激光全息干涉计量术测量触点对单端固定桥位移的影响
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摘要
随着材料学的发展，烤瓷修复在临床上已广泛使用，单端固定桥的烤瓷修复由于受力时桥体处形成力臂，基牙根部产生旋转中心使基牙倾斜扭转，容易导致触点丧失，引起食物嵌塞，致使修复失败。
正常牙列中，天然牙依靠触点相互连接成为一个整体，触点的存在有利于防止牙齿的不正常移动，使牙列处于平衡的位置，同时对牙龈乳突有生理性的自洁作用。在固定桥修复中，牙体的预备使触点暂时丧失，而后再利用修复体加以恢复。由于牙邻面接触关系的多样性和复杂性，临床上触点的恢复主要根据患者的主观感受和医师的临床经验进行判断，触点的恢复与否及触点的松紧、位置对单端固定桥基牙的位移及牙槽骨的应力分布有无影响至今尚无报道。
激光全息干涉计量术是一种测量物体微小位移的实验方法，利用光的干涉原理使相干波在同一全息底片上形成干涉条纹，通过分析条纹的形状和分布从而计算物体的运动或形变。生物力学分析已证明，下颌第二磨牙缺失时，用第一磨牙和第二前磨牙做联合基牙行单端固定桥修复可提供足够的支持力和固位力。本研究以此为基础，在新鲜人离体下颌骨上制作单端固定桥，在第一前磨牙远中接触区预备洞形后置入弹簧以恢复触点，通过调整弹簧的长度和位置模拟不同的触点松紧和位置，然后采用二次曝光全息干涉术测量单端固定桥在不同触点条件下垂直和舌向30°受载后的位移情况，通过分析位移的变化规律以探讨触点因素对单端固定桥位移的影响。
实验结果表明：
1．在桥体中央窝集中加载时，基牙主要向远中、舌侧、龈方运动，随加载量的增加，位移增大。斜向加载和垂直加载只影响各方向位移的大小，不改变位移的变化趋势。
2．在桥体中央窝集中加载时，应力集中在基牙的颈部，桥体的位移大于基牙的位移，大于牙槽骨和邻牙的位移，近中基牙的位移大于远中基牙。
3．触点恢复后，桥体、基牙及牙槽骨位移较无触点时减小，随着触点力值的增加，桥体、基牙及基牙牙槽骨的位移减小，邻牙及邻牙牙槽骨的位移先减小后增大。
4．随触点力值的增加，基牙牙槽骨的应力水平降低，邻牙牙槽骨的应力水平升高，应力增大。建议触点恢复的力值约为1.0N。
5．垂直加载时，固定桥和牙槽骨的位移以触点位于中1／3最小，斜向加载时，以触点位于颊1／3位移最小，两种加载方式下均以舌1／3触点产生的位移最大。建议修复时以中1／3恢复触点位置，使触点接触面积最大以减小固定桥和牙槽骨的位移。
综上所述，研究结果初步提示，单端固定桥触点的有无、松紧、位置将影响桥体、基牙、邻牙及牙槽骨的位移，通过恢复触点，选择适宜的触点松紧和位置可以减小单端固定桥基牙、邻牙和牙槽骨的位移，减小受力时的杠杆作用，获得更佳的应力分布。考虑到生物医学的个体差异性和生物力学研究模型的复杂性，最佳的触点设计还有待进一步改进研究模型，扩大样本含量以使研究结果更接近临床实际，更好地为临床修复工作服务。
With the development of material science, porcelain-fused-to-metal(PFM) prosthesis has been widely used in practice. But because of unfavorable leverages during mastication, the use of cantilever fixed partial denture(GFPD) may lead to the loss of contact area, food impaction and finally the failure of restoration.
In normal dentitions, natural teeth are integrated by contact areas which may remain them in balance, avoid their abnormal movement, and are helpful for the self cleaning of gingival papilla. Although contact areas are so important for the dentition, clinicians usually restored them depending on patients' feelings and their own experience, and there has been no report about the effect of proximal contact area on the movement of CFPD.
Laser holography interferometry(LHI) is a method to measure the micro displacement of a subject, which is achieved by analyzing the figure and distribution of stripes produced by interferometric principles. It has been agreed that when the mandible second molar is lost, the edentulous distal extension area can be restored with a posterior CFPD using the mandible first molar and second premolar as free-end abutments. Based on that, this study establishes a CFPD model in vitro, and investigates the effect of proximal contact area on the displacement of prosthesis and alveolar bone by double-exposure holography interferometry(DHI).
