Root canal morphology of the mandibular second premolar: a systematic review and meta-analysis

The aim of this paper was to systematically review the root canal configuration (RCC) and morphology literature of the mandibular second premolar (Mn2P).

Systematic research of five electronic databases was performed to identify published literature concerning the root canal configuration (RCC) of the Mn2P up through July 2020. Studies were selected according to predefined search terms and keywords inclusion criteria: "root canal configuration", "root canal system", "root canal morphology", "mandibular second premolar", "mandibular premolars", "morphology" and "anatomy". Further possible studies were identified by cross-referencing and screening the bibliographies of the selected articles.

From 1622 retrieved studies, 44 studies investigating the internal morphology of 17,839 Mn2Ps were included. Most examined Mn2Ps were single-rooted (89.5-100%); two-rooted (0.1-8%) and three-rooted (0.1-3.5%) Mn2Ps at lower frequency. Most frequent RCCs reported were 1-1-1/1 (55.3-99.6%) followed by 1-1-2/2 (0.5-57%) and 2-2-2/2 (0.6-18%). The meta-analysis of seven studies demonstrated that a significantly higher number of RCC type 1-2-1/1 (OR [95%CI] = 2.05 [1.27, 3.33]) and 2-2-2/2 (OR [95%CI] = 2.32 [0.65, 8.63]) were observed in male than in female patients.

Different RCC research methods have been reported. Whereas clearing and radiographs were commonly used in the past, CBCT has been prevalent in recent years. A globally high frequency of a 1-1-1/1 RCC in the Mn2P has been reported. Nevertheless, the probability that different, more complicated RCCs can appear in Mn2Ps should not be underestimated and, thus, should be taken into consideration when making decisions during an endodontic treatment.