What types of cells regulate bone growth?

Osteoblasts and osteoclasts are the two types of bone cells that control bone growth by working together to form new bone tissue and break down old or damaged bone tissue. 

Role of osteoblasts in regulating bone growth

Osteoblasts regulate bone growth by forming new bone cells and adding growth to existing bone tissue. 

Hormones or chemical reactions resulting from bone growth or changes in a bone activate osteoblasts to create and secrete a mix of proteins called bone matrix. The bone matrix is deposited in spaces on a bone that needs to grow or be repaired or strengthened where it solidifies and hardens into new, healthy bone. On completing their job of forming new bone tissue, osteoblasts differentiate into osteocytes and become part of the bone. The unused osteoblasts that are no longer needed undergo programmed death or apoptosis and die.  

Role of osteoclasts in regulating bone growth

Osteoclasts break down and dissolve old and damaged bone cells to make room for the new, healthier cells produced by osteoblasts. 

Osteoclasts regulate bone growth by releasing enzymes that dissolve the surface of old bone tissue and break down hardened bone matrix, creating space for the formation of healthier and stronger tissue. The breaking down of the bone matrix leaves microscopic pits and divots on the bone surface. Osteoblasts move in and deposit new bone in those spaces. The process of dissolving bone tissue is tightly regulated, so that only osteoclasts only target specific areas tagged by osteocytes.