Significant Anterior Bolton Discrepancy Caused by Small Mandibular Incisors

Tooth size discrepancies are often overlooked during the initial stages of orthodontic diagnosis. However, even when skeletal and dental relationships appear favorable, disproportionate tooth sizes can create significant finishing challenges.

In this case study, we analyze a patient presenting with a notable Bolton discrepancy, particularly within the anterior segment. The measurements reveal a mandibular tooth-size deficiency that may influence overjet, overbite, and final occlusal outcomes.

Bolton Analysis Overview

Bolton analysis evaluates the proportional relationship between the maxillary and mandibular dentitions.

Two key ratios are calculated:

• Anterior Ratio – based on the six anterior teeth
• Overall Ratio – based on twelve teeth from first molar to first molar

The classical Bolton norms are:

• Anterior Ratio: approximately 77.2%
• Overall Ratio: approximately 91.3%

Anterior Bolton Ratio

The patient's anterior Bolton ratio is:

71.83%

• Maxillary anterior sum: 48.71 mm
• Mandibular anterior sum: 34.99 mm

This value is significantly below the Bolton norm.

The discrepancy indicates that the mandibular anterior teeth are proportionally smaller than the maxillary anterior teeth.

A difference of this magnitude is clinically relevant and should be considered during treatment planning.

Without addressing the discrepancy, achieving ideal anterior intercuspation may become difficult.

Overall Bolton Ratio

The overall Bolton ratio is:

87.29%

• Maxillary overall sum: 95.39 mm
• Mandibular overall sum: 83.26 mm

This value is also considerably below the Bolton norm of 91.3%.

The discrepancy therefore extends beyond the anterior teeth and affects the entire dentition.

The mandibular arch is globally smaller relative to the maxillary arch.

Identifying the Source of the Discrepancy

One advantage of digital Bolton analysis is the ability to identify the teeth contributing most to the discrepancy.

Maxillary Dentition

Several upper teeth present relatively large mesiodistal widths:

• 11: 9.06 mm
• 21: 9.29 mm
• 13: 7.92 mm
• 23: 8.32 mm
• 16: 10.03 mm
• 26: 9.65 mm

The maxillary dentition is generally broad and contributes significantly to the low Bolton ratios.

Mandibular Dentition

The lower incisors are relatively narrow:

• 31: 5.09 mm
• 41: 5.10 mm
• 42: 5.43 mm
• 32: 6.17 mm

Compared with the larger maxillary incisors, the mandibular anterior teeth create a substantial tooth-size deficiency.

This explains the particularly low anterior Bolton ratio.

Clinical Consequences

When the mandibular anterior teeth are proportionally too small, several clinical situations may occur:

• Excessive overjet despite proper alignment
• Difficulty obtaining ideal canine relationships
• Residual spacing in the maxillary arch
• Black triangles becoming more visible after alignment
• Compromised anterior intercuspation

Recognizing these issues before treatment begins allows the orthodontist to anticipate potential finishing challenges.

Possible Treatment Considerations

Treatment decisions should always be individualized, but several options may be considered when managing a significant Bolton discrepancy:

• Restorative enlargement of mandibular incisors using composite bonding
• Selective interproximal reduction of maxillary teeth when appropriate
• Acceptance of minor occlusal compromises
• Careful management of overjet and anterior guidance during finishing

The ideal approach depends on facial aesthetics, occlusal goals, periodontal considerations, and patient expectations.

How Ortho-Analyser Simplifies Bolton Analysis

Accurate Bolton analysis begins with accurate tooth measurements.

With Ortho-Analyser, clinicians can:

• Visualize digital models directly in the browser
• Place mesial and distal landmarks on each tooth
• Automatically calculate tooth widths
• Instantly generate Bolton ratios
• Identify problematic teeth within seconds
• Store results within the patient's digital record

This transforms a traditionally time-consuming process into a fast and efficient diagnostic workflow.

Key Takeaways

This case demonstrates a significant tooth-size discrepancy characterized by:

• Anterior Bolton Ratio: 71.83%
• Overall Bolton Ratio: 87.29%
• Relatively large maxillary dentition
• Small mandibular anterior teeth
• Potential finishing challenges if unrecognized

The analysis highlights why Bolton evaluation remains an essential part of comprehensive orthodontic diagnosis.

By identifying tooth-size discrepancies early, orthodontists can anticipate occlusal challenges and develop more predictable treatment plans.