Iran Dental Specialty Board - Orthodontics cheat sheet

Neural crest cells form most of the facial skeleton; cranial base cartilage (chondrocranium) forms by endochondral ossification, while the mandible and maxilla form largely by intramembranous ossification.

Cranial base growth: synchondroses (spheno-occipital, sphenoethmoidal) contribute early; spheno-occipital synchondrosis closes roughly ages 12-15 in females and 14-17 in males, marking near-end of cranial base growth.

Scammon's curve: neural tissue grows fastest early (by age 6-7 ~90% of adult size), lymphoid grows fastest then involutes, general body tissue follows an S-curve, genital tissue grows late.

Cephalocaudal gradient: growth proceeds head to feet; facial growth completes later than cranial growth, so mandibular growth continues into late teens/early twenties.

Mandibular growth: condylar cartilage is secondary cartilage; growth occurs by endochondral ossification at the condyle plus surface apposition and remodeling, with anterior relocation of the condyle and posterior drift of the ramus.

Maxillary growth: displacement downward and forward from cranial base growth plus sutural growth; the maxilla remodels by resorption on the anterior surface and apposition on the posterior/palatal surfaces.

Dental age indicators: Nolla stages, Demirjian stages, and Moorrees crown/root stages; cervical vertebral maturation (CVM) stages CS1-CS6 estimate the pubertal growth spurt, with CS3-CS4 indicating peak mandibular growth.

Growth modification timing: functional appliances are most effective during the pubertal growth spurt; a hand-wrist radiograph or CVM staging estimates remaining growth.

Soft tissue growth follows the general body curve; nasal tip and chin grow downward and forward, and lip prominence decreases relative to the nose and chin with age.

Problem-oriented diagnosis: list problems by (1) facial/skeletal, (2) dental, (3) soft tissue, (4) functional (airway, TMD, habits), (5) periodontal/restorative; then set goals, then choose mechanics.

Skeletal classification: Class I, II, III by ANB and by clinical profile; note that dental and skeletal classifications may disagree and must be recorded separately.

Angle's classification uses the first molars; note that molar relationship alone may be misleading when teeth are missing or migrated, so record canine and incisor relationships as well.

Crowding estimate: arch length discrepancy = available arch perimeter minus sum of mesiodistal widths of teeth; values >4-5 mm usually need extraction or arch expansion.

Extraction decision inputs: arch length discrepancy, profile (lip prominence), incisor inclination, molar relationship, growth remaining, periodontal status, and patient preference.

Anchorage classification: maximum, moderate, minimum; record anchorage demand before choosing mechanics; use the ratio of anterior retraction to posterior anchorage loss.

Airway screening: enlarged tonsils, adenoid facies, mouth breathing, and obstructive sleep apnea symptoms warrant ENT referral; do not attribute all malocclusion to airway without evidence.

Informed consent must document alternatives (including no treatment and extraction vs nonextraction), risks (root resorption, decalcification, relapse, TMD uncertainty), and costs/time.

SNA: angle from sella-nasion to nasion-A point; normal ~82 degrees; larger indicates maxillary protrusion or anterior cranial base effects.

SNB: angle from sella-nasion to nasion-B point; normal ~80 degrees; larger indicates mandibular protrusion.

ANB = SNA - SNB; normal ~2 degrees; >4 suggests Class II skeletal pattern, <0 suggests Class III.

Skeletal discrepancy can be masked by cranial base length and rotation; verify with Wits appraisal (AO-BO projected on occlusal plane; normal ~0 mm) and soft tissue profile.

Mandibular plane angle: Go-Gn to SN (SN-MP) normal ~32 degrees; FMA (Frankfort-mandibular plane angle) normal ~25 degrees; high angle suggests hyperdivergent pattern with poorer prognosis for some mechanics.

Facial axis (B-J to Pt-Gn) ~90 degrees; Y-axis (S-Gn to SN) ~66 degrees; used to assess growth direction.

Holdaway ratio: lower incisor to NB line (mm) vs pogonion to NB line (mm); ideally ~1:1; larger indicates incisor flaring relative to chin.

