Effect of abutment screw-access hole on the fatigue performance of implant-supported lithium-disilicate luted simplified restorations.

The present study aimed to evaluate the impact of the existence of an abutment screw-access hole and the filling effects on the fatigue mechanical behavior of a luted lithium-disilicate glass-ceramic. Seventy-two discs (Ø = 10 mm, 1.0 mm in thickness) of lithium disilicate (IPS e.max CAD, Ivoclar AG) were obtained from prefabricated blocks. Thirty-six abutment specimens of an opaque zirconia (Yz - IPS e.max ZirCAD, Ivoclar AG) and titanium (Ti - Luminesse Ti-Cam discs, Talladium Inc.) were confectioned, and allocated according to 6 groups: Yz and Ti rigid (without screw access hole); Yz unfilled, Yz filled, Ti unfilled and Ti filled (with the screw access (Ø = 2.5 mm) in the center). For the unfilled groups, only a polytetrafluoroethylene tape was used. Resin composite (Tetric N-Ceram, Ivoclar AG) was applied to the screw access hole for the filled groups (Yz and Ti). A cyclic fatigue test was carried out (load of 200 N, 10,000 cycles each; 20 Hz of frequency, step size of 100 N until failure detection (radial/cone crack). The fatigue failure load (FFL) and number of cycles until failure (CFF) were recorded for statistical purposes. The stress distribution (MPa) was evaluated by finite element analysis. A statistically positive effect of the abutment material and the presence of the screw access hole was observed (p ≤ 0.05). The rigid groups (without screw access holes) depicted almost 100% of survival after the fatigue tests. Among the other groups, the Yz-filled group showed the best performance (p ≤ 0.05), followed by the Yz unfilled group. The Ti groups depicted lower values of FFL and CFF, with the Ti unfilled group showing the most unfavorable fatigue behavior (p ≤ 0.05). The lowest tensile stress concentration in the restorative material was observed with the use of rigid abutments, the filled groups depicted intermediate values, while unfilled groups showed the highest stress concentration (Yz rigid = 306.3 MPa; Ti rigid = 310.4 MPa < Yz filled = 490.7 MPa; Ti filled = 498.9 MPa < Yz unfilled = 707.6 MPa; Ti unfilled = 719.7 MPa). Therefore, the presence of a screw-access hole decreases the mechanical performance of a lithium disilicate ceramic regardless of the abutment material. In the presence of a screw-access hole, zirconia abutments depicted a higher fatigue failure load when compared with titanium. The filling of the abutment screw-access hole with resin composite increased the mechanical performance of the simulated restoration.

Masking ability of CAD/CAM monolithic ceramics: effect of ceramic type and thickness, and try-in paste shade.

OBJECTIVE: This in vitro study evaluated the color differences when discolored tooth substrates were restored with CAD/CAM monolithic ceramics depending on ceramic type and thickness, and the try-in paste shade. METHOD AND MATERIALS: Six ceramic types were tested: high-translucent lithium disilicate (LD-HT); medium-translucent lithium disilicate (LD-MT); low-translucent lithium disilicate (LD-LT); low-translucent leucite (LC-LT); feldspathic ceramic (FC); and BL1 low-translucent lithium disilicate, stained to A1 shade (LD-BL1-LT). The ceramics were tested in disk-shaped specimens with 0.5-, 1.0-, and 1.5-mm thickness (n = 10; N = 180; shade A1). The try-in pastes were tested to simulate luting materials and corresponded to colors A1 and Opaque White. Six substrates were used: A1 (reference), B2, B3, A3, C2, and C3. Color differences (∆E00) and translucency parameter (TP00) were assessed with the CIEDE2000 formula. The results were compared with acceptability (1.77) and perceptibility (0.81) thresholds. RESULTS: Ceramic type, thickness, and the try-in paste shade influenced the color differences. LD-LT and LC-LT ceramics and Opaque White try-in paste provided, in general, lower ∆E00 values. The most adequate ceramic thickness varied according to the substrate discoloration. With 1.0 mm of ceramic thickness, it was possible to obtain ∆E00 lower than the perceptibility threshold for substrates C2 and A3, and ∆E00 lower than the acceptability threshold for C3 and B3. ∆E00 lower than the acceptability threshold were obtained with 0.5 mm of ceramic thickness for B2, A3, and C2. CONCLUSION: The use of low-translucent glass-ceramics and Opaque White try-in paste are useful to reduce color differences. The most adequate ceramic thickness depends on the substrate discoloration.

