Fabrication of hybrid crosslinked network with buffering capabilities and autonomous strengthening characteristics for dental adhesives

Abstract

Ingress of bacteria and fluids at the interfacial gaps between the restorative composite biomaterial and the tooth structure contribute to recurrent decay and failure of the composite restoration. The inability of the material to increase the pH at the composite/tooth interface facilitates the outgrowth of bacteria. Neutralizing the microenvironment at the tooth/composite interface offers promise for reducing the damage provoked by cariogenic and aciduric bacteria. We address this problem by designing a dental adhesive composed of hybrid network to provide buffering and autonomous strengthening simultaneously. Two amino functional silanes, 2-hydroxy-3-morpholinopropyl (3-(triethoxysilyl)propyl) carbamate and 2-hydroxy-3-morpholinopropyl (3-(trimethoxysilyl)propyl) carbamate were synthesized and used as co-monomers. Combining free radical initiated polymerization (polymethacrylate-based network) and photoacid-induced sol-gel reaction (polysiloxane) results in the hybrid network formation. Resulting formulations were characterized with regard to real-time photo-polymerization, water sorption, leached species, neutralization, and mechanical properties. Results from real-time FTIR spectroscopic studies indicated that ethoxy was less reactive than methoxy substituent. The neutralization results demonstrated that the methoxy-containing adhesives have acute and delayed buffering capabilities. The mechanical properties of synthetic copolymers tested in dry conditions were improved via condensation reaction of the hydrolyzed organosilanes. The leaching from methoxy containing copolymers was significantly reduced. The sol-gel reaction provided a chronic and persistent reaction in wet condition-performance that offers potential for reducing secondary decay and increasing the functional lifetime of dental adhesives.

Evolution of Network Structure and Mechanical Properties in Autonomous-Strengthening Dental Adhesive

“…The increase in soaking time from 3 to 9 days did not result in a significant increase in the concentration of HEMA leached from the samples. Compared to our previous investigation that used ethanol as the aging solvent, the amount of leached HEMA was significantly lower and no BisGMA was detected [8,9,11,47].…”

New silyl-functionalized BisGMA provides autonomous strengthening without leaching for dental adhesives

“…Round disc samples (~4 mm diameter and ~1.2 mm thickness) were used for the leachable study [36, 47]. The polymerized disc was submerged in 1 mL ethanol (200 proof) at 23±2 °C for 1 to 28 days.…”

Autonomous-Strengthening Adhesive Provides Hydrolysis-Resistance and Enhanced Mechanical Properties in Wet Conditions

“…To address the hydrolytic instability of dental adhesives, several strategies have been proposed that involve alterations to physicochemical properties of the adhesives, for example by tailoring the hydrophobicity [ 11 , 30 , 31 , 32 ], enhancing the monomer conversion at the hybrid layer [ 33 , 34 , 35 , 36 ], or addition of inhibitors [ 14 , 37 , 38 ]. Despite the promise of these methodologies, the intrinsic tendency of the methacrylate-based dental adhesives to water sorption renders the hydrolytic degradation inevitable in a wet oral environment [ 9 ]. Alternatively, the dental adhesives that can demonstrate the self-strengthening property have enabled improved hydrolytic stability [ 6 , 17 , 18 , 19 ].…”

“…Under in vivo conditions, it is difficult, if not impossible, to repair the adhesive [ 6 ]. With the increased use of dental composites in restorative dentistry [ 9 ], there is a dire need to develop dental adhesives that resist hydrolysis. Improving the physicochemical properties of dental adhesives has been identified as a promising approach to counteract hydrolytic degradation.…”