Quartz 4

Unit Self-Test

37 min read

Level III Biomechanics — Unit B Self-Test

Module 1: Space Management in Preadolescent Children

Instructions

  1. View the teaching program.
  2. Use the mouse to mark the correct answer(s) to each question.
  3. Review the feedback from the program—it will tell you if you’re right or wrong, and why.

Reading: Contemporary Orthodontics, 3rd edition, pages 165-170, 418-429, and 452-462.

Question 1

Which of the following is not an underlying assumption of a complete mixed dentition space analysis (like the UNC analysis)?

  1. All succedaneous teeth are present and developing normally.
  2. Males have larger teeth than females.
  3. Molar position is predictable. ✓
  4. The size of the erupted mandibular incisors is well correlated with the unerupted buccal segments.
  5. Prediction tables are valid for all patients.

Correct

That’s right; even though males do have larger teeth than females, that is not one of the assumptions of the UNC mixed dentition space analysis. Mesial drift of the 1st permanent molars is assumed to occur when 2nd primary molars are lost, and calculating the amount of drift to correct the molar relationship is an important part of the space analysis procedure. It is assumed that all teeth are present and will erupt, that the size of the incisors can be used to predict the size of the unerupted canine, premolars can be used to predict the size of the unerupted teeth, and that prediction tables for this purpose will be valid.

Question 2

Which of the following additional factors are evaluated during interpretation of the numerical results in sections 7-10 of the UNC Space Analysis Form?

a. Lip posture

b. Molar shift

c. Facial profile analysis results

d. Depth of the curve of Spee

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

Correct

That’s right; all of these factors are evaluated in sections 7 through 10 of the UNC Space Analysis Form except the depth of the curve of Spee. The facial profile analysis is used to analyze lip posture, mandibular incisor position, and skeletal jaw relationship, which all have a direct relationship on space analysis in the dental arches. The depth of the curve of Spee, although it does have implications to the space required to align the teeth in the mandibular arch, is not part of the UNC Space Analysis Form.

Question 3

(A) A lower lingual arch is recommended for bilateral space maintenance in the mixed dentition prior to the eruption of the mandibular permanent incisors, because (B) The mandibular permanent incisors erupt lingually to the primary incisors.

  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. A lower lingual arch is contraindicated for use in the primary or early mixed dentition prior to the eruption of the mandibular permanent incisors. Bilateral band and loop space maintainers are indicated in these situations. The second statement is true as the mandibular incisors usually erupt lingual to the primary incisors. A lower lingual arch would impede the eruption of the mandibular permanent incisors.

Question 4

Which of the following can be used as space regaining appliances?

a. Distal shoe

b. Lower lingual arch

c. Transpalatal arch

d. Band and loop

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

Correct

That’s right. Lower lingual arches and transpalatal arches can be used as passive space maintenance appliances, but they can also be used as active appliances to regain space in the maxillary or mandibular arches. Omega loops in the lingual arch can be opened that will distally tip the molars and procline the lower incisors. Transpalatal arches can be adjusted to derotate and distalize a maxillary molar. The band and loop and distal shoe appliances are passive space maintainers and cannot be adjusted to regain space.

Question 5

Space regaining should be limited to cases with

  1. 0-3 mm of generalized space loss.
  2. 3-5 mm of generalized space loss.
  3. 0-3 mm of localized space loss. ✓
  4. 3-5 mm of localized space loss.
  5. bilateral space loss.

Correct

That’s correct. If space maintenance is not instituted after extraction of a primary tooth, space loss will occur in a number of months. Repositioning the teeth to regain space is then required. Up to 3 mm of space can be reestablished in a localized area with relatively simple appliances. Localized space loss greater than 3 mm constitutes a severe problem and is more difficult to manage.

Question 6

(A) Space management can be used to accommodate up to 4 mm of crowding in the transition from the mixed dentition to the permanent dentition, because (B) This much space typically is lost as the permanent first molars shift mesially after exfoliation of the primary second molars.

  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 and related. Space management uses a lingual arch to prevent loss of the leeway space during the late mixed dentition. The leeway space, which can be up to 4 mm in the mandibular arch, can then be used to accommodate mild crowding in the permanent dentition. Loss of the leeway space occurs when the primary second molars are exfoliated and the permanent molars shift mesially.

