Department of Prosthodontics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.
Int J Oral Maxillofac Implants. 2009 Nov-Dec;24(6):1045-53.
This study evaluated the effect of different screw-tightening sequences, forces, and methods on the stresses generated on a well-fitting internal-connection implant (Astra Tech) superstructure.
A metal framework directly connected to four parallel implants was fabricated on a fully edentulous mandibular resin model. Six stone casts with four implant replicas were made from a pickup impression of the superstructure to represent a "well-fitting" situation. Stresses generated by four screw-tightening sequences (1-2-3-4, 4-3-2-1, 2-4-3-1, and 2-3-1-4), two forces (10 and 20 Ncm), and two methods (one-step and two-step) were evaluated. In the two-step method, screws were tightened to the initial torque (10 Ncm) in a predetermined screw-tightening sequence and then to the final torque (20 Ncm) in the same sequence. Stresses were recorded twice by three strain gauges attached to the framework (superior face midway between abutments). Deformation data were analyzed using multiple analysis of variance at a .05 level of statistical significance.
In all stone casts, stresses were produced by the superstructure connection, regardless of screw-tightening sequence, force, and method. No statistically significant differences for superstructure preload stresses were found based on screw-tightening sequences (-180.0 to -181.6 microm/m) or forces (-163.4 and -169.2 microm/m) (P > .05). However, different screw-tightening methods induced different stresses on the superstructure. The two-step screw-tightening method (-180.1 microm/m) produced significantly higher stress than the one-step method (-169.2 microm/m) (P = .0457).
Within the limitations of this in vitro study, screw-tightening sequence and force were not critical factors in the stress generated on a well-fitting internal-connection implant superstructure. The stress caused by the two-step method was greater than that produced using the one-step method. Further studies are needed to evaluate the effect of screw-tightening techniques on preload stress in various different clinical situations.
本研究评估了不同螺钉拧紧顺序、力和方法对内连接种植体（AstraTech）上部结构产生的应力的影响。
在全口义齿下颌树脂模型上制作了一个直接连接到四个平行种植体的金属框架。从上部结构的拾音器印象中制作了六个带有四个种植体复制品的石铸模型，以代表“合适”的情况。评估了四种螺钉拧紧顺序（1-2-3-4、4-3-2-1、2-4-3-1 和 2-3-1-4）、两种力（10 和 20 Ncm）和两种方法（一步法和两步法）产生的应力。在两步法中，螺钉按预定的螺钉拧紧顺序拧紧至初始扭矩（10 Ncm），然后按相同顺序拧紧至最终扭矩（20 Ncm）。通过附接到框架上的三个应变计（在基牙之间的中间位置的上表面）两次记录应力。使用方差分析对变形数据进行了分析，统计显著性水平为.05。
在所有的石铸模型中，无论螺钉拧紧顺序、力和方法如何，上部结构连接都会产生应力。基于螺钉拧紧顺序（-180.0 至-181.6 µm/m）或力（-163.4 和-169.2 µm/m），上部结构预载应力均无统计学差异（P >.05）。然而，不同的螺钉拧紧方法会对上部结构产生不同的应力。两步法（-180.1 µm/m）产生的应力明显高于一步法（-169.2 µm/m）（P =.0457）。
在本体外研究的限制内，螺钉拧紧顺序和力不是内连接种植体上部结构产生的应力的关键因素。两步法引起的应力大于一步法产生的应力。需要进一步的研究来评估在各种不同临床情况下螺钉拧紧技术对上部结构预载应力的影响。
