The Effect of Liquid Rubber Addition on the Physicochemical Properties, Cytotoxicity, and Ability to Inhibit Biofilm Formation of Dental Composites

Abstract

The aim of this study was to evaluate the effect of modification with liquid rubber on the adhesion to tooth tissues (enamel, dentin), wettability and ability to inhibit bacterial biofilm formation of resin-based dental composites. Two commercial composites (Flow-Art-flow type with 60% ceramic filler and Boston-packable type with 78% ceramic filler; both from Arkona Laboratorium Farmakologii Stomatologicznej, Nasutów, Poland) were modified by addition of 5% by weight (of resin) of a liquid methacrylate-terminated polybutadiene. Results showed that modification of the flow type composite significantly (p < 0.05) increased the shear bond strength values by 17% for enamel and by 33% for dentine. Addition of liquid rubber significantly (p < 0.05) reduced also hydrophilicity of the dental materials since the water contact angle was increased from 81-83° to 87-89°. Interestingly, modified packable type material showed improved antibiofilm activity against Steptococcus mutans and Streptococcus sanguinis (quantitative assay with crystal violet), but also cytotoxicity against eukaryotic cells since cell viability was reduced to 37% as proven in a direct-contact WST-8 test. Introduction of the same modification to the flow type material significantly improved its antibiofilm properties (biofilm reduction by approximately 6% compared to the unmodified material, p < 0.05) without cytotoxic effects against human fibroblasts (cell viability near 100%). Thus, modified flow type composite may be considered as a candidate to be used as restorative material since it exhibits both nontoxicity and antibiofilm properties.

Keywords: biofilm formation; cytotoxicity; resin composite; wettability.

Figure 1

The surface water contact angles determined for tested materials. Asterisks (*) point at statistically significant differences (p < 0.05) according to the unpaired t test.

Figure 2

The shear bond strength estimated for tested materials depending on type of the tooth tissue. Asterisks (*) point at statistically significant differences (p < 0.05) according to the unpaired t test.

Figure 3

Quantification of the adhered bacteria to the B, BM, F, and FM materials compared to the control surface (polystyrene): (a) biofilm formation on materials in BHI broth; (b) biofilm formation on materials in BHI broth with 0.25% sucrose; results are shown as mean values ± SD from triplicate experiments; * indicates statistically significant results (p < 0.05) compared to the control, # indicates statistically significant results (p < 0.05) between unmodified and corresponding modified composite (the unpaired t test).

Figure 4

CLSM images of biofilm formed by S. sanguinis, S. mutans, and mixed species: S. sanguinis and S. mutans on B, BM, F, FM composite materials in BHI medium (a) and in BHI + 0.25% sucrose medium (b). Magn. 400×, scale bar = 70 µm (green fluorescence—viable cells, yellow and red fluorescence—dead cells).

Figure 4

CLSM images of biofilm formed by S. sanguinis, S. mutans, and mixed species: S. sanguinis and S. mutans on B, BM, F, FM composite materials in BHI medium (a) and in BHI + 0.25% sucrose medium (b). Magn. 400×, scale bar = 70 µm (green fluorescence—viable cells, yellow and red fluorescence—dead cells).

Figure 5

Cytotoxicity of the materials assessed by WST-8 test after direct 48 h contact of BJ fibroblasts with the materials (*significantly different results compared to the negative control of cytotoxicity, #significantly different results compared to the B material, $significantly different results compared to the FM material, ^significantly different results compared to the F material, according to one-way ANOVA test followed by Tukey’s multiple comparison test, p < 0.05).

Figure 6

Qualitative evaluation of materials’ cytotoxicity by live/dead double staining of BJ fibroblasts cultured for 48 h on the materials’ surfaces, and grown around the samples (viable cells—green fluorescence, nuclei of dead cells—red fluorescence, apoptotic cells—green and red florescence); magn. 100×, scale bar = 150 µm.