Jean Soares Miranda

Effect of fatigue protocols on flexural strength of lithium disilicate bars with clamped-ends

The aim of this study was compare the effect of two in vitro ageing protocols to intraoral aging on the flexural strength of a lithium disilicate (LD) ceramic bars with clamped ends. After polishing and crystallization, the both ends of the bars were cemented to a metallic device and subjected to mechanical cycling, thermomechanical cycling, or intraoral ageing. Ten volunteers used an intraoral device - similar to an occlusal splint with a balanced contact condition on the occlusal surface of the ceramic bar - during 8 h night time / 30 days. Both in vitro and intraoral ageing decreased the flexural residual strength of LD, with the lowest values obtained after intraoral ageing. Thus, the in vitro ageing protocols tested in this study revealed to be less deleterious than intraoral ageing of LD.

Can low-fusing glass application affect the marginal misfit and bond strength of Y-TZP crowns?

To evaluate the effect of different surface treatments on the marginal misfit and retentive strength between Y-TZP crowns and an epoxy resin. Forty (40) epoxy resin (G10) abutments (height: 5mm, conicity: 60, finish line: large chamfer) with equal dimensions were milled and included in polyurethane to simulate the periodontal ligament. Next, 40 Y-TZP crowns (thickness: 1mm) were milled (Cerec in Lab) and randomly divided into four groups (n=10) according to the surface treatment: GS(glaze spray), GP(glaze powder/liquid), P(zirconia primer) and RS(tribochemical silica coating). The conditioned surfaces were cemented with dual self-adhesive cement, light cured and submitted to thermomechanical cycling (2x106, 100N, 4Hz, 5°/55°C). Marginal misfit was analyzed by a stereomicroscope and SEM. Retentive strength test was performed (1mm/min) until crown debonding. Glaze layer thickness was also performed to GS and GP groups. Marginal misfit data were analyzed by Kruskal Wallis and Dunn tests; one-way ANOVA and Tukey (5%) analyzed the tensile strength data. The marginal misfit of the GS (48.6±19.9μm) and GP (65.4±42.5μm) were statistically lower than the RS (96±62.9μm) and P (156±113.3μm) (p=0.001). The retentive strength of the GP (470.5±104.1N) and GS (416.8±170.2N) were similar to the P (342.1±109.7N), but statistically higher than those of the RS (208.9±110N). The GS and GP glaze layer was 11.64μm and 9.73μm respectively. Thus, glaze application promoted lower marginal discrepancy and higher retentive strength values than conventional techniques.

Bond strength of glass fiber posts submitted to different luting protocols

Objective: evaluate the effect of different luting protocols on the bond strength of glass fiber posts. Methods: Forty human canine teeth were randomly divided into four groups: Relyx U100/Endofill (R+E), Panavia F2.0/EndoFill (P+E), Relyx U100/Sealer 26 (R+S), Panavia F2.0/Sealer 26 (P+S). After the luting procedures, the samples were subjected to thermocycling (6.000 cycles; at 5±1 oC and 55±1 oC) and then sectioned in a precision cutting machine (Isomet 1000 Precision Saw) into 4 cuts of 2mm regarding to different deepness: Apical, Medium Apical, Medium Coronal, and Coronal. Next, the cuts were submitted to push-out test in a universal testing machine (EMIC) with load cell of 50N, at crosshead speed of 0.5mm/min. Results: They were obtained according to the different luting deepness (p≥0.05) (MPa): 1) apical – R+E (1.35±1.28), P+E (2.70±0.89), R+S (3.89±0.70), P+S (4.30±1.02); 2) medium apical – R+E (1.38±1.28), P+E (2.98±1.43), R+S (4.02±1.14), P+S (4.49±1.82); 3) medium coronal – R+E (2.46±0.73), P+E (3.72±0.78), R+S (4.85±0.71), P+S (6.14±0.73); 4) coronal R+E (5.59±1.08), P+E (5.74±1.06), R+S (6.71±1.07), P+S (7.40±1.51). Conclusion: There was a relationship between the luting protocol of the glass fiber post and the endodontic cement. Eugenol plays an important role inside the dentinal tubules by interfering negatively in the bond strength to root dentin.