Development of radiopaque, biocompatible, antimicrobial, micro-particle fillers for micro-CT imaging of simulated periodontal pockets

Objectives: Approximately 10⁹ bacteria can be harbored within periodontal pockets (PP) along with inflammatory byproducts implicated in the pathophysiology of systemic diseases linked to periodontitis (PD). Calculation of this inflammatory burden has involved estimation of total pocket surface area using analog data from conventional periodontal probing which is unable to determine the three-dimensional (3-D) nature of PP. The goals of this study are to determine the radiopacity, biocompatibility, and antimicrobial activity of transient micro-particle fillers in vitro and demonstrate their capability for 3-D imaging of artificial PP (U.S. Patent publication number: 9814791 B2). Methods: Relative radiopacity values of various metal oxide fillers were obtained from conventional radiography and micro-computed tomography (μCT) using in vitro models. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were used to measure the biocompatibility of calcium tungstate (CaWO₄) particles by determination of viable keratinocytes percentage (%) after exposure. After introducing an antibacterial compound (K21) to the radiopaque agent, antimicrobial tests were conducted using Porphyromonas gingivalis (P. gingivalis) and Streptococcus gordonii (S. gordonii) strains and blood agar plates. Results: CaWO₄ micro-particle-bearing fillers exhibited an X-ray radiopacity distinct from tooth structures that enabled 3-D visualization of an artificial periodontal pocket created around a human tooth. MTT assays indicated that CaWO₄ micro-particles are highly biocompatible (increasing the viability of exposed keratinocytes). Radiopaque micro-particle fillers combined with K21 showed significant antimicrobial activity for P. gingivalis and S. gordonii. Significance: The plausibility of visualizing PP with 3-D radiographic imaging using new radiopaque, biocompatible, transient fillers was demonstrated in vitro. Antibacterial (or other) agents added to this formula could provide beneficial therapeutic features along with the diagnostic utility.