臺灣博碩士論文加值系統

實驗目的： 雙甲基丙烯酸氨基甲酸乙酯（UDMA），是牙科樹脂材料中重要且現今常被使用的單體之一，未聚合的單體釋放是造成組織細胞毒性的來源。本研究的目的在於探討UDMA對人類牙髓細胞的毒性，以及對產生氧化壓力(ROS),影響細胞週期進行及發生細胞凋零(apoptosis)之效應做進一步的探討。
實驗方法： 將人類牙髓細胞暴露於不同濃度的UDMA(0.025~0.35mM)下培養後，以顯微鏡觀察細胞的形態以及數量變化，以MTT assay來測定細胞存活的比例，另以流式細胞儀（flow cytometry）來進行細胞週期的分析。藉由反轉錄聚合酶連鎖反應(RT-PCR)和西方墨點法(Western blot)來觀察基因以及蛋白的表現。也分析活性氧過高(ROS overproduction)與氧化壓力相關基因(HO-1, CES2)和發炎相關(COX-2)基因及蛋白表現之間的關係。至於UDMA所導致產生的活性氧與各類抗氧化劑之間的關係，是藉由加入抗氧化劑NAC (1, 3 mM) 和catalase (1000, 2000 U/ml)、esterase (2, 4 U/ml) 前處理30分鐘再暴露於0.35 mM UDMA濃度下作用24小時後做MTT assay來證實。另加入HO抑制劑Zn-P (1, 2.5 μM)、 CES抑制劑BNPP (0.5, 1 mM)和CES2抑制劑 Loperamide (10, 20 μM)前處理30分鐘的牙髓細胞緊接著暴露於UDMA 0.1mM 濃度下共同培養24小時後再以MTT assay測定細胞存活率的變化。統計方式是使用單因子變異數分析搭配Tukey事後檢定來分析實驗數據。
實驗結果： 人類牙髓細胞經濃度0.25 mM和0.35 mM UDMA作用24 小時之後，可觀察到細胞形態之改變和細胞存活率降低的情況。在MTT assay結果中可見，0.1mM UDMA能造成細胞存活率下降至約70%，而加入0.25 mM和0.35 mM UDMA作用後，細胞存活率更是下降至約40%。在0.35 mM UDMA濃度下能造成細胞週期的分布變化，G0/G1細胞數量的下降達統計上的顯著差異，G2/M細胞數量有明顯上升，但未達統計上的顯著差異（P=0.32），同時相關基因和蛋白cdc2, cyclin B1, cdc25C的表現被抑制，p21則是有基因表現上的些微促進。在細胞凋零相關的基因和蛋白表現中，Bax、Bad被促進，Bcl2被抑制。在加入超過0.1mM的UDMA作用24小時候可以看到HO-1表現量上升, 在加入超過0.25 mM的UDMA作用24小時候，CES2和COX-2的表現量才大幅上升。實驗也發現，經過catalase、esterase和高濃度NAC前處理的細胞，UDMA所造成的細胞存活率降低現象會被抑制，而Zn-P、BNPP和Loperamide前處理的細胞則是會更加促進UDMA所造成的細胞毒性。
結論： UDMA超過0.1 mM就會造成一定程度的細胞毒性以及活性氧的顯著增加，而UDMA濃度高過0.25 mM則會有非常明顯的細胞毒性。UDMA在0.35mM的濃度下會造成細胞週期G0/G1的細胞數量減少。這些細胞型態改變、存活率降低、細胞週期停滯都是與活性氧產生有關，進一步造成細胞週期相關基因及蛋白(cdc2, cyclin B1, cdc25C抑制，p21些微促進)的表現變化，以及細胞凋零相關基因和蛋白(Bax、Bad被促進，Bcl2被抑制)表現的變化。另外，HO-1和CES2可能扮演了保護細胞的角色，對於細胞遭受氧化壓力做出反應。COX-2的基因以及蛋白表現則證實UDMA與牙髓細胞所產生的慢性發炎反應有關，需進一步再去研究證實。另外在抗氧化劑以及氧化壓力相關基因的抑制劑共同作用下則會影響UDMA所導致的細胞毒性，其可能與阻止或增強活性氧的產生有關。雖然在牙科樹酯產品中的UDMA濃度並不會到達很高的濃度，但當未聚合的UDMA擴散到體積相對較小的牙髓腔時，所滲出的濃度所造成的毒性就有可能相對較高，進而對牙髓細胞產生相當的毒性。對體外細胞培養來做UDMA毒性的探討將有助於牙醫師在臨床應用上，使用上須慎選樹酯的使用條件以及評估合適的臨床狀況，適時使用基底材料保護牙髓，降低病人在填補後所產生的牙髓慢性發炎甚至壞死的不良反應。

Aim: Urethane dimethacrylate (UDMA) is one of the monomers usually be included in dental resin materials. The purpose of our study is to investigate the effects of UDMA on cytotoxicity to human dental pulp cells, involving the relationship between ROS formation and UDMA toxicity. The influences UDMA on the expression of cell cycle- and apoptosis-related genes and proteins were also evaluated.