Cone-beam CT provides 3D assessment of impacted canines, root resorption, airway, and bone thickness; use low-dose protocols and justify each exposure.

Panoramic radiograph: assess root parallelism, supernumerary teeth, impactions, condylar morphology; not reliable for caries or fine bone detail.

Center of resistance (CR) of a single-rooted tooth is roughly at 1/3 to 1/2 root length from the alveolar crest; of a multirooted tooth near the furcation.

Moment-to-force ratio (M/F) determines movement type: low M/F = tipping; M/F near the tipping threshold = controlled tipping (rotation about apex); higher M/F = translation; highest M/F = root torque.

Optimal orthodontic force is light and continuous: roughly 50-150 g for intrusion, 100-200 g for translation of anterior teeth; heavy force does not speed movement and increases hyalinization and root resorption risk.

Pressure-tension theory: compression side shows necrosis/hyalinization followed by undermining resorption; tension side shows osteoid deposition; heavy forces increase the avascular zone and delay movement.

Rate of tooth movement is often described as ~1 mm/month; movement slows after initial phase due to hyalinization and the lag phase.

Anchorage: reciprocal movement occurs unless anchorage is reinforced; use palatal coverage, TADs, or transpalatal arches to increase posterior anchorage.

Temporary anchorage devices (miniscrews) are placed in attached gingiva or palate; success depends on bone quality, root proximity, and oral hygiene; they provide absolute anchorage.

Root resorption risk increases with heavy forces, long duration, intrusion, and torque; monitor with periapical radiographs in high-risk patients.

Cortical bone is denser and resists movement; teeth move faster through medullary bone; bone density and turnover affect the rate of orthodontic movement.

Stainless steel brackets: high stiffness, low friction, corrosion-resistant; nickel-titanium (NiTi) archwires: superelasticity and shape memory, low stiffness, used for leveling and alignment.

NiTi wire phases: austenite at higher temperature (stiff), martensite at lower temperature (flexible); stress-induced martensite gives superelastic behavior; transition temperature range (TTR) determines clinical behavior.

Beta-titanium (TMA) wire: intermediate stiffness between NiTi and stainless steel, weldable, used for finishing and torque.

Stainless steel wire: high stiffness, low springback; used for sliding mechanics and consolidation; requires loops for deflection.

Bonding: acid-etch (37% phosphoric acid) of enamel creates microporous surface; moisture control is critical; self-etching primers reduce steps but have lower bond strength in some studies.

Bond strength of brackets to enamel: adequate when >6-8 MPa; failure often at the bracket-adhesive interface or enamel-adhesive interface.

Elastomeric chains and modules lose force over time (force decay); metal ligatures are more stable; consider replacing elastomerics at each visit.

Clear aligners: thermoplastic polyurethane; efficacy depends on attachment design, compliance, and case selection; less effective for severe rotations and extrusion.

Ceramic brackets: esthetic but brittle and higher friction; avoid in deep bite or heavy occlusal forces; use with caution on lower incisors.

Edgewise appliance: rectangular wire in rectangular slot gives three-dimensional control; straight-wire (pre-adjusted) appliance builds in tip, torque, and in-out compensations.

Begg appliance: light continuous forces with differential tooth movement; less commonly used today.

Self-ligating brackets: passive, active, and interactive types; evidence does not consistently show faster treatment or fewer visits compared with conventional brackets.

Removable appliances: Hawley retainer, Essix (clear overlay), and functional appliances; patient compliance is the main determinant of success.

Functional appliances (Twin Block, Herbst, activator, Bionator): modify mandibular position and growth; best during pubertal growth; evidence for skeletal vs dental effects is debated.

Headgear: cervical, high-pull, and combination; used for maxillary restraint or distalization; compliance-dependent and can cause distal tipping if not controlled.

Expansion: rapid maxillary expansion (RME) uses heavy forces to open the midpalatal suture; slow expansion uses lighter forces; RME is most effective before sutural fusion (before mid-teens).

