Beta Angle in Orthodontics: How to Measure and Read It

The beta angle is a cephalometric measurement of the sagittal relationship between the maxilla and the mandible, designed to work without the cranial base or the occlusal plane, the weak points of ANB and the Wits appraisal. This guide covers its construction, the values reported in different populations, what comparison studies found, and why it should complement ANB and Wits, not replace them. Every figure below comes with its source.

What the beta angle measures

The original description

Baik and Ververidou proposed the beta angle in 2004 as a new way to assess sagittal jaw discrepancies (Baik and Ververidou, 2004, Am J Orthod Dentofacial Orthop, PubMed). Their starting point: the usual angular and linear measurements can be inaccurate because they depend on factors other than the jaw relationship itself.

The angle uses three skeletal landmarks only:

• Point A, on the anterior concavity of the maxilla;
• Point B, on the anterior concavity of the mandibular symphysis;
• Point C, the apparent axis of the condyle.

The authors measured it on 76 pretreatment cephalograms of white patients selected by four criteria of a skeletal Class I pattern, then compared them with Class II and Class III groups. From their receiver operating characteristic (ROC) analysis, they concluded that a beta angle between 27° and 35° can be considered a skeletal Class I pattern. A more acute angle indicates a Class II pattern, a more obtuse one a Class III pattern.

Constructing the angle

The construction, as later studies describe it (Prasad et al., 2013, J Nat Sci Biol Med, PubMed; Sundareswaran and Kumar, 2015, J Nat Sci Biol Med, PubMed):

1. Locate points A, B and C on the lateral cephalogram.
2. Draw the C-B line, from the condylar point to point B.
3. From point A, drop a perpendicular to the C-B line. Sundareswaran and Kumar call its foot point X.
4. Draw the A-B line.
5. The beta angle is the angle at point A, between the perpendicular (A-X) and the A-B line.

Points A, X and B therefore form a right triangle, with the right angle at X. The beta angle is the angle XAB, and its tangent equals XB / AX. This geometry explains how the angle behaves: anything that lengthens XB relative to AX opens it.

A note on point C. The original abstract defines it as the "apparent axis of the condyle"; we could not read the full text of the original paper, so we cannot describe exactly how the authors locate it. Later papers phrase it differently: Sundareswaran and Kumar write the C-B line as "Condylion-B point", Perinetti and colleagues as a "CA-B" line. Condylion and a condylar axis are not necessarily the same point. Check which definition your software or your course uses, and keep it constant from one radiograph to the next.

Reading the direction

The beta angle runs opposite to ANB: smaller toward Class II, larger toward Class III. Prasad et al. found a significant negative correlation between beta and both ANB and the Wits appraisal in their Class II and Class III groups.

Why it was proposed: the limits of ANB and Wits

ANB, the angle between N-A and N-B, is the reference sagittal measurement of the Steiner analysis, with a usual norm of 2° ± 2°. It is convenient, but several factors change it without any change in the relationship between the jaws: the position of Nasion, the inclination of S-N, jaw rotation, and the vertical distance from N to points A and B. A clockwise rotation can push point B back and make an ANB look normal in a hyperdivergent Class III.

The Wits appraisal (Jacobson) projects points A and B onto the functional occlusal plane. It escapes Nasion, but it depends directly on how the occlusal plane is traced, which is difficult in the mixed dentition or with a deep curve of Spee. Its norms also differ between traditions: 0 ± 2 mm in Steiner course materials, 2 ± 2 mm on Tweed sheets.

The beta angle sidesteps both: its three points sit on the jaws themselves. The rationale, as Sundareswaran and Kumar report it: when the mandible rotates backward, point B and the C-B line rotate in the same direction, carrying the perpendicular from point A with them, so the angle should stay relatively stable. They add that this only holds if the mandible rotated like a rigid wheel, which is not how it grows.

Reported values: one study, one population

The 27° to 35° range comes from a sample of white patients. Each value below belongs to its study, sample and population; none of them is a universal norm.

