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TISSUE ENGINEERING Mammalian Teeth Regrown in Lab A team of researchers has successfully used tissue engineering techniques to regenerate mammalian tooth crowns containing dentin and enamel, an achievement that may lead to a biological tooth substitute to replace human teeth. The findings also suggest the existence of dental stem cells. Joseph Vacanti, the John Homans professor of surgery at HMS and Massachusetts General Hospital, director of the hospital's Laboratory for Tissue Engineering and Organ Fabrication, and an author on the paper, said of the work, "By combining the new science of stem cell biology with the engineering concepts and techniques of tissue engineering, it demonstrates that complex structures such as living teeth can be created." As reported in the Oct. 1 Journal of Dental Research, the study involved seeding cells from the immature teeth of six-month old pigs onto biodegradable polymer scaffolds. The researchers then placed these structures into rat hosts. Within 30 weeks, small, recognizable tooth crowns had formed. These contained dentin; odontoblasts, cells that secrete dentin-forming protein; a well-defined pulp chamber; Hertwig's root sheath epithelia; cementoblasts, which form a mineralized tissue that covers the roots; and a morphologically correct enamel organ. The results, demonstrated in some two dozen experiments, represent the first successful generation of mature tooth crowns containing both dentin and enamel. They also suggest that it may be possible to grow teeth of a particular size and shape, according to principal investigator Pamela Yelick, HSDM instructor in oral and developmental biology at the Forsyth Institute and an assistant member of the Forsyth staff. The institute, where the research was based, is an independent nonprofit research organization focusing on oral, craniofacial, and other biomedical sciences. Previous investigators had used alternative approaches to form partial tooth structures with dentin and pulp, but none had grown complete structures that included enamel. The team is the first to report using tooth buds enzymatically digested into single cells combined with polymer scaffolding to regenerate teeth. Also of note is the discovery that dental stem cells appear to exist in porcine third molar tissues. "Finding putative epithelial and mesenchymal dental stem cell populations in mammals suggests that similar cells might exist in human beings," Yelick said. She speculated that within five years "we will know whether dental stem cells can be manipulated to bioengineer teeth. To generate a human tooth might take an additional five to 10 years." In addition to Yelick and Vacanti, the team included first author Conan Young, HSDM instructor in oral and developmental biology and research associate at Forsyth; John Bartlett, associate member of the Forsyth staff; Shinichi Terada, HMS research fellow in surgery at MGH; and Masaki Honda of the Department of Oral and Maxillofacial Surgery, Nagoya University School of Medicine in Nagoya, Japan. "The ability to identify, isolate, and propagate dental stem cells to use in biological replacement tooth therapy has the potential to revolutionize dentistry," said Dominick DePaola, president and chief executive officer of the Forsyth Institute. --Adapted from text by Anita Harris