The Etiology of Orthodontic Problems | PPT
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The Etiology of Orthodontic Problems
Malocclusion and Dentofacial deformities result not only from some pathological processes, but also by moderate distortions of normal development.
Causes of Orthodontic Problems
Either from Environmental influences
Eg. Mandibular deficiency secondary to jaw fracture during childhood
Genetic influences accompanied some rare genetic syndromes.
Orthodontic problems seem to arise from
environmental and hereditary influences
Etiologic Factors for malocclusion are
Specific causes of malocclusion.
Specific causes of malocclusion:-
Disturbances in Embryologic Development.
Skeletal Growth Disturbances .
Disturbances of Dental Development .
Disturbances in Embryologic Development
are either teratogenic or non teratogenic. Teratogenic drugs can cause specific defects with low doses ,or death in high doses.
This table lists the teratogens known to produce orthodontic problems
Skeletal Growth Disturbances
Fetal Molding & Birth Injures.
Childhood fractures of the jaws.
Acromegaly and Hemi mandibular Hyper trophy.
1.Fetal Molding and Birth injures :
Injures at birth have two major categories:
Intra uterine molding.
Trauma to the mandible during birth from the forceps that used in delivery.
A. Intra uterine Molding :
Any pressure against the developing face lead to distortion of rapidly growing areas.
Its not a true birth injury such as maxillary defeciency due to arm pressure
flexing of head against chest leading to abnormal mandibular growth (Pierre Robin Syndrome) accompanied with cleft palate .
If cartilage formation defect is present with (PRS) this will be called Stickler Syndrome .
Child can recover if the source is stopped ,so early treatment should be avoided.
Some others need surgical interference to catch up with future growth.
B. Birth Trauma to the Mandible :
Facial deformities that are not caused by birth injures but referred by parent like birth injury such as Treacher Collins Syndrome & Crouzons Syndrome .
Facial deformities caused by forceps usage lead to tempro-mandibular joints damage (due to internal hemorrage ,loss of tissue &a subsequent underdevelopment of the mandible).
2. Childhood Fractures of the Jaw :
Fractures of the condylar neck .
Trauma to maxilla & mandible .
Rheumatoid arthrities lead to asymmetric mandibular defeciency.
Hemi facial microsomia.
Asymmetric mandibular growth.
3. Muscle Dysfunction :
Facial muscles can affect jaw growth in two ways:
formation of bone at muscle attachments point.
2. musculature is an important part of the total soft tissue matrix whose growth lead to jaw growth. Also damage to the motor nerve causes muscle atrophy.
Excessive muscle contraction (torticollis) can restrict growth like scaring after injury (especially sternocliedomastoid muscle).
Treatment is surgical detachment of the muscle.
Muscular dystrophy ,cerebral palsy ,muscle weakness syndromes lead :
to increased anterior facial height.
distortion of facial proportions & mandibular form.
excessive eruption of the posterior teeth
narrowing of the maxillary arch.
anterior open bite.
4. Acromegaly and Hemi- mandibular Hypertrophy :
Tx is an orthognathic surgery though tumor is removed or irradiated .
Hemi-mandibular hypertrophy or condylar hyperplasia occur mostly in 10 yrs old females or at 30 yrs on both sexes .
When condylar cartilage proliferation & body of the Mandible growth stop the affected area will be removed & reconstructed .
Cause is unknown.
Significant Disturbances Include:
Congenitally Missing teeth.
Malformed & Supernumerary teeth.
Interference with Eruption.
Early loss of Primary teeth.
Traumatic Displacement of Teeth.
1. Congenitally missing teeth
It results from disturbance during initial stages of tooth formation ,initiation and proliferation. Missing of teeth can be:-
Many teeth (oligodontia).
Both are rare & are associated with ectodermal dysplasia (systemic abnormality).
C. Few teeth (hypodontia) is more common.
Missing of primary teeth lead to missing of its permanent successor.
The sequence of missing teeth are 3rd molars, lateral insicors,2nd premolars, and rarely Canine.
2. Malformed and supernumerary teeth
Abnormalities in tooth
size and shape will be
due to disturbances
during morpho & histo differentiation
stages of its development.
Most common abnormality is seen in lateral incisors & 2nd premolars .
