A new arginine-based dental adhesive system: formulation, mechanical and anti-caries properties

Abstract

Secondary caries at the margins of composite restorations has been attributed to adhesive failure and consequent accumulation of cariogenic biofilms.

Objectives: To develop and evaluate an etch-and-rinse adhesive system containing arginine for sustainable release and recharge without affecting its mechanical properties. Arginine metabolism by oral bacteria generates ammonia, which neutralizes glycolytic acids and creates a neutral environmental pH that is less favorable to the growth of caries pathogens, thus reducing the caries risk at the tooth-composite interface.

Methods: Experimental adhesives were formulated with methacrylate monomers and arginine at 5%, 7%, and 10% or no arginine (control). Adhesives were tested for: (i) mechanical properties of true stress (FS and UTS), modulus of elasticity (E), degree of conversion (DC), Knoop hardness number (KHN) and dentin microtensile bond strength (μ-TBS), (ii) arginine release and recharge, and (iii) antibacterial activities. Data was analyzed by t-test, one-way ANOVA and Tukey's tests.

Results: FS and UTS results showed no statistically significant differences between the 7% arginine-adhesive and control, while the results for E, DC, KHN and μ-TBS showed no difference among all groups. The 7% arginine-adhesive showed a high release rate of arginine (75.0μmol/cm²) at 2h, and a more sustainable, controlled release rate (up to 0.2μmol/cm²) at 30days.

Conclusions: Incorporation of 7% arginine did not affect the physical and mechanical properties of the adhesive. Arginine was released from the adhesive at a rate and concentration that exhibited antibacterial effects, regardless of shifts in biofilm conditions such as sugar availability and pH.

Clinical significance: Secondary caries is recognized as the main reason for failure of dental restorations. The development of an arginine-based adhesive system has the potential to dramatically reduce the incidence and severity of secondary caries in adhesive restorations in a very economical fashion.

Keywords: Arginine; Caries; Dental adhesives; Oral biofilms; Secondary caries.

Fig. 1

SEM images of the resin-dentin interface created with the adhesive systems containing arginine in different concentrations: a) Arg0 (no arginine), b) Arg5 (5 wt% arginine), c) Arg7 (7 wt% arginine) and d) Arg10 (10 wt% arginine). C = composite; AL = adhesive layer; D = dentin; white arrows indicates different sizes of arginine particles within the adhesive layer. Magnification used ranged from 1.140 to 1.510 X.

Fig. 2

Arginine release and recharge. (A) arginine release rates of the Arg7 group during 30 days; (B) cumulative release of arginine during 30 days; (C) cumulative arginine release per cycle over 3 days of recharge; d: day; h:hour.

Fig. 3

Planktonic growth curves of oral bacterial strains in BHI broth at pH 7.0 or pH 5.7. UA159: Streptococcus mutans U159; DL1: Streptococcus gordonii DL1; +A: growth in the presence of Arg7 discs; –A: growth in the presence of Arg0 discs; C: growth in the absence of adhesive discs (control).

Fig. 4

Images of biofilm formation obtained from confocal microscopy during bacterial growth in TY and glucose in pH 7.0. Control: growth in the absence of adhesive discs; Arg0: growth in the presence of discs without arginine; Arg7: growth in the presence of discs containing 7wt% arginine.

Fig. 5

Images of biofilm formation obtained from confocal microscopy during bacterial growth in TY and glucose in pH 5.7. Control: growth in the absence of adhesive discs; Arg0: growth in the presence of discs without arginine; Arg7: growth in the presence of discs containing 7wt% arginine.