Background: Multiple signaling molecules have been shown to play crucial roles in dental root develop-ment. Therefore, we aimed to investigate the prevalence of S-shaped roots and also to investigate, if single nucleotide polymorphisms (SNPs) in BMP2, BMP4 and SMAD6 are associated with this phenotype in hu-mans. Methods: This is a cross-sectional phenotype-genotype association study that used radiographs to de-termine the phenotypes and DNA to investigate SNPs in candidate genes. During the radiographic exam, teeth presenting root canal(s) doubly curved were considered S-shaped roots. SNPs in BMP2 (rs10 05464 and rs235768), BMP4 (rs17563) and SMAD6 (rs2119261 and rs3934908) were blindly genotyped by real-time PCR using TaqMan assay. The relative and absolute frequency of S-shaped roots were calculated. Chi-square test was used to compare the genotype distributions between control and S-shaped groups. Results: Among the 578 subjects, 61 (10.6 %) presented at least one tooth with an S-shaped root. The most commonly affected type of tooth was the premolar. rs1005464 in BMP2 was statistically associated with an S-shaped root (p = 0.036). rs235768 in BMP2 was associated with an S-shaped root also in mandibular teeth (p = 0.017). A statistical significance was observed for the rs3934908 in SMAD6 (p = 0.049) for S-shaped root in the mandible. In the analysis stratified according to the type of tooth, rs235768 in BMP2 was associated with S-shaped roots in premolars (p = 0.029). Conclusion: The prevalence of S-shaped roots is 10.6 % in permanent teeth. SNPs in BMP2 and SMAD6 could be involved in a higher chance to present S-shaped roots. (c) 2022 Elsevier GmbH. All rights reserved.