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ORIGINAL ARTICLE
Year : 2021 | Volume
: 24
| Issue : 3 | Page : 435-442
Analysis of root and canal morphology of fused and separate rooted maxillary molar teeth in Turkish population
H Aydin
Private Practice, Antalya, Turkey
Correspondence Address:
Dr. H Aydin
Private Ballıpınar Dental Center, Çağlayan Mahallesi, Barınaklar Bulvari, 07230 Muratpaşa, Antalya
Turkey
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/njcp.njcp_316_20
Abstract
Aims: To investigate the root canal anatomy and the incidence of fused roots in maxillary first molar (MFM) and maxillary second molar (MSM) teeth in the Turkish population and compare them to teeth with separate roots using cone-beam computed tomography (CBCT). Methods: CBCT images of 616 MFMs and 703 MSMs were analyzed from 402 patients for the number of roots and the presence of fusion. The canal configuration of teeth with separate and fused roots was compared. Type of fusion and canal merging positions were determined. A P value of less than 0.05 was considered significant. Results: Five hundred and seventy-one (92.69%) MFMs had three separate roots, one (0.16%) had four roots and the incidence of root fusion was 7.14%. An additional mesiobuccal (MB) canal was present in 79.34% of the teeth with three separate roots. There was no merging of canals in 36 of 44 teeth with fused roots. The prevalence of fusion was higher in the MSMs (23.47%). The incidence of three and four separate roots in MSM teeth was 74.68% and 1.85%, respectively. The prevalence of additional MB canals in teeth with three separate roots was 53.14%. There was no canal merging in 60% of the fused rooted teeth. There were two-merged canals in 31.52% and multiple merged canals in 8.48% of the MSMs. Conclusions: In the Turkish population, the incidence of root fusion in the MFMs and MSMs was 7.14% and 23.47%, respectively, with more canal merging in the MSMs.
Keywords: Cone-beam computed tomography, fused roots, maxillary molars, root canal configuration, Turkish populatio
Introduction 
Endodontic treatment involves the cleaning and disinfection of the root canal complexity and the hermetic filling of this space. Although variations occur in the root and canal morphology in all groups of teeth, the maxillary molar (MM) teeth are one of most variable.[1] Therefore, they are associated with high treatment failure rates.[2] The main factor consistently related to treatment failure is the presence of untreated canals due to variable root canal morphology. Failure is 4.38 times higher in teeth with root canals that are not treated.[3]
Although MM teeth generally have four canals, three roots (double canals in mesiobuccal [MB] root), they may show one or two roots depending on the fusion between the roots or fourth extra root.[4] MMs have been investigated frequently because of their complex morphology.[5],[6],[7] A high occurrence of root fusion has been reported (up to 42%) in different populations, particularly in maxillary second molars (MSM).[8] Fused rooted teeth have more complex canal configurations than those with separate roots.[8],[9] MMs show a higher incidence of root fusion than mandibular molars.[10] The C-shaped root canal configuration has also been observed in these teeth.[11] Few studies have evaluated the root and canal anatomy of the MMs in the Turkish population, and none of them have included fused roots.[1],[12],[13],[14] Variations in root canal anatomies have been reported due to ethnic differences.[15] Therefore, proper knowledge of root canal anatomy in different ethnic groups is crucial for clinicians to identify all possible variations encountered during treatment.
Several in-vitro techniques such as root grinding under a microscope,[16] clearing,[1],[5] and microcomputed tomography[8] have been used to examine the root canal system. These methods require the processing of extracted teeth. Thus, a limited number of teeth can be examined, and comparison with adjacent symmetrical teeth is not possible. Cone-beam computed tomography (CBCT) has recently become a popular diagnostic tool in endodontic procedures for nondestructive testing. It eliminates the superimposition of surrounding structures, allows rapid, non-invasive and adequate image resolution, and offers three-dimensional and multi-planar views of hard tissues in the maxillofacial region.[17]
This study aimed to investigate the root and canal morphology and the prevalence of root fusion in MM teeth in the Turkish population using CBCT.
