R. J. G. De Moor
Department of Operative Dentistry and Endodontology, Dental School, Ghent University Hospital, Ghent University, Gent, Belgium.

Key learning points.

• C-shaped root canal morphotypes may occur in the distal portion of the pulp chamber in maxillary first molars.
• The C-shape results from a fusion of the distobuccal and palatal roots.
• The C-shape may extend to the apical third of the fused roots.

Introduction.
The literature describes various root canal morphotypes in maxillary molars. The most common finding is the prevalence of two canals in the mesiobuccal root (Fogel et al. 1994). In addition, aberrations such as one (Carlsen et al. 1992), four (Christie et al. 1991) and five (Fahid & Taintor 1988) roots with a corresponding number of root canals have been discussed. Case reports with four (Benenati 1985), five (Wong 1991, Jacobsen & Nii 1994) and six root canals (Martinez-Berna & Ruiz-Badanelli 1983, Bond et al. 1988) have also been presented.
However, the C-shaped root canal configuration in a two-rooted maxillary first molar has only been reported in a limited number of case reports (Newton & McDonald 1984, Dankner et al. 1990). Apparently, this type of canal configuration in the maxillary first molar has not yet been described in studies describing tooth anatomy and root canal anatomy on the basis of extracted teeth and/or using cross-sections.
The present report describes root canal treatment in two maxillary first molars with Cshaped canal systems. This particular aberration is also demonstrated by means of crosssections in two additional two-rooted maxillary first molars.

Report 1.
A 44-year-old Caucasian female patient was referred by the otorhinolaryngologist (ORL) for treatment of her maxillary left first molar. The tooth had been periodically percussion sensitive for 5 years. After clinical and radiographic examination by the ORL, the diagnosis of maxillary sinusitis was excluded. Radiographic examination (Fig. 1) revealed radiopaque material in the pulp chamber with little evidence of root canal preparation or filling. After removal of the coronal amalgam, the paste in the pulp chamber was removed and the chamber cleaned ultrasonically and rinsed with a 2.5% sodium hypochlorite solution. The pulp chamber floor was then explored to locate the canal orifices, which had not been opened. Two mesial orifices were found, as well as a broad distal semilunar orifice (Fig. 2).

Figure 1. Case 1: preoperative periapical radiograph of the maxillary left first molar.


Figure 2. Case 1: access opening after removal of the amalgam filling and cleaning of the pulp chamber floor. Two orifices in the mesiobuccal root and a semilunar opening connecting the palatal with the distobuccal canal can be seen.

The two mesial canals were preflared with a ProFile Orifice Shaper (O.S.) number 3 and shaped with ProFiles .04 and .06 taper (Dentsply Maillefer, Baillaigues, Switzerland) to a size 25 with the crown-down technique to an estimated 3 mm from the radiographic apex. The distal canal was flared with Gates Glidden drills (numbers 4–3–2) and initially prepared with Flexofiles (Dentsply Maillefer) to 3 mm from the radiographic apex. Working length determination was performed radiographically with two size 25 files in the mesial canals and a size 30 file in the palatal orifice of the C-shaped canal and a size 20 in the distobuccal orifice (Fig. 3a). The two files in the C-shaped canal appeared to join and were connected by an isthmus, separating the two files. The mesial canals were then further prepared with ProFiles .04 and .06 taper up to 1 mm from the radiographic apex to size 25 –.06 taper. An apical stop was created with a size 30 Flexofile (Dentsply Maillefer). The distal C-shaped canal was debrided up to 1 mm from the radiographic apex with Flexofiles to a size 35 and the preparation was refined with Hedström files (Dentsply Maillefer). An interappointment dressing of calcium hydroxide (Control Stabilized Calcium Hydroxide, La Maison Dentaire, Balzers, Switzerland) was sealed in the pulp chamber with Cavit (ESPE, Seefeld, Germany) and covered with Fuji Cap II (GC., Tokyo, Japan) as a coronal temporary filling.

Figure 3. Case 1: a) root length determination radiograph with four endodontic instruments (two in the mesiobuccal root and two in the distal root); b) radiograph of the obturated canal system.


Figure 4. Case 1: a,b) radiographs of the obturated canal system 6 months and 1 year after completion of the root canal treatment (arrow indicating the radiographic outline of the combined palatal and distobuccal canals and roots, that were not discernible at any point in treatment, despite different angulations of the X-ray beams).

