Simulated clinical adjustment and intra-oral polishing of two translucent, monolithic zirconia dental ceramics: An in vitro investigation of surface roughness

Comparative effects of glazing versus polishing on mechanical, optical, and surface properties of zirconia ceramics with different translucencies

OBJECTIVES

This study compared the effects of glazing versus polishing on mechanical, optical, and surface properties of zirconia ceramics with different translucencies.

MATERIALS AND METHODS

In this in vitro study, 120 bar-shaped specimens (25 × 4 × 1.2 mm) were fabricated from three different types of zirconia with different translucencies (n = 40, DD Bio ZW, ZX2, and Cube X2). After sintering, each zirconia group was randomly divided into five subgroups of control (glazing), glazing + bur abrasion, glazing + bur abrasion + polishing with EVE Diacera® kit, glazing + bur abrasion + reglazing, and glazing + bur abrasion + polishing with EVE Diacera® kit + reglazing. The specimens underwent surface roughness, hardness, flexural strength, and translucency tests, as well as X-ray diffraction (XRD) and scanning electron microscopy (SEM) for assessment of surface topography. Data were analyzed by one-way analysis of variance, Tukey test, and Pearson test (α = .05).

RESULTS

Flexural strength, surface hardness, and translucency were significantly correlated with zirconia type. ZW zirconia had significantly higher flexural strength and surface hardness and significantly lower translucency than Cube X2 and ZX2 (p < .001). Surface roughness had no significant correlation with zirconia type (p = .274). Polishing created the smoothest, and bur abrasion created the roughest surface (p < .001). Flexural strength and hardness in most experimental groups were significantly lower than in the control group (p < .001). Translucency was not significantly different in bur abrasion and polishing groups, compared with the control group; however, reglazing significantly increased the translucency (p < .001). SEM micrographs confirmed the surface roughness results. XRD showed monoclinic phase only in reglazed groups.

CONCLUSION

Of different surface treatments, polishing improved the surface properties and caused the smallest change in mechanical properties of zirconia with different translucencies.

Dimensional accuracy, mechanical property, and optical stability of zirconia orthodontic bracket according to yttria proportions

This in vitro study evaluated comprehensively the performances of zirconia brackets with varying yttria proportions in manufacturing advanced orthodontic brackets. Three experimental groups of zirconia brackets were fabricated using yttria-stabilized zirconia (YSZ) materials with different yttria proportions-3 mol% yttria (3Y-YSZ), 4 mol% yttria (4Y-YSZ), and 5 mol% yttria (5Y-YSZ) (Tosoh Ceramic, Japan). A polycrystalline alumina ceramic bracket (3M™ Clarity™ Advanced, MBT 0.022-in. slot) was employed as the control group. Morphological properties, including slot surface structure and dimensions, were examined using scanning electron microscopy and surface profiler analysis. Manufacturing accuracy was assessed with root mean square calculations of trueness and precision. Mechanical properties were tested, encompassing static and kinetic frictional resistance (FR) and fracture strength. Optical stability was evaluated through 20,000 cycles of thermocycling and a 7-day immersion in various coloring agents. Within the limitations of this study, zirconia brackets containing 3 to 5 mol% YSZ presented enhanced reliability in terms of dimensional accuracy and demonstrated favorable optical stability. Notably, owing to its advantageous mechanical properties, the 3Y-YSZ variant showed remarkable potential as an advanced material for fabricating orthodontic brackets.

Surface Roughness and Hardness of CAD/CAM Ceramic Materials after Polishing with a Multipurpose Polishing Kit: An In Vitro Study

OBJECTIVE

 This article evaluates the effect of multipurpose polishing kit on surface roughness and hardness of three computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic materials at different polishing durations. Weight changes of the polishing bur were also determined.

