Table 4.

Outcome of the studies

Reference	Results	Grooves	Canal configuration			Accessory canals	C shapes anatomy	Isthmus	Foramen	Intercanal communication	Conclusion
Dou, L., et al. [3]	All the mandibular first premolars included in the study were single rooted except for two (0.6%) where two roots were found Canals: 1 canal: 64.04% 2 canals: 34.27% 3 canals: 1.69% Other findings were radicular grooves and C shaped canals. Grade 3 and 4 radicular grooves were termed as Tome’s anomalous roots	Radicular grooves were noticed among 44.34% of total samples Distribution according to tooth surface Mesial: 41.57%, distal:2.81%, lingual:2.81%, buccal:1.12%, One proximal &two lingual: 1.67% Two proximal and lingual: 1.12% Scoring according to ASUDAS Grade 0: 56.74%, grade 1: 16.85%, grade 2: 12.36%, grade 3: 10.11%, grade 4: 3.37% and grade 5: 0.56%	Vertucci’s classification: Type I: 64.04% Type II: 1.12% Type III: 10.67% Type IV: 0.56% Type V: 21.91% Type VIII: 1.12% Type (1–3-1): 0.56%			Lateral canals were found in 39.89% of teeth samples Location Coronal: 5.95% Middle: 46.43% Apical: 47.62% Apical delta was seen in 10.11% of teeth	C shaped canals were noted in 12.36% of teeth	_	Apical foramen: Single: 76.4% Double: 23.6% Central:53.37% Lateral:46.63%	10.67% of teeth had intercanal communication Location Coronal: 10% Middle: 60% Apical: 30%	Multiple canals and varied root canal morphology was observed which specified the need of careful examination for successful endodontic procedure
Sierra-Cristancho, A., et al. [10]	Results stated that 99.46% of teeth had one root and two roots were found in only one tooth. Radicular grooves, accessory canals, C shaped canals and isthmus were located. Tome’s anomalous root was found only in multiple root canals teeth whereas teeth with one root canal had no evidence of them	Radicular grooves as stated by ASUDAS scoring: Grade 0: 60.75% Grade 1: 13.98% Grade 2: 12.36% Grade 3: 10.22% Grade 4: 2.15% Grade 5: 0.54% Non tomes root: 74.69%	Type	Vertucci’s classification	Ahmed’s et al. classification	Accessory canals were noticed in 62.90% of total teeth sample Location of accessory canals Coronal: 0% Middle: 6.99% Apical: 43.55% Middle and apical: 12.37% Apical delta was found in 26.88% of first mandibular premolar	29.57% of samples possessed C shaped canals Coronal: 0% Middle: 6.99% Apical: 3.23% Combining middle and apical: 19.35%	Percentage of teeth samples according to the location of isthmus is as follows: Coronal: 05 Middle: 19.35% Apical: 9.68% Middle & apical: 2.69%	One: 36.56% Two: 27.42% Three: 15.59% Four: 20.43% Location of apical foramen Central: 37.63% Lateral: 62.37%	_	Variations in roots and canals were noticed. Radicular groves were found among the teeth with complex root anatomy and multiple canals. Tome’s anomalous roots were present in the roots with multiple canals
			Type I Type II Type III Type IV Type V Type VI Type VII Type VIII Type IX Non classified:	65.05% 0% 5.38% 0% 24.19% 0% 2.15% 0% 2.69% 0.54%	65.05% 0% 5.38% 0% 24.19% 0% 2.15% 0% 0.54% Double rooted: 0.54%
Alkaabi, W., et al. [20]	Mandibular first premolar had varied root canal configuration, two additional types of canal configuration type 1–2-3 and type 1–3 which were not classified by Vertucci’s criteria were found. Further lateral canals, C shaped canals, apical delta, apical foramen, inter canal communication and apical loops were assessed	Out of the scanned samples, 20% of them had deep grooves on mesiolingual side and distal side had shallow depressions. Further a groove was found on either mesial or distal surface in 24% of specimen, later superficial depression was noticed among 24% of teeth on each of two -proximal surfaces	Vertucci’s classification: Type I: 62% Type III: 2% Type IV: 4% Type V: 20% Type VI: 4% Type VII: 2% Extra canal type: 6%			Lateral canals were found in 44% of included teeth with increased incidence in the apical region of root	C shaped canal configuration appeared in 28% of sample teeth	_	Apical foramina were 70 amongst examined teeth Number One: 76.6% Two: 16.6% Three: 6% Position Centra: 37.2% Lateral: 62.8% Apical delta was present in 60% of examined specimen	Intercanal canal communication was recognized in 12% of sample teeth	It was concluded from the study that, involved population had complex root canal morphology with higher incidence of multiple root canals and their configuration
