Twin study suggests caution in dental ageing techniques.

Ageing papers – they are normally of little interest to anyone – especially given that the techniques are so well established and there has been endless re-iterations of them.  However, I thought this paper,

Twins and the paradox of dental-age estimations: A caution for researchers and clinicians

The biological age difference among twins is frequently an issue in studies of genetic influence on various dental features, particularly dental development. The timing of dental development is a crucial issue also for many clinicians and researchers. The aim of this study was therefore to verify within groups of twins how dental development differs, by applying Demirjian’s method, Mincer’s charts of development of third molars and two of Cameriere’s methods for dental age estimation, which are among the most popular methods both in the clinical and the forensic scenario. The sample consisted of 64 twin pairs: 21 monozygotic, 30 dizygotic same-sexand 13 dizygotic opposite-sex with an age range between 5.8 and22.6 years. Dental age was determined from radiographs using the mentioned methods. Results showed that dental age of monozygotic twins is not identical even if they share all their genes. The mean intra-pair difference of monozygotic pairs was low and similar to the difference in dizygotic same-sex twins; the maximum difference between monozygotic twins, however, was surprisingly large (nearly two years). This should lead to some circumspection in the interpretation of systematic estimations of dental age both in the clinical and forensic scenario.

was of interest.  Twin studies are, of course, a common methodology in medical research – usually within a case control scenario.  Here the identical and non identical twins were age assessed using a variety of ageing techniques – these are employed in living individual and included Mincer’s adaptation of the Demirjian;s method, Demirjian’s itself and Cameriere’s methods. Here are their results :

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As you can see the % agreement is low and the max age difference predicted by the different techniques can range up to 4 years.  So what does this tell us?  That dental development is an individualised process – even in identical twins.

The authors state ” Regardless of the methods used and their different performance, the results of our research con-firmed that the rate of tooth development is an individual matter and as indicated before, it is not completely concordant even in monozygotic twins. The mean intra-pair difference of monozygotic pairs observed by three applied methods was never greater than six months in children as well as in young adults. On the other hand, the difference in dental age between co-twins was found by all applied methods and the maximum difference in dental age between monozygotic twins was surprisingly large. According to our results, the difference within monozygotic pairs could be nearly two years (in children under 16 years of age) and in adolescents and young adults even four years.

Although monozygotic twins are much more similar than dizygotic twins and singletons in timing of dental development, the maximum discordance among monozygotic twins illustrates that environmental factors are extremely important.This study proves once again the great variability of growth even among twins and this should be food for thought; in other words this study seems to indicate using 3 samples of twins distinguished by zygosity and sex that mean intra sample differences were greater than inter sample differences and especially when comparing maximum intra sample differences. This should lead to some circumspection in the interpretation of systematic estimations of dental age both in the clinical and forensic scenario.”

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