Current status of zirconia restoration

Effect of acid-etching solution on surface properties, crystallography, and shear bond strength of ultra-translucent zirconia to enamel

Ultra-translucent zirconia has gained popularity in restorative dentistry due to its excellent esthetic properties and high strength. Surface treatment methods play a crucial role in optimizing the bond between zirconia and enamel. This laboratory study aimed to investigate the influence of acid-etching solution on the surface properties of ultra-translucent zirconia and its subsequent shear bond strength to enamel. Thirty-six ultra-translucent zirconia disks were divided into three groups (n = 12): as-sintered (C) as the control group, airborne-particle-abraded (AB), and acid-etched with Zircos-E™ etching solution (ZE). Surface topography, roughness, and phase composition were assessed using scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), and X-Ray diffraction analysis (XRD), respectively. The remaining disks were bonded to enamel using resin cement, and shear bond strength (SBS) was tested after 10,000 thermo-cycles between 5℃ and 55℃. Data were statistically analyzed using one-way ANOVA (α = 0.05). ZE induced higher surface roughness compared to AB, with a more stable crystalline structure. ZE group exhibited the highest SBS (22.48 ± 2.97 MPa), followed by AB (16.72 ± 2.52 MPa), while C group had the lowest SBS (7.55 ± 2.73 MPa). ZE solution demonstrated enhanced surface properties and higher shear bond strengths to human enamel compared to conventional airborne-particle abrasion. This finding highlights the potential of acid-etching solutions in improving the bond between ultra-translucent zirconia and enamel in restorative dentistry applications.

Wear behavior of crown restoration materials and bovine tooth enamel opposed by pure titanium

The purpose of this study was to investigate the wear behavior of pure titanium when opposed to six different crown restorative materials. Abrader specimens were prepared by casting pure titanium and these were paired with substrates including pure titanium, resin composite, lithium disilicate, zirconia, silver-palladium-copper (Ag-Pd-Cu) alloy, and bovine enamel. The wear volume of each abrader and substrate specimen was measured using the two-body wear test, and factors affecting wear behavior, such as microstructures and hardness, were evaluated. Results indicated that titanium-to-titanium abrasion caused significant wear in both the abrader and the substrate. In contrast, no significant wear was observed for the zirconia and Ag-Pd-Cu alloy against titanium. SEM images showed linear wear marks in most specimens other than zirconia and resin composite, microcracks in enamel, and filler fall in resin composite. A strong correlation between the wear volume and Vickers hardness was found for ceramics, resin composites, and enamel. However, due to the small slope of the approximate straight line in this correlation suggests that the wear behavior of materials when abraded by titanium is only partially influenced by the microstructure and hardness of the material.

Shear bond strength of resin cement to additively manufactured zirconia with customized surface texture and porosity: Part 1

STATEMENT OF PROBLEM

The additive manufacturing of zirconia has been reported to present promising mechanical properties. However, studies on bonding to additively manufactured (AM) zirconia are lacking.

PURPOSE

The purpose of this in vitro study was to investigate the effect of customized porosity and surface texture on the shear bond strength (SBS) of resin cement to 3-dimensionally (3D) printed zirconia.

MATERIAL AND METHODS

A total of 60 zirconia disks (Ø12×5 mm) were designed with different surface porosity using a computer-aided design (CAD) software program and manufactured via stereolithography (SLA) 3D printing. The disks were divided into 4 groups (n=15) based on surface texture and porosity: Control (no designed porosities), G1:50 (50×50-µm pores 200 µm apart), G2:100 (100×100-µm pores 400 µm apart), and G3:200 (200×200-µm pores 800 µm apart). The specimens were cleaned, and the binder removed before sintering. The microstructural analysis of the specimen's surface before SBS was performed using a profilometer to determine surface texture (n=5). SBS was measured using a universal testing machine, and thermal cycling was performed to simulate aging (n=10). Data for SBS were analyzed using 2-way ANOVA (α=.05).