Materials and Methods The protocol of the study was submitted to the Akdeniz University Medical Faculty Clinical Trials Ethics Committee, and ethical approval was received. CBCT images were obtained from patients who applied to the private Ballıpınar Dental Center from January 2016 to November 2019. The reasons for CBCT evaluation included implant surgery and other complicated surgical procedures, orthodontic treatment, and endodontic therapy. The inclusion criteria for the MMs were as follows: teeth with fully formed apices; absence of apical periodontitis; absence of any odontogenic or nonodontogenic pathology. The exclusion criteria were as follows: endodontically treated teeth and restored with posts and cores; low-quality images with the presence of artifacts; inability to determine the tooth number.
CBCT images were acquired with Orthophus XG3D (Sirona Dental Systems GmbH, Bensheim, Germany) using the following parameters; 85 kV, 6.0 mA, 8 × 8 scan field of view, and 0.160-mm3 voxel size. Images were analyzed in the axial, coronal, and sagittal planes using Sidexis 4 software (Sirona). The study evaluated the parameters as follows:
The number of teeth with separate roots further categorized as 3-rooted and 4-rooted teeth. Canal configurations, according to the Vertucci classification, were recorded (type 1-8). A morphology that did not fall into this classification was categorized as type 9.The number and canal configurations of teeth with fused roots. The roots where the canals joined were considered merged, and the Vertucci classification was not used.Canal morphology in teeth with normal anatomy; completely independent root canals with no merging (to Vertucci classification)Canal morphology in teeth, where one root is separate, and the other two are joined (to Vertucci classification). Only teeth with two fused roots were examined. Thus, P root in type 1, distobuccal (DB) root in type 2, and the MB root in type 3 were analyzed.The number of merged canals and merging positions in the partial or complete (multiple) canal merging systemsThe number and type of root fusionThe percentage of C-shaped canalsThe criteria to determine fused roots were as follows: the ratio of the distance from the cementoenamel junction to the lower point of fusion and the distance from the cementoenamel junction to the root apex was more than 70%, as per Zhang et al.'s study.[8]
A new fusion classification was developed by adding modifying the work of Martins et al.[10][Figure 1]:
Type 1: Fusion between the MB and DB rootsType 2: Fusion between the MB and P rootsType 3: Fusion between the DB and P rootsType 4: In addition to a fusion of MB and DB roots, a fusion between the MB/DB root and P rootType 5: Fusion of the P root with both MB and DB rootsType 6: Fusion of the P root with the DB and MB roots, forming a conical-shaped root structureType 7: MB, DB, and P roots fused to an equal degree, resembling a three-leaf cloverType 8: MB, DB, and P fused as a single root to resemble a single massType 9: Presence of only one B (no signs of fusion, no depression on the root surface or grooves) and P root with similar P and B root sizeType 10: Unusual anatomy, not in any other classificationAge groups were divided as follows: 18–30, 31–40, 41–50, 51–60, and ≥61 years.
Statistical analysis
Kappa test was performed to determine the agreement of the evaluations. Chi-square analysis was performed to examine the relationships of fusion, according to gender and age groups. The Z-test was used to compare proportions between independent groups. P values less than 0.05 were considered significant. The data were analyzed using the SPSS 22.0 package program (IBM SPSS Statistics, Chicago, IL).
Results The images of 402 patients with a mean age of 35.86 ± 10.70 years (min-max; 18–74) were examined. Of these, 196 patients were male (48.8%), and 206 were female (51.2%). A total of 616 maxillary first molars (MFM) and 703 MSMs were included. Twenty percent of all teeth were re-examined 1 month after the first observation. The intrarater reliability was 86.7%, with an asymptotic standard error of ± 7.4%.