MATERIAL AND METHODS

 Three CAD/CAM ceramic materials were lithium disilicate glass ceramic (IPS e.max CAD), translucent zirconia (VITA YZ), and zirconia-reinforced lithium disilicate ceramic (Celtra Duo). Ceramics were ground with a diamond bur, and polished with the multipurpose polishing kit (Eve Diacera HP), which comprises coarse and fine polishing burs. Surface roughness value (Ra) was measured using a noncontact optical profilometer (n = 10 per group) after grinding and every 15 seconds of coarse and fine polishing until 60 seconds. The complete polishing Ra was compared with the lab as-received specimens and human enamel. Surface morphology was examined using a scanning electron microscope after 60-second coarse and fine polishing and compared with the lab as-received specimens. Hardness was measured using a Vickers hardness tester on the lab as-received specimens and after the final polishing process (n = 4 per group). Changes in surface roughness and polishing bur weight of each material were analyzed using one-way repeated-measures analysis of variance (ANOVA) and dependent t-test. One-way ANOVA was used to detect differences in surface roughness, Vickers hardness, and bur weight among materials within the same polishing duration (α = 0.05).

RESULTS

 From grinding to complete polishing, the greatest Ra reduction was found in VITA YZ, followed by Celtra Duo and IPS e.max CAD. Final Ra values of all ceramics after 60-second fine polishing were not significantly different, and were similar to that of enamel and lab as-received specimens. Vickers hardness of ceramic materials did not change after grinding and polishing. Coarse polishing bur demonstrated the highest weight loss after polishing VITA YZ, followed by Celtra Duo and IPS e.max CAD.

CONCLUSION

 The multipurpose polishing kit reduced surface roughness of CAD/CAM ceramic materials to the similar level of the lab as-received specimen and enamel regardless of material's hardness. The reductions of surface roughness and a coarse polishing bur weight were highest in VITA YZ, followed by Celtra Duo and IPS e.max CAD.

Effectiveness of Porcelain Polishing Methods on the Roughness and Color Stability of CAD-CAM Ceramics after Orthodontic Bracket Debonding

Increased utilization of all ceramic restorations for aesthetic consideration in combination with routine adult orthodontic practice has led to numerous clinical challenges. Obtaining adequate bond strength between the orthodontic bracket and all-ceramic restoration and damage to the ceramic surface during the bracket debonding procedure needs to be better understood. This study analyzed the surface texture and color change of glazed and bracket-debonded ceramic CAD-CAM materials and the efficiency of porcelain polishing systems in restoring surface morphology and color. A total of 30 rectangular test specimens from each lithium disilicate CAD (LD-CAD), polymer-infiltrated ceramic (PICN), zirconia-reinforced lithium silicate glass ceramic (ZLS), and 5YTZP zirconia (5YZP) were prepared. The ceramic samples were embedded within acrylic resin, and baseline surface roughness and color were recorded using an optical profilometer and a reflected color spectrophotometer. The porcelain samples were bonded with lower incisor ceramic brackets. The samples were thermocycled 2000 times between 5 and 55 °C. Afterward, the brackets were peeled with bracket-removing pliers. The resin adhesive from the debonded surface was eliminated with tungsten carbide bur, and samples were randomly divided into three subgroups of (n = 10) to be polished with Diapol-twist (DT), a Keramik-Politur 4313B Komet polishing kit (KK), and a Horico diamond polisher (HDP). The polished surface roughness and color were recorded. The data were statistically analyzed using a two-way analysis of variance at p < 0.05. The debonded porcelain surfaces across the groups displayed significantly higher mean surface roughness (Ra) compared to glazed surfaces. The debonded 5YZP showed the least Ra at 0.661 (0.09), while the highest Ra was recorded by PICN at 4.057 (0.82). All of the polishing systems evaluated in the study significantly reduced the surface roughness. However, they were unsuccessful in regaining the surface topography of the glazed surface. The flexible discs (DT) produced the smoothest surface, followed by the diamond-impregnated rubber points (KK). Unpolished porcelain surfaces had a discernable mean color difference from glazed surfaces. Polished surfaces from the different polishing systems among the all-ceramic groups achieved a clinically acceptable mean color difference. Polishing debonded rough porcelain surfaces is imperative, and flexible discs performed better in all of the tested CAD-CAM ceramic materials.

