Growth/development Exam 1

Front 1

Describe ideal occlusion in terms of the relationship of the teeth to the line of occlusion.

Back 1

The line of occlusion is a smooth (catenary) curve passing through the central fossa of each upper molar and across the cingulum of the upper canine and incisor teeth. The same line runs along the buccal cusps and incisal edges of the lower teeth, thus specifying the occlusal as well as inter arch relationships once the molar position is established.

Front 2

Describe ideal occlusion in terms of the occlusal relationship of the teeth in all three planes of space (transverse, antero-posterior and vertical).

Back 2

Cusp to fossa or Cusp to marginal ridge occlusal contact areas on all teeth.
A-P
Mesial buccal cusp of Max First molar occluding in buccal groove of Mand first molar. Occlusal table oriented along a curve of spee.
Transverse
Fossa/cusps follow smooth arch of line of occlusion. Occlusal table oriented along a curve of Wilson
Vertical
Marginal ridges of equal height to adjacent teeth.

Front 3

List the dental characteristics on which the Angle classification is based.

Back 3

Max first molars - key to occlusion because of position at base of zygomatic arch. Max first molar Mesiobuccal cusp should occlude in buccal groove of mand first molar. Teeth well aligned in smooth curve.
Line of occlusion passes through central fossae of the max posterior and cingulum of anteriors. Also buccal cusps of mand posterior and incisal edges of anterior.

Front 4

Discuss the advantages of the Angle system for classification.

Back 4

1. Subdivided major types of malocclusion providing the first useful classification system.
2. Clear and simple description of normal occlusion and maloclusion.

Front 5

Describe the functional, health and psychosocial reasons for orthodontic treatment, and place them in perspective in terms of their relative importance.

Back 5

1. Discrimination because of facial appearance
- Social handicap affecting self image and self esteem.
- Society judges based on appearance
- Front teeth stick out, intellectually challenged
- Deficient midface and long jaw, witch
- Tall, skinny, long faced man, no education or social skills
- Seek Tx to remove or lessen a psychosocial handicap
- Major deformities easier to cope with than minor. Unpredictable social responses create anxiety and greatly impact self image.
2. Problems with oral function, jaw movement, mastication, speech, or swallowing
- Very weak relationship of malocclusion and TMD, more related to stress.
- Swallowing and speech, very rare.
- Bottom line: not a major reason of tx, can help some but not for most.
3. Greater susceptibility to trauma, periodontal disease or tooth decay.
- Class II (protruding upper incisors and excess overjet) increases risk for trauma. But usually just minor chips in enamel.
- Extreme overbite can lead to soft tissue damage and is an indication for tx.
- No evidence supports increased risk for caries or periodontal disease due to malocclusion or alignment

Front 6

Describe realistic goals for orthodontic treatment, and indicate the way they have changed as modern dentistry developed.

Back 6

Modern Goal - Achieve correct relationships of oral and facial soft tissues, then establish ideal jaw and teeth relationships.

Early history efforts were directed to aligning irregular or crowded teeth attempting to improve the appearance of teeth and face.
As prosthetic devices were invented (1800s) focus shifted to occlusion, with the establishment of angles classification. View was that if dental occlusion was correct, dental and facial esthetics also would be ideal.
Cephalometric radiology established malocclusion was skeletal not malposed teeth. Therefore with soft tissue matrix theory, achieving correct oral and facial soft tissues would result in proper facial and dental esthetics where jaws and teeth could then be aligned into correct occlusion.

Front 7

Discuss how need for orthodontic treatment compares with demand in the U.S. at present and how demand is likely to change in the near future.

Back 7

Orthodontists estimate that 1/3 of the patients they see have normal occlusion and that 55% require some level of Tx. IOTN data suggest that roughly 60% of adolescents exhibit tx need. The demand for tx is based in large part on family income.
1. Can more easily afford tx
2. Dental/Facial appearance is important for more prestigious social positions and better paying occupations. Higher aspirations for child lead parents to seek tx.

Its also becoming more socially acceptable for an adult to have braces.

As financial needs are met, with with increased household income or programs like medicaid funding, the percentage seeking treatment will approach 35% of the population. This is the level of need recognized by parents in which adolescents need treatment.

Front 8

Describe known causes of malocclusion in terms of major categories, and put the known causes in perspective relative to the total number of patients with malocclusion.