Question 7

A lower lingual arch that utilizes the mandibular leeway space to align the mandibular teeth may

a. interfere with the early mesial shift.

b. require that the maxillary molars be distalized to obtain a Class I molar relationship.

c. be indicated for use in cases with a mild amount of crowding.

d. be indicated for use in cases with a moderate amount of crowding.

  1. a and b
  2. a and c
  3. b and c ✓
  4. a, b, and c
  5. a, b, and d

Correct

That’s correct. During space management the late mesial shift of the mandibular molars is prevented. The late mesial shift and loss of the mandibular leeway space usually allows the lower first permanent molars to shift mesially into a Class I molar relationship. If a lower lingual arch is placed to utilize the leeway space to align the permanent mandibular teeth, a Class I molar relationship may not result. In cases where a lower lingual arch is used for space management, headgear may then be required to distalize the maxillary molars to establish a Class I molar relationship. Space management is indicated for use in cases with mild crowding. The leeway space is not sufficient to accommodate moderate crowding.

Question 8

In the early mixed dentition, premature unilateral loss of a primary mandibular canine

a. indicates significant incisor crowding.

b. results in a shift of the dental midline to the affected side.

c. occurs during the eruption of the adjacent permanent lateral incisor.

d. requires no intervention.

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

Correct

That’s right. Premature unilateral loss of a primary mandibular canine usually indicates significant incisor crowding. There is insufficient space for the eruption of the adjacent permanent lateral incisor. As the lateral incisor erupts, it prematurely resorbs the mesial surface of the primary canine, which causes it to be lost early. The unilateral loss of the primary canine then results in a shifting of the dental midline to the affected side. Intervention is usually recommended in these cases. The contralateral primary is extracted and a lingual arch is placed to encourage self-correction of the midline. Active correction of the midline can also be done.

Question 9

(A) The normal eruption sequence in the maxillary arch makes serial extractions more challenging in the maxillary arch because (B) The eruption of a maxillary permanent tooth can be accelerated if the extraction of the overlying primary tooth is timed correctly.

  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 while the second statement is true. A major objective of serial extraction is to extract the first premolars before the permanent canines erupt. In the maxillary arch the first premolars usually erupt before the canines, which is favorable. The mandibular arch is more challenging because the canines often erupt before the first premolars. It’s true that the eruption of a permanent tooth can be accelerated if the overlying primary tooth is extracted when this uncovers the underlying permanent tooth, so timely removal of first primary molars can accelerate the eruption of first premolars, allowing their extraction before canines erupt.

Question 10

Serial extractions are done to

a. accelerate the eruption of the first premolars.

b. prevent loss of the leeway space.

c. eliminate the need for future orthodontic treatment.

d. allow early alignment of the permanent incisors.

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

Correct

That’s right. One of the objectives of serial extractions is the early resolution of permanent incisor crowding. The extraction of the primary canines creates space for the permanent incisors to erupt into normal positions and align early. Another objective is to accelerate the eruption of the first premolars, so they can be removed early. Serial extractions do not eliminate the need for future orthodontic treatment. First premolars are removed during serial extractions, and leeway space is not relevant since these teeth have been removed.

Module 2: Crossbites and Vertical Problems in Children

Instructions

  1. View the teaching program.
  2. Use the mouse to mark the correct answer(s) to each question.
  3. Review the feedback from the program—it will tell you if you’re right or wrong, and why.

Reading: Contemporary Orthodontics, 3rd edition, pages 63-64, 216-217, 220-221, 231-233, 435-447, and 491-508.

Question 1

The correction of anterior crossbites in children is recommended to

a. prevent periodontal involvement of the lower incisors.

b. eliminate significant CR-MI interferences.

c. correct localized space loss.

d. prevent abnormal incisor wear patterns.

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

Correct

That’s right; all of these are reasons why the correction of anterior crossbites in children is recommended. An anterior crossbite may force the mandibular incisors to be positioned more facially in the lower arch. If positioned too far facially, the periodontal support of the lower incisors may be compromised due to loss of attached gingiva and gingival recession. The correction may also allow normal jaw function by eliminating significant CR–MI functional interferences that may interfere with lateral jaw excursions and cause abnormal incisal wear patterns that can compromise incisor esthetics. Single tooth crossbites are commonly due to localized space loss, the space must be regained first to allow the incisor to be repositioned in the dental arch.