The results showed as following:
1.When a concentrated load is exerted on the pontic, abutments move distally, lingually and gingivally. With increasing load, the movement increases. The direction of load only affects the value of displacement, but not the changing trend of it.
2. When loaded on the pontic, stress is concentrated at the cervical area of abutments. The displacement of pontic is larger than abutments, alveolar bone and the adjacent tooth, and the displacement of distal abutment is greater than that of medial abutment.
3.After the proximal contact area is restored, the displacement of pontic, abutments and alveolar bone decreases. With the increase of contact force, the displacement of pontic, abutments and alveolar bone around abutments decreases; the displacement of adjacent tooth and alveolar bone around it decreases firstly, and then increases.
4. With the increase of contact force, the stress of abutments' alveolar bone decreases, and that of the adjacent tooth's bone increases. A contact force of 1.0N is recommended.
5.Under oblique loading, the displacement is smallest when the proximal contact is located at buccal area. Under vertical loading, the displacement is smallest when the contact area is located at the middle of the proximal area, and this location is also recommended to decrease the displacement of cantilever bridge and alveolar bone.
正常牙列中，天然牙依靠触点相互连接成为一个整体，触点的存在有利于防止牙齿的不正常移动，使牙列处于平衡的位置，同时对牙龈乳突有生理性的自洁作用。在固定桥修复中，牙体的预备使触点暂时丧失，而后再利用修复体加以恢复。由于牙邻面接触关系的多样性和复杂性，临床上触点的恢复主要根据患者的主观感受和医师的临床经验进行判断，触点的恢复与否及触点的松紧、位置对单端固定桥基牙的位移及牙槽骨的应力分布有无影响至今尚无报道。
激光全息干涉计量术是一种测量物体微小位移的实验方法，利用光的干涉原理使相干波在同一全息底片上形成干涉条纹，通过分析条纹的形状和分布从而计算物体的运动或形变。生物力学分析已证明，下颌第二磨牙缺失时，用第一磨牙和第二前磨牙做联合基牙行单端固定桥修复可提供足够的支持力和固位力。本研究以此为基础，在新鲜人离体下颌骨上制作单端固定桥，在第一前磨牙远中接触区预备洞形后置入弹簧以恢复触点，通过调整弹簧的长度和位置模拟不同的触点松紧和位置，然后采用二次曝光全息干涉术测量单端固定桥在不同触点条件下垂直和舌向30°受载后的位移情况，通过分析位移的变化规律以探讨触点因素对单端固定桥位移的影响。
实验结果表明：
1．在桥体中央窝集中加载时，基牙主要向远中、舌侧、龈方运动，随加载量的增加，位移增大。斜向加载和垂直加载只影响各方向位移的大小，不改变位移的变化趋势。
2．在桥体中央窝集中加载时，应力集中在基牙的颈部，桥体的位移大于基牙的位移，大于牙槽骨和邻牙的位移，近中基牙的位移大于远中基牙。
3．触点恢复后，桥体、基牙及牙槽骨位移较无触点时减小，随着触点力值的增加，桥体、基牙及基牙牙槽骨的位移减小，邻牙及邻牙牙槽骨的位移先减小后增大。
4．随触点力值的增加，基牙牙槽骨的应力水平降低，邻牙牙槽骨的应力水平升高，应力增大。建议触点恢复的力值约为1.0N。
5．垂直加载时，固定桥和牙槽骨的位移以触点位于中1／3最小，斜向加载时，以触点位于颊1／3位移最小，两种加载方式下均以舌1／3触点产生的位移最大。建议修复时以中1／3恢复触点位置，使触点接触面积最大以减小固定桥和牙槽骨的位移。
综上所述，研究结果初步提示，单端固定桥触点的有无、松紧、位置将影响桥体、基牙、邻牙及牙槽骨的位移，通过恢复触点，选择适宜的触点松紧和位置可以减小单端固定桥基牙、邻牙和牙槽骨的位移，减小受力时的杠杆作用，获得更佳的应力分布。考虑到生物医学的个体差异性和生物力学研究模型的复杂性，最佳的触点设计还有待进一步改进研究模型，扩大样本含量以使研究结果更接近临床实际，更好地为临床修复工作服务。
With the development of material science, porcelain-fused-to-metal(PFM) prosthesis has been widely used in practice. But because of unfavorable leverages during mastication, the use of cantilever fixed partial denture(GFPD) may lead to the loss of contact area, food impaction and finally the failure of restoration.
