Biological and nano-indentation properties of polybenzoxazine-based composites reinforced with zirconia particles as a novel biomaterial

Characterization of dental light-curing resin composites incorporating multiple modified low-shrink monomers

OBJECTIVE

Polymerization shrinkage poses a significant challenge in dental resin composites. The objective of this study is to introduce spiroorthocarbonate monomer 3,9-dimethylene-1,3,5,7-tetraoxa-spiro[5,5]undecane (BMSOC) and epoxy resin monomer 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (ECHM-ECHC) into bisphenol-S-bis(3-methacrylato-2-hydroxy propyl)ether (BisS-GMA) based resin composites to develop composites with reduced shrinkage properties.

METHODS

BMSOC and BisS-GMA were synthesized and thoroughly mixed with ECHM-ECHC, followed by inorganic fillers and photoinitiators. Based on the composition of the resin matrix, five groups of experimental composites were prepared, with traditional bisphenol A-dimethacrylate glycidyl ester (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) based composite serving as the control. The polymerization properties, including degree of conversion (DC) and polymerization shrinkage (PS), as well as marginal microleakage, wettability, flexural strength (FS), flexural modulus (FM), and biocompatibility were evaluated.

RESULTS

The results demonstrated that compared with the control group, the PS of BisS-GMA based composites containing BMSOC and ECHM-ECHC were significantly reduced (P < 0.05), and the lowest PS (0.96 ± 0.08 %) was observed when the ratio of BisS-GMA: (Epoxy + BMSOC) was 4:6. Additionally, the experimental composites also exhibited improved DC, minimal microleakage, low hydrophilicity, enhanced mechanical properties, qualified in vivo biocompatibility, and slight/moderate in vitro biocompatibility.

SIGNIFICANCE

The resin composites incorporating multiple modified low-shrink monomers are promising for dental applications to prevent various clinical problems caused by PS and extend restoration longevity.

Two high toughness and flame retardant DOPO-containing polybenzoxazines based on polyether-urea

In this current work, two new-style DOPO-containing benzoxazines based on polyether-urea were successfully synthesized by a modified version via three-step procedures, and the corresponding polybenzoxazines with high toughness and flame retardancy were obtained by thermal activated polymerization. The single and double DOPO-containing benzoxazines were named as BzD1 and BzD2, respectively. The corresponding polymers followed were named as PBzD1 and PBzD2, respectively. The curing behaviors of the two new benzoxazines were investigated by differential scanning calorimetry. The thermal and mechanical properties of the materials were evaluated by TGA and dynamic mechanical analysis. The flame retardant properties were elucidated via limiting oxygen index (LOI). The toughness properties were expressed by bending tests. The results showed that the Yc for PBzD1 and PBzD2 were approximately 22.2% and 24%, respectively, distinctively higher than the value 2.57% of pristine polybenzoxazine PBz1, at 800 °C in N2 atmosphere. The Tgs of PBzD1 and PBzD2 distinctly increased by 42.8 °C and 20 °C, respectively, in comparison to −35 °C for pristine PBz1. The LOI values of PBzD1 and PBzD2 were 28.5 and 31, respectively. The length and weight-loss of PBzD1 and PBzD2 samples were significantly less than that of PBz1 when they were burned in the air environmental condition. The burning behavior demonstrated that the flame retardant properties was obviously improved as DOPO was introduced. All of the three specimens of PBz1, PBzD1 and PBzD2 presented excellent flexible property.

Expanding Monomers as Anti-Shrinkage Additives

Commonly, volumetric shrinkage occurs during polymerizations due to the shortening of the equilibrium Van der Waals distance of two molecules to the length of a (significantly shorter) covalent bond. This volumetric shrinkage can have severe influence on the materials’ properties. One strategy to overcome this volumetric shrinkage is the use of expanding monomers that show volumetric expansion during polymerization reactions. Such monomers exhibit cyclic or even oligocyclic structural motifs with a correspondingly dense atomic packing. During the ring-opening reaction of such monomers, linear structures with atomic packing of lower density are formed, which results in volumetric expansion or at least reduced volumetric shrinkage. This review provides a concise overview of expanding monomers with a focus on the elucidation of structure-property relationships. Preceded by a brief introduction of measuring techniques for the quantification of volumetric changes, the most prominent classes of expanding monomers will be presented and discussed, namely cycloalkanes and cycloalkenes, oxacycles, benzoxazines, as well as thiocyclic compounds. Spiroorthoesters, spiroorthocarbonates, cyclic carbonates, and benzoxazines are particularly highlighted.