Materials and methods: Primary-cultured human dental pulp cells were obtained from human extracted premolars and third molars. Cells were treated with different concentrations of UDMA (from 0.025 to 0.35 mM), incubated 24 hours and then observed the changes of cell morphology in phase contrast microscope. Cell proliferation was evaluated by MTT assay. Cell cycle analysis was investigated by flow cytometry. Influences in mRNA expression were evaluated by reverse transcription polymerase chain reaction (RT-PCR) and the changes in protein production were determined by Western blot. For the purpose of link the rule of ROS and antioxidant mechanism, pulp cells were pre-treated for 30 minutes with NAC (1, 3mM) and catalase (1000, 2000 U/ml), esterase (2, 4 U/ml) to check their ability of removing overproduced ROS. And Nrf2, HO-1, CES1A1, CES2 and CES3 mRNA expression can be the evidences of cells facing oxidative stress. By adding HO inhibitor Zn-P (1, 2.5 μM), CES inhibitor BNPP (0.5, 1 mM) and CES2 inhibitor Loperamide (10, 20 μM) 30 minutes before co-incubation with 0.1mM UDMA to evaluate the influences to cell viability by MTT assay. And the testing of expression of COX-2 gene and protein was to link UDMA and chronic inflammatory effect. One-way ANOVA and post hoc Tukey test were used to analyze differences between experimental and control groups.
Results: In human dental pulp cells, UDMA induced morphological changes and a significant decrease of cell viability at the concentration of 0.1mM UDMA to about 70%, and at the concentration of 0.25 and 0.35 mM UDMA to about 40%. At the concentrations of 0.35mM UDMA, it could lead to increase of G2/M cell percentage and decrease of G0/G1 cell percentage. The expression of production of cdc2, cyclinB1, cdc25C was inhibited, while that of p21 was slightly promoted in both PCR and Western blot examination. For apoptosis analysis, Bax, Bad were promoted, and Bcl2 was inhibited. Besides, the increase of HO-1, CES2 and COX-2 expression was noted after 24 hours. The reduction of cell viability caused by UDMA can be inhibited by NAC, catalase and esterase pre-treatment, and can be promoted by BNPP, loperamide and Zn-P pre-treatment.
Conclusion: UDMA at a concentration higher than 0.1 mM had a significant cytotoxicity. Under the concentration higher than 0.1 mM, UDMA can cause changes of cell morphology, reduction of cell viability, and 0.35mM UDMA can cause increase of G2/M phase cell percentage. These changes may be related to ROS overproduction, which can cause expressional variations of many genes, such as cdc2, cyclin B1, cdc25C, p21, Bax as well as Bcl2. As for HO-1 and CES2, the induction of its expression may play a role in cell protection. The finding of COX-2 gene and protein expression suggest UDMA can be a critical factor of inflammation related to resin-based dental biomaterials, and that COX-2 is involved in the inflammatory reaction of the resin monomers. We know the concentration of UDMA in dental resin product is not very high, but the concentration of UDMA elute can be high enough to damage pulp cells once the residual UDMA diffuses to pulp chamber with a relatively small volume. Therefore, we should use resin materials carefully in daily practice and should select proper case and the situation of enough residual dentin thickness to do the resin restoration procedure.