In normal dentitions, natural teeth are integrated by contact areas which may remain them in balance, avoid their abnormal movement, and are helpful for the self cleaning of gingival papilla. Although contact areas are so important for the dentition, clinicians usually restored them depending on patients' feelings and their own experience, and there has been no report about the effect of proximal contact area on the movement of CFPD.
Laser holography interferometry(LHI) is a method to measure the micro displacement of a subject, which is achieved by analyzing the figure and distribution of stripes produced by interferometric principles. It has been agreed that when the mandible second molar is lost, the edentulous distal extension area can be restored with a posterior CFPD using the mandible first molar and second premolar as free-end abutments. Based on that, this study establishes a CFPD model in vitro, and investigates the effect of proximal contact area on the displacement of prosthesis and alveolar bone by double-exposure holography interferometry(DHI).
The results showed as following:
1.When a concentrated load is exerted on the pontic, abutments move distally, lingually and gingivally. With increasing load, the movement increases. The direction of load only affects the value of displacement, but not the changing trend of it.
2. When loaded on the pontic, stress is concentrated at the cervical area of abutments. The displacement of pontic is larger than abutments, alveolar bone and the adjacent tooth, and the displacement of distal abutment is greater than that of medial abutment.
3.After the proximal contact area is restored, the displacement of pontic, abutments and alveolar bone decreases. With the increase of contact force, the displacement of pontic, abutments and alveolar bone around abutments decreases; the displacement of adjacent tooth and alveolar bone around it decreases firstly, and then increases.
4. With the increase of contact force, the stress of abutments' alveolar bone decreases, and that of the adjacent tooth's bone increases. A contact force of 1.0N is recommended.
5.Under oblique loading, the displacement is smallest when the proximal contact is located at buccal area. Under vertical loading, the displacement is smallest when the contact area is located at the middle of the proximal area, and this location is also recommended to decrease the displacement of cantilever bridge and alveolar bone.
引文
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[13] Awadalla HA, Azarbal M, Ismail YH, et al. Three-dimensional finite element stress analysis of a cantilever fixed partial denture[J]. Journal of Prosthetic Dentistry, 1992, 68(2): 243-248
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[15]Stegaroiu R, Sato T, Kusakari H, et al. Influence of restoration type on stress distribution in bone around implants: a three-dimensional finite element analysis[J]. International Journal of Oral & Maxillofacial Implants, 1998, 13(1): 82-90
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[19]Romeed SA, Fok SL, Wilson NH. Biomechanics of cantilever fixed partial dentures in shortened dental arch therapy [J]. Journal of Prosthodontics, 2004, 13(2): 90-100
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[15]Stegaroiu R, Sato T, Kusakari H, et al. Influence of restoration type on stress distribution in bone around implants: a three-dimensional finite element analysis[J]. International Journal of Oral & Maxillofacial Implants, 1998, 13(1): 82-90
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[23]Lewinstein I, Ganor Y, Pilo R. Abutment positioning in a cantilevered shortened dental arch: a clinical report and static analysis [J]. J Prosthetic Dentistry, 2003, 89(3): 227-231
[24]Laurell L, Lundgren D. Interfering occlusal contacts and distribution of chewing and biting forces in dentition with fixed cantilever prosthesis[J]. J ProstheDent, 1987, 58: 626-632
[25] Laurell L, Lundgren D. Influence of occlusion on posterior cantilevers[J]. ProstheDent, 1992, 67: 645-653
[26] Carlson BR, Yontchev E. Long-term observations of extensive fixed partial dentures on mandibular canine teeth[J]. Journal of Oral Rehabilitation., 1996, 23(3): 163-169
[27] Falk H. On occlusal forces in dentitions with implant-supported fixed cantilever prostheses[J]. Swedish Dental Journal- Supplement, 1990, 69: 1-40
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[31] ErasLan O, Sevimay M, Usumez A, et al. Effects of cantilever design and material on stress distribution in fixed partial dentures--a finite element analysis[J]. Journal ofOralRehabilitation., 2005, 32(4): 273-278
[32] 李美华，冯剑桥．用三维有限元方法对单端固定桥进行应力分析[J]．口腔医学纵横，2000，16(3)：197-199
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[36] 张艺权，王宝成，邓再喜，等．非贵金属烤瓷冠桥金属基底的要求和打磨方法[J]．实用口腔医学杂志，2003，19(5)：410
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