Optical properties of recycled zirconia for dental applications.

STATEMENT OF PROBLEM: While waste zirconia can be recycled, whether the optical properties of recycled zirconia match those of commercially available zirconia is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the optical properties of recycled zirconia by assessing its color, translucency, and opalescence across different thicknesses and shades. MATERIAL AND METHODS: Sixty specimens were prepared from 3 mol% yttria-stabilized tetragonal zirconia polycrystal blocks (Lava Plus; 3M ESPE) (group C); 60 other specimens were prepared from waste blocks of the same zirconia (group R). The specimens were further categorized into 4 subgroups (n=15) based on their thicknesses (1.0 mm or 1.5 mm) and shades (A1 or A3). Specimen color was measured with a spectrophotometer (Easyshade Advance 4.0; Vita ZahnFabrik). The parameters of color difference (ΔE00), translucency (TP), contrast ratio (CR), and opalescence (OP) were calculated. Grain size analysis was performed using scanning electron microscopy. Data were analyzed with analysis of variance (ANOVA) (α=.05). RESULTS: Significant differences in translucency and opalescence were observed between groups C and R in all specimens (P<.001). Group R exhibited a range of TP (4.89 to 11.27), CR (0.74 to 0.91), and OP (3.36 to 8.65) values. The ΔE00 values between groups C and R ranged from 13.99 to 21.31. Both thickness and shade significantly affected the ΔE00 values (P<.001). The grain size in group C was not significantly different from that in group R (F=0.364, df=1, P=.555). The TP and OP values of group R decreased with increasing thickness (P<.001). CONCLUSIONS: Recycled zirconia was less translucent and opalescent than commercially available zirconia. The color difference between commercially available and recycled zirconia exceeded the acceptable threshold, even when using the same staining procedure. Recycled zirconia exhibited reduced translucency and opalescence with increasing thickness.

Bonding affinity and durability of recycled zirconia.

STATEMENT OF PROBLEM: While repurposing waste materials into zirconia blocks presents a promising avenue, uncertainty remains regarding whether the bonding properties of recycled zirconia align with those of commercially available zirconia. PURPOSE: The purpose of this in vitro study was to evaluate the bonding affinity and durability of composite resin to recycled zirconia. MATERIAL AND METHODS: A series of processing steps were performed with recycled zirconia residuals (Lava Plus; 3M Oral Care), including pulverization, sieving, heating, compaction, isostatic pressing, and presintering. The presintered blocks of recycled zirconia (Group R) and commercially available zirconia (Group C) were sectioned and sintered to create test specimens (10×10×1.5 mm). After polishing and airborne-particle abrasion, specimens within each group were bonded to composite resin cylinders using a resin cement (Multilink Speed; Ivoclar AG). The specimens were then divided into 3 subgroups for shear bond strength (SBS) testing: no further treatment, 10 000 thermocycles, and 30 000 thermocycles (n=10). X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), surface roughness, and contact angle were used to analyze the surface physicochemical differences between Groups C and R. Data were analyzed with 2-way ANOVA followed by the Tukey post hoc test for SBS values, Pearson chi-squared test for failure modes, and independent t test for grain size, surface roughness, and wettability (α=.05). RESULTS: No significant difference was found in the SBS values between Group R and Group C (P=.403), while thermocycling significantly affected the SBS values (P<.05). Group R showed significantly greater Ra, Rz, and Rq values (P<.05) than did Group C. SEM analysis revealed that Group R exhibited more prominent grooves than Group C, while the XRD and EDS patterns exhibited similarities in both the crystalline phase and elemental composition. No significant difference was observed in the water contact angle between the 2 groups (P=.196). CONCLUSIONS: The bonding protocol established for commercially available zirconia was comparable with that of recycled zirconia, but both decreased after thermocycling. The recycling process did not affect the crystalline phase or elemental composition of the zirconia, but it induced alterations in the surface roughness.

Effects of Cathepsin K Inhibitors on Dentin Erosion: An in vitro Study.

Cathepsin K (catK) modulates the degradation of dentin collagen. This study aimed to evaluate the effects of catK inhibitors on dentin erosion. Dentin beams were eroded (4 times/d for 5 days) and immersed in deionized water (negative control), 0.1 M NaCl, 0.3 M NaCl, 0.5 M NaCl, or 1 µm odanacatib (each n = 16) for 30 min after each erosive challenge. Erosive dentin loss (EDL) and demineralized organic matrix (DOM) thickness were evaluated profilometrically. Additionally, dentin beams were demineralized, immersed in the respective solutions for 30 min each (n = 5), and then incubated in artificial saliva for 5 days. Dentin collage degradation was evaluated by quantifying the levels of the C-terminal peptide of type I collagen (CTX), C-terminal cross-linked telopeptide of type I collagen (ICTP), and hydroxyproline (HYP) in the incubation media. Significantly lower EDL and dentin collagen degradation (CTX, ICTP, and HYP) and thicker DOM layers were observed in the samples treated with 0.3 m NaCl and 1 µm odanacatib than in those treated with deionized water (all p < 0.05). The samples treated with 1 µm odanacatib showed significantly lower levels of CTX and HYP than those treated with 0.3 M NaCl (all p < 0.05). The present findings support the potential use of catK inhibitors in controlling dentin erosion.

