Mimicking nature: Self-strengthening properties in a dental adhesive

Abstract

Chemical and enzymatic hydrolysis provoke a cascade of events that undermine methacrylate-based adhesives and the bond formed at the tooth/composite interface. Infiltration of noxious agents, e.g. enzymes, bacteria, and so forth, into the spaces created by the defective bond will ultimately lead to failure of the composite restoration. This paper reports a novel, synthetic resin that provides enhanced hydrolytic stability as a result of intrinsic reinforcement of the polymer network. The behavior of this novel resin, which contains γ-methacryloxyproyl trimethoxysilane (MPS) as its Si-based compound, is reminiscent of self-strengthening properties found in nature. The efforts in this paper are focused on two essential aspects: the visible-light irradiation induced (photoacid-induced) sol-gel reaction and the mechanism leading to intrinsic self-strengthening. The FTIR band at 2840 cm−1 corresponding to CH3 symmetric stretch in −Si−O−CH3 was used to evaluate the sol-gel reaction. Results from the real-time FTIR indicated that the newly developed resin showed a limited sol-gel reaction (<5%) during visible-light irradiation, but after 48h dark storage, the reaction was over 65%. The condensation of methoxysilane mainly occurred under wet conditions. The storage moduli and glass transition temperature of the copolymers increased in wet conditions with the increasing MPS content. The cumulative amounts of leached species decreased significantly when the MPS-containing adhesive was used. The results suggest that the polymethacrylate-based network, which formed first as a result of free radical initiated polymerization, retarded the photoacid-induced sol-gel reaction. The sol-gel reaction provided a persistent, intrinsic reinforcement of the polymer network in both neutral and acidic conditions. This behavior led to enhanced mechanical properties of the dental adhesives under conditions that simulate the wet, oral environment.

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

“…The hydrolysis is preceded by protonation of the alkoxy groups and the hydrolysis rates of alkoxy groups are generally related to their steric bulk, such as CH 3 O > C 2 H 5 O [59,60], a methoxysilane hydrolyzed at 6–10 times the rate of an ethoxysilane. In the previous MPS study, the degree of hydrolysis of methoxysilane was found to be ~50% within 8 h [47]. From the real-time FTIR spectroscopic study (Fig.…”

“…In our previous study, an autonomic, self-strengthening, Si-based (γ-methacryloxyproyl trimethoxysilane, MPS) hybrid system was developed for potential application as a dental adhesive [47]. The methoxy groups of MPS are hydrolyzed to form silanol-containing species, which are highly reactive intermediates and can generate Si—O—Si or Si—O—C covalent bonds.…”

“…The degree of conversion (DC) and polymerization behavior were determined by FTIR as reported [47]. A time-based spectrum collector (Spectrum TimeBase, Perkin-Elmer) was used for continuous and automatic collection of spectra during polymerization.…”

“…However, MEMA-functionalized copolymers showed fast neutralization behavior when loosely crosslinked network was formed, which would potentially limit the long-term performance of these materials under clinical conditions. Recently, we have developed a self-strengthening dental adhesive by introducing photoacid-induced sol-gel reaction together with the free radical photo-polymerization of methacrylate [46,47]. The results indicated that whether in wet conditions (pH ~ 5.5 @25 °C) or in acidic conditions (pH ≤ 3.5 @25 °C), the sol-gel reaction is a suitable and novel approach to enhance the mechanical properties of the newly developed dental adhesive copolymers [46,47].…”

<i>In vitro</i>/<i>in silico</i> investigation of failure criteria to predict flexural strength of composite resins

“…Using experimental CR containing irregular silica fillers and 2,2-bis[4-(2-hydroxy-3-methacrylyloxypropoxy)-phenyl]-propane (Bis-GMA)/triethyleneglycol dimethacrylate (TEGDMA), flexural strengths were measured according to ISO4049:2009 using a universal testing machine (EZ-SX, Shimadzu, Kyoto, Japan) with crosshead speed 1.0 mm/min (n=10 24) were used as fillers. Each specimen was light-cured for 10 s with the light-emittingdiode curing light (Pencure 2000, Morita, Kyoto, Japan) which had a maximal light density of 2,000 mW/cm 2 .…”