Showing papers by "Daniel Edelhoff published in 2008"

Digital dentistry: an overview of recent developments for CAD/CAM generated restorations

Abstract: As in many other industries, production stages are increasingly becoming automated in dental technology. As the price of dental laboratory work has become a major factor in treatment planning and therapy, automation could enable more competitive production in high-wage areas like Western Europe and the USA. Advances in computer technology now enable cost-effective production of individual pieces. Dental restorations produced with computer assistance have become more common in recent years. Most dental companies have access to CAD/CAM procedures, either in the dental practice, the dental laboratory or in the form of production centres. The many benefits associated with CAD/CAM generated dental restorations include: the access to new, almost defect-free, industrially prefabricated and controlled materials; an increase in quality and reproducibility and also data storage commensurate with a standardised chain of production; an improvement in precision and planning, as well as an increase in efficiency. As a result of continual developments in computer hardware and software, new methods of production and new treatment concepts are to be expected, which will enable an additional reduction in costs. Dentists, who will be confronted with these techniques in the future, require certain basic knowledge if they are to benefit from these new procedures. This article gives an overview of CAD/CAM-technologies and systems available for dentistry today.

HIP zirconia fixed partial dentures--clinical results after 3 years of clinical service.

Abstract: Objective: To evaluate prospectively the clinical performance of 3- to 6-unit zirconia fixed partial dentures (FPDs) after more than 3 years of clinical service. Method and Materials: Since August 2002, 22 conventional all-ceramic FPDs have been inserted in 18 patients. Nineteen of the FPDs were placed with a resin-reinforced glass-ionomer cement. The frameworks were manufactured by a universal CAD/CAM production system, milling the zirconia out of the densely sintered stage. The frameworks were designed as 3-unit (14), 4-unit (3), 5-unit (2), and 6-unit FPDs (3) for the anterior and posterior regions. A new synthetic sintering glass-ceramic was employed as the veneering material. In the follow-up examinations at baseline, 6, 12, 24, and 36 months, 21 FPDs were inspected predominantly for framework fractures and chipping of the veneering material. Besides these parameters, periodontal status, sensitivity of the abutment teeth, esthetic outcome, as well as the incidence of secondary caries, were evaluated. Results: After a mean clinical observation of over 39 months, no framework fracture occurred. However, chipping of the veneering material was reported in 2 cases. Conclusion: All-ceramic FPDs based on zirconia frameworks exhibited satisfactory clinical performance.

Effect of Preparation Design on the Fracture Resistance of Zirconia Crown Copings

Abstract: The aim of this in vitro study was to evaluate the effects of different preparation designs on the fracture resistance of single-crown zirconia frameworks. To this end, maxillary molar dies of CrCo alloy were fabricated with five different preparation designs: shoulderless, slight and pronounced deep chamfer, beveled and non-beveled shoulder. Ten zirconia copings with a wall thickness of 0.4 mm were fabricated for each type of preparation. After cementation by glass ionomer cement, they were loaded until fracture. There were significant differences in the breaking load of the experimental groups (ANOVA, p<0.01). The shoulder preparation had a mean breaking load of 2286 N, the shoulderless preparation 2041 N, the beveled shoulder 1722 N, the pronounced deep chamfer 1752 N, and the slight chamfer 1624 N. Based on the results of this study, a shoulder preparation is highly recommended whenever possible. Moreover, for endodontically treated teeth that are structurally compromised or which have anatomically limited areas, the slight chamfer preparation is an optimal recommendation.

Effect of preparation angles on the precision of zirconia crown copings fabricated by CAD/CAM system.