Boschetti, E., et al. [24]	Root canal morphology and radicular grooves were evaluated Canal orifices ranged from 1 to 4 and higher frequency of two canal orifices were seen in apical third of teeth (63.7%). Mean volume (10.78 m $m^3$), surface area (58.51${\mathit{mm}}^2$) and structure model index was determined. Mean length of radicular groove and root were 8.5 mm and 13.43 mm individually. Depth of radicular groove was different and deeper across the root length. At the half level of radicular groove length, the mean dentinal thickness in mesial or distal surface of the root was ranging between 1.0 to 1.31 mm	Location of radicular grooves: Mesial: 95.70% Distal: 2.85% Vestibular: 1.45% ASUDAS scoring: When canals are not divided the scoring is as follows Grade 2: 11.42% Grade 3: 1.43% Grade 4: - When canals are divided Grade 2: 67.15% Grade 3: 17.15% Grade 4: 2.85%	Vertucci’s classification Type I: 12.85% Type III: 11.43% Type V: 58.57% Type VII: 10%			One accessory canal was 20 in number that emerged from middle third and 18 from apical third Two accessory canals were only two in number emerging from middle third and 14 from apical third. Apical delta was seen in 4.35% of total examined teeth	C shaped root canal configuration was noticed in 18.57% of assessed teeth	_	_	_	The study concluded wide range of variations of radicular grooves. Anatomical complexities like C-shaped canals and division of the main root canal were noticed
Chen, J., et al. [25]	Radicular grooves were assessed which stated that 40.9% of included sample teeth had RG most of which were present on mesial side of root (69.5%) and their incidence was higher in multiple root canals than single canal. Depth and mean length of radicular grooves were apparently deeper and longer in type V and other canal configurations than type I	Distribution according to type of canals: Type I: 17.4% Type III, V and other complex type: 90.2% Most grooves were present on the mesial side (69.5%) of root. 84% of them began at the coronal third and similar percentage of them terminated at the apical third, further extension to the apex was shown by 40.8% of the grooves. Mean length of grooves: Type I: 6.06 ± 2.12 mm Type V: 7.70 ± 2.16 mm Other types: 6.91 ± 2.67 mm	_			_	_	_	_	_	The morphology of the root canal was influenced by the radicular groove’s anatomy. Hence it was stated that multiple canals and complex root morphology had higher prevalence of radicular grooves than simple and single root canals
Fan, B., et al. [21]	Results stated the morphology of radicular grooves and anatomy of C shaped root canals. The majority of grooved were present on the mesiolingual side of the root and C shaped canals varied greatly in shape. Frequency of two canals was higher at apical (80%) than middle (20%)	Distribution of the groves according to surfaces: 73 grooves were present on the mesial lingual side, out of which 66 were single and 7 were double, 10 grooves were found on distal lingual, and they were single, 3 single grooves were present on lingual side and 7 double grooves were found on buccal surface Mean distance of the groove from coronal top plane to CEJ was 3.46 mm. Similarly, mean distance from apical bottom plane to the apex was 1.38 mm. extension of the grooves to the apex was 43% and 8.77 mm was the mean length of grooves. The ratio of length of the grooves to the length of the root was 65%. Mean distance and mean depth of the grooves were 5.41 and 1.44 mm respectively	_			_	C shaped canals were classified as follows: C1: continuous c shape C 2: semicolon shape due to discontinuous outline C3: two different canals with round, oval or flat shape C4: one canal with round, oval or flat shapes C4a: long diameter of canal is equal to short diameter of round canal C4b: long diameter of canal was two times smaller than short diameter of oval canal C4c: long diameter of canal was two times bigger than short diameter of flat canal C5: three or more different canals C6: no intact canal C4b and C4c were usually single canal present at coronal third, however C1, C2 and C3 were higher at middle third. Gradually C1 reduced apically but C2 and C3 were found	_	_	_	Study stated that, the radicular grooves may present relative morphological changes in the presence of C-shaped root
