How Scientists Estimate a Child's Age from Teeth
Amidst the chaos of a mass disaster or the quiet of a lab, a single X-ray can reveal one of the most fundamental aspects of our identity: our age.
Imagine a child arrives in a new country with no documents, their future hinging on whether they are considered a minor or an adult. Or consider a natural disaster where victims need to be identified. In these high-stakes scenarios, forensic scientists turn to one of the most reliable clocks nature has to offer: our teeth.
Teeth are the hardest substances in the human body and can survive extreme conditions that destroy other tissues, making them invaluable in forensic investigations.
While skeletal bones can suggest age, they're influenced by nutrition and health. Teeth, however, develop with remarkable consistency, creating a biological timeline that remains largely unaffected by environmental factors 4 . Among the various methods to read this timeline, one stands out for its elegance and widespread use: the Nolla method. This systematic review delves into the precision of this technique, analyzing global research to determine its reliability in estimating the age of sub-adults across different populations.
To understand how teeth reveal age, we must first appreciate their development. Unlike bones, which remodel throughout life, teeth follow a strict, predetermined developmental sequence. From the formation of tiny tooth buds in the jawbone to the complete closure of the root tips, each tooth progresses through predictable stages at relatively consistent ages 4 .
Initial appearance of the tooth crypt
Complete closure of the root tip
The Nolla method, developed by Dr. Carmen Nolla in the 1960s, capitalizes on this predictable pattern. It categorizes the development of each permanent tooth into ten distinct stages, from the initial appearance of the crypt (Stage 1) to the complete closure of the root apex (Stage 10) 2 5 . By examining a panoramic dental X-ray—a single image capturing all teeth in both jaws—a forensic expert can assign Nolla stages to the seven left permanent teeth, calculate a total score, and match it to standardized tables to estimate age 5 .
When scientists want to know how well a method works across different populations, they turn to systematic reviews and meta-analyses—studies that compile and analyze data from multiple existing research papers. One such comprehensive analysis published in Cureus in 2024 compared the Nolla method with another popular technique, the Demirjian method, across 25 studies 1 .
+0.5 years
Average overestimation
-0.28 years
Average underestimation
The findings revealed a consistent pattern: the Demirjian method tended to overestimate age by an average of 0.5 years across all age groups, while the Nolla method consistently underestimated age by approximately 0.25-0.28 years 1 . This systematic difference between methods amounted to nearly 0.7 years on average—a significant gap when precise age determination carries legal consequences.
| Method | Overall Trend | Average Magnitude of Error | Most Accurate Population |
|---|---|---|---|
| Nolla Method | Underestimation | 0.25-0.28 years | Females (closest to chronological age) |
| Demirjian Method | Overestimation | 0.5 years | Varies by population |
| Combined Approach | Balanced | Reduced bias | All populations (through cross-verification) |
The review also uncovered that accuracy varies by both age and gender. The Demirjian method showed the greatest overestimation in younger children (0.71 years for males aged 6-6.99) and early adolescent girls (0.82 years for females aged 11-11.99) 1 . These patterns highlight why population-specific and demographic-specific calibrations are essential for precise age estimation.
To understand how researchers evaluate the Nolla method in a specific population, let's examine a detailed study from northwestern Romania, published in Children in 2025 2 5 . This research provides a perfect case study of the method's application and limitations.
Digital panoramic radiographs were collected from a dental practice in Oradea, Romania. All images were originally taken for diagnostic purposes, not specifically for the study. Patients with conditions that could affect tooth development were excluded 5 .
Chronological age was calculated precisely from the difference between the patient's date of birth and the date of the radiographic examination 5 .
Using the Nolla method, a single investigator evaluated the development of the seven permanent teeth on the left side of the mouth, assigning each tooth a stage from 0 to 10. The scores were then matched to gender-specific dental age norms 5 .
The team used specialized statistical tests including the Wilcoxon signed-rank and Mann-Whitney U tests to compare dental age with chronological age and assess consistency across genders and age groups 2 .
The Romanian study revealed findings that would significantly impact forensic practice in the region. The average chronological age of participants was 9.95 years, but the Nolla method estimated an average dental age of only 8.43 years—an underestimation of approximately 1.5 years 2 .
1.7 years
More pronounced underestimation
1.15 years
Less pronounced underestimation
| Age Group (Years) | Discrepancy (Years) | Sample Representation |
|---|---|---|
| 3-3.9 | 0.3 | Smallest difference |
| 8-8.9 | 1.5 | Highest representation (14.7%) |
| 9-9.9 | 1.5 | High representation (13.3%) |
| 14-14.9 | 2.6 | Peak discrepancy |
| All Groups | 1.5 (median) | 860 radiographs total |
What does it take to perform dental age estimation in a forensic setting? Here's a look at the key tools and materials researchers and forensic experts rely on:
Single image capturing all teeth and jaws. Primary data source for assessing tooth development stages 2 .
Standardized charts matching dental scores to age. Converting observed development stages to estimated age 5 .
Software for precise stage assessment. Enhancing measurement consistency in radiographic analysis.
Data analysis and comparison. Calculating correlations between dental and chronological age 2 .
These tools form the foundation of reliable dental age estimation. The panoramic radiograph serves as the canvas, while the Nolla classification provides the language to interpret the developmental story written within the teeth. Statistical software then helps quantify the relationship between dental development and chronological age, revealing patterns and discrepancies that might otherwise go unnoticed.
The systematic investigation into Nolla's method reveals both its value and its limitations. As a 2022 comprehensive review in Scientific Reports noted, while all major dental age estimation methods show validity, they differ significantly in precision 9 . The Nolla method offers a balanced approach, often with less systematic error than the overestimation tendency of the popular Demirjian method 1 .
Recent research explores deep learning models that can analyze dental radiographs with remarkable precision 6 . One 2025 study reported a modified Xception model that effectively classified individuals relative to the 12-year-old threshold important in criminal responsibility cases 6 .
As these advancements continue, the combination of traditional methods like Nolla's with modern technology and population-specific calibration promises even more reliable age estimation. In a world where justice often depends on accurately determining a child's age, this scientific progress isn't just academic—it's a matter of fundamental human rights and dignity.
The next time you smile, remember that your teeth contain more than just enamel and dentin—they hold a chronological record of your development, one that science is learning to read with ever-increasing precision.