牙科複合樹脂材料已經被廣泛的應用在牙科修復物上。但樹脂和牙齒的彈性性質和黏彈性質並不相同。因為複合樹脂修復物在口腔中長期受到咬合力的影響，樹脂和牙齒不同的黏彈性質會造成修復物的損壞。然而修復物黏彈性質對牙齒的影響並未被探討。本實驗目的為研究牙科修復物其黏彈性質在class II 修復物之機械響應的影響並將黏彈性質帶入有限元素法中模擬應力及應變並與實驗做比較。
在本研究中，在四十顆完整的大臼齒上給予寬為4mm，深度為4mm、class II MOD的凹槽。三種牙科樹脂 Z250、P60、Z350 flowable以單獨的形式或混和的形式填補在牙齒上。Z250組為填補材料為Z250；P60組為填補材料為P60；Z250/F組為1mm的Z350 flowable墊在Z250的下面；P60/F為1mm的Z350 flowable墊在P60的下面。首先給予試件靜態測試。對試件施加200N的壓力一小時。過程中以兩台相機記錄其影像並在卸載後記錄一小時。試件在加載過程中的應變及卸載後的應變經由3D DIC可以得到。在靜態測試後，將試件繼續固定在拉伸試驗機上，並進行動態試驗。給予試件週期5000次頻率為1 Hz，100N的力。在動態試驗過程中，試件上的應變經由3D DIC可以得到。
有限元素法被用來研究黏彈性質對應力態的影響。實驗得到的結果與牙齒的3D模型透過有限元素法分析後的結果做比較並利用有限元素法模擬在受力過程中的應力狀態。
從靜態實驗結果可得到有加Z350 flowable的組別，其應變比無Z350 flowable的組別大，且其應變隨著時間的增加而增加。Z250/F有最大的應變在底層中特別的明顯。在卸載後皆幾乎回復到零。在動態實驗中P60的應變比Z250大但Z250/F並沒有比P60/F大。從有限元素法的分析結果得到有Z350 flowable的組別其潛變比無Z350 flowable的組別大。從有限元素法得到的應變與實驗得到的結果相近。在中間部分，應力在加載過程中隨著時間的增加而上升，但在底層部分P60/F和Z250/F此現象不明顯。
黏彈性質在有墊層的組別比沒有墊層的組別來的明顯。使用流動性樹脂做為墊層可降低收縮應力在本實驗中可被觀察到。

Resin composite (RC) materials have been widely used in dental restoration, but their elastic and the viscoelastic properties are different from tooth. Since the dental RC restorations receive long-duration loadings, different viscoelastic properties between RC and tooth may cause the failure of restorations. However, the effects of viscoelastic properties of RC have not been evaluated. The purpose in this study was to investigate the effects of viscoelasticity of dental RCs on mechanical responses of class II restorations by experimental measurements and a finite element analysis (FEA).
In this study, forty intact extracted human molars were used. A class II MOD cavity sized 4(W)x4(D) mm was prepared on each tooth. Different RCs were restored in the cavity alone or with a liner as: a microhybrid composite Z250 filling; a packable composite P60 filling; Z250 filling with Z350-flowable lining (Z250/F); and P60 filling with Z350-flowable lining (P60/F). The restored teeth received static loading test first. A constant force of 200 N was applied for one hour. After removing the load, the specimens were observed for one hour as strain recovery. After static test, dynamic test was applied on the teeth. Mechanical loading was executed by a cyclic load of 100 N at a frequency of 1 Hz for 5000 cycles. The strain and displacements in these tests was calculated by 3D-digital image correlation. The finite element method was used to study the effect of viscoelastic properties on stress state. The resultant strain was compared with the experiments. Principal and Von Mises stress on tooth and restorations were analyzed.
From the results of static test, the strains of the lining groups were greater than the groups without lining, and continued to increase with time. Z250/F showed the greatest strain especially on the bottom. The strain almost recovered to zero after removing loading except P60/F. In dynamic test, the strain of P60 was greater than Z250, but P60/F was not greater than Z250/F.
The creep strain of lining groups was greater than groups without lining in FEM. The strains in FEA were similar to the experiment result. The lining groups showed higher and increasing stress on the mid of restorations. However, the lining groups showed low stress on the bottom.
The effect of viscoelastic property on lining groups was more obvious than the groups without lining. Using flowable RC as lining was thought to decrease the contraction stress in this study.

[1] R. G. Craig, and J. M. Power, RESTORATIVE DENTAL MATERIALs, 2002.
[2] C.-P. Ernst, Martin, Monika, Stuff, Silke, Willershausen, Brita, “Clinical performance of a packable resin composite for posterior teeth after 3 years,” Clinical Oral Investigations, vol. 5, no. 3, pp. 148-155, 2001.
[3] C.-P. Ernst, G. Cortain, M. Spohn, G. Rippin, and B. Willershausen, “Marginal integrity of different resin-based composites for posterior teeth_ an in vitro dye-penetration study on eight resin-composite and compomer,” Dental Materials, vol. 18, pp. 351-358, 2002.
