臨床所使用的矯正支架黏著劑可分為三類：（1）樹脂類，（2）玻璃離子樹脂類，（3）樹脂加強型玻璃離子樹脂類，而依聚合方式則可分為（1）光照聚合，（2）調拌式化學聚合，（3）不需調拌式化學聚合( Mitchell L. , 1994 )。過去的樹脂類材料應用於矯正方面已有許多文獻報告，如細胞毒性測試來探討樹脂材料之生物相容性，比較樹脂對細胞毒性的強弱等。
外來的刺激造成細胞毒性的結果可能會引起細胞的死亡。細胞死亡的方式不外透過兩條路徑：一、 壞死( necrosis )，二、 凋零( apoptosis )。對於矯正黏著劑引起之細胞毒性，其細胞反應的途徑是壞死或是凋零則少有文獻報告。本研究目的：乃欲探討矯正黏著劑材料作用於細胞之後，其胞內致毒性的機轉。本實驗以目前臨床上使用的矯正支架黏著劑：「光聚合玻璃樹脂類（GC Fuji Ortho LC）」及「光聚合樹脂類（3M Transbond XT）」利用MTT細胞活性分析法決定其細胞毒性之inhibition dose ( ID50 )濃度。
結果發現細胞毒性隨著試劑濃度增加而增加。ID50的比較結果得知未聚合與聚合後的玻璃離子樹脂類與樹脂類之黏著劑都有細胞毒性的存在，而毒性以聚合前高於光照聚合後。於顯微鏡下觀察兩組實驗細胞加藥後形態的變化，結果發現細胞內核染質聚集( chromatin aggregation )及凋零體( Apoptotic Body ) 出現。
以此ID50濃度下，利用Western Blotting方法，分析胞內蛋白質之反應，結果發現ERK磷酸化與p53蛋白的表現( expression )，而JNK和p38蛋白並沒有磷酸化。
結論：矯正支架黏著劑造成細胞毒性之死亡途徑可能是經由ERK磷酸化後進一步磷酸化p53之訊息傳遞路徑，引起細胞凋零死亡( apoptosis )。
There are three types of orthodontic bracket bonding agents used in clinic, they are resin, glass ionomer and resin reinforced glass ionomer.
To reach setting, different polymerization methods are performed as light cured polymerization and chemical polymerization. In past, the biocompatibility study of bonding agent was shown toxicity and may cause cell death. But none of the studies indicated the mechanism of cell death.
The purpose of the present study was to evaluate the mechanism of the cell death which was induced by the orthodontic bonding agents.
The light cure glass ionomer cement ( GC , Fuji Orthod LC ) and light cure bonding resin ( Transbond XT , 3M Unitek ) were extracted in DMSO solution. The extraction were added to the human osteosarcoma cell line(U2OS). The survival rate was evaluated by MTT assay. The cell inhibition dose ( ID50 ) was calculated. The morphologic change of the U2OS treated by bonding was observed and recorded. The mechanism of the cell death which treated with bonding agents was analyzed by Western blotting. The one way ANOVA analysis of variance statistic method was performed by Jump soft ware.
The results showed that either light cure glass ionomer or light cure bonding resin were revealed degree toxicity to U2OS. ( p<0.05 ) Under microscope observation( 100X ), U2OS cell were chromatin aggregation. The apoptotic bodies were found in the treatment group. The mitogen-activated protein kinase(MAPK), ERk 1 and ERk 2, were found in experiment group by Western blotting. But the JNK 1, JNK 2 and p38 kinase were not found in above assay. The p53 protein was expressed in the experiment group.
Conclusion: From the present study, the bonding agent treated U2OS cell was shown apoptosis. The mechanism of cell death was through the p53 protein which was mediated by ERk 1 and ERk 2 activation.
