Racial predilection of C-shaped canal configuration in the mandibular second molar.

AIM: The purpose of this article is to determine the racial predilection of C-shaped canal configuration in a mandibular second molar.
BACKGROUND: Unusual root canal anatomy always poses a diagnostic and treatment challenge. Identification of such variation is important for the success of root canal treatment outcome. C-shaped canal configuration is such an aberrant morphology of molar teeth that vary in different population and is commonly seen in a mandibular second molar. Thus, knowledge of racial predilection of C-shaped canal configuration in different population for early diagnosis is obligatory.
MATERIALS AND METHODS: An exhaustive search was undertaken to identify published research articles related to C-shaped canal configuration in mandibular second molars. Forty-three research articles were analyzed which included 12,481 mandibular second molars. Chi-square test using value of P < 0.05 was performed to assess the statistical significance of this anomalous anatomic variation among the different population.
RESULTS: Statistical test revealed a significant variation between the Asian and nonAsian population. The highest incidence of racial predilection was observed in China (Asia) with 93.1%, and the minimum was observed in America with 2.7%.
CONCLUSION: This research reported that racial predilection of C-shaped canal configuration in mandibular second molar varies significantly.

INTRODUCTION

Mandibular molars exhibit different anatomical variations. C-shaped canal configuration is one of the most common anatomical variants observed in a mandibular second molar. It is an aberrant morphology of mandibular second molar in which the horizontal cross section is in the form of a letter C, with canals which may or may not be separate. In this configuration, the canals are connected by ribbon-like structure such as a slit, fin, or web.[1] This configuration develops either due to the fusion between roots or by coalescence due to deposition of cementum with time. The root canal configuration depends on the growth of the Hertwig's epithelial root sheath (HERS), which bends in a horizontal plane below the cementoenamel junction and fuses in the center leaving an opening for roots. Thus, failure of HERS to fuse on the lingual or buccal root surface is the main cause of C-shaped root canal configuration.[2]

Predominantly, this type of configuration occurs in mandibular second molars, but it has also been reported in mandibular first and third molars, maxillary first molars, and in mandibular premolars by various researchers.[3] If the C-shaped canal is present on one side, it may be found in the contralateral tooth in over 70% of individuals.[4] C-shaped canal configuration is difficult to prepare during biomechanical preparation.[5] Therefore, it requires a different regimen of endodontic treatment.

Literature search reveals that C-shaped canal configuration is not uncommon, and this is confirmed by various studies in which prevalence ranges from 2.7 to 41.27%.[36] This prevalence is estimated to be between 2.7 and 9.0% in nonAsian population and is as high as 41.27% among the Asian population such as Chinese, Korean, and Hong Kong Chinese which indicate its racial distribution. With the advent of three-dimensional imaging and dental operating microscope further increase in the detection of C-shaped configuration in the Asian population were also reported.[789]

Systematic reviews are a type of literature review that collects and critically analyzes multiple research studies or papers, using methods that are selected before one or more research questions are formulated, and then finding and analyzing studies that relate to and answer those questions in a structured methodology. Therefore, it uses an objective and transparent approach, with the aim of minimizing bias.

As there are very few systematic reviews available in the literature, this study was undertaken to re-evaluate the racial predilection of the C-shaped canal in mandibular second molars. Further, racial predilection in different continents and especially in India as a country in the South Asian geographical location was also studied.

MATERIALS AND METHODS

Literature Search and Data Extraction: An exhaustive search was undertaken through MEDLINE/Pub Med/Elsevier/Google Scholar/Web of Science (ISI)/Scopus/IndMED database, various Journals indexed in PubMed/Medline to identify published literature related to the prevalence of C-shaped canal in permanent mandibular second molar by using keywords “mandibular molar,” “root canal,” “fused mandibular teeth,” and “cross-sectional study.” Related research articles were identified, and a literature review was performed for articles dated February 2018 and before.