Retention: fixed lingual retainers and removable retainers; long-term or lifelong retention is often recommended, especially for lower incisors.

Interceptive treatment aims to remove or reduce the cause of malocclusion and guide growth; examples: habit correction, space maintenance, serial extraction, and early crossbite correction.

Anterior crossbite: correct early to prevent mandibular displacement and gingival recession; options include removable appliance with springs, 2x4 appliance, or tongue blade exercises.

Posterior crossbite: correct with expansion; unilateral crossbite often associated with functional shift; evaluate for constricted maxilla.

Space maintenance: band-and-loop, crown-and-loop, and removable space maintainers; indicated when primary tooth is lost prematurely and space closure would compromise eruption.

Serial extraction: planned removal of primary canines and first premolars in selected crowding cases; requires careful case selection and monitoring.

Habit correction: thumb sucking, tongue thrust; use reminder appliances, palatal cribs, and behavioral approaches; address airway if mouth breathing is present.

Timing of first orthodontic evaluation: age 7 per AAO recommendation; not all children need treatment at that age, but early screening identifies problems.

Ectopic eruption of first permanent molars: intercept with separators, distal tipping, or extraction of primary second molar if severe.

Orthognathic surgery indications: severe skeletal discrepancies beyond orthodontic camouflage, airway issues, functional impairment, and psychosocial concerns.

Common procedures: Le Fort I osteotomy (maxillary advancement/impaction), bilateral sagittal split osteotomy (BSSO) for mandibular advancement/setback, and genioplasty.

Presurgical orthodontics: decompensate the dentition to allow surgical correction; typically 12-18 months before surgery, then postsurgical finishing.

Surgical planning: cephalometric prediction tracing, model surgery, and now virtual surgical planning (VSP) with CBCT; consider soft tissue changes (e.g., 1 mm maxillary advancement ~0.5-0.7 mm upper lip advancement).

Distraction osteogenesis: gradual lengthening of bone; used for severe mandibular hypoplasia (e.g., Pierre Robin, hemifacial microsomia); latency, distraction rate (~1 mm/day), and consolidation phases.

Orthopedic appliances: headgear, facemask (protraction), chin cup; effects are largely dentoalveolar with some skeletal change, best during growth.

Relapse after orthognathic surgery: mandibular setback has higher relapse risk than advancement; rigid internal fixation and overcorrection help.

Airway and OSA: maxillomandibular advancement is an effective surgical option for obstructive sleep apnea in selected patients.

Retention is lifelong in many cases; relapse occurs due to periodontal fiber memory, growth, and continued soft tissue forces.

Hawley retainer: acrylic base with wire clasps; allows some occlusal settling; Essix retainer: clear overlay, esthetic but less durable and can cause bite changes if worn full-time long term.

Fixed lingual retainer: bonded canine-to-canine or full arch; effective for lower incisor retention; risk of bond failure and calculus accumulation.

Debonding: remove brackets and adhesive, polish enamel, and take final records; check for decalcification and gingival health.

Retention after expansion: use a transpalatal arch or removable plate to maintain width; relapse of expansion is common.

Retention after orthognathic surgery: often combined fixed and removable retention; monitor for skeletal relapse.

Patient instructions: wear retainer as prescribed, clean it, and attend follow-up; loss of retainer requires prompt replacement to prevent relapse.

Clearing (debanding) criteria: acceptable occlusion, no active inflammation, stable arch coordination, and patient understanding of retention.

Periodontal risk assessment before orthodontics: bone loss, recession, furcation, mobility, and plaque control; uncontrolled periodontitis is a contraindication until treated.

Orthodontic forces in periodontally compromised patients: use lighter forces and monitor closely; inflammation increases the rate of bone loss and can worsen attachment loss.

Gingival recession: orthodontic movement can worsen thin biotype; consider gingival graft before or during treatment; avoid excessive expansion or labial movement in thin biotype.

Interdisciplinary treatment: coordinate with restorative for implants, crowns, and veneers; orthodontic movement can improve implant site and prosthetic space.

