Influence of implant-abutment angulations and crown material on stress distribution on central incisor: a 3D FEA

Aim: To investigate the effect of implant-abutment angulation and crown material on stress distribution of central incisors. Finite element method was used to simulate the clinical situation of a maxillary rightcentral incisor restored by two different implant-abutment angulations, 15° and 25°, using two different crown materials (IPS E-Max CAD and zirconia). Methods: Two 3D finite element models were specially prepared for this research simulating the abutment angulations. Commercial engineering CAD/CAM package was used to model crown, implant abutment complex and bone(cortical and spongy) in 3D. Linear static analysis was performed by applying a 178 N oblique load.The obtained results were compared with former experimental results. Results: Implant Von Misesstress level was negligibly changed with increasing abutment angulation. The abutment with higherangulation is mechanically weaker and expected to fail at lower loading in comparison with thesteeper one. Similarly, screw used with abutment angulation of 25° will fail at lower (about one-third)load value the failure load of similar screw used with abutment angulated by 15°. Conclusions: Bone (cortical and spongy) is insensitive to crown material. Increasing abutment angulation from15° to 25°, increases stress on cortical bone by about 20% and reduces it by about 12% onspongy bone. Crown fracture resistance is dramatically reduced by increasing abutment angulation. Zirconia crown showed better performance than E-Max one.

Influence of fabrication techniques and artificial aging on the fracture resistance of different cantilever zirconia fixed dental prostheses.

PURPOSE: To evaluate the influence of dynamic fatigue on fracture load and failure mode of different types of adhesive zirconia restorations. MATERIALS AND METHODS: Eighty adhesive cantilever fixed dental prostheses (CFDP) were fabricated and assigned to four equal groups (n = 20) using the following materials and techniques. Group 1: machine copy-milling zirconia (Cercon), group 2: manual copy-milling technique (ZirkonZahn), group 3: slip casting technique (Vita In-ceram Zirconia), group 4: metal-ceramic CFDP. Specimens in groups 1and 2 received selective infiltration-etching surface treatment, specimens in group 3 were acid etched with hydrofluoric acid and silanated, while those of group 4 were airborne particle abraded. All specimens were bonded with resin cement (Panavia F2.0) and thermocycled (5000 cycles/ 5 to 55°C). Then, half the number of the specimens of each group (n = 10) underwent dynamic loading (one million cycles at alternating loads between 10 and 40 N in a water bath at 37°C). All specimens were subjected to one-cycle loading to failure to evaluate fracture resistance. One-way and two-way ANOVA and Bonferroni post-hoc tests were used to analyze the data (α = 0.05). The intaglio surfaces of fractured specimens were examined using stereomicroscopy and scanning electron microscope (SEM). RESULTS: Statistical analysis revealed that the failure load of metal (413 ± 26 N) and machine copy-milled zirconia (368 ± 24 N) restorations was significantly higher (F = 129, p < 0.001) than manually copy-milled (316 ± 18) and In-ceram zirconia (210 ± 17) restorations. Dynamic fatigue significantly (p < 0.03) reduced failure load of the manually copy-milled and In-ceram zirconia restorations, while metal and machine copy-milling zirconia restorations were not influenced by fatigue. CONCLUSIONS: The fatigue strength of adhesive zirconia restorations is influenced by cyclic loading and the technique used to manufacture these restorations.

Study of the effect of different surface treatments and surface roughness of veneered crowns on shear bond strength of ceramic brackets.

The orthodontist is often faced with the problem of bonding brackets to ceramic restorations. The purpose of this study was to find the most reliable method for bonding ceramic brackets onto ceramic crowns.

Fracture resistance of metal- and galvano-ceramic crowns cemented with different luting cements: in vitro comparative study.

This study aimed to compare the fracture resistance of galvano-ceramic crowns with metal-ceramic crowns cemented to natural premolar teeth with different luting cements. Sixty intact maxillary premolars were prepared to receive full-coverage crown restorations and were divided into 2 equal groups (n = 30): galvano-ceramic crowns and metal-ceramic crowns. Each group was further subdivided into 3 equal subgroups (n = 10) according to the luting cement used: zinc-phosphate, glass-ionomer, or adhesive-resin cement. The specimens were then compressively loaded until failure in a universal testing machine. The metal-ceramic crowns exhibited higher resistance to fracture compared to galvano-ceramic crowns, but both exceeded the normal documented values of occlusal masticatory forces.