Yes, it would separate out a 14 year old from a 40 year old. But you're creating unnecessary work here, because a 40 year old wouldn't get as far as an age assessment in the first place.
The way it works is that an individual presents and claims to be a minor. Let's say our individual claims to be 16.5, born in April 2006.
If there is "clear and credible" evidence that they are under 18 - like a reliable passport - then their claimed date of birth is accepted. Off he goes to school with his April 2006 birth date.
If there isn't any such evidence, and if two immigration officers, one at a senior level, both agree that "their appearance very strongly suggests they are significantly over 18 years of age and there is little or no supporting evidence for their claimed age," they're treated as an adult without the need for any further assessment. So your 40 year old would fall in this category.
If their claimed age is not accepted BUT they don't appear "significantly" over 18 then a Merton compliant age assessment is conducted. Typically the HO will say that someone is 18 or 19, and they will say they're 16 or 17. This is the category for which an age assessment is done, and for this cohort, dental checks which are accurate only to +/- two years, won't be very helpful.
A Merton compliant assessment is conducted by social workers. They're not perfect either but they are generally quite thorough. If our claimed 16yo is assessed as 18, he is given an 01/01 date of birth, so he would be given 01/01/2004 and moved to adult accommodation.
The British Dental Association lobbied - against their own interests, as they'd be paid for providing the checks - against dental age checks. dentistry.co.uk/2022/03/10/government-defeated-on-dental-age-checks-for-asylum-seekers/
One interesting development is that the local authority can require an applicant to provide details from their Facebook account if they have one.