Forced eruption: orthodontic extrusion of a tooth with a crown-root fracture or periodontal defect; can improve gingival margin and bone level.

Implant site development: orthodontic space opening and uprighting of adjacent teeth before implant placement; avoid placing implants in growing patients.

Root proximity and bone: CBCT assesses bone thickness for miniscrew placement and root proximity; avoid placing miniscrews in areas with inadequate bone.

Oral hygiene: essential during orthodontic treatment; use fluoride and chlorhexidine as needed; decalcification (white spot lesions) is a common complication.

TMD classification: masticatory muscle disorders (myofascial pain), disc displacement (with/without reduction), arthralgia, degenerative joint disease, and headache attributed to TMD.

TMD diagnosis: history and clinical exam; imaging (CBCT, MRI) for disc position and bony changes; MRI is gold standard for disc displacement.

Occlusal factors and TMD: evidence does not support a strong causal link between malocclusion and TMD; avoid irreversible occlusal therapy for TMD without clear indication.

Splint therapy: stabilization splint (flat plane) is commonly used; evidence for efficacy is modest; avoid irreversible occlusal adjustment as first-line.

TMD and orthodontics: orthodontic treatment is not a proven cause or cure of TMD; document pre-existing TMD before treatment.

Occlusal scheme: mutually protected occlusion (canine guidance in lateral excursion, anterior guidance in protrusion) is a common treatment goal; group function is acceptable in some cases.

Bruxism: parafunctional habit; manage with splint, behavioral therapy, and awareness; can cause tooth wear and restoration failure.

Airway and occlusion: mouth breathing and OSA can affect craniofacial growth; screen for sleep-disordered breathing in selected patients.

Evidence hierarchy: systematic reviews/meta-analyses > randomized controlled trials > cohort studies > case-control > case series > expert opinion.

PICO framework: Population, Intervention, Comparison, Outcome; used to formulate a clinical question and search strategy.

Randomization and blinding reduce bias; intention-to-treat analysis preserves randomization; per-protocol analysis can overestimate effect.

Statistical significance vs clinical significance: p-value indicates probability under null; effect size and confidence intervals indicate clinical relevance.

Study designs: RCTs for causality; cohort for incidence and prognosis; case-control for rare outcomes; cross-sectional for prevalence.

Ethics: informed consent, confidentiality, and avoiding conflicts of interest; research ethics boards (IRB) approval required for human subjects research.

Publication bias: positive results are more likely to be published; funnel plots and Egger's test assess small-study effects.

Critical appraisal: check sample size, randomization, blinding, follow-up completeness, and generalizability before applying evidence to a patient.

Cephalometric tracing landmarks: S, N, A point, B point, porion, orbitale, gonion, menton, gnathion, pogonion; identify and verify each landmark before measuring.

Arch form: ovoid, tapered, square; select archwire form to match the patient's arch; avoid over-expansion which can cause relapse and periodontal problems.

Bolton analysis: anterior and overall ratios; anterior ratio ~77.2%, overall ~91.3%; discrepancy indicates tooth size imbalance requiring interproximal reduction or restoration.

Mixed dentition analysis: Tanaka-Johnston and Moyers prediction tables estimate unerupted canine and premolar widths; use for space analysis.

Model analysis: measure arch length, tooth widths, and curve of Spee; curve of Spee >2 mm may need leveling.

Treatment plan sequencing: address transverse first, then anteroposterior, then vertical; correct crossbites before arch coordination.

Anchorage loss: monitor with cephalometric superimposition and model analysis; use TADs or extraoral anchorage when needed.

Patient compliance: assess motivation and expectations; document discussions about treatment duration and outcomes.

Lateral cephalometric tracing: use a standardized technique with the patient in centric occlusion and lips relaxed; verify landmark reproducibility.

Cephalometric superimposition: cranial base superimposition (S-N) assesses skeletal change; maxillary and mandibular regional superimposition assesses dental change.

Ricketts analysis: includes facial axis, facial depth, mandibular plane, and lower incisor to A-Po; useful for growth prediction.

