Cementum

Question 1

where is cementum located

Answer 1

• covers root
• overlies root dentin
• attaches tooth to alveolar bone via PDL

Question 2

where does cementum originate from

Answer 2

• embryonic layer: ectoderm
• primary tissue: mesenchyme -> CT
• cells from dental sac differentiate ->fibers -> PDL
• PDL produces cementum and lamina dura

Question 3

what is the colour of cementum

Answer 3

• yellow - clinically looks like dentin

Question 4

what is the thickness of cementum

Answer 4

• 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

Question 5

what is the chemical composition

Answer 5

• 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

Question 6

what is the histological structure of cementum

Answer 6

• 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

Question 7

what is the formation like for cementum

Answer 7

• 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

Question 8

what are the 3 relationships cementum will have with enamel

Answer 8

1. overlaps enamel at CEJ - 60%
2. meets enamel at CEJ - 30%
3. does not meet enamel at DEJ - 10%. causes sensitivity, exposing dentinal tubules

Question 9

what are lacunae

Answer 9

• 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

Question 10

what are the 2 types of cementum

Answer 10

1. acellular cementum:
   - first layer cementum deposited
   - one layer covers full root
   - many layers cover apical portion (thin at cervical portion)
2. 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

Question 11

wha is cementoid

Answer 11

• 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

Question 12

what are sharpey’s fibers

Answer 12

• ends of the fibers of the PDL that become trapped in the developing cementum
• attach the PDL firmly to the tooth

Question 13

what is hypercementosis/cementum hyperplasia

Answer 13

• 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

Question 14

what are cementicles

Answer 14

• small bodies of cementum
• found in the PDL (either attached to root or free in PDL)
• no clinical significance

Question 15

what is the clinical importance of cementum

Answer 15

1. anchors tooth to bony socket - via sharpey’s fibers remain embedded in cementum and bone
2. 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
3. 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
4. role in orthodontics: lateral pressure applied by braces

Question 16

what are the 2 types of tensions on the PDL during Ortho tx

Answer 16

1. pressure tension -> compression PDL. transmitted to bone, and bone is resorbed, not the root = osteoclasts resorb bone
2. pull tension -> opposite side tooth, tension zone develops in PDL which is transferred to bone = osteoblasts produce bone

Question 17

how is cementoid different than cementum

Answer 17

• 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