PDL mechanical strength testing apparatus. A, Location of test section; B, resin-embedded testing block; C, loading on testing machine; D, strain-stress curve created from testing. TS, testing section; TR, root; AB, alveolar bone; TB, testing block; APP, custom-made loading apparatus. Definitions in stress-strain curve: B-M, steepest slope, indicating Young's modulus (stiffness); Y, yield point: zero slope, indicating transition from elastic to plastic deformation under compressive loading; F, failure point: <20% drop from maximal stress.