Degradation in the dentin–composite interface subjected to multi-species biofilm challenges

Abstract

Oral biofilms can degrade the components in dental resin-based composite restorations, thus compromising marginal integrity and leading to secondary caries. In this study, we investigated the mechanical integrity of the dentin-composite interface challenged with multi-species oral biofilms. While most studies used single-species biofilms, we used a more realistic, diverse biofilm model produced directly from plaques collected from donors with a history of early childhood caries. Dentin–composite disks were made using bovine incisor roots filled with Z100™ or Filtek™ LS (3M ESPE). The disks were incubated for 72hr in paired CDC biofilm reactors, using a previously published protocol. One reactor was pulsed with sucrose, and the other was not. A sterile saliva-only control group was run with sucrose pulsing. The disks were fractured under diametral compression to evaluate their interfacial bond strength. Surface deformation of the disks was mapped using digital image correlation (DIC) to ascertain fracture origin. Fracture surfaces were examined using SEM/EDS to assess demineralization and interfacial degradation. Dentin demineralization was greater under sucrose-pulsed biofilms, as the pH dropped below 5.5 during pulsing, with LS and Z100 specimens suffering similar degrees of surface mineral loss. Biofilm growth with sucrose pulsing also caused preferential degradation of the composite-dentin interface, depending on the composite/adhesive system used. Specifically, Z100 specimens showed greater bond strength reduction and more frequent cohesive failure in the adhesive layer. This was attributed to the inferior dentin coverage by Z100 adhesive which possibly led to a higher level of chemical and enzymatic degradation. The results suggested that factors other than dentin demineralization were also responsible for interfacial degradation. We have thus developed a clinically relevant in vitro biofilm model which would allow us to effectively assess the degradation of the dentin-composite interface subjected to multi-species biofilm challenge.

Is secondary caries with composites a material-based problem?

“…Kermanshahi et al [101] also demonstrated that the synergistic activity of salivary esterases, CE and PCE, may result in degradation of Bis-GMA-based resins, extensive enough to allow bacterial leakage at the interface. Recently, it was shown that bacteria from dental plaque, for example Streptococcus mutans, with a similar esterase activity as in saliva, may also partake in the interfacial degradation [102,103].…”

Accelerated fatigue testing of dentin-composite bond with continuously increasing load

“…In total, 60 dentin-composite disc samples were prepared using bovine incisors as described previously [17,23,27]. Root sections from below the cementum-enamel junction with a root canal diameter less than 2 mm and an outer diameter larger than 5 mm were used.…”

Secondary caries and microleakage

“…While it should be possible to engineer repetitive cycles of pH, solute-solvent combinations, thermal cycling and mechanical loading that generate compressive, tensile and shear stress, other key parameters are the patient's salivary composition and amounts, shifting occlusal loads, dietary habits and oral cleanliness. Emerging research can be interpreted as if even the individual's intra-oral bacterial profile may play a role in the biodegradation of some polymers [43], which is a factor that is very difficult to simulate in a laboratory model [44].…”