Tooth Root Canal Test for Telling Adults from Minors Gets Its First Spanish Trial

Every year, thousands of young people arrive in Europe without documents that prove how old they are. Whether they are treated as children or as adults can determine where they sleep, what schooling they receive, and whether they can be detained or deported. Because the stakes are so high, forensic scientists have spent decades searching for biological markers that reliably indicate whether a person has reached the age of majority, which in most legal systems is set at eighteen years. Teeth, which mature on a predictable schedule and survive fire, decay, and time better than almost any other tissue, have long been the favorite source of such markers. Now a team at the University of Granada has put one of the newest dental age tests through its first rigorous trial in a Spanish population, and the results are a masterclass in both the promise and the limits of forensic science.

The method under scrutiny was proposed by researchers at King’s College London led by Graham Roberts and Victoria Lucas. It focuses on a subtle feature visible on ordinary dental panoramic X-rays, known as orthopantomographs: the width of the root canal in the lower molars. As a tooth matures, dentin is laid down continuously inside the pulp chamber and root canals, gradually narrowing the dark canal space seen on radiographs. The London team observed that the relative width of the distal root canal, the rear canal of the lower left molars, follows recognizable patterns once the root tip, or apex, has fully closed. Because complete apical closure of the second and third molars typically occurs around the late teenage years, the pattern of canal narrowing can, in principle, act as a maturity marker at the crucial eighteen-year threshold.

In practice, the method works by classifying each molar into one of three lettered categories. Category A describes canals that remain wide, with the canal walls roughly parallel, a pattern typical of younger individuals whose roots have only recently closed. Category B shows a canal that has begun to narrow toward the apex, an intermediate stage. Category C represents the most mature pattern, in which the canal has narrowed so far that its width is less than half the width it would have had at completion of root growth, or in the most advanced cases the canal is barely visible at all. A fourth designation, U, is reserved for teeth that cannot be classified, whether because of restorations, decay, image distortion, or anatomical variation. The logic is straightforward: the more category C patterns a person displays across the lower molars, the more likely it is that they have passed the biological milestone corresponding to legal adulthood.

But a method that works in one country does not automatically work in another. Dental maturation timing varies between populations for reasons that include genetics, nutrition, socioeconomic conditions, and overall health, a fact documented repeatedly since the earliest days of age estimation research in the early twentieth century. Studies of third molar development in Japanese, Turkish, Maltese, South Indian, and South African samples have all shown population-specific differences. That is why validation in each region where a method will be used is considered an ethical and scientific necessity, and it is precisely what the Granada team, led by Blanca Jazmín Ortiz-González together with Rosa María Maroto-Benavides, Adela Baca-García, and Candelaria Reyes-Botella, set out to do for Spain.

Their study, published in the International Journal of Legal Medicine, took the form of a retrospective cross-sectional analysis of 576 digital panoramic radiographs. All the images came from individuals aged sixteen to twenty-four whose lower left molars, the first, second, and third molars designated LL6, LL7, and LL8, had already achieved complete apical closure, the prerequisite for applying the method at all. The researchers examined the distal root canal of each of these three teeth, assigned the A, B, C, or U categories, and then asked a series of statistical questions. How consistently could trained observers repeat the classifications? Did any particular pattern reliably distinguish minors from adults? And how well did the method perform overall when judged by the standard tools of diagnostic testing, including sensitivity, specificity, predictive values, and receiver operating characteristic curves?

The reproducibility results were excellent. Both within a single observer rating the same images twice and between different observers rating the same images independently, the agreement statistics exceeded a kappa value of 0.80, a level conventionally interpreted as almost perfect agreement on the scale introduced by Landis and Koch in 1977. This matters enormously in forensic practice, because an age estimate that changes depending on which examiner happens to look at the X-ray would be worthless in court. The Granada findings confirm that the root canal width categories are clearly defined enough to be applied consistently by different examiners working with ordinary clinical radiographs.

The diagnostic performance, however, told a more nuanced story. Only one pattern, category C, was significantly associated with having reached legal adulthood, with an odds ratio of 2.58 and a p-value of 0.006. When a person showed the C pattern, it was a strong signal: the specificity was 84.6 percent, meaning the pattern was absent in most genuinely underage individuals, and the positive predictive value reached 94.2 percent, meaning that when the pattern appeared, it correctly indicated an adult more than nine times out of ten. But the sensitivity was only 31.9 percent, which means that more than two-thirds of the adults in the sample did not show the C pattern at all. In other words, the marker is far better at confirming adulthood than at excluding it. A missing C pattern tells you almost nothing, because many adults simply have not yet developed it.

The receiver operating characteristic analysis reinforced this caution. The area under the curve, a summary of overall discriminative ability that ranges from 0.5, equivalent to a coin flip, to 1.0, perfect classification, came out at 0.665 for males and 0.616 for females. These values indicate modest performance, well short of the levels that would justify using the method as a standalone test. The authors are explicit about the consequence: the distal root canal width method should be used only as a complementary tool within a multimodal forensic age estimation protocol, never on its own. This aligns with the consensus recommendations of the international forensic community, which since the influential work of Andreas Schmeling and colleagues on clavicular ossification has insisted that age estimates for living individuals should combine multiple independent indicators, typically including a physical examination, an X-ray or MRI of the hand, and imaging of the clavicle, with dental findings as one component among several.

The Spanish validation also fits into a growing international literature testing Roberts’ method beyond its original British sample. Davidson and colleagues validated it in a South African cohort in 2021, Tangkabutra and colleagues examined a Maltese population in 2022, and Vedula and colleagues applied it to South Indian juveniles and sub-adults in 2024. Each study has grappled with the same trade-off the Granada team encountered: the C pattern is a specific, reproducible sign of maturity, but its sensitivity varies across populations, and no single dental feature can carry the entire burden of an age determination. The Granada study is notable for its size, nearly six hundred radiographs, and for its careful attention to the ethical context, having been approved by the Human Research Ethics Committee of the University of Granada and conducted in accordance with the Declaration of Helsinki.

What emerges from this work is a clear-eyed picture of where forensic dental science stands. The root canal width method adds a genuine new instrument to the forensic toolkit: it is cheap, requiring only a panoramic radiograph that is routinely taken in dental practice; it is objective, based on recognizable pattern categories rather than subjective impressions; and it is now demonstrably reproducible in a Spanish sample. At the same time, its modest sensitivity and area under the curve values are a reminder that biology does not respect legal deadlines. The transition from minor to adult is a line drawn by statute, while the body matures along a continuum with wide individual variation. The responsible use of any maturity marker, whether dental, skeletal, or radiological, demands that it inform, rather than dictate, the final estimate. For the young people whose futures depend on these assessments, and for the courts that must rule on them, the Granada study offers both a useful new piece of evidence and a sober lesson in its proper limits.

Subject of Research: Population-specific validation of a dental root canal width method for forensic estimation of the age of majority

Article Title: Population-specific validation of the distal root canal width method for forensic age estimation in a Spanish sample

Article References: Ortiz-González, B. J., Maroto-Benavides, R. M., Baca-García, A., & Reyes-Botella, C. (2026). Population-specific validation of the distal root canal width method for forensic age estimation in a Spanish sample. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-04033-3

Image Credits: AI Generated

DOI: 10.1007/s00414-026-04033-3

Keywords: forensic age estimation, root canal width, dental maturity, orthopantomography, mandibular molars, legal adulthood, forensic dentistry, panoramic radiography, age of majority, population validation, International Journal of Legal Medicine, University of Granada