odontology
by Leif Kullman
Age estimation
Age estimation can be of interest in forensic cases of several reasons. If an unknown dead body is recovered it can be important to decide the time since this human was living. Is it an archaeological or an contemporary finding? Should we call for the police or for the archaeologists?
However, most research is performed on estimating the chronological age of an living human being or the age at death for a dead, unknown person. This estimation is rather difficult, more difficult the older a person is. In spite of this in Sweden for example, the age of a lot of adoptive children are estimated at the request of the authorities. This is connected with the increasing number of such children coming to Sweden with an uncertain chronological age. Every dentist can be asked by the authorities to assist in these matters and to write a statement.
Different methods
During estimation of chronological age in children and juveniles, a lot of different growth parameters can be used, e.g., body length, weight and puberty characteristics, in addition to the usual anamnestic records. Weight and length are variables which can be easily measured but the terminal values of these variables are unknown at the time of measurement and the biological variation among human beings are very wide.
Two additional important and objective methods are based on the skeletal and dental development. Practically, these variables are measured or evaluated in the individual and related to the same measurements in a population with known age. Compiled charts are then used.
The different dental methods used can be based on counting available primary or permanent teeth in the mouth or studying the mineralization of the teeth as seen in a radiograph or on a combination of these two parameters. The radiographic method is often used, since the clinical eruption of the teeth is more variable than the radiographic development stages. It is important to declare which method you have used during an estimation.
The accuracy and precision of most of the dental methods used during childhood, have been studied and found to be rather low. Since a lot more developing parameters can be used in younger years and the development rate is faster in young children, it is to be expected that accuracy and precision are inferior in older juveniles and this fact has been proved by research. Only the third molars can be used after the age of 14-15 years, since all other permanent teeth are fully matured. First, the stage of development is estimated from radiographs (figure 1). Next, the development stage is related to the same stage in a population with known age. This estimation method is based on subjective evaluations of stages and has many shortcomings. The normal biological variation in the development is also large for all teeth.
Figure 1.
About the final conclusion
By using these kinds of dental methods it is possible to calculate the estimated average age for an arrived stage of root or crown development. The used method and population must be declared, since there are differences between methods and populations of different origin. To be able to state anything about the certainty in this prediction a confidence interval must be constructed around this average age. In this manner most methods for age determination of children have arrived at a 90-95% confidence interval of about two years around the estimated age, a rather low precision. This is during childhood when several not fully developed teeth can be used.
In juveniles, when only the third molars have some root development left, this precision will be even lower but since we lack better methods, the third molar is one of the best available predictor to use besides skeletal age. Skeletal age should always be used from childhood up to about 18 years when all hand- and wrist bones fully developed. During this the hand as a whole according to a radiograph is compared with atlas standards, consisting of photos of radiographs and schematic drawings of the different bone stages of the bones in the hand and wrist. A written description of the different stages are also usually used.. A standard age for the found stage is then given in the atlas.
An age of 18 years has many legal consequences in several countries and is therefore important to establish. If, for example, an individual in Sweden is condemned in a court of law for a serious crime, he must be 18 years to be sent to jail. If he has not reached his eighteenth birthday, the social authorities will supervise him.
In conclusion, research has shown that the individual variation in tooth development varies largely within the same chronological age group making accurate and reliable age estimations difficult. This fact must be kept in mind when estimations are performed.
Next month I will report on some cases where a dental age estimation played an important role to solve the criminal investigations.
Leif Kullman