RESULTS

Surface texture and porosities were confirmed by profilometry. In all comparisons, the G3:200 group demonstrated the highest mean SBS with 8.78 MPa (P<.001); however, it was similar to the Control group, which had a mean of 8.41 MPa (P=.631). The G1:50 showed significantly lower SBS values at 3.90 MPa (P<.001), followed by the G2:100 group with 5.14 MPa (P<.001). Thermal cycling generally decreased SBS in all groups (P<.001).

CONCLUSIONS

Customized surface textures can improve bond strengths, with larger pores (200×200 µm) providing values comparable with those of traditional mechanical pretreatments surfaces, while smaller pores resulted in lower bond strengths. This approach avoids surface damage and phase transitions caused by traditional treatments. These findings provide a foundation for future research aimed at developing more durable and reliable zirconia restorations, ultimately enhancing clinical outcomes.

Strategies for Masking Metal Show-Through in Disilicate Dental Ceramics: A Systematic Evaluation Using Different Assessment Techniques

OBJECTIVES

The aim of this study was to assess the masking effect of two lithium disilicate ceramics at various thicknesses, when bonded to opaqued and nonopaqued silvery metallic core buildups, using spectrophotometry and digital photocolorimetric analysis.

MATERIALS AND METHODS

Sixty bis-acrylic blocks in A2 shade were fabricated to serve as control unrestored substrates, and 120 blocks were prepared (8.0 mm × 8.0 mm × 3.0 mm, W × L × H) and restored with amalgam. Sixty amalgam-restored blocks were treated with 0.65 mm (±0.10 mm) resin-based opaquer. Low-translucency (LT) lithium disilicate CAD/CAM blocks from two different manufacturers (Ivoclar IPS e.max CAD and GC Initial LiSi) were sectioned, crystallized (e.max), and polished, then divided into three subgroups according to their thickness (1.0, 1.5, and 2.0 mm, n = 30). The ceramic slices were treated and bonded to the three substrate types (control, opaqued amalgam, and nonopaqued amalgam) using a resin-luting cement. The masking effect of the resulting ceramic-substrate assemblies was investigated using a spectrophotometer and polarized digital photocolorimetric (PDPC) analysis. CIE L*a*b* coordinates were measured, and color difference analysis (ΔE00) was performed using the CIE ΔE00 formula. Acceptability and perceptibility thresholds were set at ΔE00 ≤ 1.8 and ΔE00 ≤ 0.8, respectively. The data were statistically analyzed using three-way and two-way ANOVA, followed by Tukey's test (α ≤ 0.05).

RESULTS

Spectrophotometric analysis showed that, for nonopaqued amalgam substrate, IPS e.max achieved ΔE00 mean (SD) of 4.2(0.4), 2.8(0.3), and 2.1(0.2), for 1.0, 1.5, and 2.0 mm thicknesses, respectively. Initial LiSi achieved ΔE00 mean (SD) of 3.8 (1.1), 2.8(0.9), and 2.7(0.4) for 1.0, 1.5, and 2.0 mm thicknesses, respectively. When the substrate was opaqued amalgam, IPS e.max and LiSi both resulted in a mean ΔE00 of 2.3(0.7). As the thickness increased to 1.5 and 2.0 mm, IPS e.max achieved an acceptable (ΔE00 = 1.3(0.4)) and an excellent (ΔE00 = 0.8(0.3)) masking, respectively. Initial LiSi achieved a moderately unacceptable color difference (ΔE00 = 2.0(0.8)) at 1.5 mm and an acceptable masking (ΔE00 = 1.5(0.6)) at 2.0 mm. PDPC analysis presented similar trends for both ceramic types and substrates, except for LiSi on opaqued amalgam. Individual CIE L*a*b* color coordinates, however, showed significant differences between the two analysis methods.

CONCLUSIONS

The use of opaquer proved to be an effective strategy for masking silvery metallic core buildups in preparation for lithium disilicate-based restorations. IPS e.max CAD provided a superior masking effect compared to Initial LiSi when used in conjunction with a resin opaquer.

