Quartz 4

Unit Self-Test

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Level III Biomechanics — Unit A Self-Test

Module 1: Essentials of Orthodontic Diagnosis

Question 1

Which of the following must be evaluated during orthodontic diagnosis?

a. Dental alignment

b. Dental occlusion

c. Facial proportions

d. Patient attitude toward dental condition

  1. a and b
  2. a and c
  3. a, b, and c
  4. a, b, and d
  5. all of the above ✓

Correct

That’s right, all must be evaluated. Whether dental alignment and occlusion and/or facial proportions are a problem depends to a considerable extent on whether the patient thinks they are a problem. Some patients tolerate conditions that are not tolerable for others—a fact that is recognized in problem-oriented diagnosis. One way to look at it is that if the patient thinks he or she has a problem related to the dentition and facial proportions, that is a reason for an orthodontic diagnostic evaluation.

Question 2

At what point in orthodontic diagnosis is the process of classification used?

  1. As soon as problems are detected, typically during the interview
  2. In clinical examination, when the occlusion is evaluated
  3. When diagnostic records are ordered
  4. After the database is completed ✓

Correct

That’s right, classification (systematic description) is used to organize the information collected in the database after the interview and clinical examination have been completed and diagnostic records have been ordered and analyzed. The goal of modern classification is to obtain a list of the patient’s problems, taking everything into account. The classic Angle classification of malocclusion, therefore, is just one aspect of the larger process.

Question 3

Which of the following are appropriate questions to be answered in the interview part of an orthodontic diagnostic evaluation?

a. Why are you seeking treatment, and why now?

b. How did things get to be the way they are now?

c. What is likely to change in the near future?

d. What do you (your parents) expect as a result of treatment?

  1. a and b
  2. b and c
  3. c and d
  4. a, b, and d
  5. all of the above ✓

Correct

That’s right, all these questions need to be answered during an orthodontic diagnostic evaluation. It’s important to know why the patient is seeking treatment, how things came to be as they are from the perspective of both medical/dental history and etiology, what is likely to change from the perspective of both pathology and growth, and what the patient expects as a result of treatment.

Question 4

Which of the following are not goals of the clinical examination in an orthodontic diagnostic evaluation?

a. Evaluation of the alignment of the teeth b. Evaluation of the dental occlusion c. Evaluation of gingival/periodontal health d. Evaluation of TM joint function

  1. a and b ✓
  2. b and c
  3. c and d
  4. c only
  5. none of the above

Correct

That’s right. The dental alignment and occlusion can be evaluated better from the diagnostic records, so the clinical examination does not focus on these characteristics. Its goals are to evaluate facial proportions and tooth-lip relationships, the health of oral hard and soft tissues, and jaw function, and to determine what diagnostic records are needed, so the last two items are important goals of the clinical examination.

Question 5

Which of the following is it important to look for in the frontal examination of the face?

a. Symmetry

b. Vertical facial proportions

c. Tooth-lip relationships

d. Lip protrusion

  1. a and b
  2. b and c
  3. a, b, and c ✓
  4. a, c, and d
  5. all of the above

Correct

That’s correct. Lip protrusion is better evaluated from the profile than the frontal view, so it is not included as a major goal of the frontal examination, whereas the other characteristics are examined in the frontal view. In the clinical examination, it is particularly important to examine tooth-lip relationships on smile and at rest, because these are difficult to capture completely in the diagnostic records.

Question 6

On orthodontic clinical examination, what is the most important single indicator of whether TM joint function is within normal limits?

  1. Extent of maximal opening ✓
  2. Deviation on maximal opening
  3. Limited lateral excursion
  4. Limited protrusive movement
  5. TM joint sounds on opening

Correct

That’s right, all these characteristics could indicate a potential problem with the TM joint, but the most important single indicator of TM joint function is the extent of maximal opening. If any of the other findings like deviation on opening were present, the extent of maximal opening almost surely would be affected, so limited opening indicates particular care in examining other aspects of TM joint function.

Question 7

Which of the following diagnostic records is least likely to be included in an orthodontic diagnostic evaluation?

  1. Panoramic radiograph
  2. Bitewing radiographs
  3. Lateral cephalometric radiograph
  4. P-A cephalometric radiograph ✓
  5. Facial photographs

Correct

That’s correct. The primary indication for a P-A cephalometric radiograph is clinically apparent facial asymmetry, which is relatively rare. The other records are taken routinely except for bitewing radiographs, which are included if there is clinical evidence of caries or if restorations are present. Bitewings are more likely to be needed than a P-A ceph.

Question 8

Which of the following are important aspects of dental cast analysis?

a. Space analysis

b. Dental arch symmetry

c. Palatal width evaluation

d. Dental protrusion

  1. a and b
  2. b and c
  3. a, b, and c ✓
  4. a, c, and d
  5. all of the above

Correct

That’s right, dental protrusion cannot be evaluated from the dental casts and is not part of cast analysis, but space analysis, dental arch symmetry, and palatal width evaluation all are parts of cast analysis. The width of the palate is a skeletal dimension that can be seen on the dental casts, and if a posterior crossbite is present, it is particularly important to check whether the palate is narrow or whether the alveolar processes are tipped lingually.

