Construction of new resin core restoration system using mega-filler

为了降低树脂的聚合收缩应力，增强树脂芯在直接树脂芯修复中的强度，我们提出了在树脂芯中插入巨型填料的新型树脂芯构建体系。采用经MDP单体处理的硅化氧化铝（Al_2O_3 93%/SiO_2 5%）球和不锈钢（SUS304）球作为超大填料（3或4 mm φ）。通过对圆柱形树脂芯（5mmφ×8mm）的抗压强度（CS）、弹性模量（EM）和屈服应力（YS）的测定，评价了填料的补强效果。虽然超大填料树脂芯的CSs与树脂芯本身几乎相等，但超大填料树脂芯的EMs和YSs显著高于树脂芯本身。这说明掺有超大填料的树脂芯比纯树脂芯不易变形，说明掺有超大填料的树脂芯能有效提高树脂芯的耐久性。在牛牙根上制备直径5mm、深度5mm的空腔，仅用芯树脂或用树脂和巨型填料修复。所有恢复的样品进行热循环试验（在4℃和55℃水中各1min） 5000或10000次，并切成两半。用立体光学显微镜观察切片表面，观察树脂芯与腔壁之间是否存在间隙。对于纯树脂组，树脂与牙本质之间的间隙形成在接近腔底的部分在许多样品中发现。对于超大填料组，在任何样品中均未发现间隙形成。结果表明，巨型填料的加入可降低树脂芯体的聚合应力和热收缩应力，提高树脂芯体的密封能力和粘接耐久性。

In order to decrease the polymerization shrinkage stress of resin and reinforce resin core in a direct resin core restoration, we proposed the new resin core build-up system with inserting of mega-filler into core. The silanated alumina (Al_2O_3 93%/SiO_2 5%) balls and stainless steel (SUS304) balls treated with MDP monomer were used as mega-filler (3 or 4 mm φ). The compressive strength(CS), elastic modulus(EM) and yield stress(YS) of cylindrical resin cores (5mmφ×8mm) with or without mega-filler were measured to evaluate the reinforcing effect of mega-filler. Although the CSs of resin cores with mega-filler were almost equal to that of resin core itself, the EMs and YSs of resin cores with mega-filler were significantly higher than that of resin core itself. This means that the resin core with mega-filler is hard to deform comparing to resin core only and it is suggested that the inserting of mega-filler is effective to improve the durability of resin core.The cavities of 5mm in diameter and 5mm in depth were prepared in bovine tooth roots and restored with core resin only or with resin and mega-filler. All restored samples were applied to a thermal cycling test (for 1min each in 4℃ and 55℃ water) for 5,000 or 10,000 times and sectioned in halves. The sectioned surface was observed with a stereo optical microscope and the existence or absence of gap between resin core and cavity wall was examined. For core resin only group, the gap formations between resin and dentin in portions near to cavity floor were found in many samples. For mega-filler group, no gap formation was found in any samples. From these results, it is suggested that the inserting of mega-filler decrease polymerization and thermal shrinkage stresses and improve sealing ability and bonding durability of direct resin core restorations.