Little molars

The presence of 3 rooted premolars called, little molars, is pretty infrequent. Found in only 1-4% of cases with regional variation. The two morphological types involve either two buccal and one palatal root or two palatal and one buccal root. Managing these cases is demanding due to the rarity and challenges in diagnosis, access, instrumentation, and restoration. Diagnosing without CBCT imaging can be difficult. Precise conservative access, cautious instrumentation, and a minimally invasive approach using minimally invasive instruments are crucial for effective treatment.

Every experienced endodontist dreams of having a three-rooted premolar in their endodontic portfolio. What causes this anatomical variation to be so desirable? Above all, it's a very rare occurrence. According to a literature review, the prevalence of three-rooted premolars, also known as "miniature molars," ranges between 4% and 1% for first premolars and below 1% for second premolars. Interestingly, the prevalence of "small molars" varies across different populations and countries. According to some studies, the average prevalence of three-rooted cases ranged from 0.4% to 9.2%. In the USA, it accounted for 6% to 4% (Carns and Skidmore, 1973; Vertucci, 1984). In Brazil, it ranged from 3.5% to 2.5% (De Deus, 1986; Pecora et al, 1991). In India, it was between 2.3% and 0.4% (Neelakantan et al, 2011; Gupta et al, 2015). In Turkey, it ranged from 1.3% to 1.2% (Kartal et al, 1998; Özcan et al, 2012). Interestingly, in contrast to type C canals and additional roots in mandibular molars (Radix Ento and Paramolaris), three-rooted premolars are almost absent in the Asian population. In southern China, according to Walker's study in 1987, no three-rooted premolars were observed. According to Cheng and Weng's study in 2008 and Tian et al.'s study in 2012, three-rooted variations constituted only 1.2% and 0.7%, respectively. In Singapore, according to Loh's study in 1998, no presence of three-rooted premolars were observed. According to the literature review, three-rooted premolars were most frequently found in the populations of Poland (9.2%) and Kosovo (8.1%). 

When discussing the morphological variations of three-rooted premolars, there are two types. The first and most commonly encountered type has two buccal roots and one palatal root, while the second type has two palatal roots and one buccal root. This is almost always classified as type 8 according to Vertucci's classification, where each root contains one canal. Three-rooted premolars belong to some of the most demanding and challenging endodontic cases, not only due to their very rare occurrence but also because of difficulties such as accurate diagnosis, access, instrumentation, and prosthetic restoration, which are caused by the delicate root structure.

As previously mentioned, diagnosing three-rooted premolars can be challenging without access to CBCT imaging. However, there are certain radiological features that may indicate the presence of an additional root. For example, if the tooth crown is more flattened in the mesiodistal direction than the buccolingual direction, this could suggest the presence of a buccal or palatal additional root. If the mesiodistal width of the middle or coronal part of the root is the same as or greater than the mesiodistal width of the tooth crown, there is a high likelihood of three-rooted anatomy. A crucial aspect of successful root canal treatment is proper access preparation. For so-called small premolars, a different access approach is recommended compared to the classical oval shape. This access shape resembles a triangle with the base directed buccally and the apex toward the palate, or vice versa if there are two palatal roots.

Regarding instrumentation, it can be more challenging due to potential curvature, and in difficult access cases, there's a risk of instrument separation. Due to the flattening of the mesial and distal buccal roots in the mesiodistal direction, associated with the presence of "danger zones," improper canal instrumentation can lead to complications such as strip perforation. The dangerous zones in the apical part of the buccal and palatal roots of three-rooted premolars were found to be only 0.4 mm and 0.6 mm, respectively. The critical dentin thickness of buccal roots ranged from 0.8 mm in the thinnest area to 1.3 mm, while for palatal roots, it ranged from 1.3 to 2.7 mm.

The critical dentin thickness for canal instrumentation in buccal roots was observed to be 4 mm below the orifice, leading to complete restriction in the use of instruments like Gates-Glidden burs or orifice openers, as their usage significantly increases the risk of perforation. When it comes to instrumentation, caution is advised, particularly for buccal canal preparation, due to their delicate structure and the presence of danger zones. A minimally invasive approach is recommended, involving the use of small or regressed taper instruments. The use of post and core is not recommended.