目的:6°的总咬合收敛角φ是典型的牙冠准备要求。结果表明,临床上很难实现。本研究旨在比较学生判断不同陡度的能力,包括在临床条件下用不同的模拟工具对准备好的犬齿和磨牙进行-1°底切。
方法:在没有牙齿16、23、33、46的情况下复制患者的全口义齿。对于这些差距中的每一个,用φ/2=-1°铣削了6个冠状树桩,3°,6°,9°,12°和15°,每个都可以使用微型磁铁插入。从1号开始,每人48名学生,第6和第9学期用各种辅助工具对这些角度进行口内评估:除了基本的牙科器械,一个平行镜,具有6°可视化的模拟时钟刻度盘和φ/2在-1°和15°之间的齿桩刻度。
结果:几乎无法识别广泛需求的3°,但被认为是更陡甚至削弱。相比之下,-1°发散的残端壁主要被估计为平行壁或略微圆锥形。随着锥度的增加,树桩往往被归类为更陡,即“更好”。额外的工具没有导致估计性能的总体改善。来自较高学期的学生没有取得更好的成绩。
结论:我们质疑完全视觉评估冠端锥度的客观性。看来,牙科培训至少应将重点放在避免底切上,这是准确的口内扫描程序的最低先决条件。通过口内扫描对准备角度的数字控制以及这些结果的即时临床实施可以帮助产生适当的准备。
OBJECTIVE: A total occlusal convergence (TOC) angle (ϕ) of 6 degrees is a typical crown preparation requirement. It has been shown that this is difficult to achieve clinically. The present study therefore aims to compare the ability of students to judge different steepnesses, including a -1-degree undercut of prepared canines and molars, under clinical conditions with different analog tools.
METHODS: The complete dentures of a patient were duplicated without denture teeth 16, 23, 33, and 46. For each of these gaps, six crown stumps were milled with ϕ/2 = -1, 3, 6, 9, 12, and 15 degrees, each of which was insertable using mini-magnets. A total of 144 dental students, 48 students each from the 1st, 6th, or 9th semester, estimated these angles intraorally with various aiding tools: In addition to basic dental instruments, they used a parallelometer mirror, an analog clock dial with a 6-degree visualization, and a scale of tooth stumps with ϕ/2 between -1 and 15 degrees.
RESULTS: The widely demanded 3 degrees were hardly recognized, but assumed to be steeper or even undercut. In contrast, the -1-degree divergent stump walls were predominantly estimated as parallel-walled or slightly conical. With increasing taper, the stumps tended to be classified as steeper, ie, \"better.\" The additional tools did not result in a general improvement of the estimation performance. Students from higher semesters did not achieve better results.
CONCLUSIONS: The present authors question the objectivity of an exclusively visual assessment of crown stump taper. It appears that dental training should at least focus on avoiding undercuts as the minimal prerequisite for an accurate intraoral scanning procedure. Digital control of the preparation angle by an intraoral scan and immediate clinical implementation of these results could help to produce appropriate preparations.