Abnormalities are :-
Multiple numeraries can be seen in cleidocranial Dysplasia.
Supernumeraries (mesiodens, lateral incisors, premolars, & 3rd molars ).
is teeth with separate pulp chambers joined at dentin .
is teeth with common pulp chamber.
They are almost similar ,so you should count no of teeth.
3. Interference with eruption
Eruption of permanent teeth can be impaired due to :-
Heavy fibrous gingiva.
All the previous can be seen in cleidocranial dysplasia .Tx is removal of the cause.
Drifting of teeth. Ex. ankylosed deciduous molar
4. Ectopic eruption
It occurs as a result of a permanent tooth bud malposition. Ex:-
Mesial drifting of maxillary first molar.
Mandibular 2nd premolar erupt distally.
Impacted Maxillary canines
5. Early loss of primary teeth
Early loss of teeth will lead to dental arch collapse, but it’s not the only cause for crowding & Malalignment.
Collapse will be due to :
Mesial drifting of posterior teeth.
Distal drifting of incisors a/f canine & 1st decidious molar loss.
Distal drifting caused by 2 sources :-
Active contraction of transseptal
fibres in the gingiva.
Pressure from lips and cheeks.
If loss of teeth is present only on one side a symmetry & crowding will be present .
6. Traumatic displacement of teeth
Dental trauma can lead to development of malocclusion in 3 ways:
Damage to permanent tooth buds from injury to primary teeth.
Drift of permanent teeth a/f premature loss of primary teeth.
Direct injury to permanent teeth.
Trauma to primary tooth lead to 2 results:-
The crown may be displaced relative to the root causing less root formation & short root or dilacerations .
What is dilaceration ?
Dilaceration is formation of root at an angle to the traumatically displaced crown.
It will be due to trauma especially in incisors, or to ankylosed primary tooth resulting in mechanical interference with eruption.
Sever trauma can lead to dilaceration & projection of root outside the bone. Tx is extraction of severely dilacerated tooth.
2.Genetic Influences :
It is apparent that certain types of malocclusion runs in families
Inheritance can affect malocclusion in 2 ways:
Inherited disproportion b/w size of teeth & jaws lead to either crowding or spacing .
2. Inherited disproportion b/w size or shape of the upper & lower jaws cause improper occlusal relationships
Why primitive population has less malocclusion than modern groups ?
They are characterized by genetic isolation & uniformity.
2. Absence of processed food & better masticatory function .
3. No out breeding b/w the originally distinct human population .
What is the main cause of malocclusion ?
It is the great increase in out breeding b/w human populations. Eg Chinese ,Japanese, Europeans ,Polynesian, and Hawaiian.
Many studies were conducted on humans as well as animals to confirm that inheritance plays major role in malocclusion.
On animals such as mixing b/w different types of dogs resulting on achondroplasia Which is very rare in humans.
What are the characteristic features of achondroplasia ?
deficient cranial base length (due to deficient growth of synchodrosis).
mid face deficiency (due to lack of maxillary growth) .
3. Environmental Influences :
Function of teeth and jaws must adapt to the environment. Ex :
Chewing and swallowing pressures can affect jaw growth & eruption.
Changes in body form although it has minimal effect ,but individual who does heavy physical work has both stronger muscles & a sturdier skeletal system than the one who is sedentary.
Although teeth are subjected to a variety of forces such as masticatory forces, swallowing & speaking, they do not move to a new location. But when they tend to move they move to a static equilibrium.
Equilibrium effects on the dentition
To understand equilibrium you should observe the effect of various pressure types.
Forces are not coming from mastication only but also from lips ,cheeks ,& tongue at rest & at function.
Mechanism of bone response to occlusal forces :
Contributors for equilibrium theory :
The chewing forces.
The pressure from lips, cheeks & tongue are very light but with greatest duration/cause movement of them.
Scaring of lips or soft tissue / lingual tooth position.
Large tongue / labial displacement of teeth.
3. The external forces such as habits & orthodontic appliances.
Bilateral expansion to align teeth.
Playing of musical instrument.
4. The periodontal fiber system.
Space closure a/f teeth loss due to forces exerted from transseptal fibres in the gingiva.
Eruption of teeth due to eruption forces from gingiva.
