Lecture 9- Periodontium (part 3).pdf

The Periodontium (Part 3) Alveolar bone and the alveolar process By the end of this lecture, you should be able to: Identify the main components of the alveolar process Summarise the developmental origins of alveolar bone Describe the histological properties and function of alveolar bone “The Tooth”...

The Periodontium (Part 3) Alveolar bone and the alveolar process By the end of this lecture, you should be able to: Identify the main components of the alveolar process Summarise the developmental origins of alveolar bone Describe the histological properties and function of alveolar bone “The Tooth” It also consists of the periodontal (“around the tooth”) tissues that support it and anchor it into the jaws: cementum, the periodontal ligament (PDL), and alveolar bone. Enamel Dentine Pulp PDL Alveolar bone Cementum “The Tooth” Adding the periodontal tissues to ”the tooth” is not arbitrary: their developmental origins are from the teeth, not from the jaw (more on that in the development of the periodontium lecture) Enamel Dentine Pulp PDL Alveolar bone Cementum Alveolar bone- the basics Alveolar bone (“socket bone”) is the bone that forms and defines the alveolus (the tooth socket). In healthy teeth, the alveolar bone is found all around the toot, extending between tooth roots and neighbouring teeth, but also up to the cervical margins of the teeth, Alveolar bone In radiographs, the alveolar bone is usually more radiopaque than dentine and enamel. Ten Cate’s Oral Histology (8th Edition); Fig. 8-6 Alveolar bone- the basics Alveolar bone vs alveolar process: Alveolar bone I will use “alveolar bone” to refer to a specific developmental and histological feature: the bone formed by each tooth during development. “Alveolar process” will be an anatomical term: the bone found around teeth (it is made of alveolar bone proper, and other bone types). ***These are often synonyms in textbooks and are used interchangeably. Alveolar process Alveolar bone- the basics Lamina dura Alveolar process contains several layers that are visible in a radiograph: Spongiosa A radiopaque socket-lining layer known as the lamina dura. A spongy trabecular region or spongiosa. A radiopaque outer cortical region. Cortical region Ten Cate’s Oral Histology (8th Edition); Fig. 8-6 Alveolar bone- the basics Lamina dura (Bundle bone) Alveolar process contains several layers that are visible in a radiograph: A radiopaque socket-lining layer known as the lamina dura. A spongy trabecular region or spongiosa. A radiopaque outer cortical region. Cortical region Spongiosa Alveolar bone- the basics Transplanted tooth germ A point of confusion for dentists: Alveolar bone is produced by each tooth, NOT by the bone of the jaw! Alveolar bone is as much a dental tissue as cementum and the PDL! Skin Alveolar bone Alveolar bone A very important set of experiments summarized by: Ten Cate (1997) Periodontology 2000 Alveolar bone- the basics A point of confusion for dentists: Alveolar bone is produced by each tooth, NOT by the bone of the jaw! Alveolar bone is as much a dental tissue as cementum and the PDL! (not to scale) A very important set of experiments summarized by: Ten Cate (1997) Periodontology 2000 Alveolar bone- the basics A point of confusion for dentists: Alveolar bone is produced by each tooth, NOT by the bone of the jaw! Alveolar bone is as much a dental tissue as cementum and the PDL! (not to scale) A very important set of experiments summarized by: Ten Cate (1997) Periodontology 2000 Alveolar bone- the basics Radiograph through a dinosaur jaw A point of confusion for dentists: Alveolar bone is produced by each tooth, NOT by the bone of the jaw! Alveolar bone is as much a dental tissue as cementum and the PDL! Alveolar bone (grey) Images from Butler et al. (2012) PLoS One; LeBlanc (2023) Odontodes Ch. 6 Alveolar bone- the basics A point of confusion for dentists: Alveolar bone is produced by each tooth, NOT by the bone of the jaw! Alveolar bone is as much a dental tissue as cementum and the PDL! This helps explain why patients experience bone loss (alveolar process) after the extraction or loss of teeth. Alveolar bone- composition Alveolar bone has a similar composition to bone from other regions of the body: Matrix: collagen-rich (mostly type I collagen, but contains some noncollagenous proteins [bone salioprotein, osteocalcin, osteopontin, proteoglycans]) Mineral phase: hydroxyapatite (67%) Tooth root PDL Alveolar bone Alveolar bone- composition Cells that produce the organic matrix (osteoid) are called osteoblasts. Osteoblasts Osteoblasts deposit bone matrix towards the tooth