Effectiveness and safety of bleaching agents on lithium disilicate glass ceramics

Background

Aesthetic expectations have increased the use of aesthetic materials in dentistry. Lithium disilicates are frequently used materials for these expectations. Bleaching is another method used to provide aesthetics. Bleaching processes on restorative materials are not fully known. This study investigated the effect of at-home and in-office bleaching methods on the color change, surface roughness, and topography of lithium disilicate glass-ceramic materials produced with two different techniques and subjected to different polishing procedures.

Methods

A total of 144 disc-shaped pressed and computer-aided design (CAD) lithium disilicate glass-ceramic specimens were randomly divided into four groups. Glazing and three different chair-side polishing procedures were performed. The specimens in each group were randomly divided into two groups and subjected to at-home and in-office bleaching processes (n=9). The home bleaching process was repeated with 16% carbamide peroxide agent for six hours for seven days, while the in-office bleaching process was applied with 40% hydrogen peroxide agent for two sessions of 20 minutes. After the bleaching processes, the final color and surface roughness experiments of the specimens were carried out, and the results were recorded. ANOVA and Tukey multiple comparison tests were used FOR the statistical analysis of the data (α=0.05).

Results

The material*polish*bleaching, polish*bleaching, material*bleaching, and material*polishing interactions were not statistically significant regarding color and roughness changes of both specimens (P>0.05).

Conclusion

Both bleaching processes can be safely applied to lithium disilicate glass-ceramic materials.

Color Changes Associated with Sandblasting, Hydrofluoric Acid Etching, and Er:YAG Laser Irradiation of Milled Feldspathic Porcelain Laminate Veneers

OBJECTIVES

To evaluate color changes in milled feldspathic porcelain laminate veneers following hydrofluoric acid etching (HFA), sandblasting (SB), or Er:YAG laser irradiation (LI).

METHODS AND MATERIALS

Disc-shaped specimens (thickness=1 mm, diameter=8 mm) were milled from feldspathic porcelain blocks (n=40). Glazed specimens were randomly assigned to four subgroups (n=10 each) according to surface treatment: negative control, HFA, SB, and LI. A layer of translucent, light-cured resin cement (thickness=0.1 mm) was then applied following silanization. The color was characterized by the L*, a*, and b* uniform color space (CIE) using a reflection spectrophotometer. CIEDE2000 (ΔE00) was calculated to determine the color difference between each surface treatment and negative control groups. Data were statistically analyzed using analysis of variance (ANOVA), Kruskal-Wallis, and Dunn-Bonferroni post hoc tests.

RESULTS

There were no significant differences in CIEL* and CIEb* coordinates between negative control and all surface treatment groups (p≥0.108). The SB group demonstrated significantly lower mean CIEa* (higher greenish hue) compared to other groups (p≤0.003). HFA exhibited significantly higher CIEa* (closer to red) when compared to LI (p=0.039). LI induced the smallest overall color change compared to negative control (ΔE00=1.43 [1.07]). However, the differences in ΔE00 values were not statistically significant (p=0.648).

CONCLUSIONS

The tested surface treatments did not affect the lightness or the yellowness of the 1-mm-thick milled feldspathic porcelain veneers. However, sandblasting resulted in a significant increase in the greenish hue. The Er:YAG laser resulted in the closest ΔE00 (1.43) to the 50:50% perceptibility threshold (ΔE00=1.2).