CLINICAL SIGNIFICANCE

This study shows the potential of resin-based opaquers to mask metallic restorations when combined with lithium disilicate at different thicknesses. Providing knowledge in this aspect may emphasize conservative dental practices by preventing the replacement of metallic restorations and the accompanying unnecessary removal of tooth structure.

Adhesion of Streptococcus mutans on highly translucent zirconia: Influence of surface properties and polyelectrolyte multilayer coatings

STATEMENT OF PROBLEM

Low-pressure airborne-particle abrasion has been used to improve the adhesion of zirconia to resin cement. However, whether a polyelectrolyte multilayer can be used to reduce bacterial adhesion to abraded zirconia is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate whether polyelectrolyte multilayers added to airborne-particle abraded zirconia can minimize biofilm development.

MATERIAL AND METHODS

Commercially available zirconia powders with yttria content between 3 and 5 mol% were isostatically pressed into Ø20-mm disks and sintered at 1450 °C for 2 hours (n=8). Untreated specimens were compared with airborne-particle abraded ones. Specimens with 3 mol% yttria were further coated with polyelectrolyte multilayers (n=4). The surfaces were characterized by measuring the roughness, hydrophobicity, and surface charge using profilometry, atomic force microscopy, tensiometry, and electrokinetic analyzer, respectively. The extent of bacterial adhesion was determined using spectrophotometry and scanning electron microscopy. Data were analyzed with a single-factor ANOVA and F-test for variance (α=.05).

RESULTS

The airborne-particle abrasion of zirconia increased the surface roughness, which led to the pronounced adhesion of Streptococcus mutans. However, polyelectrolyte multilayer coatings made of chitosan and pol(yacrylic acid) reduced the extent of bacterial adhesion, especially in as-sintered specimens, with 70% fewer adhered bacteria than airborne-particle abraded specimens. The effect of polyelectrolyte multilayer coating on the airborne-particle abraded series was greatest with the poly(acrylic acid)-terminating specimens, with 50% fewer adhered bacteria than the uncoated ones.

CONCLUSIONS

Airborne-particle abraded zirconia specimens coated with biocompatible polyelectrolyte multilayer coatings with a negatively charged terminating layer were associated with a 50% reduction in bacteria adhesion compared with uncoated specimens.

Tooth Preparation Assessment Criteria for All-Ceramic CAD/CAM Posterior Crowns: An Evidence Map

BACKGROUND

An evidence map review was used to determine universal criteria for all-ceramic CAD/CAM posterior crowns to ensure standardized assessments by dental faculty, students, and practitioners.

MATERIALS AND METHODS

Covidence was used to perform the evidence map review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Web of Science (WOS), Embase, Dentistry and Oral Sciences Source (EBSCO), and MEDLINE (Ovid) were searched over a 10-year range (January 2012-December 2023), English only. This was complimented by a manual search. Descriptive statistics (i.e. frequencies and modes) and a chi-square goodness of fit test were used.

RESULTS

A total of 640 articles were identified, out of which 73 were selected for review across six reduction parameters: occlusal reduction, axial reduction, finish line reduction, total occlusal convergence (TOC), preparation surface finish, and anatomic form. Zirconia was excluded from this analysis. Significant differences were found between the observed and expected frequencies of consolidated parameters associated with occlusal reduction and finish line shoulder parameters at the p ≤ 0.05 level. There were no significant differences found between the observed and expected frequencies of the consolidated reduction parameters associated with finish line chamfer, axial reduction, surface finish, or TOC (p > 0.05).

CONCLUSIONS

Recommendation parameters for all-ceramic CAD/CAM posterior crown preparations are 1.5-2.0 mm for the occlusal reduction and 1.0 mm for the reduction of the shoulder finish line. Recommendations of at least 1.0 mm for the chamfer reduction, 12° for the TOC, 1.0-1.5 mm for the axial reduction, and a smooth preparation surface finish with internally rounded angles were also made, though none of these results were statistically significant. The literature review revealed the "finish line" category is multi-dimensional suggesting a more encompassing term as "finish boundary profile (FBP)."

