Diagnosis & Classification MCQ

Orthodontic diagnosis starts at the first molar. Angle's classification reads the anteroposterior molar relationship; the canine reads it again. The cephalometric ANB reads the skeletal pattern, which can disagree with the dental classification. The vertical pattern (deep bite, open bite) and the transverse pattern (crossbite) round out the three planes. Photographs and radiographs (panoramic plus lateral cephalogram) document the starting point. Indices like the IOTN and PAR quantify need and outcome for orthodontic care.

Angle's Classification

• Angle's classification uses the relationship of the maxillary and mandibular first permanent molars; in Class I (neutroclusion), the mesiobuccal cusp of the maxillary first molar occludes in the mesiobuccal groove of the mandibular first molar.
• Class II (distoclusion) is when the mandibular molar is positioned distally relative to Class I (i.e., the maxillary molar is forward of the lower); Class III (mesioclusion) is when the mandibular molar is positioned mesially (i.e., the lower is forward of the upper).
• Class II Division 1 has proclined (flared) maxillary central incisors and a large overjet; Class II Division 2 has retroclined (lingually inclined) maxillary central incisors, often with a deep overbite, and laterals that may flare.
• Subdivisions describe one side being Class I and the other Class II or III (e.g., 'Class II Subdivision Right' means right side Class II, left side Class I).

Skeletal vs Dental Classification

• The dental class (Angle) reads where the teeth are; the skeletal class reads where the jaws are. They can disagree (for example, a skeletal Class II patient with dental compensation can present with a Class I dental occlusion).
• Cephalometric SNA reads the maxilla's position relative to the cranial base (about 82°); SNB reads the mandible's position (about 80°); the difference ANB is the most-cited skeletal A-P parameter (about 2° in Class I, >4° in Class II, <0° in Class III).
• Vertical pattern is read by the mandibular plane angle (FMA, SN-MP); high angles indicate dolichofacial (long-face) growth tendencies, low angles indicate brachyfacial (short-face) tendencies.
• Distinguishing skeletal from dental Class II changes the treatment: a growing skeletal Class II can be treated with a functional appliance, while a dental Class II is treated with intra-arch mechanics and elastics.

Overjet, Overbite, and Crossbite

• Overjet is the horizontal anterior overlap (normal 2-3 mm); a large overjet is the headline finding of Class II Div 1 and is a risk factor for traumatic dental injury.
• Overbite is the vertical anterior overlap (normal about 2 mm or 30 percent of the lower incisor crown); a deep overbite is common in Class II Div 2; an open bite has no vertical overlap.
• Posterior crossbite is when the buccal cusp of an upper molar or premolar is lingual to the buccal cusp of the lower; it may reflect a narrow maxilla, a unilateral functional shift, or a thumb-sucking habit; anterior crossbite is when one or more lower incisors lie labial to the uppers.
• Open bite is most often anterior; it can be skeletal (high-angle pattern) or habitual (thumb sucking, tongue thrust, prolonged digit habit) and is treated differently in each case.

Cephalometric Basics

• The lateral cephalogram is the primary radiograph for orthodontic skeletal diagnosis; the panoramic film documents the dentition and supporting structures.
• Cephalometric points include S (sella), N (nasion), A (subspinale), B (supramentale), Go (gonion), Me (menton), and Po (porion); planes include SN (anterior cranial base), Frankfort horizontal (Po-Or), occlusal plane, and mandibular plane (Go-Me or Go-Gn).
• Key A-P measurements: SNA (~82°), SNB (~80°), and ANB (the difference, about 2° in Class I, >4° in Class II, <0° in Class III).
• Key vertical measurements: FMA (Frankfort to mandibular plane, ~25°), SN-MP, and the face-height ratio; high angles indicate vertical growth tendencies.

Records, Indices, and the Diagnosis Summary

• Orthodontic records include extraoral photographs (frontal, frontal smile, profile), intraoral photographs (frontal, lateral, occlusal), panoramic radiograph, lateral cephalogram, and study models (digital or stone); CBCT is selectively used for impactions, supernumeraries, and asymmetry.
• The IOTN (Index of Orthodontic Treatment Need) and PAR (Peer Assessment Rating) are widely used indices: IOTN measures need (DHC and AC), PAR measures outcome and case complexity.
• Models are analyzed for crowding (space available vs space needed), arch form, midline, Bolton ratio (tooth-size discrepancy between arches; 91 percent overall, 78 percent anterior), and curve of Spee/Wilson.
• The diagnosis summary names the malocclusion in three planes (A-P, vertical, transverse), the skeletal vs dental component, and the specific problem list that will guide the treatment plan.