Nance analysis is a fundamental orthodontic method used to assess the arch length for the permanent dentition by comparing the space occupied by specific primary teeth with their permanent successors. This analysis, first defined by H. N. Nance in 1947, helps clinicians understand potential space discrepancies during the transition from primary to permanent dentition.
Understanding Nance Analysis
At its core, Nance analysis quantifies the natural difference in mesiodistal width (front-to-back dimension) between certain primary teeth and their corresponding permanent replacements. Specifically, it calculates the difference in length between:
- The primary canine and the two primary molars (first and second).
- The permanent canine and the two permanent premolars (first and second) that will replace them.
This comparison is crucial because the primary teeth are generally wider than their permanent successors, creating what is known as "leeway space" or "E-space." Understanding this space is vital for predicting potential crowding or spacing issues in the developing permanent dentition.
How Nance Analysis Works
Nance analysis involves measuring the mesiodistal width of specific teeth in the dental arch. This is typically done on study models (casts of the patient's teeth) or directly in the mouth. The measurements are taken for each quadrant (upper right, upper left, lower right, lower left).
The Measurement Process
- Primary Dentition Space: Measure the combined width of the primary canine, primary first molar, and primary second molar.
- Permanent Dentition Space: Estimate or measure the combined width of the permanent canine, permanent first premolar, and permanent second premolar for the same quadrant.
- Calculate the Difference: Subtract the sum of the permanent teeth widths from the sum of the primary teeth widths.
The resulting value indicates the amount of available leeway space. A positive value means there is excess space (leeway space), while a negative value suggests a potential space deficiency.
Leeway Space: Primary vs. Permanent Tooth Dimensions
The concept of leeway space is central to Nance analysis. The following table illustrates the typical size difference that creates this critical space.
| Tooth Type | Primary Tooth (Average Mesiodistal Width) | Permanent Successor (Average Mesiodistal Width) |
|---|---|---|
| Canine | 5.0 - 6.0 mm | 6.5 - 7.5 mm |
| First Molar / Premolar | 7.0 - 8.0 mm | 6.5 - 7.0 mm |
| Second Molar / Premolar | 8.5 - 9.5 mm | 7.0 - 7.5 mm |
| Total (Sum) | ~20.5 - 23.5 mm | ~20.0 - 22.0 mm |
| Leeway Space | ~1.0 - 2.5 mm per quadrant (mandible usually greater) |
Note: These are average values and can vary significantly among individuals.
As you can see, while the permanent canine is typically wider than its primary counterpart, the permanent premolars are generally narrower than the primary molars they replace. This net difference usually results in a small amount of extra space, particularly in the lower arch.
Clinical Significance and Applications
Nance analysis provides valuable insights for orthodontic diagnosis and treatment planning, especially during the mixed dentition phase (when both primary and permanent teeth are present).
Key Applications:
- Space Management: It helps orthodontists predict if there will be enough space for the eruption of permanent canines and premolars.
- Crowding Prevention: If the analysis shows insufficient leeway space, proactive measures can be taken to prevent future crowding, such as:
- Space maintainers: To hold existing space if primary teeth are lost prematurely.
- Serial extractions: In severe cases, a planned removal of certain primary teeth to guide the eruption of permanent teeth.
- Arch expansion: To create more space in the dental arch.
- Treatment Planning: It guides decisions on whether interceptive orthodontic treatment is necessary.
- Anchorage Control: The leeway space can be utilized to move permanent molars forward slightly, gaining space for other teeth, if needed.
Practical Insights:
- The mandibular arch (lower jaw) typically has more leeway space (around 1.7-2.5 mm per side) than the maxillary arch (upper jaw), which has about 0.9-1.5 mm per side. This difference is clinically significant.
- Understanding leeway space allows for strategic timing of orthodontic interventions to guide tooth eruption and achieve a well-aligned permanent dentition.
Advantages and Limitations
Advantages:
- Simple and Quick: Relatively easy to perform using study models or intraoral measurements.
- Predictive Value: Offers a good estimation of future space availability.
- Foundation for Treatment: Helps in early diagnosis and planning for potential space problems.
Limitations:
- Average Values: Relies on average tooth sizes, which may not accurately reflect individual variations.
- Does Not Account for Growth: It is a static measurement and does not predict future jaw growth or changes in arch dimensions.
- Requires Accurate Measurements: Inaccurate measurements can lead to incorrect conclusions.
Nance analysis remains a foundational tool in orthodontics, providing a straightforward method to evaluate arch length sufficiency and guide early interventions to ensure healthy dental development.