Er:YAG laser settings for debonding zirconia restorations: An in vitro study.

This in vitro study aimed to determine the optimal frequency and energy settings for debonding zirconia restorations using an erbium-doped yttrium aluminum garnet (Er:YAG) laser. A total of 200 zirconia specimens (5 mm × 5 mm × 1.5 mm) were fabricated from two types of materials: (1) 3 mol% yttria oxide stabilized tetragonal zirconia polycrystalline (3Y-TZP) and (2) 5 mol% yttria oxide stabilized tetragonal zirconia polycrystalline (5Y-TZP). The zirconia specimens were bonded to dentin using resin cement (RelyX Ultimate, 3 M) and divided into 20 groups based on their laser treatments (n = 5). Er:YAG laser treatment was applied at various frequencies (10 Hz and 20 Hz) and energies (80 mJ, 100 mJ, 120 mJ, 140 mJ, 160 mJ, 180 mJ, 200 mJ, 220 mJ, 240 mJ, and 260 mJ). The time required to debond the specimens and the temperature changes that dentin underwent during the laser treatment were recorded. The surface morphologies of the debonded dentin and zirconia specimens were observed using scanning electron microscopy (SEM). Additional zirconia specimens were fabricated for 4-point flexural strength testing and surface roughness measurements. Statistical analyses were conducted using three-way analysis of variance (ANOVA) and Student-Newman-Keuls (SNK)-q tests (α = 0.05). The debonding time of each specimen varied between 4.8 and 160.4 s, with an average value of 59.2 s. The dentin temperature change for each specimen ranged from 2.3 to 3.6 °C, with an average value of 2.7 °C. The debonding time was significantly influenced by the zirconia material type and laser energy, but it was not affected by the laser frequency. Among the specimens, those made of 3Y-TZP needed significantly more time for debonding than 5Y-TZP. The optimal energies were 220 mJ for 3Y-TZP and 200 mJ for 5Y-TZP. The laser frequency, laser energy, and type of zirconia material had no effect on the dentin temperature change. Additionally, no surface alternations were observed on the dentin or zirconia materials after laser treatment. The surface roughness and flexural strength of the zirconia materials remained unchanged after laser treatment. In summary, Er:YAG laser treatment effectively and safely removes zirconia restorations without impacting their mechanical properties, with a safe temperature change of less than 5.6 °C. The optimum frequency and energy settings for debonding 3Y-TZP and 5Y-TZP restorations were found to be 10/20 Hz and 220 mJ and 10/20 Hz and 200 mJ, respectively.

15-Methacryloyloxypentadecyl Dihydrogen Phosphate Improves Resin-to-Zirconia Bonding Durability.

PURPOSE: To investigate the bond durability of composite cement to zirconia after treatment with a 15-methacryloyloxypentadecyl dihydrogen phosphate (15-MPDP)-containing adhesive and 2 commercially available adhesives. MATERIALS AND METHODS: Ninety zirconia bars were fabricated and bonded to prepolymerized resin composite cylinders with a composite cement after surface treatment for 20 s using the following adhesives: Adper Easy One (AEO, negative control), Single Bond Universal (SBU, positive control), and 10 wt% 15-MPDP powder mixed with Adper Easy One (15- MPDP). After storage in distilled water at 37°C for 24 h, the specimens were divided into 3 subgroups according to the aging treatment applied (n = 10): no aging treatment (0/TC), 10,000 thermocycles (1/TC), and 37,500 thermocycles (3/TC). Shear bond strength (SBS) was analyzed using two-way ANOVA (p < 0.05), and the fracture surfaces were examined under a dental microscope. RESULTS: Significant differences in the SBSs among the surface treatments and aging treatments were observed (both p < 0.001). The 15-MPDP and SBU groups showed significantly higher SBSs than the AEO group, whereas similar SBSs were found in the 15-MPDP and SBU groups. Significant reductions in the SBSs were found after 37,500 thermocycles (p < 0.001), although no significant difference between specimens aged with 10,000 thermocycles and non-aged specimens was observed. CONCLUSIONS: The 15-MPDP-containing dental adhesive exhibited bond durability comparable to that of a well-established 10-MDP-containing universal adhesive. Aging by 10,000 thermocycles may be insufficient to disrupt the bond of composite cement to zirconia.

