In this study three novel dimethacrylates of different chain lengths having bulky bicycloaliphatic rings were synthesized and proposed as possible dental monomers for dental resin mixtures.
The monomers were prepared by the reaction of glycidyl methacrylate with dicarboxylic acid esters obtained from nadic anhydride and ethylene, 1,4-butylene and 1,6-hexylene glycols. The addition reaction of glycidyl methacrylate and the acidic compound was carried out in the presence of basic catalyst—tetraethylammonium bromide. The monomers were photopolymerized in the presence of a photoinitiator which was 2,2-dimethoxy-2-phenyloacetophenone. Unfilled homopolymers were evaluated for photopolymerization conversion and volumetric curing shrinkage. Water sorption, water solubility, flexural strength and hardness were measured. The prepared polymers were also subjected to dynamic mechanical studies (DMA).
The proposed dimethacrylates exhibit low curing shrinkage (about 4–5%) and high degree of double bond conversion (up to 84%). Their water sorption and water solubility are comparable to those of Bis-GMA composite resin. Furthermore, their thermo-mechanical properties are better than those of the commonly known dimethacrylates.
The new dimethacrylates are promising photocurable dental monomers owning to simple synthesis, high degree of conversion coupled with low curing shrinkage and good mechanical properties.
Photoinitiated polymerization of dimethacrylate monomers produces densely crosslinked polymers which find wide application in dentistry such as dental composites, dental adhesives, bonding agents and cements, fissure sealants and elastomeric impression materials .
A typical dental composite currently used for the restoration of teeth consists of an organic matrix in which inorganic filling particles are imbedded. The polymerizable material provides about 95% by weight of the organic portion, which itself amounts only to 10–30% by weight of the composite, the rest being inorganic fillers. As main components of the organic part 2,2-bis[4-(2′-hydroxy-3′methacryloxypropoxy)phenyl]-propane (Bis-GMA), triethyleneglycol dimethacrylate (TEGDMA) and 1,6-bis(2′-methacryloxyethoxycarbonylamino)-2,4,4-trimethylhexane (UDMA) are commonly used.
In order to improve the performance of dental materials, intensive investigations are being made. The main topics include reduction of polymerization shrinkage, water sorption and water solubility as well as improvement of biocompatibility . Polymerization shrinkage is still a major cause of clinical failure of composite restorations . Due to volume decrease, a gap is formed between the wall of the cavity and the filling material. This gap is easily accessible for bacteria, which can initiate biodegradation processes, in consequence, worsening marginal adaptation of a composite. Water sorption is also one of the major concerns because it causes gradual long-term deterioration of mechanical properties of composite resins . Besides, the intra-oral photocuring must be carried out to the highest obtainable monomer conversion, so as to minimize the elution of components from the polymer matrix into the oral cavity. It is well known that methacrylic monomers are toxic, allergic, and mutagenic, especially for the pulp .
In this work three novel dimethacrylates with relatively high molecular weights are proposed as dental monomers of low polymerization shrinkage as well as high double bond conversion. Their thermo-mechanical properties were compared with those of the dimethacrylates presently used in dental applications. The DMA technique was used to measure the glass transition temperatures ( T g ) of the new photopolymerization systems. Water sorption and solubility were also measured.