Lihua Yu,1,2,* Chunxia Zhang,3,* Jie Yang,4 Lu Li3 

1Department of Pediatric Dentistry, Tianjin Stomatological Hospital, School of Medicine, Nankai University, Tianjin, 300041, People’s Republic of China; 2Tianjin Key Laboratory of Oral and Maxillofacial Function Reconstruction, Tianjin, 300041, People’s Republic of China; 3Tianjin Baogang Rare Earth Research Institute Co., Ltd, Tianjin, 300300, People’s Republic of China; 4Department of Stomatology, The Second Hospital of Tianjin Medical University, Tianjin, 300211, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Chunxia Zhang, Tianjin Baogang Rare Earth Research Institute Co., Ltd, Block B, Building 5, No. 6, Huafeng Street, Huaming High-Tech Industrial Zone, Dongli District, Tianjin, 300300, People’s Republic of China, Tel +86-022-58910562, Email zcx19941002@163.com

Purpose: The primary goals of endodontic therapy are to eliminate microbes and prevent reinfection. Persistent root canal infections and failure of root canal therapy are primarily attributed to the presence of bacteria, particularly E. faecalis. Chemical irrigants play a crucial role in complementing mechanical instrumentation in ensuring adequate disinfection. However, current techniques and available irrigants are limited in their ability to achieve optimal sterilization of the root canal system. In this study, we developed a novel material called La@PCDs by combining CQD-PVA and lanthanum for root canal irrigation.
Methods: A one-pot hydrothermal method was used to prepare composites of lanthanum and CQD-PVA (La@PCDs). Scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and the particle size were employed to characterize La@PCDs. ROS generation was evaluated by measuring the fluorescence intensity emitted at 525 nm from 2′,7′-dichlorodihydrofluorescein diacetate (DCFH-DA). In vitro experiments were conducted to assess the effectiveness of the nanoparticles in combating Enterococcus faecalis and eradicating in situ biofilm eradication in root canal. Furthermore, cytotoxicity assessments were carried out to demonstrate the safety of La@PCDs.
Results: SEM and FTIR results showed that La@PCDs were successfully prepared and exhibiting a homogeneous size distribution and irregular morphology. ROS assessment demonstrated that La@PCDs have a synergistic effect, promoting the production of a large number of ROS. This effect only occurred under acidic PH conditions. The inherent acidity in the biofilm microenvironment can act as internal stimulus. In vitro experiments revealed superior antibacterial efficiency under acidic conditions without causing significant cytotoxicity compared to the commonly used NaClO irrigant. The biosafety of La@PCDs was confirmed.
Conclusion: Compared to existing materials, these nanoparticles exhibit favorable antibacterial and anti-biofilm properties, along with improved biocompatibility. These findings emphasize the potential of the integrated La@PCDs as a promising option for enhancing root canal irrigation and disinfection.

Keywords: lanthanum, La, reactive oxygen species, ROS, pH-response, antimicrobial, root canal irrigation