Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/4208
Dental caries is one of the most common infectious diseases and is linked to bacteria in the dental plaque overlying the dental hard tissue. This link between plaque bacteria and the caries process has mainly been described by three hypotheses; (I) The Specific plaque hypothesis, which says only a very limited number of species are involved in the disease. (II) The Non-specific plaque hypothesis which says that all bacteria are equally effective in causing disease.(III) The ecological plaque hypothesis states that disease is due to a change in local environmental conditions, for example increased sugar consumption, which consequently disrupts the natural balance between plaque and the host, leading to increased growth of acid producing bacteria.
For studying the specific plaque hypothesis, cultivation of specific bacteria using selective media, is an excellent method. However, it can be difficult to investigate the changes in the dental plaque and identify the complete oral microflora, by traditional cultivation methods, when studying the ecological plaque hypothesis. With the development of the accurate and simple diagnostic equipment (DIAGNOdent®) it is possible to diagnose small differences between the healthy tooth surface and initial caries. This, in addition to the use of molecular methods for bacterial identification, allows investigation of the localized changes on the tooth surface that might be linked to certain bacterial flora.
The main aim of this project was to investigate the microflora of dental plaque samples from different stages of dental caries: (i) dental plaque on healthy tooth surface, (ii) dental plaque from initial caries, (iii) from early cavitated lesion and (iv) deep caries. Furthermore the aim was to compare the results of traditional cultivation methods with the results of bacterial identification by molecular methods, 16S rRNA gene analysis and T-RFLP analysis (Terminal restriction fragment length polymorphism). These two molecular methods are built on the amplification of the 16S rRNA gene but the methodological approach is slightly different. The sequence of the 16S rRNA gene is well known for most bacteria, is a well conserved sequence and the variations in the gene make it possible to distinguish between unrelated bacteria.
The main results showed that microbial composition in the dental plaque changed significantly with the progression of dental caries. Greatest microbial diversity was detected in the dental plaque on healthy tooth surface, dominated by various Streptococcus species. Results from cultivation and molecular methods were consistent in showing increased growth of Lactobacillus sp. with increased caries. Other acid-tolerant bacteria and less acid-tolerant bacteria such as Actinomyces sp. could only be detected by molecular analysis but not cultivation. Results of this study demonstrated, in part, the reduced variety of the dental plaque microflora from the healthy tooth to initial caries and further into early cavitated lesions. The study adds to the increasing knowledge and understanding of the bacterial flora linked to dental caries.