Three precautions:

• The groups were defined differently. Most teams classified patients with ANB, Wits and the profile, then measured beta in each group, so the values partly reflect those criteria.
• The ranges overlap. In the Davangere sample, the Class I range (26° to 34°) overlaps the Class II and Class III cut-offs.
• Age and sex. Sadeghian et al. found the angle increased with age in children (r = 0.435), with no sex difference; Prasad et al. found no sex difference in adults; Qamruddin et al. reported one in Pakistani Class II patients only (Qamruddin et al., 2016, J Coll Physicians Surg Pak, PubMed).

Prasad et al. found no significant difference between their Indian values and Caucasian norms, and concluded that the angle is stable across ethnic groups. That rests on one district sample and says nothing about populations never measured. Our PubMed search found no beta angle study in North African patients.

What comparison studies show

Agreement with ANB and Wits

The results are mixed and depend on the population and on how the "true" skeletal class was defined:

• In 146 normodivergent Pakistani adults in whom at least one parameter disagreed with the others, the class was set by the majority of six measurements. ANB agreed best with that diagnosis (kappa 0.802), the beta angle 0.511. Beta performed well in Class III (sensitivity 0.902) but poorly in Class II (0.452) (Ahmed et al., 2018, Dental Press J Orthod, PubMed).
• In 85 patients in Karachi, the correlation between ANB and the beta angle was weak (r = 0.377) (Gul-e-Erum and Fida, 2008, J Coll Physicians Surg Pak, PubMed).
• On 213 CBCT scans, the correlation of the beta angle with ANB was moderate (0.760), lower than that of the Wits appraisal (0.858) (Almaqrami et al., 2018, J Clin Exp Dent, PubMed).
• On 209 Pakistani cephalograms, ANB, Wits, beta, Yen and W angles were all found equally reliable for classifying skeletal patterns (Qamaruddin et al., 2017, Saudi Dent J, PubMed).
• In an Indian sample of 94 cephalograms, the authors concluded that no single parameter can diagnose the sagittal discrepancy in every case, and proposed an algorithm that combines several (Khandelwal et al., 2021, J Orthod, PubMed).

These are cross-sectional studies, mostly single-center and from South Asia, with 85 to 213 patients. They do not show that the beta angle is "better" than ANB; they show that it adds a reading based on different landmarks.

Is it independent of the vertical pattern? A disagreement

• Sundareswaran and Kumar (2015) divided 179 patients aged 15 to 25 by vertical pattern. In vertical growers, the beta angle increased significantly in Class I and Class II, pushing them toward Class III and Class I respectively: agreement with the skeletal class fell to about 47%, while Class III stayed at 100% whatever the pattern. Their explanation: a steep C-B line moves point X distally, lengthens XB and opens the angle. They also report that the 2004 sample had normal vertical proportions.
• Singh et al. (2016), on 120 subjects, found only a weak correlation between the beta angle and FMA, and concluded that it is not affected by the growth pattern.
• Perinetti et al. (2018) found that the beta angle was associated with SNA and with SN/MP (facial divergence), although less distorted than ANB, and proposed floating norms that adjust it to these two angles.

When a patient is clearly hyperdivergent, read a beta angle in the Class I or Class III range with caution, especially if ANB and Wits point toward Class II.

Measurement reliability

When the same examiner retraces the same films, repeatability looks good: Ahmed et al. reported an intraclass correlation coefficient of 0.989 on 30 retraced cephalograms, and Sundareswaran and Kumar found good agreement between two tracings two weeks apart. These are intra-examiner figures; we found no data on agreement between different clinicians for the beta angle.

How to use it: a complement, never alone

The beta angle earns its place when the usual measurements are doubtful:

• ANB looks unreliable: Nasion clearly forward or back, an unusual S-N inclination, a marked rotation of the jaws;
• the Wits appraisal is hard to trace: mixed dentition, deep curve of Spee, open bite, an occlusal plane hard to define;
• ANB and Wits disagree, and you are looking for another reading before going back to the clinical examination.

