Stress trajectories /prosthodontic courses

Stress Trajectories of Force
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

Stress trajectories
History
 Galileo (1638) & Monro(1776)
 Mechanical implications of bone shape
 Andre (1741)
 Deformation could govern bone shape and that shape
could be changed through the application of mechanical
forces

Julius Wolff –
 “ Das Gesetz der Transformation der Knochen ”i.e.,
“The law of bone transformation”
 Wolff’s law-
Bony trabeculae – delicate lace in
accordance to stress trajectories
In 1986, Maquet &Furlong
 “The law of bone remodelling”

Das Gesetz der Transformation der Knochen
 Epoch making book
 Researchers – form & function relation – not accurate
 Inadequate understanding of histology & physiology
Wilhelm Roux
 Uncovered the foundations of form-function interaction
 In 1881, “Der Kampf der Theile im Organismus”
I.e.,(The struggle of the components with in organisms)

The origin of Wolff’s law
In 1853, Meyer
 Mechanics of the human skeleton
• Drawings

In 1860, Meyer –
 C.S of long bones
 Trajectories cross at right angles
Cullmann -
 Method of drawing trajectories
Wolf –
 Added a crane type schema
 Form –Trab organisation of bones involved the arrangement
of minm material to withstand maxm load
 Law of orthogonality – definite mechanical mathematical laws
 Interpritation of function was biased

“Function can influence the overall pattern and
relationship of the structures”.

Wolff’s biases –
 His theory on interstitial bone growth
 Role of heredity
 Concept of function

Interstitial bone growth-
 Similar to soft tissue growth
 Wolff’s statement-
• Each and every particle [of a bone]contributes
proportionally to the enlargement
 Wegner & Koelliker –1872
• Remodelling
• Wegner’s statement
 Wolff –1875
• Wegner’s expt – not fundamental
 Baehr -1898

Interstitial bone growth-
 Hunter & Fluorens
 Wolff –
 Carried the incorrect notion
 Remodeling – absent
 Expts
 His view – Trab architecture was not the result of
dynamic process, but was preexisting in the
compacta

Heredity –
 Trab –already existed in the compacta
 Predesigned structure
 Statements –1870
 The initial architectonic configuration of bone is not the
result of static influences…but is preformed & inherited
from the parents
 The appropriate architecture under normal conditions will
develop during the intrauterine period and is explained by
heredity
 No dynamic interaction during development

Function –
 Static requirement/constraints to be met as in
engineering…(metaphors)
 Good design above good repair capabilities
 Roux –
• Loading & Unloading generated information for the
developing bone
 Function –static role of bone .i.e.,support of body
weight

Function-
Function –static role of bone .i.e.,support of body weight
A year before the book –
 “The form of bone is exclusively determined by the
static load which it has to match, or- what is identical –
by its function”
Form – prerequisite for functioning
Ideal or normal form was defined by nature

Wolff & Roux
 1885, Roux
 Functional stimulus shaped bone
 Ex ; thickened fibula
 Joint venture faltered

Conclusion
 Author has won the battle against time
 His law is an accepted phenomenon
 The fact that he was wrong on all the biological
aspects concerning his law appears to be minor
concern
 Roux only remembered in the historical section of a
good library

Subsequent Research
 Both Tension & Pressure - Loss of bone
tissue
 Trabeculae cross at varying angles
 Irregular & wavy
 Vary from bone to bone
 Function - Density
 Function - Density
 Ex ; Milwaukee Brace
 Tooth c no opp Tooth

Stress Trajectories of Force
Benninghoff made an exhaustive study of
the architecture of the cranial &facial
skeleton and so called “Stress Trajectories”
or “Lines of force” evolved.

Benninghof –
 Traj/Lines of Forces-
• Involve both compact & spongy bone
• In response to – local function
-epigenetic influences
• Obeyed no individual bone limits
• But rather demands of functional forces
• Head –2 Bones –Craniofacial skeleton
Mandible

3 main vertical pillars of stress trajectories
can be seen in the nasomaxillary region.
a.Canine pillar
b. Zygomatic pillar.
c.Pterygoid pillar

The Mandible
Trabecular
columns
radiate –
terminate in
mand condyle

The Basic structure is designed to
meet the demands of a lifetime of
varied Functional activity

