What is your objective?

Some people are more susceptible to tooth decay (the specialist term for which is "dental caries") than others, and we call this individual difference. My objective is to find out why from a genetic approach. Risk factors for tooth decay include environmental factors such as brushing and eating habits, infection with oral bacteria or other pathogens, tooth structure and quality, immune capacity, and the buffering capacity and secretion volume of saliva. Recently, it has gradually become clear that, of all these factors, it is when the genes determining tooth structure, immune capacity, and saliva quality are of a specific type that the risk of tooth decay increases.

As you all know, the DNA structure of the gene is made up of four nucleic acids, A, C, G, and T, arranged in a particular sequence. However, even within the same gene, the DNA sequence is not always the same, but varies slightly from person to person. This slight variation in DNA sequence is called gene polymorphism. We are currently studying the relation between susceptibility to tooth decay and gene polymorphism.

This sort of information has now reached the stage of practical application in the field of clinical medicine. For example, when prescribing a drug, reference is made to the relation between specific genetic polymorphisms and the effectiveness and/or side effects of the drug. In the case of side effects specifically, a list of their relation to genetic polymorphisms has been published for more than118 pharmaceutical products.

Another of my research themes is to explore the tooth decay prevention mechanism of fluoride. It is commonly known that fluoride, which is contained in toothpaste, is absorbed into teeth and increases their resistance to acids, thus preventing erosion by the acids produced by bacteria and other sources. We are using radioactivation analysis to study how fluoride penetrates into the teeth and how it moves within the teeth. We believe this will allow us to understand how fluoride penetrates into the teeth from materials that contain fluoride, and how it displays a tooth decay-preventing effect.

 

What kind of devices do you use for what sort of experiments?

1) For genetic polymorphism analysis, we use a real-time PCR device and a DNA sequencer. PCR is a technique that amplifies specific ranges of a DNA sequence, and real-time PCR, by monitoring the amplification in real time, allows the original amount of DNA to be measured. By using an analysis method called High Resolution Melting-curve Analysis (HRMA), it is additionally possible to detect genetic polymorphism within a specific range.

2) In order to investigate the tooth decay-preventing effect, we have created an oral pH simulation device for use in analysis. With this device, it is possible to conduct simulation tests under the same conditions as in the human oral cavity.

3) For research on the penetration and spread of fluoride within the tooth structure, radioactivation analysis with a microbeam is used. Elemental analysis with a microbeam uses a beam roughly 1? in diameter for high-precision analysis of the distribution of fluoride. The fluoride concentration can be quantified from the beam count. We are using samples from the oral cavity pH simulation device to analyze via microbeam how the fluoride moves within the teeth and to what extent it prevents tooth decay within the oral cavity environment (Figure 2).

Figure 1 A: Real- time PCR device B: HRMA analysis of PCR product Figure 2 A: Microbeam analysis device B: Control screen of analysis device

 

What's next?

1) I will use teeth with different genetic polymorphisms as research materials and test them using the oral cavity environment simulation device to directly check their susceptibility to tooth decay. 2) I will analyze the effects of fluoride on these research materials with the microbeam. 3) Next, by combining my two research strands, I will be in a position to explore the relationship between genetic polymorphism and susceptibility or resistance to tooth decay in individual teeth. With additional research into individual differences in saliva, I believe I will eventually be able to develop tailor-made treatments for tooth decay.