Question 9

On inspection of a cephalometric tracing, which of the following would indicate the prominence of the upper incisors?

a. Point A relative to N vertical line

b. Upper incisor relative to N vertical line

c. Inclination of upper incisor relative to SN

d. ANB angle

  1. a only
  2. b only ✓
  3. a and b
  4. a, b, and c
  5. all of the above

Correct

That’s right, the prominence of the upper incisor would be indicated by its position relative to a true vertical line dropped from nasion, but not by the other measurements. The inclination of the upper incisor to SN can be suggestive of incisor prominence, but the incisor can be tipped without being protrusive, so its inclination is only part of the picture. What counts is how far forward the incisal edge is. The position of point A relative to that line indicates the position of the maxilla, and the ANB angle indicates the relative position of the jaws—neither indicate tooth position.

Question 10

Which of the following is not one of the five steps in systematic description of orthodontic problems?

  1. Patient’s reaction to the dental condition ✓
  2. Dental alignment/symmetry
  3. Dental protrusion/facial esthetics
  4. Transverse/posterior crossbite relationships
  5. Vertical/open-deep bite relationships

Correct

That’s right, the patient’s reaction to the dental condition is important in helping establish the need for treatment of orthodontic problems, but it is not part of systematic description. The other items are part of this 5-step process. Experience has shown that this grouping of problems makes it easier to keep up with the treatment possibilities for patients with severe problems—and the same diagnostic method is applicable to all potential orthodontic patients, however simple or complex their problems may be.

Question 11

Which of the following are examined to evaluate the impact on facial esthetics of tooth and jaw positions?

a. Interview data

b. Clinical examination notes

c. Photographs

d. Cephalometric radiograph

  1. a, b, and c
  2. a, b, and d
  3. b, c, and d ✓
  4. all of the above
  5. none of the above, done in clinic

Correct

That’s right, clinical examination notes, photographs, and the cephalometric radiograph all are used to evaluate esthetic considerations—but interview data as to what the patient thinks are used later, not in this objective part of the evaluation.

Question 12

Which of the following would be noted during the last step in systematic description?

a. Anterior open bite

b. Posterior open bite

c. Deep bite

d. Mandibular asymmetry

  1. a, b, and c ✓
  2. a, b, and d
  3. b, c, and d
  4. all of the above
  5. none of the above, done in clinic

Correct

That’s right, the last step in systematic description is to evaluate vertical dental and skeletal relationships, using the dental casts, photographs, and lateral cephalometric radiograph. So open bite/deep bite are examined at this stage—but asymmetry is examined earlier, because it primarily affects the transverse plane of space.

Question 13

Which of the following uses of cone-beam CT requires a large field of view?

  1. Analysis of skeletal asymmetry ✓
  2. Locating an impacted tooth
  3. Evaluation of an edentulous site to be restored with an implant
  4. 1 and 3
  5. 1 and 2

Correct

That’s correct. Analysis of skeletal asymmetry is a major indication for the use of CBCT in orthodontics and requires a field of view large enough to capture all of the craniofacial skeletal units. While CBCT is indicated for the localization of impacted teeth and implant planning, only a field of view large enough to visualize the teeth or site in question is needed.

Question 14

In examination of patients with temporomandibular pain and dysfunction (TMD), which of the following are advantages of MRI over cone-beam CT?

a. lower radiation dose b. no radiation dose c. better visualization of condyle and glenoid fossa d. better visualization of TM disk e. better visualization of cranial base

  1. all the above
  2. b, c, and d
  3. a, d, and e
  4. a and c
  5. b and d ✓

Correct

That’s right, MRI has no radiation dose and provides much better visualization of soft tissues, so both of those characteristics are better than CBCT in determining the extent of soft tissue problems (like a displaced disk) in patients with TMD. But it gives inferior views of hard tissues like the mandibular condyle and the glenoid fossa, and it costs more.

Module 2: Concepts of Orthodontic Treatment Planning

Question 1

Which of the following must be taken into account in planning orthodontic treatment?

a. Dental alignment

b. Dental occlusion

c. Facial proportions

d. Patient attitude toward dental condition

  1. a and b
  2. a and c
  3. a, b, and c
  4. a, b, and d
  5. all of the above ✓

Correct

That’s right, all must be evaluated during the diagnostic evaluation that must precede treatment planning. The first step in planning treatment is to place the items on the problem list in priority order. To do that, it is necessary to take the patient’s attitudes into consideration.

Question 2

(A) Diagnosis is a scientific procedure, while treatment planning cannot be because (B) the goal of treatment planning is truth, not wisdom.

  1. A true, B true, A and B related
  2. A true, B true, A and B not related
  3. A true, B false ✓
  4. A false, B true
  5. A and B false

Correct

That’s correct, the first statement is true, but the second is false. The goal of treatment planning is wisdom, which requires judgment. Diagnosis is a matter of gathering the facts—its goal is truth, so it is a scientific procedure, but treatment planning cannot be.

Question 3

(A) Pathologic problems are separated from developmental problems and given priority for treatment because (B) pathologic problems are inherently different from developmental problems.

  1. A true, B true, A and B related
  2. A true, B true, A and B not related ✓
  3. A true, B false
  4. A false, B true
  5. A and B false

Correct

That’s right, both statements are true, but they are not related, i.e., the second statement isn’t the reason for separating out pathologic problems. Pathologic problems receive priority for treatment, not because they are inherently different (although that’s true) but because they must be brought under control to protect the patient’s health during treatment of the developmental problems.

