Surface properties and Streptococcus mutans biofilm adhesion of ion-releasing resin-based composite materials

Resin-based composites (RBCs) were developed initially as an esthetic alternative to dental amalgam restoration [1]. Throughout the years, research on dental RBCs has led to the development of materials that have greatly improved properties that make them the first choice for direct restorations [2]. Some contemporary RBCs were found to have comparable mechanical properties as dental amalgam while simultaneously fulfilling the esthetic requirements [1,2]. Despite all the improvements in this class of dental materials, recurrent dental caries remains the leading cause of failure [3], [4], [5]. Furthermore, evidence reports that the success rate of posterior RBC restorations is lower than that of dental amalgam; this is more evident in patients with a higher caries risk [6].

The interaction between the microbial biofilm and the underlying dental hard tissues is a key factor in caries development [7]. The oral biofilm harbors many bacteria involved in developing a disease, such as dental caries and demineralization of the tooth structure [8]. Streptococcus mutans (S. mutans) is considered the primary pathogen related to dental caries development and, therefore, the most studied microorganism in oral microbiology [9]. Furthermore, the susceptibility of dental restorative material to the adhesion of microorganisms is of great importance for their clinical longevity [7,10]. Surface roughness, surface free energy, hydrophobicity of the restorative material, and the chemical composition of the material can influence bacterial adhesion [11].

Recently restorative dentistry has become more directed toward research and using bioactive materials in the dental office. Although the term bioactive is not new [12,13], it is still controversial [14], [15], [16], [17]. Due to the expected benefits associated with this term, it can be misused in advertisements. Therefore, the FDI published a Policy Statement on bioactive restorative materials to clarify the terms and provide guidelines for its use [16,17]. The FDI statement concludes that releasing ions from restorative materials does not necessarily mean the material is bioactive unless the other criteria listed in the statement are met [17]. Since ion release is one of the prerequisites for bioactivity, the development and use of ion-releasing restorative materials in the dental field have increased [18]. The ability to release ions such as fluoride (F), calcium (Ca), and phosphate (P) can retard recurrent caries as well as promote remineralization [19]. Furthermore, ions may inhibit the growth of cariogenic microorganisms [20], [21], [22].

Cention N (Ivoclar Vivadent, Schaan, Liechtenstein) (CN) and ACTIVA™ Bioactive Restorative (Pulpdent, MA, USA) (ACT) are relatively new materials that belong to this category. Although both ACT and CN were reported to release different levels of ions, including F+ and Ca2+ [19,[23], [24], [25], [26]], however evidence of apatite formation was only found with CN [23,26]. Nevertheless, studies investigating the biofilm formation on these materials and its relation to their surface properties are still lacking. Therefore, this study evaluates the surface roughness, water contact angle and S. mutans adhesion to CN and ACT compared to conventional RBC and RMGIC dental restorative materials.

The null hypotheses were tested as follows:

No differences would be observed in the surface roughness values of the tested restorative materials.

No differences would be observed in the contact angle values of the tested restorative materials.

No differences would be observed in the amount of S. mutans adhesion on the tested restorative materials.

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