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Townie Casefile: One File, Two 90-Degree Curves

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Townie Casefile: One File, Two 90-Degree Curves 

A single-file approach to a severely curved, calcified molar

Townie Casefiles spotlight exceptional case studies from our own community. Each article highlights real-world clinical techniques, decision-making strategies, and long-term outcomes from Townies who share their expertise on the Dentaltown message boards.

Casefile Summary
Clinician: Dr. Ghassan Yared

Diagnosis: Mandibular left third molar (#17) requiring root canal treatment; three canals (two mesial, one distal); heavy canal calcification; severe curvature (~90°) in a mesial canal and the distal canal

Treatment:
  • Single-file reciprocation, one R25 instrument per root (150°/30°, 300 rpm, 4 Ncm), no scouting and no glide path; small pecks with irrigation every three pecks to working length
  • Working length confirmed with an apex locator
  • Final irrigation with full-strength sodium hypochlorite and sonic activation
  • Single-cone obturation with matching gutta-percha and an epoxy-resin sealer (AH Plus)
Tooth #17, a mandibular left third molar, presented to Dr. Ghassan Yared with three canals and a 90-degree problem in more than one of them. Two mesial canals and one distal, all heavily calcified, with severe curvature of roughly 90 degrees in a mesial canal and again in the distal (Fig. 1). On a wisdom tooth sitting that far back, with that little access, the conventional way to open canals like these is also the way most likely to go wrong. Yared shaped and obturated all three canals using a single reciprocating file for each root, without scouting and without creating a glide path.


The textbook sequence, and why it didn’t fit
Canal preparation in calcified, curved teeth usually runs through four steps: preflaring, scouting with small hand files, a glide path, then shaping. The scouting is the tedious part, and in a tooth like this it’s also the dangerous part. Working a size 6, 8, then 10 hand file down a calcified canal that bends 90 degrees is slow going for anyone, and glide-path instruments can break under exactly those conditions. Add the posterior position of a wisdom tooth and the limited opening that comes with it, and the most failure-prone step in the sequence is the one the anatomy punishes hardest.

That’s the reasoning behind skipping it. As Yared put it in the Dentaltown message board thread, the safest and most efficient scouting technique is no scouting, when the canal allows it.


One file, no glide path
The whole case was instrumented with a single-file reciprocating system (Reciproc Blue, size R25), one new file per root. The motor ran in reciprocation, 150 degrees in the cutting direction and 30 in the release direction, at 300 rpm and 4 Ncm. Yared advanced the file in small pecks, irrigated after every three pecks, and repeated that rhythm until the file reached full length. An apex locator controlled working length throughout, so no hand file was needed to confirm it.

Progress was slow, which is what you’d expect from this much calcification and curvature: six or seven series of three pecks in each canal. He used a fresh R25 for the mesial canals and another for the distal, because severe curvature and calcification fatigue the file, and a tired file is a file that separates. Figs. 2–3 show the file tracing the 90-degree bends in a mesial canal and in the distal. Final irrigation was full-strength sodium hypochlorite with sonic activation, followed by single-cone obturation using matching gutta-percha cones and an epoxy-resin sealer (AH Plus).
Townie Casefile: One File, Two 90-Degree Curves
Fig. 1: Preoperative radiograph.


The result
All three canals were shaped and filled to length, curves and all, without a single hand file leading the way (Fig. 4). For a calcified wisdom tooth with two right-angle bends, that’s the whole point: The obturation follows the original anatomy instead of a ledged or transported version of it.
Townie Casefile: One File, Two 90-Degree Curves
Fig. 2: R25 in a mesial canal, with its roughly 90-degree curvature.
Townie Casefile: One File, Two 90-Degree Curves
Fig. 3: R25 in the distal canal, with a similar 90-degree curvature.
Townie Casefile: One File, Two 90-Degree Curves
Fig. 4


What colleagues asked
One of the most practical questions raised in the thread was what happens when the file won’t go. Yared’s answer is that it still earns its place. Even when the R25 can’t reach length on its own, it’s a reliable orifice opener that cleans out the coronal third, so if you do switch to small hand files, you’re scouting a canal that’s already preflared. That’s the crown-down idea in practice, and it makes the hand-filing that follows far easier than starting cold.

The discipline is knowing when to stop. If the file quits advancing, Yared stops immediately. “I don’t push, I don’t insist,” he wrote; he scouts to a 10 file passive at length, creates a glide path, then goes back to the reciprocating file. He puts the no-scouting success rate above 90% in canals that aren’t constricted, and around 75% in calcified or constricted ones, MB2s included.

Curvature, he noted, isn’t really the deciding factor. A severe curve just slows the file down, and as long as it keeps advancing, even barely, it stays safe. Calcification and constriction are what tell you whether scouting is coming.

Separation worried a few people, reasonably, since these files don’t unwind to warn you. Yared’s figures put the risk between 0 and 0.2% across studies, but he’s blunt that the files aren’t magical: reuse and heavy pressure are what break them. He emphasized single-patient use and noted that any visible untwisting of the flutes is reason to discard the instrument.

Yared developed the reciprocating single-file concept and the instruments used here, and he’s candid about why. He built them to solve his own calcified-canal headaches. “It was self-serving,” he wrote. He’s since moved to a smaller, more conservative version (Reciproc Minima) that he says reaches length without scouting in even more canals.


The takeaway
The reflex with a frightening canal is to reach for the smallest files and feel your way to the apex. This case makes the opposite argument: In a calcified, severely curved canal with poor access, leading with small hand files is the slow, fracture-prone part, and a single reciprocating file left to advance on its own can shape what looks unshapeable. The skill isn’t forcing the file to length. It’s reading the moment it tells you to stop.

View the full case study and join the conversation!

Great Dentists, Great Dentistry
Dr. Ghassan Yared Dr. Ghassan Yared, known as GhassanYared on the Dentaltown message boards, has been a member since 2007. An endodontist, educator, and inventor, Yared is widely recognized for pioneering single-file endodontics and reciprocating instrumentation. He has taught at the Lebanese University and the University of Toronto, and continues to lecture internationally. On Dentaltown, he is known for sharing challenging cases while helping clinicians navigate even the most difficult canals.

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