Bolton Discrepancy: When Tooth Sizes Don't Match

What Bolton analysis measures

Bolton analysis, developed by Wayne Bolton in 1958, compares the sum of the mesiodistal (front-to-back) widths of upper and lower teeth to determine whether the two arches are proportionate. The anterior Bolton ratio compares the combined widths of the six upper front teeth (central incisors, lateral incisors, and canines) against the corresponding six lower teeth. The overall Bolton ratio compares the combined widths of the twelve upper teeth against the twelve lower teeth. Normal ratios are approximately 77.2% for the anterior comparison and 91.3% for the overall comparison. A value above or below these norms indicates a discrepancy — either the lower teeth are collectively too wide relative to the upper teeth, or the upper teeth are too wide relative to the lower.

What causes a Bolton discrepancy

The most common causes of clinically significant anterior Bolton discrepancy are peg-shaped or congenitally small upper lateral incisors, which reduce the upper anterior sum relative to the lower, and congenitally missing upper teeth (hypodontia), which similarly reduce the upper total. Oversized lower incisors — broad, wide lower front teeth relative to average — can also create a lower excess. Overall Bolton discrepancy can arise from extra-wide lower molars, impacted or missing teeth that alter the arch lengths, or simply genetic tooth size variation. A Bolton discrepancy does not mean anything is wrong with the teeth themselves — it is simply a measurement of proportionality between the two arches.

How a Bolton discrepancy affects treatment outcomes

If a Bolton discrepancy is not identified and planned for before treatment begins, the end result may be suboptimal despite technically well-aligned teeth. An anterior upper excess — too much upper tooth material — may prevent the overjet from being reduced to the correct amount, leaving the upper front teeth protruding slightly. An anterior lower excess — too much lower tooth material — may mean the lower front teeth cannot be fully retracted behind the upper teeth, leaving a reverse overjet tendency or poor interdigitation. Spacing may remain at the end of treatment that cannot be closed by moving teeth alone. Identifying the discrepancy in advance allows the clinician to factor in corrective procedures at the planning stage.

Clinical solutions for Bolton discrepancy

The available solutions depend on whether there is an excess in the upper or lower arch. Where there is a lower excess — too much lower tooth material relative to the upper — interproximal reduction (IPR) can be used to reduce the widths of the lower teeth by polishing small amounts of enamel from the contact points between teeth. This is most commonly applied to the lower front teeth. Where there is an upper deficit — teeth that are too small — the solutions involve building up the smaller teeth. Composite bonding can add width to peg-shaped lateral incisors or small upper front teeth. Porcelain veneers offer a more durable solution for the same purpose. Crowns may be appropriate where a tooth is structurally compromised. In cases with missing teeth, orthodontic space management followed by an implant, bridge, or partial denture may be required.

When Bolton analysis is carried out

Bolton analysis is typically performed during orthodontic treatment planning, either from study models (plaster casts or digital scans of the teeth) or from digital measurements taken on intraoral scan software. It is most relevant for cases involving anterior aesthetic work, cases where perfect occlusal interdigitation is a goal, and cases involving peg laterals, missing teeth, or unusually sized teeth. Not all orthodontists routinely perform a formal Bolton analysis for every case — mild discrepancies in straightforward cases may have minimal clinical impact — but for complex cases or those combining orthodontics with restorative work, it is an important step.

Bolton discrepancy and combined orthodontic and restorative treatment

The clearest clinical application of Bolton analysis is in planning combined orthodontic and restorative cases. For a patient with peg-shaped upper lateral incisors, for example, the orthodontist and restorative dentist should agree in advance on the intended final width of the built-up lateral incisors. The orthodontist then spaces the upper arch accordingly during treatment, leaving the correct amount of space adjacent to each lateral for the dentist to fill with composite or a veneer. Without this coordination, the orthodontist may close space that the dentist needs, or leave space that is the wrong shape for the intended restoration. Bolton analysis provides the quantitative basis for this planning conversation.

Useful related pages

This guide is for general information only. It is not a diagnosis, treatment plan, or substitute for advice from a registered dentist or orthodontist.