Tiu Janine, Al-Amleh Basil, Waddell J Neil, Duncan Warwick J
Doctoral student, Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, Dunedin, New Zealand.
Senior lecturer and Prosthodontist, Department of Oral Rehabilitation, Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, Dunedin, New Zealand.
J Prosthet Dent. 2015 Jul;114(1):75-80. doi: 10.1016/j.prosdent.2015.01.007. Epub 2015 Apr 7.
Determining the retention and resistance of a tooth preparation for a complete crown has only existed in theory, and these theories have never been measured on tooth preparations performed in vivo.
The purpose of this study was to measure the theoretical retention and resistance of clinically produced complete crown preparations by using an objective measuring method.
Stone dies from 236 complete crown preparations were collected from dental laboratories. The dies were scanned and analyzed with the coordinate geometry method. Cross-sectional images were captured, and the surface area was measured with a cone frustum and right truncated pyramid formula. Two different theories of resistance form, the "on" or "off" theory (limiting taper) and the linear model (resistance length), were calculated for premolar and molar preparations.
The mean surface areas ranged from 33.97 mm(2) to 105.44 mm(2) for the cone frustum formula and 41.75 mm(2) to 117.50 mm(2) for the right truncated pyramid formula. The facial side of maxillary premolars exhibited the highest percentage of resistance form with the limiting taper, at 58%, and the mesial side of the mandibular molars exhibited the lowest percentage of resistance form, at 6%.
The objective method used in this study provides a way for retention and resistance theories to be tested and for further clinical implications to be investigated.
确定全冠牙体预备的固位力和抗力仅存在于理论中，且这些理论从未在体内进行的牙体预备上得到测量。
本研究的目的是通过使用一种客观测量方法来测量临床制作的全冠预备体的理论固位力和抗力。
从牙科实验室收集了236个全冠预备体的石膏模型。使用坐标几何方法对模型进行扫描和分析。采集横截面图像，并使用截头圆锥体和直角截棱锥体公式测量表面积。针对前磨牙和磨牙预备体，计算了两种不同的抗力形式理论，即“开”或“关”理论（极限锥度）和线性模型（抗力长度）。
截头圆锥体公式的平均表面积范围为33.97平方毫米至105.44平方毫米，直角截棱锥体公式的平均表面积范围为41.75平方毫米至117.50平方毫米。上颌前磨牙的颊侧在极限锥度下表现出最高的抗力形式百分比，为58%，下颌磨牙的近中侧表现出最低的抗力形式百分比，为6%。
本研究中使用的客观方法为测试固位力和抗力理论以及研究进一步的临床意义提供了一种途径。