Question 4

(A) Prioritizing the orthodontic problem list is a critically important step in treatment planning because (B) the same problem list prioritized differently will produce a different plan.

  1. A true, B true, A and B related ✓
  2. A true, B true, A and B not related
  3. A true, B false
  4. A false, B true
  5. A and B false

Correct

That’s right, these statements are true and related. If you don’t prioritize the problem list correctly, you won’t end up with the correct treatment plan for that patient. A key to informed consent in planning treatment is to be sure that the patient agrees with the prioritization of the problem list. Informed consent problems are particularly likely to arise when the doctor places the emphasis on a problem that was not a high-priority item to the patient and failed to correct something that was important to the patient.

Question 5

Which of the following are “practical considerations” to be reviewed as treatment possibilities are evaluated?

a. Compromises related to treatment priorities

b. Interactions among the treatment possibilities

c. Relative cost of treatment possibilities

d. The amount of patient cooperation necessary

  1. a and b
  2. b and c
  3. c and d
  4. a, b, and c
  5. all of the above ✓

Correct

That’s right, all these are important practical considerations, and all must be reviewed as treatment possibilities are evaluated. Compromises, interactions, and costs always must be considered. Remember that cooperation is part of the “burden of treatment” that is also a cost consideration.

Question 6

Which of the following are not appropriate in the consultation appointment for a 14-year-old?

a. Presentation to the parents only

b. Review of computer-generated image predictions

c. Recommendation of implants as immediate replacements for missing premolars

d. Questions as to what the family want as a result of treatment

  1. a and b
  2. b and c
  3. a and c ✓
  4. b and d
  5. none of the above

Correct

That’s right, it’s an error to leave a 14-year-old out of the consultation appointment, and implants should not be placed for at least another 4-5 years, so both are inappropriate. It’s highly appropriate to review computer image predictions of alternative treatment approaches if these are available and important to be sure what the patient and parents want as a result of treatment.

Question 7

What is the chance that a severely delayed premolar will eventually complete its root formation and erupt normally?

  1. 5-10% ✓
  2. 20-25%
  3. 50%
  4. 60-75%
  5. Impossible to predict, could be anything

Correct

That’s right. It is possible (but quite unlikely) that a severely delayed premolar will eventually complete normal root formation and erupt into the correct position. It is rarely good treatment planning to wait for years to see what such a tooth will eventually do, because the chance of a good outcome is so low.

Question 8

Which of the following are advantages of orthodontic treatment to close the space of a congenitally missing tooth?

a. Short-term prosthodontic cost avoided

b. Long-term prosthodontic cost avoided

c. Better facial esthetics

d. Treatment completed at an earlier age

  1. a, b, and c
  2. b, c, and d
  3. a, b, and d ✓
  4. all of the above

Correct

That’s correct. Closing the space avoids both short- and long-term prosthodontic costs, and the treatment is completed at an earlier age because it is not necessary to wait until vertical growth is completed—but space closure must be done very carefully to keep from making facial esthetics worse and is unlikely to make the facial appearance better. Closing spaces bilaterally tends to retract the incisors and decrease lip support. Closing a unilateral space tends to create an asymmetry within the arch and a midline discrepancy. Both can affect facial esthetics unfavorably unless the treatment is done very carefully.

Question 9

When lower molars are moved mesially to close the space of missing second premolars, what is the effect on the maxillary second molars? These teeth

  1. must also be moved mesially.
  2. tend to extrude. ✓
  3. usually end up in lingual crossbite.
  4. often end up in a Class II relationship.
  5. no effect, they’re in the other dental arch.

Correct

That’s right, when lower molars are moved mesially, the upper second molars can’t go with them (unless a space has been created in the upper arch), and they tend to extrude because they do not have an occlusal antagonist until the mandibular third molars erupt. For this reason, a retainer to control their vertical position is important after the type of space closure used in Anna’s case. What’s wrong with the other answers? Extracting teeth in the upper arch to allow the upper molars to be moved mesially rarely is indicated, the 2nd molars do not move lingually, and the eventual molar relationship is Class III, not Class II.

Question 10

Which of the following is not a goal of establishing a problem list with the problems placed in priority order?

  1. Improve the chances of obtaining true informed consent
  2. Facilitate treatment planning
  3. Improve communication with other dentists
  4. Increase the chance of insurance coverage for the necessary treatment ✓

Correct

That’s right, insurance companies are unlikely to base a decision as to coverage on whether a systematic approach to diagnosis and treatment planning was used, so that really isn’t a goal—but the other items certainly are.

Question 11

Which of the following are important to discuss at the planning conference with the patient and parents?

a. Consequences of no treatment

b. Alternative treatment approaches

c. Cost of alternatives

d. Chance that treatment will fail

  1. a and b
  2. b and c
  3. a, b, and c
  4. b, c, and d
  5. all of the above ✓

Correct

That’s right, all of these things should be discussed at the planning conference. Doing nothing is always an alternative to treatment, and the patient should be informed as to the consequences of that choice as well as being told about the alternative treatment approaches and their cost-effectiveness.

