1
Q
where is cementum located
A
- covers root
- overlies root dentin
- attaches tooth to alveolar bone via PDL
2
Q
where does cementum originate from
A
- embryonic layer: ectoderm
- primary tissue: mesenchyme -> CT
- cells from dental sac differentiate ->fibers -> PDL
- PDL produces cementum and lamina dura
3
Q
what is the colour of cementum
A
- yellow - clinically looks like dentin
4
Q
what is the thickness of cementum
A
- 1 hair
- cervical: 16-60 microns (0.02 to 0.06 mm)
- apical half: thicker 150-200 microns (0.15 to 0.2 mm)
- removedly brushing, scaling, polishing
- decays easily
- no blood vessels or nerves
5
Q
what is the chemical composition
A
- mineralized tissue
- about same hardness as bone
- softest of tooth calcified tissues
- organic matrix and hydroxyapatite crystals
- 45-50% inorganic HA crystals
- 50-55% organic components and water
6
Q
what is the histological structure of cementum
A
- organic matrix: composed of fine collagen fibrils help together by amorphous cementing ground substance
- cementocytes: cementoblasts of PDL produces cementum; become trapped in organic matrix -> remain embedded as cementocytes in cementum
7
Q
what is the formation like for cementum
A
- forms in layers
- develops from dental sac
- forms on roots after disintegration of hertwig’s epithelial sheath
- cells of PDL migrate and contact dentin -> cementoblasts
- secrete ground substance
- eventually calcifies, some become entrapped in calcifying cementum (cementocytes); no cementocytes at the cervical area (think cementum); usually more apical region (thickest)
- cementoblasts that do not become entrapped, like cemental surface in PDL -> subsequent layers of cementum if needed - injury
8
Q
what are the 3 relationships cementum will have with enamel
A
- overlaps enamel at CEJ - 60%
- meets enamel at CEJ - 30%
- does not meet enamel at DEJ - 10%. causes sensitivity, exposing dentinal tubules
9
Q
what are lacunae
A
- spaces in cementum - occupied by cementocytes
- cementocytes connected through cytoplasmic projections in small canals - canaliculi. canaliculi oriented toward PDL
- to diffuse nutrient from the ligament which is vascularized
10
Q
what are the 2 types of cementum
A
- acellular cementum:
- first layer cementum deposited
- one layer covers full root
- many layers cover apical portion (thin at cervical portion) - cellular cementum:
- last layers of cementum deposited over acellular cementum
- apical 1/2 or 1/3 of the root
- thicker, contains cementocytes, makes cementum vital and alive tissue
- at PDL end, have cementoblasts, allow future production of cellular cementum if needed
11
Q
wha is cementoid
A
- non mineralized layer of cementum
- most recent layer of cementum formed by cementoblasts
- outer surface of cellular cementum
- next to the PDL
- less mineralized -> not easily destroyed osteoclast
- important role in orthodontics
12
Q
what are sharpey’s fibers
A
- ends of the fibers of the PDL that become trapped in the developing cementum
- attach the PDL firmly to the tooth
13
Q
what is hypercementosis/cementum hyperplasia
A
- thickening of cellular cementum (excess production)
- mainly occurs at the root of apex
- may result from:
- occlusal trauma
- chronic periodical inflammation
- to compensate loss crown length during attrition
- causes no problem unless being extracted
14
Q
what are cementicles
A
- small bodies of cementum
- found in the PDL (either attached to root or free in PDL)
- no clinical significance
15
Q
what is the clinical importance of cementum
A
- anchors tooth to bony socket - via sharpey’s fibers remain embedded in cementum and bone
- compensates for loss of enamel: continuous deposit cementum apically intermittently throughout life (cementoblasts) due to continuous attrition of teeth, keeps max/mand teeth in contact/occlusion, very slight movement upward
* also during more extensive loss enamel/dentin - attrition - replace resorbed dentin due to trauma:repairs tooth root, example - 3rd molar impacted, pushing on tooth, can cause resorption of bone and root of tooth in front
- role in orthodontics: lateral pressure applied by braces
16
Q
what are the 2 types of tensions on the PDL during Ortho tx
A
- pressure tension -> compression PDL. transmitted to bone, and bone is resorbed, not the root = osteoclasts resorb bone
- pull tension -> opposite side tooth, tension zone develops in PDL which is transferred to bone = osteoblasts produce bone
17
Q
how is cementoid different than cementum
A
- more resistant to being destroyed by osteoclasts because less mineralized (osteoclasts destroy bone, cementoid does not resemble bone as cementum does)
- protects the roots
- if too much pressure applied resorption of root can occur
Histology
flashcards
Decks in class (15)
# Cards
