La boîte de Steiner, le bilan d’espace pas à pas
Remplir la boîte de Steiner ligne par ligne : encombrement, repositionnement incisif, courbe de Spee, molaires, leeway, extractions. Règles d’équilibrage et exemple chiffré.
Bolton analysis: free calculator for the anterior and overall ratios
Enter the mesiodistal widths of the teeth, from first molar to first molar: the anterior and overall ratios are calculated live and compared with the Bolton norms, with the excess in millimeters and its clinical reading.
- Free
- No sign-up
- Every calculation explained
The principle of the Bolton analysis
For the teeth to intercuspate with normal overjet and overbite, the size of the mandibular teeth must be in proportion to that of the maxillary teeth. Bolton quantified this proportion by comparing the sums of the mesiodistal widths of the two arches. When it is disrupted, there is a tooth-size discrepancy: one or more teeth are too small (microdontia) or too large (macrodontia) for the opposing arch.
| Ratio | Calculation | Mean | Standard deviation | Range |
|---|---|---|---|---|
| Anterior | Σ of the 6 mandibular teeth (33 to 43) / Σ of the 6 maxillary teeth (13 to 23) × 100 | 77.2% | 1.65 | 74.5 to 80.4% |
| Overall | Σ of the 12 mandibular teeth (36 to 46) / Σ of the 12 maxillary teeth (16 to 26) × 100 | 91.3% | 1.81 | 87.5 to 94.8% |
These values from Bolton (1958, 1962) come from his original sample: 55 excellent occlusions, measured to the nearest quarter of a millimeter. The range shows that an excellent occlusion can accommodate notable deviations: the mean is not a target to the nearest tenth, and norms may differ between populations.
Measuring tooth widths
- In the permanent dentition: in the mixed dentition, the size of the primary teeth does not predict that of the permanent teeth, and a transient discrepancy is possible.
- On a cast or digital model, measure the greatest mesiodistal width of each tooth, from first molar to first molar, with a caliper or the measuring tool of your software.
- Be precise: a small error repeated over twelve teeth adds up and shifts the ratio.
- Enter the values tooth by tooth: the sums and ratios update with each entry.
Expressing the excess in millimeters
A percentage means little at the chair: it is converted into millimeters, as with the Bolton chart. For the patient's maxillary sum, the expected mandibular sum is calculated, then the difference from the actual sum.
- Ratio too high, mandibular excess: excess = Σ mandibular − Σ maxillary × 0.772 (anterior) or × 0.913 (overall).
- Ratio too low, maxillary excess: excess = Σ maxillary − Σ mandibular / 0.772 (anterior) or / 0.913 (overall).
The ratio does not tell which arch is at fault. A “mandibular excess” can come from wide mandibular incisors as well as from small maxillary lateral incisors, the most common example of microdontia. The tool gives both readings; examining the teeth settles it.
What the discrepancy changes clinically
- Anterior mandibular excess: lower incisor crowding with aligned, or even spaced, upper incisors. At the end of treatment, it becomes difficult to obtain both a Class I canine relationship and normal overjet and overbite.
- Anterior maxillary excess: spacing in the mandibular arch, or increased overjet and overbite; a maxillary excess is one of the causes of deep bite.
- Overall discrepancy with a normal anterior ratio: the difference lies in the posterior segments (premolars, molars) and affects the intercuspation of the buccal segments.
Options to discuss
- Microdontia: build-ups are usually preferred, with composite or prosthetic restorations. Small lateral incisors, for example, are positioned in a Class I canine relationship with mesial and distal spaces, then restored.
- True or relative macrodontia: interproximal reduction (IPR, stripping) or extractions.
- Extraction of a mandibular incisor: considered only for a mandibular excess of 4 to 6 mm, and after a set-up. If unjustified, it increases overjet and overbite.
- Diagnostic set-up: before any irreversible procedure, it reproduces the planned tooth axes and confirms, or not, the discrepancy.
Limits of the index
Harmony between the arches does not depend on tooth widths alone: incisor inclination, the occlusal plane, the curves of Spee and Monson, cusp height and above all incisor overbite also matter. According to Neff, there is in fact no standard anterior ratio: it varies with overbite, and a deep overbite may be an adaptation to a discrepancy. The Bolton ratio should therefore not be used as a strict cut-off: a deviation of at least one standard deviation raises the suspicion of a discrepancy, and the set-up confirms it.
Frequently asked questions
What is the Bolton analysis?
It compares the sum of the mesiodistal widths of the mandibular teeth with that of the maxillary teeth. Two ratios are calculated: the anterior ratio (6 teeth, canine to canine) and the overall ratio (12 teeth, first molar to first molar). A ratio far from the norm indicates a tooth-size discrepancy: the teeth of one arch are too large, or too small, relative to those of the other.
What are the Bolton norms?
Anterior ratio: 77.2% on average (standard deviation 1.65; 74.5 to 80.4% in the excellent occlusions studied). Overall ratio: 91.3% (standard deviation 1.81; 87.5 to 94.8%). Bolton established them on 55 excellent occlusions, measuring to the nearest quarter of a millimeter. They may differ between populations.
From what deviation is there a discrepancy?
A ratio slightly different from the mean is common: excellent occlusions cover the whole range of the norms. A discrepancy is suspected from a deviation of one standard deviation from the mean, then confirmed with a diagnostic set-up before any decision. This is the threshold used by the tool.
How is the excess in millimeters calculated?
As with the Bolton chart: for the patient’s maxillary sum, the expected mandibular sum is calculated (maxillary sum × 0.772 for the anterior ratio, × 0.913 for the overall ratio). If the ratio is too high, the mandibular excess is the difference between the actual and the expected mandibular sum. If it is too low, the expected maxillary sum is calculated instead (mandibular sum / 0.772 or / 0.913), and the maxillary excess is the difference from the actual maxillary sum.
Can the analysis be done in the mixed dentition?
No. In the mixed dentition, the size of the primary teeth does not predict that of the permanent teeth and a transient discrepancy is possible: the Bolton analysis is done in the permanent dentition.
What if a tooth is missing?
The analysis assumes all twelve teeth of each arch. To estimate the space to keep for a missing tooth, the width of its contralateral counterpart is often used if that tooth is normal; the set-up remains the reference.
Are the measurements I enter sent anywhere?
No. The calculation is done entirely in your browser: no measurement is transmitted or stored.
Learning and decision-support tool: it applies Bolton’s norms and formulas and does not replace clinical examination, the set-up or the practitioner’s judgment.