Read it in a set: ANB, Wits, the beta angle, SNA and SNB, and the divergence (SN-GoGn or FMA). If the measurements agree with the profile, the diagnosis is solid. If they disagree, no single number settles it: the clinical examination of the profile and the incisor position take over. Our French course on cephalometrics (in French) explains this reading in pairs, ANB with Wits.

Like ANB, the beta angle says that there is a discrepancy, not where it comes from: SNA, SNB and jaw lengths answer that question.

The limits of the beta angle

• Point C depends on a clear view of the condyle. It is the only posterior landmark of the angle, and bilateral structures often appear doubled on a lateral cephalogram; our cephalometric tracing guide explains how to handle double contours. An uncertain point C moves the C-B line, and therefore the angle.
• Points A and B remain the weak points of every sagittal measurement. They are low in contrast and, as Prasad et al. recall, influenced by growth and by dentoalveolar remodeling during treatment.
• Point C is not defined identically in every paper, the vertical pattern may open the angle, and norms depend on population and age.
• It describes, it does not decide. No beta angle value, on its own, indicates a treatment.

Does the free GS Ortho tool calculate it?

No. Our free cephalometric analysis tool calculates SNA, SNB, ANB, SN-GoGn, the incisor measurements of the Steiner analysis (U1-NA, L1-NB in degrees and millimeters, interincisal angle) and the Tweed triangle (FMA, IMPA, FMIA) from the landmarks you place. It has no condylar point and computes neither the beta angle nor the Wits appraisal: measure the beta angle on the tracing, following the construction above.

In practice: a checklist

1. The condyle is identifiable on the cephalogram; if it is not, do not compute the beta angle.
2. Points A, B and C are placed carefully, with one stated definition of C kept at every time point.
3. The perpendicular is dropped from point A onto C-B, and the angle is read at A, between it and A-B.
4. The value is read in reverse: smaller toward Class II, larger toward Class III, compared with a norm from a stated study and population.
5. The beta angle is read with ANB, Wits, SNA, SNB and the divergence, then checked against the profile.
6. In a hyperdivergent patient, a "normal" or "Class III" beta angle is treated with caution.

Frequently asked questions

What is a normal beta angle?

In the original study of 76 white patients, Baik and Ververidou considered a beta angle between 27° and 35° a skeletal Class I pattern. Other populations gave close Class I means: about 31° in several Indian samples, 32.5° in a Pakistani sample, 31.7° in Iranian children and 30.3° in Italian children. These values come from specific samples; none of them is a universal norm, and children’s values change with age.

Beta angle vs ANB vs Wits: which is best?

None is best in every case. ANB depends on Nasion, the cranial base and jaw rotation; Wits on the occlusal plane; the beta angle avoids both but depends on point C and, according to some studies, on the vertical pattern. In one Pakistani comparison, ANB agreed best with the final diagnosis and beta performed well mainly in Class III. Use them together, checked against the profile.

Which landmarks does the beta angle use?

Three skeletal landmarks: point A, point B and point C, described in the original paper as the apparent axis of the condyle. The angle is formed at point A between the A-B line and the perpendicular from A to the C-B line. Some later studies use condylion as point C, so state the definition you use.

Can the beta angle be used in children?

It has been measured in children: a mean of 31.7° ± 3.31° in 235 Iranian children aged 6 to 17, increasing with age, and 30.3° ± 3.5° in 119 Italian children aged 8 to 14. Because it changes with growth, compare a child with a sample of a similar age and keep the same definition of point C over time.

With GS Ortho

In GS Ortho, AI places 29 landmarks on the lateral cephalogram and the Steiner and Tweed analyses are calculated straight away. You check each landmark, correct it if needed, then validate: the decision stays yours. The measurements feed into the guided diagnostic studio, residents can be supervised case by case, and an orthodontist’s opinion can be requested in one click, straight from the case. Patient data stays hosted at the practice. The GS Ortho interface is currently available in French.

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beta angle cephalometrics sagittal discrepancy ANB wits appraisal