以二異氰酸鹽和甲基丙烯酸-2-羥基乙酯做為側鏈的牙科用壓克力樹脂的性質探討

Abstract

複合樹脂是目前最受歡迎的牙科填補材料。複合樹脂具有許多好處，例如美觀，易操作，低花費等。但是同時也有一些缺點，例如聚合收縮，抗磨耗力低，邊緣變色等。複合樹脂主要由有機單體和無機填料所組成。分子量大，收縮小的甲基壓克力，如雙酚A丙三醇雙甲基丙烯酸酯(Bis-GMA)，常被使用做為樹脂基質。但Bis-GMA的高黏稠度，使得無機填料的添加量和轉化率受到限制。低分子量的單體，如TEGDMA常被添加來降低黏稠度，增加反應性和轉化率。然而，稀釋單體也會增加聚合收縮，產生收縮應力，導致填補物和牙齒交界面粘著失敗，邊緣變色，繼發性蛀牙，術後敏感及牙髓發炎等問題。聚合收縮是造成臨床上複合樹脂填補失敗的最主要原因。所以，如何降低聚合收縮，是研發新複合樹脂的重要方向。 目前，市面上仍未出現「零收縮」的複合樹脂。在本實驗中，我們想研發一種適合牙科使用的低收縮複合樹脂。我們預期，樹脂單體的分子量和體積愈大，聚合收縮就會愈小。複合樹脂最常使用的基質就是Bis-GMA及其衍生物。我們將甲基壓克力接上側鏈，以增加分子量和體積。氨基甲酸乙酯(urethane)，具有低收縮，抗磨耗及生物相容性佳等優點，可做為側鏈的材料。我們選擇三種二異氰酸鹽(HDI，H12MDI 和TDI)，分別加上HEMA，做為側鏈材料。HDI是線性分子結構，H12MDI具有兩個氫化六角環，TDI則有一個苯環結構。不同分子結構和密度的側鏈，可能會對樹脂造成不同的影響。 實驗組樹脂的分子量和黏稠度，會隨著側鏈密度的增加而增加。樹脂的聚合收縮和轉化率則隨著側鏈密度的增加而減少。DM-M-1.5c和DM-T-1.5c這兩組的聚合收縮明顯小於所有實驗組。雖然這兩組的轉化率明顯低於對照組，但是表面硬度卻相當或是高於對照組，可能是因為官能度較高的緣故。而這兩組的細胞存活率和控制組並沒有明顯差異。樹脂的生物相容性，和單體分子結構的立體障礙有關。當側鏈的密度增加，立體障礙就會增加，形成交聯結構後，有毒的樹脂單體，就會被包覆在複雜結構中，而不會釋放出來。本實驗發現用氨基甲酸乙酯做側鏈的壓克力樹脂，可以有效減少收縮及增加硬度，並具有良好的生物相容性，未來可以應用在牙科材料上。

Composite resins are currently the most popular dental restorative materials worldwide. Composite resins provide certain advantages such as good esthetics, easy application, and lower costs. However, there remain some disadvantages to their use, such as polymerization shrinkage, low wear resistance, and marginal discoloration. Composite resins are composed of organic monomers and inorganic fillers. High molecular weight dimethacrylate monomers with low polymerization shrinkage and high strength, such as bisphenol A-glycidyl dimethacrylate (bis-GMA), are most commonly used. The high viscosity of bis-GMA reduces the loading of fillers and also the degree of conversion of the monomers in the absence of other low viscosity diluents. Low molecular weight diluent monomers, such as triethylene glycol dimethacrylate (TEGDMA), are often added to reduce viscosity and increase the reactivity and conversion rate. However, the diluent monomers also increase polymerization shrinkage, leading to polymerization stress, debonding at the restoration-tooth interface, secondary caries, postoperative sensitivity, pulpal irritation, and marginal discoloration. Polymerization shrinkage is the principal cause of failure of clinical dental composite resin fillings. Reducing this shrinkage, thus, represents one of the most important goals in the development of new matrices for composite resins. Currently, there remains a lack of “non-shrinkage” composite resins worldwide. In this study, we aimed to develop low-shrinkage composite resins for dental application. As expected, the higher the molecular weight and volume the monomer, the less extensive the shrinkage when polymerized. Most commercial dental composite resins are composed of bis-GMA or its derivatives. We increased the molecular weight and volume of the dimethacrylate molecule by conjugating functional side chains to the dimethacrylate structure. Urethane, which is a compound of diisocyanate and 2-hydroxyethyl methacrylate (HEMA), is a material suitable for use as a dimethacrylate side chain. Polyurethane displays certain advantages, such as low shrinkage, high wear resistance, and good biocompatibility. We selected three diisocyanates with different chemical structures as side chain materials: 1,6-Diisocyanatohezane (HDI), 4,4’-diisocyanatodicyclohexylmethane (H12MDI) and toluene 2,4-diisocyanate (TDI). HDI is a linear structure molecule. H12MDI contains two aliphatic rings (cyclohexane) linked by a methyl group, whereas TDI contains a toluene moiety. When conjugated to dimethacrylate, these three chemical structures reduced polymerization shrinkage and increased the mechanical strength of the composites. Different structures and numbers of side chains on dimethacrylate provided different results. The molecular weight and viscosity of experimental resins were increased as functional side chain density was increased. The polymerization shrinkage and degree of conversion were decreased when functional side chain density was increased. Polymerization shrinkage in the DM-M-1.5c and DM-T-1.5c groups was significantly less extensive than in the other groups (p<0.05). Although the degree of conversions of these two groups were significantly lower than that of the control group, the surface hardness values were equal to or significantly higher than that of the control group because of increasing functionalities of the side chain-modified groups. There were non-significant differences between these two groups and the control group in cell vitality. The biocompatibility of dental resin is related to the stereo hindrance of resin matrix molecular structures. When the ratio of HDI, H12MDI or TDI functional side chain to dimethacrylate is increased, the stereo hindrance of resin structure is increased, more toxic resin monomers are trapped in the complicated resin structure, and thus the resin matrix reveals less cytotoxicity. The urethane modification of dimethacrylate, therefore, represents an effective means of reducing polymerization shrinkage and increasing surface hardness. The modified dimethacrylate with good biocompatibility might be suitable for dental use in the future.