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

The research, led by Oguzhan Ekizoglu together with Marine Dario, Maxime Pastor, Catherine Cyteval, and Laurent Martrille, focused on a bone that has been comparatively neglected in the MRI-based age estimation literature: the proximal humerus, the ball-shaped top of the upper arm bone. While the hand-wrist region and the knee have been extensively mapped with MRI for forensic purposes, the shoulder has received far less systematic attention, particularly in Western European populations. The team retrospectively analyzed 346 shoulder MRI examinations drawn from a French cohort spanning the ages of 7.18 to 33.82 years, comprising 204 males and 142 females. Because the scans had been acquired for clinical reasons and were fully anonymized, the ethics committee of CHU Montpellier approved the study and waived the need for individual informed consent, an approach consistent with the Declaration of Helsinki.

The technical backbone of the study is the combined Schmeling–Kellinghaus staging system, a widely used framework originally developed for the medial end of the collarbone. In this system, ossification of the epiphysis, the secondary growth center that fuses to the main bone shaft after puberty, is graded in discrete stages, from an entirely cartilaginous growth plate through progressive partial fusion to complete union, with an optional subdivision for the earliest signs of fusion. On T1-weighted MRI sequences, the developing bone and the cartilaginous plate between epiphysis and metaphysis produce distinct signal intensities, allowing a trained observer to assign each shoulder to a stage. Two independent raters, blinded to each subject’s age and sex, staged all 346 scans, providing a direct test of how reproducible the method is when applied to the humeral head.

The results were strikingly consistent. The correlation between chronological age and ossification stage was strong and statistically significant across the whole sample, with a Spearman’s rank correlation coefficient of 0.878, and nearly identical values of 0.880 in males and 0.878 in females, all with p-values below 0.001. In practical terms, this means that as the humeral epiphysis progresses through its developmental stages, age increases in a tight, predictable relationship, and that this relationship holds equally well for both sexes. Statistical testing with the Mann–Whitney U method found no significant difference between males and females in the ages associated with any given stage, a finding that simplifies the application of the system, since a single set of stage descriptions may suffice for both sexes in this population.

Reliability, the measure of whether different observers reach the same conclusion from the same image, was equally impressive. Cohen’s kappa, a statistic that quantifies agreement beyond what would be expected by chance, reached 0.911 within observers rating their own scans twice and 0.890 between the two independent raters. Values above 0.8 are conventionally considered to indicate very good agreement, and these figures place the proximal humerus staging on par with, or better than, many established forensic imaging indicators. For a method that might one day inform legal decisions with life-changing consequences, this level of observer agreement is not a technical nicety but an essential prerequisite, because inconsistent readings between experts would undermine the credibility of any age estimate offered in court.

The most legally consequential finding concerns the age of majority, the threshold at 18 years that separates minors from adults in most jurisdictions. In this cohort, the youngest individual showing stage 4, defined by the presence of a visible epiphyseal scar after fusion, was 18.33 years in males and 18.06 years in females. In other words, once the epiphyseal scar is visible on the proximal humerus, the data suggest the person has very likely passed their eighteenth birthday. Notably, stage 5, the final stage of the amplified scheme, was never observed despite the cohort including individuals up to nearly 34 years of age, an observation the authors interpret in light of the persistent visibility of the epiphyseal scar in adult shoulders and the anatomical characteristics of trabecular bone in this region.

Beyond the conventional minimum-age approach, the team applied an ordinal probit transition analysis, a statistical framework borrowed from paleodemography that models the probability of moving from one ossification stage to the next as a function of age. Rather than relying on the single youngest individual observed at a stage, a figure that is highly sensitive to how many older or younger people happen to be in the sample, transition analysis yields sex-specific ages at which the probability of progression to the next stage reaches 50 percent. This provides a more statistically robust characterization of the timing of skeletal maturation and has been increasingly advocated in forensic age research, including recent work on third molars and other skeletal indicators. The authors are careful, however, to stress that both minimum-age and transition-age estimates derived from any single cohort should not be applied as forensic thresholds without independent, population-specific validation, a caution that reflects the well-documented variation in skeletal maturation across populations and socioeconomic conditions.

Perhaps the most original contribution of the study is the description of a previously unreported interpretive pitfall. The authors identified a trabecular hypointense pattern, a dark appearance of the internal bone architecture on T1-weighted images, that can potentially mimic a persistent gap between the epiphysis and the metaphysis, the appearance that would normally indicate an unfused, and therefore juvenile, growth plate. Mistaking this normal variant for an open growth plate could lead an examiner to underestimate a person’s age, with serious implications in asylum or criminal proceedings. The paper includes recommendations for recognizing this pattern, underscoring that even a highly reliable staging system depends on the examiner’s ability to distinguish true developmental landmarks from imaging artifacts and anatomical variants of the cancellous bone in the proximal humerus.

The broader context of this work is a slow but decisive shift in forensic practice. European radiation protection directives and international basic safety standards from bodies such as the International Atomic Energy Agency have sharpened the ethical and legal scrutiny applied to X-ray-based age assessments in healthy young people, pushing researchers toward MRI as a non-ionizing alternative. Previous MRI studies of the proximal humeral epiphysis, including earlier work by Ekizoglu and colleagues on Turkish cohorts and studies from China and Turkey using both 1.5 and 3.0 Tesla scanners, have demonstrated the promise of the approach, but population-specific data remained sparse for Western Europe. By extending the combined Schmeling–Kellinghaus system to a French cohort for the first time, the Montpellier team has filled an important geographic gap and shown that the staging framework travels well across populations, at least in terms of correlation strength and observer reliability.

What remains before shoulder MRI can enter routine forensic use is a matter of validation and standardization rather than proof of concept. Large, independently collected cohorts from different populations will be needed to confirm the minimum ages and transition probabilities reported here, and the newly described trabecular pitfall will need to be characterized across scanner types and imaging protocols. Cost and scanner availability also remain practical constraints, since MRI is more expensive and less widely accessible than plain radiography. Nevertheless, the study offers a compelling vision of the field’s future: a radiation-free, highly reproducible, and anatomically well-characterized method for answering one of forensic science’s most sensitive questions. For the hundreds of thousands of young people whose ages are contested each year in legal systems worldwide, the humeral head, imaged safely with magnets rather than X-rays, may soon become a key witness.

Subject of Research: Non-ionizing forensic age estimation using T1-weighted MRI of the proximal humeral epiphysis in a French cohort

Article Title: T1-Weighted MRI of the proximal humerus: Toward a non-ionizing approach to forensic age estimation in a French cohort

Article References: Ekizoglu, O., Dario, M., Pastor, M., Cyteval, C., & Martrille, L. (2026). T1-Weighted MRI of the proximal humerus: Toward a non-ionizing approach to forensic age estimation in a French cohort. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-03996-7

Image Credits: AI Generated

DOI: 10.1007/s00414-026-03996-7

Keywords: forensic age estimation, MRI, proximal humerus, epiphyseal fusion, Schmeling-Kellinghaus staging, age of majority, transition analysis, non-ionizing imaging, forensic medicine, immigration, radiation protection, French cohort