Question 2

Patients with a pseudo-Class III malocclusion

  1. invariably have an underlying Class III skeletal relationship.
  2. have a significant anterior shift from CR-MI due to an anterior crossbite. ✓
  3. cannot be manipulated into an end-to-end incisor relationship in CR.
  4. usually present with maxillary skeletal retrusion.
  5. cannot be treated with orthodontics alone and must be treated with surgery.

Correct

That’s right. Patients with a significant anterior shift of the mandible from CR to MI due to interferences caused by a dental anterior crossbite may appear to have a significant skeletal crossbite. An anterior dental crossbite with a significant anterior shift is called a pseudo-Class III malocclusion. It is very important to evaluate the patient’s occlusion and facial profile in CR and MI. These patients usually can be manipulated into an edge-to-edge incisor relationship in centric occlusion prior to shifting forward. When these patients shift forward into MI, facial profile analysis reveals an apparent mandibular prognathism due to the anterior shift of the mandible. Orthodontic treatment of the crossbite eliminates the CR-MI shift and the apparent skeletal discrepancy.

Question 3

Which of the following is not a usual component of a removable appliance to correct an anterior dental crossbite?

  1. Finger spring
  2. Adams’ clasps
  3. Bite plane
  4. Labial bow
  5. Palatal expansion screw ✓

Correct

That’s right, a palatal expansion screw is not a usual component of removable appliances used to correct an anterior crossbite. Palatal expansion screws are more commonly used in removable appliances to correct a posterior crossbite. Finger springs are commonly used to tip incisors into the correct position. Adams’ clasps on posterior teeth provide retention, while a labial bow contoured to the labial surfaces of the incisors provides a stop for the incisor as it is advanced. Bite planes may be used to open the occlusion to allow forward movement of the incisor during correction.

Question 4

A) Children with skeletal anterior crossbites due to mandibular excess can easily be treated with growth modification, because (B) Once the crossbite is corrected, future skeletal growth doesn’t affect the treatment result.

  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 false. Children with skeletal anterior crossbites due to mandibular excess are very difficult to treat with growth modification. The chin cup appliance has been designed to restrict the forward growth of the mandible but has limited success because it requires an extended period of compliance and must be worn during the majority of the adolescent growth spurt to be effective. If the patient has not completed all of his or her mandibular growth, future mandibular growth tends to undo the treatment and the anterior crossbite reappears. The end result is that the patient outgrows any early correction of the underlying skeletal problem.

Question 5

(A) Young children with both anterior and posterior crossbites may have an underlying Class III skeletal malocclusion, because (B) Significant AP discrepancies between the maxilla and mandible may also present as a posterior crossbite even though jaw width is normal.

  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. Class III skeletal malocclusions usually present with an anterior crossbite as well as a posterior crossbite. The upper and lower jaws may be of normal transverse width but due to an abnormal anteroposterior relationship, present as an anterior crossbite as well as a posterior crossbite. The AP discrepancy prevents the normal interdigitation of the U-shaped maxillary and mandibular dental arches in both planes of space. You should be very suspicious of an underlying Class III malocclusion in children who present with both a posterior and anterior crossbite.

Question 6

A child in the mixed dentition presents with a left posterior crossbite and a mandibular midline shifted to the left in MI. Both dental arches appear symmetric. Your most probable diagnosis would be

  1. pseudo-Class III malocclusion.
  2. left unilateral posterior dental crossbite.
  3. unilateral mandibular crowding on the left side.
  4. bilateral posterior crossbite with a functional shift to the left. ✓
  5. asymmetry of the mandibular ramus on the left side.

Correct

That’s right. Posterior crossbites in children often appear to be unilateral in nature, but closer examination usually reveals that the majority of these result from a true bilateral constriction of the maxillary arch with a transverse shift of the mandible from CR to MI. These patients will also present with the mandibular dental midline deviated to the side in crossbite or the direction of the mandibular shift. A true unilateral posterior crossbite due to an intra-arch or jaw asymmetry is less common in children.

Question 7

Which of the following appliances is recommended to correct a posterior dental crossbite in a preadolescent patient?

  1. Quad-helix appliance ✓
  2. Hyrax appliance
  3. Rapid palatal expander
  4. Haas appliance
  5. Mini-expander

Correct

That’s correct. Of these choices, the quad-helix is preferred because the midpalatal suture is most likely open and heavy-force application is unnecessary to achieve dental and skeletal expansion. All the other choices are examples of appliances that use rapid palatal expansion and unnecessarily heavy forces to expand the palate.