Question 12

For a patient with congenitally missing teeth for whom space is to be closed, which of the following is the greatest advantage of doing it during the late mixed or early permanent dentition, as compared to doing it in the early mixed dentition?

  1. Restorations can be placed at the ideal time
  2. Jaw growth can be modified best at that time
  3. Cooperation with treatment is best then
  4. Second molars become available for additional anchorage
  5. Growth tends to end as treatment does, making retention easier ✓

Correct

That’s right, if treatment starts in the late mixed or early permanent dentition, it usually ends about the time the adolescent growth spurt ends, and that makes retention easier and more successful. It is difficult to maintain the correction of a malocclusion if orthodontic appliances are removed before most adolescent growth has been completed, even if there was not a major skeletal problem initially.

Question 13

Which of the following are different for the treatment plan concept and the treatment plan details?

a. Extent to which it is shared with the patient

b. Specifics of treatment procedures

c. Treatment methods used by various doctors

d. Language used

  1. a and b
  2. b and c
  3. a, b, and c
  4. b, c, and d
  5. all of the above ✓

Correct

That’s right, all of these are different for the treatment plan concepts and details. The concept is in broad terms that the patient can understand, and its language reflects that. The details specify which doctor is to do what, when, and how, and are accessible in the chart to guide clinical activity.

Module 3: Biologic Response to Orthodontic Force

Question 1

Which of the following is not correct regarding piezo-electricity?

  1. important for maintaining calcification
  2. affected by exercise level
  3. important for orthodontic signaling ✓
  4. occurs in both biologic and non-biologic crystals
  5. all are correct

Correct

That’s right. Piezo-electricity is important for maintaining calcification, it’s affected by exercise level because it’s generated by bone bending during function, and it occurs in both biologic and non-biologic crystalline materials—but it is not important for orthodontic signaling.

Question 2

Why is some shortening of tooth roots likely to occur after prolonged orthodontic treatment?

  1. it isn’t, osteoclasts don’t attack cementum
  2. cementum repair only occurs along the sides of the tooth, not at the apex
  3. craters in cementum fill in, but cementum islands are cut off and lost ✓
  4. unstained and therefore unprotected cementum is found mostly at the root apex
  5. poor blood supply around the apex prevents cementum repair in that area

Correct

That’s right, stained or marked cementum adjacent to necrotic areas is likely to be found around the apex of the tooth because it is easy to severely compress the PDL in that area. This leads to attack by clast cells during repair, and if the resulting craters coalesce, cementum islands that resorb during repair may be formed.

Question 3

Force against a tooth creates pressure in the periodontal ligament. If an equal force is used for the following types of tooth movement, which will have the lightest pressure?

  1. intrusion
  2. tipping
  3. rotation
  4. torque
  5. translation ✓

Correct

That’s right, with equal amounts of force against the crown, translation (bodily movement) would produce the lightest pressure because the force is distributed over the largest PDL area, and intrusion would have the highest pressure because the force is concentrated on a small area.

Question 4

What’s the first thing that happens when an orthodontic spring is applied against a tooth?

  1. the tooth moves relative to the facial skeleton ✓
  2. the tooth moves within the periodontal ligament space
  3. distorted cells release prostaglandins and cytokines
  4. blood flow decreases in some areas and increases in others
  5. it depends on how much force the spring exerts, could be 1 or 2

Correct

That’s correct, the tooth moves relative to the facial skeleton as the alveolar bone bends, but it doesn’t move within the PDL space until 1-2 seconds pass and the bone begins to spring back as fluid is squeezed out. Cell distortion and blood flow changes all start a minute or two after that.

Question 5

What’s the chance that severe shortening of the maxillary incisors (>25% of the root length) will occur during typical orthodontic treatment?

  1. less than 0.5%
  2. 1%
  3. 2-3% ✓
  4. 4-5%
  5. 10%

Correct

That is correct. The best data suggest that there is a 2-3% chance of severe resorption, with the maxillary incisors most likely to be affected, during typical treatment (which has about a 2-year duration). Fortunately, even when this occurs the chance of premature loss of the affected teeth remains very low.

Question 6

What is the chance that severe generalized resorption (loss of much of the root of most of the teeth) will occur during typical orthodontic treatment?

  1. less than 0.5% ✓
  2. 1%
  3. 2-3%
  4. 4-5%
  5. 10%

Correct

That’s right, severe generalized resorption is quite rare, with a prevalence of much less than 0.5%. It is as likely to occur in patients who don’t have orthodontic treatment as in those who do, so orthodontics isn’t the cause—but the cause remains unknown.

Question 7

What happens if orthodontic force is heavy enough to totally compress blood vessels in the PDL?

  1. hyaline cartilage forms in the compressed area
  2. sterile necrotic areas develop in the compressed area ✓
  3. sterile necrotic areas develop in the pulp
  4. persistent piezo-electric signals are observed
  5. all the above

Correct

That’s right. Sterile necrotic areas develop in the compressed area. These areas often are called hyalinized areas because some early observers thought they looked like hyaline cartilage, but cartilage doesn’t form there. Mild pulpitis can occur after activation of orthodontic appliances, but there are no necrotic areas in the pulp. Persistent piezo-electric signals are seen only during rhythmic function as bone bends, and have nothing to do with PDL compression.

Question 8

When orthodontic appliances are removed, why are retainers needed full-time for 3-4 months?

