ScienceDOI: 10.3290/j.ijcd.b4110975Pages 1-19, Language: EnglishBlankenstein, Felix H. / Plake, Jelka
Aim: A total occlusal convergence angle φ of 6° is a typical crown preparation requirement. It was shown that it is hard to achieve clinically. The present study aimed to compare ability of students to judge different steepnesses including a -1° undercut of prepared canines and molars under clinical conditions with different analogue tools.Materials and methods: The complete dentures of a patient were duplicated without the teeth 16, 23, 33, 46. For each of these gaps, 6 crown stumps were milled with φ/2 = -1°, 3°, 6°, 9°, 12° and 15°, each of which was insertable using mini-magnets. 48 students each from the 1st, 6th and 9th semester estimated these angles intraorally with various aiding tools: In addition to basic dental instruments, a parallelometer mirror, an analogue clock dial with a 6° visualization and a scale of tooth stumps with φ/2 between -1° and 15°.Results: The widely demanded 3° were hardly recognized, but assumed to be steeper or even undercut. In contrast, the -1° divergent stump walls were predominantly estimated as parallel-walled or slightly conical. With increasing taper, the stumps tended to be classified as steeper, i.e. “better”. The additional tools did not result in a general improvement of the estimation performance. Students from higher semesters did not achieve better results.Conclusion: We 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 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.
Keywords: crown stumps, dental students, intraoral estimation, preparation angle, visualization tools
