During what trimester does cartilage begin to harden?

The embryonic cartilage begins to harden into bone at anytime around the 2nd trimester. The embryonic cartilage undergoes endochondral ossification wherein the chondrocytes is slowly replaced by osteocytes with subsequent deposition of calcium and hydroxyapatite; therefore converting the cartilages into bones.

Iwould say overuse ( but not 100% sure ) in the u.s. we tend to overuse water by leaving it running, throwing it away, taking long showers, etc.