  1. PDL reorganization takes 3-4 months ✓
  2. most patients are still growing when treatment ends
  3. sometimes teeth have been moved into unstable positions
  4. teeth are particularly likely to move post-treatment as they erupt
  5. all the above

Correct

That’s right. All the response statements are reasons for retention, but only the first one is the reason for full-time retention for a few months after orthodontic treatment is completed. It takes 3-4 months for the PDL to reorganize, and for that length of time the teeth need to be held against soft tissue pressures that they may be able to withstand after the reorganization is comleted. Growing patients, or patients whose teeth are not in stable positions, need long-term retention but can wear retainers only part-time.

Question 9

How many hours a day do you have to wear your removable orthodontic appliance in order to gain any treatment effect?

  1. no minimum, every little bit helps
  2. at least 2 consecutive hours
  3. at least 3-4 hours
  4. at least 4-8 hours ✓
  5. at least 10-12 hours

Correct

That’s right, there is a time threshold somewhere between 4-8 hours. If you wear your removable appliance that much, some treatment response will occur (although if you wore it more there would be a better response). Less than 4 hours is likely to produce no response.

Question 10

What’s the optimal force in grams to intrude a tooth?

  1. approximately 10 ✓
  2. approximately 20
  3. approximately 50
  4. approximately 75
  5. approximately 100

Correct

That’s right, 10 grams (or even a bit less for a small tooth like a lower incisor) is the optimal force for intrusion. The reason, of course, is the small PDL area that’s compressed by an intrusive force.

Question 11

How long does it take to generate chemical signals (for example, prostaglandin release) when steady orthodontic pressure is applied against a tooth?

  1. a minute or so ✓
  2. 5-10 minutes
  3. an hour or so
  4. about 4 hours
  5. could be any of the first three, depending on force magnitude

Correct

That’s right. Chemical signals begin to be generated almost immediately after fluid is squeezed out of the PDL space and the ligament is compressed, because mechanically distorted cells release some of their contents. Within one minute the process is well underway. It takes about 4 hours to begin to see evidence of secondary messengers that will lead to cell differentiation, but release of signals started long before that.

Question 12

(A) Intermittent force from a fixed orthodontic appliance is inevitable because (B) there is no such thing as a perfect spring—they all have some decay of the force as teeth move.

  1. A true, B true, A and B related
  2. A true, B true, A and B not related
  3. A true, B false
  4. A false, B true ✓
  5. A and B false

Correct

That’s right, the first statement is false but the second one is true. Decay of the force is reflected in whether the force still can be considered continuous (doesn’t go to zero between appointments) or interrupted (decays to zero before reactivation). Intermittent force is seen with removable appliances, where the force goes to zero when the appliance is removed and resumes when it is reinserted.

Question 13

What is the optimal age to start facemask treatment for Class III correction?

  1. age 4 to 6
  2. age 6 to 8 ✓
  3. age 8 to 10
  4. age 10 to 12
  5. any age is OK prior to adolescence

Correct

That’s right, the optimal age to start facemask treatment is 6 to 8, because the amount of favorable skeletal change tends to decrease as children get older than that. It often is wise to wait until the maxillary first permanent molars erupt so they can become part of the anchorage unit, but there is no advantage in waiting longer than that—if the patient is seen in time to start then, which means that early referral for maxillary deficient children Is potentially important.

Question 14

What is the optimal age to start Class III elastics to skeletal anchors for Class III correction?

  1. age 4 to 6
  2. age 6 to 8
  3. age 8 to 10
  4. age 10 to 12 ✓
  5. any age is OK prior to adolescence

Correct

That’s right, the best age to begin treatment with Class III elastics to skeletal anchors is age 10 to 12, the earliest age at which the skeletal anchors can be expected to be stable. In younger children the bone is too immature and screws are too likely to be displaced. Of course maturation, not chronologic age, is the key determinant, so an average child probably would be a better candidate for this treatment at age 11 than 10. In less mature children, treatment starting as late as age 13 can be effective.

Module 4: Mechanical Principles in Controlling Orthodontic Force

Question 1

(A) Gold wires rarely are used in modern orthodontics because (B) the price of gold increased greatly in the second half of the 20th century.

  1. A true, B true, A and B related
  2. A true, B true, A and B not related ✓
  3. A true, B false
  4. A false, B true
  5. A and B false

Correct

You’re right, both statements are true but they aren’t related. The strength and spring qualities of stainless steel had led to the replacement of gold by steel wires even before the cost difference increased greatly. At any price, gold is no longer competitive as a material for orthodontic wires.

Question 2

Which of the following is the correct description of the elastic limit for an orthodontic arch wire? the point at which

  1. it deviates from totally elastic behavior
  2. it deviates at a measurable level ✓
  3. superelastic behavior is first noted
  4. it begins to fail
  5. it breaks

Correct

That’s right. Yield strength, measured in the laboratory as the lowest point on a stress-strain curve at which a measurable amount of permanent bending can be observed, typically is used to describe the elastic limit of the wire. The proportional limit is an alternative term, and sometimes elastic limit and proportional limit are used interchangeably.

Question 3

On a stress-strain curve, which of the following reflects the formability of a wire (the extent to which you can permanently deform it while bending it)?

