Effect of toothbrushing with conventional and whitening dentifrices on monolithic zirconia after finishing procedures.

PURPOSE: To evaluate the effect of toothbrushing with conventional and whitening dentifrices on the color difference (ΔE00), gloss (Δgloss), and surface roughness (SR) of stained stabilized zirconia with 5 mol% of yttrium oxide (5Y-TZP) after polishing or glazing. METHODS: Specimens were divided into four groups (n=20): C (control), S (staining), SG (staining and glazing) and SP (staining and polishing). 50,000 toothbrushing cycles were performed with conventional (n=10) and whitening (n= 10) dentifrice slurries. The ΔE00 and Δgloss were measured using a spectrophotometer and CIEDE2000 system while SR was measured by laser confocal microscope. The ΔE00 and Δgloss data were analyzed using 2-way ANOVA, and SR data were analyzed using the linear repeated measures model, with Bonferroni's complementary test (α= 0.05). RESULTS: The ΔE00 values were beyond the acceptability threshold and no differences were found among the groups. There was no difference among groups to Δgloss after toothbrushing with conventional dentifrice while SP presented the highest values of Δgloss after toothbrushing with whitening dentifrice. Conventional dentifrice decreased the SR of stained groups and whitening dentifrice decreased SR of S and SG. The toothbrushing with conventional and whitening dentifrices promoted color difference, but did not impair gloss and surface roughness of stained 5Y-TZP. CLINICAL SIGNIFICANCE: Monolithic zirconia has been routinely used for esthetic restorations, however the type of finishing procedures that is carried out on it must be taken into consideration, in addition to the fact that brushing can influence the color difference of the material as well as interfere with surface roughness and gloss.

Screw loosening of different UCLA-type abutments after mechanical cycling

AIM: To evaluate the loss of applied torque (detorque) values in cast and pre-machined abutments for external hex abutment/implant interface of single implant-supported prostheses subjected to mechanical cycling. METHODS: Ten metal crowns were fabricated using two types of UCLA abutments: cast and pre-machined with metal base in NiCrTi alloy and tightened to regular external hex implants with a titanium alloy screw, with an insertion torque of 32 N.cm, measured with a digital torque gauge. Samples were embedded with autopolymerizing acrylic resin in a stainless steel cylindrical matrix, and positioned in an electromechanical machine. Dynamic oblique loading of 120 N was applied during 5 x 10(5) cycles. Then, each sample was removed from the resin and detorque values were measured using the same digital torque gauge. The difference of the initial (torque) and final (detorque) measurement was registered and the results were expressed as percentage of initial torque. The results of torque loss were expressed as percentage of the initial torque and subjected to statistical analysis by the Student's t-test (p<0.05) for comparisons between the test groups. RESULTS: Statistical analysis demonstrated that mechanical cycling reduced the torque of abutments without significant difference between cast or pre-machined UCLA abutments (p=0.908). CONCLUSIONS: Within the limitations of this in vitro study, it may be concluded that the mechanical cycling, corresponding to one-year use, reduced the torque of the samples regardless if cast or pre-machined UCLA abutments were used.

Abutment rotational freedom evaluation of external hexagon single-implant restorations after mechanical cycling.

PURPOSE: The purpose of this study was to evaluate the rotational freedom between implant and abutment counterpart of two abutments types over external hexagon implants submitted to mechanical cycling. MATERIALS AND METHODS: Ten implants with external hexagon (3.75 mm × 13 mm), five cast abutments, and five premachined abutments both with 4.1 mm plataform size were used in this study. Ten metallic crowns were fabricated using the two types of abutments and were fixed to each implant using titanium screws (Ti6Al4V). Rotational freedom measurements were made before and after the cast procedure and after the mechanical cycling. Groups were classified according to the rotational misfit register using University of California, Los Angeles abutment and implants as new (group 1 = G1); using crowns and implants after crown casting (group 2 = G2); and using crowns and implants after mechanical cycling (group 3 = G3). Oblique loading of 120N at 1.8 Hz and 5 × 10(5) cycles was applied on specimen. RESULTS: Statistical analysis (p < .05) showed that no significant difference was observed when cast abutment was compared with premachined abutment after casting (p = .390) and mechanical cycling (p = .439); however, significant difference was noted before the casting (p = .005) with higher values for the cast abutments. CONCLUSIONS: Within the limitations of this in vitro study, it could be concluded that the abutment type used do not influenced the rotational freedom after casting and the amount of applied cycles (500,000 cycles) was not sufficient to significantly alter the values of rotational freedom at the implant/abutment joint.