Doxycycline-laden fibrous microparticles as a therapeutic ingredient for etch-and-rinse adhesive systems: Effects on optical, physical and bonding properties to dentin

Objectives

To evaluate the effects of the modification of an etch-and-rinse (ER) adhesive system with fibrous particles with or without doxycycline (DOX) as a therapeutic ingredient.

Methods

Polymeric fibers were synthesized via electrospinning using a 10 wt% polymer solution based on poly-(ε-caprolactone) (PCL). The PCL solution was separated into two aliquots: one was kept unchanged, and the other was laden with 25 wt% of DOX. Each electrospun fiber mat was further processed in a cryogenic impact mill to obtain small-sized fibrous particles, which were characterized with morphological, chemical (FTIR), and antibacterial activity (against Streptococcus mutans and Lactobacillus) analyses. The 2-step ER adhesive One-Step (Bisco) was separated into three aliquots: one was kept unmodified to serve as an unfilled control, and the other two aliquots were added with 20 wt% of DOX or PCL fibrous microparticles. The fiber-modified adhesives were tested for degree of conversion (DC), optical properties (color change [ΔE₀₀], translucency, and refractive index [RI]), wettability properties, and bonding potential (microtensile bond strength/µTBS) to dentin after immediate testing and one-year of water storage. The data were statistically analyzed using ANOVA and Kruskal-Wallis tests with α= 5 %. The bond strength data was also analyzed using Weibull analysis.

Results

The morphology of the PCL and DOX particles demonstrated a nonuniform diameter distribution similar to each other. While the PCL particles did not inhibit the growth of S. mutans and Lactobacillus, the DOX particles resulted in significant inhibition halos greater than chlorhexidine (control). The incorporation of the fibrous particles into the adhesive altered the color appearance of the material (ΔE₀₀>1.8 – above the acceptability threshold); translucency was slightly reduced only in the PCL adhesive, and the RI was similar among the tested adhesives. DC was similar among the adhesive groups, but their wetting ability increased in the following order: Control (42.7°±5.1°) < PCL (35.3°±3.4°) < DOX (28.9°±3.3°). All adhesives resulted in similar μTBS after 24 hours of water storage, but after one year of storage, the resin-dentin bonds obtained with DOX adhesive were greater than the control and stable over time. The characteristic strength of the resin-dentin bonds created with the DOX adhesive was as stronger than that obtained with the unmodified control.

Significance

The incorporation of fibrous particles, especially those based on therapeutic compounds like doxycycline, is an alternative to improve the biological and wetting ability of etch-and-rinse adhesive systems to dentin. Also, the presence of fibrous particles contributed to stable resin-dentin bonds over time.