Gu, Y., Y. Zhang, and Z. Liao [26]	Micro-CT examination of sample was performed to assess the root canal morphology, C shaped canals radicular grooves and Tome’s root. Out of the total sample 81.1% were non-Tome’s root, 18.9% of sample had Tome’s root 0.4% were double rooted premolars. Further accessory canals and canal communication was also detected	155 radicular grooves were found among the examined teeth, and they were mostly observed on mesiolingual side. Shallow grooves were 37.5% and deep grooves were 18.5% Mean depth and angle of mesial radicular groove: ASU (1): 0.18 mm, 28.8∘ ASU (2): 0.36 mm, 47.5∘ ASU (3): 1.24 mm, 101.∘7 ASU (4): 0.95 mm, 87.0∘ Mean depth and angle of distal radicular groove: ASU (1): 0.27 mm, 29.3∘ ASU (2): 0.21 mm, 25.4∘ ASU (3): 0.13 mm, 18.1∘ ASU (4): 0.55 mm, 59.2∘ The mean length of root was 12.98 ± 1.36 mm and the mean angle and depth of concavities were 21.0∘ and 0.20 mm ASUDAS scoring (3–5) represents the Tome’s root, seen in 18.9% of teeth	Higher number of Type I canal configuration had ASUDAS scoring 0,1 and 2, non-Tome’s root had 78.2% of Type I canal configuration while 8.5% of Type I had Tome’s root Further complicated canal configuration ranges between 15.5% (ASU-0) to 100% (ASU-4 & 5)			Accessory canals were found in 48% of teeth and 19.6% of teeth had lateral canals, similarly apical delta was found in 37.8% of teeth. 10 accessory canals had communication between radicular groove and the main canal	19.6% of examined samples had C shaped canals and were categorized into C1 (44), C2 (42) and C3 (21). The majority of C1 and C2 canals were 7–9 mm distance away from the CEJ	_	_	_	Severity of radicular grooves determine the complexity of root and canal morphology which was scored by ASUDAS. Hence success of an endodontic treatment relies on understanding the internal anatomy of root and radicular grooves
Guerreiro, D., et al. [27]	Radicular groove accessory canals (RGAC) were assessed, which shows their presence in 49.9% of teeth and were predominantly present in the middle third. They were majorly found in ASUDAS group 3 and 4 and had different vertucci’s configuration of the root canal	Relationship between presence of RGAC and ASUDAS scoring: Grade 1: 3.2% Grade 2: 11.1% Grade 3: 68.3% Grade 4: 17.5%	Relationship between presence of RGACs and canal morphology (Vertucci’s classification): Type I: 0% Type III: 1.6% Type V: 46% Type VII: 6.3% Non classified (others): 46%			49.9% of radicular groove accessory canals were found upon examination, out of which 53.9% originated from semilunar buccal canal, 46.1% from pulp chamber extension to radicular groove	_	_	Out of the assessed teeth that showed the presence of RGACs, single foramen was seen in 74.6% of teeth at the groove, two foramina in 11.2% and three or more foramina in 14.3% of specimen. Their incidence was higher in the mid third of the root The average diameter of RGAC foramen was 0.088 ± 0.048, similarly average distance was 8.83 ± 2.53 from CEJP to FP at the groove	_	The present study derived an association between radicular groove accessory canals and internal and external teeth anatomy, and it was also concluded that accessory canals, radicular groove are often present in the mandibular first premolars with radicular grooves
Li, X., et al. [28]	The lingual canal of mandibular first premolar was examined, 69% of them were present in the middle third and the remaining were found in apical third of the tooth. However, lingual view showed 73% of canals in the middle third and remaining in the coronal third In proximal view, mean angle α and β were 33.54∘ and 26.66∘ and angles were extremely curved while in the lingual view, they were less curved with mean angle α 8.31∘ and β 11.31∘ respectively	_	_			_	_	_	_	_	The study provided the details of lingual canal, however the information obtained was influenced by the view used
