R. LANG*, M. ROSENTRITT, M. BEHR and G. HANDEL
(Department of Prosthetic Dentistry, University of Regensburg, Germany)
During clinical application provisional crown and bridge restorations may fail due to fracture. In this in vitro study the fracture strength of three-unit bridges of five provisional crown & bridge materials and two experimental formulations (Exp) were determined. Identical alloy dies (Biosil F, Degussa, Hanau, G) were fixed in resin at a distance of 10 mm simulating posterior gap (artificial periodontium). Twenty bridges of each material were bonded with Procem (Espe). After 24days/ H20 storage and subsequent thermal cycling and mechanical loading (TCML: 50 N, 480000 times; 600 cycles 5°/55° C, 2 min each; automatic failure detection) ten samples of each group were loaded to fracture (Zwick, Ulm, G; v=1mm/min). Ten samples of each material were stored for 24 hours/H20 as a control group and loaded to fracture. Fracture forms were determined optically. Medians and 25%/75% percentiles were calculated. Statistics: One-Way- Anova (alpha=0,05).
Results: During the observation time no technical failures occured in 80.5% of all cases.Fracture of circumferencial retainers never occured in combination with a complete denture in the opposite jaw. The loss of artificial teeth was reported with all types of the opposing dentures, but repeatedly occurred only when the opposite jaw also had a removable partial denture. Removable partial dentures with circumferencial retainers showed a low frequency of technical complications (19.5%). These complications did not limit the survival time of the dentures when compared to the group of removable partial dentures with circumferencial retainers without reported technical failure.