The influence of thermal tempering on the fracture resistance, surface microstructure, elemental surface composition, and phase analysis of four heat-pressed lithia-based glass ceramic crowns

BACKGROUND

This in-vitro study aimed to evaluate the impact of thermal tempering and ceramic type on the fracture resistance, surface microstructure, elemental surface composition and phase analysis of four heat-pressed glass ceramics.

METHODS

A total of 84 glass-ceramic crowns were pressed and randomly allocated into four equal groups (n = 21) according to the ceramic type: Group (E): IPS e.max Press, Group (L): GC initial LiSi Press, Group (C): Celtra Press and Group (A): VITA Ambria. The crowns of each group were equally allocated into three subgroups (n = 7) regarding the subsequent thermal tempering temperature. Subgroup (T0): No tempering. Subgroup (T1): Tempering at 9% below pressing temperature. Subgroup (T2): Tempering at 5% below pressing temperature. Samples were tested for fracture resistance using a universal testing machine. A scanning electron microscope, X-ray diffraction, and Energy Dispersive x-ray analysis were utilized to disclose the microstructural features.

RESULTS

When there is no tempering, IPS e.max press showed a significant elevated fracture resistance (P-value = 0.002). There was an insignificant difference between other ceramics. While with tempering (T2) as well as (T1), Lisi press (L) showed a significant elevated fracture resistance. There was an insignificant difference between other ceramics (P-value = 0.004).

CONCLUSIONS

Incorporation of zirconia oxide into the lithium disilicate glass matrix did not show improvement in the fracture resistance. Thermal tempering procedure had significant effect on fracture resistance. Thermal tempering technique had no influence the elemental surface composition and phase analysis yet T2 samples showed changes in crystal size and orientation.

Direct colour printing on zirconia using 222 nm UV-C photons

OBJECTIVES

To proof the feasibility of direct colour printing on 3Y-TZP using 222 nm UV-C through investigating the degree and durability of the colour changes, and testifying whether surface, mechanical and biological properties are influenced by the treatment.

METHODS

222 nm UV-C light (Irradiance: 1.870 mW/cm2) was used to treat 3Y-TZP for durations from 15 min to 24 h. ΔE*, TP, crystalline structure, surface morphology, Sa, BFS and biological activities were investigated before and after irradiation. SPSS 28.0 was used for statistical analysis (α = 0.05).

RESULTS

222 nm UV-C irradiation was capable to shade white 3Y-TZP into tooth colours. With the increase of ΔE*, TP decreased, such that the longer the irradiation time, the higher the ΔE* (logarithmic relationship) and lower the TP. Despite the induced optical changes being prone to fade, the process can be predicted by inversely proportional relationships between ΔE*, TP and the testing points. The treated surface exhibited enhanced hydrophilicity, while the recovery phenomenon was observed. Other properties were not altered by the treatment.

SIGNIFICANCE

This is the seminal study demonstrating the feasibility of direct colour printing on 3Y-TZP using 222 nm UV-C. The new relationship between the colour centre and Eg of 3Y-TZP was established, whereas the induced optical changes were stabilised after a certain period and were highly predictable by controlling the irradiation periods. The irradiation was only correlated to the electron excitation and oxygen vacancies, and would not lead to any changes of other properties. A simple, safe and promising approach to achieve satisfactory colours on 3Y-TZP in clinical practice can be developed.

Exploring the Properties and Indications of Chairside CAD/CAM Materials in Restorative Dentistry

