Cyclic mechanical loading promotes bacterial penetration along composite restoration marginal gaps

Area of Science:

• Dental Materials Science
• Microbiology
• Biomechanical Engineering

Background:

• Secondary caries is a primary cause for replacing composite restorations.
• Bacterial infiltration at the dentin-restoration interface is a key factor in secondary caries development.

Purpose of the Study:

• To evaluate the combined effects of cyclic loading and bacterial exposure on bacterial penetration into marginal gaps.
• To assess bacterial invasion at the dentin-resin composite interface using a novel bioreactor system.

Main Methods:

• Human molars with standardized cavity preparations received resin composite restorations with introduced marginal gaps (15-30 μm or ~300 μm).
• Samples with Streptococcus mutans biofilms were subjected to 2 weeks of testing in a novel bioreactor, with and without cyclic loading.
• Bacterial penetration depth was analyzed after cross-sectioning the restored samples.

Main Results:

• Bacteria readily penetrated large gaps regardless of loading conditions.
• Cyclic loading significantly enhanced bacterial penetration in small marginal gaps, reaching 100% of the gap depth.
• Non-loaded samples with small gaps showed an average bacterial penetration of only 67%.

Conclusions:

• A novel bioreactor system effectively simulates combined mechanical loading and bacterial challenges on dental restorations.
• Cyclic loading exacerbates bacterial penetration into narrow marginal gaps, suggesting a mechanism for accelerated secondary caries.
• Findings underscore the importance of mechanical factors in the longevity of dental restorations.