  1. slope of the linear portion of the curve
  2. area under the linear portion of the curve
  3. distance along the stress axis (x axis) to the failure point
  4. area under the curve between ultimate strength and failure point
  5. area under the curve between yield strength and failure point ✓

Correct

That’s right, the area under the curve between yield strength (where permanent deformation starts, for all practical purposes) and failure point (where the wire breaks) describes the formability of the material.

Question 4

For a superelastic NiTi wire, what portion of a stress-strain graph represents the portion of the curve that contributes most of the force applied to a tooth?

  1. initial linear portion, loading
  2. initial plateau, loading
  3. second linear portion, unloading
  4. second plateau, unloading ✓
  5. final linear portion, unloading

Correct

That’s right. The superelastic plateau is the most important part of a graph that shows the force delivered to a tooth by a superelastic spring or section of an archwire—but it’s the lower of the two plateau curves, the unloading section of the curve.

Question 5

It’s quite effective to bend a helix in a finger spring to increase its length because (B) springiness goes up when you do this while range goes down.

  1. A true, B true, A and B related
  2. A true, B true, A and B not related
  3. A true, B false ✓
  4. A false, B true
  5. A and B false

Correct

That’s correct, the first statement is true but the second is false. Springiness goes up more than strength goes down when you lengthen the spring by bending a helix, and range also increases, not decreases.

Question 6

For any elastic material, what determines the smallest size of wire that you could use to form a finger spring? It’s inherent

  1. strength ✓
  2. springingess
  3. range
  4. resilience
  5. 1,2 and 3

Correct

That is correct. The strength of the material determines the smallest size of wire that you can use, because if it deforms permanently when you activate a spring made from it or the patient bites against it, it will be ineffective. Once you have a wire that’s strong enough, you can improve its spring properties by lengthening the beam—which of course is what is done in fabricating most finger springs.

Question 7

In 1920 gold was the preferred material for orthodontic appliances. Which of the following is most likely to be the preferred material in 2020?

  1. new precious metal alloys
  2. improved stainless steel
  3. titanium alloys
  4. chrome-cobalt alloys
  5. composite plastics ✓

Correct

That’s right. Already composite plastic materials offer better combinations of strength, springiness and range than metal alloys, and these new materials are being used to build the most advanced airplanes. Since orthodontic technology tends to follow aerospace technology by 10-15 years, it is highly likely that composite plastics will be the preferred material for orthodontic appliances in another decade or so.

Question 8

(A) When a single force is applied against the crown of a tooth, the center of resistance and center of rotation are the same because (B) the moment of the force is determined by the distance from the point of force application to the center of reistance.

  1. A true, B true, A and B related
  2. A true, B true, A and B not related ✓
  3. A true, B false
  4. A false, B true
  5. A and B false

Correct

That’s right. The two statements are both true, but they don’t have a cause-and-effect relationship. The center of resistance and center of rotation are the same because there is a moment of the force, not because of what determines its magnitude. The only way to keep a force from rotating the tooth around its center of resistance is to apply the moment of a couple to counteract the moment of the force.

Question 9

Which of the following is a correct ratio if you want to torque the root of an incisor lingually?

  1. M
  2. M
  3. M
  4. M ✓
  5. all could be correct, depends on location of center of resistance

Correct

That’s right, torque requires a MC / MF ratio greater than 1, so that the root moves more than the crown. The location of the center of resistance has nothing to do with it.

Question 10

How does the formability of a superelastic NiTi wire compare to the formability of a stainless steel wire? The formability of the NiTi wire is

  1. much greater
  2. a little greater
  3. about the same
  4. a little less
  5. much less ✓

Correct

That’s right, the formability of superelastic NiTi wire is much less than the formability of a stainless steel wire. It’s so much less that for all practical purposes, you can’t really change the shape of the wire that you purchased from the manufacturer—quite unlike steel wire that you can readily bend to make orthodontic springs.

Question 11

When a rectangular arch wire is used to torque a tooth, how does the force with which the wire contacts the walls of the bracket compare to the force felt by the PDL?

  1. much greater ✓
  2. a little greater
  3. about the same
  4. a little less
  5. much less

Correct

That’s right, the force with which the edges of the twisted wire contact the inner and outer surfaces of the bracket is much greater than the force felt by the periodontal ligament. The wire creates a couple within the bracket, and because the moment arm from one side of the wire to the other is quite small, the equal and opposite forces to form the couple have to be quite large.

Question 12

(A) The resistance to sliding a tooth along an arch wire increases when a wider bracket is used because (B) the wider bracket allows an arch wire to create a moment across it with less force on the corners of the bracket.

  1. A true, B true, A and B related
  2. A true, B true, A and B not related
  3. A true, B false
  4. A false, B true ✓
  5. A and B false

Correct

That’s right, the first statement is false but the second one is true. All other things being equal, resistance to sliding decreases, not increases, when a wider bracket is used. A wider bracket allows creation of a moment to control root position with less force against the bracket corners, because the moment arm is longer. It’s the force against the bracket corners that creates almost all of the resistance to sliding.

Question 13

Which of the following types of tooth movement require 2-point contact with the crown of the tooth being moved?