Effect of quercetin pretreatment on the immediate and aged bond strength of bleached dentin.

This in vitro study aimed to investigate the effect of quercetin pretreatment on the bond strength of bleached dentin. Human dentin blocks (2 × 2 × 1 mm) were prepared and randomly divided into 5 groups (n = 16): deionized water pretreatment + no bleaching treatment (DNB); deionized water pretreatment + bleaching treatment (DYB); 75 µg/mL quercetin pretreatment + bleaching (Q75B); 150 µg/mL quercetin pretreatment + bleaching (Q150B); and 300 µg/mL quercetin pretreatment + bleaching (Q300B). The surfaces of superficial dentin (bonding surfaces) were treated with the respective solutions for 2 min, and then the surfaces opposite to the bonding surfaces (near pulp, bleaching surfaces) were subjected to bleaching treatment with 40% hydrogen peroxide (Ultradent, USA) for two 15-min sessions (groups DYB, Q75B, Q150B, and Q300B). After the bleaching procedure, the bonding surfaces were bonded with resin cements (Panavia V5, Kuraray, Japan). The bonded specimens were then divided into 2 subgroups (n = 8): the aging group (subgroup T), which was subjected to 10,000 thermocycles, and the nonaging group (subgroup N), which was not subjected to thermocycling. The microshear bond strength (µSBS) was obtained using a universal testing machine (AGS-X, Shimadzu, Tokyo, Japan). Additional dentin blocks (5 × 5 × 1 mm) were prepared and treated the same as the groups DYB, Q75B, Q150B, and Q300B (n = 8) to evaluate the color change, defined as groups CCDYB, CCQ75B, CCQ150B, and CCQ300B, respectively. Color evaluation was performed using a spectrophotometer (Vita Easyshade Advance 4.0, Vident, USA) to obtain a baseline and again at the end of the bleaching treatment. The data were analyzed via two-way analysis of variance (ANOVA) and Tukey's post-hoc test (α = 0.05). For the immediate bond strength, the specimens in the groups Q75B, Q150B, and Q300B showed significantly higher µSBS values than those in the group DYB (all P < 0.05). No significant differences in the µSBS values were found among the groups Q75B, Q150B, Q300B, and DNB, respectively (all P > 0.05). For the aged bond strength, both the groups Q150B and Q300B exhibited significantly higher µSBS values than groups DYB and DNB (all P < 0.05), whereas no significance differences were found between groups Q150B and Q300B (P = 1.00) or between the groups DYB and DNB (P = 1.00). No significant differences were observed in the △E values among all the groups tested (P = 0.80). Therefore, the application of quercetin for 2 min prior to the bleaching procedure preserved the immediate bond strength and improved the aged bond strength of bleached dentin while maintaining the effectiveness of bleaching.

Erosion of CAD/CAM restorative materials and human enamel: An in vitro study.

This in vitro study used the same frequency and duration of acid contact as a previous in situ/in vivo study to evaluate the effect of erosion on CAD/CAM restorative materials and human enamel and to compare the effects of in vitro and in situ/in vivo acid challenges on CAD/CAM restorative materials and human enamel. The CAD/CAM restorative materials (IPS e.max CAD, Lava Ultimate, and PMMA block) and human enamel were eroded by immersion in 150 ml of cola drink for 14 days (4 × 5 min/day). The surface microhardness and surface roughness of the specimens were measured at baseline (T1), day 7 (T2), and day 14 (T3). The substance losses were measured at T2 and T3. The data were statistically analyzed using repeated measures ANOVA and Bonferroni's test (α = 0.05). Erosion significantly decreased the surface microhardness of the CAD/CAM restorative materials and human enamel (all P < 0.001). The overall percentage of surface microhardness loss (%SMHl) of the PMMA block and enamel due to in vitro erosion was significantly higher than that due to in situ/in vivo erosion (P = 0.02 and P < 0.001, respectively). Consistent with in situ/in vivo erosion, the surface roughness and profile of the tested restorative materials remained unchanged after in vitro erosion. A significant increase in the surface roughness and substance loss was observed for enamel after in vitro erosion (all P < 0.001). The overall substance loss of enamel due to in vitro erosion was significantly higher than that due to in situ/in vivo erosion (P < 0.001). In conclusion, erosion decreased the surface microhardness of the CAD/CAM restorative materials and human enamel. Moreover, erosion negatively influenced the substance loss and surface roughness of human enamel. For the substance loss of enamel and %SMHl of PMMA block and enamel, the in vitro erosive effects were approximately 1-2 times greater than the in situ/in vivo effects. However, for the surface roughness and profile of the CAD/CAM restorative materials, no significant difference was found between in vitro and in situ/in vivo erosion.