[4] S. El-Safty, R. Akhtar, N. Silikas, and D. C. Watts, “Nanomechanical properties of dental resin-composites,” Dent Mater, vol. 28, no. 12, pp. 1292-300, Dec, 2012.
[5] R. V. Mesquita, D. Axmann, and J. Geis-Gerstorfer, “Dynamic visco-elastic properties of dental composite resins,” Dent Mater, vol. 22, no. 3, pp. 258-67, Mar, 2006.
[6] Y. Abe, P.Lambrechts, S. Inoue, M.J.A.Braem, and M. Takeuchi, “Dynamic elastic modulus of 'packable' composites,” Dental Materials, vol. 17, pp. 520-525, 2001.
[7] Nuray Attar, L. E. Tam, and D. McComb•, “Flow, Strength, Stiffness and Radiopacity of Flowable Resin Composites,” J Can Dent Assoc, vol. 69, no. 8, pp. 516-521, 2003.
[8] D. Y. Papadogiannis, R. S. Lakes, Y. Papadogiannis, G. Palaghias, and M. Helvatjoglu-Antoniades, “The effect of temperature on the viscoelastic properties of nano-hybrid composites,” Dent Mater, vol. 24, no. 2, pp. 257-66, Feb, 2008.
[9] M. J. Taylor, and E. Lynch, “Microleakage,” 1992.
[10] B. Y. H, I. HBaltacioglu., and K. S, “Comparing microleakage and the layering methods of silorane-based resin composite in wide Class II MOD cavities,” Oper Dent, vol. 34, no. 5, pp. 578-85, Sep-Oct, 2009.
[11] Chuang Shu-Fen , Liu Jia-Kuang , Chao Chen-Chi , Liao Feng-Pin , and C.-H. Melody, “Effects of flowable composite lining and operator experience on microleakage and internal voids in class II composite restorations,” THE JOURNAL OF PROSTHETIC DENTISTRY, pp. 177-183, 2001.
[12] M. Sadeghi, and C. D. Lynch, “The effect of flowable materials on the microleakage of Class II composite restorations that extend apical to the cemento-enamel junction,” Oper Dent, vol. 34, no. 3, pp. 306-11, May-Jun, 2009.
[13] P. S. Huang, “Inverstigations of Polymerization Shrinkage of Dental Composites with Different Lidgt-Curing Approach,” 2012.
[14] D. C. Reel, and R. J. Mitchell, “Fracture resistance of teeth restored with class II composite restorations ” PROSTHETIC DENTISTRY, vol. 61, no. 2, pp. 177-180, 1989.
[15] S. Shahrbaf, B. Mirzakouchaki, S. S. Oskoui, and M. A. Kahnamoui, “The effect of marginal ridge thickness on the fracture resistance of endodontically-treated, composite restored maxillary premolars,” Oper Dent, vol. 32, no. 3, pp. 285-90, May-Jun, 2007.
[16] D. Robert A. Lowe, "Sectional Matrices and the Restoration of Class II Direct Composite Restorations," 2009.
[17] M. Kaleem, K. Masouras, J. D. Satterthwaite, N. Silikas, and D. C. Watts, “Viscoelastic stability of resin-composites under static and dynamic loading,” Dent Mater, vol. 28, no. 2, pp. e15-8, Feb, 2012.
[18] R. V. Mesquita, and J. Geis-Gerstorfer, “Influence of temperature on the visco-elastic properties of direct and indirect dental composite resins,” Dent Mater, vol. 24, no. 5, pp. 623-32, May, 2008.
[19] K. Baroudi, S. Nick, and W. D. C., “Time-dependent visco-elastic creep and recovery of flowable composites,” European Journal of Oral Sciences, vol. 115, no. 6, pp. 517-521, Dec, 2007.
[20] Y. Papadogiannis, D. B. Boyer, M. Helvatjoglu-Antoniades, R. S. Lakes, and C. Kapetanios, “Dynamic viscoelastic behavior of resin cements measured by torsional resonance,” Dental Materials, vol. 19, no. 6, pp. 510-516, 2003.
[21] S. El-Safty, N. Silikas, and D. C. Watts, “Creep deformation of restorative resin-composites intended for bulk-fill placement,” Dent Mater, vol. 28, no. 8, pp. 928-35, Aug, 2012.
[22] H. Huang, Wei, “Warpage Modeling of Electronic Package During the Post-Mold Curing Process,” 2010.
[23] B. H. F., and B. L. Catherine, “Polymer Engineering Science and Viscoelasticity An Introduction,” 2007.
[24] M. A. Sutton, J.-J. Orteu, and H. W. Schreier, "Image Correlation for Shape, Motion and Deformation Measurements," Springer, ed., 2009.
[25] K.-C. Su, C.-H. Chang, S.-F. Chung, and E. Y.-K. Ng, “The effect of dentinal fluid flow during loading in various directions- Similation of fluid-structure interaction,” Oral Biology, 2012.
[26] D. C. Watts, “Elastic moduli and visco-elastic relaxation,” J.Dent., vol. 22, pp. 154-15008, 1994.