Bowley John Francis, Kaye Elizabeth Krall, Garcia Raul Isidro
Department of Veterans Affairs, Boston Healthcare System, Jamaica Plain, MA, USA.
Restorative Sciences & Biomaterials, Boston University Henry M. Goldman School of Dental Medicine, Boston, MA, USA.
J Adv Prosthodont. 2017 Aug;9(4):278-286. doi: 10.4047/jap.2017.9.4.278. Epub 2017 Aug 16.
The aim of this study was to determine the influence of long base lengths of a fixed partial denture (FPD) to rotational resistance with variation of vertical wall angulation.
Trigonometric calculations were done to determine the maximum wall angle needed to resist rotational displacement of an experimental-FPD model in 2-dimensional plane. The maximum wall angle calculation determines the greatest taper that resists rotation. Two different axes of rotation were used to test this model with five vertical abutment heights of 3-, 3.5-, 4-, 4.5-, and 5-mm. The two rotational axes were located on the mesial-side of the anterior abutment and the distal-side of the posterior abutment. Rotation of the FPD around the anterior axis was counter-clockwise, Posterior-Anterior (P-A) and clockwise, Anterior-Posterior (A-P) around the distal axis in the sagittal plane.
Low levels of vertical wall taper, ≤ 10-degrees, were needed to resist rotational displacement in all wall height categories; 2-to-6-degrees is generally considered ideal, with 7-to-10-degrees as favorable to the long axis of the abutment. Rotation around both axes demonstrated that two axial walls of the FPD resisted rotational displacement in each direction. In addition, uneven abutment height combinations required the lowest wall angulations to achieve resistance in this study.
The vertical height and angulation of FPD abutments, two rotational axes, and the long base lengths all play a role in FPD resistance form.
本研究的目的是确定固定局部义齿（FPD）长基托长度对垂直壁角度变化时抗旋转阻力的影响。
进行三角计算以确定在二维平面中抵抗实验性FPD模型旋转位移所需的最大壁角。最大壁角计算确定了抵抗旋转的最大锥度。使用两个不同的旋转轴，对具有3mm、3.5mm、4mm、4.5mm和5mm五种垂直基牙高度的模型进行测试。两个旋转轴分别位于前基牙的近中侧和后基牙的远中侧。在矢状面中，FPD绕前轴的旋转为逆时针方向，即后-前（P-A）方向，绕远轴的旋转为顺时针方向，即前-后（A-P）方向。
在所有壁高类别中，都需要低水平的垂直壁锥度（≤10度）来抵抗旋转位移；一般认为2至6度是理想的，7至10度有利于基牙的长轴。绕两个轴的旋转表明，FPD的两个轴向壁在每个方向上都能抵抗旋转位移。此外，在本研究中，不均匀的基牙高度组合需要最低的壁角来实现抗力。
FPD基牙的垂直高度和角度、两个旋转轴以及长基托长度在FPD抗力形式中均起作用。
