Every mechanism in the last two chapters can fail in a specific, recognizable way. A blocked path stalls a tooth in impaction. The follicle that clears bone can instead trap fluid and become a cyst. A ligament that never regenerates after injury lets bone fuse directly onto root, freezing a tooth in place. And a primary tooth's own exfoliation depends on the same resorption machinery being aimed at its root instead of bone. This chapter follows each failure back to the normal process it broke.