The longevity of dental composites in the oral environment is critically affected by bacterial colonization on the restoration surface, and biofilm growth at the interface between the composite and the tooth structure. These processes undermine the structural integrity and durability of the composite, mainly resulting in secondary caries and pulpal inflammation [1]. Such clinical challenges highlight the need to develop composites with intrinsic antibacterial properties, aiming to enhance their performance under demanding oral conditions. This advancement would not only extend the lifespan of restorations but also significantly improve patient outcomes [2]. In response to these challenges, bioactive restorative materials have gained increasing attention as a promising scientific and clinical solution. "Bioactivity" refers to dental material's ability to elicit specific and beneficial biological responses at the interface with biological tissues. This includes effects at the cellular level through the release of bioactive molecules that support the preservation and repair of dental tissues, as well as enamel and dentin remineralization [3]. According to the material clinical application, bioactivity can be mediated through chemical interactions, biological processes, or a combination of both [4], [5]. Furthermore, antibacterial properties form a critical component of bioactivity, as they reduce the risk of secondary caries lesions and infections, thereby promoting durable and clinically successful restorations.

For this end, new anti-biofilm resin-based composites were developed to reduce plaque accumulation on the surfaces of dental materials by incorporating antibacterial agents such as fluoride [6], [7] chlorhexidine [8]and antibiotics like ciprofloxacin [9]. Nanoparticules like silvers (AgNPs) [10], titanium dioxide (TiO₂) [11], or zinc oxide (ZnO) [12] was also explored. These agents are dispersed within the composite and exhibited antibacterial properties in vitro through the controlled release of bioactive ions, which effectively targeted key dental plaque microorganisms, including Streptococcus mutans and Candida albicans [13]. Another promising approach involves using Quaternary Ammonium Methacrylate (QAM), as an antibacterial immobilized monomer within the resin matrix such as Dimethyl Hexadecyl Methacryloxyethyl Ammonium Iodide (DHMAI), which has shown strong bactericidal effects via contact killing [14], [15].

A growing interest in “organic and natural” alternatives to harmful chemical additives is emerging across food, cosmetic, and medical fields, now extending to dental materials. Recent studies have explored the integration of natural bioactive agents into composites as bio-friendly and sustainable antimicrobial solutions. Zhou et al. [11] used thyme oil-functionalized TiO₂ nanoparticles, achieving strong antimicrobial effects without altering mechanical strength. Yaseen et al. [16] similarly reported antibacterial activity with cinnamon nanoparticles in orthodontic resin. In this context, Salvadora persica (S. persica) named Siwak or Miswak, traditionally used as a natural toothbrush and rich in phytochemicals, was selected for its antibacterial, antioxidant, antifungal, and anti-inflammatory properties [17], [18], [19]. It also releases calcium and phosphate, potentially contributing to enamel remineralization [20], [21].

In vitro studies conducted on Siwak extracts revealed significant antibacterial properties against a variety of microorganisms, involved in dental caries such as Streptococcus mutans, Staphylococcus aureus, Lactobacillus acidophilus [22] Pseudomonas aeruginosa [23], as well as Porphyromonas Gingivalis [24], [25], which is considered one of the main pathogens involved in periodontal diseases. Siwak extracts also demonstrated potential antiprotozoal activity against Blastocystis [26].

Siwak contains more than one type of antimicrobial agent capable of inhibiting both Gram-positive and Gram-negative bacteria associated with periodontal disease. In addition to benzyl isothiocyanate, the principal antibacterial agent of Siwak [27], other bioactive constituents include ellagic acid, N-benzyl-2-phenylacetamide, sulfated flavonoids [28], sulfur compounds, butane diamine, chloride, fluoride [29], calcium, alkaloids (salvadorine) and trimethylamine [30] have been shown to contribute to the broad-spectrum antimicrobial activity of Siwak. The synergistic effects of these bioactive compounds not only suppress bacterial growth but also interfere with biofilm formation, highlighting Siwak’s potential as a natural alternative for oral infection control and as a candidate in the fight against multidrug-resistant pathogens. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Siwak against Streptococcus mutans were found to be 3.12 mg/ml and 6.25 mg/ml, respectively [27].

Additionally, antioxidants were found to decrease the toxic effect of dental composite resins by neutralizing free radicals and reactive oxygen species (ROS) generated during incomplete polymerization. They protect oral cells from oxidative damage, preserve mitochondria and reduce cytotoxicity [31]. Research on Siwak has shown that its raw extracts, contain high levels of antioxidant enzymes such as peroxidase, catalase, and polyphenol oxidase, making it an excellent mediator for oral hygiene [32], [33].

Siwak extracts show low cytotoxicity at typical concentrations for oral hygiène applications. Balto et al. [34] reported > 88 % fibroblast viability with ethanol and hexane extracts (0.5–1 mg/ml), while ethyl acetate reduced it to ∼60 %. Hammad et al. [35] found toxicity only at ≥ 11.25 mg/ml, with 2.25 mg/ml even enhancing cell viability. In contrast, chlorhexidine caused toxicity at just 0.001 % [36]. These findings confirm that siwak remains safe at typical concentrations (≤1 mg/ml), supporting its suitability for dental applications.

To the best of our knowledge, Siwak has not yet been assessed in dental composites. The aim of this work was to develop an experimental dental composite with natural bioactive properties without compromising its mechanical and physicochemical stability. Furthermore, different forms of Siwak were prepared and incorporated in experimental composites and their behaviors were studied using flexural and modulus strength testing and degree of conversion measurements. The antioxidant potential of Siwak-based composites was assessed. The antibacterial activity of pure Siwak was investigated in vitro using metabolic activity assays. Then, the antibacterial effectiveness of Siwak-incorporated resin composites was evaluated in vitro using various biological parameters. The study aimed to compare Algerian Siwak with two commercial samples of Oriental Siwak. Two hypotheses were suggested: (1) Siwak would act as an effective antioxidant, inhibiting bacterial growth and adhesion on the experimental composite surfaces; (2) the form of Siwak used could influence its bioactive effectiveness.