Liu, N., et al. [29]	Micro-CT assessment of first mandibular premolar was performed to analyze the root and canal morphology, accessory canals, intercanal communication, isthmus and apical foramina Teeth with mesial invaginations (27.8%) had multiple canals and majority of them were in the middle third of the root	_	Vertcci’s classification: Type I: 65.2% Type III: 2.6% Type V: 22.6% Type VII: 0.9% 1–3-2: 2.6% 1–3: 5.2% 1–2-3: 0.9% Mesial invagination was present in 27.8% (32) of teeth, they were classified according to vertucci’s criteria as: Type I: 2 Type III: 2 Type V: 21 Type VII: 1 1–2-3: 1 1–3: 2 1–3-2: 3			Teeth with accessory canals were 35.7% Number of accessory canals: 1–87.8% 2–9.8 3–2.4% Location of accessory canals: Coronal: 0 Middle: 3 Apical: 38 Apical delta was seen in 6.1% of teeth	_	Only 2 isthmuses were observed, one in the middle and the other in the apical third of teeth Loops were 8 in number, three in the middle and five in the apical third of specimen	Out of the assessed teeth that showed the presence of RGACs, single foramen was seen in 74.6% of teeth at the groove, two foramina in 11.2% and three or more foramina in 14.3% of specimen. Their incidence was higher in the mid third of the root The average diameter of RGAC foramen was 0.088 ± 0.048, similarly average distance was 8.83 ± 2.53 from CEJP to FP at the groove	Intercanal canal communication was recognized in 12% of sample teeth	Micro-CT scanning of the mandibular first premolar among the included population revealed the complex morphology of the root with multiple canals and varied canal configurations
Moreno, J.O., et al. [30]	Results analyzed canal configuration according to vertucci’s criteria and C shaped canals (1.8%) Mean values of parameters at 1,2 and 3 mm from apical foramen are as follows: Perimeter in mm: 1.07 ± 0.57, 1.27 ± 0.78 and 1.57 ± 0.84 Circulatory in mm: 0.59 ± 0.19, 0.57 ± 0.20 and 0.56 ± 0.22 Major diameter in mm: 0.41 ± 0.23, 0.48 ± 0.33 and 0.60 ± 0.37 Minor diameter in mm: 0.24 ± 0.10, 0.26 ± 0.11 and 0.21 ± 0.13 The overall area and volume are 61.27 ± 16.47 mm2 and 12.47 ± 4.95 accordingly	_	Vertucci’s classification: Type : 40% Type III: 4% Type V: 24% Type VII: 4% Additional types: 1–3: 3 1–4: 1 1–2-3: 6 1–3-2: 1 1–2-1–2: 1 1–2-1–2-1–3: 1 1–2-4–3-4–3: 1			_	_	_	_	_	The study concluded wide variations of the involved teeth among Colombian population emphasizing the need for appropriate anatomical knowledge of the teeth to establish more effective endodontic treatment
Ordinola‐Zapata, R., et al. [31]	All the mandibular first premolars had one root except for three teeth where two roots were found C -shaped roots were present in 67.47% mandibular first premolars. Mean distances were in the range of 5.36–5.65 mm from furcation to CEJ	_	Vertucci’s classification: Type I: 13% Type III: 8% Type V: 37% Type VII: 2% 1–2-3: 8% 1–2-3–2: 7% 1–2-3–2-3: 2% 1–2-1–2-4: 1%			Apical delta was present in 43% of specimen and furcal canals were noticed in 33%	67.47% of specimen revealed C-shaped roots and C-shaped canal was found only in buccal canal.C1 and C2 type of canals were frequent in the middle and apical middle levels whereas cervical third commonly had C4c cross section	_	_	_	The study concluded that 67% of the specimen had C-shaped canals with radicular grooves. Vertucci’s type I and V were more common. C-shaped cross section was frequently noticed in the middle third
Zhang, D., et al. [32]	136 mandibular first premolars were examined, and root canal morphology was evaluated by vertucci’s classification system	_	Type I: 74.13% Type III: 3.50% Type V: 13.99% Type V11: 0.70% Type IX: 7.69% Additional types 1–3: 7 1–2-3: 2 1–3-2: 2			_	_	_	_	_	Micro-CT provided more detailed anatomical information of the included mandibular first premolar teeth along with root and canal variations