Question 8

(A) Rapid palatal expansion is indicated for the treatment of skeletal crossbites in late adolescence because (B) The mature palatal suture is highly organized and the bone is well interdigitated and nearly fused.

  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 correct and related. The palatal suture becomes well organized and highly interdigitated in late adolescence. As this occurs, more force is required to expand the suture, and a jackscrew as employed in rapid palatal expansion is recommended to accomplish the skeletal expansion at this age.

Question 9

One must be cautious when correcting posterior crossbites in children with

a. a shallow mandibular plane.

b. a steep mandibular plane angle.

c. decreased lower anterior face height.

d. increased lower anterior face height.

  1. a and c
  2. b and c
  3. a and b
  4. a and d
  5. b and d ✓

Correct

That’s right. One must be cautious when correcting posterior crossbites in children with an excessive vertical growth component. Forces applied to posterior teeth to correct a posterior crossbite have a vertical vector as well as a transverse vector that tends to alter vertical relationships. This vertical vector tends to extrude the posterior teeth as well as tipping the lingual cusps downward. Both of these will result in a bite opening effect. In patients with short lower face height and a shallow mandibular plane angle, this may have a positive effect. However, in patients with a steep mandibular plane and increased lower face height, such vertical changes will make the situation worse. One way to minimize these vertical effects during expansion is to use a bonded expander that uses bite blocks.

Question 10

Which of the following is most likely to be found in a child with a long-standing thumb-sucking habit?

  1. Proclined mandibular incisors
  2. Deep overbite
  3. Reduced overjet
  4. Posterior crossbite ✓
  5. Undererupted posterior teeth

Correct

That’s right. Children with a long-standing thumb-sucking habit usually present with a posterior crossbite. The other findings are quite unlikely. Lingually directed forces usually retrocline or upright the lower incisors. The upper incisors are proclined by the thumb resulting in an increased overjet. Overeruption of the posterior also causes an anterior open bite.

Question 11

(A) Successful treatment of thumb-sucking habits can be accomplished with dental appliances such as a fixed thumb crib because (B) Crib appliances are very successful in noncompliant patients.

  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 statement is false. Dental appliances such as a fixed thumb crib act as a reminder and can be effective in patients stopping a thumb-sucking habit. For these appliances to be effective, a child must wish to stop the habit—any intervention must not be perceived as punishment by the child. Appliance therapy requires a compliant patient who wishes to stop the habit since noncompliant patients can easily distort or remove the appliances if they wish.

Question 12

Anterior deep bite patients usually

a. present with over-erupted mandibular incisors.

b. present with a flat mandibular curve of Spee.

c. are treated by increasing lower face height.

d. require a downward rotation of the mandible during treatment.

  1. a and c
  2. b and d
  3. a, b, and c
  4. b, c, and d
  5. a, c, and d ✓

Correct

That’s right. Deep bite patients usually present with overerupted mandibular incisors. This overeruption of the mandibular incisors is often seen with a Class II malocclusion because when there is excessive overjet, the lower incisors are free to erupt until they contact the palatal mucosa. This also results in a deep curve of Spee in the lower arch, not a flat curve of Spee. Deep bite patients also tend to have a decreased lower face height due to an upward and forward growth of the mandible. Treatment is usually aimed at creating a downward rotation of the mandible to increase lower face height.

Question 13

Patients with vertical excess (the long face syndrome) usually present with

  1. increased upper face height.
  2. steep mandibular plane angle. ✓
  3. decreased anterior face height.
  4. increased posterior face height.
  5. superiorly positioned posterior maxilla.

Correct

That’s right. Patients with vertical excess or long face syndrome usually present with a steep mandibular plane angle, but the other characteristics are not characteristic of this condition. The upper face height may be normal, while there is usually a decreased posterior face height and increased anterior face height. The posterior maxillary plane is usually inferiorly positioned, which causes the mandible to rotate downward and backward thus further increasing the anterior face height.

Question 14

Nongrowing patients with a combination of severe vertical excess and a Class II relationship are best treated with

  1. high pull headgear.
  2. high pull headgear with a maxillary splint.
  3. functional appliance with bite blocks.
  4. high pull head gear to a functional appliance with bite blocks.
  5. orthognathic surgery. ✓

Correct

That’s right. Orthognathic surgery is required to achieve optimum dentofacial relationships in nongrowing patients with severe vertical excess and Class II skeletal relationships. In growing patients, growth modification using a high pull headgear to a functional appliance with bite blocks may reduce the skeletal disproportions but rarely is successful in the more severely affected individuals. For them, orthognathic surgery may the best treatment option.

