Download Periodontal and bone response to normal function

In the name of GOD
Periodontal and bone response
to normal function
Presented by:
Dr Somayeh Heidari
Orthodontist
Reference:
Contemporary Orthodontics
Chapter 8
William R. Proffit, Henry W. Fields, David M.Sarver. 2013. Mosby
The principle of orthodontic treatment:
if prolonged pressure is applied to a tooth, tooth movement will occur as
the bone around the tooth remodels.
The tooth moves through the bone
carrying its attachment apparatus with it,
as the socket of the tooth migrates.
Tooth movement is primarily a periodontal ligament phenomenon.
The biologic response to the orthodontic therapy includes not only
the response of the periodontal ligament but also the response of
growing areas distance from the dentition.
Pattern of bone apposition and resorption in:
sutures of the maxilla
bony surfaces of temporomandibular joint
Periodontal ligament
Normal structure and function
Periodontal ligament (PDL)
heavy collagenous supporting structure that attached to a tooth and
separate it from the adjacent alveolar bone.
Approximately 0.5 mm in width around all
parts of the root.
The major component is a network of parallel collagenous fibers
The supporting fibers run in at an angle:
attaching farther apically on the tooth (cementum) than on the adjacent
alveolar bone (lamina dura)
This arrangement resists the displacement
of the tooth expected during normal function
PDL components:
• Collagenous fiber bundles
most of the PDL space
• Cellular elements
mesenchymal cells
• Vascular and Neural elements
• Tissue fluids
All play an important role in normal function and orthodontic tooth
movement.
 The principal cellular elements are undifferentiated mesenchymal cells
and their progeny in the forms of fibroblasts and osteoblasts
 the collagen of the ligament is constantly being remodeled and renewed
 the stem cells can serve as both fibroblasts and fibroclasts
 fibroblasts, producing new collagenous matrix materials.
 fibroclasts, destroying previously produced collagen.
 remodeling and recontouring of the bony socket and the cementum of
the root is constantly carried out, as a response to normal function.
 fibroblasts in the PDL have properties similar to osteoblasts.
 new bone probably is formed by osteoblasts that differentiated from the
local cellular population.
 bone and cementum are removed by specialized osteoclasts and
cementoclast
 the origin of these multinucleated giant cells s controversial:
most are of hematogenous origin
some may be derived from local area stem cells
 although PDL is not highly vascular, it contains blood vessels and cells
from the vascular system
 nerve endings within the PDL:
unmyelinated free ending (pain)
more complex receptors (pressure and proprioception)
 PDL space is full of fluid
derived from vascular system
the fluid allows the PDL space to play the role of “shock absorber”
Response to normal function
During masticatory function the teeth and periodontal structures are
subjected to intermittent heavy forces:
Tooth contacts last for 1 second or less
Forces are quite heavy:
1-2 kg
to
50 kg
Quick displacement of the tooth within the PDL space is prevented by the
incompressible tissue fluid
The force is transmitted to the alveolar bone, which bends in response
 bone bending during normal function of the jaws (and other skeletal
elements) is often not appreciated.
 the body of the mandible bends as the mouth is opened and closed
 upon wide opening, the distance between the mandibular molars
decreased by 2 to 3 mm.
In heavy function:
• individual teeth are slightly displaced as the alveolar bone bends
to allow this to occur.
• bending stresses are transmitted over considerable distances
Bone bending in response to normal function generates piezo-electric
currents.
An important stimulus to skeletal regeneration and repair
First second of pressure
very little of the PDL space fluid is squeezed out
normal mastication: 1 second or less force application
Maintained pressure
the fluid s rapidly expressed
the tooth displaced within the PDL space
compressing the ligament against adjacent bone
Pain is normally felt after 3 to 5 seconds of heavy force application
PDL
Is beautifully adapted to resist forces of short duration
It rapidly loses its adaptive capability as the tissue fluid is squeezed out
Prolonged force, even of low magnitude, produces a different physiologic
response – remodeling of the adjacent bone
Orthodontic tooth movement is made possible by the application of
prolonged forces.
Light prolonged forces in the natural environment- forces from the lips,
cheeks, or tongue resting against the teeth- have the same potential as
orthodontic forces to cause teeth movement.
Physiologic response to heavy pressure against a tooth
Time (seconds)
Event
PDL fluid incompressible
<1
Alveolar bone bends
Piezoelectric signal generated
1-2
PDL fluid expressed
Tooth moves within PDL space
PDL fluid squeezed out
3-5
Tissues compressed
Immediate pain if pressure is heavy
Role of PDL in eruption and stabilization of the teeth
Tooth eruption makes it plain that forces generated within the PDL itself can
produce tooth movement.
The eruption mechanism depends on metabolic events in the PDL, including
but perhaps not limited to:
formation
cross linkage
maturational shortening of collagen fibers
This process continues, although at a reduced rate, into adult life.
Active stabilization of the teeth
 against prolonged forces of light magnitude
 light prolonged pressure against the teeth are not in perfect balance
In the mandibular anterior , tongue pressure is greater than lip pressure.
In the maxillary incisor region, lip pressure is greater
The ability of the PDL to generate a force and thereby contribute to
the set of forces that determine the equilibrium situation, probably
explained this.
Active stabilization also implies a threshold for orthodontic force
Forces below the stabilization level
ineffective
The threshold for outside force would vary depending on the extent
to which existing soft tissue pressures were already being resisted
by the stabilization mechanism.
Active stabilization can overcome prolonged forces of a few grams at
most, perhaps up to the 5 to 10 gm/cm2
Thanks for your attention