Contact guidance of endodontic pathogens on micro-grooved polymethylmethacrylate discs

Abstract

Bacteria are the primary cause of pulp and periapical pathology. They gain entry into the tooth through exposed dentinal tubules. Although bacteria have been shown to invade these dentinal tubules, the cell interactions or processes involved in invasion are still not clear. This study will look at one possible process, contact guidance/thigmotropism, that has been shown in plants, some animal cells and with a known oral microbe Candida albicans. Aim: To determine contact guidance characteristics by endodontic pathogens Streptococcus mutans NG8, Streptococcus gordonii DL-1, Enterococcus faecalis JH2-2 and C. albicans ATCC 10261 on micro-grooved polymethylmethacrylate (PMMA) discs. In addition, to determine the effect an amino acid sequence in collagen type I (Glycine-Proline-Alanine) has on growth characteristics. Methods: Micro-grooves of various dimensions (2 µm x 2 µm x 2 µm (Width Depth Spacing), 2 µm x 2 µm x 4 µm (WDS), 4 µm x 2 µm x 2 µm (WDS) for bacteria and 4 µm x 4 µm x 2 µm (WDS), 4 µm x 4 µm x 4 µm (WDS) for Candida were produced on PMMA to simulate some characteristics of dentinal tubules. Blank discs were used as a control. Discs were inoculated with collagen type I overnight then incubated in mono-solutions of each test organism; 2 days for bacteria and 3 hours for Candida followed by processing discs for scanning electron microscopy (SEM). Images were captured using SEM micrographs. The methods were repeated with Glycine-Proline-Alanine inoculated into the mono-solutions. Results: Qualitative analysis demonstrated that C. albicans ATCC 10261 hyphae when incubated on blank PMMA discs did not exhibit contact guidance/thigmotropism. In contrast C. albicans ATCC 10261 hyphae exhibited contact guidance along grooves and edges on grooved substrate. In comparison, the bacteria S. gordonii DL-1 and S. mutans NG8 showed some evidence of contact guidance by chain growth along grooves while E. faecalis JH2-2 gave no indications of exhibiting contact guidance. Glycine-Proline-Alanine affected cell adhesion and length of chaining growth in S. gordonii DL-1 and S. mutans NG8, and hyphae formation in C. albicans ATCC 10261. The Glycine-Proline-Alanine had no effect on E. faecalis JH2-2. Conclusion: The results suggest that contact guidance could be involved in microbial invasion of dentine.