Non-linear 3D finite element analysis of full-arch implant-supported fixed dentures.

Despite the necessity for faster clinical protocols for immediate loading of implant-supported dentures, there is a lack of biomechanical studies to confirm the rigid splinting effectiveness. We compared the stress in mandibular full-arch implant-supported fixed dentures under immediate loading through three-dimensional finite element analysis. Edentulous human mandible models were restored with a 4-implant fixed denture. Implants were splinted with a metallic framework and submitted to conventional loading (group A-control), with acrylic resin and submitted to immediate loading (group B), with a metallic framework and submitted to immediate loading (group C), and with acrylic resin and a prefabricated distal bar and submitted to immediate loading (group D). Models were supported by masticatory muscles. A 100-N oblique load was applied on the first molar. Group A presented the lowest stress and implant displacement values, whereas group D showed the highest values. In bone, groups under immediate loading exhibited the highest stress, whereas the group experiencing conventional loading showed an approximately 50% reduction. All groups submitted to immediate loading presented similar stress values in peri-implant bone. The loading protocol influenced the stress and implant displacement, but the design of the fixed denture did not affect the stress in the peri-implant bone. Rigid splinting of implants submitted to immediate loading is not essential for treatment success.

Influence of abutment-to-fixture design on reliability and failure mode of all-ceramic crown systems.

OBJECTIVE: Evaluate the effect of implant connection designs on reliability and failure modes of screw-retained all-ceramic crowns. METHODS: Central incisor ceramic crowns in zirconia abutments were screwed and torqued down to external hexagon (EH), internal hexagon (IH) and Morse taper (MT) implant systems. Single-load-to-fracture (SLF) test (n=4 per group) determined three step-stress fatigue profiles with specimens assigned in the ratio of 3:2:1. Fatigue test was performed under water at 10 Hz. Use level probability Weibull curves and reliability for missions of 50,000 cycles at 400 N and 200 N were calculated (90% confidence bounds-CB). Weibull probability distribution (90% CB) was plotted (Weibull modulus vs characteristic strength) for comparison between the groups. Fractographic analyses were conducted under polarized-light microscopy and SEM. RESULTS: Use level Weibull probability calculation indicated that failure was not associated with fatigue in groups EH (ß=0.63), IH (ß=0.97) and MT (ß=0.19). Reliability data for a mission of 50,000 cycles at 400 N revealed significant reliability differences between groups EH (97%), IH (46%) and MT (0.5%) but no significant difference at 200 N between EH (100%) and IH (98%), and IH and MT (89%). Weibull strength distribution (figure) revealed ß=13.1/η=561.8 for EH, ß=5.8/η=513.4 for IH and ß=5.3/η=333.2 for MT. Groups EH and IH exhibited veneer cohesive and adhesive failures. Group IH also presented adhesive failure at zirconia/titanium abutment insert while MT showed fracture at abutment neck. SIGNIFICANCE: Although group EH presented higher reliability and characteristic strength followed by IH and MT, all groups withstood reported mean anterior loads.

Effect of bleaching agents and soft drink on titanium surface topography.

The effects of carbamide peroxide, hydrogen peroxide and cola soft drink on the topographic modifications of commercially-pure titanium (CP-Ti) and Ti-6Al-4V were investigated. Ti discs were divided into 18 groups (n = 4) based on the solution treatment and Ti type. Specimens were immersed in 3 mL of each solution for 4 h per day (for the remaining 20 h, discs were left dry or immersed in artificial saliva) for 15 days. For control, specimens were immersed in only artificial saliva. Ti surfaces were examined using scanning electron (SEM) and atomic force (AFM) microscopes and their surface roughness (in µm) and surface chemical modifications were investigated. Data were analyzed by ANOVA and Tukey's test (α = 0.05). Groups immersed in 35% hydrogen peroxide showed the highest roughness (Ra) (171.65 ± 4.04 for CP-Ti and 145.91 ± 14.71 for Ti-6Al-4V) (p < 0.05), followed by groups treated with carbamide peroxide 16% (110.91 ± 0.8 for CP-Ti and 49.28 ± 0.36 for Ti-6Al-4V) and 35% (65.67 ± 1.6 for CP-Ti and 53.87 ± 1.98 for Ti-6Al-4V); treatment with artificial saliva did not affect the results. These values were statistically superior to those observed prior to the treatment and to those of the control group (31.0 ± 0.99 for CP-Ti and 29.95 ± 0.58 for Ti-6Al-4V). Cola soft drink did not alter the surface roughness of either Ti type (p > 0.05). SEM and AFM revealed dramatic changes in the specimens surfaces immersed in the 35% hydrogen peroxide, mainly for CP-Ti. No detectable chemical modifications on the Ti surface were observed. Bleaching agents promoted significant changes in Ti topography, which could affect the longevity of implants treatments.

Color degradation of acrylic resin denture teeth as a function of liquid diet: ultraviolet-visible reflection analysis.

The effect of different beverages on acrylic resin denture teeth color degradation is evaluated. Ten acrylic resin denture teeth brands were evaluated: Art Plus (AP), Biolux (BX), Biotone IPN (BI), Magister (MG), Mondial 6 (MD), Premium 6 (PR), SR Vivodent PE (SR), Trilux (TR), Trubyte Biotone (TB), and Vipi Dent Plus (VP). Teeth were immersed in staining solutions (coffee, cola, and orange juice) or artificial saliva (control) (n=6) for 1, 7, 15, or 30 days. Specimen colors were evaluated spectrophotometrically based on the Commission Internationale d'Eclairage L*a*b* system. Color differences (ΔE) were calculated between the baseline and post-staining results. Data were evaluated by analysis of variance and Tukey test (α = 0.05). BI (1.82 ± 0.95) and TR (1.78 ± 0.72) teeth exhibited the greatest ΔE values, while BX (0.88 ± 0.43) and MD (1.09 ± 0.44) teeth were the lowest, regardless of solution and measurement period, and were different from BI and TR teeth (P < 0.05). Cola and coffee promoted higher denture teeth color alterations than orange juice and saliva (P < 0.05). Saliva generated the lowest denture teeth color alterations. Greater immersion times caused higher denture teeth color changes. The lifespan of removable dentures and the aesthetic satisfaction of several edentulous patients may be increased with the use of stain-resistant artificial denture teeth.