Behavior of failed bonded interfaces under in vitro cariogenic challenge

• This is the first study to evaluate the caries susceptibility of failed bonded interfaces.
• The failed bonded samples showed an intermediate caries development between the non-bonded groups.
• Lesion development was lowest for the non-bonded samples with bonding applied on the dentin and highest for the non-bonded samples with no bonding on dentin.
• For the non-bonded groups, the self-etch adhesive showed deeper lesion and more mineral loss than the etch-and-rinse bonding material.
• Mechanical loading aging resulted in deeper caries lesions than the water storage aging.

ObjectiveThis in vitro study aimed to compare dentin wall caries development at different composite–dentin interfaces.MethodsDentin samples (10.4 mm2) were restored with composite resin using two adhesive systems (etch-and-rinse and self-etch techniques). Different composite–dentin interfaces with gaps were produced: (a) failed bonded, which were fractured at interface after being submitted to aging protocols (no aging, mechanical loading or water storage); (b) non-bonded interfaces, both without any adhesive material or with adhesive material applied only on the dentin. Adhesively fractured and non-bonded samples were subjected to a lactic acid gel (pH = 5) caries model with a continuous opening/closing movement of the interfacial gap for 10 days. Transverse wavelength-independent microradiographs were taken, and lesion depth and mineral loss were measured. Data were analyzed with linear mixed-effects regression models.ResultsCaries development differed among the composite–dentin interfaces (p < 0.001). The non-bonded interface with adhesive material on the dentin showed less lesion depth than the failed bonded groups, while the non-bonded interface without adhesive on dentin showed the deepest wall lesions. Difference between the adhesive systems was observed only in the non-bonded groups (p = 0.003), with the self-etch adhesive applied on the dentin showing more severe lesions. Samples broken after mechanical loading aging showed deeper lesions than those broken after water storage (p < 0.001).SignificanceComposite–dentin interfaces failed after aging presented different demineralization from interfaces that were never bonded, indicating that the restorative treatment changes the tissue in a way relevant to secondary caries development.