  1. tipping
  2. bodily movement
  3. torque
  4. 1 only
  5. 2 only
  6. 1 and 2
  7. 2 and 3 ✓
  8. all require 2-point contact

Correct

That’s right, tipping results from one-point contact, while bodily movement and torque require two-point contact. That means that tipping is the primary outcome of treatment with a removable appliance and finger springs, while bodily movement and torque all but require a fixed appliance.

Question 14

When clear aligners are used for orthodontic treatment, which types of tooth movement require bonded attachments?

  1. tipping
  2. rotation
  3. extrusion
  4. intrusion
  5. 1 and 2
  6. 1 and 3
  7. 2 and 3 ✓
  8. 2 and 4
  9. 1 and 4

Correct

That’s right. With clear aligners, rotation and extrusion are almost impossible without the use of a bonded attachment on the tooth so that the aligner can get a better grip on it. Interestingly, intrusion can be accomplished with an aligner without bonded attachments because light force is all that is needed. An aligner has enough grip to do that, and also to tip teeth.

Question 15

Which of the following are part of the prescription for a modern straight-wire bracket?

  1. specific type of tooth
  2. base thickness
  3. angulation of bracket slot
  4. facio-lingual orientation of bracket slot
  5. 1 and 2
  6. 3 and 4
  7. 1, 2, and 3
  8. 2, 3, and 4
  9. all ✓

Correct

That’s right, all four of these items are part of the prescription. The basic idea for the modern bracket is that it is intended for a specific type of tooth. The thickness of the base compensates for the varying thickness of teeth (particularly the incisors and canines), thereby reducing the need for in-out bends in arch wires. The angulation of the bracket slot reduces the need for bends to obtain proper mesio-distal root position, and the facio-lingual orientation of the slot provides torque as needed to control facio-lingual root position.

Question 16

Which of the following correctly describe active self-ligation for an orthodontic bracket? Springiness of a clip

  1. adds to springiness of the archwire
  2. makes the wire more resilient
  3. effectively makes the wire stronger
  4. 1 only ✓
  5. 1 and 2
  6. 2 and 3
  7. 1 and 3
  8. all the above

Correct

That’s right. Active self-ligation means that the clip that holds the wire in place is springy and adds to the springiness of the wire during initial alignment. The clip, however, doesn’t change the properties of the archwire. Resilience and strength of the wire are independent of how it’s held in a bracket.

Module 5: Orthodontic Anchorage and Controlled Tooth Movement

Question 1

Regarding heavy vs. light orthodontic force: which of the following statements are correct?

  1. heavy force tends to cause more pain
  2. heavy force tends to burn anchorage
  3. heavy force requires more effort to conserve anchorage
  4. 1 and 2
  5. 1 and 3
  6. 2 and 3
  7. none are correct
  8. all are correct ✓

Correct

That’s right, all these statements are correct. With heavy force, not only is there more pain, it is more difficult to control anchorage and anchorage is more likely to be lost.

Question 2

Which of the following are examples of reinforced anchorage in retraction of protruding incisors?

  1. adding 2nd molars to the posterior anchorage unit
  2. adding teeth from the other arch to the anchorage unit
  3. adding bone screws to anchorage unit
  4. allowing the incisors to tip distally while anchor teeth move bodily
  5. 1 and 3
  6. 2 and 4
  7. 1, 2, and 3 ✓
  8. 1, 2, and 4
  9. all the above

Correct

That’s right, the first 3 items are examples of reinforcement of anchorage, the fourth isn’t. Reinforcement can be done by adding more teeth in the same arch to the anchorage unit, by adding teeth in the other arch, or by adding temporary anchorage devices. Pitting tipping of the teeth to be moved against bodily movement of the anchor teeth is an example of stationary anchorage.

Question 3

(A) In orthodontics, the anchorage unit is what the dentist says it is because (B) the amount and distribution of pressure in the PDL that a tooth experiences is a critical variable in how it responds.

  1. A true, B true, A and B related
  2. A true, B true, A and B not related ✓
  3. A true, B false
  4. A false, B true
  5. A and B false

Correct

That’s right, both statements are true but there’s no cause-effect relationship between them. Orthodontic anchorage is defined by how the orthodontic appliance is set up, and the anchorage is what the dentist thinks it is as he connects one tooth or group of teeth to others. Whether the anchorage concept produces the desired tooth movement is determined by the way the teeth respond. In an important sense, you have to think rationally about anchorage as tooth movement is planned, because wishful thinking about the response of the teeth isn’t the way to get what you’d like to happen.

Question 4

With reciprocal anchorage for closing a maxillary midline diastema, what would be the effect on the speed of tooth movement if you increased the amount of force from 50 to 150 grams?

  1. much more rapid tooth movement
  2. more rapid tooth movement
  3. little or no effect ✓
  4. slower tooth movement
  5. much slower tooth movement

Correct

That’s right, in a reciprocal situation there would be little or no effect. Since each tooth (or group of teeth) is both an anchor and a movement tooth, they’d move toward each other at the same rate, almost independent of the force. The difference with heavier force would be much more in decreased patient comfort than speed of movement.

Question 5

(A) Heavy force in orthodontic treatment makes it difficult to control anchorage because (B) it compromises the anchorage value of all the teeth in the anchorage unit.