Root morphology of maxillary first molars
The morphologic root characteristics of MFM teeth are shown in [Table 1]. Among MFMs, 572 teeth (92.86%; 95% CI, 91%–95%) had separate roots; 92.69% (95% CI, 91%–95%; n = 571 teeth) had three separate roots; only one tooth (0.16%; 95% CI, 0%–1%) had four roots. The prevalence of fused roots was found to be 7.14% (95% CI, 5%–9%; n = 44 teeth). There was a difference between proportions of fusion types (P < 0.001), listed in [Table 2]. Type 3 was the most common type of fusion with a prevalence rate of 75% (95% CI, 62%–88%). The incidence of types 1, 2, 3, and 5 were 2.43% (95% CI, 0%–7%), 2.43% (95% CI, 0%–7%), 6.81% (95% CI, 0%–14%), and 4.55% (95 CI, 0%–11%), respectively. There was a single root in 4 teeth with no signs of fusion grooves on the B side (Type 9, 9.09%; 95% CI, 1%–18%). Fusion types 6, 7, 8, and 10 were not observed.
Table 1: Number and percentages of root and canal morphologies of the maxillary first molars
Table 2: Number and percentages of fusion types and canal merging positions in maxillary first molarsRoot morphology of maxillary second molars
The external root anatomy of the MSMs had more variations than that of the MFMs, as shown in [Table 3]. The incidence of 3-separate roots was 74.68% (95% CI; 72%–78%). Thirteen teeth (1.85%; 95% CI, 1%–3%) had 4-separate roots. The incidence of fused rooted MSMs was 23.47% (95% CI; 20%–27%; n = 165). There was a significant difference in the incidence of fusion compared to MFMs (P < 0.001). All types of fusion were observed, and there was a difference in frequency among groups (P < 0.001) [Table 4]. The most frequent type of fusion was between the MB and P roots (36.97%; 95% CI, 29%–44%).
Table 3: Number and percentages of root and canal morphologies of the maxillary second molarsAge and gender differences in root anatomy
The percentage of root fusion was higher in women for both MFMs and MSMs (P = 0.008 and P < 0.001, respectively). Among the MFMs, 31 teeth (9.84%) in women and 13 teeth in men (4.4%) had fused roots. Among the MSMs, 110 teeth (29.76%) in women and 55 teeth (16.22%) in men had fused roots. In both groups, the 41–50 years age-group showed the highest fusion rate. While this difference was not significant in the MFMs (P > 0.05), it was significant in the MSMs (P < 0.001).
Canal configurations of maxillary first molars
The values of teeth for separate and fused roots (3-independent and separate root canals in fusion types 1–3) are shown in [Table 1]. Of the 44 fused rooted teeth, 36 (81.82%) did not have any merging between the canals [Table 2]. Eight teeth showed 2-merged canals. Of these, 4 teeth showed merging of the MB-DB canals, and the other 4 showed intercanal merging between the DB-P canals. No merging of multiple canals was observed. An additional MB canal was found in 79.34% (95% CI, 76%–82%) of teeth with 3-separate roots [Figure 2]a,[Figure 2]c,[Figure 2]e and 68.75% (95% CI, 50%–86%) of the fused rooted teeth with 3-independent root canals [Figure 2]b. This difference was not significant (P > 0.05). The most common canal configuration in the MB roots was type 2 (42.9%; 95% CI, 38%–46%) [Figure 2]a. The incidence of additional canals was very low in the DB and P roots of the MFMs (1.75% for both; 95% CI, 0%–2%) [Figure 2]d. Type 9, was seen in 24 MB and one DB root [Figure 2]c. C-shaped canal was seen in only one tooth (0.16%; 95% CI, 0%–1%).
