Bolton Analysis: Understanding Tooth Size Discrepancy in Orthodontic Planning
Achieving ideal occlusion requires more than proper tooth alignment—it depends on precise proportional relationships between the maxillary and mandibular teeth. One of the most important tools for evaluating these relationships is the Bolton Analysis, a diagnostic method used to identify tooth size discrepancies that can interfere with optimal alignment, intercuspation, and long-term stability.
Bolton Analysis is routinely used in orthodontics and interdisciplinary treatment planning to ensure that both arches are compatible before, during, and after treatment.
What Is Bolton Analysis?
Bolton Analysis measures the mesio-distal width of teeth to evaluate proportional relationships between the upper and lower dental arches. By comparing summed tooth widths, clinicians can determine whether a patient has excess tooth material in one arch relative to the other.
When tooth size proportions are not ideal, even perfectly aligned teeth may fail to achieve proper occlusion. This mismatch is referred to as a Bolton discrepancy.
Types of Bolton Analysis
Bolton described two separate analyses: the Overall Bolton Analysis and the Anterior Bolton Analysis. Each evaluates a different segment of the dentition.
Overall Bolton Analysis
The Overall Bolton Analysis compares the combined mesio-distal widths of 12 mandibular teeth (from first molar to first molar) to the corresponding 12 maxillary teeth.
The established normal overall ratio is 91.3%.
This means that, on average, the total mesio-distal width of the mandibular teeth should be approximately 91.3% of the maxillary tooth width for ideal occlusal compatibility.
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An overall ratio greater than 91.3% indicates that the mandibular teeth are proportionally larger than normal.
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An overall ratio less than 91.3% indicates that the mandibular teeth are proportionally smaller than normal.
Either deviation represents an overall Bolton discrepancy.
Anterior Bolton Analysis
The Anterior Bolton Analysis focuses on the front teeth and compares the mesio-distal widths of the six mandibular anterior teeth to the six maxillary anterior teeth.
The normal anterior ratio is 77.2%.
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An anterior ratio above 77.2% suggests excess mandibular anterior tooth width.
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An anterior ratio below 77.2% suggests deficient mandibular anterior tooth width or relatively large maxillary anterior teeth.
Anterior Bolton discrepancies are especially important in esthetic cases, as they directly affect overjet, overbite, spacing, and smile balance.
What Is a Bolton Discrepancy?
A Bolton discrepancy occurs when the measured tooth size ratios differ from the established norms. Even small discrepancies can have significant clinical consequences.
When tooth widths are disproportionate, achieving proper alignment and intercuspation becomes difficult or impossible without compensatory measures. This can lead to residual spacing, excessive overjet or overbite, improper contacts, or unstable occlusion following orthodontic treatment.
Clinical Significance of Bolton Analysis
Bolton Analysis plays a critical role in orthodontic diagnosis and interdisciplinary planning. Identifying tooth size discrepancies early allows clinicians to plan appropriate interventions, which may include enamel reduction, restorative buildups, selective extractions, or modified orthodontic mechanics.
Failure to recognize a Bolton discrepancy can result in compromised treatment outcomes, even when tooth alignment appears ideal. For this reason, Bolton Analysis is considered a foundational diagnostic step in comprehensive orthodontic care.
Bolton Analysis in Interdisciplinary Care
In cases involving orthodontics combined with restorative dentistry, implant planning, or orthognathic surgery, Bolton Analysis helps ensure that final tooth proportions support both function and esthetics. Collaboration between orthodontists, oral surgeons, and restorative dentists is often required to address significant discrepancies.
Conclusion
Bolton Analysis is an essential diagnostic tool for evaluating tooth size relationships between the maxillary and mandibular arches. By measuring mesio-distal tooth widths and comparing them to established ratios, clinicians can identify discrepancies that may compromise alignment, occlusion, and long-term stability.
Recognizing and addressing Bolton discrepancies early in treatment planning allows for predictable outcomes, improved esthetics, and functional occlusal harmony.