The data were analyzed according to the geographical population, sample size, prevalence of C-shaped canal configuration, and evaluation technique. The geographical population studied was categorized based on various continents such as Asia and non-Asian such as Australia, Europe, South America, North America, and Africa. Various evaluation techniques have been documented in the literature which includes the routine analysis such as clinical examination and intraoral periapical and panoramic radiography. With the evolution of time, the advanced analysis includes clearing technique, micro/spiral computed tomography (CT), cone-beam CT (CBCT), and stereomicroscopy.

Statistical comparisons were made between different population and within the same population, using Chi-square test with P < 0.05.

RESULTS

A summary of the findings of these studies based on the geographical population, their sample size, racial predilection percentage, and evaluation technique were tabulated. A total of 43 anatomic studies were analyzed which included 12,768 mandibular second molars.

Among the Asian population, East Asians showed the maximum prevalence of C-shaped canal of 93.1% (Fan et al., 2004) from China, 52% (Walker et al., 1988) from Hong Kong, and 45.5% (Jin et al., 2006) from Korea followed by West Asia of 34.37% (Salma et al., 2013) from UAE, Southeast Asia of 22% (Gulabivala et al. 2001) from Burma and least in the South Asian population of 7.5% (Neelkanthan et al., 2010) from India. However, a minimum of 3% racial predilection was observed in various populations from such as Srilanka (Peiris et al., 2008) and Iran (Jahromi et al., 2013 and Nourmadipour et al., 2007) [Table 1].

Table 1

Racial predilection of C-shaped canal configuration in Asian races

Population	Authors	Years	Sample size	Racial predilection of C-shaped canal (%)	Evaluation technique
East Asia
China	Thong and Abukasim[10]	1995	100	27.5	Clearing technique
	Fan et al.[7]	2004	58	93.1	Micro CT
	Zhang et al.[11]	2011	157	29	CBCT
	Zheng et al.[12]	2011	528	39	CBCT
	Wang et al.[13]	2012	1146	34.64	Radiographic examination
				39.18	Clinical examination with microscope
				41.27	Combination of radiography and clinical examination
Korea	Seo and Park[14]	2004	272	32.7	Clinical examination of working length radiographs
			96	31.3	Cross-sectional study using endodontic cube
	Jin et al.[8]	2006	220	45.5	Micro CT (serial axial section)
	Jung et al.[15]	2010	311	29	Panoramic radiograph
	Seo et al.[9]	2012	92	42.6	CBCT
	Park et al.[6]	2013	710	41.2	CBCT
Hong Kong	Yang et al.[16]	1988	581	13.9	Clearing technique
	Walker[17]	1988	100	52	Not reported
	Jayasinghe et al.[18]	2008	207	30	CT
Japan	Kotoku et al.[19]	1985	100	8	Morphological studies
West Asia
Iran	Nourmandipour and Nasiri[20]	2008	145	3	Stereomicroscope
	Rahimi et al.[21]	2008	139	7.2	Clearing technique
	Hasheminia and Hashemi[22]	2005	300	6.25	Clearing technique
	Kuzekanani et al.[23]	2012	150	3	Clearing technique
	Naseri et al.[24]	2013	1062	7	Systematic review
	Zare Jahromi et al.[25]	2013	100	3	Combination of clinical examination and clearing technique
Turkey	Cimilli et al.[26]	2005	491	8	Spiral CT
	Helvacioglu-Yigit[27]	2015	271	8.9	CBCT
UAE	Al-Fouzan[28]	2002	151	10.6	Radiography and clinical analysis
	Abdo SB and Alkaisi.[29]	2013	100	34.37	CBCT
Israel	Tamse and Kaffe[30]	1981	581	10.9	X-ray
Lebanon	Haddad et al.[31]	1999	94	19.1	Radiography and clinical analysis
Tehran	Ashraf and Grayeli[32]	2003	68	13.8	Clinical examination
South Asia
Sri Lanka	Peiris et al.[33]	2007	100	6	Clearing technique
	Peiris et al.[34]	2008	240	3	Clearing technique
India	Neelakantan et al.[35]	2010	345	7.5	Clearing technique (transverse section)
	Nikita et al.[36]	2016	110	4.55	Spiral CT
	Wadhwani et al.[37]	2017	238	9.7	CBCT
Southeast Asia
Burma	Gulabivala et al.[38]	2001	134	22.4	Clearing technique
Thailand	Gulabivala et al.[39]	2002	60	10	Clearing technique
Total sample size			9557

CT: Computed tomography, CBCT: Cone beam CT

Among the nonAsian population, Brazil showed a maximum prevalence of C-shaped canal of 15.9% (Rocha et al., 1996) followed by 12.8% (Manning et al., 1990) from Australia [Table 2].

