Degradation of Methacrylate Monomers in Human Saliva

Abstract

INTRODUCTIONDegradation of dental resins in human saliva, that lead to decrease in mechanical strength and surface hardness, have been reported in in vitro studies 1,2） . The results of these studies suggested that such degradation arose from the chemical degradation of methacrylate polymers due to enzyme-catalyzed hydrolysis reaction of ester bond. However, methods that can adequately investigate the enzymatic degradation mechanism involved in the breakdown of methacrylate polymers are not available. Therefore, the chemical degradation of methacrylate monomers has been a subject of research to clarify the hydrolytic degradation behavior of ester linkages in polymer networks 3-5） . Several studies have been conducted to reveal the degradation behavior of bisphenol A diglycidyl dimethacrylate （BisGMA） and triethylenglycol dimethacrylate （TEGDMA） monomers in phosphate buffer solution containing cholesterol esterasewhich simulates salivary enzyme solution 6,7） . The hydrolyzed products of these monomers were detected in the simulated solution by enzymatic attack. The results of these studies revealed that a rapid hydrolysis reaction with the enzyme occurred within several days.It is known that esterase, a salivary enzyme, displays structure-dependent hydrolytic activity in the hydrolysis of esters such as fatty acid ester 8） . However, there is a lack of information regarding the relationship between the chemical structure of methacrylate monomers and the hydrolysis by salivary enzymes. It is expected that the development of a new methacrylate monomer with higher resistance to hydrolysis by salivary enzymes would contribute to improving the durability of composite resins in vivo.Recently, Jaffer et al. 9） measured the chemical stability of dimethacrylate monomers in human saliva and revealed that the degradation of BisGMA was faster than that of urethane methacrylate oligomer. The findings of this study should serve to expedite research activities that focus on how the structural dependency of methacrylate monomers influence their resistance to hydrolysis. In particular, BisGMA is the most common dimethacrylate monomer of composite resin materials 10,11） . Therefore, improvement in the chemical stability of BisGMA in human saliva would result in enhanced biostability of composite resin restorations.Jaffer et al. 9） had demonstrated that the human saliva contains sufficient esterase activity to catalyze the degradation of monomers.The aim of this study, therefore, was to assess the chemical stability of methacrylate monomers in human saliva to reveal the relationship between enzymatic degradation resistance and the chemical structure of monomers. Further, to examine the stability of the experimental monomers under clinical conditions, degradation test was carried out in human whole saliva. Six types of model monomethacrylate monomer and two BisGMAderivative monomers were synthesized, and their degradation as a function of time was investigated by using high-performance liquid chromatography （HPLC） . Deg...

Compositional design and optimization of dentin adhesive with neutralization capability

“…Different strategies have been developed to enhance the hydrolytic stability of dentin adhesive resins. These strategies include changing the monomer structure with an emphasis on increasing the hydrophobicity of the monomers by introducing urethane groups [17–19], branched methacrylate linkages [20], or ethoxylated BisGMA (BisEMA) [21]. The extent and rate of water uptake are depressed temporarily, but most of the materials still reach saturation within 7–60 day [22].…”

Biodegradation Studies of Novel Fluorinated Di-Vinyl Urethane Monomers and Interaction of Biological Elements with Their Polymerized Films

“…UDMA, another commonly used monomer that contains urethane bonds, has greater stability against hydrolysis when compared to BisGMA. In human saliva, BisGMA undergoes complete hydrolysis by 48 h while after 72 h of incubation more than 70% of UDMA is still left in solution [28]. Work by Hagio et al [28] has shown that modifying BisGMA by replacing the hydroxyl moieties with short hydrocarbon side chains coupled via a urethane bond increases the hydrolytic stability in the presence of human saliva [28].…”

“…In human saliva, BisGMA undergoes complete hydrolysis by 48 h while after 72 h of incubation more than 70% of UDMA is still left in solution [28]. Work by Hagio et al [28] has shown that modifying BisGMA by replacing the hydroxyl moieties with short hydrocarbon side chains coupled via a urethane bond increases the hydrolytic stability in the presence of human saliva [28]. The enhanced stability was attributed to the difference in molecular structure, such as steric hindrance and the addition of the urethane bonds.…”

Durable bonds at the adhesive/dentin interface:an impossible mission or simply a moving target?

“…The susceptibility of acrylate dental materials to degradation by esterases is well established [119,[122][123][124][125][126]. The esterase-catalyzed degradation of monomethacrylates, dimethacrylates and commercial dental resins has been documented in solution [122][123][124]126], in saliva samples [124,125,127], and in vivo [92]. In vitro studies have typically used one or more of the following esterases: cholesterol esterase (CE; EC 3.1.1.13) [122,124,126] acetylcholinesterase (ACHE; EC 3.1.1.7) [122,126] and pseudocholinesterase (PCE, aka butyrylcholinesterase; EC 3.1.1.8) [122,124,126].…”