- OBJECTIVES: Secondary caries is the most common reason for composite restoration replacement and
usually forms between dentin and the filling. The objective of this study was to investigate the
combined effect of cyclic loading and bacterial exposure on bacterial penetration into gaps at the
interface between dentin and resin composite restorative material using a novel bioreactor system
and test specimen design.
METHODS: Human molars were machined into 3 mm thick disks with 2 mm deep x 5 mm diameter
cavity preparations into which composite restorations were placed. A ~15-30 micrometer (small) or
~300 micrometer wide (large) dentin-restoration gap was introduced along half of the interface
between the dentin and restoration. Streptococcus mutans UA 159 biofilms were grown on each
sample prior to testing in a bioreactor both with and without cyclic loading. Both groups of samples
were tested for 2 weeks and post-test biofilm viability was confirmed with a live-dead assay.
Samples were fixed, mounted and cross-sectioned to reveal the gaps and observe the depth of
RESULTS: It was shown that for large gap samples the bacteria easily penetrated to the full depth of
the gap independent of loading or non-loading conditions. The results for all cyclically loaded small
gap samples show a consistently deep bacterial penetration down 100% of the gap while the
average penetration depth was only 67% for the non-loaded samples with only two of six samples
SIGNIFICANCE: A new bioreactor was developed that allows combining cyclic mechanical loading and
bacterial exposure of restored teeth for bacterial biofilm and demineralization studies. Cyclic
loading was shown to aid bacterial penetration into narrow marginal gaps, which could ultimately
promote secondary caries formation.
- Khvostenko, D., Salehi, S., Naleway, S. E., Hilton, T. J., Ferracane, J. L., Mitchell, J. C., & Kruzic, J. J. (2015). Cyclic mechanical loading promotes bacterial penetration along composite restoration marginal gaps. Dental Materials, 31(6), 702-710. doi:10.1016/j.dental.2015.03.011
|Funding Statement (additional comments about funding)
- This work was supported by NIH/NIDCR GRANT DE021372.