口試委員會審定書………………………………………………………………… i
誌謝………………………………………………………………………………… ii
中文摘要…………………………………………………………………………… iii
英文摘要…………………………………………………………………………… v
Chapter I. Literature Review……………………………………………1
1.1. Introduction………………………………………………………………………1
1.1.1. Methacrylate-based monomers introduction…………………………...1
1.1.2. Resin monomers release………………………………………………….2
1.2. Urethane dimethacrylate (UDMA)……………………………………………..4
1.2.1. UDMA toxicity……………………………………………………………5
1.3. UDMA‐induced oxidative DNA damage --Reactive oxygen species (ROS)…6
1.3.1. ROS induced DNA damage and changes in regulation of the cell cycle
……………………………………………………………………………………..7
1.3.2. Gutathione (GSH) mechanism…………………………………………..8
1.3.3. Anti-oxidant mechanism…………………………………………………8
1.4. Cell cycle regulation: cell cycle, cell survival and cell death…………………10
1.4.1. Cyclin-dependent kinases (CDKs) …………………………………….11
1.4.2. Cell cycle checkpoints…………………………………………………..12
1.4.3. The G2/M checkpoint response………………………………………..14
1.5. The Bcl2 family…………………………………………………………………15
1.6. Carboxylesterase (CES1A1, CES2, CES3) …………………………………..16
1.7. Activation of the Nuclear factor E2 p45-related factor (Nrf2)………………17
1.8. Heme oxygenase-1 (HO-1) and Heme oxygenase-2 (HO-2)………………….18
1.9. Cycloxygenase-1(COX-1) and COX-2 ………………………………………..19

Chapter II. The Purposes of the Study…………………………………21

Chapter III. Materials and Methods………………………………… ..22
3.1. Materials…………………………………………………………………………..22
3.2. Culture of human dental pulp cells……………………………………………...22
3.3. Morphology of human dental pulp cells………………………………………...23
3.4. Cytotoxicity of UDMA affects Cell proliferation evaluated by MTT assay…..23
3.4.1. Effects of different concentrations of UDMA on cell viability………….23
3.4.2. Effects of NAC, catalase and esterase on UDMA cytotoxicity…………24
3.4.3. Effects of loperamide, BNPP, and Zn-P pretreatment on UDMA cytotoxicity……………………………………………………..………….25
3.5. Effects of UDMA upon the cell cycle distribution……………………………...26
3.5.1. Cell cycle analysis: PI assay………………………………………………27
3.6 Expressions of c ROS overexpression, inflammation, cell cycle and apoptosis related genes by reverse transcription-polymerase chain reaction(RT-PCR)……..28
3.6.1. Isolation of total RNA…………………………………………………….28
3.6.2. RNA Quantitation…………………………………………………………29
3.6.3. Reverse Transcription (RT)………………………………………………30
3.6.4. Polymerase Chain Reaction(PCR)……………………………………….30
3.7. Expressions of ROS overexpression, inflammation, cell cycle and apoptosis related proteins by Western blot..................................................................................32
3.7.1 Protein estraction..........................................................................................32
3.7.2. Protein quantification..................................................................................33
3.7.3. Western Blot……………………………………………………………….34
3.8. Statistical analysis………………………………………………………………...36

Chapter IV. Results……………………………………………………...37
4.1. Density and morphological alterations of human dental pulp cells…………...37
4.2. Effects of UDMA on cell viability of pulp cells: MTT assay…………………...37
4.3. Effects of UDMA on cell cycle progression and regulation of pulp cells……...38
4.3.1. Cell cycle analysis with PI assay…………………………………………38
4.3.2. Expression of cell cycle-related genes and proteins: focused on G2/M phase………………………………………………….………………………….39
4.4. Effects of UDMA on cell death of human dental pulp cells……………………40
4.4.1. Expression of apoptosis-related genes and proteins: focused on Bcl2 family………………………………………..……………………………………40
