An in Vitro Model for Secondary Caries

Objectives: To evaluate the feasibility and reproducibility of a calibrated model for simulating recurrent caries in debonded dentin-composite specimens.
Methods: Dentin discs (5mm outer diameter, 2mm inner diameter, 2mm thick) were prepared using bovine incisor roots with resin composite (Z250, 3M OCSD, St. Paul, MN, USA) and adhesive (Scotchbond Universal, 3M OCSD, St. Paul, MN, USA). The samples were subjected to cyclic diametral compression at 1Hz with loading increasing at 0.04N/s until debonding.
The debonded specimens were exposed to lactic acid buffer using a CDC bioreactor at 37°C and pH 4.5 for 48 hours. The test (n=6, including controls) was conducted thrice. The specimens were sectioned perpendicularly to the vertical load and analyzed using SEM (TM3000, Hitachi, Tokyo, Japan), with BSE imaging used to differentiate between intact and demineralized dentin. EDS was employed to quantify mineral loss in the demineralized regions and the data statistically analyzed (t-test, p<0.05).
Results: Interfacial debonding was successfully created in ~97% of the specimens in the mechanical test. Following acid challenge, the specimens developed a consistent demineralized band of 60–80μm deep adjacent to the interfacial gap (~160μm wide). When comparing the demineralized area of the acid-challenged samples with the corresponding area in the control samples, carbon (C) levels increased from exposed collagen, while calcium (Ca) and phosphate (P) levels significantly decreased. Despite these changes, no significant difference was observed in the Ca/P ratio between the samples.
Conclusions: Consistent marginal demineralization around debonded model dentin-composite restorations was obtained using lactic acid buffer. This indicates the potential of this model for simulating secondary caries. Future work will make use of a biofilm model.