Figure 2: Canal morphologies for maxillary first molars, red arrows (MB-1), green arrows (MB-2), blue arrows (MB-3), black arrow (palatal-1), orange arrow (palatal-2); a) Vertucci type-2; b) Vertucci type-6; c) Vertucci type 9; d) double palatal canals; e) five canalsCanal configurations of maxillary second molars
The values of teeth for separate and fused roots (3-independent and separate root canals in fusion types 1–3) are shown in [Table 3]. There was no merging in 98 of 165 fused rooted MSMs (59.39%) [Table 4]. Fifty-two teeth (31.52%) had 2-merged canals. The most common variation was the merging of the MB-DB canals (n = 39, 23.63%). Multiple canal merging was seen in 15 fused rooted teeth (9.09%). The incidence of additional MB canals in teeth with 3-separate roots was 53.14% (95% CI, 49%–57%) [Figure 3]a,[Figure 3]b,[Figure 3]c,[Figure 3]d; in 3-independent canals with fusion, the incidence of MB2 canals was only 15.06% (95% CI, 7%–22%). The difference was significant (P < 0.01). The most common MB root anatomy in teeth with 3-separate roots was type 1 (46.86%) (95% CI, 43%–51%). For MB2 canals, type 2 was the most common incidence (24%) (95% CI, 20%–28%), followed by type 4 (18.86%) (95% CI, 16%–22%) [Figure 3]b. Nine teeth had a type 9 configuration [Figure 3]d. MB canals of 4-rooted teeth showed a single canal configuration in 84.61% (95% CI, 65%–100%) of the cases, and the remaining showed type 2 canal configuration [Figure 3]e. Eighteen teeth showed a C-shaped canal configuration (2.56%; 95% CI, 1%–4%) [Figure 3]f.
Figure 3: Root and canal morphologies for maxillary second molars, red arrows (MB-1), green arrows (MB-2), blue arrows (MB-3), black arrow (MB-2'), a) Vertucci type-5; b) Vertucci type-4; c) more than two canals, d) unusual canal morphology; e) four-rooted; f) C-shaped canal
Table 4: Number and percentages of fusion types and canal merging positions in maxillary second molars Discussion With the emergence of new methods to evaluate the root and canal anatomy, the number of studies examining different populations has increased. Larger sample sizes can be evaluated by analyzing the images in the data pool using CBCT. With more teeth examined, the actual values of the population can be statistically approached.[10]
Root fusion can be a developmental disturbance during root formation, or it may be due to the continuous deposition of cementum around the roots with aging.[8] Although root fusion can be seen in mandibular molars, types of fusion and canal configurations are more complex due to more fused roots in the MMs.[10] Merged canals are more commonly seen in developmental root fusion; independent canals are more common in fusion caused by the age-related deposition of cementum.[18]
In the present study, the rate of fusion was 7.14% in the MFMs and 23.47% in the MSMs in Turkish society. Endodontic literature has limited and contradictory results on root fusion. Although studies on Turkish people have investigated the root and canal anatomy of MMs, teeth have reported only canal configuration or the root anatomy as regards the number of roots, without addressing fusion.[1],[12],[13],[14] Hence, these results could not be compared to the Turkish population.
A study that did not define the fusion criteria reported root fusion in 8.3% of the MSMs and no root fusion in the MFMs.[19] Some studies considered teeth with fusion along the entire root surface as fused roots.[6],[9] Using this methodology, studies conducted in Korean[6] and Chinese[9] populations showed that the fusion prevalence was 0.7% and 1.4% in the MFMs, and 10.7% and 23.9% in the MSMs, respectively. Zhang et al.[8] considered fusion when the ratio of the distance from the to the lower point of fusion and the distance from the cementoenamel junction to the root apex was not less than 70%, and this methodology was more readily applied. They reported a high incidence of fusion (42.25%) in the MSMs. As the study was performed on a limited number of teeth ex vivo, it is somewhat doubtful whether it reflects normal population values. An Irish population study[5] reported a high incidence of root fusion 11% in the MFMs; 43% in the MSMs, but the criterion for root fusion was unclear. As the study was conducted only on 123 teeth, it is doubtful if it adequately reflects the population. According to a recent Latin American population study, the incidence of root fusion was 23.4% in the MFMs, and 57.6% in the MSMs.[20] However, this study considered fusion up to the middle level of the roots. Another report applied the current study criteria for fusion to show similar results (incidence of 7.1% in the MFMs; 25.2% in the MSMs).[10] A Saudi Arabian population study[21] that used a methodology in line with present research showed compatible results (incidence of 7% in the MFMs; 21% in the MSMs). Proportions may vary depending on the applied criteria for root fusion and ethnic differences. Therefore, care must be taken when comparing results.
