Interfacial degradation of adhesive composite restorations mediated by oral biofilms and mechanical challenge in an extracted tooth model of secondary caries

Abstract

Objective: To study the combined effect of simulated occlusal loading and plaque-derived biofilm on the interfacial integrity of dental composite restorations, and to explore whether the effects are modulated by the incorporation of sucrose.

Methods: MOD-class-II restorations were prepared in third molars. Half of the specimens (n=27) were subjected to 200,000 cycles of mechanical loading using an artificial oral environment (ART). Then, both groups of specimens (fatigued and non-fatigued) were divided into three subgroups for testing in CDC-reactors under the following conditions: no biofilm (Control), biofilm with no sucrose (BNS) and biofilm pulsed with sucrose (BWS). BNS and BWS reactors were incubated with a multispecies inoculum from a single plaque donor whereas the control reactor was not. The BWS reactor was pulsed with sucrose five times a day. The biofilm challenges were repeated sequentially for 12 weeks. pH was recorded for each run. Specimens were examined for demineralization with micro-CT and load capacity by fast fracture test.

Results: Demineralization next to the restorations was only detectable in BWS teeth. Fracture loads were significantly reduced by the concomitant presence of biofilm and sucrose, regardless of whether cyclic mechanical loading was applied. Cyclic loading reduced fracture loads under all reactor conditions, but the reduction was not statistically significant.

Conclusions: Sucrose pulsing was required to induce biofilm-mediated degradation of the adhesive interface. We have presented a comprehensive and clinically relevant model to study the effects of mechanical loading and microbial challenge on the interfacial integrity of dental restorations.

Keywords: Adhesive interface; Cyclic loading; Mechanical fatigue; Oral biofilms; Resin composite; Sucrose.

Figure 1

Cyclic loading setup. Each tooth was mounted in acrylic resin and located in the lower chamber of the artificial oral environment. A steatite bead attached to the upper loading arm acted as the antagonist.

Figure 2

(a) Diagram of the specimens’ allocation in each CDC reactor (b) CDC reactor setup for experimental runs with labeled components.

Figure 3

Mean real-time pH recording from the twelve-biofilm challenges for BNS and BWS growth conditions. Black bars indicate the standard deviation at each time point.

Figure 4

Representative micro-CT cross-sectional images and 3D reconstructions of the restored teeth after fatigue and biofilm challenge. (a) No Fatigue control (no biofilm) (b) Fatigue control (no biofilm). (c) No Fatigue BNS. (d) Fatigue BNS (e) No Fatigue BWS. (f) Fatigue BWS. Red circles and red arrows indicate zones with observed demineralization in the 2D cross-sections and 3D reconstructions, respectively.

Figure 5

Average mineral profiles obtained from three different regions in the teeth for each of the groups. (a) occlusal margin (b) gingival margin, and (c) proximal wall. Inset in each plot is a representative image indicating the approximate locations from where the profiles were obtained.

Figure 6

Data distribution and mean profile of fracture loads: a) Box plots displaying the median fracture load (black bar dividing each box) for each group and condition. Each box represents the inter-quartile range. End of whiskers are the minimum and maximum load values (except for outliers). b) Profile plots presenting the mean fracture load values and standard deviation for each group and condition.

Figure 7

Fracture load reduction of each group relative to non-fatigued Control group. The magnitude of fracture load reduction by adding fatigue challenge to BNS and BWS suggests only a modest additive effect.