This question has been in the news today in relation to verifying the age of child migrants wanting to enter the UK. It has been suggested that their teeth should be examined to determine their age.
In my first year at dental school I was taught to identify different types of teeth and had to learn the ages that teeth came through into the mouth. In addition I had to learn the ages each tooth type started forming and the ages that the roots were fully formed, these can only be determined from an xray of the mouth. That was quite a lot of dates to learn! Once you know these you can determine the dental age of a patient from their mouth or an xray (an xray being more accurate as you have more information on unerupted teeth and the root development). This is possible because the order in which the teeth develop is fairly consistent.
Notice that I used the term 'dental age'. The dates that I learnt are based on averages. Much as the height or development of a child cannot tell you their exact age, dental age is the same. Dental age can be the same, more, or less than actual age. The main clinical purpose for its use is to monitor how the teeth develop and look for anomalies, for example teeth not appearing at the time they should. Alterations in the order that teeth develop is (to me as a clinician) more important than a difference between dental age and real age. Dental age is also used in forensics to help with determining age at time of death, but this would always be in conjunction with other data and could only give an approximation.
For example, the age that all the milk teeth are lost is 12 years old on average. A year or even two either way is not unusual, and I have seen it very between 9 and 15 years, that's quite a big difference! Once all the adult teeth are through it become more difficult to estimate dental age, and this might be done using an xray to look at development of the wisdom teeth if they are present, or looking at wear or dental damage. I'd expect someone with a poor quality of life living in a refugee camp to have poor dental health, which would cloud the issue. So using dental age on someone between the ages of 15-21 would be likely to be very inaccurate, this is just the age group that would need it most in this situation.
If dental age was to be used it might be necessary to take an xray to do so. However we have strict guidelines about the use of ionising radiation (of which xrays is one form) due to the risks to both individuals and the public in general. Xrays should only be taken when they are clinically necessary, that is they could alter how the treatment is carried out. Dental professionals have a responsibility to keep xray exposure 'as low as reasonably achievable'. Taking an xray purely for the purpose of determining dental age is therefore unethical and should not be done.
I do understand the need to try and determine someone's age to be able to help those genuinely in need, but dental age is not going to help in this situation.
