Investigating the Effect of Different Surface Treatments on Vickers Hardness and Flexural Strength of Zirconium and Lithium Disilicate Ceramics

Comprehensive Evaluation of Titanium, Zirconia, and Ceramic Dental Implant Materials: A Comparative Analysis of Mechanical and Esthetic Properties

BACKGROUND

Dental implant materials play a pivotal role in the success of restorative dentistry. This study comprehensively compares the mechanical and esthetic properties of three commonly used dental implant materials: titanium, zirconia, and ceramic.

OBJECTIVE

This study aimed to provide insights into the suitability of titanium, zirconia, and ceramic for various clinical applications within implant dentistry.

METHODS

Ninety dental implants, 30 for each material, were selected based on their well-established usage in dental implantology. Mechanical properties, including tensile strength, modulus of elasticity, and fatigue resistance, were assessed using state-of-the-art testing machines. Esthetic properties, such as color stability and translucency, were scrutinized through immersion in staining solutions and spectrophotometer measurements. Fracture properties and biocompatibility were also evaluated.

RESULTS

Mechanical testing revealed that titanium exhibited the highest tensile strength (810 ± 55 MPa), while zirconia demonstrated the highest modulus of elasticity (208 ± 8 GPa). Titanium also displayed the greatest fatigue resistance (1,010,000 ± 95,000 cycles), whereas zirconia had the highest hardness (1190 ± 45 Vickers hardness number (VHN)). Esthetically, zirconia showed superior color stability (ΔE: 1.7 ± 0.2), while ceramic exhibited the highest translucency (TP%: 15.3 ± 1.7). Zirconia presented the lowest surface roughness (0.28 ± 0.04 μm).

CONCLUSION

This study provides insights into potential dental implant material performance, with zirconia emerging as a promising alternative. Future research should validate these findings in clinical settings, considering a broader array of variables and long-term outcomes.

Mechanical properties of additively manufactured zirconia with alumina air abrasion surface treatment

This study aimed to evaluate the mechanical properties of zirconia fabricated using additive manufacturing technology and compare them to those of zirconia fabricated using subtractive manufacturing technology. Sixty disc-shaped specimens were fabricated for the additive (n = 30) and subtractive manufacturing groups (n = 30), and each group was divided into two subgroups according to their air-abrasion surface treatment: control (n = 15) and air-abrasion groups (n = 15). Mechanical properties including the flexural strength (FS), Vickers hardness, and surface roughness were determined, and the values were analyzed by one-way ANOVA and Tukey's post hoc test (α = 0.05). X-ray diffraction and scanning electron microscopy were used for phase analysis and surface topography evaluation, respectively. The SMA group exhibited the highest FS (1144.97 ± 168.1 MPa), followed by the SMC (944.58 ± 141.38 MPa), AMA (905.02 ± 111.38 MPa), and AMC groups (763.55 ± 68.69 MPa). The Weibull distribution showed the highest scale value (1213.55 MPa) in the SMA group, with the highest shape value in the AMA group (11.69). A monoclinic peak was not detected in both the AMC and SMC groups, but after air abrasion, the monoclinic phase content ([Formula: see text]) reached 9% in the AMA group, exceeding that in the SMA group (7%). The AM groups exhibited statistically lower FS values than those of the SM groups under the same surface treatment (p < 0.05). Air-abrasion surface treatment increased the monoclinic phase content and FS (p < 0.05) in both the additive and subtractive groups, while it increased the surface roughness (p < 0.05) only in the additive group and did not affect the Vickers hardness in either group. For zirconia manufactured using additive technology, the mechanical properties are comparable to those of zirconia manufactured using subtractive technology.

Effect of acidic media on flexural strength and fatigue of CAD-CAM dental materials

OBJECTIVE

To investigate the effect of acidic media, including beverages and gastric fluids on flexural strength and fatigue of CAD-CAM materials.

METHODS

Four CAD-CAM materials (high-translucency zirconia (Ceramill Zolid HT+), lithium disilicate (IPS e-max CAD), hybrid ceramic (Vita Enamic), and nanohybrid resin composite (Grandio Blocs) were prepared and immersed in one of five media (gastric HCl, white wine, Coca-Cola, orange juice, and artificial saliva) in an incubator (37 ℃, 24 h). Surface topography and roughness were obtained using a scanning electron microscope (SEM) and a stylus contact profilometer, respectively. Initial 3-point flexural strength was measured for half of the bars (n = 20/gp) using a universal testing machine (0.5 mm/min). The other bars underwent 10⁶ cyclic fatigue loadings before measurement of residual 3-point flexural strength. Data were statistically analyzed (two-way and three-way ANOVA, Tukey's post-hoc, p < 0.05). Weibull distributions were plotted for reliability analysis.