Steiner analysis: SNA, SNB, ANB, S-N to mandibular plane, occlusal plane, and interincisal angle; interincisal angle normal ~130 degrees.

Tweed analysis: FMA, IMPA, FMIA; Tweed's diagnostic triangle; IMPA normal ~90 degrees, FMIA ~65 degrees.

CBCT radiation dose: lower than conventional CT but higher than panoramic; use ALARA and limit field of view to region of interest.

3D imaging: assess impacted teeth, airway volume, condylar position, and bone thickness; useful for orthognathic planning and TAD placement.

Digital models: intraoral scans replace plaster models; accuracy is high; use for space analysis and treatment planning.

Force systems: a couple produces pure rotation; a single force produces translation and rotation unless balanced; combine force and couple for controlled movement.

Moment-to-force ratio thresholds: for a single-rooted tooth, M/F ~10:1 for translation; higher for torque; lower for uncontrolled tipping.

Friction: sliding mechanics involve friction at bracket-wire interface; friction increases with bracket angulation, ligature force, and surface roughness; use low-friction brackets or self-ligating systems when appropriate.

Anchorage loss: reciprocal movement occurs with equal and opposite forces; reinforce anchorage with TADs, palatal coverage, or extraoral appliances.

Intrusion: requires light continuous force; heavy forces cause root resorption and hyalinization; use TADs for absolute anchorage.

Extrusion: lighter forces (~50 g) are sufficient; heavy forces can cause root resorption and gingival recession.

Rotation: overcorrection and retention are needed due to periodontal fiber memory; use a couple for efficient rotation.

Bone remodeling: compression side shows osteoclast activity and resorption; tension side shows osteoblast activity and deposition; the periodontal ligament mediates the response.

Bracket slot size: 0.018-inch and 0.022-inch; 0.022 slot allows more wire sizes and sliding mechanics; 0.018 slot allows better control with smaller wires.

Archwire sequence: NiTi for alignment, then stainless steel or TMA for leveling and finishing; increase wire size gradually.

Bonding agents: primer and adhesive; light-cured composites allow longer working time; self-curing for moisture-sensitive areas.

Band vs bond: bands for molars when needed for anchorage or headgear; bonds for esthetics and easier hygiene.

Elastomeric ligatures: force decay over 4-6 weeks; metal ligatures more stable; self-ligating brackets use clips.

Retainer materials: Hawley acrylic and wire; Essix clear polyurethane; fixed lingual wire; choose based on patient needs and compliance.

Sterilization: autoclave for instruments; single-use items should not be reused; follow infection control protocols.

Appliance failure: bracket debonding, wire breakage, and lost retainers; document and repair promptly to avoid treatment delay.

Straight-wire appliance: pre-adjusted brackets with built-in tip, torque, and in-out; requires accurate bracket placement for optimal results.

Begg appliance: light forces, differential tooth movement; less commonly used; requires careful wire selection.

Functional appliance timing: best during pubertal growth spurt; assess with CVM or hand-wrist radiograph.

Twin Block: two-piece appliance that allows mandibular advancement and lateral excursions; compliance-dependent.

Herbst appliance: fixed functional appliance; continuous mandibular advancement; can cause root resorption and TMJ changes; monitor.

Headgear: cervical for maxillary restraint; high-pull for intrusion and distalization; combination for control; compliance-dependent.

RME: rapid maxillary expansion with heavy forces; opens midpalatal suture; best before sutural fusion; use with caution in adults (surgical assist).

Retention protocols: fixed and removable; long-term retention for lower incisors; monitor for relapse.

First orthodontic evaluation at age 7; identify problems such as crossbite, crowding, and impacted teeth.

Anterior crossbite correction: removable appliance with springs, 2x4 appliance, or tongue blade; correct early to prevent displacement.

Posterior crossbite: expansion with RME or quad helix; evaluate for functional shift.

Space maintenance: band-and-loop, crown-and-loop, or removable; indicated after premature loss of primary teeth.