Abstract: The aim of this in vitro study was to evaluate the effects of different preparation angles on the precision of fit of zirconia crown frameworks. Dies were fabricated with three different preparation angles: 4, 8, and 12 degrees total taper. Ten copings were fabricated for each angle by a laboratory and a milling-center CAD/CAM system. After cementation, cross-sections were obtained and cement gaps were measured. Preparation angle (ANOVA, p < 0.01) and measurement location (ANOVA, p < 0.01) exhibited statistically significant influence on the precision of fit. On the other hand, no statistically significant influences were detected between copings prepared using the laboratory and milling-center CAD/CAM systems (ANOVA, p = 0.92). All groups showed marginal openings ranging between 36.6 and 45.5 microm. In light of the results obtained in this study, a preparation angle of 12 degrees is hence recommended with the confidence that the marginal gap will be consistently less than 50 microm.

Chemical strengthening of a dental lithium disilicate glass-ceramic material.

Abstract: Chemical strengthening of dental ceramics by ion exchange has hitherto only been confirmed for feldspathic porcelains. The objective of this study was to examine whether the strength of lithium disilicate glass-ceramics can be increased by ion exchange as well. A lithium disilicate glass-ceramic material was treated in different molten salts. The concentration gradients of the relevant ions in the surface layer were investigated by means of electron probe microanalysis and secondary ion mass spectroscopy. Characteristic strength and Weibull modulus data were determined. An increase in strength of 25% was achieved by treatment in potassium nitrate. The chemical analyses revealed that the increase in strength resulted from an exchange of potassium for lithium ions. We conclude that ion-exchange treatments can increase the strength of lithium disilicate glass-ceramics. The improved material could be used for highly stressed applications, such as posterior crowns or inlay-retained bridges, with higher mechanical reliability.

Long-term clinical performance of resin-bonded fixed partial dentures with retentive preparation geometry in anterior and posterior areas.

Abstract: Purpose The aim of this prospective clinical evaluation was to show the long-term clinical behavior of resin-bonded fixed partial dentures (RBFPD) with a retentive, minimally invasive preparation design. Materials and methods Since 1985, 232 RBFPDs with a retentive preparation design were placed under controlled clinical conditions. In 2005 and 2006, 84 fixed partial dentures could be re-evaluated. Using Kaplan-Meier analysis, the survival rate was determined. The probability of survival was calculated with several risk factors: location (anterior/posterior, maxilla/mandible), metal alloy of the framework (titanium/CoCr), number of pontics, and number of supporting teeth. Results A total of 12 failures was observed and resulted in a survival rate of 77% after 10 years. However, only 4 catastrophic failures occurred. In such cases, the restoration was lost, or could not be re-bonded or repaired (survival rate 88% after 10 years). RBFPDs made of a titanium alloy exhibited a statistically significantly higher survival rate than RBFPDs made of a nonprecious CoCr alloy in terms of all failures. Only slight but not statistically significant differences between the covariates maxilla, mandible, anterior/posterior region, number of pontics, and number of abutment teeth were observed. Conclusion Within the limitations of this study, RBFPDs seem to be a reliable restorative alternative to conventional short-span fixed dental prostheses.

Experiencia clínica con subestructuras de puentes de óxido de zirconio CAD/CAM del sistema Digident

Abstract: El presente articulo expone las primeras experiencias clinicas de un estudio prospectivo con puentes de ceramica sin metal cuyas estructuras fueron fabricadas con oxido de zirconio sinterizado utilizando el sistema Digident. Las subestructuras, formadas por hasta seis piezas, fueron recubiertas con una ceramica vitrea adaptada que en aquel momento se acababa de introducir y, exceptuando algunos casos, fueron cementadas con un cemento de vidrio ionomero reforzado con resina. Las exploraciones clinicas de seguimiento se llevaron a cabo en 22 puentes cementados en los sectores anterior y pos­terior. El periodo medio de observacion fue de 38 me­ses. Durante dicho periodo no se produjeron fracturas en ninguna de las subestructuras. Si se observaron, en cambio. desprendimientos de la ceramica de recubrimiento en dos restauraciones, que pudieron ser reparadas intraoralmente. Cumpliendo las normas de actuacion preestablecidas se consiguio una buena adaptacion clinica de las subestructuras de los puentes. La ceramica de recubrimiento se pudo procesar de forma sencilla y ofrece ademas un alto potencial estetico.