Some studies did not mention fusion but only reported the number of roots.[13],[22] Multiradicular forms of fusion with 3-roots were considered as a single root. For example, a type-4 case with normal anatomy without canal merging, a type-5 case with all canals merged, or a type-8 case with a single large canal, were included in the same group. Despite variations in the canal anatomy, they were classified in the same category. This approach did not support the results of the study that showed a strong correlation between external morphology and internal anatomy.[18]
Types of fused roots were studied in a micro-CT study, and a few samples were divided into six categories (first six groups of this study).[8] Later, some authors added to these groups in large-sample studies.[10],[21] Martins et al.[10] grouped a single conical root into type 7 (type 8 group in this study). In the present study, the classification of root types was based on canal morphology. Type-9 cases included a single buccal root without a fusion groove on the root surface. These teeth had a single round canal in the B and P roots. Type-6 cases showed a prominent fusion depression between the B roots. If the B canals merged, they were oval in cross-section, rather than round. Type-8 cases generally showed a single root mass and a large oval canal in the center of the root. The external form of type 7 resembled a cloverleaf instead of a conical structure, and they were considered different from type 6.
According to the current study results, the most common type of fusion in the MFMs was found between the DB-P roots (75%). This finding is compatible with other studies.[10],[20],[21] The most common type of fusion in the MSMs was observed between the MB-P roots (37%). This finding was in agreement with some studies.[10],[21] However, it is inconsistent with some studies that reported a higher incidence of fusion between the B roots.[8],[18] A Latin American subpopulation study[20] reported that the most common type of fusion was type 6 conical fusion. In the fused rooted MFMs, merged canals were observed only in 8 of 44 teeth (18.2%), and no multiple canal merging was observed. Canal merging was found in 67 of 165 MSMs (40.61%). Canal merging was most frequently seen between the MB-DB roots. Also, 9.1% of the fused rooted MSMs showed multiple canal merging. These findings are compatible with previous studies.[8],[10],[21] In a micro-CT study, merged canals were observed in 28 of 79 fused rooted teeth, and canal merging was more common in multiradicular types of fusion involving three roots, similar to the current study.[8]
Worldwide MB2 prevalence ranges 48%–97% for MFMs[23] and 14%–83.4% for MSMs.[24] In some studies, it was challenging to analyze the canal configurations in fused rooted teeth, according to the Vertucci classification.[6],[9] Hence, the authors excluded the fused rooted teeth and included only those cases with independent canals. In the current study, the incidence of MB2 canal in MFMs with 3-separate roots was 79.3%.
In two ex vivo studies in the Turkish population, the incidence of extra MB canal was reported as 93.5% and 65% in the MFMs (1,12). In a CBCT study, 62.9% were reported in Turkish people.[13] The reason for the low MB2 incidence, according to the current study, maybe that the voxel size used for the CBCT unit was 0.30 mm3. In the present study, a CBCT unit at 0.160 mm3 voxel size was used. It is well known that decreasing the voxel size aids the visualization of canals and improves the detection of additional canals.[25] Another CBCT study in Turkish population reported a very low prevalence of the MB2 (19.65%).[14] This finding may be attributed to the differences in image interpretation, as the study was conducted by oral radiologists, not endodontists.
Present study revealed that the incidence of an additional MB canal in the MSMs was 53.1%. This finding was consistent with the results of ex vivo studies described above (55% and 59%).[1],[12] In CBCT studies, mentioned in the previous paragraph, 37.1% and 17.7% were reported.[13],[14] In the current study, lower incidences were observed in the MB roots of the MFM and MSM teeth with fused root, regular canal anatomy, with 68% and 14.61%, respectively.
Conclusion The incidence of root fusion was 7.14% in MFMs and 23.47% in maxillary second molars in the Turkish society. Different types of root fusion and canal merging were more commonly observed in the maxillary second molars.
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Conflicts of interest
There are no conflicts of interest.
References 
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