Angle Classification: Class I, II and III by Molar Relation
"Class 1", "Class 2 bite", "Class 3 underbite": Angle’s terms appear in every orthodontic report and in many patient questions, and they are often used loosely. Angle’s classification describes how the first permanent molars meet front to back. It does not say whether the jaws are involved, what happens in the vertical and transverse planes, or what to do. This guide, written for dentists, residents and students, covers the definitions as taught in university orthodontic programs (the D.U. courses behind GS Ortho), the canine relationship, the divisions of Class II, the primary dentition, the limits of the classification, and how to tell a dental class from a skeletal one.
Class I, II and III at a glance
| Class I | Class II division 1 | Class II division 2 | Class III | |
|---|---|---|---|---|
| First molars | Mesiobuccal cusp of the upper first molar in the buccal groove of the lower first molar | Lower arch distal (distocclusion) | Lower arch distal (distocclusion) | Lower arch mesial (mesiocclusion) |
| Canines | Usually Class I | Class II, often more severe than at the molars | Class II | Class III |
| Upper incisors | Variable | Proclined; overjet at least equal to the molar Class II | Two or four retroclined; deep bite; overjet small or nil | Crossbite, edge to edge or normal overlap, depending on compensation |
| Everyday words | "Normal bite" (not always) | "Overbite", "buck teeth" | "Deep bite" | "Underbite" |
| Frequent pattern (not a rule) | Variable | Convex profile, low- or high-angle | Low-angle pattern, strong lips | Concave (low-angle) or flat (high-angle) profile |
| Skeletal class of the same name, if the jaws are involved (Ballard) | ANB 0° to 4° | ANB above 4° | ANB above 4° | ANB below 0° |
The last row is a separate measurement: a dental Class I can sit on a skeletal Class II, and the reverse. The rest of this article explains why.
What is a malocclusion?
In the D.U. terminology course, a malocclusion is an abnormal intercuspation of the arches in maximum intercuspation (MI). It is distinguished from a dysmorphosis, a morphological deviation from the norms of a population. One can exist without the other: a Class I occlusion can hide a discrepancy between the jaws, and a skeletal discrepancy can be masked by compensated teeth.
The standard nomenclature (FDI, and the French orthodontic society SFODF) is purely descriptive: it names what you see, in the basal bones, the alveolar processes, the arch relationships and the tooth positions, without prejudging the cause or the treatment. Each anomaly is described in three planes: sagittal, vertical and transverse. Angle’s classification covers only one of them.
Angle’s classification: the molar relationship
Angle’s classification is based on the sagittal relationship of the first permanent molars, observed in MI on their buccal surfaces:
- Class I: the mesiobuccal cusp of the upper first molar (16, 26) sits in the buccal groove of the lower first molar (36, 46);
- Class II: the lower arch is distal to the upper arch (distocclusion);
- Class III: the lower arch is mesial to the upper arch (mesiocclusion).
The canine relationship
The same reasoning applies to the canines. The courses ask you to record the canine and molar classes, right and left, in millimeters. They do not always agree: in Class II, the canine relationship is often more severe than the molar one, partly because of the curve of Spee, and a mesially rotated upper molar exaggerates the apparent molar discrepancy.
Class II: division 1, division 2 and subdivision
| Form | Definition in the courses |
|---|---|
| Division 1 | Proclined upper incisors, overjet at least equal to the amount of molar Class II. Can be low-angle or high-angle |
| Division 2 | Two or four upper incisors retroclined, masking the discrepancy; deep bite; overjet small or nil |
| Subdivision | Unilateral distocclusion: Class I on one side, Class II on the other, in either division |
Division 2 has a special status: according to the terminology course, it is the only form in the classification that is a clinical entity in its own right (low-angle pattern, strong lips, strong hereditary component). It is not managed like a division 1. Our French guide on Class II division 2 (in French) covers it.
Class III and subdivision
In an Angle Class III, the lower first molar and canine are in mesiocclusion. The incisors can be in anterior crossbite, edge to edge or even in normal overlap, depending on dentoalveolar compensation. A unilateral Class III is a right or left subdivision.
In any anterior crossbite, compare MI with centric relation (CR). Incisors that reach edge to edge in CR indicate a forward functional shift (a functional or pseudo-Class III); CR identical to MI indicates a true Class III. The course treats a functional shift as a priority, because it can evolve into a structural form.
Before the permanent molars: the primary dentition
There is no Angle molar class in the primary dentition. The sagittal reference is the terminal plane of the second primary molars: flush, mesial step or distal step. The primary canines are classified as in the adult and remain the first interarch reference during the transition. A figure quoted in the courses: a flush terminal plane evolves into a Class I in 70% of cases; in 30%, it stays end to end or slides into Class II.