Effect of pigmentation techniques on the fatigue mechanical behavior of a translucent zirconia for monolithic restorations.

This study aims to characterize the effect of pre- and/or post-sintering pigmentation techniques on the fatigue behavior of a 4YSZ ceramic (4 mol% yttrium stabilized zirconia). First, 4YSZ ceramic discs (IPS e.max ZirCAD, 15 mm diameter, and 1.2 mm thickness) were obtained and allocated according to the 'pigmentation technique' factor into 5 groups: Ctrl - unshaded ceramic disc (IPS e.max ZirCAD BL); Manuf - ceramic discs shaded by the manufacturer at block formation (IPS e.max ZirCAD MT A2); Brush - unshaded ceramic disc pigmented in the pre-sintered stage using a brush; Stain - unshaded ceramic disc pigmented in the post-sintering stage using a stain glaze (shade A2); Brush + Stain - combination of Brush and Stain techniques. The specimens were sintered and analyzed by a spectrophotometer (VITA Easyshade) for color differences (ΔE00 calculated according to CIEDE, 2000) to ensure that they present the same perceived color (ΔE00 ≤ 1.77, acceptability threshold). The specimens (n = 15) were submitted to biaxial flexural fatigue testing using a cyclic fatigue method (frequency of 20 Hz; 10,000 cycles per step; initial stress of 200 MPa; and step-size of 25 MPa) until specimen fracture. Fatigue strength (FS) and number of cycles until failure (CFF) were recorded with statistical purposes. Fractographic, complementary topography, elemental and roughness analyses were performed. The Ctrl shown the highest FS, CFF, and survival rates compared to the other conditions (p < 0.05), being only statistically similar to Brush. Stain showed the lowest FS, CFF and survival rates (p < 0.05). The Manuf and Brush + Stain shown intermediary performance. In regards of Weibull moduli, Brush shown the lowest values (lowest structural reliability), for both FS and CFF, being only statistically similar to Manuf. Topography analysis shown a uniform size of zirconia crystals in Ctrl, Manuf and Brush. In addition, a smooth glassy surface with some spots of impregnated pigment was observed in the groups where glaze was applied (Stain and Brush + Stain). This finding was corroborated by elemental analysis. Despite that, Stain and Brush + Stain presented the roughest surface (p < 0.05). In summary, the pigmentation techniques used to provide a Vita classical A2 color shade have a detrimental effect on the mechanical fatigue properties of a 4YSZ ceramic, except for the technique performed with the brush in the block pre-sintering stage. Despite this, the brush technique presents great variability in mechanical performance, resulting in lower structural reliability.

Does adhesive luting promote improved fatigue performance of lithium disilicate simplified crowns?

