biology of tooth movement

1. The biologic basis of
tooth movement
Presented by Dr Casius . C

2. Periodontal ligament structure and function
•The pdl occupies the periodontal space, located between
alveolar bone and cementum
•Major component of the ligament is a network of parallel
collagenous fibers inserting into the cementum and bony
plate
• principal cells of pdl are undifferentiated mesenchymal cells
and their progeny in the form of fibroblasts and osteoblast

3. • pdl space is filled with a fluid derived from vascular system
which allows the pdl space to play the role of a shock
absorber
•Under normal circumstances pdl occupy about 0.25mm of
pdl space

5. Response to Normal function
•During mastication tooth contact lasts for 1 sec or less,
•forces ranging from 1-50kg are experienced under such load
quick displacement of tooth in pdl is prevented by tissue fluid
in pdl space
•forces are then transmitted to bone which bends in response
•Bone bending generates piezo electricty which appear to be
a stimulus for skeletal regeneration and repair

6. •If prolonged heavy forces are applied pain is felt after
3-5secs as the fluid gets squeezed out of the periodontal
space
•Orthodontic tooth movement is made possible by
application of prolonged forces

7. Periodontal ligament and bone response to
sustained force
• sustained heavy forces lead to rapidly developing pain
necrosis and undermining resorption of alveolar bone
•Sustained lighter forces is compatibile with survival off cells
in pdl and leads to frontal resorption of tooth socket which is
relatively painless
•In orthodontics ,the objective is to produce tooth movement
by frontal resorption

8. Biologic control of tooth movement
Two possible control elements involved in tooth movement
are:
1. biologic electricity
2. Pressure-tension in periodontal ligament

9. Biologic electricity
• Piezoelectricity is a phenomenon In which a deformation of
the crystal structure provides a flow of electric current
,sources of piezoelectricity in the periodontium are bone
,collagen ,collagen- hydroxyapetite interface.
•Piezoelectricity has 2 unusual characteristics
1. Quick decay rate
2. Production of an equivalent signal ,opposite in direction,
when forces are released

10. •Ions that bathe bone interact with electric fields generated
when the bone bends causing electric signals in the form of
volts as well as temperature changes , as a result both
convection and conduction currents are affected by nature of
fluids
•The small voltages that are observed are callled streaming
potential , these voltages are different from piezolelectric
current flow but have in common their rapid onset and
alteration as changing stresses are placed on bone
•Electromagnetic fields affect cell membrane potentials and
permeability and thereby trigger changes in cellular activity

11. Pressure –tension in periodontal ligament
Pressure –tension theory is a classic theory of tooth
movement , relies of chemical rather than electric signals as
stimulus for cellular differentiation and tooth movement.
The mechanical effects on cells within the pdl cause the
release of cytokines , prostaglandins and other chemical
messengers
Blood flow decreases in pressure side and increases in tension
side which create changes in chemical environment ,for
instance oxygen is decreased in compressed area and CO2
increased and vice versa on tension side
These change stimulate cellullar differentiation and activity

12. Effects of force duration and force decay
•Sustained force is key to orthodontic tooth movement
•Approximately 4 hrs sustained force is required o increase
cyclic nucleotide levels in pdl
•Types of force
1. Continuous force – force maintained at some appreciable
fraction of orginal force

14. • Intermittent force- force levels decline
abruptly to zero intermittently

15. • Interupted force – force levels decline to zero between
activation

16. Tissue response in periodontium
•Initial period of tooth movement/initial phase
•Hyalinization phase/ lag phase
•Secondary period of tooth movement/post lag phase

17. Initial period of tooth movement
•Application of a continuous force on the crown of the
tooth leads to rapid tooth movement by narrowing of
the periodontal membrane, particularly in the
marginal area
•It takes about 30-40hrs for osteoclasts to
differentiate along the alveolar bone wall
•Direct resorption of alveolar bone

19. Hyalinization Phase/lag phase
•During the initial application of force, compression in limited
areas of the membrane impedes vascular circulation and cell
differentiation, causing degradation of the cells and vascular
structures
•tissue reveals a glasslike appearance in light microscopy,
which is termed hyalinization
•Hyalinization represents a sterile necrotic area,
characterized by three main stages: degeneration ,
elimination of destroyed tissue, and establishment of a new
tooth attachment.
•Little or no tooth movement occur in this phase until
adjacent bone has been resorbed

21. If the forces used are heavy the area of hyalinization
is large and resorption occurs in a rearward direction
which is termed as undermining resorption
swelling of the mitochondria and the endoplasmic
reticulum and continuing with rupture and dissolution
of the cytoplastic membrane. This leaves only isolated
nuclei between compressed fibrous elements
(pyknosis)

22. Hyalinized Zone and Root Resorption
• side effect of the cellular activity during the removal
of the necrotic hyalinized tissue is that the cementoid
layer of the root and the bone are left with raw
•Root resorption then occurs around this cell-free
tissue, starting at the border of the hyalinized zone

23. •(initial phase ) was defined as a penetration of cells
from the periphery of the necrotic tissue where
mononucleated fibroblast-like cells, stained negatively
by tartrate-resistant acid phosphatase (TRAP), started
removing the cementum surface
•Root resorption beneath hyalinized zone occurred in
a later phase during which multinucleated
TRAP-positive cells were involved in removing the
main mass of necrotic PDL tissue and resorbing the
outer layer of the root cementum.

