ALVEOLAR BONE

1. Dr. SaleemShaikh www.mu.edu.sa/sfaiz ALVEOLAR BONE

2. Objectives: To describe the formation of alveolar bone To give a detailed picture of the structure of alveolar bone To explain the internal reconstruction of bone To enumerate the functions and age changes seen in alveolar bone.

3. Bone is a living mineralized tissue of the body, which serves various functions. ex – shape, support, attachment of muscles and protection, development and storage of blood cells. • Classification – • Shape : • Long • Short • Flat • Irregular bone • Development: • endochondral • intramembranous • Microscopic structure: • compact bone, • cancellous bone • woven bone. Introduction

4. composition

5. Osteoblasts: these are mononucleated cells which synthesise and secrete the bone matrix • Osteocytes: inactive osteoblasts which get entrapped within the bone are called as osteocytes. • Osteoclasts: cells responsible for resorption of bone. These are large cells having 15-20 nuclei. • Derived from monocytes – macrophages • Contain acid phosphatase enzyme • Has a ruffled border on the cell surface, more mitochondria and less rough endoplasmic reticulum. • Always found in concave areas know as “Howships lacunae” Cells of the bone

7. Alveolar bone

8. Alveolar bone (process) • Definition: alveolar process is that part of maxilla and mandible that forms and supports the sockets of teeth. • Development: it starts in the second month of fetal life • Maxilla and mandible forms a groove that is open towards the surface of the oral cavity. Developing tooth buds are enclosed in these grooves. • Major portion of the alveolar process begins with root formation and eruption of the teeth. • During rapid growth alveolar crest shows characteristics of cartilage and bone - CHONDROID BONE

9. Structure of alveolar bone

10. It surrounds the root of the tooth and gives attachment to the periodontal ligament fibres. • It consists of • Lamellated bone • Bundle bone Lamellated bone consists of osteons. Concentric lamellae along with a central blood vessel form an osteon. Alveolar bone proper

13. Part of the alveolar bone where periodontal ligament fibres are inserted (attached). Bundle – bundles of fibres Sharpeysfibres – principal fibres of the periodontal ligament that are embedded in the bone or cementum. Sharpeysfibres are seen perpendicular to the bundle bone. Other fibrils are less and are arranged parallel to the bundle bone surface Radiographically is more radiodense due to presence of thick bone without trabeculations and is called as “lamina dura” Alveolar bone proper has many openings for blood vessels and nerves – is perforated and is called as “cribriform plate” Interdental and interradicular septa have canals known as canals of “ zukerkandl and hirschfeld” Bundle bone

15. Supporting alveolar bone • It consists of two parts – • Cortical plates (Outer and inner) • Spongy bone Cortical plates: these are made up of compact bone & form the outer and inner plates of alveolar bone. Cortical bone varies in thickness in different areas – it is thicker in the mandible than in the maxilla and thicker in the premolar-molar region than in the anteriors.

16. Spongy bone: it fills the area between the cortical plates and the alveolar bone proper. • It contains trabaculae of bone and marrow spaces. • Types of spongy bone (spongiosa) :- • Type I: the trabaculae are regular and horizontal like a ladder. This is seen most commonly in the mandible. • Type II: irregularly arranged delicate and numerous trabaculae. This is seen most commonly in the maxilla. The spongy bone is very thin or absent in the anterior regions of both the jaws.

18. Alveolar crest (crest of alveolar septa): the shape and position of the crest is dependent on the adjacent teeth. • In healthy mouths the alveolar crest is around 1.5 to 2 mm below the cementoenamel junction.

19. Internal reconstruction of bone • Bone is a dynamic tissue and is always undergoing changes to adapt for functional forces, mesial drift, and eruption of teeth. • There is constant formation and resorption of bone. Periods of resorption alternate with periods of rest and repair. • Lines seen in bone: • Resting line: these lines correspond to the resting period in the process of continous bone formation. • Reversal line: when a period of bone resorption is followed by bone formation, a dark line is seen which seperates the new bone from old bone, this resembles the shape of howships lacunae.

20. Clinical considerations • Orthodontic treatment • Fracture, extractions • Periodontal diseases • Pattern of resorption of maxilla & mandible. Thank you!!