root, but can become entombed in the matrix, where they differentiate into osteocytes. Osteocytes help maintain the mature bone tissue. o te s O id Osteocytes Alveolar bone- composition To nourish the osteocytes and mature bone tissue, alveolar bone is perforated my many blood vessels, which leave vascular spaces throughout the bone. Vascular space Blood vessel Alveolar bone- composition The socket-lining layer of alveolar bone is often the region where the ligament fiber bundles of the PDL are attached. Sharpey’s fibers PDL These leave Sharpey’s fibers entombed within this layer. For this reason, it is called the bundle bone layer. Alveolar bone- composition The bundle bone layer is less vascularized than the surrounding bone. Bundle bone This is the lamina dura seen in radiographs. Alveolar bone- composition Often need to use crosspolarized light to visualize Sharpey’s fibers in alveolar bone. Cross-polarized light lets you see the texture of a tissue that is otherwise invisible under white light. PDL Sharpey’s fibers Alveolar bone- composition Often need to use crosspolarized light to visualize Sharpey’s fibers in alveolar bone. Cross-polarized light lets you see the texture of a tissue that is otherwise invisible under white light. PDL Sharpey’s fibers Alveolar bone- composition New layers of alveolar bone (like those of the bundle bone region) are made of a rapidly-deposited, poorly organized collagen matrix. (we’ll talk about this stuff) The mature bone that forms from this matrix is called woven bone. Again, best viewed under crosspolarized light… PDL Bundle bone Alveolar bone- composition Cross-polarized light often reveals a clear difference between bundle bone and the more external layers of the alveolar process. (we’ll talk about this stuff) PDL Bundle bone Alveolar bone- composition The bundle bone layer is the site of active attachment of the PDL fiber bundles to the alveolar bone. It is therefore a rapidly changing part of the alveolar process, hence the rapid, disorganized nature of the bundle bone matrix. PDL Bundle bone Alveolar bone- composition What about the rest of the bone within the alveolar process? It has a much different texture than the bundle bone facing the tooth. This is due to bone remodeling. Alveolar bone- remodeling Bone undergoes a natural turnover process (remodeling): Primary bone matrix is first removed through resorption by osteoclasts, which carve out space for new blood vessels. New bone is laid down around these blood vessels in concentric rings (lamellae). This produces secondary osteons (blood vessel space surrounded by circumferential lamellae) Ten Cate’s Oral Histology (8th Edition); Fig. 6-4, 6-5 Alveolar bone- remodeling Bone remodeling in the alveolar process turns woven bone (primary texture) into Haversian bone (secondary, or remodeled texture). Woven bone (not remodeled) Ten Cate’s Oral Histology (8th Edition); Fig. 6-3 Haversian bone (remodeled) Alveolar bone- composition Bone remodeling in the alveolar process turns woven bone (primary texture) into Haversian bone (secondary, or remodeled texture). Haversian bone (remodeled) Woven bone (not remodeled) Tooth root Alveolar bone- composition Bone remodeling in the alveolar process turns woven bone (primary texture) into Haversian bone (secondary, or remodeled texture). Haversian Bone (remodeled) PDL Bundle bone Alveolar bone- composition Bone remodeling in the alveolar process turns woven bone (primary texture) into Haversian bone (secondary, or remodeled texture). Haversian Bone (remodeled) PDL Bundle bone Alveolar bone- composition Cautionary note: Teeth are constantly moving and shifting positions within the jaws through minor adjustments and bone remodeling. This is a generalization of what types of bone you find lining the socket à they can change! Saffar et al. (1997) Periodontology 2000 Alveolar bone- composition The spongiosa of the alveolar process is made of trabecular bone: Strut-like arrangement of bone tissue. Not compact (hence the “spongy” texture). Bone marrow fills the rest of the space. Spongiosa Ten Cate’s Oral Histology (8th Edition); Fig. 9-17 Spongiosa Alveolar bone- composition The compact bone/compacta, or cortical plates: These are the outer walls of bone surrounding our teeth. These are made of compact (or cortical) bone- the bone tissue that forms the outer walls of most of our bones. Ten Cate’s Oral Histology (8th Edition); Fig. 9-17 By the end of this lecture, you should be able to: Identify the main components of the alveolar process Summarise the developmental origins of alveolar bone Describe the histological properties and function of alveolar bone