The present review provides an up-to-date overview of chairside CAD/CAM materials used in restorative dentistry, focusing on their classification, properties, and clinical applications. If CAD/CAM technology was only an aspiration in the past, a higher proportion of clinics are employing it nowadays. The market is overflowing with biomaterials, and these materials are constantly evolving, making it challenging for practitioners to choose the most appropriate one, especially in correlation with patients' medical diseases. The evolution of CAD/CAM technology has revolutionized dental practice, enabling the efficient fabrication of high-quality restorations in a single appointment. The main categories of chairside CAD/CAM materials include feldspathic ceramics, leucite-reinforced ceramics, lithium disilicate, zirconia, hybrid ceramics, and acrylic resins. The mechanical, physical, and aesthetic properties of these materials are discussed, along with their advantages and limitations for different clinical scenarios. Factors influencing material selection, such as strength, aesthetics, and ease of use, are also assessed. Ultimately, the guiding principle of dentistry is minimally invasive treatment following the particularity of the clinical case to obtain the envisioned result. Correlating all these factors, a simple, up-to-date classification is required to begin an individualized treatment. By synthesizing current evidence, this comprehensive review aims to guide clinicians in selecting appropriate chairside CAD/CAM materials to achieve optimal functional and aesthetic outcomes in restorative procedures. The integration of digital workflows and continued development of novel materials promise to further enhance the capabilities of chairside CAD/CAM systems in modern dental practice.

Do 3D printed and milled tooth-supported complete monolithic zirconia crowns differ in accuracy and fit? A systematic review and meta-analysis of in vitro studies

STATEMENT OF PROBLEM

Additive (3-dimensional printing) and subtractive (milling) methods are digital approaches to fabricating zirconia restorations. Comparisons of their resultant fabrication accuracy and restoration fit are lacking.

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the accuracy and fit of monolithic zirconia crowns fabricated by 3-dimensional printing and milling.

MATERIAL AND METHODS

The PubMed (Medline), Scopus, Embase, Web of Science, Cochrane Library, and Google Scholar databases were searched up to August 2023. Eligible records were included, and the standardized mean difference (SMD) analyzed 4 outcomes: marginal fit, intaglio fit, trueness, and precision. Publication bias was analyzed with Trim-and-fill, the Egger regression test, and Begg funnel plot. Methodological quality was rated using the QUIN tool.

RESULTS

A total of 15 publications were found eligible out of the initial 6539 records. The 3-dimensional printing group demonstrated a lower marginal fit (SMD=1.46, 95% CI=[0.67, 2.26], P<.001; I2=83%, P<.001) and trueness (SMD=0.69, 95% CI=[0.20, 1.18], P=.006; I2=88%, P<.001) and a significantly higher precision (SMD=-2.19, 95% CI=[-2.90, -1.48], P<.001; I2=56%, P=.045). The intaglio fit did not differ significantly across the study groups (SMD=0.77, 95% CI=[-0.22, 1.77], P=.127; I2=87%, P<.001).

CONCLUSIONS

Given the high degree of heterogeneity, it can be cautiously concluded that while 3-dimensional printing led to greater precision, the outcomes of the 2 accuracy and adaptation parameters most crucial to the longevity of the restorations-trueness and marginal fit-showed the superiority of the milling technique.

Effect of Grinding and Polishing Protocols on Surface Roughness, Flexural Strength, and Phase Transformation of High-Translucent 5 mol% Yttria-Partially Stabilized Zirconia

OBJECTIVES

 This study evaluated surface roughness, biaxial flexural strength, and phase transformation of 5Y-PSZ after grinding and polishing with different protocols.

MATERIAL AND METHODS

 Two commercial 5Y-PSZ, Lava Esthetic (L) and Cercon xt (C), were used and divided into 3 groups: LC and CC represented unpolished control groups; LE and CE were polished with protocol I (EVE DIASYNT® PLUS HP following with EVE DIACERA RA); and LJ and CJ were polished with protocol II (Superfine diamond bur following with Jota ZIR Gloss polishing kit). Surface roughness was evaluated after polishing step-by-step with a contact-type profilometer. After high-gross polishing, the specimens were subjected to biaxial flexural strength test, crystallographic microstructure analysis using an X-ray diffractometer (XRD), and surface micro-topography using scanning electron microscopy (SEM).

STATISTICAL ANALYSIS

Surface roughness differences after each step and biaxial flexural strength between groups were evaluated with one-way ANOVA, followed by Bonferroni post-hoc analysis. Changes in surface roughness across four different time points within groups were assessed using one-way repeated measures ANOVA, followed by Bonferroni post-hoc analysis.

