6. Etiology of Orthodontic and Dentofacial Abnormalities Flashcards
Malocclusion is a ____ condition.
In most instances, malocclusion and dentofacial deformity are caused, not by some pathologic process, but by moderate (occasionally severe) distortions of ____ development.
Only about one-third of the U.S. population has normal occlusion, while ____ have some degree of
malocclusion.
developmental
normal
two-thirds
In the malocclusion group, only about 5% have problems attributable to a ____ known cause
The remainder are the result of a complex and poorly understood combination of ____ influences.
About 5% have a problem of such severity that it would fall into the dentofacial deformity category and potentially require ____ treatment.
specific
inherited and environmental
surgical-orthodontic
ETIOLOGY OF ORTHODONTIC AND DENTOFACIAL ABNORMALITIES
SPECIFIC CAUSES OF MALOCCLUSION
Disturbances in Embryologic Development Growth Disturbances in the Fetal and Perinatal Period Progressive Deformities in Childhood Disturbances Arising in Adolescence or Early Adult Life Disturbances of Dental Development \_\_\_\_ INFLUENCES \_\_\_\_ INFLUENCES Equilibrium Considerations Masticatory Function Sucking and Other Habits Tongue Thrusting Respiratory Pattern
genetic
environmental
Use of Family Data to Predict Growth
____ have been noted as often showing similar types of malocclusion.
This is applicable to Class 2 malocclusions and associated skeletal patterns but the inheritance patterns are ____ and the current morphology of the patient is the primary source of information about future growth.
Each child receives half of his or her genes from each parent, but not likely the same combination of genes as a sibling unless the children are ____ twins.
With polygenic traits the highest phenotypic correlation that can be expected based on genes in common by inheritance from one parent to a child, or between siblings, is ____.
Because the child’s phenotype is likely to be influenced by the interaction of genes from both parents, the “mid-parent” value may increase the correlation with their children to ____ because of the regression to the mean of parental dimensions in their children.
siblings polygenic monozygotic 0.5 0.7
Use of Family Data to Predict Growth
Squaring the correlation between the two variables derives the amount of ____ predicted for one variable in correlation with another variable.
Therefore, at best, using mid-parent values, only ____% of the variability of any facial dimension in a child can be predicted by consideration of the average of the same dimension in the parents.
Only ____% of the variability of any facial dimension in a child can be predicted, at best, by considering the same dimension in a sibling or one parent.
Because varying effects of environmental factors interact with the multiple genetic factors, the usual correlation for facial dimensions between parents and their children is about ____%, yielding even less predictive power.
variation
49
25
30
Consideration of the cause of a malocclusion requires careful consideration of the following:
Most problems in orthodontics (or any outcome of growth), unless acquired by trauma, are not strictly the result of only ____ or only environmental factors.
Growth is the result of the interaction of genetic and ____ factors over time.
Most of the studies regarding the genetics of craniofacial growth are analyses of ____ that estimate the proportion of the total phenotypic variation of a quantitative trait that can be attributed to genetic differences between individuals but that do not determine the type of genetic influences—that is, monogenic versus ____.
genetic
environmental
heritability
complex
Consideration of the cause of a malocclusion requires careful consideration of the following:
Even if the growth outcome is influenced heavily by multiple genetic (polygenic) factors, that does not mean that the growth from that point on is necessarily or absolutely ____ or on a particular immutable track, although it may be predisposed to remain on the same track if the influence is ____.
The most important practical question regarding orthodontics and genetics is whether different individuals respond to some degree to a changed environment (treatment) in different ways according to the influence of their particular ____ factors.
predetermined
monogenic
genetic
Mandibular ____ in the Hapsburg family became known as the ____ jaw as it recurred over multiple generations in European royalty and was recorded in many portraits.
Phillip II and Prince Ferdinand, 1575 (Titian).
Phillip IV, 1638 (Velasquez).
Charles IV and family, 1800 (Goya).
prognathism
hapsburg
Inherited characteristics as factors of malocclussion
Inherited disproportion between the size of the teeth and the size of the jaws, which would produce ____ or spacing.
Inherited disproportion between the size or shape of the upper and lower jaws, which would cause improper ____.
The more ____ these characteristics are determined, the more likely that disproportions could be inherited.
crowding
occlusal relationships
independently
Malocclusions in primitive and modern human populations
Primitive human populations are characterized by genetic ____ and uniformity.
Malocclusions in primitive human populations are less frequent than in ____ groups.
If everyone in a group carried the same genetic information for tooth size and jaw size, there would be no possibility of a child inheriting ____.
Different human groups have developed impressive ____ in facial proportions and jaw relationships.