Module 3: Concepts of Adjunctive Orthodontic Treatment

Question 1

Which of the following are not goals of typical adjunctive treatment?

a. Improve the periodontal prognosis for a second molar

b. Improve smile esthetics

c. Concentrate the costs of treatment on the problem most important to the patient

d. Allow treatment with a removable rather than a fixed appliance

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

Correct

That’s correct, the first three statements are true, but the last one is false. Adjunctive treatment isoften used to improve smile esthetics, and when costs and treatment time for more extensive orthodontics are a factor, to focus the financial resources on the patient’s most important problem. Eliminating fixed appliances isn’t a goal, however. Successful adjunctive treatment often requires a fixed appliance simply because removable appliances are neither as effective nor as efficient.

Question 2

Which of the following are reasons that intrusive tooth movement is rarely part of an adjunctive orthodontic treatment in general dental practice?

a. Risk of creating a periodontal problem around the tooth being intruded

b. Greater technical difficulty in creating and maintaining the necessary force system

c. Possibility of facial or lingual displacement of the tooth

d. Increased chance of root resorption

  1. a and b
  2. b and c
  3. c and d
  4. a, b, and c
  5. b, c, and d ✓

Correct

That’s right, the first statement isn’t a reason for avoiding intrusion in adjunctive treatment, but the other three are. Periodontal problems rarely occur when intrusion is carried out, but doing it requires a complex fixed appliance so that forces are kept very light and force directions are carefully controlled. Otherwise root resorption and unexpected displacement of teeth can occur. As a general rule, intrusion isn’t recommended in adjunctive orthodontics.

Question 3

Which of the following are advantages of reducing the crown height of a tooth that is deliberately being extruded during adjunctive treatment?

a. Facilitates subgingival extension of restoration margins

b. Improves the crown-root ratio

c. Eliminates occlusal interferences to the tooth movement

d. Makes it easier and more effective to use a removable appliance

  1. a and b
  2. b and c ✓
  3. c and d
  4. a and d
  5. b, c, and d

Correct

That’s right, reducing the height of the crown of a tooth that is being extruded often is necessary to eliminate occlusal interferences that would prevent the desired tooth movement, as for instance when a molar is being uprighted before a bridge or implant is placed. It also improves the crown-root ratio, which can be important in improving the periodontal prognosis when bone loss has occurred. Extrusion does not make it easier to place margins subgingivally, and this type of tooth movement is very difficult to accomplish with a removable appliance, so it does not make using removables easier or more effective.

Question 4

Which statement most correctly describes the place of adjunctive orthodontics in the treatment of temporomandibular dysfunction? For such a patient, adjunctive orthodontics is

  1. often the key to success.
  2. frequently an important aid in managing the patient’s problems.
  3. largely irrelevant to TMD, as a cause or cure. ✓
  4. as likely to make things worse as better.
  5. almost always to be avoided because of the chance of making TMD symptoms worse.

Correct

That’s right, orthodontic treatment is best described as having little relationship to TMD, either as a cure or as a cause of additional/worsening symptoms. Certainly neither the first nor last statement, the extreme view on either side, is correct. Sometimes adjunctive treatment can aid on controlling TMD, but that isn’t predictable. There are a number of valid reasons for adjunctive orthodontic treatment. Correcting TMD isn’t one of them.

Question 5

Which of the following are differences in the diagnostic records needed for adjunctive orthodontics in adults as compared to treatment for children? In adults who are candidates for adjunctive orthodontics,

a. cephalometric analysis is more likely to be needed.

b. articulator-mounted models are less important.

c. periapical radiographs are more likely to be required.

d. evaluation of periodontal disease status is even more important.

  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. The second and third statements are correct, the other two are not. In adults who are candidates for adjunctive orthodontics, periapical radiographs are more likely to be required because evaluation of periodontal disease status is even more important than it is in children. In adults who will have limited rather than comprehensive orthodontics, however, cephalometric analysis is less, not more, likely to be needed than in children. The articulator-mounted models that are of little use in growing children—because growth changes the relationship of the condyles to the dentition, making the articulator relationship wrong quite quickly—can be important in adults in planning the restorative and/or surgical treatment.