Equilibrium Effects on Jaw size & shape
The functional processes of bone will be altered if the function is lost or changed such as :.
Tooth presence or absence (extraction or impaction).
Muscle attachments & growth change the shape of the jaw (particularly coronoid process & angle of the mandible).
Many studies suggest that size of tongue & forces from the lips &cheeks may affect shape of the jaw.
However, from the perspective equilibrium theory , it’s concluded that the intermittent pressures or forces have little if any effect on either the position of teeth or size and shape of the jaws.
Functional Influences on Dentofacial Development
Function & Dental Arch Size.
Biting Force & Eruption.
Sucking &Other Habits.
1. Masticatory Function
The pressure generated by chewing activity potentially could affect dentofacial development in 2 ways:
Prolonged biting force & greater use of jaws can increase jaw dimensions & dental arches .
Decreased biting force could affect eruption of teeth thereby affecting lower facial height ,over bite/deep bite relationships .
Function & Dental arch size
The size & shape of the muscular processes of the jaws should reflect muscle size & activity.
Enlargement of mandibular gonial angles in humans can be seen with hypertrophy of the mandibular elevator muscles.
Biting force and eruption
The biting force is not a major
determinant of either dental arch size or vertical dimensions ,if syndromes is not present .
2. Sucking & other habits
If the child continue the habit beyond the eruption time of the permanent teeth ,it may lead to malocclusion (such as flared & spaced maxillary incisors, lingually positioned lower incisors, anterior open bite, and constricted maxilla .
The magnitude of pressure and prolonged duration can cause significant malocclusions :.
Anterior open bite is resulting from excessive eruption of posterior teeth and impeding of anterior teeth.1 mm elongation posteriorly can opens the bite 2 mm anteriorly .
2. Maxillary constriction during sucking the tongue will be lowered and buccinator muscle will contract so a negative great pressure will be produced b/w the tongue & cheeks that lead to constriction of the maxillary arch.
Tx: Stop the habit and expand the arch.
Placement of the tongue tip forward b/w the incisors during swallowing.
Individual swallows about 800 times per day , which lasts for few minutes ,and its not enough to produce a tremendous effect either for teeth or equilibrium.
But if the patient has a continuous forward resting posture of the tongue this could affect tooth position vertically or horizontally.
Respiratory needs are the primary determinants of the posture of the jaws and tongue.
Therefore ,mouth breathing changes posture of head, jaws ,and tongue.
If this posture is maintained it leads to increase lower facial height, super eruption of posterior teeth , narrow maxillary dental arch ,increased over jet and anterior open bite .
It is called the adenoid face .
Nasal obstruction can be due to many causes:-
Chronic respiratory obstruction.
Large adenoids and tonsils.
Common cold .
Total nasal obstruction (rare in humans).
When this obstruction is removed ,the original posture immediately returns ,but if persists it causes 3mm increase in facial height , over jet /over bite, & constricted maxilla.
Researches on respiration established 2 opposing principles :
Total nasal obstruction alter the pattern of growth & lead to malocclusion in humans (esp long –face population)& animals .
The majority of long-face individuals have no nasal obstruction & may have some other etiologic factors.
Etiology in Contemporary Perspective
Changing Views of Etiologic Possibilities :
Edward Angle & his contemporaries influenced the finding that malocclusion is a disease of civilization .
While, Mendelian developed a different view which was that malocclusion is primarily the result of inherited dentofacial proportions which may be altered by developmental variations, trauma ,or altered function.
Etiology of Crowding and Malalignment :
Causes of skeletal problems:
Disproportion b/w jaw & tooth size.
Increased out breeding b/w population.
Mouth breathing alter the tongue-lip/cheek equilibrium.
Therefore the conclusion is that Cl I problems ,especially non skeletal cross bite ,often are caused by alterations in function, On the other hand major problems usually have an additional genetic or developmental component.
Etiology of Skeletal Problems:-
Skeletal orthodontic problems resulting
from malposition or malformation of the
jaws rather than irregularity of the teeth
can arise from
number of causes : .
Causes of skeletal problems:
Defects in embryologic development & genetic syndromes (rare).
Trauma (common cause).
3. Open bite can be due to :
Sucking habit .
Tongue posture accompany nasal obstruction.
Excessive eruption of posterior teeth.