What happens when there is outbreeding between
originally distinct human population groups?
isolation
modern
discordant characteristics
variations
In breeding experiments with dogs in the 1930s, Professor Stockard demonstrated that severe malocclusions could be developed by crossing ____ different breeds.
His analogy to human malocclusion was a powerful influence in the rejection of the prevailing belief of the 1920s that improper jaw function caused ____.
morphologically
malocclusion
In this 14-year-old girl with moderately severe achondroplasia, note the deficient ____, particularly at the bridge of the nose.
This results from decreased growth of cartilage in the ____, with a resulting lack of forward translation
of the ____.
midface
cranial base
maxilla
Investigations of Human Populations
The best data are from investigations carried out for human populations in ____ were by Chung et al.
Before its discovery by the European explorers of the eighteenth century, Hawaii had a homogeneous Polyneesian population.
Large scale migration to the islands resulted in an exceptionally heterogeneous modern population.
Tooth size, jaw size, and jaw proportions became ____ for the Hawaiian melting pot.
Therefore, if tooth and jaw characteristics were inherited independently, a high prevalence of severe ____ would be expected in this population.
hawaii
diverse
malocclusion
Investigations of Human Populations
The effects of interracial crosses appear to be more ____ than multiplicative.
About 10% of the Chinese who migrated to Hawaii had Class III malocclusion, whereas about 10% of the Polynesians had crowded teeth.
The offspring of this cross seem to have about a ____% prevalence of each characteristic, but there is no evidence of dramatic facial deformities like those seen in the crossbred dogs.
If malocclusion or a tendency to malocclusion is inherited, the mechanism is not the ____ of discrete morphologic characteristics like
tooth and jaw sizes.
additive
10
independent
Environmental influences during growth and development
____ relationships during the lifetime of an individual may be significant in the development of malocclusion.
If function could affect the growth of the jaws, altered function could be a major cause of malocclusion as well.
If function had no effect upon the individual’s pattern of development, altering his or her jaw function would have little if any impact upon the development or our ability to treat ____.
form-function
malocclusions
Equilibrium
The laws of physics state that an object subjected to unequal forces will be ____ and thereby will move to a different position in space.
If any object is subjected to a set of forces but remains in the same ____, any forces must be in balance or equilibrium.
From this perspective, the dentition is obviously in ____, since the teeth are subjected to a variety of forces but do not move to a new location under usual circumstances.
accelerated
position
equilibrium
Scarring of the corner of the mouth in this child will occur as the burn from biting an electrical cord heals.
From equilibrium theory, one would expect a distortion in the form of the ____ in the region of the contracting scar, and exactly this occurs after an injury of this type.
dental arch
In this individual, a large part of the cheek was lost because of a tropical infection.
Note the outward ____ of the teeth on the affected side after the ____ force of the cheek was lost.
splaying
restraining
After a paralytic stroke, this patient’s tongue rested against the mandibular posterior teeth.
Before the stroke, the occlusion was normal.
In this patient, an outward splaying of the teeth occurred on the affected side because of the increase in ____.
resting tongue pressure
The reaction of supporting structures of the dentition to forces
The ____ and alveolar bone are constructed to withstand heavy forces of short duration such as those from mastication.
During mastication, the fluid in the PDL space acts as a ____, so that the soft tissues in the PDL are not compressed although bending of alveolar bone occurs.
Only if pressure is maintained long enough to squeeze out the fluid (about ____) is there an impact on the soft tissues.
Persistent biting force creates ____ so the pressure is released and the fluid returns before the next chew
periodontal ligament
shock absorber
3 seconds
pain
Table 5-3
TAKE A LOOK YA BISH
Skeletal changes due to muscular forces
The bony processes to which muscles attach are especially influenced by the ____ and the location of the ____.
The form of the ____, because it is largely dictated by the shape of its functional processes, is particularly prone to alteration.
The ____ of the facial bones, like the skeleton as a whole, increases when heavy work is done and decreases in its absence.
muscles
attachments
mandible
density
Hypertrophy of the masseter muscles leads to excessive bone formation at the ____, as would be expected in a bony area that responds to muscle attachment.
Note the bony enlargement at the ____ angles, especially on the right side of the face.
angles of the mandible
gonial
Comparison of occlusal force for swallowing, simulated chewing, and maximum effort at 2.5 mm molar separation in normal face (blue) and long face (green) adults.
Note that the normal subjects have much greater ____ during swallowing and chewing as well as at maximum ____. The differences are highly ____ statistically. (From Proffit WR, Fields HW, Nixon WL. J Dent Res 62:566-571,1983.)
occlusal force
effort
significant
TAKE A LOOK AT THESE GRAPHS WITH TRANSCRIPTIONS, YA VIRG
YA
Values for both groups of children and the long-face adults are similar; values for normal adults are significantly higher than any of the other three groups.
