Fig. 6

Irregular root canal files. Reproduced with permission. Source: USPTO, www.uspto.gov: CNIPA, www.cnipa.gov.cn. a–b 3D root canal files [56, 57]. c Multi-curvature root canal files [58]. d A spatial spiral shape [59]. e A root canal file with two edgeless sides [60]. f A guided tip structure [61]. g A first cusp and a second section at the tip of the file [62]. h A left-handed pattern [63]. i A vertical pattern [64]. j Increasing the chip-tolerant space [65]