RESULTS

Zirconia bars has the highest initial flexural strengths followed by lithium disilicate, while resin composite and hybrid ceramic groups had the lowest strength regardless of the erosive medium. Cyclic fatigue significantly reduced initial flexural strengths for all materials except for hybrid ceramic and resin composite. Weibull moduli were the highest for zirconia, lithium disilicate and resin composite and lowest for hybrid ceramic.

SIGNIFICANCE

Erosive media significantly changed surface roughness of CAD-CAM materials except for zirconia and resin composite without jeopardizing the flexural strength of the CAD-CAM materials. Despite the higher flexural strengths for zirconia and lithium disilicate, resin composite and hybrid ceramic were more resistant to cyclic fatigue.

Lithium disilicate and ZLS glass-ceramics for CAD/CAM dental restorations. Biocompatibility, mechanical and microstructural properties after crystallization.: Microstructure and Properties of Glass Ceramics for CAD/CAM Applications

OBJECTIVES

The objective of this study was to define the impact of heating rate on the crystal growth, the mechanical properties, and the biocompatibility of three different kinds of CAD/CAM glass-ceramics treated with a conventional furnace.

METHODS

Lithium disilicate (IPS EMax-CAD, Ivoclar Vivadent) (LS₂) and two zirconia reinforced lithium silicate (ZLS) ceramics (Vita Suprinity PC, VITA Zahnfabrik; Celtra Duo, Dentsply Sirona) (ZLSS; ZLSC) were used. The mechanical properties and the crystal growth were evaluated on 42 specimens (n=14 per group). The thermal treatments recommended by the manufacturers were carried out. All groups were tested for fracture toughness (Ft) and Vickers hardness (Hv). Scanning electron microscope (SEM) images were taken after a slight surface etching with hydrofluoric acid solution (1% for 20 sec). Differential Thermal Analysis (DTA) was performed and cellular adhesion with human periodontal ligament stem cells (hPDLSCs) culture was qualitatively assayed. Data were analysed with Repeated Measurements ANOVA and ANOVA followed by Tukey post hoc test.

RESULTS

The crystals' mean size (±SD) after heat treatment was 1650.0 (±340.0) nm for LS₂, 854.5 (±155.0) nm for ZLSS and 759.9 (±118.4) nm for ZLSC (p<0.05 among the groups). As consequence of crystallization, the Hv was 6.1±0.3 GPa for LS₂, 7.6±0.7 GPa for ZLSS and 7.1±0.5 GPa for ZLSC (p<0.05 for LS₂ vs ZLSS and ZLSC), while the Ft was 2.2±0.1 MPa m^1/2 for LS₂, 4.7±0.8 MPa m^1/2 for ZLSS and 3.8±0.6 MPa m^1/2 for ZLSC (p<0.05 among the groups). The DTA curves showed a crystallization process for LS₂, ZLSS and ZLSC at a temperature range 810°C to 840°C. The amount of adherent hPDLSCs was superior on LS₂ than on ZLS.

CONCLUSIONS

All the CAD/CAM materials can be properly crystallized if heat treated following the manufacturers' instructions. The crystallization process highly depends on temperature. ZLS glass ceramics show significantly inferior crystals dimensions and higher fracture toughness and Vickers hardness than LS₂ ceramic. hPDLSCs cultured on LS₂ have a superior adhesion than those cultured on ZLS.

CLINICAL SIGNIFICANCE

The clinical interest of this study relies on the demonstration that a proper heat-treatment of CAD/CAM lithium disilicate and ZLS glass ceramics generates products that are suitable for clinical service. The differences highlightable in mechanical properties and biocompatibility behaviour do not affect their successful clinical application.

Phase Transformations and Subsurface Changes in Three Dental Zirconia Grades after Sandblasting with Various Al2O3 Particle Sizes

Although sandblasting is mainly used to improve bonding between dental zirconia and resin cement, the details on the in-depth damages are limited. The aim of this study was to evaluate phase transformations and subsurface changes after sandblasting in three different dental zirconia (3, 4, and 5 mol% yttria-stabilized zirconia; 3Y-TZP, 4Y-PSZ, and 5Y-PSZ). Zirconia specimens (14.0 × 14.0 × 1.0 mm³) were sandblasted using different alumina particle sizes (25, 50, 90, 110, and 125 µm) under 0.2 MPa for 10 s/cm². Phase transformations and residual stresses were investigated using X-ray diffraction and the Williamson-Hall method. Subsurface damages were evaluated with cross-sections by a focused ion beam. Stress field during sandblasting was simulated by the finite element method. The subsurface changes after sandblasting were the emergence of a rhombohedral phase, micro/macro cracks, and compressive/tensile stresses depending on the interactions between blasting particles and zirconia substrates. 3Y-TZP blasted with 110-µm particles induced the deepest transformed layer with the largest compressive stress. The cracks propagated parallel to the surface with larger particles, being located up to 4.5 µm under the surface in 4Y- or 5Y-PSZ subgroups. The recommended sandblasting particles were 110 µm for 3Y-TZP and 50 µm for 4Y-PSZ or 5Y-PSZ for compressive stress-induced phase transformations without significant subsurface damages.

