Fracture resistance of metal-free inlay FPDs made from polymer in combination with a prefabricated frame

Objectives: Objectives of this in-vitro study were to investigate the influence of gap size, adhesive cementation, and fatigue on the stability of metal-free fixed partial dentures (FPDs) anchored by polymer inlays. Methods: Inlay preparation was performed on a second mandibular molar and a premolar. Replicas from the prepared abutment teeth were casted with a CoCr-alloy and fixed in PMMA models simulating tooth mobility by a rubber coverage on the root surface. Gap size was either a first molar or a premolar. Metal-free prefabricated PMMA Frames® (HeraeusKulzer, Germany) were adapted to the boxes of the inlay preparation preserving minimal dimensions of 3 mm in height and 2 mm in width. Then, the inlay FPDs were finished with Artglass® material (HeraeusKulzer) following manufacturers' recommendations. FPDs were cemented with resin cement. However, only half of the metal abutments were conditioned with Rocatec (ESPE) prior to cementation. All FPDs underwent 10,000 thermal cycles between 5° and 55°C, when half of them were additionally loaded with 50N for 600,000 cycles. Then, the FPDs were loaded to failure in a universal testing machine. Results: Mean fracture load of FPDs replacing a premolar ranged from 690N to 800N depending on fatigue and cementation technique. FPDs with a gap size of a molar demonstrated significantly (p=0.001) lower fracture loads ranging between 266N and 414N. Additional fatigue resulted in a significant decrease of the stability of molar FPDs from 390N to 266N (p=0.003), whereas fatigue had no effect on premolar FPDs. Adhesive bonding of the cement to the metal abutments using Rocatec resulted in a significant decrease of the stability of premolar FPDs after fatigue simulation (800N to 656N). Conclusions: The data of this in-vitro test indicate that Artglass FPDs with the metal-free Frame® offer acceptable stability for FPDs replacing a premolar but not for molar FPDs.