I’ve noticed an increasing number of posts recently about master cone radiographs that ultimately result in a lengthy final obturation after the gutta-percha (GP) has been sealed. Taking master cone (MC) radiographs is a commendable practice, yet it is not comprehensive without the correct preliminary step. Wondering what the “proper preliminary step” is? I’m glad you asked.
Here’s the issue: at a certain point during the instrumentation process, we need to establish the working length (WL). This can be achieved with an apex locator (the most accurate method) or a WL radiograph (the older method taught in most dental schools). This then typically serves as our reference as we instrument the canals, known as the “working length.”
So far, so good. However, during the instrumentation phase, the filing process actively straightens the canal, mostly due to the reduced canal curvature from filing.
At this juncture, to accurately determine the final canal length, we need to remeasure before obturation.
Again, there are two options: We can remeasure with an apex locator (still the most accurate method) or we can take a MC radiograph (the time-honored method).
There you go, problem nearly solved. We’re down to the final steps, but we can’t relax yet. We need a way to ensure that the GP will be sealed at our WL and not extend beyond the end of the root. The simplest, most convenient, and most efficient way to do this is to crimp the GP point at the level of our measurement mark on the tooth.
Now, as long as the crimp in the GP and our measurement mark align, there should be no surprises in the final radiograph. Without this “proper” preliminary step, we cannot be certain where the GP will ultimately land. We might hope for the best, but without this verification step, there’s a fair amount of guesswork involved. Aligning the crimp with the measurement mark eliminates this guesswork.
So, if you rely heavily on the final radiograph and feel anxious until you see that final image on the screen, try crimping the gutta-percha to ensure it aligns with your measurement point, resulting in a beautiful final obturation. Now, you can leave the Tums at home.
Until next time,
Dr. Aaron Nicholas
Dental Success Blackbelt Coach
Founder Monday Morning Dentistry
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