RESULTS

 After high-gross polishing, both polishing protocols showed significantly lower surface roughness than the grinding group (p < 0.05). The LE and CE groups exhibited the highest surface roughness values, which were significant differences from the LJ and CJ groups (p < 0.05). The LE group showed significantly lower biaxial flexural strength compared to the LC group (p < 0.05). However, there was no statistically significant difference in the CE and CJ groups compared to the control group (p > 0.05). Furthermore, all polishing protocols did not change the phase transformation of zirconia.

CONCLUSION

 Polishing protocol II provided a smoother surface than the protocol I after high-gross polishing, while the biaxial flexural strength of materials remained unaffected.

Minimally Invasive Fixed Prosthodontics: A Narrative Review

OBJECTIVE

Minimally invasive dentistry is being widely practiced. The center stone is to be as conservative as possible to minimize unnecessary removal of healthy tooth structure. In prosthodontics the patients have generalized and combined nature of diseases. This narrative literature review analyzed available evidence on minimally invasive treatment protocols in fixed prosthodontics and raised awareness on the importance of longevity of treatments and secondary prevention.

OVERVIEW

The long-term clinical survival of ceramic and resin composite materials was reviewed. Loss of tooth vitality after prosthodontic treatment was also explored. And finally, treatment options for patients with severe wear were examined. The search of the literature resulted in evidence of superior survival of ceramic restorations over resin composites. The literature is also clear that ceramic partial coverage inlay and onlay restorations have excellent long-term clinical performance in posterior dentition. Glass ceramic lithium disilicate showed to be an adequate material not only for anterior but also for posterior dentition, including the patients with severe wear.

CONCLUSIONS

Minimally invasive dentistry as applied in fixed prosthodontics needs updates in its concepts to account for secondary prevention and longevity of chosen treatment techniques.

CLINICAL SIGNIFICANCE

This narrative review article critically reviews available evidence on long-term clinical performance of minimally invasive and traditional treatment concepts and materials in fixed prosthodontics. Awareness is raised for secondary prevention and longevity of chosen treatments.

Impact of surface pre-treatment on bond strength between cement and zirconia: A systematic review and network meta-analysis

STATEMENT OF PROBLEM

The optimal zirconia pretreatment, contingent upon the type of cement used, warrants further research.

PURPOSE

The purpose of this investigation was to evaluate the influence of various surface pretreatments on the bonding efficacy of cement to zirconia.

MATERIAL AND METHODS

A comprehensive search was conducted across the PubMed, Embase, Scopus, and Web of Science databases for in vitro studies related to bonding with zirconia up to April 2024, supplemented by a manual search. A network meta-analysis was executed to compare different types of cement.

RESULTS

Of the 6118 articles screened, 21 were selected for inclusion in this review. These studies examined various surface pretreatment techniques, primers, resin cements, aging protocols, and bond strength testing methods. The highest bond strengths were observed with 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based cements. The network meta-analysis indicated that mechanical and mechano-chemical pretreatments yielded superior results across all cement types.

CONCLUSIONS

The existing evidence indicates that both surface pretreatments and the specific type of cement should be considered when interpreting the findings of in vitro studies for their application in clinical practice.

Evaluation of Extra-High Translucent Dental Zirconia: Translucency, Crystalline Phase, Mechanical Properties, and Microstructures