24. Secondary Period of Tooth Movement/post lag phase
•In this period , the PDL is considerably widened
•The osteoclasts attack the bone surface over a much wider
area.
•As long as the force is kept within limits bone resorption is
predominantly direct fibrous
•attachment apparatus is reorganized by the production of
new periodontal fibrils.

26. • Large number of osteoclasts appear along bone
surface on pressure side and tooth movement is rapid
•Deposition of alveolar bone on tension side
•Osteoblasts with darkly stained nucleus observed
along stretched fiber bundles

28. Effects of force magnitude

31. •Experiments show after about 4 hrs of sustained pressure
there is increase in cAMP which is the second messenger for
many cellular functions including differentiation
•Orthodontic tooth movement only occur if force is present
over the threshold of 4-6 hrs
•After 1st hr of sustained force prostaglandins and interleukin-
1 beta levels rise in pdl,it is now clear that the PgE is an
important mediator of cellular response

32. •Concentration of RANKL in and OPG in GCF increase with
orthodontic tooth movement which suggest that pdl cells
under stress induce formation of octeoclasts through
upregulation of RANKL
•PgE stimulate both osteoclastic and osteoblastic activity
•Parathyroid hormone if injected induces osteoclastic activity
in few hours while it take 48hrs when mechanical
deformation is the stimulus
•Osteoclasts arrive in 2 waves ,1st wave from local population
and second wave from distant areas through blood

33. •Light forces induce frontal resorption where
osteoclasts directly resorb adjacent bone on
pressure side of pdl
• heavy forces produce undermining resorption
where osteoclasts appear within adjacent bone
marrow spaces and begin attack on underside of
bone adjacent to necrotic area

34. Effects of force distribution and the type of tooth movement
Pdl response is determined not by force alone but force per
unit area or pressure
Tipping
•Produced with single force
•Tooth rotates around its center of resistance a point located
halfway down the root
•PDL is compressed near root apex on same side as the spring
and at crest of alveolar bone on opposite side from spring

35. •Maximum pressure is at the alveolar crest and root
apex and minimum pressure in center of resistance
•Force used to tip tooth should be low
•Tipping forces should not exceed 50 gms and lighter
forces are better for smaller teeth
•Tipping can be of two types:
Controlled tipping and uncontrolled tipping

37. Bodily movements/translation
•Obtained by force couples acting along parallel lines
and distributing force over alveolar bone surface
•PDL is loaded uniformly
•70-120gms of force required for this type of
movement

39. Torquing
Tipping of apex ,pressure area located close to middle
region of root due to pdl being wider in apical 3rd than
middle 3rd charecterized by lingual movement of root

40. Rotation
•Buccal or lingual movement of tooth around its long axis

41. •35-60gms of force required since entire PDL is
engaged
•Forces to bring about rotation creates two pressure
side and two tension side in the pdl

42. Extrusion

43. •Forces are directed along the long axis of the tooth
•Does not cause any compression of pdl ,rather only cause
tension in the pdl
•35-60 gms of force is required to bring about this movement
•Heavy forces must be avoided as it poses risk of extraction

44. Intrusion
Bodily displacement of tooth along its long axis in apical
direction

45. •Intrusion can only be accomplished using light forces since
forces is concentrated in a small area at the tooth apex
•In other cases alveolar bone may be closer to apex
increasing risk of root resorption
•Causes stretch on principal fibers and may cause bony
spicules in marginal area
•May cause pulpal changes such as pupal edema and
vascularization of odontoblasts

47. Movement in labial direction
•Heavy forces in the labial and buccal direction may result in
alveolar bone dehiscence which may lead to soft tissue
recession
•Labial bone reforms in area of dehiscence with intact
epithelial junction when tooth is retracted towards a proper
positioning of root within alveolar process
•When moved labially,areas with thin gingiva serve as a locus
minor resistentiae to developing soft tissue defects in
presence of plaque induced inflammation

48. •Careful examination of dimension of tissues covering facial
aspect of teeth to be moved should precede labial tooth
movement
• as long as tooth Is moved within the envelop of the alveolar
process the risk of harmful side effects in marginal tissue is
minimal

49. Movement into reduced alveolar bone height
By position teeth toward edentulous area improved
aesthetics and functional results may be gained
Many of such cases have a reduced alveolar bone height
When tooth is moved to edentulous area newly formed bone
on pressure side showed resorption on the surface near
root and apposition on opposite side of the thin boneplate

