Class II Division 1: Proclined Incisors, Large Overjet

Class II division 1 is the "Class 2 overbite" of patient searches: upper incisors that stick out over a lower arch sitting too far back. Behind the same overjet, though, you can find a forward maxilla, a retruded mandible, Class I jaws with proclined incisors, or a growth pattern rotating the wrong way. This guide, written for dentists, residents and students, follows the D.U. courses behind GS Ortho and Boileau, a French orthodontic textbook used in those courses, and adds what systematic reviews report. The decision stays with the clinician; a personal case belongs with an orthodontist.

Class II division 1 at a glance

What is Class II division 1?

In Angle’s classification, Class II means that the lower first molar, and by extension the lower canine, is distal to the upper one. The D.U. courses define division 1 by proclined upper incisors and an overjet at least equal to the amount of molar Class II. It can be low-angle or high-angle, which changes the whole picture. A subdivision is a unilateral Class II.

Division 2 is a separate entity, not treated like a division 1. One warning from the courses: retracting the upper incisors of a division 1 without torque control in the mixed dentition can create an iatrogenic division 2.

"Class 2 overbite": a word of vocabulary

Patients say "overbite" for teeth that stick out. In orthodontic terms, that is an increased overjet; overbite is the vertical overlap, and an increased overbite is a deep bite. Our guide to overjet and overbite gives the norms: overjet about 2 mm in the courses and Boileau, overbite 2 to 2.5 mm, deep bite above 3 mm.

Two diagnoses, not one

The first step is to establish two separate diagnoses: the occlusal class (Angle: molars, canines, overjet) and the skeletal class (Ballard: the jaws relative to the cranial base). They are independent. You will see a skeletal Class II with a Class II occlusion (the most frequent case), a skeletal Class I with a Class II occlusion, and a skeletal Class II compensated into a Class I occlusion. A course example: ANB 6° with a Class I occlusion, the discrepancy masked by very proclined lower incisors (IMPA 103°, L1-NB 35°). Inferring the skeletal class from the occlusion is the first trap.

How common is it? In a systematic review of 53 studies, Class II (all forms) accounted for about 19.6% of the permanent dentition and 23% of the mixed dentition worldwide (Alhammadi et al., 2018, Dental Press J Orthod, PubMed); an older review gives "about one third" of the United States population (McNamara et al., 1996, Semin Orthod, PubMed). The figures depend on the population and the definition.

Skeletal Class II: locate, then explain

Locate

The courses distinguish four locations: basal maxillary prognathism, maxillary alveolar protrusion, basal mandibular retrognathia and mandibular alveolar retrusion. Treatment differs depending on whether the anomaly is basal or alveolar, maxillary or mandibular. A useful figure from the courses: about three Class II cases in four are retrognathic, involving mainly the mandible.

The literature points the same way. In a mixed dentition Class II sample, mandibular skeletal retrusion, transverse maxillary discrepancy and increased lower anterior facial height were common findings (McNamara et al., 1996, PubMed). In 253 adult Class II surgery patients, the most common combination included a retrusive maxilla and a retrusive mandible, with protrusive incisors and a long lower face (Lawrence et al., 1985, J Oral Maxillofac Surg, PubMed): a "forward maxilla" should be measured, not assumed.

Explain: three mechanisms

1. Position: a mandible of normal size placed too far back under the cranial base.
2. Size: a maxilla too long, a mandible too short, or both.
3. Direction: jaws of normal size, but a posterior growth rotation (high-angle pattern) that moves the chin back.

Boileau adds "structural" causes with a poor prognosis (long or open cranial base, condylar conditions). Heredity is strong (ask about the family), and functional factors (mouth breathing, thumb sucking, lip interposition) are looked for systematically.

Dentoalveolar Class II division 1

When the jaws are in Class I, the anomaly lies in the alveolar processes and teeth. According to Boileau, a division 1 on a skeletal Class I reflects a maxillary alveolar protrusion or a mandibular alveolar retrusion; when it is limited to the incisors, the buccal segments stay in Class I.

Two look-alikes: mesial drift of the upper molar after early loss of a second primary molar (a "false" Class II, sometimes unilateral), and the compensations of a true skeletal Class II, which make it look purely dental. The courses speak of alveolar protrusion or retrusion only when the incisor angle and distance are changed together.

Cephalometric criteria

The lateral cephalogram quantifies and locates the discrepancy. The values below are those of the D.U. courses for Class II.

