複合樹脂由於其強度與抗磨耗度已可與汞齊相提並論，以及患者對牙科美容之需求日益增加，故近年來逐漸被廣泛運用為牙科前後牙直接填補的材料；然而複合樹脂卻有聚合收縮的缺點，當聚合收縮所產生之收縮力大於複合樹脂與齒質界面的結合強度時，臨床上常造成牙齒介面的破壞。本研究目的藉由有限元素分析探討在不同尺寸之二級MOD窩洞復形中，樹脂收縮而在界面造成的界面應力大小及其分佈情況。實驗方法以不同深度及寬度的MOD窩洞為模型，以切片取得牙齒輪廓經影像建立三維網格模型，給予材料性質後，進行有限元素分析，觀察在不同界面之正向收縮力、平均正向應力、最大正向應力。結果發現窩洞尺寸對頰側及舌側壁正向力之影響並不一致；而在平均界面應力方面，平均界面應力並未隨窩洞深度及寬度的增加而增加，經進一步模擬探討發現剩餘齒質之強度亦是影響界面應力的重要因素。較大的窩洞尺寸會增加樹脂收縮力以致提高界面應力，但較大的窩洞也會降低剩餘齒質強度，使的樹脂收縮時界面應力降低。本研究推論，影響界面應力的大小並非只有窩洞尺寸此參數，剩餘齒質的強度，亦是影響界面應力的重要因素之一，同時這些參數都會彼此互相影響，所以不應單獨考量。

The strength and wear resistance of resin composite have been improved to those presented by amalgam. Also, with a better esthetic appearance, resin composite is becoming a wildly used material for direct anterior and posterior restorations. However, resin composite materials possessed some disadvantages, including the polymerization shrinkage. When the shrinking force exceeds the bonding strength between composite and tooth substance, it could damage the interfacial bonding and tooth structure and result in restorative failure. It was generally believed if cavity size increases, the shrinking stress would be also increased. The objective of this study was to investigate the interfacial contraction stress in class II MOD cavities with various widths and depths by finite element simulation. The investigated mechanical parameters including shrinkage force and average shrinkage on the buccal, lingual and floor surfaces and peak normal stress on buccal surface. Results showed that the normal contraction force over buccal and lingual walls would increase as the cavity depth increased when cavity width was 2mm. The averaged interfacial stress over buccal and lingual walls decrease as the cavity increased either in depth or width. While the averaged interfacial stress over the cavity floor increased when the cavities got deep, but decreased when cavities got wide. An advanced simulation demonstrated that the stiffness of the remaining tooth also play an important role on the interfacial stress. In larger cavities, the remaining tooth would be less stiff and tend to be deflected inward thus the interfacial stress was diminished. It was concluded that both the cavity size and stiffness of the remaining tooth are important factors affecting the interface stress, and they cannot be considered separately.

1. Dietschi D ＆ Dietschi JM（1996）, “Current development in composite materials and techniques”, Practical Periodontics and Aesthetic Dentistry 8：603-613.
2. Davidson CL ＆ de Gee AJ（1984）, “Relaxation of polymerization contraction stresses by flow in dental composites”, Journal of Dental Research 63：146-148.
3. Feilzer AJ, de Gee AJ ＆ Davidson CL（1987）, “Setting stress in composite resin in relation to configuration of the restoration”, Journal of Dental Research 66：1636-1639.
4. Bowen RL, Nemoto K ＆ Rapson JE（1983）, “Adhesive bonding of various materials to hard tooth tissues：forces developing in composite materials during hardening”, Journal of the American Dental Association 106：475-477.
5. Eick JD, Byerley TJ, Chappell RP, Chen GR, Bowles CQ, Chappelow CC（1993）, “Properties of expanding SOC/epoxy copolymers for dental use in dental composites”, Dental Materials 9：123-127.
6. Stansbury JW（1992）, “Synthesis and evaluation of novel multifunctional oligomers for dentistry”, Journal of Dental Research 71：434-437.
7. Goracci G, Mori G, de Martinis LS（1996）, “Curing light intensity and marginal leakage of resin composite restoration”, Quintessence International 27：355-362.
8. Ferracane JL, Mitchem JC, Condon JR, Todd R（1997）, “Wear and marginal breakdown of composites with various degrees of cure”, Journal of Dental Research 76：1508-1516.
9. Lutz F, Krejci I, Olderburg TR（1986）, “Elimination of polymerization stresses at the margins of posterior composite resin restorations：a new restoration technique”, Quintessence International 17：777-784.
10. Versluis A, Douglas WH, Cross M, Sakaguchi RL（1996）, “Does an incremental filling technique reduce polymerization shrinkage stresses”, Journal of Dental Research 75：871-878.
11. Modelli J, Stengall L, Ishikirma A, Delima-Navarro MF, Socres FB（1980）, “Fracture strength of human teeth with cavity preparations”, Journal Prosthetic Dentistry 43：419-422
12. Penn RW（1986）, “A recording dilatometer for measureing polymerization shrinkage”, Dental Materials 2：78-79
13. Miyazaki M, Fukuishi K, Onose H（1999）, “Influence of light irradiation on th volumetric change of polyacid-modified resin composites”, Journal of Dentistry 27：149-153
14. Cook WD, Forrest M, Goodwin AA（1999）, “A simple method for the measurement of polymerization shrinkage in dental composites”, Dental Materials 15：447-449
15. Attin T, Buchalla W, Kielbassa AM, Hellwig E（1995）, “Curing shrinkage and volumetric changes of resin-modifed glass ionomer restorative materials”, Dental Materials 11：359-362
16. Watts DC, Cash AJ, （1991）“Determination of polymerization shrinkage kinetics in visible-light-cured materials：methods development”, Dental Materials 7：281-287
17. Sakaguchi RL, Versluis A, Douglas WH（1997）, “Analysis of strain gauge method for measurement of post-gel shrinkage in resin composites”, Dental Materials 13：233-239