Differences in occlusal force in adults result from failure of the ____ group to gain strength during adolescence, not to the long condition itself.
long-face
Occlusal relationships of a pair of identical twins.
A, this child sucked her ____ up to the time of orthodontic records at age 11 and the other did not.
B, her non-thumbsucking twin.
Note the increased ____ and forward ____ of the dentition of the thumbsucker.
thumb
overjet
displacement
Cephalometric tracings of the previous two girls superimposed on their cranial bases.
As one would expect with identical twins, the ____ morphology is nearly identical.
Note the forward displacement of not only the maxillary dentition but also the ____ itself.
cranial base
maxilla
A child sucking their thumb usually places it against the roof of the mouth, causing pressure that pushes the ____ lingually and the ____ labially.
lower incisors
upper incisors
In addition, the jaw is positioned ____, providing additional opportunity for ____ teeth to erupt, and cheek pressure is increased while the tongue is lowered vertically away from the maxillary posterior teeth, altering the equilibrium that controls ____ dimensions.
If the thumb is placed on one side instead of in the midline, the ____ of the arch may be affected.
downward
posterior
width
symmetry
Cephalometric tracing showing the effects of posterior eruption on the extent of anterior opening.
The only difference between the red and black tracings is that the first molars have been elongated ____ in the red tracing.
Note that the result is ____ of separation of the incisors
because of the geometry of the jaw
2mm
4mm
Diagrammatic representation of soft tissue pressures in the molar region in a child with a sucking habit.
As the tongue is lowered and the cheeks contract during sucking, the pressure balance against the upper teeth is altered, and the ____ but not the lower molars are displaced lingually.
upper
The typical appearance of a “tongue thrust swallow“ with the lip pulled back.
The term tongue thrust is a misnomer as it implies that the tongue is forcefully thrust forward.
Laboratory studies indicate that individuals who place the tongue tip ____ when they swallow frequently have ____, not higher tongue force against the teeth.
Note the tongue tip between the incisors protruding forward toward contact with the elevated lower lip.
forward
lower
This shows the prevalence of anterior open bite, thumbsucking, and tongue thrust swallowing as a function of age.
At every age above 6, the number of children reported to have a ____ is about 10 times greater than the number reported to have an anterior open bite. (Data from Fletcher SG, Casteel RL, Bradley DP. J Speech Hear Disord 26:201-208, 1961; Kelly JE, et al. DHEW Pub No
[HRA] 77-144, 1977.)
tongue thrust swallow
There is no reason to believe that a tongue thrust swallow always implies an ____ and will lead to malocclusion.
In a child who has an open bite, tongue posture may be a factor, but the ____ itself is not.
Open bite occurs much more frequently in ____ than in whites.
altered rest position
swallow
blacks
The classic “adenoid facies,” characterized by narrow ____ dimensions, ____ teeth, and lips separated at ____, has often been attributed to ____.
width
protruding
rest
mouth breathing
Assessing Mouth Breathing
Since it is perfectly possible to breathe through the nose with the lips separated, simply by creating an oral seal posteriorly with the soft palate, the ____ is not diagnostic of the respiratory mode.
On careful study, many patients with this facial type are found not to be obligatory ____.
facial appearance
mouth breathers
Data from an experiment with dental students, showing the immediate change in head posture when the ____ are totally blocked: the head tips back about 5 degrees, increasing the separation of the ____.
When the obstruction is relieved, head posture returns to its original position.
nostrils
jaws
Cephalometric superimposition showing the effect of total nasal obstruction produced by a ____ (for ____ speech) that sealed off the nose posteriorly.
From age 12 (black) to 16 (red), the mandible rotated ____ and ____ as the patient experienced considerable growth.
pharyngeal flap operation
cleft palate
downward
backward
Comparison of the percentage of nasal respiration in long-face versus normal-face adolescents.
About one-third of the long-face group have less than ____% nasal respiration, whereas none of the normal-face group have such a low nasal percentage, but most of the long-face group are predominantly ____ breathers.
50
nasal
The data suggest that impaired nasal respiration may contribute to the development of the ____ condition
but is not the sole or even the ____ cause.
long-face
major
- Composite (mean) cephalometric tracings for a group of Swedish children requiring adenoidectomy for medical purposes, compared with a group of normal controls.
- The adenoidectomy group had statistically significantly greater ____ height and steeper ____ angles than the controls, but the differences were quantitatively not ____.
anterior face
mandibular plane
large
Comparison of mandibular plane angles in a group of postadenoidectomy children compared with normal controls.
Note that the differences existing at the time of adenoidectomy decreased in ____ but did not totally
____.
size
disappear
