Dental MCQ
Force and how teeth move · Orthodontics · INBDE Patient Cases

Biomechanics of Tooth Movement INBDE Patient Cases

By Dr. Isaac Sun, DDS

7 ADA INBDE-format patient cases on biomechanics of tooth movement. Each case is a shared patient box (chief complaint, history, medications, allergies, exam) followed by linked multiple-choice questions with full distractor explanations. Practice the way the real exam is structured.

7 patient cases35 linked questionsADA INBDE formatFull distractor explanations

Seven ADA INBDE-format patient cases on orthodontic biomechanics: tipping versus bodily translation in a canine retraction (M/F ratio and the bracket-to-CR distance), heavy force producing pressure-side PDL hyalinization and slower undermining resorption (with pain and root resorption), maximum (Group A) anchorage with TADs and reinforcement options for space closure, apical root resorption mid-treatment with the multifactorial risk profile and pause-and-reassess management, NiTi superelastic shape-memory archwires in the alignment phase moving to TMA and stainless steel for working and finishing, Class II elastics as a clear example of reciprocal mechanics and Newton's third law with the high-angle caveat, and adult molar intrusion with TAD-supported absolute anchorage at light continuous force. Topics include force/moment/couple, center of resistance and center of rotation, types of tooth movement, optimal force levels, the cellular biology of frontal versus undermining resorption, and anchorage planning across Groups A, B, and C.

Case Coverage Map
What each case is testing
Tipping versus bodily translation in a canine retraction:
Single force = tipping; force + counter-couple at the bracket = bodily translation (M/F ~8-10:1); CR ~1/3-1/2 down the root; Newton's third law and anchorage planning.
Heavy force and stalled tooth movement:
Hyalinization of the pressure-side PDL, undermining resorption from deeper marrow spaces, increased pain and root resorption, and the corrective force reduction.
Maximum anchorage in space closure with TADs:
Group A maximum anchorage, TADs as near-absolute anchorage, reinforcement options (headgear/TPA/lingual arch/extra anchor teeth), and compliance issues with headgear.
Apical root resorption during treatment:
Risk factors (heavy force, long duration, jiggling, intrusion, susceptibility); maxillary incisor vulnerability; pause-and-reassess; periodic monitoring.
NiTi superelastic alignment phase:
NiTi shape-memory superelastic plateau, archwire sequence (NiTi → TMA → stainless steel), and nickel allergy alternatives.
Reciprocal anchorage: Class II elastics:
Class II elastics' reciprocal effect on both arches, lower molar mesialization/extrusion side effect, high-angle caveat, and anchorage reinforcement options.
Intrusion of extruded molar with TADs:
Adult molar intrusion with TADs (absolute anchorage), ~10-20 g per-tooth intrusion force, reaction force into bone, and root resorption protection.
Patient case: Tipping versus bodily translation in a canine retraction
0 of 5 answered, 0 correct
Patient
Female, 15 years old
Chief Complaint
Bilateral first premolar extractions completed; planning canine retraction.
Background and/or Patient History
  • Bilateral upper first premolar extractions for crowding
  • Plan to retract the upper canines into the extraction space
  • Discussion of tipping versus bodily translation
Allergies
NKDA
Medications
  • None
Current Findings
  • Canine retraction case requiring control of crown and root position
  1. Question 1
    Moderate
    A SINGLE force applied at the bracket of the canine (no counter-couple) produces:
  2. Question 2
    Hard
    To produce BODILY translation of the canine, the M/F at the bracket should be approximately:
  3. Question 3
    Moderate
    The center of resistance of an upper canine lies approximately:
  4. Question 4
    Hard
    If the canine TIPS during retraction (because no counter-couple was added), the most likely root position after retraction is:
  5. Question 5
    Moderate
    Anchorage in this case is:

Reset this case?

This clears your answers for this patient case only.

Patient case: Heavy force and stalled tooth movement
0 of 5 answered, 0 correct
Patient
Male, 17 years old
Chief Complaint
Tooth is not moving despite heavy elastics; new pain after adjustments.
Background and/or Patient History
  • Class II elastics being used at heavier-than-recommended forces
  • Tooth movement has stalled and pain has increased
  • Discussion of hyalinization and force reduction
Allergies
NKDA
Medications
  • None
Current Findings
  • Stalled tooth movement under heavy force
  • Pain and concern for root resorption
  1. Question 1
    Moderate
    Heavy compressive force on the pressure-side PDL produces:
  2. Question 2
    Hard
    Once hyalinization occurs, movement resumes by:
  3. Question 3
    Moderate
    Heavy forces also raise the risk of:
  4. Question 4
    Easy
    The correct response is to:
  5. Question 5
    Easy
    The teaching point is that orthodontic force is:

Reset this case?

This clears your answers for this patient case only.

