PubMed ID (PMID): 25558759Pages 185-195, Language: English, GermanKordaß, Bernd / Ruge, Sebastian / Quooß, Alexandra / Hugger, Alfons / Mundt, Torsten
Die okklusale Performance bestimmt substanziell die Qualität einer prothetisch-restaurativen Arbeit. Bei einer bevölkerungsrepräsentativen Population von insgesamt 3.300 Probanden des Follow-ups (SHIP 1) der regionalen Basisstudie "Study of Health in Pomerania (SHIP)" wurde in einer ersten orientierenden Auswertung die Okklusion künstlicher Zähne von Teilprothesen im "Kauzentrum", das heißt im Bereich des 1. Molaren untersucht. Zum Einsatz kamen okklusale Registrate in habitueller Interkuspidation, die mit der Software GEDAS (Greifswald Digital Analyzing System) auf Grundlage transparenter Kontaktareale digital ausgewertet wurden. 562 Probanden waren mit Teilprothesen im Oberkiefer versorgt (280 Männer: 61,7 ± 11,9 Jahre und 282 Frauen: 60,7 ± 10,7 Jahre). 619 Probanden hatten Teilprothesen im Unterkiefer (271 Männer: 65,0 ± 11,5 Jahre und 348 Frauen: 62,4 ± 10,6 Jahre). Teilprothesen waren mit 11,7 % im Ober- und 11,7 % im Unterkiefer rein geschiebeartig verankert, in 38,4 % der Fälle im Ober- und in 40,7 % im Unterkiefer nur mit Modellgussklammern, in 15,7 % im Ober- und 19,1 % im Unterkiefer rein teleskopierend mit Doppelkronen und in 16,4 % im Ober- und 8,2 % im Unterkiefer nur mit Drahtklammern. Darüber hinausgehend gab es Versorgungen mit Kombinationen aus den genannten Attachments. Durchschnittlich waren im Oberkiefer 7,8 ± 2,9 Zähne ersetzt, im Unterkiefer 7,5 ± 3,0 Zähne. Die Prothesenkonstruktionsarten unterschieden sich im Chi2-Test hinsichtlich der Häufigkeit kontakttragender Ersatzzähne des 1. Molaren nur im Unterkiefer. Dabei hatten Teleskopprothesen zu 74,4 % (Zahn 36) und 77,1 % (Zahn 46) am häufigsten Kontakte; die Häufigkeit bei Drahtklammerprothesen war mit 48,4 % (Zahn 36) und 45,2 % (Zahn 46) am niedrigsten. Bei Freiendsätteln waren die Ergebnisse vergleichsweise analog; bei Schaltsätteln waren die Kontaktunterschiede nicht signifikant. Auffällig war, dass okklusale Kontakte insgesamt am Ersatzmolar 46 mit 62,9 % häufiger zu finden waren als am Zahn 36. Fazit: Ersatzzähne im Kauzentrum profitieren in Bezug auf okklusale Kontakte vor allem bei rein teleskopierend verankerten Prothesen im Unterkiefer und sorgen damit für bessere okklusale Stabilität.
Keywords: Okklusion, Teilprothese, Verankerung, künstliche Zähne, bevölkerungsbezogene Auswertung
PubMed ID (PMID): 25558760Pages 199-218, Language: English, GermanFingerhut, Christopher / Schindler, Hans J. / Schweizerhof, Karl / Kordaß, Bernd / Lenz, Jürgen
Objectives: The primary goal of the present finite element (FE) analysis of a special removable prosthesis, the conical telescopic crown (CTC), was to validate established results based on a rigid model of the CTC and to analyze its characteristic features as a function of the essential material and geometric parameters. Furthermore, the effectiveness of a new element, the composite stop (CS), was investigated.
Materials and methods: The study used an axisymmetric FE model containing the inner and outer crown including resin or ceramic veneer, the CS, the cement layer between the interior crown and the tooth, and the upper part of the tooth itself.