4.5. Effects of UDMA on oxidative stress of human dental pulp cells……………..41
4.5.1. Effects of catalase, NAC and esterase pre-treatment on cell proliferation………………………………………….…………………………..41
4.5.2. Expression of CES1A1, CES2, CES3 genes on human dental pulp cells.........................................................................................................................42
4.5.3. Effects of BNPP and loperamide pre-treatment on cell proliferation……..………………………………………………………………42
4.5.4. Expression of oxidative stress-related genes: focused on HO-1 on human dental pulp cells…………………………………………………………………43
4.5.5. Expression of antioxidant-related genes on human dental pulp cells: focused on Nrf2…………………………………………………………………43
4.5.6. Effects of Zn-P pre-treatment on cell proliferation……………………44
4.6. Expression of inflammation-related genes and proteins on human dental pulp cells: focused on COX-2……………………………………………………..............44
Chapter V. Discussion………………………………………………….45
5.1. Morphological and proliferations aberratons…………………………………45
5.2. Cell cycle aberrations……………………………………………………………47
5.3. UDMA-induced cell Death……………………………………………………...48
5.4. UDMA-induced oxidative stress on pulp cells………………………………….49
5.5. Back to clinical situations………………………………………………………..52

Chapter VI. Conclusion…………………………………………………53

References………………………………………………………………..55

1. Maria Wisniewska-Jarosinska, Tomasz Poplawski, Cezary J. Chojnacki, Elzbieta Pawlowska, Renata Krupa, Joanna Szczepanska, Janusz Blasiak. Independent and combined cytotoxicity and genotoxicity of triethylene glycol dimethacrylate and urethane dimethacrylate. Mol Biol Rep 2011;38:4603–4611.
2. Ebru Urcan, Harry Scherthan, Marianthi Styllou, Uschi Haertel, Reinhard Hickel, Franz-Xaver Reichl. Induction of DNA double-strand breaks in primary gingival fibroblasts by exposure to dental resin composites. Biomaterials 2010;31: 2010–2014.
3. Assumption HJ, Mathias LJ. Photopolymerization of urethane dimethacrylates synthesized via a non-isocyanate route. Polymer 2003;44: 5131–5136.
4. Hsiao-Hua Chang, Mei-Chi Chang, Li-Deh Lin, Jang-Jaer Lee, Tong-Mei Wang,
Chun-Hsun Huang, Ting-Ting Yang, Hsueh-Jen Lin, Jiiang-Huei Jeng. The mechanisms of cytotoxicity of urethane dimethacrylate to Chinese hamster ovary cells. Biomaterials 2010;31: 6917-6925.
5. Huang FM, Chang YC. Induction of cyclooxygenase-2 mRNA and protein expression by dentin bonding agents in human gingival fibroblasts. J Biomed Mater Res B Appl Biomater 2004;70:297–302.
6. Alexander Eckhardt, Nicol Gerstmayr, Karl-Anton Hiller, Carola Bolay, Claudia Waha, Gianrico Spagnuolo, Carlos Camargo, Gottfried Schmalz, Helmut Schweikl. TEGDMA-induced oxidative DNA damage and activation of ATM and MAP Kinases. Biomaterials 2009;30:2006–2014.
7. Ali Jazayeri, Jacob Falck, Claudia Lukas, Jiri Bartek, Graeme C. M. Smith, Jiri Lukas, Stephen P. Jackson. ATM- and cell cycle-dependent regulation of ATR in response to DNA double-strand breaks. Nature Cell Biology 2006;8(1):37-45
8. Franz-Xaver Reichl, Magali Esters, Sabine Simon, Mario Seiss, Kai Kehe, Norbert Kleinsasser, Matthias Folwaczny, Jurgen Glas, Reinhard Hickel. Cell death effects of resin-based dental material compounds and mercurials in human gingival fibroblasts. Arch Toxicol 2006; 80: 370–377.
9. K.L. Van Landuyt, Tim Nawrot, B. Geebelen, J. De Munck, J. Snauwaert,
K. Yoshihara, Hans Scheers, Lode Godderis, P. Hoet, B. Van Meerbeek. Review: How much do resin-based dental materials release? A meta-analytical approach. Dental materials 2011; 27: 723–747.
