C. KOLBECK*, M. ROSENTRITT, M. BEHR and G. HANDEL,
(Department of Prosthetic Dentistry, University of Regensburg, Germany)
This in-vitro study was carried out in order to examine fracture strength and marginal adaptation of three-unit posterior FPDs made of the polyethylene-fibre-reinforced-composite-system ConnectTM/belleGlassTMHP (Belle de St. Claire, USA). 32 freshly extracted human third molars were flexibly positioned in PMMA resin (Palapress, Kulzer, FRG) to simulate the human periodontium. The distance (10mm) represented a molar gap. Preparation was performed resulting in a 1mm deep shoulder respectively chamfer with both finishing lines in dentin. 16 FPDs were made following the manufacturer´s instructions and adhesively luted using Syntac/Variolink II (Vivadent, FL). After thermal cycling and mechanical loading (TCML) in an artificial oral environment (6000x5°C/55°C, 2min/cycle; 1.2x106x50N, 1.66Hz = 5 years of intraoral service) 8 of the FPDs were mechanically loaded to failure (v = 1mm/min, Zwick 1446, FRG). Epoxy-replicas (Vivadent, FL) of the 8 remaining FPDs were made before and after TCML and used for analysis of marginal adaptation in a scanning electron microscope (SEM Stereoscan 240, FRG). Both the cement-restoration- (CR) and the cement-tooth-interfaces (CT) were classified in areas of perfect margin (PM) or marginal gap (MG). A dye penetration test was performed by incubating the 8 FPDs in 0.5% basic fuchsine solution for 16h. Then the abutment teeth were cut into slices (600µm) and the percentual depth of dye penetration (DPD) was evaluated (Optimas, Bothell, USA) for both interfaces (CR, CT). For all results median values and percentiles (25/75%) were calculated. Statistics were performed using Mann-Whitney-U-Test (p=0.05). With a median value (25%/75%-percentiles) of 944N (758/1298) the system showed good fracture strength. The two preparation forms did not show significant different dye penetration depths. TCML did show a decrease of the marginal quality for the shoulder preparation but not for the chamfer finishing line. Both the high fracture strength and the good marginal adaptation even after TCML encourage further clinical investigations. If the FPDs are luted adhesively they might even be used for definite reconstructions. Supported by Girrbach Dental, FRG.