The present study aimed to determine the influence of adhesive luting on the fatigue mechanical properties of simplified lithium disilicate crowns luted to dentin analogues preparations, and to compare two different approaches of simulation of a non-adhesive luting procedure. To this end, 30 prosthetic preparations of glass fiber-filled epoxy resin used as dentin analogues were milled and lithium disilicate crowns were pressed (1.5 mm thickness), which were allocated into three different groups: resin cement (RC), resin cement isolated by paraffin oil (RCI) and zinc phosphate cement (ZP). For luting procedures, the ceramic crowns of the RC and RCI groups had their internal surface treated with 5% hydrofluoric acid and universal primer. Afterwards, a thin layer of paraffin oil was applied onto the ceramic crown intaglio surface in the RCI group. The dentin analogues were treated with 10% hydrofluoric acid, followed by primer application and luting as recommended by the manufacturer. No previous surface treatments were performed for the ZP group, and the cement was applied as recommended. The fatigue test was run under cyclic fatigue (load 400-2000 N, step-size 100 N, 15,000 cycles/step, frequency 20 Hz) until failure detection (radial crack) by transillumination. The fatigue failure load (FFL), number of cycles until failure (CFF), and survival rate in each testing step were recorded. The RC group presented a higher FFL, CFF and survival rate compared to the other groups (p < 0.001), which were statistically equal to each other (p > 0.05). Weibull analysis detected no difference between groups for the Weibull module. Therefore, loss of adhesion between the evaluated substrates induces a significant reduction in load-bearing capacity under fatigue of the lithium disilicate crowns, strengthening the strong-importance of long-lasting adhesion for crown's survival. In addition, different methods for the simulation of non-adhesive conditions induce the same performance in the explored outcomes, confirming that both are valid approaches for laboratory studies.

Pre-sintering pigmentation techniques do not affect the fatigue behavior of adhesively luted 4YSZ restorations.

This study aims to characterize the effect of shading techniques on the fatigue behavior of a 4YSZ ceramic (4 mol% yttrium stabilized zirconia) adhesively bonded to a dentin analogue (fiber-reinforced epoxy resin). 4YSZ ceramic discs (IPS e.max ZirCAD, Ø = 10 mm and 1 mm of thickness) were allocated according to the factor 'shading technique' into 4 groups: Brush- unshaded ceramic disc (IPS e.max ZirCAD BL) pigmented at the pre-sintered stage with pigment solution applied manually using a round liner brush; Immersion- unshaded ceramic disc pigmented through immersion in the solution for 1 s on only one side of the ceramic disc; Manufacturer- specimens already shaded by the manufacturer (IPS e.max ZirCAD MT A2 - Manufacturer group); Control- a control condition with absence of pigment (i.e. non-pigmented specimens). The specimens were sintered and a spectrophotometer (SP60, EX- Rite) was used to ensure that the same perceived color (i.e. pigment saturation) was achieved in the different shading strategies (Manufacturer, Brush or Immersion groups). To do so, the color differences (ΔE00) were calculated using the CIEDE 2000 equation; and an ΔE00 of up to 1.77 was considered as an acceptability threshold. Dentin analogue discs were obtained (Ø = 10 mm and 2.5 mm of thickness) and randomly allocated into pairs with the 4YSZ ceramic discs. Next, the pairs were adhesively bonded using a resin cement (Multilink N). The bonded assemblies (n = 15) were tested for fatigue using the step-stress test method (frequency of 20 Hz; 10,000 cycles per step, initial load 200 N; step-size of 100 N, up to 700 N; and after, step-size of 50 N, until specimen failure/fracture or radial cracks). Fatigue failure load (FFL) and number of cycles for failure (CFF) were recorded for statistical analysis. Fractographic features were accessed, and complementary roughness, topography, grain size and phase content analyses were performed. No statistical differences were observed in the fatigue behavior among the non-shaded condition (Control group - 880 N) and the shaded specimens (Manufacturer - 887 N, Brush - 820 N, and Immersion - 850 N groups; p > 0.05). However, the use of a brush shading technique induced slightly inferior fatigue mechanical behavior of the restorative set compared to the specimens already shaded by the manufacturer (p = 0.027). No differences in Weibull modulus were observed among the tested groups. The specimens pigmented by the brush technique demonstrated a rougher surface, with statistically higher Rz values, in addition to a larger grain size in comparison to all other conditions (p< 0.05). No m-phase content was identified (only t and c phases were detected). Thus, the shading techniques used to provide a Vita classic A2 shade does not negatively affect the mechanical fatigue properties of a bonded 4YSZ ceramic. However, the brush technique has detrimental effect on the fatigue behavior compared to when the ceramic was already provided in a shaded format by its manufacturer.