Back 8

1. Hereditary factors
- Idea that jaw and tooth size is heritable is not true. Hawaii is the most heterogeneous population and there is no elevated malocclusion because of this.
- Cross breeding of dogs demonstrated dominance traits of achondroplasia gene and not genes for occlusion.
- Skeletal and dental characteristics can be heritable. Demonstrated by Hapsburgs Royal family, very prominent chins.
- 2 opposing views. Lundstrom estimates 50% of malocclusion is hereditary factors while Corrucini and Potter estimate 0%.
- Data suggest 50% might be maximum. Bottom line, skeletal malocclusion seems influenced by heredity than dental, more likely to inherit large jaws than crooked teeth.
2. Interference with normal development
- Fetal Alcohol Syndrome (FAS)
- Hemifacial microsomia
- Intrauterine molding (Pierre Robin)
- Embryologic development disturbances are isolated and do not contribute much to population malocclusion. However, dental defects frequently occur.
- Supernumerary, congenitally missing, distorted tooth form.
3. Trauma
- Functional matrix theory. Degree of distortion is determined by extent of soft tissue damage and healing.
- Soft tissue more important than hard tissue, exhibited by tractor boy. Broke all bones in skull, no damage to soft tissue, 100% recovery.
- Fractured Condyle, 75% recover, 25% do not because of soft tissue damage.
- Electrical burns cause loss/scaring of facial tissue and result in malocclusion.
- Tooth loss causing drifting of remaining teeth.
- PDL damage can cause dilacerations.
4. Disturbance in normal function
- Thumb sucking. Causes outward rotation of incisors and hypereruption of posterior teeth. Results in overjet and increased vertical height causing open bite.
- Mouth breathing. "adenoid faces" partial blocking of nasal airway causes patient to mouthbreath. Changes equilibrium pressures resulting in hypereruption of posterior teeth, open bite and long face.
- Tongue thrusting. Not a cause but more of an adaption to tooth position.

Front 9

Indicate the two types of malocclusion most likely to be due to inherited jaw proportions, and describe the evidence to support your categorization.

Back 9

Class III malocclusion. Demonstrated by Hapsburg, had very prominent mandibular prognathism. Study determined that 1/3 of children that presented with CL III had a parent or sibling with same problem. Twin studies resulted in a 0-50% estimate that heritable jaw sizes were the cause of malocclusion.

Long Face - per an old exam, but couldnt find the supporting data.

Front 10

Indicate the mechanism by which trauma to the mandible can affect its future growth.

Back 10

Based on soft tissue matrix theory. If soft tissue surrounding mandible is affected, future growth of mandible is compromised and deformities occur. Fracture of condyle head, 25% is mal deformed.

Front 11

Identify the magnitude of force needed to cause movement of a tooth, and relate this to the observed threshold for tooth movement.

Back 11

Almost any force above 0 gms has the ability to cause tooth movement if its applied over a long enough duration. However, the force threshold required for tooth movement is around 5 gms. Teeth are under constant loading in various directions resulting in an equilibrium environment. In order for tooth movement to occur, the applied force must be great enough to overcome the equilibrium forces and that threshold is around 5 gms. So while almost any magnitude force has the potential for movement, only a force above the equilibrium threshold will actually cause tooth movement.

Front 12

Identify the duration of force needed to cause movement of a tooth, and relate this to the impact of habits like thumb sucking on the dentition.

Back 12

The duration of force must be greater than 4 hours a day to cause tooth movement. Habits, such as thumb sucking, must occur more than a duration of 4 hours per day in order to have an affect on dental occlusion. Meaning an intense thumb sucker of short duration will show little or no effect and a light thumb sucker of long duration (over 4 hours) will demonstrate malocclusion.

Front 13

Describe the maturation of oral function from infancy to adult life, with particular emphasis on the pattern of swallow.

Back 13

- Principal physiologic functions of the oral cavity are respiration, swallowing, mastication and speech. At birth, infants are obligatory nose breathers and the mandible must be moved downward/forward to create air space through the pharynx. Suckling and swallowing is the infants next priority. The infantile swallow is a sequence of events characterized by contractions of the lips, tongue brought forward touching the lower lip, and little activity of posterior tongue or pharyngeal muscles. The infantile swallow disappears around 1 year of life when the infant switches food consistency which requires more complex tongue motions to position food for swallowing. Mastication then is apparent in children approximately 1 year old. Chewing cycle occurs by first moving laterally then back to midline. When primary molars erupt through canine eruption this cycle is transition to the adult cycle by first opening downward then moving lateral and back into occlusion.
- Maturation typically occurs anterior to posterior. When suckling stops the swallow cycle changes to a more adult swallow which is characterized by cessation of lip activity, placement of tongue to the lingual alveolar process of max incisors, and posterior teeth brought into occlusion.

Front 14

Discuss myofunctional therapy for tongue thrusting as a potential therapy for anterior open bite in children, with emphasis on its underlying assumptions and their validity.

Back 14

Tongue thrusting is viewed as an adaptation to on open bite rather than the cause of malocclusion. A person swallows approx 1000 times each day with a sustained duration during swallow of around 1 sec. therefore the total duration of force is only a couple minutes which would not cause orthodontic movement. Therefore, by performing myofunctional therapy for tongue thrusting would not have a clinical impact for anterior open bite as it would not affect the equilibrium forces which are causing the anterior open bit to occur.

Front 15

Describe the possible role of nasal obstruction in the etiology of malocclusion, and indicate the probable mechanism by which it would have an effect.

Back 15

Respiratory control is the primary determinant of the posture of the jaws and tongue. The location of these two structures can, and does, have an effect on the equilibrium forces affecting the dental occlusion. Nasal breathing requires more effort than mouth breathing, but at physiological rest nasal breathing supplies the demands for most individuals. If a nasal obstruction were to occur, the individual would shift to a mouth breathing posture with a lowered mandible and tongue. If sustained over long enough duration, equilibrium forces would be affected causing face height increases and hypereruption of posterior teeth. The vertical growth of the ramus of the mandible would cause a downward and backward rotation of the mandible resulting in anterior open bite and increasing openjet. The open mouth would cause the cheeks to stretch tighter against the teeth causing a narrower dental arch.