Oops, It Happened Again!
Summer is here and the heat is on the rise, and guess what? It's better than the screwy winter we had without question. I'll take 90 and humid over 16 and snow any day! Now onto some meat and potato ROOT CANAL stuff. Obviously, the first and foremost obstacle is that we are dealing with a failure of some sort and must make some sort if a determination and diagnosis of why the case failed. Let's look at the success rate of endodontic therapy. There is approximately a 93%, give or take, success rate for root canal treatment, which implies, conversely, a 7% failure rate (if I’m doing the math correctly). And believe it or not, that's under normal conditions, taking into account that the RCT was done correctly. Divergent apical anatomy in the apical 1/3 of the root such as dilacerations, deltas and lateral canals that we are dependent upon good irrigation technique to open, cleans and disinfect these rascals and the expression of sealer to seal them as well can be reasons for failure if not done adequately. Hence, a failure of treatment although the final radiograph is "textbook"!
Another biggie is micro fractures, which the literature is showing more and more to be associated with rotary instrumentation creating greater tapered preparation of the canal, which is further compounded with condensation techniques that put stress on the root-- another example of looking perfect but feeling bad due to an eventual failure.
Ok, so we have a failure and need to rule out why. Inadequate fills, missed canals, calcified canals, inadequate instrumentation and irrigation are only some of the obvious reasons. Poor restorative and the periodontal condition can also lend a helping hand. Length of time between the insertion of a temporary closure of the access cavity and permanent restorative can have a direct effect on the failure rate. The longer the wait, the greater the chance for a breakdown in the temporary seal and recontamination of the canal or even catastrophic fracture of the tooth.
A good radiograph and now, more importantly, a CBCT scan are valuable tools for diagnosing reasons for failure, particularly in looking for missed divergent anatomy. For example, a missed MB2 in an maxillary molar, either first or even second, is a prime reason for upper molar failure. CBCTs identify unfilled fins and apical splits in canal anatomy. Once the retreat is under way, a microscope is also a key to success. The scope provides the dentist with the ability to identify fractures and assists in the hunt for missed canals identified on the CT scan. Obviously it's futile to retreat a tooth that failed due to fracture, especially if you can't see it. And drilling blindly into a tooth is completely out of the question.
It is important when retreating a case to discuss with the patient the alternatives, such as apicoectomy, extraction and replacement. Each has its advantages and disadvantages, and your patient must know the risks and rewards of successful retreatment. (P.S. please enter that into your chart legibly so that, God forbid, the S**T hits the fan, you are protected.)
Additionally, I will speak the obvious! If you think the RCT is problematic on the first round, refer it out to your friendly neighborhood Endo man. If it fails because it’s just a tough tooth or you can't find a canal, it's unproductive to assume you'll fix the problem if and when they have to come back for a retreatment. Your patient will ultimately appreciate the referral if it's done correctly the first time.
Ok, now on to the clinical portion of the show. This is a patient who presented with pain related to tooth numbers 14 and 15. PA images showed RCT's done with an obviously separated instrument in the MB root of number 15. The clinical symptoms were pain on chewing and on percussion. After discussing the need for a CBCT to confirm any other issues with the tooth, one was done which re-confirmed the separated instrument in #15 and a missed MB2 in #14 as well as the PA radiolucency associated with the roots in question. After discussing the appropriate risks and alternatives, we decided to retreat the teeth in question. Tooth #14 was accessed through the existing crown UNDER RUBBER DAM using a barrel diamond to remove porcelain and a new #4 round bur to cut through the metal substructure with water -- and lots of it -- to avoid damaging the crown. The core material was removed using a high and low speed hand piece and the orifice of each canal was identified as the floor of the chamber was cleared of any remaining core material. Using the CBCT as a road map and the microscope as my eyes, I quickly found the MB2 using Muntz burs and the ultrasonic diamond tips to excavate for it. The existing gutta percha was removed by loosening it coronally with a solvent solution and then by using a #10 file in the reciprocating hand piece to negotiate through the remaining canal fill. The canals were re-instrumented to an appropriate diameter when clean dentinal filings were seen on the instrument and they were devoid of any remaining gutta percha. They were irrigated copiously with EDTA and disinfected with chlorhexidine, dryed and obturated using EZ-Fill cement and single cone gutta percha. (Quick hint: when attempting to get measurements with an apex locator, it is important to remember that the existing gutta percha at the apical end of the canal can act as an insulator and throw off you reading. Thus, a working length X-ray would be appropriate to make sure you're on target.)
Now that was the easy tooth! Tooth #15 was to be a bit more difficult. A separated instrument can really be a road block to a successful retreatment. Not being able to remove it is both a clinical problem as well as a psychological problem. First, hopefully, they were told by whomever separated it that it happened. If not, there's always that litigious shadow that overhangs and it is incumbent upon the retreater to soften the blow and assure the patient that this was and is a risk of any RCT procedure. Although there are techniques that minimize that risk, it is a risk nonetheless. And, fortunately, the implications are minimized by our ability to retreat, remove and/or surgerize the area. So in regards to number 15, access was gained and the old canal filling material was located and removed. In the mesial buccal canal, I was able to remove the gutta percha to the coronal end of the separated instrument. Using a .06 reamer with a small 45-degree bend at the tip I was able to negotiate a path around the piece of file. With copious EDTA and or RC-Prep, I slowly expanded my guide path using my reciprocating hand piece. Using reciprocation means one thing: you will not separate another instrument next to the existing piece!
Things were looking up, at least for a bypass. Using the microscope I was able to visualize the separated instrument and, with my ultrasonic and a very thin tip under low power, I was able to loosen the instrument enough to screw in a Hedstrom file and extract the instrument from the apical end. (Phew!!!!) Now, mind you, this is not a one-visit retreat, for the procedure took time and patience. But at the end of the day mission accomplished, instrument removed and patient, referrer and endodontist all very happy.
It's important to leave my readers with a few tidbits of helpful knowledge. First: if in doubt, refer it out. Second: if a separation occurs, alert the patient, reassure them, and try to remedy the problem, but enter it into their chart. Lastly, avoid separation by using techniques that minimize risk, reciprocation and SafeSiders (obligatory plug!!). Any technique that forsakes the limits of the metallurgical properties of the instrumentation you are using should theoretically and clinically not be used. Stick to low-risk and low-stress endodontics. See you next issue.