Fig. 1

Classification given by Carlsen and Alexanderson (1990) [6] 

according to the location of the cervical part of the RE.
This classification allows for identification of separate and non-separate RE in conjunction with the location of the distal root. 

Type A – Distally located cervical part with two normal distal root components. 

Type B – Distally located cervical part but only one normal distal component. 

Type C – Mesially located cervical part. 

Type AC – Central location between mesial and distal root components. 

Fig. 2

De Moor et al (2004) [7]

classified RE-based on the curvature in buccolingual orientation into three types. 

Type I – a straight root/root canal. 

Type II – an initially curved entrance which continues as a straight root/root canal. 

Type III – an initial curve in the coronal third of the root canal and a second buccally oriented curve starting from middle to apical third.

Fig. 3

Song et al. (2010) [8]

added two more newly defined variants of RE.

  1. Small – Length shorter than half of the length of the distobuccal root
  2. Conical – Smaller than the small type and having no root canal within it.
Fig. 4

Duman et al.(2020)  [9]

according to the location of the cervical part on axial slices of CBCT images.

  1. Type A
  2. Type B
  3. Type C 
  4. Type AC
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Fig. 5

How to diagnose? 

To reveal the RE, first, a second radiograph should be taken from a more mesial or distal angle (30 degrees). Second, clinical inspection of the tooth crown and analysis of the cervical morphology of the roots by means of periodontal probing can facilitate identification of an additional root. An extra cusp (tuberculum paramolare) or more prominent occlusal, distal or distolingual lobe, in combination with a cervical prominence or convexity, can indicate the presence of an additional root [4].

How to manage?

Regarding Access cavity: to avoid perforation or stripping in the coronal third of a severe curved root, care should be taken not to remove an excessive amount of dentin on the lingual side of the cavity and orifice of the RE [4]. 

Regarding root canal preparation; A severe root inclination or canal curvature, particularly in the apical third of the root (as in a type III RE), can cause shaping aberrations such as straightening of the root canal or a ledge, with root canal transportation and loss of working length resulting. The use of flexible nickel-titanium rotary files allows a more centered preparation shape with restricted enlargement of the coronal canal third and orifice relocation [4]. 

Nevertheless, unexpected complications such as instrument separation do occur, and are more likely to happen in an RE with severe curvature or narrow root canals.

Fig. 6

The (separate) RE is mostly situated in the same buccolingual plane as the distobuccal root, a superimposition of both roots can appear on the preoperative radiograph, resulting in an inaccurate diagnosis. 

A thorough inspection of the preoperative radiograph and interpretation of particular marks or characteristics, such as an unclear view or outline of the distal root contour, can indicate the presence of a ‘hidden’ RE [4]. 

Fig. 7

The location of the orifice of the root canal of an RE has implications for the access opening. The orifice of the RE is located disto - to mesio-lingually from the main canal or canals in the distal root. An extension of the triangular access opening to the (disto) lingual results in a more rectangular or trapezoidal outline form. 

Fig. 8

Clinical case n 1. Female 45 years-old. The presence of RE has been diagnosed at radiographic examination. After Access cavity, relocation and enlargement of the orifice of the RE, initial root canal exploration with small manual K-files (#8 and #10) together with radiographic estimation of working length and curvature determination, and the creation of a glide path before preparation, are step-by-step actions to avoid procedural errors. 

Fig. 9

Clinical case n 2. Male 50 years-old. The presence of RE has been diagnosed at radiographic examination (Red line) due to unclear view or outline of the distal root contour and the root canal. Intraoperative Rxs are useful to better understand the anatomy of mesial canal configuration and RE.

Fig. 10

Clinical case n 3. Female 25 years-old. The presence of RE has been diagnosed and confirmed preoperatively from radiography.

Fig. 11

Carlsen and Alexandersen (1991) [10] 

classified RP into two different types

  1. Type A - Cervical part is located on the mesial root complex
  2. Type B - Cervical part is located centrally between the mesial and distal root complexes. 
Fig. 12

Clinical case n 4. Male 27 years-old. The presence of RP has been diagnosed at radiographic examination, negotiated and treated.


  • The frequency of a RE in mandibular molars varies in accordance with specific racial traits. The incidence of a RP is very rare and occurs less frequently than the RE. 
  • Clinicians should be aware of the unusual root morphology in mandibular first molars.
  • Pre-operative diagnosis of RE and RP is essential to avoid procedural errors that may compromise the root canal treatment result. 
  • Radiographs should be taken at two different horizontal angles to identify and locate this extra root.
  • Careful clinical inspection of tooth crown and cervical morphology is necessary. 
  • The access cavity must be modified in a distolingual direction in order to visualize and treat the RE, resulting in a trapezoidal access cavity.


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