Effect of guide sleeve material, region, diameter, and number of times drills were used on the material loss from sleeves and drills used for surgical guides: An in vitro study

STATEMENT OF PROBLEM

How material loss from sleeves and drills is affected when different guide sleeve materials and different sizes of implant drills are used for different regions of surgical guides is unclear.

PURPOSE

The purpose of this in vitro study was to compare the amount of material loss from different guide sleeves (zirconia and cobalt-chromium) and drills of different diameters during osteotomy preparation in different regions.

MATERIAL AND METHODS

Three tooth-supported surgical guides with sleeve holes positioned in the first premolar and second molar sites were prepared. Guide sleeves (Ø 2.20 mm, 3.40 mm, and 4.05 mm) were milled from zirconia (n=60) and cobalt-chromium (n=60) blocks. A total of 12 titanium nitride-coated stainless steel twisted drills (n=6 per sleeve material) of different diameters (Ø 2.00, 3.20, 3.85 mm) were used with corresponding sleeves during the drilling. The weight loss from the drills and the volume loss from the guide sleeves after drilling were analyzed by using multiple linear mixed effect models (α=.05).

RESULTS

According to the 4-way ANOVA for volume loss from sleeves, no significant interaction was found among the 4 main effects (number of times a drill was used, region, diameter, and material), but interactions between the number of times a drill was used and diameter (P=.001) and between the number of times the drill was used and material were significant (P<.001). For weight loss from the drills, a significant interaction was detected between the number of times the drill was used and diameter (P=.024).

CONCLUSIONS

Less sleeve material was lost when zirconia sleeves were used. All sleeves had more material loss in the molar region than in the premolar region. The diameter had varying effects on the amount of material loss from drills and sleeves. The sleeve material and the region did not affect the material loss from drills.

Influence of surface treatments and cyclic fatigue on subsurface defects and mechanical properties of zirconia frameworks

OBJECTIVES

To evaluate the effect of laser fused and air abraded fluorapatite particles on flexural strength σf and fracture toughness (K_IC) of Yttria tetragonal zirconia polycrystal (Y-TZP).

METHODS

160 polished Y-TZP bars received one of the following surface treatments: airborne particle abrasion (APA) with fluorapatite glass-ceramics (FGC), APA with tribochemical silica-coated alumina (CoJet), laser fused FGC using Nd:YAG Laser (FGC + Laser), while as-sintered polished specimens served as control. Initial flexural strength σfI was measured to half of the specimens, while the rest underwent cyclic fatigue (1,000,000 cycle of 15N load and 3 s contact time) followed by measuring residual flexural strength σfR. Fractographic analysis was performed and K_IC was calculated. The effect of surface treatment and fatigue on flexural strength was statistically analysed using 2-way ANOVA (α = 0.05). Weibull probability was measured to assess the reliability of flexural strength.

RESULTS

The highest σf before or after the fatigue was reported for the control group while the lowest was for FGC + Laser group. Cyclic fatigue significantly decreased the flexural strength of all groups except for FGC + Laser group. There was no significant difference between the K_IC between the control and FGC groups, however, a significant reduction of K_IC was found in the CoJet group, while FGC + Laser reported the significant lowest value compared to all groups (P = 0.00).

SIGNIFICANCE

Fluorapatite glass-ceramic powder offers a promising alternative for particle abrasion of zirconia-based frameworks.

Effects of laser debonding treatment on the optical and mechanical properties of all-ceramic restorations

The objective of this study was to evaluate how erbium-doped yttrium aluminium garnet (Er:YAG) laser debonding treatment affects the optical and mechanical properties of dental ceramics. In total, 120 rectangular (22*5*1.2 mm) IPS E.max Press specimens were fabricated and divided into 4 groups: the control group, 3 W laser group, 4 W laser group, and 5 W laser group. For each group, 10 specimens were used for the colour test (colour difference (△E) and transparency parameter (TP)), 10 specimens were used for the flexural strength test, and 10 were used for the Vickers hardness test. One random sample from each colour test specimens was observed by scanning electron microscopy (SEM). The L*, a*, b*, △E, TP, flexural strength, and Vickers hardness values were measured and calculated. According to the Kruskal-Wallis test, the L*, a*, and b* values showed no significant variations (P > 0.05), except for the b* value in the 5 W laser group (P < 0.05). The △E, TP, flexural strength, and Vickers hardness values were analysed by one-way analysis of variance (ANOVA). The 5 W laser group exhibited a higher △E value, which exceeded the perceptible threshold and significantly lower TP values than the other groups (P < 0.05). The mean flexural strength and Vickers hardness values after Er:YAG laser debonding revealed no significant changes (P > 0.05). Microcracks were detected during the SEM analysis of the 5 W laser group. Er:YAG laser debonding treatment did not affect the mechanical properties, but changed the optical properties of dental ceramics.