How fast do teeth and bones grow? A new method can quantify this, opening up further possibilities for tissue engineering

Jan Křivánek attracted attention in scientific circles three years ago when he mapped and categorized cells in mouse teeth and subsequently also in human teeth, which are overwhelmingly similar at the molecular and cellular level. On that occasion, he discovered several new types of stem cells and described the differentiation processes by which they are transformed into the cells that form the hard tissues of the teeth. "We are trying to understand the general principles of organ and tissue regeneration by studying them," says the young scientist, fascinated by rodents whose front incisors grow throughout their lives. "What is interesting is not only the regrowth itself, but also that when a mouse breaks off a tooth, it has evolved a special principle that the tooth even accelerates its growth. And it does so dramatically."

The Brno scientists have now developed a method to describe and quantify these growth dynamics at micrometer scales, the first in the world to do so: BEE-ST. As the full name - Bones and TEEth Spatio-Temporal Growth Monitoring - suggests, it allows the development of hard tissues to be monitored in all three dimensions and over time. It consists of precisely timed delivery of fluorescent dyes, their incorporation into emerging bone and teeth, and subsequent optical brightening, but without the need for prior decalcification, which in conventional methods also removes incorporated chemicals.

"Our method builds on a combination of several established approaches. There are dozens of dyes that are incorporated into the emerging hard tissues and have been known for years. We tested many of them, selected the two that work best - alizarin and calcein - wrote procedures on how to apply them, and devised new approaches to quantify growth and healing," Křivánek explains. In addition, by collaborating with colleagues from the Faculty of Science, they have tested the BEE-ST in multiple animal species and confirmed its universal use for monitoring the development of any calcium-based tissue. "Although we initially focused only on mouse incisors, in parallel we found that our method can be applied to other tissues."

BEE-ST thus opens up opportunities for further research and application in areas ranging from developmental biology, tissue healing and regeneration, bone and dental engineering, and the study of congenital developmental defects of the support system and teeth. Meanwhile, Křivánek himself and his team are taking their work further. "No one has yet figured out what it is that makes mice's teeth grow back so quickly after injury. No one knows how it is detected, how the stem cells respond to it, and no one has been able to quantify the growth rate accurately. We can do it now," he hints at the future direction of his research.