Class 1, Class 2 and Class 3 bite: matching everyday words
Patients’ words do not always match ours. A short translation helps when you explain a finding:
| What patients say | What it usually means | Why the words can mislead |
|---|---|---|
| "Class 1 bite" or "normal bite" | Molars in Class I | Crowding, open bite, deep bite or crossbite can coexist |
| "Overbite" | Usually an increased overjet (protruding upper teeth) | In orthodontics, overbite is the vertical overlap; see our guide to overjet and overbite |
| "Class 2 bite" | Lower teeth behind the upper teeth | Can be dental only, or skeletal |
| "Underbite" or "Class 3 bite" | Lower incisors ahead of the upper ones | Can be a functional shift, a dental anomaly or a skeletal Class III |
For any individual case, the answer comes from an examination by an orthodontist, not from the label.
How common is each class?
A systematic review pooled 53 prevalence studies. In the permanent dentition, the worldwide distribution was about 74.7% Class I, 19.6% Class II and 5.9% Class III; in the mixed dentition, about 73%, 23% and 4% (Alhammadi et al., 2018, Dental Press J Orthod, PubMed). The ranges between studies were very wide (Class II from 2% to 63%), Africans showed the highest prevalence of Class I, Caucasians the highest prevalence of Class II, and Class III was most frequent in the mixed dentition of the group the review calls Mongoloid (East Asian populations). In other words, "Class I" is the most common finding, but Class I is not the same as "no malocclusion": the same review found deep bite in about 22% of individuals and posterior crossbite in about 9%.
The limits of Angle’s classification
Angle’s classification is the common language, but the D.U. courses insist on what it does not say.
- It is not a diagnosis. It describes the molars and has to be completed by the canine, incisor and skeletal relationships.
- It describes only the sagittal plane. A Class I can come with an open bite, a deep bite, a crossbite or crowding.
- It is dental, not skeletal. It says nothing about the jaws or the treatment.
- The molar position can mislead. After the early loss of a second primary molar, the upper first molar can drift mesially and create a "false" Class II, sometimes unilateral.
- Do not mix Angle and Andrews. The courses describe a "super Class I" (Andrews’ Class I): canines in Class I, molars in Class III by 2 mm on each side, with good lateral interdigitation. The occlusion is then recorded as Class I, but mixing the two conventions in the same summary is a known trap: choose one.
Reliability is a further limit. In a study where seven orthodontists examined the same 52 schoolchildren, agreement on molar classification, overjet, overbite, facial convexity and lower anterior crowding was only acceptable (median kappas from 0.48 to 0.72), agreement on the anteroposterior position of the jaws judged clinically was poor (kappa below 0.40), and only posterior crossbite reached excellent agreement (kappa 0.79). The authors concluded that the language of clinical orthodontic diagnosis is imprecise (Keeling et al., 1996, Angle Orthod, PubMed). Recording the canine and molar relationships in millimeters, on both sides, is the practical answer.
Dental or skeletal: Angle and Ballard
Ballard’s classification completes Angle by looking at the jaws, on the lateral cephalogram, and makes compensations visible: according to Bassigny, an older French reference used in the courses, a skeletal Class II often comes with proclined incisors, a skeletal Class III with retroclined lower incisors.
| Measurement | Norm (D.U. courses) | Skeletal Class II | Skeletal Class III |
|---|---|---|---|
| ANB | 2° ± 2° | Above 4° | Below 0° |
| Wits appraisal (AO-BO) | 0 ± 2 mm (Steiner course materials) | Above 2 mm | Below −2 mm |
The Wits norm is not the same everywhere: other sheets, such as the Tweed-Merrifield sheet, use 2 ± 2 mm. State which one you use. In Class III, Boileau, a French orthodontic textbook used in the courses, considers the Wits more reliable than ANB in high-angle patients, whose point B moves back and brings ANB falsely closer to the norm. Our guide to the ANB angle covers these pitfalls, and the Beta angle is another Nasion-free option.
The key point: occlusal class and skeletal class are independent. A skeletal Class II usually comes with a Class II occlusion, but it can also be compensated into a Class I occlusion: in a course example, ANB was 6° in a Class I occlusion, masked by very proclined lower incisors (IMPA 103°, L1-NB 35°). The same applies to Class III. And you do not write "mandibular prognathism" or "retrognathia" without having shown it on the cephalogram.
The reasoning is detailed in our guides to Class II diagnosis and Class III diagnosis (both in French).