Three reading rules:

1. Confirm ANB with the Wits. ANB depends on the vertical pattern and the position of Nasion; the Wits, measured on the occlusal plane, much less. Its norm differs between sources (0 ± 2 mm in the Steiner course materials, 2 ± 2 mm on the Tweed sheets): state the one you use. In 146 adults, ANB showed the best agreement with the final diagnosis and the highest sensitivity (0.928) and positive predictive value (0.951) in the Class II group (Ahmed et al., 2018, Dental Press J Orthod, PubMed), a single-center study whose reference standard was built from the same measurements. Our ANB angle guide details the pitfalls.
2. SNA and SNB tell you where. The same ANB of 7° can come from a forward maxilla or a retruded mandible. The courses note that SNB barely changes during treatment and increases only if the vertical dimension decreases.
3. The incisors tell you whether it is compensated. An already proclined lower incisor reduces the margin for orthodontic compensation and weighs on the choice of orthopedics; it will have to be decompensated if surgery is chosen. The Tweed triangle (IMPA, FMIA) and the mandibular plane angle quantify the vertical side.

From diagnosis to Steiner’s chevrons

In Steiner’s prognosis, the end-of-treatment ANB is estimated at initial ANB / 2 + 1 in a growing patient with favorable conditions, and kept unchanged in an adult. The compromise is defined only for a final ANB between −1° and 8°: beyond, incisor compensation alone is not enough. See our Steiner analysis guide; the free cephalometric analysis tool measures ANB and the Steiner’s chevrons calculator applies the rules.

Clinical criteria

Cephalometrics is not enough: the examination tells you what treatment will change.

• Profile: convex, more so in high-angle patients; a low-angle pattern softens the Class II signs through chin projection (Boileau).
• Lips: lips apart at rest, lower lip trapped under the upper incisors, mentalis strain on closure.
• Overjet and overbite: large overjet in division 1, deep bite in low-angle patients, open bite in high-angle patients.
• Molar and canine relationships, measured in millimeters, on each side, with the midlines.
• Functions: breathing, swallowing, habits, tongue posture. A reading clue from Boileau: a large overjet without anterior alveolar compensation points to a functional cause.
• Occlusal locks: deep bite, marked curve of Spee, narrow upper arch, rotated upper molars, crossbite. They hold the mandible back; a transverse deficiency may only appear when the casts are placed in Class I.

The trauma risk

A large overjet is a recognized risk factor for injury to the upper incisors. 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 rise with overjet size (Nguyen et al., 1999, Eur J Orthod, PubMed). Lips that do not cover the upper incisors add to it.

The role of growth

Before discussing orthopedics, two questions: how much growth remains, and in which direction?

How much

Chronological age is not enough. Skeletal age is read with cervical vertebral maturation on the existing cephalogram (the peak lies between stages CS3 and CS4) or on a hand-wrist film. The average landmarks vary by source:

• pubertal peak at about 10 to 11 years in girls and 11 to 12 in boys according to one course, about 12 and 14 according to Björk;
• Pancherz’s window: from two years before to two years after the peak;
• the Lyon school defends an earlier start, between 7 and 10 years, based on series without control groups.

These positions coexist. One point favors Class II: the maxilla finishes growing about two years before the mandible. Our guide to cervical vertebral maturation (in French) details the stages.

Which direction

ANB is compared on two cephalograms taken 6 months to 1 year apart. Tweed’s growth types give the prognosis:

Björk’s structural signs complete the reading: an anterior rotation favors Class II correction, a posterior rotation works against it. Without growth, there is no orthopedics.

Orthopedics, camouflage or surgery: the criteria

The reasoning path

The etiological tree of the courses reads:

• secondary (functional) form: remove the cause first;
• large remaining growth in a favorable direction: orthopedics;
• primary (hereditary) form with weak or unfavorable potential: surgery;
• no growth: orthodontics if severity, compensation and associated anomalies allow it, otherwise surgery.

Boileau adds that a small discrepancy may only need monitoring or unlocking of the occlusion.

What functional appliances do

The courses call the skeletal effect of functional appliances "debatable", often masked by dentoalveolar compensations. The literature says much the same:

• in a systematic review of 22 controlled studies, two thirds of the samples showed a supplementary mandibular length gain greater than 2 mm, larger when treatment was performed at the pubertal peak, but none of the 4 randomized trials, 3 of which treated prepubertal children, reported a clinically significant change (Cozza et al., 2006, Am J Orthod Dentofacial Orthop, PubMed);
• in a meta-analysis of 10 studies, the Twin Block consistently proclined the lower incisors, retroclined the upper incisors and increased mandibular length, without clinically significant restraint of maxillary growth; most changes were small individually and no long-term data were available (Ehsani et al., 2014, Eur J Orthod, PubMed).

