DCPD-containing composites prevent secondary caries: An in-vitro biofilm model

Purpose/aim: The aim of this study was to evaluate the ability of dicalcium phosphate dihydrate (DCPD) filler-containing resin-based composites (RBC) to prevent secondary caries formation using two in vitro models of cariogenic biofilm challenge. Materials and methods: Eight sound human molars had their root removed 3 mm apical to cement-enamel junction, and the pulp chamber filled (Majesty ES-2, Kuraray, Japan). Four Class II cavities were made in each tooth having cervical margin in dentin. Cavities were filled with: a conventional resin-modified glass ionomer cement (RMGIC, Ionolux, VOCO GmbH, Germany) or experimental RBCs having a BisGMA-TEGDMA resin blend and: 60 vol% Ba glass (RBC-0); 40 vol% Ba glass, 20 vol% DCPD (RBC-20); 20 vol% Ba glass, 40 vol% DCPD (RBC-40). Restorations were finished (diamond burs, silicon carbide papers), then specimens were sterilized, stored in artificial saliva for one week and randomly divided into 2 groups (n = 4/group) according to the biofilm model. Group 1: specimens were inserted in 6-well plates, and Streptococcus mutans biofilm formation on the specimens’ surfaces was obtained in an orbital shaker (37 °C, 100 rpm) incubating in 1:25 diluted BHI + 5 wt% sucrose for two weeks. Culture broth was changed daily. Group 2: specimens were inserted into the flow-cell of a continuous flow bioreactor (37 °C, 20 ml/h), and S. mutans biofilm formation on the specimens’ surfaces was obtained incubating in 1:25 diluted BHI + 5 wt% sucrose for two weeks. pH values of the culture broth and absence of contamination were checked daily in both groups. Before and after microbiological procedures, specimens were scanned using microCT (Skyscan 1176, 9 μm resolution, 80 kV, 300 mA). Image reconstruction was performed, and demineralization depths (μm) were evaluated at the margins and at 1.0 mm from the margins. Results: pH values stayed constant throughout the incubation time (Group 1: 4.2 ± 0.1; Group 2: 4.3 ± 0.1), and no contamination was observed. Dentin demineralization (no enamel demineralization) could be observed in all specimens. Significantly higher overall demineralization depth was found in specimens from Group 2 compared to Group 1. RBC-0 and RBC-20 showed secondary caries development, while RBC-40 and RMGIC showed a secondary caries prevention effect (Table 1). Table 1. Mean demineralization depth (μm ± 1 SD) of the tested specimens according to the microbiological models. Different superscript letters indicate significant differences between materials (Tukey test, p < 0.05). Material Group 1 Group 2 Margin Margin + 1.0 mm Margin Margin + 1.0 mm RBC-0 146.8(28.7)a,b 132.8(12.5)a,b 217.4(32.5)a 156.4(21.0)a RBC-20 156.5(42.8)a 108.8(11.6)b 214.5(44.9)a 163.4(29.8)a RBC-40 80.8(33.6)b 144.8(4.6)a 84.4(47.6)b 157.9(58.1)a RMGIC 87.8(20.8)b 125.5(25.4)a,b 100.0(51.0)b 176.8(60.9)a Conclusions: Experimental RBC-40 is a promising bioactive material, able to prevent secondary caries in vitro, similarly to the control RMGIC material. The bioreactor model displayed secondary caries formation in a similar way as in vivo.