Chlorhexidine release and water sorption characteristics of chlorhexidine-incorporated hydrophobic/hydrophilic resins

Abstract

Objectives: The aim of this study was to evaluate chlorhexidine release from unfilled non-solvated methacrylate-based resins of increasing hydrophilicity and to examine relationships among Hoy's solubility parameters, water sorption, solubility and the rate of chlorhexidine release.

Methods: Resin discs were prepared from light-cured, experimental resin blends (R1, R2, R3, R4 and R5) containing 0.0, 0.2, 1.0 and 2.0 wt.% chlorhexidine diacetate (CDA). Discs were immersed in distilled water at 37 degrees C, and mass changes were recorded at different periods. Spectral measurements were made to follow change in optical densities of storage solution to examine chlorhexidine release kinetics. After a 28-day period, water sorption, solubility, and the cumulative chlorhexidine release were obtained. Additionally, antibacterial study was performed by observing the presence of inhibition zone against Streptococcus mutans.

Results: The most hydrophilic resin (R5) exhibited the highest chlorhexidine release rate. The most hydrophobic resin (R1) exhibited the lowest rate. However, no inhibition zone was produced by any specimens stored in water for 2 weeks. The addition of CDA increased solubility significantly but had no effect on water sorption. Significant positive correlations were seen between water sorption and the cumulative chlorhexidine release.

Significance: Chlorhexidine release from resins may be related to water-induced swelling, which in turn is enhanced by the hydrophilicity of cured polymer matrix.

Fig.1

Changes in mass of the chlorhexidine diacetate (CDA)-incorporated resin blends (R1–R5) over 28 days of water storage. Symbols represent mean values of mass changes as percentages of their initial mass (n = 6). A. CDA-incorporated R1. B. CDA-incorporated R2. C. CDA-incorporated R3. D. CDA-incorporated R4. E. CDA-incorporated R5.

Fig.2

Chlorhexidine release rates from CDA-incorporated resin disks containing 0% (control), 0.2%, 1.0% and 2.0% CDA. A. CDA-incorporated R1. B. CDA-incorporated R2. C. CDA-incorporated R3. D. CDA-incorporated R4. E. CDA-incorporated R5.

Fig.3

Cumulative chlorhexidine release after 28 days of water storage, expressed as mg per g of samples that contain different CDA concentrations. A. 0.2 % CDA-incorporated resin blends. B. 0.1 % CDA-incorporated resin blends. C. 2.0 % CDA-incorporated resin blends.

Fig. 4

Regression analysis of water sorption of resins 1–5 with 0, 0.2, 1.0 or 2.0 wt% CDA, versus the Hoy’s solubility parameter (δ_h).

Fig.5

Regression analyses of the cumulative chlorhexidine release for 28 days against the water sorption of resins (R1–R5). The cumulative chlorhexidine release represents as mg per g of samples. Equations for 0.2%, 1.0% and 2.0% are Y = 0.0007X + 0.00578 (R² = 0.6557, p = 0.097), Y = 0.0015X + 0.3734 (R² = 0.926, p = 0.009) and Y = 0.0019X + 0.4789 (R² = 0.8243 p = 0.0033), respectively.

Fig. 6

Regression analysis of cumulative chlohexidine release from the five experimental resins (R1–5) containing 0.2, 1.0 or 2.0 wt% CDA plotted versus the Hoy’s δ_h values for the resins.

Fig.7

Antibacterial effects of CDA-incorporated resin disks against Streptococcus mutans after different periods of water storage, as evaluated by the dimensions of their inhibition zones. The same superscript letters indicate no significant difference (p > 0.05). A. Inhibition zone (mm) produced by 1.0 % CDA-incorporated resin disks. B. Inhibition zone (mm) produced by 2.0 % CDA-incorporated resin disks. No inhibition zones were observed by the 0.0% and 0.2% CDA-incorporated resin disks at any time (not shown).