Table 2

Racial predilection of C-shaped canal configuration in non-Asian races

Geographical population	Authors	Years	Sample size	Racial predilection (%)	Method of study
Australia	Manning[2]	1990	149	12.8	Clearing technique
Europe
Greek	Lambrianidis et al.[40]	2001	480	4.58	Periapical radiograph
Portugal	Martin et al.[41]	2016	1088	8.5	CBCT
South America
Brazil	Rocha et al.[42]	1996	396	15.9	Not reported
	Silva et al.[43]	2013	100	3.5	CBCT
North America
United States	Cooke and Cox[5]	1979	100	8	Clinical observation
	Weine et al.[44]	1988	75	2.7	Clinical observation
Africa
Sudan	Ahmed et al.[45]	2007	100	10	Clearing technique
Mixed	Weine[46]	1998	811	7.6	Radiographic and clinical analysis
	Sutalo et al.[47]	1998	150	12.5	Contrast methylene blue
Total sample size			3449

CBCT: Cone beam computed tomography

Overall C-shaped canal racial predilection was estimated, it showed 16.41%. When routine and advanced analysis of C-shaped canal racial predilection was assessed, the routine methods such as clinical examination showed 16.56%, radiographic examination showed 14.8%, and when both the clinical and radiographic method was assessed, it showed 19.6%. However when the advanced analysis was estimated, clearing technique showed 10.36%, CBCT showed 26.01%, and micro CT showed 44.15% [Table 3].

Table 3

Mean percentage of C-shaped canal configuration based on routine and advanced analysis

Analysis	Number of studies reported	Total samples	C-shaped canal configuration	Mean percentage of C-shaped canal configuration
Routine analysis
Clinical examination	6	1761	294	16.56
Radiographic examination	3	1372	433	14.8
Clinical and radiographic examination	4	2202	551	19.6
Advanced analysis
Clearing technique	14	2693	192	10.36
CBCT	8	3056	382	26.01
Micro CT	5	1133	244	44.15
Total	40	12,768	2096	16.41

CT: Computed tomography, CBCT: Cone beam CT

When micro CT was compared with all the other techniques in analyzing the racial predilection of C-shaped canal configuration, it showed a statistically highly significant result with P < 0.0001 except when compared with CBCT which showed a significant value of P = 0.0303 [Table 4].

Table 4

Comparison of average percentage of micro computed tomography to others

Micro CT	χ2	P
Clinical examination	12.53	<0.0001 (HS)
Radiographic examination	14.61	<0.0001 (HS)
Clinical and radiographic examination	9.45	<0.0001 (HS)
Clearing technique	20.94	<0.0001 (HS)
CBCT	4.69	0.0303 (S)

CT: Computed tomography, CBCT: Cone beam CT, S: Significant, HS: Highly significant

The country-wise the racial predilection of C-shaped canal configuration was assessed as there were more than one studies from the same population, and hence, racial predilection was statistically calculated for each population [Table 5]. This racial predilection was statistically compared between Asian versus nonAsian population using the Chi-square test and this difference was found to be statistically significant. Even in the Asian population, difference in racial predilection between East, West, South, and Southeast Asia was statistically significant [Table 6].