The patient returned after 10 days for completion of the treatment. The tooth was asymptomatic and isolation and access were made without anaesthesia. Instrumentation was repeated with Flexofiles and the canals were thoroughly rinsed with 2.5% sodium hypochlorite. The canals were obturated with AH-26 (De Trey, Dentsply, Konstanz, Germany) root canal sealer and four gutta-percha master cones, using cold lateral condensation with accessory cones up to 3 mm from the apical constriction followed by thermo-mechanical condensation with Gutta-Condensers (Dentsply Maillefer) (hybrid gutta-percha condensation, De Moor & De Boever 2000) (Fig. 3b). The access cavity was sealed with Fuji Cap II and the occlusion was adjusted.
At the 6-month (Fig. 4a) and 1-year recall examinations (Fig. 4b), the tooth remained asymptomatic and the apical response was normal on the radiograph.
There was no opportunity to verify whether this particular root canal configuration was present bilaterally (Sabala et al. 1994).

A 21-year-old Caucasian male patient was referred for endodontic treatment of his maxillary left first molar. The tooth was periodically percussion sensitive, but not sensitive to temperature. Radiographic examination (Fig. 5) revealed the presence of a deep amalgam restoration in close proximity to the pulp chamber. There was no evidence of root canal preparation or filling. According to the patient, the last treatment on this tooth was completed at the age of 13 years. The root structure was not clearly demonstrated on the radiograph. After removal of the coronal amalgam, a cotton pellet was found in the pulp chamber as well as an orange-brown paste on the pulp chamber floor. The pulp chamber was cleaned ultrasonically and rinsed with a 2.5% sodium hypochlorite solution. The pulp chamber floor was then explored to locate the canal orifices, which had not been opened. One mesial orifice was found, as well as a broad distal C-shaped orifice with two canals separated by an isthmus (Fig. 6). A second mesiobuccal canal was not found, even though magnification was used.

Figure 5. Case 2: preoperative periapical radiograph of the maxillary left first molar.


Figure 6. Case 2: access opening - one orifice in the mesiobuccal root and a semilunar opening connecting the palatal with the distobuccal canal can be seen.

The canal lengths were determined electronically with the AFA Apexfinder (EIE Analytic Technology, Orange, CA, USA). The two canals in the C-shape appeared to join in the apical third. The clinical conclusion was that the palatal and distobuccal canals merged in a C-shaped single canal and that there was only a small isthmus separating the orifices. The root canals were then instrumented in a conventional manner and obturated by means of hybrid guttapercha condensation, as in case 1, and AH-26 sealer (Fig. 7).

Figure 7. Case 2: radiograph of the obturated canal system.


Figure 8. Case 2: radiograph of the contralateral first molar, with normal root anatomy.

The radiographic examination of the contralateral first molar revealed a normal root anatomy and the presence of three roots (Fig. 8).

A 17-year-old Caucasian female patient was referred for endodontic treatment of her maxillary right first molar. The patient had not received dental treatment for more than 10 years. The contralateral maxillary first molar was severely decayed. Only two root fragments of approximately 4–5 millimetres remained. After reconsulting the referring dentist, it was decided to extract the tooth. The radiograph clearly demonstrated the palatal and mesiobuccal root. The distobuccal root-end was not identified and it was believed to be superimposed on the palatal root (Fig. 9). The extracted tooth appeared to have two separate roots (Fig. 10a). Upon sectioning through the crown, two root canals were identified in the mesiobuccal root and a deep semilunar groove extending from the palatal to the distobuccal aspects of the cavity was noted (Fig. 10b). Neither the palatal nor the distobuccal root canal orifices were identified. A section through the middle and apical third of the roots confirmed the presence of two mesiobuccal canals and a combined palatal and distobuccal canal merging in one C-shaped canal (Fig. 11).

Figure 9. Case 3: preoperative view of the maxillary right first molar. Carious pulp exposure necessitated extraction.


Figure 10. Case 3: (a) distal view on the extracted tooth. Note the presence of only two roots; (b) horizontal section through the pulp chamber showing two orifices in the mesiobuccal root and a semilunar opening connecting the palatal with the distobuccal canal.


Figure 11. Case 3: (a) horizontal section through the middle third of the roots; (b) horizontal section through the apical third of the roots.

