step which is the post and core. Everything was going smoothly because the post preparation proceeded without any hiccups. The only thing left to do was to cement the prefabricated post with the core build up dental material.

To be honest, I had actually just purchased a different brand of dental core material called Fluorocore 2+. I haven’t had the chance to even use it yet because this was going to be the first case. I had to unbox the product on the spot and attach it to the mixing tip for this brand new tube of core buildup.

Now all I had to do was inject the core paste into the canal and then insert the prefab post into it to cement it. Immediately after putting the post in you would simply continue to express the core material to build up all of the missing tooth structure. After that, you just needed to wait for about 5-10 minutes for the material to set.

Most of the core build up materials are dual cured which means that they will self cure and also cure with the assistance of a curing light. There are some that are self cure only which means that the curing light does not work on it.

valo curing light showing depth of cure
Credit: Ultradent

I patiently waited for the material to set. After 5 minutes I checked it with my stainless steel explorer but the material didn’t set. It wasn’t hard at all because I could still poke into it. Well, that isn’t quite right because its supposed to turn completely hard.

I decided to try to speed up the curing process by blasting it with the curing light and then proceeded to wait another 5 minutes. I checked it once more and the core material still didn’t set.

The realization

I was confused… Did I buy a defective product? Was this expired? I looked at the box and it was not expired. After a couple of minutes of pondering I realized that the core build up in the patient’s tooth didn’t look very blue.

The fluorocore 2+ that I bought was supposed to come in a very pretty blue color because I liked it more than the white one. The blue won’t show through in the final product because you’re supposed to cover it with a porcelain crown afterwards.

I removed the tip from the product and attached a new tip on it. I squirted out more of the material and it came out significantly more blue in color. That is when it hit me.

I forgot to bleed the cartridge prior to using it so it didn’t mix properly and that is why the color wasn’t how it was supposed to be. Rookie mistake that dental students do but I was no longer a student. That was embarrassing because I was a new grad dentist and I was supposed to be better than that. But at least now I know how to fix it.

How I fixed it

All of the core build up material in the tooth is not going to set because it wasn’t mixed properly. What I needed to do was to remove the post and remove all of the core material. Essentially I had to redo the entire procedure all over again.

It was quite simple to take the post out. I just had to grab it with the college pliers and pull it out to retrieve it. Since the material did not harden at all, it came right out without much resistance.

Next I had to flush out the entire canal to remove the unmixed core. I used a combination of the air water syringe and also drilled out any residue.

Once it was all cleaned out, I was ready to redo the cementation and core build up dental procedure once more. I attached a new tip to the fluorocore and expressed the material into the canal. Inserted the post and then continued to express more of the core on top of it to build up everything.

I waited 5 minutes and checked if it was set. It indeed got hard and it had the blue color that I was looking for. The procedure is now a success! I dismissed the patient and asked them to schedule the next appoint for a dental crown.

The need for bleeding dental materials

Dental materials are either activated by a curing light or by mixing a catalyst into it. Core build up products tend to utilize a catalyst in order to initiate the reaction. They do permit the curing light to speed up the reaction but it still requires a catalyst.

mixing tip for core build up

The core material sets when the base gets mixed with the catalyst via a mixing tip. This tip attaches to the cartridge and automatically mixes the material as it gets expressed.

It is of utmost importance to have the same quantity of base and catalyst coming out of the cartridge at the same time. This ensures that it gets mixed properly.

  • If only base is coming out then its not mixed properly.
  • If only catalyst is coming out it is also not mixed properly.

This becomes an issue especially for a brand new cartridge of core material. Usually for an unopened one that is being used for the first time, when you go to express the material it will come out unevenly. The photo below demonstrates how only one side of the cartridge is coming out of a new tube of core.

expressed core paste showing uneven amount of material from a new tube

In order to get an even amount coming out you need to “bleed the material”. What this means is you keep expressing the material until both sides comes out. This first portion that comes out needs to be discarded.

Once both sides are coming out evenly it is then that you are permitted to attach the mixing tip onto the tube. Now when you go to use it, it will be mixed properly.

Bleeding the material is incredibly important especially for brand new tubes of product. It is less of an issue after using it once. With each subsequent use with a new tip for the same tube, you only really need to bleed it slightly.

Lesson Learned

The most important lesson that I learned was to never forget to bleed the core build up material. In fact this lesson holds true for all dental materials that require mixing because they work via a similar mechanism. If it doesn’t mix properly it won’t set properly!

It is a simple step that merely takes two seconds to do but forgetting to do so can have big consequences. It’ll cause frustrating and add a lot of time to the appointment. All of that can be avoided by simply bleeding the cartridge!

Forgetting to do this is a big rookie mistake that seasoned dentists shouldn’t fall prey to! Thankfully I haven’t made the same mistake again, at least not yet. Maybe it’ll happen once more when I get older and grow more senile… Well that’s what this memoir is here for, to remind myself to not do it again.


David Chen, DDS


1311 Jackson Ave
Long Island City, NY 11101

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