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TOOTH fillings may be on the way out. Broken or rotten teeth could one day be
repaired by growing new tooth tissue, using stem cells harvested from wisdom
teeth. Studies in mice by American researchers showed that the cells were able
to produce dentine and pulp, two key components of human teeth.

鈥淲hat we鈥檙e looking at in the long term is to regenerate teeth with the blood
supply and everything else,鈥� says Songtau Shi at the National Institute of
Dental and Craniofacial Research near Washington DC. 鈥淚t鈥檚 early days,鈥� admits
Shi. But he hopes the technique can initially be developed to help repair holes
in teeth.

Each tooth is made from three main tissues. The centre consists of soft pulp,
which contains blood vessels and nerves. The bulk of the tooth is a harder
yellow tissue called dentine. Covering this is enamel, the hardest tissue in the
body.

Dentists usually repair holes or 鈥渃aries鈥� in teeth by filling them with
mercury-based alloys or plastic-based composites. But Shi and his colleagues
wanted to see if they could instead grow the tissues that make teeth.

Shi took wisdom teeth extracted from people aged between 19 and 29, cut them
open and tore the pulp away from the tooth鈥檚 crown and root. He mixed the pulp
with an enzyme called collagenase, which digests the matrix of connective tissue
that holds the pulp together. This left a mixture of pulp cells, which Shi
filtered to isolate dental pulp stem cells. He then cultured these cells in a
nutrient-rich liquid.

Next, Shi tested whether dental pulp stem cells would generate new tooth
tissue. He mixed batches of cells with a ceramic powder containing
hydroxyapatite, the mineral found in bone, and implanted the mixture under the
skin of mice.

After two months, Shi examined the transplants. 鈥淭he cells had produced
dentine and also a pulp-like tissue,鈥� says Shi. 鈥淭he dentine has exactly the
same structure as human dentine.鈥� Shi has yet to confirm that the pulp produced
is the same as human dental pulp, but it does contain blood vessels and nerve
tissue.

Tony Smith, who works on dental tissue repair at the University of
Birmingham, says repairing teeth by regeneration would have definite advantages
over using fillings. 鈥淭he beauty of encouraging biological regeneration is that
the new tissues are an integral part of the tooth,鈥� Smith says. 鈥淲ith fillings,
sooner or later it鈥檒l fail, or you鈥檒l get a gap down the side where bacteria can
cause secondary caries.鈥�

Smith adds that a big hurdle will be regenerating the hard enamel. 鈥淭he
structure of enamel is not simple. No one has got anywhere near replacing that
yet,鈥� he says.