The disposition of the osteocytes inside the bone produces two types of bone tissue.
a) Non-lamellar bone, also known as primary, or immature bone;
b) Lamellar bone, also known as secondary, or mature bone.
The immature bone is always the first to form in the body, such as during fetal life, during bone growth, bone remodeling, healing of the bone after a fracture. In adults, it exists only in few places in the body, one example being the dental alveoli that support the teeth.
The mature bone normally replaces the immature bone and is the predominant type in adults.
Main differences between the two types:
Immature or non-lamellar bone: the collagen fibers of the extracellular matrix are arranged in many directions, and the osteocytes are not regularly arranged lacking a specific organization.
Mature or lamellar bone: the collagen fibers are organized in thin sheets called bone lamellae. Within each sheet, the collagen fibers are arranged parallel to each other. In adjacent lamellae the sets of collagen fibers of each lamella maintain an angle in relation to the collagen fibers of their neighboring lamellae. The osteocytes have an organized distribution, according to the postion of the lamellae.
More information on lamellar and non-lamellar bone will be presented in the following pages.