10. Gil-Saeng Jeong, Dong-Sung Lee, Bin Li, Hwa-Jun Lee, Eun-Cheol Kim, Youn-Chul Kim. Effects of sappanchalcone on the cytoprotection and anti-inflammation via heme oxygenase-1 in human pulp and periodontal ligament cells. European Journal of Pharmacology 2010; 644: 230–237.
11. H. Schweikl, G. Spagnuolo and G. Schmalz. Genetic and Cellular Toxicology of Dental Resin Monomers. J Dent Res 2006; 85: 870-877.
12. Subbareddy Maddika, Sudharsana Rao Andea, Soumya Panigrahi, Ted Paranjothy, Kazimierz Weglarczyk, Anne Zuse, Mehdi Eshraghi, Kamala D. Mandad, Emilia Wiechec, Marek Los. Cell survival, cell death and cell cycle pathways are interconnected: Implications for cancer therapy. Drug Resistance Updates 2007; 10: 13–29.
13. Ionica Masgras, Samantha Carrera, Petra J. de Verdier, Paul Brennan, Aneela Majid, Wan Makhtar, Eugene Tulchinsky, George D. D. Jones, Igor B. Roninson, and Salvador Macip. Reactive Oxygen Species and Mitochondrial Sensitivity to Oxidative Stress Determine Induction of Cancer Cell Death by p21. The Journal of Biological Chemistry 2012; 287(13): 9845–9854.
14. J.Balasubramaniam. COX 2 inhibitors and nephrotoxicity. http://www.uninet.edu/cin2001-old/conf/bala/bala.html
15. J. Volk, J. Engelmann, G. Leyhausen, W. Geurtsen. Effects of three resin monomers on the cellular glutathione concentration of cultured human gingival fibroblasts. Dental Materials 2006; 22, 499–505.
16. Irini D. Sideridou, Dimitris S. Achilias. Elution Study of Unreacted Bis-GMA, TEGDMA, UDMA, and Bis-EMA from Light-Cured Dental Resins and Resin Composites Using HPLC. J Biomed Mater Res Part B: Appl Biomater 2005;74B: 617–626.
17. Tomasz Poplawski, Katarzyna Loba, Elzbieta Pawlowska, Joanna Szczepanska, Janusz Blasiak. Genotoxicity of urethane dimethacrylate, a tooth restoration component. Toxicology in Vitro 2010; 24: 854–862.
18. Stanislawski L, Lefeuvre M, Bourd K, Soheili-Majd E, Goldberg M, Perianin A. TEGDMA-induced toxicity in human fibroblasts is associated with early and drastic glutathione depletion with subsequent production of oxygen reactive species. J Biomed Mater Res 2003;66A:476–482.
19. Walther UI, Siagian II, Walther SC, Reichl FX, Hickel R. Antioxidative vitamins decrease cytotoxicity of HEMA and TEGDMA in cultured cell lines. Arch Oral Biol 2004;49: 125–131.
20. Spagnuolo G, D’Ant`o V, Cosentino C, Schmalz G, Schweikl H, Rengo S. Effect of N-acetyl-l-cysteine on ROS productionand cell death caused by HEMA in human primary gingival fibroblasts. Biomaterials 2006;27:1803–1809.
21. Schweikla, A. Hartmann, K.-A. Hiller, G. Spagnuolo, C. Bolay, G. Brockhoff, G. Schmalz. Inhibition of TEGDMA and HEMA-induced genotoxicity and cell cycle arrest by N-acetylcysteine. Dental materials 2007;23: 688–695.
22. Watson WH, Yang X, Choi YE, Jones DP, Kehrer JP. Thioredoxin and its role in toxicology. Toxicol Sci 2004;78:3–14.
23. Hayes JD, Flanagan JU, Jowsey IR. Glutathione transferases. Annu Rev Pharmacol Toxicol 2005;45:51–88.
24. Engelmann J, Leyhausen G, Leibfritz D, Geurtsen W. Effect of TEGDMA on the intracellular glutathione concentration of human gingival fibroblasts. J Biomed Mater Res 2002;63:746–751.
