In this short video (1:56), Dr. Bob Loney, Professor and Chair of the Dental Clinical Sciences Department at the Faculty of Dentistry, Dalhousie University, demonstrates how to remove gutta percha from a root canal in order to prepare an adequate post space to support a restoration on an endodontically treated tooth.
- Use non-end cutting drills to prepare the post space.
- Always start with the smallest size of Gates Glidden drill or Peeso reamer and work up to the size required to accommodate the desired size of a post.
- Size the instrument, referring to a radiograph of the tooth and pick the smallest drill size that will remove all the gutta percha at the most apical position you want to remove material from.
- Prior to using a non-end cutting drill, create an adequately sized hole in the surface of the gutta percha with either an explorer or a small round bur. This will allow for the drill side flutes to be immediately engaged and will maximize efficiency.
- No pressure is necessary because the action of the side flutes will have the effect of pulling the drill down the canal.
- Use a stopper on your drill, in order to avoid over-preparing the canal and to leave 5 mm of gutta percha at the apex of the root.
- Once the working length is established, apply a side-to-side motion as you move the drill up and down. This shapes the side walls of the canal to allow for the post to be accommodated.
- Use a post drill to square up the apical end if you are using a pre-fabricated parallel-sided post.
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So how do you measure a post if you have digital radiographs ??–all guides recommend measuring directly off of a traditional film?
What are your suggestion in preparing a post space in canals filled with carrier cores?
As far as I am aware all digital radiographic software has a measurement tool. These measurement tools have been reported to be accurate.
See:
http://jos.dent.nihon-u.ac.jp/journal/51/4/559.pdf
and 1. Mohtavipour ST, Dalili Z, Azar NG. Direct digital radiography versus conventional radiography for estimation of canal length in curved canals. Imaging Sci Dent 2011;41(1):7-10.
PURPOSE: The purpose of this study was to compare the conventional and digital radiography in the estimation of working length in mandibular molars. MATERIALS AND METHODS: Sixty molar teeth were selected and divided into three groups in the basis of canal curves (0-15 degrees , 15-30 degrees , >30 degrees ). After the placement of a 15 K-file, radiographs were taken with a conventional film (F-speed) and a digital sensor. Canal lengths were measured in these images by two observers. Statistical analysis was performed with repeated measures of ANOVA and paired sample t-test with 95% confidence. RESULTS: There was a high inter-observer agreement on the measurements of working length in conventional and digital radiographs. There was no significant difference between the mean values of measurements in conventional and digital radiography. Moreover, there was no significant difference between conventional and digital radiography with the actual values in the basis of canal curves. CONCLUSION: The accuracy of conventional and digital radiography in the determination of the working length was in an acceptable range.
As for removal of carrier cores, it depends on the type and brand of core used. I do not use them at all.
Check this out:
The first step in retreatment is to remove as
much of the gutta percha in the orifice as pos
–
sible without removing any of the core. This
can be accomplished with either chloroform or
a heated instrument. The objective is to expose
the coronal end of the plastic core. A length of
2-3 mm of exposed core should be sufficient.
Once that has been achieved, slide a Hedstrom
file along side the core between the canal wall and the core itself. Hook the inverted flutes of
the Hedstrom into the core and pull straight out.
If the Hedstrom has a good enough grip on the
side of the core, it should pull right out. If the
canal is severely curved, a second Hedstrom file
on the opposite side of the core may be neces
–
sary. Once both files have a grip on the core,
braid them together by twisting the handles to
tighten the hold on the core. Again, pull straight
out. With the core removed, the remainder of
the canal is simply gutta percha and may be filed
out in the conventional manner.
Other methods can be used, such as sonic hand
pieces, but the above method will work without
the need for additional equipment:
See:
http://www.axisdental.com/getdoc/e746d086-b157-4e2e-8675-8a300a92523b/Techniques_Endo.aspx