Clinical Implications of Growth
& Development

Importance of knowing Growth & development

Adolescent Growth Spurt
 Adolescence
 Imp period in dental & orthodontic treatment
 2 years earlier in girls

Timing of puberty-
 Seasonal & Cultural factors
 Genetic & Environmental influences

For the 3 planes of space in both maxilla &
mandible – Definite sequence of growth
completion
 WIDTH
 LENGTH
 HEIGHT

Usually completed at the time of adolescent
growth spurt.
Narrow skeletal width --- Narrow palatal vault
Narrow dental arch
Cross bite
Transverse Growth of Maxilla

Cross bite

Expansion across the suture – 2 ways
Rapid
Slow

.
.
1. Nasomaxillary Suture
2. Frontomaxillary Suture
3. Zygomaticomaxillary Suture
4. Lacrimomaxillary Suture
5. Ethmoidomaxillary Suture
6. Vomeromaxillary Suture
Circummaxillary sutures

Structure of the suture at different ages:
Infancy
Juvenile
Adulthoodwww.indiandentalacademy.com

R M E
• More skeletal changes
• Less dental changes
• Not used in preschool children
• 0.5-1mm/day
• 10-20 pounds
• Occlusal radiographs
• Clinical examination
• 3-4 months of retention

Haas expander
Hyrax expander
Minn expander

Activation of RME.
Upto 15yrs of age 1800
(2 turns daily)
15-20yrs. of age 1800
(4 turns daily)
Over 20yrs. 900
(2 turns daily)

How much to Expand?
Palatal cusps of upper maxillary teeth
should occlude with the lingual inclines of
the buccal cusps of the lower mandibular
teeth.

Effects of RME:-
-Midpalatal suture opens anteroinferiorly.
-Midline diastema.
-Buccal flaring of posteriors.

R M E

Frontal View

Ideal patients for RME treatment.
 Full cusp cross bite with a skeletal
component
 Some degree of dental as well as skeletal
constriction initially
 No pre-existing dental expansion.

Nasal hump & paranasal swelling.
Pain.
Buccal tipping of posteriors.
Root resorption.
Fenestration of roots
Adverse effects of RME:-

Undesirable changes in the nose due to RME

Root exposure due to RME

Slow expansion
 Less force
 1mm/week
 Reduced tissue damage
 Reduced hemorrhage
 2-4 pounds of force
 More physiologic response

Dental cross bites are corrected by
-Quad helix
-W arch
-Arch wire

Skeletal & Dental changes in Expansion
Rapid Slow

Anteroposterior growth of maxilla.
Maxillary excess:-For restriction of
maxillary growth in growing individuals
appliances like
1.Headgear
2.Functional appliances

Functional Appliances
They are of two types:-
-Removable
-Fixed Appliances.

Activator Bionator
Twin Block

Fixed Appliances:-
Herbst Appliance
Jasper Jumper

Cervical head gear:
used in patients with horizontal growth
pattern with reduced lower facial height.

Occipital pull Head gear:-
Used in long face patients
with high mandibular
plane angle.

Dental camouflage can be done for mild to
moderate skeletal problems.
For adult patients where growth is no longer
present surgical correction should be done.

3 major possibilities for correcting mandibular
defficiency

Maxillary Deficiency:-Growth
modulation in sagittal plane can be
done by
1.face mask
2.reverse functional appliances.

Effects of forward traction of maxilla

Face mask Therapy
Delaire Facemask

Face mask Therapy
Petit Face mask

Mandibular excess

Chin cup therapy

Twin Block
Reverse Functional appliances:
Functional Regulator

Vertical excess of maxilla can be controlled
by inhibiting the descent of maxilla and
eruption of posterior teeth.
Vertical growth of maxilla

Frequent respiratory Nasal Septal Contracted
Swollen Nasal
Mucosa Reduced Nasal Decrease in
Enlarged breathing Nasal width
adenoids
Mouth breathing
Lowered Extended
tongue position head posture
Lowered Mandibular
Posture
infection deviation Maxillary arch

-Highpull headgear to a maxillary splint

Magnetic splints for intrusion of posterior teeth

Functional appliance with increased
height of the bite blocks

Highpull headgear to a functional appliance.

Cleft lip & palate
Infant orthopedics
Late primary & early mixed dentition
treatment
Early permanent dentition treatment
Orthognathic surgery

Stress trajectories /prosthodontic courses

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