A 26-year-old Caucasian male patient was referred by the AIDS-centre of the Ghent University Hospital for the treatment of his maxillary left first molar. This tooth was extensively restored with a composite filling and was very mobile. In view of the medical background of the patient, it was decided to extract this tooth. A panoramic radiograph demonstrated the palatal and mesiobuccal root (Fig. 12). The extracted tooth had two separate roots (Fig. 13). The apex of the distal root clearly demonstrated two apical foramina. Upon sectioning the crown, two root canals were identified in the mesiobuccal root and a deep semilunar groove extending from the palatal to the distobuccal aspects of the cavity was present (Fig. 14). The palatal and the distobuccal root canal orifices were identified at a depth of approximately 5 mm in the C-shaped canal. A section through the middle and apical third of the roots confirmed the findings (Fig. 15). A comparison with the anatomy of the contralateral tooth could not be made, as this tooth had already been extracted.

Figure 12. Case 4: preoperative view of the maxillary right first molar. Carious pulp exposure necessitated extraction.


Figure 13. Case 4: (a,b) frontal and distal view on the roots of the tooth. Note the presence of only two roots. There are two apical orifices in the distal root.


Figure 14. Case 4: horizontal section through the pulp chamber showing two orifices in the mesiobuccal root and a semilunar opening connecting the palatal with the distobuccal canal


Figure 15. Case 4: (a,b) horizontal section through the middle and apical third of the roots. There are two separate canals in the apical third.

Discussion.
The variability of the root canal system of multirooted teeth represents a challenge to both endodontic diagnosis and treatment. The preoperative awareness of potential anatomic variations is essential for the success of the endodontic treatment. The only way to detect root canal morphology and anatomy is the use of a preoperative radiograph and an additional radiographic view from a 20-degree mesial or distal projection. In this respect, it becomes clear that extreme variations in root fusion are difficult to ascertain with radiographs.
The present cases demonstrate a variation in the root canal anatomy of the maxillary first molar, which has only been reported twice in the endodontic literature (Newton & McDonald 1984, Dankner et al. 1990). From the anatomical structure of these teeth on the radiograph alone, it cannot be concluded whether the distal roots are the result of total fusion of the distobuccal and palatal roots and/or canals, as has been previously described (Dankner et al. 1990). The anatomy of the floor of the pulp chambers (Figs 10b, 14) of the extracted teeth, however, reflected the general topography of the canal orifices of a maxillary first molar, but, with a distortion of the anatomy of the pulp chamber. Examination (Figs 10, 13) and sectioning (Figs 10, 11, 4, 15) of the two extracted teeth clearly demonstrated that the distal root portion was indeed a fusion of a palatal and distobuccal root. Another finding was that the mesiobuccal root was well developed and that, in the extracted teeth, two mesiobuccal canals were present in both cases.
The impression that anatomical aberrations appear frequently contralaterally (Sabala et al. 1994) cannot be confirmed or refuted in the present cases, due to a lack of contralateral teeth.
In order to quantify the presence of this particular canal aberration, the anatomy of 2175 root-filled maxillary first molars treated during the last 10 years was evaluated radiographically; the incidence of C-shapes was 0.091%. However, this percentage is only an estimate and cannot be taken as the true prevalence in the general community. A review of the available literature has mentioned C-shapes in the distal portion of the pulp chamber in only two case reports and in no endodontic text books. A more recent article by Al Shalabi et al. (2000) mentions a fusion of the distobuccal and palatal root in one of 83 extracted maxillary first molars in an Irish population. In relation to the present report, it is unfortunate that there is not a more precise description of the particular configuration than the reference to the Vertucci’s Classification (Vertucci 1984) as type II (two canals fusing into one canal in the apical area). On the other hand, the incidence of a connection between the distobuccal and the lingual root component has been described in a study of one-rooted maxillary second molars (Carlsen et al. 1992) as 7.69%. In an examination of 309 Chinese maxillary second molars, C-shaped root canals were encountered at a frequency of 4.9% (Yang et al. 1988). These canals, though, probably corresponded to both mesial and distal C-shapes. The Chinese frequencies were also derived from three-, two- and one-rooted maxillary second molars, whereas the Danish frequencies were from material that contained only one-rooted maxillary second molars. Ethnically related differences in the frequencies of number of root canals have also been reported (Trope et al. 1986, Walker 1988a,b) and therefore frequency differences are to be anticipated.

Conclusions.

1. The cases presented in this report demonstrated C-shaped root canal morphotypes in maxillary first molars, whereas this configuration is classically reported in mandibular molars.
2. The radiographic outline of the combined palatal and distobuccal roots was not clear at any point during treatment.
3. On the basis of the root structure and cross-sections of two extracted maxillary first molars, it can be concluded that the C-shape in the distal portion of the pulp chamber results from a fusion of the distobuccal and palatal roots.

References.

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