OMSB Orthodontist (OEORDNT) cheat sheet

Cephalometric norms are population means; individual variation is ±2 SD, so treat the patient, not the number.

ANB 2-4° indicates skeletal Class I; ANB >4° suggests skeletal Class II; ANB <0° suggests skeletal Class III (values shift with age and race).

Wits appraisal measures the AO-BO projection on the occlusal plane and is less affected by cranial base growth than ANB.

Overjet is measured horizontally from incisal edge of maxillary central incisor to labial surface of the mandibular incisor; normal is 2-3 mm.

Overbite is vertical overlap of incisors; normal is 2-3 mm, roughly 20-30% of lower incisor crown coverage.

Crowding assessment: arch length discrepancy = available arch perimeter minus required tooth material; >4 mm usually needs extraction or expansion decisions.

Bolton analysis: anterior ratio ~77.2% and overall ratio ~91.3%; a discrepancy >1.5 SD indicates tooth-size imbalance requiring re-evaluation.

Impacted canine localization uses parallax (two periapical views) or CBCT; buccal impaction is more common than palatal in most populations.

A treatment plan must state problem list, objectives, appliance choice, extraction decision, anchorage requirement, and retention plan.

Cranial vault grows by sutural apposition plus surface remodeling; growth completes earliest, largely by age 5-7.

Mandibular growth follows a downward and forward vector with remodeling at the condyle, posterior border resorption, and anterior symphysis apposition.

Mandibular growth continues into late adolescence; girls typically cease near 15-16 years, boys near 18-20 years.

Cervical vertebral maturation (CVM) stages CS1-CS6 estimate the pubertal growth spurt; CS3-CS4 marks peak mandibular growth.

Maxillary growth completes before mandibular growth; maxillary transverse sutural growth slows after early adolescence.

Scammon's curves: neural tissue grows early, lymphoid overshoots then declines, genital grows late, and general somatic tissue follows an S-curve.

Functional matrix theory (Moss) holds that soft tissue function drives skeletal growth, contrasting with the genetic/sutural dominance view.

Arch length decreases with age due to mesial drift and interproximal wear; leeway space is ~1.5 mm per side in the mandible and ~0.9 mm in the maxilla.

Optimal orthodontic force is light and continuous, generally 50-150 g for tooth translation; heavy force causes hyalinization and undermining resorption.

Center of resistance of a single-rooted tooth lies roughly at one-third of root length from the alveolar crest; for multirooted teeth it is near the furcation.

Moment-to-force ratio determines tooth movement: low ratio gives tipping, intermediate gives controlled tipping, high gives translation, highest gives root torque.

Anchorage classification: maximum, moderate, and minimum; reciprocal movement occurs when anchorage units are equal.

Friction in sliding mechanics increases with bracket-ligature contact and binding; frictionless or segmented mechanics reduce anchorage loss.

Aligning archwire sequence typically progresses from 0.014 NiTi to 0.016 NiTi to 0.016 x 0.022 stainless steel; slot size determines final archwire dimension.

Bracket prescription (tip, torque, in-out) differs by system; incorrect prescription selection causes unintended tooth positions at finishing.

Temporary anchorage devices (TADs) provide absolute anchorage; success depends on bone quality, root proximity, and oral hygiene.

Removable appliances are best for tipping movements, minor corrections, and retention; they cannot translate roots effectively.

Adams clasp engages mesial and distal undercuts of a tooth and provides excellent retention with minimal tooth coverage.

Functional appliances (Twin Block, activator, Herbst) alter mandibular position and influence growth; they work best during the pubertal spurt.

Twin Block uses upper and lower bite blocks with interlocking inclined planes to posture the mandible forward.

Headgear applies orthopedic force to the maxilla; cervical pull extrudes and distalizes, high pull intrudes and distalizes.

Facemask (protraction) is used for maxillary deficiency in Class III; it works best before age 10 with a patent midpalatal suture.

Rapid maxillary expansion (RME) opens the midpalatal suture; it is most effective before late adolescence when the suture is still patent.

Clear aligners are effective for mild-to-moderate crowding and spacing; they are less predictable for severe rotations, extrusion, and large space closure.

Orthognathic surgery is considered when skeletal discrepancy exceeds what orthodontics can camouflage, typically >5-6 mm or severe asymmetry.

Le Fort I osteotomy moves the maxilla in three planes; it can impact, advance, or segment the maxilla.

Bilateral sagittal split osteotomy (BSSO) is the most common mandibular procedure; it allows advancement, setback, and rotation.

Genioplasty corrects chin position independent of occlusion and is often combined with mandibular surgery.

Surgical planning uses cephalometric prediction, model surgery, or virtual surgical planning (VSP) with CBCT.

Presurgical orthodontics decompensates the dentition to expose the true skeletal discrepancy before surgery.

Distraction osteogenesis lengthens bone gradually and is used for severe mandibular or maxillary hypoplasia, especially in growing patients.

Post-surgical relapse is influenced by soft tissue tension, condylar position, and fixation stability; rigid internal fixation reduces relapse.

Relapse causes include periodontal fiber memory, soft tissue pressure, growth, and failure to address the original etiology.

Retention options include Hawley retainers, vacuum-formed (Essix) retainers, fixed lingual bonded retainers, and positioners.

Fixed lingual retainers are effective for anterior alignment but require monitoring for bond failure and calculus accumulation.

Retention duration is individualized; long-term or permanent retention is often advised for severe rotations, diastema, and periodontal cases.

Informed consent should document risks, alternatives, expected duration, and retention responsibilities.

Record-keeping includes study models, radiographs, photographs, and cephalometric tracings; retention of records follows local legal requirements.

Interceptive orthodontics addresses habits, crossbites, and space maintenance early to reduce later complexity.

Professional practice includes infection control, accurate billing, and clear communication of treatment fees and payment plans.