Figure 4: Adaptation of the SAF to an oval cross-section. The SAF inserted into a premolar with an oval cross-section. (a) Buccolingual projection: The file is narrower than when relaxed. (b) Mesiodistal projection: The file is wider than when relaxed. (c) When a file with a 1.5 mm diameter is inserted into a canal with a mesiodistal dimension of 0.2 mm, it will spread buccally and lingually, assuming a buccolingual dimension of 2.4 mm. This will happen even when the operator is not aware that the canal is oval, hence the name "Self-adjusting File"