25. Huang FM, Chang YC. Prevention of the epoxy resin-based root canal sealers-induced cyclooxygenase-2 expression and cytotoxicity of human osteoblastic cells by various antioxidants. Biomaterials 2005;26:1849–1855.
26. Spagnuolo G, Mauro C, Leonardi A, Santillo M, Paterno R, Schweikl H, et al. NF-kappaB protection against apoptosis induced by HEMA. J Dent Res 2004;83:837–842.
27. Chang HH, Guo MK, Kasten FH, Chang MC, Huang GF, Wang YL, et al. Stimulation of glutathione depletion, ROS production and cell cycle arrest of dental pulp cells and gingival epithelial cells by HEMA. Biomaterials 2005;26:745–753.
28. Noda M, Wataha JC, Kaga M, Lockwood PE, Volkmann KR, Sano H. Components
of dentinal adhesives modulate heat shock protein 72 expression in heatstressed THP-1 human monocytes at sublethal concentrations. J Dent Res 2002;81:265–269.
29. Reichl FX, Durner J, Hickel R, Kunzelmann KH, Jewett A, Wang MY, et al. Distribution and excretion of TEGDMA in guinea pigs and mice. J Dent Res 2001;80:1412–1415.
30. Ovist V, Stoltze K, Ovist J. Human pulp reactions to resin restorations performed with different acid etch restorative procedures. Acta Odontol Scand 1989;47:253-267.
31. Fuks AB, Cleaton-Jones P. Pulp response to a composite resin inserted in deep cavities with and without surface seal. J Prosthet Dent 1990;63:129-134.
32. Schweikl H, Schmalz G, Rackebrandt K. The mutagenic activity of unpolymerized resin monomers in Salmonella typhimurium and V79 cells. Mutat Res 1998;415:119-130.
33. Kleinsasser NH, Schmid K, Sassen AW, Harreus UA, Staudenmaier R, Folwaczny M, et al. Cytotoxic and genotoxic effects of resin monomers in human salivary gland tissue and lymphocytes as assessed by the single cell microgel electrophoresis (Comet) assay. Biomaterials 2006;27:1762-1770.
34. W. Geurtsen. Biocompatibility of resin-modified filling materials. Crit Rev Oral Biol Med 2000;11(3): 333-355.
35. Maki T, Hosokawa M, Satoh T, Sato K. Changes in carboxylesterase isoenzymes of rat liver microsomes during hepatocarcinogenesis. Jpn. J. Cancer Res. 1991;82:800–806.
36. Tetsuo Satoh and Masakiyo Hosokawa. The mammalian carboxylesterase: From Molecules to Functions. Annu. Rev. Pharmacol. Toxicol. 1998; 38:257–288.
37. Na Ryoung Kim, Bum-Soon Lim, Hee Chul Park, Kyung Mi Son, Hyeong-Cheol Yang. Effects of N-acetylcysteine on TEGDMA- and HEMA-induced suppression of osteogenic differentiation of human osteosarcoma MG63 cells. Journal of Biomedical Materials Research B: Applied Biomaterials 2011; 98B (2): 300-307.
38. Barbieri SS, Eligini S, Brambilla M, Tremoli E, Colli S. Reactive oxygen species mediate cyclooxygenase-2 induction during monocyte to macrophage differentiation: critical role of NADPH oxidase. Cardiovasc Res 2003;60: 187–197.
39. Dong Hee Lee, Na Ryoung Kim, Bum-Soon Lim, Yong-Keun Lee, Hyeong-Cheol Yang. Effects of TEGDMA and HEMA on the expression of COX-2 and iNOS in cultured murine macrophage cells. Dental materials 2009;25: 240–246.
40. Geurtsen W, Spahl W, Muller K, Leyhausen G. Aqueous extracts from dentin adhesives contain cytotoxic chemicals. J Biomed Mater Res 1999;48:772–777.
41. Spahl W, Budzikiewicz H, Geurtsen W. Determination of leachable components from four commercial dental composites by gas and liquid chromatography/mass spectrometry. J Dent 1998;26:137–145.
42. Jaco H. Houtgraaf, Jorie Versmissen, Wim J. van der Giessen. A concise review of DNA damage checkpoints and repair in mammalian cells. Cardiovascular Revascularization Medicine. 2006; 7:165– 172.