Results: For a convergence angle (half-cone angle) α = 4° and a moderate chewing force F = 150 N the loosening force decreased from ~ 50 N without to ~ 10 N with CS. Increasing α values yielded a decrease of the loosening force. Adherence between the inner (IC) and outer crown (OC) was achieved for all configurations (α = 2°, 4°, and 6°), except for zirconium crowns with α = 6°. In systems without CS, the maximum tensile stress in the veneer increased proportionally to F, but remained limited in those with CS.
Conclusions: The angle α and the coefficient of static friction μ0 emerged as the decisive parameters of the CTC. The computed fitting/loosening behavior agreed well with results of a simple rigid-body model and experiments. The incorporation of a CS allows ceramic veneering of the outer crown.
Clinical relevance: The optimal angle α of the CTC is ascribed to a number of customary material combinations for IC and OC. The CS limits the loosening forces of the CTC to values which guarantee non-traumatic removal of the prosthesis.
Keywords: conical crown, removable prosthesis, double crown-retained denture, composite stop, ceramic veneer, loosening force control
PubMed ID (PMID): 25558761Pages 219-238, Language: English, GermanHajtó, Jan / Marinescu, Costin / Silva, Nelson R. F. A.
Background and purpose: Different digital software tools are available today for the purpose of designing anatomically correct anterior and posterior restorations. The current concepts present weaknesses, which can be potentially addressed by more advanced modeling tools, such as the ones already available in professional CAD (Computer Aided Design) graphical software.
Aim: This study describes the morphogenic designer (MGD) as an efficient and easy method for digitally designing tooth forms for the anterior and posterior dentition.
Materials and Method: Anterior and posterior tooth forms were selected from a collection of digitalized natural teeth and subjectively assessed as "average". The models in the form of STL files were filtered, cleaned, idealized, and re-meshed to match the specifications of the software used. The shapes were then imported as wavefront ".obj" model into Modo 701, software built for modeling, texturing, visualization, and animation.
Results: In order to create a parametric design system, intentional interactive deformations were performed on the average tooth shapes and then further defined as morph targets. By combining various such parameters, several tooth shapes were formed virtually and their images presented.
Conclusion: MGD proved to be a versatile and powerful tool for the purpose of esthetic and functional digital crown designs.
Keywords: computerized dentistry, dental 3D modeling, morphogenic tooth design, digital tooth design
PubMed ID (PMID): 25558762Pages 239-251, Language: English, GermanKurbad, Andreas
The prosthetic restoration of implants to obtain an esthetically balanced outcome is an extremely complex process - especially in terms of effective soft-tissue management. So-called hybrid abutment crowns, which can be made from polymer milling blocks in an uncomplicated process and used for immediate provisional restoration, represent an advance in the efficient production of superstructures.
Keywords: implants, superstructures, immediate loading, soft-tissue management, CAD/CAM
PubMed ID (PMID): 25558763Pages 253-258, Language: English, GermanFritzsche, Günter / Schenk, Olaf
The introduction of the Cerec Omnicam acquisition unit in September 2012 presented Sirona with a challenge: configuring the existing software version 4 for both the existing Bluecam, which uses still images, and the video-based Omnicam. Sirona has succeeded in making all the features introduced in version 4.2 (such as the virtual articulator or implant-supported single-tooth restorations, both monolithic and two-part designs) work with both camera types, without compromising the uniform, homogeneous look and feel of the software. The virtual articulator (Figs 1a to 1c) now has even more individual configuration options and allows the setting of almost all angles derived from the individual transfer bow based on precalculated average values. The new software version 4.3, presented in July 2014, fixes some minor bugs, such as the time-consuming "empty grinding" after necessary water changes during the grinding process, but also includes many features that noticeably ease the workflow. For example, the important scanning precision in the region of the anterior incisal edges has been improved, which makes the scanning process more reliable, faster, and far more comfortable.