Competing Proteins Influence Strength Of Tooth Enamel

The team's study of the two proteins, dentin sialoprotein (DSP) anddentin phosphoprotein (DPP), has been accepted by the Journal ofBiological Chemistry and is available on the journal's Website.

Lead author Michael Paine of the USC School of Dentistry saidboth proteins derive from the gene for dentin sialophosphoprotein,which plays an important role in the formation of the tooth coveringsenamel and its softer internal cousin dentin.

"We were able to dissect this gene into two different proteins and look at them individually," Paine said.

The researchers conducted animal studies in which either DSP orDPP were over-expressed in forming enamel during the period of toothdevelopment. They found that over-expression of DSP increased thehardness of enamel and its rate of formation, while over-expression ofDPP created pitted and chalky enamel that was more prone to fractureand wear.

In normal teeth, DSP is expressed only in dentin and a verythin layer of enamel at the junction with dentin. This thin enamellayer also appears to be considerably harder than the bulk enamel ofteeth, Paine said. He suggested that DSP could have the potential tobecome a protective agent in dental care.

If the protein could be incorporated into the entire layer ofenamel, Paine said, "then it might act in a similar way to fluoride inwater" by making teeth harder and more resistant to decay.

Paine cautioned that, just as heavy fluoridation can weaken teeth, excessive expression of DSP could be detrimental.

"There might be a point where if you increase the hardness anymore, teeth might be too brittle."

While the other protein, DPP, appears to weaken enamel, it too is necessary for proper tooth formation.

"All the data suggests that it [DPP] is one of the few proteinsthat seems to be involved with the very early stages ofmineralization," Paine said.

The fine balance between DSP and DPP highlights the delicacyof the critical dentin-enamel junction, where the softer dentin isjoined securely to the outer, ceramic-like enamel covering.

Dental researchers sometimes liken dentin and enamel to a bedmattress and a glass plate, respectively, Paine said, with thedifference that the supple dentin-enamel junction prevents the enamelfrom shattering over an individual's lifetime of chewing and grinding.

The study built on the work of co-author Mary MacDougall, aformer USC researcher who in 1997 was the first to show that DSP andDPP came from the same gene.

This research was supported by the National Institute of Dental and Craniofacial Research.