Anterior-Posterior Discrepancies

Anteroposterior (sagittal) discrepancies describe how the upper and lower arches relate in the front-to-back direction — the dimension the Angle classification reads at the molars and that overjet reads at the incisors. Class II (the lower arch positioned back relative to the upper) and Class III (the lower arch positioned forward) are the principal sagittal patterns, each of which may be dental, skeletal, or combined.

Definition

An anteroposterior discrepancy is a deviation of the upper and lower dental arches from the ideal sagittal (Class I) relationship: a Class II relationship has the mandibular arch positioned distally relative to the maxillary arch, and a Class III relationship has it positioned mesially; overjet is the horizontal incisor-edge distance that quantifies the relationship anteriorly.

Scope

The entry covers the sagittal plane of occlusion, the Class II and Class III relationships, the role of overjet as the incisor-level measure, and the way a sagittal discrepancy may arise from the teeth, the jaws, or both. It is a descriptive concept and does not provide treatment guidance.

Core questions

• What does the sagittal (anteroposterior) plane describe, and how is it measured?
• How do Class II and Class III relationships differ?
• When is a sagittal discrepancy dental versus skeletal?
• How does overjet relate to the molar-based Angle class?

Key concepts

• Sagittal (anteroposterior) plane of space
• Class II relationship (distal mandibular position)
• Class III relationship (mesial mandibular position)
• Overjet (horizontal incisor relationship)
• Dental versus skeletal sagittal discrepancy
• Maxillary protrusion / retrusion and mandibular protrusion / retrusion

Mechanisms

The sagittal relationship of the arches results from the combined front-to-back positions of the maxilla and mandible and the inclination of the teeth on them. A Class II pattern can stem from a retrusive mandible, a protrusive maxilla, proclined upper incisors, or a combination, and a Class III pattern from the mirror situations; the same Angle class can therefore arise from different skeletal-dental combinations. Overjet quantifies the relationship at the incisors and may diverge from the molar-based class when teeth are tipped. Because the sagittal dimension is independent of the vertical and transverse planes, it is recorded as its own diagnostic axis (Angle, 1899; Ackerman & Proffit, 1969; Proffit et al., 2018).

Clinical relevance

The anteroposterior relationship is the dimension the Angle class names, and distinguishing its dental from skeletal basis is central to interpreting an orthodontic diagnosis. This entry describes the sagittal plane for reference and is not a basis for individual diagnosis or treatment.

Epidemiology

Class I sagittal relationships are the most common across populations, with Class II and Class III less frequent; a systematic review and meta-analysis estimated Class III prevalence to vary substantially by region, and a broader review of malocclusion traits documented similar geographic variation across the Angle classes (Hardy et al., 2012; Alhammadi et al., 2018).

History

The anteroposterior dimension has been central to malocclusion description since Angle's 1899 molar-based classification, which reads precisely this plane. Modern schemes retained the Class I/II/III sagittal language while embedding it alongside the vertical and transverse planes and the skeletal-dental distinction, and epidemiologic reviews have since charted how the sagittal classes are distributed worldwide (Angle, 1899; Ackerman & Proffit, 1969; Hardy et al., 2012).

Key figures

• Edward Angle
• William Proffit
• James Ackerman

Seminal works

• angle-1899
• ackerman-proffit-1969

Frequently asked questions

What is the difference between Class II and Class III?

In a Class II relationship the lower arch sits back relative to the upper arch, while in a Class III relationship the lower arch sits forward; both describe deviations from the ideal Class I sagittal relationship.

How is overjet different from the Angle class?

Overjet is the horizontal distance between the upper and lower incisor edges, measured at the front, whereas the Angle class is read at the first molars; the two can diverge when teeth are tipped relative to the jaws.