Osteology of the Skull - First Lecture

What do bones do (4)?

support tissue and vital structures (heart/lungs)

mechanical basis for movement

regulate calcium/salt levels

provide continuous supply of new blood cells

What is the axial skeleton made up of?

the head, neck, and trunk

What is the appendicular skeleton made up of?

limb bones

What are osteoblasts?

bone building cells that secrete extracellular/bone matrix

What are osteocytes?

mature bone cells derived from osteoblasts surrounded by bone matrix

What are osteoclasts?

bone reabsorbing cells, important during bone remodeling and repair, derived from cells in the bone marrow

What are long bones?

tubular bones, longer in one dimension (humerus, tibia, metacarpals)

What are short bones?

bones appearing cuboidal due to being nearly equal in length and diameter (tarsus and carpus bones)

What are flat bones?

thin or plate-like bones serving protective function (skull bones, sternum)

spongy bone

cancellous bone that forms the mesh work of interior bone, consisting of trabeculae

Trabeculae

thin tubule network of spongy bone

compact bone

dense bone forming the outer portion of bones

What is irregular bone?

bones of various shapes, bones of the face

What are sesamoid bones?

unique classification of bones where tendons cross the ends of long bones in the limbs, protecting tendons from wear (patella)

What is intramembranous ossification?

bone formation without a cartilage precursor, formed directly from mesenchyme; bone forms from a membranous sheet of connective tissue where membranous models of bone form and ossify in the embryo during the fetal period

What are some bones developed by intramembranous ossification?

flat bones of the skull, mandible, maxilla

What does this picture show?

intramembranous ossification

What does this image show?

endochondral ossification

What is endochondral ossification?

cartilagenous bone formation where cartilage models of bones form from the mesenchyme during the fetal period, and bone replaces most of the cartilage

What are some bones developed by endochondral ossification?

bones of the extremities, vertebrae, or cranial base

What is cranial synchondroses?

cartilaginous joints of the base of the skull that act as growth centers until puberty where they begin to ossify

when is calcification usually complete?

25 years old

What are the 5 zones of the growth plate?

zone of reserve cartilage, zone of proliferation, zone of hypertrophy, zone of calcified cartilage, and zone of resorption

zone of reserve cartilage

no cellular proliferation or matrix production

zone of proliferation

chondrocytes divide and organize into columns, actively producing collagen and matrix proteins

zone of hypertrophy

enlarged chondrocytes, metabolically active

zone of calcified cartilage

matrix is being calcified and serves as a scaffold for new bone

zone of resorption

osteoprogenitor cells are invading this area

Bone modeling

bone size and shape can change

Bone remodeling

selective bone resorption by osteoclasts and bone apposition by osteoblasts and size and shape remain the same

True or False: Orthodontics involve both modeling and remodeling

True

Elements of cleidocranial dysplasia

birth defect causing failure to shed primary teeth, delayed eruption of permanent teeth, more teeth than normal (supernumerary), lack of collarbones, lack of Runx2 gene

osseointegration

direct structural and functional connection between ordered living bone and the surface of a load bearing implant

prerequisites to osseointegration (4)

immobilization, adequate cells, adequate nutrition of cells, adequate stimulus for bone repair

immobilization (dental implant)

minimal movement of the implant

adequate cells (dental implant)

mesenchymal cells that can differentiate into osteoblasts, osteoclasts should arise at the bone implant interphase through the bloodstream

adequate nutrition of cells (dental implant)

diffusion of nutrients that will facilitate the process will occur locally until microcirculation is reestablished

adequate stimulus for bone repair (dental implant)

trauma from surgery and inflammatory response will trigger healing

phases of bone healing (3)

inflammatory response, regeneration, remodeling

inflammatory response (bone healing)

48 hours after surgery, chemotaxis of mesenchymal cells and phagocytosis of tissue debris, blood clotting and formation of fiber network attaching to implant surface, osteogenic cells migrate to the implant surface and form osteoids, followed by bone directly on the implant surface

regeneration (bone healing)

microcirculation restored in 10 days following surgery, osteogenesis occurs between 4-6 weeks, immature/woven bone is first formed and replaced by dense lamellar bone

remodeling (bone healing)

18 months post op, occurs in response to functional loading, low strain stimulates regeneration while high strain will prevent it

bisphosphonates

drug suppressing osteoclast function and increasing bone density and mineralization, increasing jaw osteonecrosis that may delay or inhibit healing