Our guides to the Twin Block and the Herbst appliance cover these appliances. Do not promise mandibular growth.

Early or one-phase treatment

The sources disagree. One D.U. course considers the long-term skeletal effects of a first phase weak and favors a single phase, early treatment being kept for specific indications (anterior guidance, trauma risk, locks, quality of life). Horn and Thiers-Jegou, French authors, defend intercepting most Class II cases, and Boileau stands in between. The Cochrane review of 27 randomized trials (1,251 participants) found that early two-phase treatment with a functional appliance reduced new incisal trauma (19% against 30% in the late group; odds ratio 0.56), with no difference in final overjet or ANB once both groups had finished treatment, and no other advantage of early treatment (Batista et al., 2018, Cochrane Database Syst Rev, PubMed). The evidence was rated low to moderate quality.

Numeric thresholds, and their limits

One D.U. course considers camouflage after growth when ANB is below 8°, and orthodontic-surgical treatment above 8°. Boileau gives no ANB threshold and reasons on the periodontium, functional balance, the vertical pattern, asymmetry and the profile. Horn’s favorable pattern (FMA below 29°, FHI above 65%, ANB 6° or less) also helps quantify the skeletal handicap.

In nongrowing adults, a comparison of 33 patients treated by premolar extraction camouflage with 57 treated by mandibular advancement surgery found that surgery reduced overjet more and improved most cephalometric criteria more; the esthetic ratings of the camouflage group were unchanged after treatment, while the surgical group improved but did not reach the pretreatment level of the camouflage group (Proffit et al., 1992, Am J Orthod Dentofacial Orthop, PubMed). It is a retrospective study, but it illustrates a key point: camouflage corrects the occlusion, not the jaws, and the profile has to be discussed before choosing it.

In practice: a checklist

1. Establish the occlusal class (molar, canine, overjet, both sides) and the skeletal class separately.
2. Confirm ANB with the Wits, stating the norm used; locate with SNA and SNB.
3. Look for incisor compensations (U1-NA, L1-NB, IMPA) and classify the vertical pattern.
4. Examine profile, lips, functions and occlusal locks; note the trauma risk.
5. Place growth with skeletal age, and its direction with two cephalograms or Björk’s signs.
6. Quantify the lower arch discrepancy, which decides extractions first.
7. Compare these criteria with the three approaches, then explain the possible compromises to the patient.

Frequently asked questions

What is Class 2 division 1?

It is an Angle Class II malocclusion (lower molars distal to the upper ones) with proclined upper incisors and an overjet at least equal to the amount of molar Class II. It can be dentoalveolar or skeletal, low-angle or high-angle.

Is a "Class 2 overbite" the same as Class II division 1?

Usually, yes, in everyday language: patients call protruding upper teeth an "overbite", which is an increased overjet, the hallmark of division 1. In orthodontic terms, overbite is the vertical overlap; a division 1 may have a deep bite, a normal overbite or an open bite.

What is the difference between Class II division 1 and division 2?

In division 1, the upper incisors are proclined and the overjet is increased. In division 2, they are retroclined, mask the discrepancy and come with a deep bite, usually on a low-angle pattern. They are two distinct entities and are not managed in the same way.

What ANB indicates a skeletal Class II?

The courses use an ANB above 4°, with a Wits above 2 mm. An ANB between 4° and 7° is a mild Class II in the Tweed analysis. ANB alone can mislead when the vertical pattern is unusual or Nasion is misplaced.

Can a Class II division 1 be corrected without surgery in adults?

Camouflage is discussed for mild to moderate Class II without esthetic impact or severe vertical anomaly; one course places the limit near an ANB of 8°, Boileau gives no threshold. It corrects the occlusion, not the jaws; for a personal case, an orthodontist decides.

With GS Ortho

In GS Ortho, AI places 29 landmarks on the lateral cephalogram; you check and correct them, and the Steiner and Tweed analyses are calculated straight away. The 12-panel guided diagnostic studio puts the clinical examination, the photos, the cephalometrics and the treatment plan of the same patient side by side, so the occlusal and skeletal diagnoses are read together. The decision stays yours. For a borderline case between camouflage and surgery, "Request an opinion" sends your question, panel attached, to a colleague or supervisor you choose; the answer stays in the record. The GS Ortho interface is currently available in French.

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