Question 6

(A) At the doctor-patient conference in which a treatment plan is presented, a major role for the doctor is to be sure the patient accepts the total package of perio-ortho-restorative treatment that has been worked out, because (B) There is nothing to be gained from correcting only some, not all of the patient’s 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 these statements are false. The doctor’s role at the conference is to outline the patient’s problems, evaluate the alternative treatment possibilities, and present the alternatives as clearly and objectively as possible. The goal is to get the patient to understand the alternatives. That’s the heart of informed consent to treatment. It’s the patient’s choice, not the doctor’s, as to what treatment is to be done—but of course the doctor does not have to provide treatment that he or she does not think is in the patient’s best interest.

Question 7

For a patient with spacing of maxillary incisors that he wants you to correct, who has no major restorations, no clinical evidence of periodontal disease or caries, and no symptoms indicating pulpal pathology, what radiographs would you order beyond a panoramic radiograph?

  1. Full periapical series, always needed for adult orthodontics
  2. Periapicals of the maxillary incisors that would be moved orthodontically
  3. Bitewings only
  4. Incisor periapicals, bitewings, and lateral ceph
  5. No other radiographs indicated in this situation ✓

Correct

That’s correct. For this patient, there is no indication for periapicals (no evidence of pulpal pathology or periodontal breakdown), no indication for bitewings (no caries or previous restorations), and no indication for a lateral ceph (no major change in tooth position or jaw relationships expected). Taking too many radiographs, of course, is as much a clinical error as taking too few.

Question 8

If your goal in adjunctive treatment is to slide teeth along an archwire to obtain proper positioning for restorations, which of the following are important parts of an appropriate fixed appliance?

a. Flexible undersized archwire

b. Full-dimension rectangular archwire

c. Rigid archwire with clearance in the bracket slots

d. Tightly tied ligatures to hold the archwire in place

  1. a only
  2. b only
  3. c only ✓
  4. a and d
  5. c and d

Correct

That’s right, a rigid archwire with clearance in the bracket slots is needed if your goal is to slide teeth along it. It needs to be rigid so the wire doesn’t distort as the teeth slide, undersized relative to the bracket so that there is enough clearance to allow the teeth to slide, and tied loosely to reduce frictional resistance to sliding. So a flexible wire wouldn’t be a good choice, a full-dimension wire with no clearance wouldn’t work, and using tightly tied ligatures would all but prevent the teeth from moving along the archwire.

Question 9

When half the bone support for a tooth has been lost, and you need to move that tooth so you can restore the area properly, what adjustment must be made in the orthodontic force?

  1. Twice as much force needed in this situation to activate the cells
  2. Half again more force needed
  3. Movement stays the same, so does the force
  4. Half the regular force is needed ✓
  5. Force must reduce to one-fourth the regular amount

Correct

That’s right, pressure in the PDL is the key to producing the tooth movement, so if half the volume of the ligament has been lost, the force must be cut in half to obtain the correct pressure.

Question 10

Which of the following are potential problems in the use of a removable appliance in adjunctive orthodontics for adults?

a. Much easier to obtain the moment of a couple than the moment of a force

b. Almost impossible to correct rotations

c. Interrupted force rather than continuous force

d. Increased difficulties with speech

  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, the last three statements are correct, but the first one isn’t. With a removable appliance and springs against the surface of a tooth, you get not only a force but a moment that tips the tooth—whether you wanted it or not. The problem is that without a fixed attachment, it’s very difficult to generate the moment of a couple so that root position can be controlled and almost impossible to correct rotations. If an orthodontic appliance can be removed, it will be, so the force is interrupted rather than continuous, and removable appliances are more likely to generate speech problems (because they extend into tongue space). Fixed lingual appliances, occasionally used for comprehensive but not for adjunctive orthodontics, also create speech problems for many patients.

Question 11

If your goal is to upright a mesially tipped lower second molar without changing the position of the premolars and canine that serve as anchorage, how should you place the brackets on the anchor teeth?

  1. In a straight line along the crowns, so that a flat wire segment will fit ✓
  2. In the center of the crowns
  3. As recommended by the manufacturer, at variable distances from the cusp tips
  4. At any convenient place, since these teeth won’t move anyway

Correct

That’s right, it’s most efficient to place the brackets in a straight line along the crowns of the anchor teeth, so you won’t have to put bends in the wire to get it to fit passively. If you position them in the center of the crown, or relative to the cusp tips, or in some other apparently convenient way, it will be difficult to contour a wire so that it fits passively—but it has to be passive to prevent movement of these teeth in addition to movement of the molar. Of course, if you want to reposition the premolars as well as the molar—and often you will—the brackets need to be positioned so that a straight wire will fit when they’re in the ideal position, not when they’re misaligned as they are initially.

