By tooth or by beak...

Researchers at the University of Sheffield and King's College London have discovered that the pufferfish, a highly poisonous but silly looking tropical fish, may hold the key to how and why humans do not replace their teeth in adulthood - which may in turn lead to advances in dental treatments.

Certain adult pufferfish have a parrot like 'beak' with a distinct cutting edge. This beak is formed by bands of dentine which continually grow to replace those lost through feeding.  In young pufferfish, the beak is not present, instead 'first-generation' teeth develop, only to be replaced by four teeth at the front of the jaw which subsequently make-up the beak structure.

 Figure 1: A, the freshwater pufferfish, Monotrete abei. B, side-view 

showing the large lips covering the beak. C & D, views of the beak itself. 

Photo courtesy of Fraser et al (2012: 2)

According to Dr Gareth Fraser, who led the project, investigating the manner and mechanisms of tooth replacement is of  "great interest for science... to understand the genes that govern the continued supply of teeth and mechanisms of dental stem cell maintenance."

Humans only replace their teeth once, in childhood.  Unlike a shark with its many rows of teeth, or a rat with it's continually erupting ones, humans cannot replace teeth naturally. The much increased longevity of modern human populations is therefore at odds with the single set of trauma-and-disease-prone adult teeth they have. Dr Fraser believes that the knowledge could eventually be used to "facilitate advances in dental therapies" with this in mind. 



References:
Fraser, GJ, Britz, A, Johanson, Z and Smith, M. 2012. Replacing the first-generation dentition in pufferfish with a unique beak. PNAS. 
Available at: http://www.pnas.org/content/early/2012/05/04/1119635109.full.pdf+html
University of Sheffield press release. 
Available at: http://sheffield.ac.uk/mediacentre/2012/pufferfish-gareth-fraser-natural-history-museum-evolution-denistry.html

Art is tooth...

The creators of an art-science sculpture, designed to stimulate debate about stem cell research, have been putting out a call for milk tooth donations from school children across the UK.

The two metre long clear crystal resin sculpture is to be encrusted with the milk teeth of thousands of children, who are being persuaded to part with them on the understanding that a 'tooth token' or letter of explanation will suffice for the traditional financial reimbursement from a visiting tooth fairy.

The crystal resin 'palace' prior to tooth encrustation (Photo courtesy of the BBC)

The project, called PALACES, is a collaboration between artist Gina Czarnecki and Professor Sara Rankin (Imperial College London). It hopes to create a wider understanding about how stem cells within dental pulp (the squishy bit inside your tooth) and other 'discarded body parts' such as umbilical cords or fat from liposuction could be ethically used for regenerative and therapeutic clinical purposes.

A close-up of the baby teeth, the first few of thousands! (Photo courtesy of the BBC)

If you know anyone - probably around the age of seven - who would like to be involved and send in their milk teeth, go to this page here to download a form to do so. The sculpture will go on display at science events and exhibitions throughout 2012.


 

When teeth go wrong!

Sometimes, whilst looking at thousands of teeth, you notice something that isn't quite right. This is one of those things:

A tooth with two crowns and one root... weird, eh?
Looking at the top front teeth (the incisors) in the upper jaw
of a c. 4-6 year old individual. Medieval.

Adult humans generally develop the same number of teeth.  Most of us have (or originally had, prior to dental intervention) four incisors, two canines, four premolars and six molar teeth in our upper and lower jaws.  It's fairly common however, for some teeth to never form (agenesis). For example, up to a third of the population is congenitally missing at least one of their wisdom teeth  - the final molar teeth to erupt.

It's much rarer to see instances of too many teeth (hyperdontia).  And it is rarer still to see teeth like the one in the picture above.  All of the baby teeth form in the womb, ready to erupt in the infant a few months after birth. This starts in the sixth week of embryonic development, when enamel-forming cells imbed themselves into the site of future primary teeth. At this point, not more than eight weeks into development, a genetic mutation must have occurred to produce such a tooth. Perhaps too many tooth buds initiated, perhaps one divided into two.

Of course, in all likelihood this unusual looking tooth wasn't even noticed, by the child or his family.  Had the child lived, it would have been replaced by the permanent teeth coming through about six years later and we would have never seen it.