Lesson 9 Flashcards
Describe the physical composition of cementum
- 50% Inorganic mineral - calcium hydroxyapatite
- 40% Organic material - collagen( extrinsic and intrinsic)
- 10% Water
Describe the physical properties of cementum
- Yellow in color
- No luster
- Irregular surface: grainy texture( rougher in older individuals)
- Softer in consistency than dentin
- NO blood vessels
- NO nerve fibers within cementum
- Cementum more permeable than bone or dentin
Describe the functions of cementum
- Seals the surface of the root dentin and covers the ends of the open tubules
- Embeds the ends of the periodontal ligament fibers to the tooth
Cementum proper = ___________
acellular & cellular cementum
Describe cementum production
Cementoblasts are formed from undifferentiated mesenchyme cells in the dental follicle (developing periodontal ligament space)
Describe acellular cementum
- The cementoblasts produce the cementum matrix
- Acellular cementum has - No cells embedded in the matrix
- Location:First layer of cementum deposited at the DCJ
- Location: cover entire root surface, thicker cervicle 1/3 near DCJ
- Produced slowly: thin layer
- Width never changes
Describe cellular cementum
- Cementoblasts become entrapped in the forming cementum
- Cementocytes lie within lacunae
- Lacunae are connected by canaliculi
- Canaliculi oriented toward the PDL for diffusion of nourishment
- Cementum is more vital, more responsive to remodeling
- Cementocytes deep within the cellular cementum inactive, few organelles
- Cementoblasts within lacunae near the surface of the cellular cementum: active, capable of forming new cementum when necessary, reactive
Describe the fibers in cementum
- Intrinsic fibers - collagen fibers within the cementum, fibers formed by the cementoblasts
- Extrinsic fibers - collagen fibers, endings of the PDL fibers which are embedded within the cementum: Sharpey’s Fibers
Describe the three transitional interfaces that may be present at points along the CEJ
- One situation is that cementum may overlap enamel (15%).
- Another situation is that they may meet end-to-end (52%)
- Finally, there may be a gap between enamel and cementum, leaving dentin exposed (33%)
Describe possible cemental changes
- Resorption due to - Aggressive tooth movement (orthodontics); Occlusal trauma
- Repair of traumatic resorption
Describe reversal lines
- Scalloped lines where there has been resorption of cementum
- Removal of cementum by odontoclasts
- More easily resorbed than bone
Describe arrest lines
Repair of traumatic resorption involves apposition of cementum by cementoblasts in the adjacent periodontal ligament. Apposition of cementum is noted by its layers of growth, arrest lines.
What are Cementicles
- Calcified bodies in cementum found either attached to the cemental root surface or lying free in PDL
- Form from apposition of cementum around cellular debris in the PDL
What is root calculus?
- Calculus embedded within the cementum
- Bacterial plaque overlies the calculus
- Often the calculus on the root is harder than the cementum or dentin
What are the clinical considerations for dentin?
- Hypercementosis at the root apex -This is due to traumatic occlusal forces of a tooth
- Resorption of the apex of the roots on maxillary anteriors occurs with trauma such as with rapid orthodontic movement - Also mechanical or chemical stimuli such as infection or pressure could be involved.
- When root surfaces undergo external resorption (i.e., resorption mediated by cells in the attached gingiva or periodontal ligament), the damage may be limited in time and extent.
- Such damage is often followed by a reparative phase, with new cementum deposited over the previously resorbed surface.
- In the early phase of repair, reparative cementum is typically composed of cellular cementum.
- Because it lacks Sharpey’s fibers, this type of cementum does not contribute to tooth anchorage.