51. mechanotransduction

52. Local biologic mediators of orthdontic tooth movement
During quiescence,osteocytes secrete sclerostin ` which
inhibits wnt cell signaling preosteoblastic differentiation and
bone formation
Upon tooth movement pdl cells,bone lining cells,alveolar
bone osteocytes secrete cytokines(TNF ,IL1B) which
stimulate autocrine and paracrine cell changes and
production of biologic mediators (CSF-1,VEGF,PGE2) which
regulate bone formation and resorption process

54. Neuropeptides and orthodontic tooth movement
•Pulpal and pdl nocioreceptors on orthodontic tooth
movement release substance p and calcitonin gene related
peptide/CGRP
•These neuropeptides enchance secretion of inflammatory
cytokines and increases vasodilation and permeability of
blood vessels and promote tooth movement

55. RANK/RANKL/OPG system for control of osteoclastogenesis
•Regulation of osteoblasts are mediated by
RANK/RANKL/OPG complex
•RANKL found on surface of osteoblast lineage cells when
RANKL binds to RANK it stimulates osteoclastogensis
•RANK-RANKL interaction is regulated by OPG which is
secreted by cells of osteoblastic lineage and is a competitive
inhibitor of RANKL hence diminishing osteoclastogensis and
bone resorption

56. •OPG expression increases in tension areas of pdl and alveolar
bone and RANKL expression increases in compression areas
•Injection of OPG-Fc /monoclonal antibody to RANKL inhibits
relapse of tooth movement beyond constraints of tooth
socket for upto 1 month after appliance therapy

57. Drug effects on the response to orthodontic force
•At present drugs that stimuate tooth movement are
unlikely to be encountered
•Direct injection of prostaglandin into pdl has shown an
increase rate of tooth movement but it causes pain hence
not practical
•Relaxin injection has been proposed to cause faster tooth
movement due its effects on collagen but studies did not
show consistent positive effect

58. Prostaglandin inhibitors
•Fall into 2 categories
corticosteroids and NSAIDs
•Corticosteroids inhibit formation of arachidonic acid thus
inhibits prostglandins an reduces tooth movement
•NSAIDS inhibit conversion of arachidonic acid to
prostaglandins
Other classes of drugs that can effect prostaglandin levels are
tricyclic antidepressant,antiarrhythmic drugs ,anti malarials
and methylxanthine

59. Bisphosphonates
•Are used in postmenopausal females to inhibit bone loss by
preventing bone resorption by disrupting intracellular
enzymatic function of osteoclasts hence they retard
orthodontic tooth movement
•Bisphosphonates are associated with unusual necrosis of
mandibular bone typically after extraction
And is most often seen in patients with metastatic bone
cancer who recieve high dose of bisphosphonate
Elective orthodontic extractions should be avoided in such
cases

60. •They get incorporated into bone due to their
pyrophosphate analouges hence stoping drug doesn’t
eliminate all its effects
•Treament is possible only if bisphosphonates are stoped for
a period of 3 months or prescribed evista which is an
estrogen analouge which has no effect on tooth movement

61. PHYSICAL METHODS THAT STIMULATE THE BIOLOGY OF
ORTHODONTIC TOOTH MOVEMENT
Injury-Facilitated Acceleration of Tooth Movement
•The biology underlying injury-facilitated acceleration of tooth
movement is generally attributed to the regional acceleratory
phenomenon (RAP), a nonspecific, dynamic healing process
of bone after sustaining trauma, and this process is generally
characterized by upregulated bone remodeling
•decortication of the alveolar bone leads to escalated
demineralization– remineralization dynamics

62. •Kole introduced a surgical procedure that involved
vertical cuts of the buccal and lingual alveolar cortical
plates (corticotomy) combined with subapical horizontal
cuts penetrating the entire alveolus (osteotomy)

63. Corticotomy assisted orthodotic tooth movement

64. Distraction osteogenesis

65. •decades later, Wilcko et al. revised this surgical procedure by
adding bone grafting to the corticotomies. This procedure is
now termed periodontally accelerated osteogenic
orthodontics (PAOO)
•Cortical bone injuries without reflecting flaps characterized
by small and local incisional cuts (called corticision or
piezocision) were subsequently Proposed by hoogeveen et al

66. •high-frequency cyclic forces were found to stimulate bone
formation and reduce osteoclast density in rabbit craniofacial
sutures and to upregulate rat alveolar bone osteogenesis.
•On the other hand, high-frequency vibrations were also
found to accelerate tooth movement in rats by upregulating
RANKL expression and enhancing bone resorption
Vibration-Induced Acceleration of Tooth Movement

67. Acceledent vibration device which consist of a mouth piece onto which
patient bite down ,produces 30 hz daily

68. Laser Irradiation-Induced Acceleration of Tooth Movement
• Data from animal studies indicate that mechanisms
such as stimulation of alveolar bone remodeling, upregulation
of matrix metalloproteinase-9, cathepsin K and integrin
expression,activation of the RANK/RANKL system, and
stimulationof fibronectin and type I collagen expression may
mediate the effect of low-energy laser irradiation