43. M. Reza Nassiri, Carl T. Hanks, Mark J. Cameron, Susan E. Strawn, and Robert G. Craig. Application of flow cytometry to determine the cytotoxicity of urethane dimethacrylate in human cells. J Biomed Mater Res. 1994(28): 153-158.
44. W.R. Hume and T.M. Gerzina. Bioavailability of Components of Resin-Based Materials Which Are Applied To Teeth. Crit Rev Oral Bio Med. 1996;7(2):172-179.
45. Eiichi Yoshii. Cytotoxic effects of acrylates and methacrylates: Relationships of monomer structures and cytotoxicity. J Biomed Mater Res. 1997; 37, 517–524.
46. Farzaneh Ahrari, Jalil Tavakkol Afshari, Maryam Poosti and Azam Brook. Cytotoxicity of orthodontic bonding adhesive resins on human oral fibroblasts. European Journal of Orthodontics 2010;32: 688–692.
47. N. M. Mohsen, R. G. Craig, C. T. Hanks. Cytotoxicity of urethane dimethacrylate composites before and after aging and leaching. J Biomed Mater Res. 1998;39: 252–260.
48. Suxing Liu, W. Robert Bishop, Ming Liu. Differential effects of cell cycle regulatory protein p21WAF1/Cip1 on apoptosis and sensitivity to cancer chemotherapy. Drug Resistance Updates 2003;6: 183–195.
49. Helmut Schweikl, Karl-Anton Hiller, Alexander Eckhardt, Carola Bolay, Gianrico Spagnuolo, Thomas Stempfl, Gottfried Schmalz. Differential gene expression involved in oxidative stress response caused by triethylene glycol dimethacrylate. Biomaterials 2008; 29: 1377-1387.
50. Dong Hee Lee, Bum-Soon Lim, Yong-Keun Lee, Sug-Joon Ahn, Hyeong-Cheol Yang. Involvement of oxidative stress in mutagenicity and apoptosis caused by dental resin monomers in cell cultures. Dental materials. 2006;22: 1086–1092.
51. Jiri Lukas, Claudia Lukas, Jiri Bartek. Mammalian cell cycle checkpoints: signalling pathways and their organization in space and time. DNA Repair 2004;3: 997–1007.
52. Stephanie Krifka, Claudia Seidenader, Karl-Anton Hiller, Gottfried Schmalz, Helmut Schweikl. Oxidative stress and cytotoxicity generated by dental composites in human pulp cells. Clin Oral Invest 2012; 16:215–224.
53. Andrew H. Wyllie.“Where, O Death, Is Thy Sting?” A Brief Review of Apoptosis Biology. Mol Neurobiol 2010; 42:4–9.
54. William R Taylor and George R Stark. REVIEW: Regulation of the G2/M transition by p53. Oncogene 2001; 20: 1803- 1815.
55. Stephanie Krifka, Christine Petzel, Karl-Anton Hiller, Eva-Maria Frank, Claudia Bosl, Gianrico Spagnuolo, Franz-Xaver Reichl, Gottfried Schmalz, Helmut Schweikl. Resin monomer-induced differential activation of MAP kinases and apoptosis in mouse macrophages and human pulp cells. Biomaterials 2010;31: 2964–2975.
56. Tetsuo Satoh, Masakiyo Hosokawa. Mini review: Structure, function and regulation of carboxylesterases. Chemico-Biological Interactions 2006;162:195–211.
57. Helmut Schweikl, Inge Altmannberger, Nico Hanser, Karl-Anton Hiller, Carola Bolay, Gero Brockhoff, Gianrico Spagnuolo, Kerstin Galler, Gottfried Schmalz. The effect of triethylene glycol dimethacrylate on the cell cycle of mammalian cells. Biomaterials 2005;26:4111–4118.
58. Olga Polydorou, Armin Konig, Elmar Hellwig, Klaus Kummerer. Special Report: Uthethane Dimethacrylate: A Molecule That May Cause Confusion in Dental Research. J Biomed Mater Res Part B: Appl Biomater 2009;91B: 1–4.