Question 12

(A) Adjunctive orthodontics is often the most important part of orthodontics in general practice because (B) Both the duration and complexity of treatment are less than in children.

  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 these statements are true and they have a cause-effect relationship. Adjunctive orthodontics in adults allows a better outcome of much perio/pros/restorative treatment. It is inherently more predictable than most orthodontic treatment in children, because the variables of growth and cooperation are all but eliminated. Technical skill in using fixed appliances is required, and with proper technique, excellent results can be obtained—which is not necessarily the case in children, no matter who does the treatment.

Module 4: Adjunctive Orthodontic Treatment Procedures

Question 1

(A) Unlike other types of tooth loss, first molars still are lost to caries as frequently as ever because (B) Fluoridation does not protect against pit and fissure caries that can lead to pulpal involvement.

  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. First molars are not lost nearly as frequently as they were 50 years ago, even though fluoridation does not protect against the occlusal decay in pits and fissures that is the usual reason these teeth once were extracted. More children now are seen by dentists before the tooth becomes an emergency and have pit and fissure sealants or restorations.

Question 2

When a mandibular second molar is to be uprighted, which of the following are reasons for extracting the third molar in that quadrant before doing the uprighting?

a. Improves the periodontal prognosis for the second molar

b. Makes it possible to tip the crown distally rather than moving the roots mesially

c. Eliminates occlusal interferences from the opposing upper molars

d. Eliminates the need to use fixed appliances because less anchorage is required

  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, the first two statements are correct, the other two are not. Removing the third molar makes it possible to reduce or eliminate the pocket usually found on the mesial of a tipped lower molar as it is uprighted and may improve the periodontal condition on the distal as well. But uprighting does not eliminate occlusal interferences. Usually it is necessary to reduce the crown height to control interferences when a molar is uprighted. Because anchorage is important, this type of movement almost always requires a fixed appliance. With removable appliances, there are both biomechanical and compliance problems. The removable appliances don’t work very well, and adults won’t wear them very well anyway.

Question 3

Which of the following are appropriate ways to upright a mesially tipped lower molar?

a. Flexible rectangular wire in premolar brackets and molar tube

b. Auxiliary spring and continuous wire in brackets and tube

c. Segmented wire in brackets and auxiliary spring to molar tube

d. Elastics from the upper molar on the same side to the tipped lower molar

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

Correct

That’s right, the first three methods are appropriate for uprighting. An elastic from the upper molar to the lower one is a way to correct a crossbite relationship but is not effective for correction of mesial tipping.

Question 4

Which of the following are characteristics of cross-elastics to correct posterior crossbite?

a. Pull the teeth across the line of occlusion

b. Extrude the teeth to which they attach

c. Require extremely high force

d. May create a need to eliminate occlusal interferences

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

Correct

That’s right, cross-elastics pull the teeth across the occlusion, also extrude the teeth to which they are attached, and for that reason may create a need to eliminate occlusal interferences—but they don’t require extremely high force. In fact, if very high force is used, the undesirable extrusive effect is magnified more than the desired crossbite correction, so very high force is a mistake.

Question 5

Which of the following are indications for the use of a T-loop appliance in uprighting a mesially tipped maxillary molar?

a. Need to tip the crown distally

b. Need to bring the roots mesially

c. Tooth in crossbite

d. Extensive bone loss around anchor teeth

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

Correct

That’s correct, a T-loop appliance is appropriate both for distal tipping of the crown of a molar that needs uprighting or for mesial movement of the roots of the teeth. For distal tipping, the distance from the anchor teeth is allowed to increase, so that the crown can move distally. For mesial root movement, the loop is restrained so that the crown cannot move distally. This loop design is not effective for crossbite correction, however, and bone loss is not an indication for its use.

Question 6

(A) In occlusal rehabilitation it is particularly important to upright tipped maxillary second molars rather than closing the old first molar extraction site because (B) Unless there is good root parallelism at an old maxillary first molar extraction site, periodontal problems are inevitable.