Highly translucent zirconia (TZ) is frequently used in dentistry. The properties of several highly translucent zirconia materials available in the market require an in-depth understanding. In this study, we assessed the translucency, crystalline phase, mechanical properties, and microstructures of three newly developed highly translucent zirconia materials (Zpex 4. m, 4 mol% yttria-stabilized zirconia: 4YSZ; Zpex Smile.m, 5YSZ; ZR Lucent ULTRA, 6YSZ). The translucency parameter (TP) was analyzed using the CIELAB system. X-ray diffraction was conducted for the crystalline phase analysis, followed by Rietveld refinement. A biaxial flexural strength test using the Weibull analysis was performed to evaluate the mechanical properties. Scanning electron microscopy, grain size distribution, and average grain size were used to analyze the microstructures. The TP content of the ZR Lucent ULTRA was the highest among the samples investigated. The Rietveld analysis revealed that the cubic zirconia phase content of the ZR Lucent ULTRA was the highest. The biaxial flexural strength of the ZR Lucent ULTRA was the lowest (622.9 MPa). The average grain size and proportion of large grains (1.0 µm < x) were the highest in ZR Lucent ULTRA. Therefore, extra-high translucent zirconia has the potential for use in anterior monolithic restorations owing to its esthetics and strength.

Evaluation of marginal accuracy of polyetheretherketone and zirconia copings fabricated using computer-aided design/computer-aided manufacturing technique: An in vitro study

AIM

The aim of this study was to compare the marginal accuracy of polyetheretherketone (PEEK) and zirconia copings fabricated using computer-aided design/computer-aided manufacturing (CAD/CAM) technology, and to assess the impact of their material properties on accuracy when produced with a 4-axis milling system under controlled conditions.

SETTINGS AND DESIGN

The study employed an in vitro design with a stainless steel die model featuring a 6 mm axial wall height, a 6-degree total occlusal convergence, and a radial shoulder finish line.

MATERIALS AND METHODS

Thirty stone dies were created from silicone impressions of the metal die and poured using type-IV dental stone. The dies were divided into two groups: Group-A (PEEK) copings and Group-B (zirconia) copings. All copings were fabricated using a CAD/CAM system. Vertical marginal accuracy was assessed with a stereomicroscope and image analysis software at ×20 magnification. The marginal gaP values were subjected to a student (independent) t-test for statistical analysis.

STATISTICAL ANALYSIS USED

The statistical analysis involved a student (independent) t-test to compare the marginal gaP values between Group A (PEEK) and Group B (zirconia).

RESULTS

The mean marginal discrepancy for Group A (PEEK) and Group B (zirconia) was 92.84 μm ± 3.48 μm and 63.12 μm ± 31.47 μm, respectively. A statistically significant variation (t = 3.635, P = 0.001) between the groups was observed, indicating better marginal accuracy with zirconia copings compared to PEEK copings.

CONCLUSION

Both PEEK and zirconia copings demonstrated vertical marginal discrepancies within the clinically acceptable limit of <120 μm. However, zirconia copings exhibited superior marginal accuracy in this in vitro study.

Shear bond strength of porcelain to milled and stereolithography additively manufactured zirconia with and without surface treatment: An in vitro study

STATEMENT OF PROBLEM

Delamination of veneering ceramic is one of the most common challenges relating to veneered zirconia restorations. Additive manufacturing (AM) is a fast-expanding technology that has gained widespread acceptance in dentistry and is increasingly being used to produce dental restorations. However, information about bonding of porcelain to AM zirconia is lacking.

PURPOSE

The purpose of this in vitro study was to investigate the shear bond strength (SBS) of porcelain to milled and additively manufactured zirconia, and the effect of surface treatment on bond strength.

MATERIAL AND METHODS

A Ø12×5-mm disk was designed virtually to fabricate all specimens, which were divided into 2 groups according to the manufacturing technique: additively manufactured or milled zirconia. The effect of airborne-particle abrasion and a zirconia liner before porcelain application was investigated in both groups. Veneering porcelain was fired into an alumina ring mold on the zirconia surface. SBS was measured by using a universal testing machine at a crosshead speed of 1 mm/min before and after aging (n=10). SBS data were analyzed with 3-way ANOVA (α=.05) RESULTS: A significant difference was found between milled and AM zirconia. The SBS of porcelain to milled zirconia was significantly higher (1.38 MPa) than to AM zirconia (0.68 MPa) (P<.001). The surface treatment of zirconia had no significant effect on porcelain SBS in either group (P=.254), whereas thermocycling significantly reduced the SBS of porcelain to zirconia in both milled and AM groups (P=.001).