Serial extraction: planned removal of primary canines and first premolars; requires careful case selection.

Habit correction: palatal crib, reminder appliances, behavioral therapy; address airway if mouth breathing.

Ectopic eruption: intercept with separators or distal tipping; monitor for self-correction.

Growth modification: functional appliances and headgear; best during growth spurt; evidence for skeletal effects is debated.

Le Fort I osteotomy: maxillary advancement, impaction, or setback; can correct vertical and transverse discrepancies.

BSSO: mandibular advancement or setback; risk of nerve injury (inferior alveolar nerve); rigid fixation.

Genioplasty: chin augmentation or reduction; can be combined with orthognathic surgery.

Presurgical orthodontics: decompensate teeth; typically 12-18 months; then surgery and postsurgical finishing.

Virtual surgical planning: CBCT-based; improves accuracy and outcomes; allows splint fabrication.

Distraction osteogenesis: gradual lengthening; latency, distraction rate (~1 mm/day), consolidation; used for severe hypoplasia.

Orthopedic appliances: facemask for maxillary protraction; chin cup for mandibular restraint; effects are largely dentoalveolar.

Relapse: mandibular setback has higher relapse risk; overcorrection and rigid fixation help; retention is essential.

Debonding: remove brackets and adhesive; polish enamel; take final records; check for decalcification.

Retention: Hawley, Essix, or fixed lingual; long-term or lifelong for many patients.

Relapse causes: periodontal fiber memory, growth, soft tissue forces; retention counteracts.

Fixed retainer: bonded canine-to-canine; effective for lower incisors; risk of bond failure.

Essix retainer: clear overlay; esthetic but less durable; can cause bite changes if worn full-time long term.

Hawley retainer: acrylic base with wire clasps; allows occlusal settling; durable.

Patient instructions: wear as prescribed, clean, attend follow-up; replace lost retainers promptly.

Clearing criteria: acceptable occlusion, stable arch coordination, healthy gingiva, and patient understanding of retention.

Periodontal assessment: bone loss, recession, mobility, furcation, plaque control; treat periodontitis before orthodontics.

Orthodontic forces in periodontally compromised patients: lighter forces; monitor closely; inflammation increases bone loss.

Gingival recession: thin biotype; consider graft; avoid excessive labial movement.

Interdisciplinary treatment: coordinate with restorative for implants, crowns, veneers; orthodontic movement can improve site.

Forced eruption: orthodontic extrusion for crown-root fracture or periodontal defect; improves gingival margin and bone.

Implant site development: space opening and uprighting; avoid implants in growing patients.

CBCT: assess bone thickness for miniscrews and root proximity.

Oral hygiene: fluoride and chlorhexidine; decalcification is a common complication.

TMD classification: muscle disorders, disc displacement, arthralgia, degenerative joint disease, headache.

Diagnosis: history and exam; MRI for disc position; CBCT for bony changes.

Occlusal factors and TMD: evidence does not support strong causal link; avoid irreversible therapy without indication.

Splint therapy: stabilization splint; evidence modest; avoid irreversible occlusal adjustment as first-line.

Orthodontics and TMD: not a proven cause or cure; document pre-existing TMD.

Occlusal scheme: mutually protected occlusion; canine guidance in lateral excursion; anterior guidance in protrusion.

Bruxism: parafunctional; manage with splint, behavioral therapy; can cause wear.

Airway: screen for sleep-disordered breathing; mouth breathing can affect growth.

Evidence hierarchy: systematic reviews > RCTs > cohort > case-control > case series > expert opinion.

PICO: Population, Intervention, Comparison, Outcome; formulate clinical question.

Randomization and blinding reduce bias; intention-to-treat analysis.

Statistical vs clinical significance: p-value vs effect size and confidence intervals.

Study designs: RCTs for causality; cohort for incidence; case-control for rare outcomes.

Ethics: informed consent, confidentiality, IRB approval for research.

Publication bias: funnel plots and Egger's test.

Critical appraisal: sample size, randomization, blinding, follow-up, generalizability.