  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 these statements are false. Good periodontal health is more likely around a tipped maxillary than mandibular second molar. Closing a maxillary molar extraction site, therefore, is more likely to be a feasible treatment choice. Uprighting maxillary molars usually is indicated for better restorations, not for better periodontal health.

Question 7

Which of the following is the most time-efficient way to obtain the desired spacing of maxillary incisors before restorations are placed?

  1. Modified Hawley retainer with finger springs
  2. Fixed functional appliance (like the Herbst appliance)
  3. A series of suckdown plastic aligners
  4. Bonded brackets with full-dimension superelastic arch wires
  5. Bonded brackets with undersized rigid wires and coil springs ✓

Correct

That’s correct. A fixed appliance with bonded brackets, undersized rigid wires (so the teeth can slide as needed along the arch wire), and coil springs is the most time-efficient way to position maxillary incisors. This is very difficult with full-dimension arch wires of any material, because of friction between the wire and the bracket. It can be done with a series of plastic aligners, but that takes longer, so this method is not as time-efficient. Neither a fixed functional appliance nor a modified retainer with finger springs is an effective way to accomplish the precise spacing needed in preparation for restorations.

Question 8

After closure of a maxillary central diastema, what is the most effective method for the long-term retention that almost always is required?

  1. Flexible bonded wire ✓
  2. Rigid bonded wire
  3. Removable plastic aligner
  4. Hawley retainer
  5. Doesn’t matter, long-term retention isn’t needed after restorations are placed

Correct

That’s right, a flexible bonded wire on the lingual of the incisors is the most effective method. A rigid bonded wire is more likely to break. Any removable appliance tends not to be worn as much or as consistently as needed to keep the midline space from reopening enough to be noticeable, so a fixed retainer is preferred.

Question 9

When a series of plastic aligners are used to reposition teeth, how much can any tooth be moved relative to the ones adjacent to it with any one aligner?

  1. 0.25 mm
  2. 0.5 mm ✓
  3. 0.75 mm
  4. 1 mm
  5. 2 mm, but only with computer technology

Correct

That’s right, 0.5 mm is about as much movement as can be produced with reasonable control with a single aligner—which is why a large number of aligners often are needed for a course of treatment.

Question 10

Which of the following are potential problems in correcting crowded lower incisors by extracting one incisor and closing the space?

a. Creation of excess overjet

b. Deepening of the bite anteriorly

c. Decrease in lip support that accentuates facial wrinkles

d. TMD because of increased bruxism

  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, the first three statements are correct, but the last one isn’t. If only one lower incisor is extracted, overjet is likely to increase, and this can be a problem in some patients. Extraction of one incisor also tends to deepen the bite anteriorly, and it can increase the prominence of facial wrinkles by decreasing lip support. These are potential problems, but not things that are inevitable—they don’t occur in patients correctly selected for this treatment. Extraction of one lower incisor has nothing to do with TMD due to bruxism. This extraction pattern, like other orthodontic extractions, is unlikely to either cause or cure TMD.

Question 11

Which of the following are not effective orthodontic appliances in nonextraction alignment of crowded lower incisors?

a. Fixed functional appliance (like Herbst appliance)

b. Aseries of suckdown plastic aligners

c. Bonded brackets with full-dimension superelastic arch wires

d. Bonded brackets with undersized wires and coil springs

  1. a and b
  2. b and c
  3. a and c ✓
  4. b and d
  5. a, b, and c

Correct

That’s right, a fixed functional appliance is not an effective way to correct crowded lower incisors (totally inappropriate in fact—such appliances are used in children to guide jaw growth, and crowding of lower incisors is a possible side effect). Neither is a fixed appliance with a full-dimension wire (because that makes sliding teeth along the arch wire almost impossible, and teeth need to slide to open up space). Plastic aligners are effective but slow and expensive. The best approach is bonded brackets, undersized arch wires, and coil springs.

Question 12

(A) After crowded lower incisors in an adult have been aligned by expanding the arch, a retainer usually is needed long term because (B) Teeth with decreased alveolar bone height in an adult are less stable and more likely to relapse after orthodontic tooth movement.

  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 these statements are true, but they aren’t related. After expansion to align the lower incisors, a retainer would be needed long-term whether bone loss had occurred or not, because the pattern of lip-tongue pressures that determines the position of incisors would not change after treatment in an adult. That’s why long-term retention is needed to keep the teeth aligned. A wire and plastic clip-on retainer like this one often is the best choice for long-term retention of lower incisors in a cooperative adult.

Graph View