Properties Of Dental Resin Composites Modified By Hyperbranched Polyester

Dental composite resins with characteristic of great esthetic properties and easy operation has become the most commonly used repair materials in current restorative and esthetic dentistry. However, the long-term clinical practice and investigation show that the light-cured composite resins still have poor durability applied in clinical, which is mainly resulted from high polymerization shrinkage and the poor mechanical properties, leading to microleakage, secondary caries, resin loss, postoperative sensitive, resin fracture and abrasion, et al. In recent years, in order to solve these problems, the scholars of composite resin at domestic and abroad committed to develop novel monomers and inorganic filler. Although the satisfactory results on some properties were obtained from these attempts, other properties were worsen at the same time, for example, better polymerization shrinkage, poorer concurrent micro-hardness. Thus, there remains a need to explore novel resin polyester which can effectively reduce the volumetric shrinkage of composite resin, without affecting the mechanical properties of the new composite resin, and ultimately achieve the dental prosthesis to enhance the performance of the base resin material.Hyperbranched polyester (HBP) can be defined as a polymer which is a monomer with a highly branched, three-dimensional spherical structure, a large number of active and end groups and difficult to crystallization. Compared to the dendrimers, the synthesis method of hyperbranched monomer is simpler, less costly and conductive to large-scale production, thus the application prospects of the HBP is broad. The Boltorn type of the HBP contains a lot of peripheral primary hydroxyl reaction higher activity, easy chemical modification, may be bonded to a variety of functional groups to impart new performance hyperbranched polyester. The hyperbranched polyester with excellent performance and wide application can improve the performance of the material foundation from multiple perspectives, thus this research aims to explore suitable for dental restoration materials hyperbranched polyester.Objectives:To study the effect of hyperbranched polyester on the properties of the conventional resin matrix. Two kinds of modified hyperbranched polyester which have methyl acrylate groups were chosen as HBP2-X, HBP2-Y, the mass fraction of 40% of MHBP were added to the resin matrix methacrylate resin matrix (Bis-GMA/ TEGDMA), as the group X and Y groups,the common methacrylate resin matrix material (Bis-GMA/TEGDMA= 2/1) without the incorporation of MHBP was used for a control group. The mechanical properties of the modified neat resin, including polymerization volumetric shrinkage, degree of conversion,Vickers hardness, water absorption and dissolution rate, as well as the mechanical properties of the composite resin with different filler content (0 wt.%、30 wt.%、50 wt.%、70 wt.%) was measured. Preliminary discussion on the basis of performance HBP modified composite resin, in order to synthesize hyperbranched polyester which is ideal monomer for dental modification.Methods:(1) 40 wt.% HBP2-X and HBP2-Y effect on the polymrization volumetric shrinkage of the neat resin was determined by pycnometer method; (2) HBP2-X and HBP2-Y effect on degree of conversion was determined by FTIR; (3) HBP2-X and HBP2-Y effect on the Vickers hardness of the neat resin was determined by HXD-1000TM type micro-sclerometer; (4) HBP2-X and HBP2-Y effect on the hydroscopicity and solubility of the modified resin was determined by water take-up test; (5) HBP2-X and HBP2-Y effect on the physical property of flexural strength of the composite resin with different filler content (0 wt.%、30 wt.%、50 wt.%、0 wt.%) was measured were obtained using universal test machine; (6) HBP2-X and HBP2-Y effect on the physical property of compressive strength of the composite resin with different filler content (0 wt.%、30 wt.%、50 wt.%、70 wt.%) was measured were obtained using universal test machine; (7) HBP2-X and HBP2-Y effect on the physical property of diametraltensile strength of the composite resin with different filler content (0 wt.%、30 wt.%、50 wt.%、70 wt.%) was measured were obtained using universal test machine.Results:(1) Polymerization shrinkage:The resin with 40 wt.% modified hyperbranched polyester greatly decreased the polymerization shrinkage of the composite resin, the value of volumetric shrinkage of the modified groups were significantly lower than that of the control group[(8.14±0.53)%] (P<0.05); (2) Degree of conversion:The neat resin with 40 wt.% modified hyperbranched polyester decreased the value of degree of conversion of the common resin; (3) Vicikers hardness:the neat resin with 40 wt.% modified hyperbranched polyester affected the Vickers hardness; (4) Water sorption and solubility:With adding modified hyperbranched polyester, the hyperbranched polymers significantly influenced the water sorption and solubility of the neat resin(P<0.05); (5) Flexural strength:Except for the composite resin with 30 wt.% inorganic filler, the value of group X was less than that of control group and group Y. The modified composite materials, with 0 wt.%,50 wt.%,70 wt.% inorganic filler, there were no significant difference among the groups(P＞0.05); (6) Compressive strength:With adding 0 wt.%,30 wt.% inorganic filler, the value of compression strength of group X and group Y were significantly lower than the control group (P＜0.05). With the increase of the proportion of inorganic filler, the value of compression strength of group X and group Y increased significantly and the value of compressive strength is the largest when adding 70 wt.% inorganic filler,.50 wt.%,70 wt.% inorganic filler, the value of group X and the control group showed no significant difference (P>0.05), while the value of group Y was significantly less than that ofcontrol group and group X (P<0.05); (7) Diametral tensile strength:With adding modified hyperbranched polyester, there is no statistical difference among the value of the three groups with 0 wt.% and 50 wt.% inorganic filler(P>0.05). However, adding 30 wt.% inorganic filler, the value of DTS of the composite resin reached the maximum. Furthermore, the value of group X with 70 wt.% inorganic filler was significantly higher than that of control group (P<0.05), and the difference between the value of group Y and that of control group had no statistical significance (P>0.05).Conclusions:Two kinds of MHBP can obviously reduce the polymerization shrinkage of composite resin, which can be uesd to give the resin modified by hyperbranched polyester to the characteristics of low shrinkage by adding them to the common resin matrix. However, some of the foundations of modified resin performance were affected by the MHBP, as well as the modification on the mechanical properties of the composite resin was still slightly unstable. Thus, it needs to combine polymerization mechanism of hyperbranched polyester with inorganic filler. With further synthesis and analysis to develop the modified hyperbranched polyester which applies to the dental practice.