  1. A true, B true, A and B related ✓
  2. A true, B true, A and B not related
  3. A true, B false
  4. A false, B true
  5. A and B false

Correct

That’s correct, both statements are true and related. Heavy force compromises the anchorage value of all the teeth in the anchorage unit by moving them closer to the plateau in the force / response curve, where there is little differential tooth movement. Heavy force creates two problems: not only does it increase the amount of pain for the patient, it makes it more difficult to control anchorage.

Question 6

(A) Headgear is a particularly effective way to reinforce posterior anchorage because (B) it provides heavy interrupted force against the posterior teeth to which it is attached.

  1. A true, B true, A and B related
  2. A true, B true, A and B not related
  3. A true, B false
  4. A false, B true ✓
  5. A and B false

Correct

That’s correct, the first statement is false but the second one is true. Headgear is a rather poor way to reinforce posterior anchorage, because it provides interrupted rather than continuous force (it’s never worn all the time) and the force tends to be too heavy when it is present.

Question 7

Why is two-stage space closure more likely to be needed when teeth are pulled along an archwire with a spring than when a loop in the wire is used as a spring?

  1. anchorage control is more difficult
  2. with the loop, teeth tip into position
  3. sliding makes it possible to control force more precisely
  4. there’s no resistance to sliding with the loop
  5. 1 and 2
  6. 2 and 3
  7. 3 and 4
  8. 1 and 3
  9. 1 and 4 ✓

Correct

That’s right, when you pull a tooth or teeth along an archwire so that brackets on the teeth slide on the wire, two-stage space closure is more likely to be needed for two reasons. First, anchorage control is more difficult when you slide teeth along an archwire because additional force beyond what is needed for tooth movement has to be used to also overcome the resistance to sliding. Second, there’s no resistance to sliding with the loop (the teeth are tied to the wire and segments of wire with teeth attached are moved). Bodily tooth movement is quite possible when a loop is used, and force control can be managed about equally well with loops vs. sliding.

Question 8

(A) Complex force systems with more than one couple present within the system make it difficult to determine forces and moments because (B) one-couple systems are indeterminate while two-couple systems are determinate.

  1. A true, B true, A and B related
  2. A true, B true, A and B not related
  3. A true, B false ✓
  4. A false, B true
  5. A and B false

Correct

That’s right, the first statement is true but the second one is false. For (B), it’s the other way around: one couple systems are determinate and the forces and moments can be determined precisely, while two-couple systems are indeterminate and the forces and moments cannot be known precisely. That’s particularly important when light forces for intrusion are needed. If you can’t determine the force, there’s no way to know whether you’re using the right force magnitude, so a one-couple force system is needed.

Question 9

Which of the following are reasons that a multi-bracketed orthodontic appliance becomes a complex two-couple system?

  1. couples are created across multiple brackets
  2. with rectangular wire, couples are created within multiple brackets
  3. wires are ligated into multiple brackets
  4. 1 only
  5. 2 only
  6. 1 and 3
  7. 2 and 3
  8. 1, 2, and 3 ✓

Correct

That’s right, all these are reasons why a multi-bracketed orthodontic appliance becomes a complex two-couple system. When a wire is ligated into a bracket, a couple across the bracket is created as soon as tooth movement begins, even if it’s a round wire, and a rectangular wire with any degree of twist produces a couple within each bracket as soon as it’s inserted.

Question 10

Which of the following can provide perfect anchorage for orthodontic tooth movement?

  1. ankylosed maxillary canine
  2. tooth with fusion of a small area of the root to alveolar bone
  3. osseointergrated implant
  4. alveolar bone screw
  5. 1 and 2
  6. 3 and 4
  7. 1, 3, and 4
  8. 2, 3, and 4
  9. all the above ✓

Correct

That’s right, all of these situations can provide perfect anchorage. It takes only a small area of fusion of the root to bone to produce ankylosis, and an ankylosed tooth can’t be moved unless that area of fusion can be released. Osseointegrated implants and alveolar bone screws lack a periodontal ligament, and therefore can’t be moved like teeth. They may become loose and fall out, but they don’t move through the bone—that takes an intact PDL.

Question 11

Which of the following are advantages of miniplates placed at the base of the zygomatic arch versus alveolar bone screws?

Miniplates

  1. become osseointegrated, bone screws don’t
  2. are held by multiple screws
  3. allow a change in force direction
  4. use flap surgery in the mucosa for insertion
  5. 1 and 2
  6. 2 and 3 ✓
  7. 1, 2, and 3
  8. 1, 2, and 4
  9. all the above

Correct

That’s right, statements 2 and 3 are advantages of miniplates, while statement 4 (although true) is a disadvantage rather than an advantage. Neither miniplates nor alveolar bone screws become osseointegrated, at least not in the way that restorative implants do. That’s more of an advantage than a disadvantage because it makes them easier to remove after orthodontic treatment is completed.

Question 12

Which of the following is the type of tooth movement that most requires miniplate rather than alveolar bone screw anchorage?

  1. positioning individual teeth
  2. retraction and intrusion of protruding maxillary incisors
  3. distal movement of the entire maxillary dental arch ✓
  4. intrusion of maxillary posterior teeth
  5. intrusion of maxillary anterior teeth

Correct

That’s right. You can’t move the entire maxillary arch distally with bone screws between the tooth roots as anchorage, because the teeth would quickly run into a bone screw as they were moved distally. Bone screws can be used to produce the other movements, although miniplates may make it easier because they allow changes in the force direction.

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