Surface Characteristics of High Translucent Multilayered Dental Zirconia Related to Aging

(1) Background: The purpose of this study was to evaluate the differences in terms of surface characteristics (roughness, topography, microhardness) among layers for multi-layered high translucent and super-high translucent zirconia and the influence of finishing and aging on surface characteristics and microstructure. (2) Methods: Three types of translucent multilayer zirconia were evaluated: STML (4Y-TZP); IPS e.maxZirCAD CEREC/in Lab MT Multi (4Y-TZP + 5Y-TZP); CeramillZolidfx ML (5Y-TZP). Ninety-six plate-shaped samples (32 for a material), 16 mm × 14 mm × 1 mm size, were cut with a precision disc, polished on both sides with sand papers and sintered respecting the manufacturer’s protocol. Half of the specimens (16) were finished by polishing and the other half by glazing and then equally divided into one control group and one group subject to aging by autoclaving (1 h, 134 °C, 0.2 MPa), resulting in four groups of eight samples, for each zirconia. The specimens were evaluated in three areas: cervical, medium, incisal-of each glazed or polished surface, before and after aging. Tests were performed to determine the surface roughness using a profilometer; the surface topography by an atomic force microscope (AFM) and a scanning electron microscope (SEM). Microhardness was recorded using a microhardness tester. Statistical analyses were performed using two-way ANOVA test, unpaired sample t-Test, paired sample t-Test (α = 0.05) and Pearson’s correlation. (3) Results: Before and after autoclaving, for glazed samples significance (p < 0.05) higher surface roughness, respectively lower microhardness in comparison with the polished group was assessed. No significant differences (p > 0.05) were reported between the three areas, on glazed or polished surfaces of a material. Although, after aging an increase in surface roughness was observed both on glazed and polished samples, statistical differences were found for STML (p < 0.05). No significant differences (p> 0.05) concerning microhardness among the same areas, on glazed and polished surfaces, recorded before and after aging, except CeramillZolidfx ML glazed samples. (4) Conclusions: For tested zirconia materials no significant differences among layers were registered regarding surface characteristics. Surface treatment (glazing or polishing) has a significant impact on surface roughness and microhardness. Both before and after aging, the surface roughness values for the glazed samples were higher than for those polished. The super translucent 4Y-TZP material was more affected by aging compared to the super-high translucent 5Y-TZP material. The combined material revealed similarities for each layer corresponding to the microstructure.

Effects of Grinding and Polishing on Surface Characteristics of Monolithic Zirconia Fabricated by Different Manufacturing Processes: Wet Deposition and Dry Milling

PURPOSE

To evaluate the effects of grinding and polishing on surface characteristics of monolithic zirconia fabricated by two different manufacturing processes.

MATERIALS AND METHODS

Two types of monolithic zirconia specimens, self-glazed zirconia (SZ) and conventional zirconia (CZ), were fabricated by wet deposition and dry milling, respectively. The specimens were randomly assigned into 4 groups (n = 10): as-sintered, ground, polished with a special zirconia polishing kit, and polished with a general-purpose ceramic polishing kit. Surface morphology and roughness (R_a ) were characterized, followed by one-way ANOVA analysis (α = 0.05).

RESULTS

The as-sintered SZ exhibited a smooth surface with obvious different morphologies compared with the as-sintered CZ (R_a : 0.26 ±0.05 μm versus 0.33 ±0.10 μm). R_a of the ground SZ was significantly higher than that of the as-sintered SZ (P<0.001) and the ground CZ (P = 0.011). For both SZ and CZ, R_a decreased significantly after polishing (P<0.001), and there was no significant difference between the two groups with different polishing kits (SZ- P = 0.144; CZ- P = 0.322). Surface morphologies of SZ and CZ became similar after grinding and polishing.

CONCLUSIONS

Monolithic zirconia SZ fabricated by wet deposition exhibited a smooth surface with specific patterns compared to the dry milled CZ. Grinding significantly changed the surface morphology of SZ and increased surface roughness of both zirconia specimens, which can be improved by polishing without being influenced by polishing kit selection. This article is protected by copyright. All rights reserved.

