A novel approach in the tissue engineering of teeth is covered in this piece. It shows promise, but is still in the early stages of development in comparison to other methodologies in which researchers have actually created whole functional teeth:
[Researchers] investigated a process called mesenchymal condensation that embryos use to begin forming a variety of organs, including teeth, cartilage, bone, muscle, tendon, and kidney. In mesenchymal condensation, two adjacent tissue layers - loosely packed connective-tissue cells called mesenchyme and sheet-like tissue called an epithelium that covers it - exchange biochemical signals. This exchange causes the mesenchymal cells to squeeze themselves tightly into a small knot directly below where the new organ will form. By examining tissues isolated from the jaws of embryonic mice, [researchers] showed that when the compressed mesenchymal cells turn on genes that stimulate them to generate whole teeth composed of mineralized tissues, including dentin and enamel.
[The researchers then] set out to develop a way to engineer artificial teeth by creating a tissue-friendly material that accomplishes the same goal. Specifically, they wanted a porous sponge-like gel that could be impregnated with mesenchymal cells, then, when implanted into the body, induced to shrink in 3D to physically compact the cells inside it. They chemically modified a special gel-forming polymer called PNIPAAm that scientists have used to deliver drugs to the body's tissues. PNIPAAm gels have an unusual property: they contract abruptly when they warm. Ultimately, they developed a polymer that forms a tissue-friendly gel with two key properties: cells stick to it, and it compresses abruptly when warmed to body temperature.
[Researchers worked to] load mesenchymal cells into the gel, then implant the gel beneath the mouse kidney capsule - a tissue that is well supplied with blood and often used for transplantation experiments. The implanted cells not only expressed tooth-development genes; they also laid down calcium and minerals, just as mesenchymal cells do in the body as they begin to form teeth. In the embryo, mesenchymal cells can't build teeth alone - they need to be combined with cells that form the epithelium. In the future, the scientists plan to test whether the shrinking gel can stimulate both tissues to generate an entire functional tooth.