Our teeth are constantly under attack. Oral bacteria produce acids from our food and drink that weaken the enamel surface, leading the way to dental cavities. Fluoridated water is now recognised as a standard protective agent but a source much closer to home could be playing an equally important role. Peptides occurring naturally in our saliva have been found to defend our teeth against tooth decay.

Dental enamel, the outside layer of the tooth, is the hardest substance in the human body, harder even than our bones. It is composed almost entirely of carbonated calcium hydroxyapatite, so essentially, your teeth are made of rock. The main function of enamel is to protect the soft dentin inside your teeth, which in turn protects the pulp where blood vessels and nerves reside. Enamel also gives a hard surface for chewing, grinding and crushing your food and biting your fingernails. Under normal circumstances, this high mineral content would render teeth resistant to bacterial attack but inside the mouth it is a different story.

Our mouths are full of bacteria which settle on our teeth in plaque, a cocktail of proteins, saliva and food debris. Here the bacteria metabolise food particles, converting sugars into acids that eat into the tooth enamel, removing calcium and phosphate and eventually creating cavities, or caries. Certain common soft drinks accelerate this process, due to their high acidity and the presence of sugars and additives. Even canned iced tea is harmful, causing about 30 times more damage than brewed tea or coffee.

According to the CDC, tooth decay is the most common chronic disease in children aged 5-17 years, affecting 5 times more people than asthma. However, as we all know, simple measures go a long way to prevent tooth decay. Regular brushing, rinsing the mouth with water after drinking soft drinks, and fluoridation of drinking water all have beneficial effects, although the uptake of fluoridation in many countries is still low, say the British Fluoridation Society.

In addition to these artificial measures, the body is capable of mounting a defence of its own. When the level of oral acidity is reduced, remineralisation of the tooth enamel occurs, reversing the decay process and restoring some of the tooth structure. It is believed that certain phosphoproteins present in the saliva are involved in this regrowth, and their role has been investigated by researchers based in Portugal.

Francisco Amado and colleagues from the Department of Chemistry at the University of Aveiro, with co-workers from the Higher Institute of Health - North and the Department of Sport Science at FCDEF collected saliva from caries-free (CF) and caries-susceptible (CS) volunteers. The proteins in whole saliva and centrifuged saliva were analyzed by LC/MS with electrospray ionisation on a high-resolution instrument, using the accurate molecular masses to identify them with high confidence from protein databases. The amounts of the proteins present were estimated from the ion chromatograms after the addition of a known amount of leucine-enkephalin as internal standard.

Saliva was also incubated with hydroxyapatite and the proteins adsorbed on the surface were extracted and analyzed in the same way. This was intended to mimic the formation of protein deposits, known as pellicle, on newly cleaned teeth, which is the first step in plaque formation. In addition, in order to study the formation of the protein layer on the teeth in situ, small pieces of bovine tooth enamel were glued onto the teeth of volunteers. Two hours later, the pieces were extracted and the adsorbed proteins were removed for analysis. The findings were described in Biomed. Chromatogr. 2004.

The amounts of identified proteins in CS and CF saliva were analysed using multivariate analysis. It was clear that the CF saliva contained large amounts of proteins in bonded form, as salivary protein complexes, whereas CS saliva contained the same proteins in free form. The proteins concerned were histatin 1, statherin and proline-rich proteins-1 and -3, all of which are phosphoproteins that are phosphorylated at serine residues. The CF group showed a strong correlation with the highest amounts of these proteins. The same proteins were strongly adsorbed onto hydroxyapatite in CF saliva and the in vivo experiments produced identical results.

The researchers proposed that these phosphoproteins are strongly adsorbed onto the enamel surface due to their phosphorylated state and once there, they contribute more effectively to remineralisation. In CS people, there are smaller amounts of these proteins on the teeth and more in the saliva, as well as protein fragments, suggesting that a high proteolytic activity degrades the salivary proteins and increases the vulnerability to caries.

So the protective role of salivary phosphoproteins against tooth decay appears to be established and may even lead the way to more effective measures for those unfortunate enough to be decay prone.

Related links:

• Dental Find on tooth enamel
• WebMD on the corrosive nature of soft drinks
• CDC on tooth decay prevention
• British Fluoridation Society
• Department of Chemistry, University of Aveiro
• Higher Institute of Health - North, Portugal
• Department of Sport Science, FCDEF, Porto
• Biomed. Chromatogr. 2004, article in press

Article by Steve Down