Surface and bulk properties of zirconia as a function of composition and aging

Yttria-stabilized zirconia (Y-SZ) materials with different levels of translucency have been used for indirect dental restorations. Y-SZ composition and microstructure are modified to improve translucency, and it is not clear how these materials respond to aging. This study evaluated the effect of hydrothermal aging (HA) performed in an autoclave on the properties of four dental Y-SZ materials with different compositions. Sintered bar-shaped specimens (14 x 4 x 2 mm) were prepared from four different zirconia-based materials (n = 40): low translucency 3 mol % Y-SZ (3Y-LT; Ceramill ZI, Amann Girrbach); high translucency 4 mol % Y-SZ (4Y-HT; Ceramill Zolid); and two high translucency 5 mol % Y-SZ (5Y-HT - Lava Esthetic, 3M; 5Y-SHT - Ceramill Zolid FX). Fully sintered specimens were exposed to HA for different times (control - 0 h, 5 h, 10 h, or 15 h at 134 °C, 2 bar pressure) and characterized for surface roughness, flexural strength (three-point bending), hardness and elastic modulus (nanoindentation), surface wettability (sessile drop technique) and crystalline content (x-ray diffraction, XRD). Data was analyzed by two-way ANOVA and Tukey HSD (p < 0.05). Zirconia composition significantly affected roughness (p = 0.016). Zirconia*aging interaction affected flexural strength (p = 0.012), surface wettability (p < 0.001), and hardness (p = 0.002). Zirconia composition (p = 0.011) and aging (p = 0.001) affected elastic modulus, while the interaction effect was not significant (p = 0.94). HA affects zirconia-based materials in different degrees. For 3Y-LT and 4Y-HT, surface and bulk properties were affected by aging to a similar extent. However, surface and bulk properties may change during clinical use as a result of prolonged degradation of Y-SZ.

Surface Modification to Modulate Microbial Biofilms-Applications in Dental Medicine

Recent progress in materials science and nanotechnology has led to the development of advanced materials with multifunctional properties. Dental medicine has benefited from the design of such materials and coatings in providing patients with tailored implants and improved materials for restorative and functional use. Such materials and coatings allow for better acceptance by the host body, promote successful implantation and determine a reduced inflammatory response after contact with the materials. Since numerous dental pathologies are influenced by the presence and activity of some pathogenic microorganisms, novel materials are needed to overcome this challenge as well. This paper aimed to reveal and discuss the most recent and innovative progress made in the field of materials surface modification in terms of microbial attachment inhibition and biofilm formation, with a direct impact on dental medicine.

Laboratory Characterization of In-Service Full-Mouth Rehabilitation with Monolithic Translucent Zirconia Restorations

The chance to critically and microscopically inspect the quality of bonded restorations once they are delivered to the patient after several pre-cementation steps is rare or nonexistent. Replicas of in-service restorations can provide a wealth of information on the integrity of the restorations and moreover make it possible to bring this information to the laboratory for further detailed analysis. This study aimed to characterize the epoxy replicas of 27 cemented monolithic yttria-stabilized zirconia crowns of the maxillary and mandibular arch to assess surface roughness, topography, and symmetry. The topography of the facial, lingual, and occlusal/incisal surfaces of each crown was observed under the optical microscope and further characterized using the scanning electron microscope. Surface roughness measurements were performed using the atomic force microscope. The optical microscope was used to measure the golden proportion and visible width of the anterior maxillary crowns. Surface damage consistent with unpolished adjustment was identified mostly in the occlusal surface of the posterior teeth. Other irregularities, such as scratch marks, small pits, and coarse pits were also found. The surface roughness had great variability. Not all of the anterior maxillary and mandibular teeth followed the golden proportion concept. This study design allows in vitro characterization of in-service restorations. It provides a framework for using replicas for early identification of patterns or features that can trigger fracture and for analysis of morphology and symmetry.