Influence of composite resin biodegradation by-products on the physiology and gene expression of oral bacteria.
Published: 2006
Language: eng
Number of pages: 216
ISBN-13: 9780494157411
Description: Bacterial microleakage along the tooth/composite restoration interface contributes to recurrent caries and pulp inflammation. Salivary esterases can catalyze the degradation of monomers in dental composites, forming biodegradation by-products (BBP's) such as methacrylic acid (MA), triethylene glycol (TEG), and bis-hydroxy-propoxyphenyl propane (BisHPPP). Also, composite resin co-monomers such as triethylene glycol dimethacrylate may promote the proliferation of important cariogenic micro-organisms. These observations have warranted the study of interactions between composite-derived BBP's and oral bacteria. Planktonic growth, the presence of hydrolytic enzyme activities, and the glycolytic rates of Streptococcus mutans and Streptococcus salivarius were measured in the presence of MA, TEG, or BisHPPP at 37&deg;C at pH values 5.5 or 7.0. Restriction fragment differential display PCR (RF-DDPCR) in conjunction with quantitative real-time PCR (q-RT PCR) techniques were employed to identify genes of S. mutans with altered expression resulting from growth in the presence of TEG at pH 5.5 followed by the examination of the expression for those genes in bacteria grown in the presence of BBP's (0-1.0 mM) at different culture conditions (pH 5.5 vs. 7.0) and growth modes (planktonic vs. biofilm). TEG stimulated the growth of all strains, while MA and BisHPPP were observed to be inhibitive of growth, with these effects most pronounced at the pathogenic pH of 5.5. Enzyme assays indicated the presence of esterolytic enzymes in bacterial cell suspensions, although the BBP's did not modulate enzyme activity levels. RF-DDPCR experiments identified the glucosyltransferase B (gtfB) (involved in biofilm formation) and yfiV (putative transcription regulator of bacterial cell-surface fatty acid genes) to have altered expression in  S. mutans cells grown in the presence of TEG at pH 5.5. Further, q-RT PCR experiments revealed that the presence BBP's modulate the expression of gtfB and yfiV in a BBP, pH, and concentration dependent manner and that the effects differed in planktonic and biofilm cells. These findings begin to elucidate possible mechanisms that may explain earlier studies showing greater plaque accumulation on composite restorations, relative to other classes of restorative materials, and point to the role of BBP's as the potential contributor to increased incidence of secondary caries associated with composite resins.
Notes: Source: Dissertation Abstracts International, Volume: 67-06, Section: B, page: 3269.

Thesis (Ph.D.)--University of Toronto, 2006.

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