Andrea Fabianelli

The effect of different surface treatments on bond strength between leucite reinforced feldspathic ceramic and composite resin.

OBJECTIVES The aim of this study was to evaluate the effect of different surface treatments on the microtensile bond strength between a leucite reinforced glass-ceramic and composite resin. METHODS Leucite reinforced ceramic blocks (n=24) were constructed using the hot pressing technique. The blocks were assigned to 4 groups, which received the following surface treatments: G1: hydrofluoric (HF) acid and silane; G2: silane alone; G3: HF acid and silane then dried with warm air (100 degrees C); G4: silane alone then dried with warm air (100 degrees C). Unfilled resin was applied, followed by composite resin. Specimens were prepared and loaded in tension to determine the microtensile bond strength. Failure modes were classified by stereo- and scanning electron microscopy (SEM). Data was analysed using Kruskal-Wallis test followed by the Dunns multiple range test. RESULTS The groups including the warm air step (G3 and G4) achieved a significantly stronger adhesion than G1 and G2. Pre-treatment of the surface with hydrofluoric acid in G1 resulted in significantly higher bond strength than G2. Failures were mostly cohesive in the luting resin for G1, G3 and G4 and mainly adhesive at the ceramic-resin interface in G2. CONCLUSIONS The method of application of silane to the ceramic surface can have a significant influence on the adhesion between the ceramic restoration and the resin cement. Enhancing the condensation reaction by drying the silane with a 100C warm air stream significantly improved the microtensile bond strength, possibly eliminating the need for the hydrofluoric acid etching step.

Microtensile bond strength of a resin cement to a novel fluorcanasite glass-ceramic following different surface treatments

OBJECTIVES This study evaluated the effect of surface treatments on the bond strength of fluorcanasite and lithium disilicate glass-ceramics, with the possibility of eliminating HF etching of these ceramics. METHODS Fifteen blocks of an experimental fluorcanasite and a lithium disilicate glass-ceramic (IPS e.max CAD) were assigned to one of the following three surface treatments: (1) machined with 60 microm finish, (2) machined and grit blasted, (3) machined and HF etched. The ceramic blocks were duplicated in composite resin (Spectrum) and cemented together with a resin luting agent (Variolink II). Thirty microbars per group (1.0 x 1.0 x 20 mm) were obtained and subjected to a tensile force at a crosshead speed of 0.5 mm/min using a universal testing machine until failure. The mode of failure was determined using scanning electron microscopy. The appropriate bonding procedure was assessed for durability by storing in water at 100 degrees C for 24 h. Statistical analyses were performed with ANOVA and Tukeys test (P<0.05). RESULTS Machining alone significantly increased the bond strength (MPa) of the fluorcanasite (27.79+/-6.94) compared to the lithium disilicate (13.57+/-4.52) (P<0.05). HF etching resulted in the lowest bond strength (8.79+/-2.06) for the fluorcanasite but the highest for the lithium disilicate (24.76+/-9.38). Regarding durability, the machined fluorcanasite (15.24+/-5.46) demonstrated significantly higher bond strength than the machined and HF etched lithium disilicate (12.28+/-3.30). SIGNIFICANCE The fitting surface of the fluorcanasite glass-ceramic should retain the machined finish and be directly treated with silane. The use of HF acid is contraindicated.

The evaluation of marginal gap with and without optical aids: clinicians versus technicians.

PURPOSE This study investigated the reliability of visual assessment of marginal gaps in relation to the use of magnification and the operators profession. MATERIALS AND METHODS A titanium bar was notched, simulating 40 marginal gaps, and 35 operators performed a quantitative evaluation of the incisions. RESULTS Visual examination was neither sensitive nor specific, as an extreme variability of data was recorded. The precision of readers improved with magnification aids only for clinicians; technicians were significantly more accurate in evaluating the incisions width. CONCLUSION The visual examinations were inadequate to decide the clinical acceptability of a restoration with regard to its marginal fit.

The Evaluation of Unscrewing Torque Values of Implant-Abutment Connections: An In Vitro Study.

PURPOSE This study investigated the stability of titanium screws in implant-abutment connections by measuring the force necessary to induce unscrewing. MATERIALS AND METHODS A total of 60 implant-abutment couplings were assigned to two groups (n = 30 each). The sequence 10-20-32 Ncm was tested in Group 1; the sequence 10-20-32-32-32 Ncm was tested in Group 2. The force necessary to unscrew each abutment-implant sample was recorded and statistically analyzed. The significance level was set at P < .05. RESULTS Significant differences were found between the two sequences. Group 2 required higher forces than Group 1 to unscrew. CONCLUSION The stability of the implant-abutment joint may be improved by tightening with the sequence 10-20-32-32-32 Ncm.