Patient case: Maximum anchorage in space closure with TADs
0 of 5 answered, 0 correct
Patient
Female, 22 years old
Chief Complaint
Bimaxillary protrusion; first premolar extractions planned with maximum anchorage retraction of anterior teeth.
Background and/or Patient History
  • Bimaxillary dental protrusion
  • Extraction of four first premolars planned
  • Maximum anchorage needed at posterior teeth
Allergies
NKDA
Medications
  • None
Current Findings
  • Maximum anchorage planning for anterior retraction
  1. Question 1
    Moderate
    Maximum (Group A) anchorage means:
  2. Question 2
    Moderate
    TADs (mini-implants) provide:
  3. Question 3
    Moderate
    Other ways to reinforce anchorage include:
  4. Question 4
    Moderate
    Headgear as anchorage works only well if:
  5. Question 5
    Easy
    The teaching point is that maximum anchorage cases:

Reset this case?

This clears your answers for this patient case only.

Patient case: Apical root resorption during treatment
0 of 5 answered, 0 correct
Patient
Female, 14 years old
Chief Complaint
Routine progress radiograph shows mild apical root resorption on the upper centrals.
Background and/or Patient History
  • Active orthodontic treatment with fixed appliances
  • Routine progress panoramic radiograph at 12 months
  • Mild apical root resorption noted on the upper central incisors
Allergies
NKDA
Medications
  • None
Current Findings
  • Mild apical root resorption mid-treatment
  • Risk-factor review and plan adjustment
  1. Question 1
    Moderate
    Apical root resorption risk during orthodontics rises with:
  2. Question 2
    Hard
    Maxillary incisors are especially vulnerable to root resorption because:
  3. Question 3
    Moderate
    If significant apical resorption is detected mid-treatment, the appropriate response is to:
  4. Question 4
    Moderate
    Periodic monitoring during long treatments should include:
  5. Question 5
    Easy
    The teaching point is that root resorption:

Reset this case?

This clears your answers for this patient case only.

Patient case: NiTi superelastic alignment phase
0 of 5 answered, 0 correct
Patient
Male, 13 years old
Chief Complaint
Fixed appliances placed last week; first archwire is a thin NiTi.
Background and/or Patient History
  • Class I crowding case; fixed appliances bonded last week
  • Initial 0.014 NiTi archwire placed
  • Discussion of why NiTi was selected first
Allergies
NKDA
Medications
  • None
Current Findings
  • Alignment-phase archwire choice
  1. Question 1
    Moderate
    NiTi (nickel-titanium) archwires are favored in initial alignment because they:
  2. Question 2
    Moderate
    After alignment, the archwire sequence typically moves to:
  3. Question 3
    Moderate
    If the patient has documented nickel allergy:
  4. Question 4
    Hard
    The 'superelastic' property of NiTi means that:
  5. Question 5
    Easy
    The teaching point of archwire selection is that:

Reset this case?

This clears your answers for this patient case only.

Patient case: Reciprocal anchorage: Class II elastics
0 of 5 answered, 0 correct
Patient
Female, 13 years old
Chief Complaint
Mild Class II Div 1 on continuous archwires; Class II elastics planned.
Background and/or Patient History
  • Mild dental Class II Div 1 on full fixed appliances
  • Class II elastics (upper canine to lower molar) planned
  • Discussion of the reciprocal effect
Allergies
NKDA
Medications
  • None
Current Findings
  • Class II elastics planned; reciprocal anchorage concept
  1. Question 1
    Moderate
    Class II elastics produce force on:
  2. Question 2
    Hard
    If the lower arch is the anchor and is well stabilized, the elastic's effect on the lower arch is:
  3. Question 3
    Hard
    In a high-angle Class II patient, Class II elastics:
  4. Question 4
    Moderate
    To reduce the reciprocal effect on the lower arch, options include:
  5. Question 5
    Easy
    The teaching point is that Class II elastics illustrate:

Reset this case?

This clears your answers for this patient case only.

Patient case: Intrusion of extruded molar with TADs
0 of 5 answered, 0 correct
Patient
Female, 35 years old
Chief Complaint
Long-standing missing lower first molar; opposing upper first molar has supraerupted.
Background and/or Patient History
  • Lower right first molar missing for years
  • Upper right first molar supraerupted into the edentulous space
  • Implant planned for lower right first molar; needs space restoration
Allergies
NKDA
Medications
  • None
Current Findings
  • Supraerupted molar requiring intrusion before restoring the opposing implant
  1. Question 1
    Moderate
    Intrusion of a supraerupted molar in an adult is best achieved with:
  2. Question 2
    Moderate
    Approximate optimal force for intrusion of a single tooth is:
  3. Question 3
    Hard
    The reaction force from a TAD-supported intrusion goes to:
  4. Question 4
    Moderate
    A risk of over-intrusion (too much force, too long) is:
  5. Question 5
    Easy
    The teaching point is that adult intrusion mechanics:

Reset this case?

This clears your answers for this patient case only.

Keep studying
Biomechanics of Tooth Movement core recall

Refresh the anatomy facts these cases depend on: nerve numbers, foramina, functions, and lesion findings.

← Back to Biomechanics of Tooth Movement