Describing a malocclusion in three planes
The D.U. courses ask for each finding in all three planes and on each side. The static interarch chart, in MI, records:
| Plane | What you record |
|---|---|
| Sagittal | Overjet in mm (tooth by tooth if teeth are malpositioned); canine and molar classes, right and left, in mm; anterior compensations |
| Vertical | Anterior and lateral overbite: normal, edge to edge, open bite, deep bite |
| Transverse | Midlines relative to the midsagittal plane; lateral overjet (normal, excessive, edge to edge, unilateral or bilateral crossbite, complete or partial); lateral compensations |
Sagittal and vertical: overjet and overbite
| Measurement | Norm in the courses | Outside the norm |
|---|---|---|
| Overjet | About 2 mm, ideally 1 to 2 mm (terminology course, Boileau) | "Increased" above 2 mm (3 mm in some literature); negative = anterior crossbite |
| Overbite | 2 to 2.5 mm, about one third of the lower incisor crown (Boileau) | Deep bite above 3 mm (published thresholds 2 to 4 mm); zero or negative = open bite |
Bassigny recommends recording both signed, to the nearest half millimeter, on the most labially placed incisor. Open bite tends to go with a high-angle pattern and deep bite with a low-angle pattern; see our guides to open bite and the mandibular plane angle.
Transverse: crossbite and midlines
Normally, the upper arch circumscribes the lower arch; a posterior crossbite reverses this relationship. Two questions structure the diagnosis: basal or alveolar (posterior teeth tipped inward on a normal base, or upright teeth on a narrow base; see our guides to the quad helix and MARPE), and functional or structural (midlines that recenter in CR point to a functional shift, a deviated chin to a skeletal asymmetry). Hence the rule in the courses: any deviated midline or crossbite requires a comparison of MI and CR.
Why the class matters: consequences
Not every malocclusion is pathological: according to the courses, an asymmetry without esthetic, functional or occlusal harm is physiological and is not treated. The consequences depend on the form and the severity.
- Dental trauma: in a meta-analysis of 11 studies, children with an overjet larger than 3 mm were about twice as likely to injure their anterior teeth, and the risk tended to increase with overjet size (Nguyen et al., 1999, Eur J Orthod, PubMed).
- Function and growth: a deep bite, a narrow upper arch or a crossbite can lock the mandible in Class II; an untreated functional shift can become a structural asymmetry or Class III.
- Periodontium: gingival impingement in division 2, lower incisor recession in anterior crossbite.
- Temporomandibular joints: Boileau states that well-conducted orthodontics neither creates, prevents nor treats temporomandibular disorders by itself. A malocclusion class is not a TMJ diagnosis.
They are read together with the functional examination, as described in our clinical examination guide (in French).
In practice: a checklist
- Examine in MI, then guide the patient into CR whenever a midline is deviated or a crossbite is present.
- Record the canine and molar classes, right and left, in millimeters; in the primary dentition, the terminal plane and the canines.
- Measure overjet and overbite, signed, to the nearest half millimeter, and state the threshold you use (2 or 3 mm for overjet).
- Describe the transverse plane: midlines, lateral overjet, crossbite, axes of the posterior teeth.
- Establish the skeletal class separately: ANB confirmed by the Wits, with the Wits norm stated.
- Look for incisor compensations before concluding "dental" or "skeletal".
- Relate the vertical findings to the facial typology.
- List the consequences actually present rather than theoretical risks.
Frequently asked questions
What is a Class 1 occlusion?
A Class I occlusion is one in which the mesiobuccal cusp of the upper first molar sits in the buccal groove of the lower first molar. It describes only the sagittal molar relationship: a Class I can still have crowding, an open bite, a deep bite or a crossbite, and it can hide a compensated skeletal Class II or III.
What is a Class 2 malocclusion?
In a Class II malocclusion, the lower first molar is distal to the upper first molar (distocclusion). Division 1 has proclined upper incisors and a large overjet; division 2 has retroclined upper incisors and a deep bite. A subdivision is a unilateral Class II. Whether the jaws are involved is a separate, cephalometric diagnosis.
Is a Class 2 bite the same as an overbite?
Not exactly. What patients call an "overbite" is usually an increased overjet, which is typical of Class II division 1. In orthodontic terms, overbite is the vertical overlap of the incisors, and an increased overbite is a deep bite, which can occur in any class.
What is a Class 3 malocclusion?
In a Class III malocclusion, the lower first molar and canine are mesial to the upper ones. The incisors can be in crossbite ("underbite"), edge to edge, or in normal overlap if the teeth compensate. A functional shift can mimic it, which is why centric relation is always checked.
Does the Angle class decide the treatment?
No. Treatment reasoning also requires the skeletal class, the vertical and transverse findings, the compensations, growth and the patient’s concerns. For a personal case, only an examination by an orthodontist can answer.
With GS Ortho
In GS Ortho, the 12-panel guided diagnostic studio brings together the clinical examination, the photos, the cephalometric analysis and the treatment plan of the same patient, so the occlusal class and the skeletal class are read side by side. On the lateral cephalogram, AI places 29 landmarks that you check and correct before validating the Steiner and Tweed analyses. The platform also includes teaching guides and fictitious training cases. From any panel, "Request an opinion" sends your question, with the panel attached, to a colleague or supervisor you choose; the answer stays in the record. Our free orthodontic clinical exam form works without sign-up. The GS Ortho interface is currently available in French.