Table 5

Average percentage of racial predilection of C-shaped canal configuration

Country	Continent	Sample size	Average percentage
China	East Asia	428	39.52
Korea	East Asia	284	37.05
Hong Kong	East Asia	154	41.00
Japan	East Asia	90	32.00
Iran	West Asia	115	5.10
Turkey	West Asia	381	8.45
United Arab Emirates	West Asia	124	22.48
Israel	West Asia	508	10.90
Lebanon	West Asia	94	19.10
Tehran	West Asia	68	13.80
Sri Lanka	South Asia	170	4.50
India	South Asia	466	9.00
Burma	Southeast Asia	134	22.40
Thailand	Southeast Asia	60	10.00
America	North America	88	5.35
Brazil	South America	248	9.70
Sudan	Africa	100	10.00
Portugal	Europe	1088	8.50
Greek	Europe	480	4.50
Australia	Australia	149	12.80
Mixed	Asian and non-Asian	481	10.05

Table 6

Comparative evaluation of racial predilection of C-shaped canal configuration between Asian population and non-Asian continent and among Asian countries

Continent	Sample size	Percentage	χ2	P
Asian	203	19.45	14.18	0.0001
Non-Asian	359	8.47
East Asia	239	37.39	80.88	<0.0001
West Asia	215	13.31
South Asia	228	7.25
Southeast Asia	97	16.20

DISCUSSION

The C-shaped canal, which was first documented in endodontic literature by Cooke and Cox in 1979,[5] is so named for the cross-sectional morphology of the root and root canal. Instead of having several discrete orifices, the pulp chamber of the C-shaped canal is a single ribbon-shaped orifice with a 180° arc (or more), which, in mandibular molars, starts at the mesiolingual line angle and sweeps around the buccal to the end at the distal aspect of the pulp chamber.[2] Knowledge and recognition of such canal configuration facilitate more effective canal identification and unnecessary removal of healthy tooth structure in an attempt to search for missing canals.[19] The literature reports that the presence of C-shaped canal is more common in the East Asian population. This co-relates with the study's results, as the sample from China had significantly higher prevalence (93.1%) when compared with other regions.

This systematic review revealed that C-shaped canal configuration varies in the mandibular second molar among the different population. Various techniques were used for the evaluation of this configuration both in vitro[7132135] and in vivo.[48] To the best of author's knowledge, there is no such study till date where comparison of prevalence for C-shaped canal between the Asian and non-Asian population has been made, moreover comparison of routine and advanced analysis and separate comparison of micro-CT with various other techniques has not been reported. This systemic study has evaluated above-mentioned details.

Among various techniques, clearing technique,[1016212223] radiography,[1315284046] and clinical analysis[51425313244] were more common. Using these techniques, various studies[1344] had reported the prevalence of this configuration ranging from 2.7% to 41.27%. Among three-dimensional imaging techniques, spiral CT,[26] micro-CT,[78] and CBCT[69] were used. The Use of micro-CT resulted in even higher prevalence up to 93.1% in the Chinese population[7] as compared to when clearing technique.[10] This increase in prevalence may also be due to the difference in sample size, increase in knowledge about configuration and decrease in jaw size during evolution leading to fusion of roots. Introduction of magnification and use of ultrasonic tips had further improved the diagnosis of this configuration.[49] More racial predilection was observed in the Asian population as compared to the NonAsian population [Figure 1]. C-shaped configuration is reported to be more prevalent among females (16.5%), as compared to that of males (10.4%).[50] The present study revealed great variability between regions regarding C-shaped canal configuration.

Figure 1

Map depicting the variation in prevalence of C-shaped canal configuration world-wide

C-shaped configuration complicates endodontic instrumentation and obturation if not diagnosed at an early stage. As this configuration is common in Asian as compared to European and American population, hence mandibular second molars in Asian must be carefully diagnosed for this configuration before the initiation of endodontic treatment for better prognosis and treatment planning.

CONCLUSION

The prevalence of C-shaped anatomy varied from region to region. The highest prevalence was observed in China (93.1%), whereas the lowest was observed in the United States (2.7%). The results from China were significantly higher than any other region. Recent imaging techniques have given a better insight into racial predilection of C-shaped configuration. It is important to be familiar with this variant because ultimately they have both clinical and anthropological significance. In clinical practice, such knowledge can aid in the location and negotiation of canals as well as in their subsequent management.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.