Trier A C, Parker M H, Cameron S M, Brousseau J S
U.S. Army Dental Activity, Fort Gordon, Ga., USA.
J Prosthet Dent. 1998 Oct;80(4):405-9. doi: 10.1016/s0022-3913(98)70003-4.
The concept of limiting taper has been described as a boundary between tapers that do and those that do not provide resistance form for a preparation. There is controversy as to whether this boundary that divides preparations with from those without resistance form translates clinically into a boundary for success.
This investigation evaluated the resistance form of abutments of crowns or retainers that have been dislodged to determine the clinical correlation between restoration dislodgment and lack of resistance form in the preparation.
Dies were fabricated from single crowns and retainers of fixed partial dentures that came loose and evaluated for resistance form. A total of 44 abutments were evaluated and included 1 incisor, 15 premolars, and 28 molars. Data from a previous study on the percentage of abutments lacking resistance form for restorations leaving a large dental laboratory was used for comparative statistical tests.
Forty-two of the 44 abutments (95%) lacked resistance form. All molar abutments and 93% of premolar abutments lacked resistance form in one or more directions. The one incisor abutment did not lack resistance form. Chi-square test revealed a statistically significant difference in the percentage lacking resistance form between the group composed of clinical failure (uncemented crowns) and the group leaving a dental laboratory with P = .0005 for the molars, and P = .0005 for the premolars.
The clinical dislodgment of cast restorations is associated with the lack of resistance form in the preparations. In this study, there was a relationship between clinical success or failure and the all-or-none nature of resistance form; dislodged crowns come almost exclusively from preparations with tapers that did not provide resistance form.
极限锥度的概念被描述为能为预备体提供抗力形的锥度与不能提供抗力形的锥度之间的界限。对于这条将有抗力形的预备体与无抗力形的预备体区分开来的界限在临床上是否转化为成功的界限存在争议。
本研究评估了已松动的冠或固位体基牙的抗力形，以确定修复体松动与预备体中缺乏抗力形之间的临床相关性。
从松动的单冠和固定局部义齿的固位体制作代型，并评估其抗力形。共评估了44个基牙，包括1颗切牙、15颗前磨牙和28颗磨牙。将先前一项关于离开大型牙科实验室的修复体缺乏抗力形的基牙百分比的研究数据用于比较性统计检验。
44个基牙中有42个（95%）缺乏抗力形。所有磨牙基牙和93%的前磨牙基牙在一个或多个方向上缺乏抗力形。唯一的切牙基牙不缺乏抗力形。卡方检验显示，临床失败组（未粘结的冠）与离开牙科实验室的组之间在缺乏抗力形的百分比上存在统计学显著差异，磨牙组P = 0.0005，前磨牙组P = 0.0005。
铸造修复体的临床松动与预备体中缺乏抗力形有关。在本研究中，临床成功或失败与抗力形的全或无性质之间存在关联；松动的冠几乎完全来自锥度未提供抗力形的预备体。
