PDL Flashcards
PDL is a ____ CT structure
fibrous
*despite being fibrous in nature; it is also has many cells
is the PDL vasculaized and innervated?
YES!
-cementum is not
the thin PDL connects?
cementum layer to adjacent alveolar bone
where is the thinnest portion of PDL?
thinnest portion around middle third of root
*0.15-0.38mm
principle function of PDL?
- supporting teeth in their sockets while permitting them to withstand forces of mastication
- *sensory receptor for positioning of jaw (full of nociceptors)
- remodeling for resorbing function
- nutritive function due to being well-veascularized
principle fibers of the PDL form
strong fibrous union between teh root cementum and the bone
ankylosis
fusion of root to bone
*PDL fibroblasts may inhibit mineralization so this doesn’t occur
Name and describe the 5 PDL type 1 collagen fibrils bundles called?
1) alveolar crest group
- -below CE junction, down, out
2) horizontal group
- -right angle to root surface, apical
3) oblique group
- -oblique angle, coronally towards bone
4) periapical group
- -around apex, base of socket
5) interradicular group
- -in multirooted teeth at crest/furcation
PDL extracellular substances?
1) fcollagen fiberes
2) oxytalan fibers
3) glycosaminoglycans and glycoproteins (ground substance)
pressure-tension hypothesis
showing tooth displacement leading to compression and tension in the surrounding bone
alveolar bending hypothesis
tooth movement causing bending of the alveolar bone
stretched fibre hypothesis**
stretching and compression of PDL fibres leading to low and high strain areas in the surrounding bone
name and describe the 5 gingival ligament fibers’s fibers are imbedded
1) dento-gingival
- -most numerous, cervical cementum to free/attached gingiva
2) bone of the alveolar crest to free/attached gingiva
3) circular
- -around neck of teeth, free gingiva
4) apically over cementum over the outer cortical plate to alveolar process or vestibule of mouth
5) trans-septal
- -cementum between adjacent teeth, over the alveolar crest
bundle bone
where unraveled PDL fibers inter mesh with adjacent fibers and insert into the bone
*contain Sharpey’s fibers
define reversal line
location where the last cycle of bone resorption was followed by bone deposition
*the latter resulted from the production by osteoblasts of a thin seam of new bone in which very short Sharpey’s fibers are imbedded
TEM of periodontal ligament fibroblasts are responsible for?
1) synthesis of collagen and its assembly into collagen fibers
2) removal of collagen fibers during the continuous remodeling
digestive vacuoles majoridly remove?
collagen
*aka intracellular collagen in digestive vacuole
collagen fibrils are digested by _____ enzymes that have been added to the vacuoles
lysosomal enzymes
*the presence of these enzymes has been confrimed by cytochemical localization
are neural elements myelinated or not?
- myelinated near the apical end
* unmyetlined more coronally
most of the neural branches near the apical end are?
MIXED. consisting of myelinated and non-myelinated axons
the distribution of nerve bracnhes is closely associated with that of?
blood vessels
PDL is rich in blood supply originating primarily from? communicating with what vessels?
- *originating off dental arteries that enter through the apical foreman, LOTS of anastomoses
- ligament vessels also communicate with supraperiosteal vessels
the PDL contains an assortment of cells that are capable of generating and maintaining 3 distinct tissues. What are they?
1) ligament itself
2) mineralized tissues
3) alveolar bone
what are the major cell types of PDL?
1) osteoblasts
2) osteoclasts
3) fibroblasts =MOST ABUNDANT
4) epithelial cells= hertwigs
5) macrophages= defense
6) undifferenciated cells
7) cementoblasts
8) vascular elements
() neural elements
What is unique about mineralization and Sharpeys fibers?
one end of the fiber may be un-mineralized while the part IN the bond is mineralized— ONLY the mineralized part is referred to as Sharpey’s fiber
cementoblasts provide?
ground substance that will imbed the fibers and allow mineralization to proceed
formation of mature PDL
- earliest remodeling along tooth and alveolar bone
- grow thicker and longer, bone side is wider, until they meet
- become organized once they meet
fibroblasts are characterized by an ability to achieve an exceptionally high rate of?
turnover of proteins within the extracellular compartment (like collagen)
what do integrins do?
bind ECM, serve as mechnotransducers to transmit the stimulus to the cell
stimulus for ECM production?
- mechanical stress
- changes in tensile and compressive forces during growth
decrease in mechanical stress leads to?
increased collagenase secretion and a thinning of PDL
epithelial cells in PDL resemble?
HERS (epithelial cell rests of Malassez)
*
importance of undifferentiated mesenchymal cells?
theyare periovascular! differenciate into fibroblasts, osteoblasts, and cementoblasts
what are the predominant collagens of PDL
1,3, 12
what are the tyeps of elastin fiebrs
1) oxytalan- perpendicular to teeth
2) eluanin- found within gingival ligament
does PDL contain immature or mature elastin protein?
immature forms of oxytalan and eluanin
oxytalan fibers
- thought to regualte vascular flow
- dense in cervical region of ligament
- associated with nueral and vascular elements
- perpendicular to teeth OR vertically from cementum surface of root apically
1) nerve supplu originates from?
2) enters from?
1) inferior or superior alveolar nerves
2) apical region and lateral socket walls
* *apical region contains more nerve endings
interstital space
- present between each bundle of ligament fibers
- contains blood vessels and nerves
- designed to withstand the impact of masticatory forces
ground substance
-amorphous, highly hydrated ~70% water
nature of ground substance explains?
why the PDL never mineralizes as it acts as an inhibitor for the process
major ground substance components
1) glycosaminoglycan- hyaluronan and dermatan sulfate
2) proteoglycans- proteodermatan sulfate, decorin, biglycan
3) glycoproteins- fibronecin, tenasin and vitrabectib
ground substance is critical for withstanding?
- forces
- ion water binding/exchange
- binding to growth factors
- collagen synthesis
- fiber orientation
PDL gets its blood supply from?
perforating arteries (from the cribiform plate of the bundle bone)
is the posterior or anterior supply of blood greater?
posterior
ligament in thicker in functioning or non-functioning teeth?
functioning and in areas of greater tension
ligament cells are capable or remodeling the ligaement and adjacent?
bone
PDL protects the tooth from normal remodeling processes why?
don’t want it getting resorbed with typical bone remodeling
what is necrosis
cell death
when would orthodontic tooth movement no longer be possible?
-when excessiev forces cause necrosis of ligament by cutting off the normal blood supply to the cells
can accidentally exfolliated teeth be replatned? complications?
yes
*complication are external root resorption and ankylosis if portion of the ligament are permanently damages
what is the mean width of PDL at coronal end of alveolus?
- premolar in heavy function= 0.35mm
* light function= 0.14
what is the mean width of PDL in middle of alveolus?
- premolar in heavy function= 0.28
* light function= 0.10
what is the mean width of PDL iat apical end of alveolus?
is somewhere between coronal end and middle
