Hypothesis: In addition to acid production, cariogenic bacteria are hypothesized to contain esterase activities that could contribute to the breakdown of the restoration-tooth margins.
Objectives: 1) To measure esterase activities from Streptococcus mutans. 2) To measure the hydrolytic-mediated degradation of cured dental resin composites and adhesives in the presence of S. mutans.
Methods: Esterase activities of S. mutans UA159 were measured using p-nitrophenylbutyrate, o-nitrophenylbutyrate, p-nitrophenylacetate, and butyrylthiocholine-iodide (BTC) substrates. Standardized specimens of resin composite (Z250), total-etch (Scotchbond, SB), and self-etch (Easybond, EB) adhesives were incubated with bacteria or bacterial media (control) for up to 30 days. Quantification of biodegradation by-product derived from BisGMA, bishydroxy-propoxy-phenyl-propane (BisHPPP), was performed using high performance liquid chromatography in combination with UV-spectroscopy and mass spectrometry. Surface analysis of the specimens was performed by scanning electron microscopy (SEM).
Results: S. mutans had activity towards the nitrophenyl esters, but not towards BTC, in levels comparable to human saliva. A trend of increasing BisHPPP release throughout the incubation period was observed for all materials. The amount of BisHPPP was elevated in the presence of bacteria versus control for EB and Z250 but not SB (p < 0.05). The amount of BisHPPP released from EB after 30 days of incubation with S. mutans UA159 (143.15±3.28 μgs/cm2) was 39 and 82 times higher than that released from Z250 (3.71±0.24 μgs/cm2) and SB (1.74±0.31 μgs/cm2), respectively (p < 0.05). SEM analyses confirmed the increased degradation of all materials with Streptococcus mutans UA159 versus control.
Conclusion: Streptococcus mutans UA159 has esterase activities at levels that degrade dental resin composites and adhesives. This could compromise the resin-dentin interface and contribute to the progression of secondary caries.