Abstract
The aim of this study was to compare the retention forces after artificial aging of telescopic crowns fabricated either by a conventional lost-wax technique or by computer-aided design/computer-aided manufacturing (CAD-CAM) technology. Two types of telescopic crowns (0°) were fabricated conventionally using high-noble (group A) and non-precious metal (group B). CAD-CAM fabricated telescopic crowns (0°) were made of non-precious metal (group C). Retention forces were assessed before and after artificial aging and after axial and non-axial loading. Initially [I.] and after artificial aging [IV.], specimens of group C (I. 16.2 N; IV. 13.6 N) exhibited the highest retention forces. The retention forces in groups B (I. 12.5 N; IV. 4.6 N) and A (I. 9.6 N; IV. 2.9 N) were found to be lower than those of group C. The retention force differences between the groups were statistically significant (p < 0.001) at all measurement times [I. vs. IV.]. Different fabricated telescopic crowns with approximately identical designs and materials exhibited different retention forces and different long-term retentive behavior. An optimized CAD-CAM process with individually defined design parameters ensured telescopic crowns with a better fit. These findings might influence prospective clinical decision-making.
Highlights
The combination of removable and fixed dentures with double crowns as anchoring elements, both on natural abutments and implants, has proven itself over decades as a treatment modality [1,2,3,4,5].Their advantages include circular and rigid support of the abutment teeth, adequate retention, their supporting and leading function combined with acceptable aesthetics, simple handling and cost-effective extensibility [3,4]
A high retention force loss of 63.5% was observed in the non-precious metal conventional telescopic crowns
With regard to the computer-aided design/computer-aided manufacturing (CAD-CAM) fabricated series, only between the measuring points after 15,000 insertion and removal cycles and the final stage could a significant drop of the retention forces be observed
Summary
The combination of removable and fixed dentures with double crowns as anchoring elements, both on natural abutments and implants, has proven itself over decades as a treatment modality [1,2,3,4,5] Their advantages include circular and rigid support of the abutment teeth, adequate retention, their supporting and leading function combined with acceptable aesthetics, simple handling and cost-effective extensibility [3,4]. High-gold alloys were used for the primary and secondary crowns. For this reason, alternative materials were used and many designs have been developed for the concept of double crowns. The high modulus of elasticity renders manual processing and the adjustment of the retention force more
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