Root canal therapy of the maxillary molars often poses considerable challenges for the dentist owing to the anatomical complexity of the root canal system. The teeth in most cases have more than three canals, and the mesial canal system in particular can have sharp curves.
Successful endodontic therapy requires removal of necrotic pulp tissue, dental debris, and microorganisms and their metabolic products to the greatest possible extent. Bacteria are the major cause of endodontic disease and endodontic failures. They can form bacterial biofilms on the walls of the root canals. If the root canal system cannot be prepared completely by chemical and mechanical means, owing to anatomical complexities for example, residual biofilm can contribute to the failure of the treatment. Highly curved root canals lead to incompletely prepared canals, and the danger of instrument fracture is considerably greater owing to the increased stress.
Mechanical root canal preparation only ever forms part of root canal preparation. For complete cleaning and disinfection of root canals, irrigation solutions must be used. To ensure application of irrigation solution also in the apical region of the root canal, irrigation cannulas that have a suitable diameter and, particularly with highly curved canals, that are highly flexible must be used. Activation of irrigation solutions can even improve the efficacy of cleaning and disinfection.
A 43-year-old female patient was referred to us for root canal therapy of tooth #26. Owing to symptomatic pulp necrosis, the referring dentist had already performed the trepanation of the pulp chamber. When the patient presented to our clinic, she was free of symptoms. On the preoperative intra-oral radiograph (Fig. 1), the significant curvature of the mesial root could already be seen.
First, there was a consultation and information session with the patient. After infiltration anaesthesia, the tooth was isolated with a dental dam (COLTENE). The access cavity was first cleaned and disinfected with 5% sodium hypochlorite (NaOCl) under the Pro Magis dental microscope (ZEISS). The cleaned access cavity was refined with EndoExplorer 1–3 instruments (Komet). A total of three canal entrances could be detected and enlarged.
In the next step, initial scouting of the coronal root canal sections was performed with C-PILOT hand files (VDW) in ISO sizes 08 and 10. In particular, the mesiobuccal canal was checked with pre-curved hand files to determine whether the curvature at the transition from the coronal to the middle root canal third could be managed. Because this was possible, this canal was enlarged and prepared up to the middle third with an R-PILOT instrument (VDW). The root canal was irrigated with 5% NaOCl using the EDDY FLEX.CANNULA (Fig.2) (VDW), and the patency of the canal was checked with a pre-curved hand file.
Using a second VDW.CONNECT Drive endodontic motor (VDW) and a R25 RECIPROC blue file (VDW), the canal was prepared in steps, alternating with the R-PILOT file initially to the apical third. Using the Root ZX mini apex locator (Morita) and a C-PILOT file ISO size 10, patency was confirmed and the working length determined. The apical canal third up to the working length was then mechanically prepared with R-PILOT and 20/.05 and 25/.04 VDW.ROTATE (Fig. 3) instruments (VDW).
Dental debris was regularly flushed out of the canal with NaOCl, and the patency of the canal checked with an ISO size 10 hand file (recapitulation to working length or patency). After apical gauging with nickel–titanium (NiTi) K-files (VDW), the root canal was finally shaped with a 30/.04 VDW.ROTATE file (VDW) to the working length. Working with the six-handed technique proved advantageous for the frequent instrument changes and repeated checking of the working length so that this difficult canal could be prepared in reasonable time.
“For complete cleaning and disinfection of root canals, irrigation solutions must be used.”
The uncomplicated distobuccal and palatal canals could subsequently be quickly accessed and prepared to working length with R25 RECIPROC blue (Fig. 4) and 30/.04 VDW.ROTATE files.
Shaping was followed by generous irrigation of all canals with 17% EDTA (COLTENE) and again with 5% NaOCl. The irrigation solutions were sonically activated with the EDDY irrigation tip (VDW). AH Temp calcium hydroxide (Dentsply Sirona) was applied as a temporary root canal filling, and the access cavity was temporarily sealed with sterile PTFE tape and GC Fuji IX GP glass ionomer cement (GC).
At the second visit about three weeks later, under infiltration anaesthesia, a dental dam and a dental micro-scope, the temporary occlusal seal was removed and the calcium hydroxide was thoroughly flushed out. The working length was again checked using endodontic length determination. Gutta-percha points (VDW) were adjusted to working length (tugback). A control radio-graph was taken with the gutta-percha points in situ (Fig. 5). The point that was too long in the palatal ca-nal was shortened and checked again. Final root canal irrigation was performed with sonically activated 17% EDTA and 5% NaOCl (Fig. 6).
After drying the canals (Fig. 7) with micro-suction, the canals were sealed with a bioceramic sealer (EndoSequence BC Sealer, Brasseler) and gutta- percha points in the single-cone technique. After complete cleaning of the cavity and sandblasting with aluminium oxide, the tooth was restored with an adhesive composite filling (everX Flow and G-ænial, both GC). After removal of the dental dam, a final radiograph was prepared (Fig. 8).
Thanks to the generous irrigation protocol and sonic activation, a lateral canal in the apical section of the palatal root canal could be cleaned and filled with sealer.
Root canal therapy of teeth with highly curved root canals is frequently associated with difficulties for the dentist. Curves always mean a greater risk of preparation errors. A common problem in curved canals is the formation of steps due to the resetting force of the instruments. This can in turn lead to sections of the canal no longer being accessible to preparation, and the bacterial microflora that is potentially present can lead to endodontic failures. When at-tempting to forcefully overcome ledges, blockages due to compaction of debris or, in the worst case, canal perforation may occur. Curved canals cause problems also for instruments because they always result in increased stress on the instrument, promoting fracture.
As always in difficult treatment situations, proceeding in a slow and controlled manner is the key to success. Pre-curved (steel) hand files for initially opening and scouting of short canal sections and small, highly flex-ible NiTi instruments applied with absolutely no pressure help to avoid fundamental preparation errors. As a user of VDW instruments, switching between pre-curved C-PILOT, R-PILOT, R25 RECIPROC blue and flexible VDW.ROTATE instruments with a taper of .04 has proved successful for our office in difficult canals. The next larger instrument is used somewhat shorter than the previous. The canal is thus enlarged from the coronal to the apical third in small sections. After the larger instrument, a smaller one can then penetrate more deeply into the canal. To prevent step formation, pressure on the instruments must be avoided as much as possible. Mechanised instruments should always be kept moving. Constantly checking patency with a small steel file and frequent (sonically activated) irrigation can prevent blockage of the canal with debris. To ensure that irrigation solutions can also reach deep canal sections, thin, flexible irrigation cannulas are useful. In my opinion, flexible plastic cannulas such as the EDDY FLEX.CANNULA are highly suitable. The sonic (or ultra-sonic) tips to activate the irrigation solutions should also be highly flexible.
“Root canal therapy of teeth with highly curved root canals is frequently associated with difficulties for the dentist.”
It is critical for the success of endodontic treatments that the entire root canal system is chemically and mechanically prepared as thoroughly as possible. Curved root canals are often a barrier to achieving this goal. Whether we were able to achieve this in the present case will be seen at the follow-up examinations.