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Subscriber: null; date: 16 October 2019

bone

Source:
A Dictionary of Dentistry
Author(s):
Robert IrelandRobert Ireland

bone n. 

The hard mineralized connective tissue that forms the skeleton of the body. It has a matrix of calcium salts (mainly calcium carbonate and calcium phosphate), deposited around protein fibres. The matrix is deposited by the activity of osteoblasts which become trapped in small hollows (lacunae) and cease laying down bone, becoming osteocytes; these have a number of thin processes which extend from the lacunae through small channels within the bone matrix (canaliculi). The external layer of the bone (compact, cortical, or lamellar bone) consists of a hard mass of bony tissue arranged in numerous concentric circles with vascular channels (Haversian canals) running along the long axis of the bone.

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Compact bone tissue

Trabecular (cancellous or spongy) bone is found beneath the cortical bone and is made up of delicate bars and sheets of bone (trabeculae) which form a sponge-like network. Bone is subject to constant remodelling by osteoblasts and osteoclasts. Alveolar bone supports the teeth and is thin and compact immediately adjacent to the periodontal membrane whereas the bone between the tooth roots (interradicular) is less compact. The crestal bone is the most coronal part of the alveolar bone. When the teeth are lost, the alveolar bone undergoes resorption. Bone can be classified according to its density, such as has been described by C. E. Misch in 1990.

Classification of bone density

Classification

Description

D1

Dense compact bone.

D2

Dense-to-porous compact bone with coarse trabecular core.

D3

Thin porous compact bone with fine trabecular core.

D4

Fine trabecular bone.

D5

Immature, non-mineralized bone.