CONCLUSIONS

Porcelain bonding to milled zirconia was better than to AM zirconia. Pretreating the zirconia substrate before porcelain application did not improve the porcelain bond.

Two-Year Clinical Evaluation of Enamel Wear Antagonistic to Polished and Glazed Monolithic Zirconia Endocrowns

OBJECTIVE

To assess the effect of chairside adjustment and polishing on the clinical performance of zirconia endocrowns and digitally calculate the opposing enamel wear.

MATERIALS AND METHODS

A total of 20 participants received zirconia endocrowns on their endodontically treated lower first molars. All endocrowns were fabricated using CAD/CAM technology. According to the occlusal adjustments needed for the restorations, patients were divided into two groups: Group ZG with 10 glazed monolithic zirconia endocrowns and Group ZP with 10 adjusted and polished zirconia endocrowns. Bonded endocrowns were evaluated clinically and radiographically for 24 months following modified FDI criteria. Wear of the antagonistic enamel was calculated at 6, 12, 18, and 24 months using an intraoral scanner and Geomagic software.

RESULTS

The overall survival rate of the 20 endocrowns was 100%, according to the Kaplan-Meier survival method. None of the endocrowns were replaced during the follow-up. After 2 years, polished zirconia caused enamel wear (0.422 ± 0.130 mm3), while glazed zirconia caused enamel wear (0.491 ± 0.105 mm3), with no statistically significant difference (p = 0.108).

CONCLUSION

Both glazed and polished monolithic zirconia endocrowns showed comparable enamel wear after a 2-year clinical follow-up, with no significant difference.

CLINICAL SIGNIFICANCE

Glazing or intra-oral polishing could be applied to monolithic zirconia endocrowns with minimal antagonist enamel wear.

Effect of different surface treatments on shear bond strength of zirconia with various yttria contents

BACKGROUND

Achieving a stable bond with zirconia requires mechanical and chemical bonding methods. Information regarding the optimal treatment method for zirconia with varying yttrium content is scarce. This study evaluated the effect of different surface treatments on the shear bond strength of zirconia with various yttria contents.

MATERIALS AND METHODS

A total of 168 disc-shaped zirconia specimens were classified into 12 groups based on the surface treatment method, including airborne-particle abrasion (APA), selective infiltration etching (SIE), hot etching (HE), and control group with no treatment; and yttria contents including Zolid Zi (4.5-5.6 wt% yttrium), Zolid HT White (6.7-7.2 wt% yttrium), and Ceramill Zolid FX (9.15-9.55 wt% yttrium). The surface roughness (Ra and Rz) of the specimens and the shear bond strength was measured (α = 0.05).

RESULTS

The results indicated that the mean bond strength of all specimens was higher after different surface treatments compared to the control group, of which the APA method resulted in higher bonding strength in all kinds of zirconia than other methods (P < 0.05). In all types of zirconia, a significant difference was observed in surface roughness (Ra and Rz) resulting from various surface treatment methods (P < 0.001). Interaction of surface treatment methods and zirconia type significantly affected shear bond strength and surface roughness (P < 0.05).

CONCLUSION

APA significantly enhanced shear bond strength and surface roughness across all zirconia types and yttria contents. The SIE and HE methods also showed promising results. Zolid Zi showed superior bond strength, whereas Zolid FX demonstrated reduced bond strength.

Three-unit posterior monolithic fixed dental prostheses made from high-translucent shade-graded zirconia: 3-Year results from a prospective clinical pilot study

OBJECTIVES

To assess the clinical performance of tooth-supported 3-unit fixed dental prostheses (FDPs) made from shade-graded monolithic 5Y-PSZ (partly stabilized zirconia) zirconia in terms of survival rate and the quality of restorations based on modified FDI criteria over three-years.

MATERIALS AND METHODS

High-translucent shade-graded monolithic zirconia (Lava Esthetic, Solventum Dental Solutions) was used to manufacture maxillary or mandibular three-unit FDPs in the posterior region (N = 22) employing subtractive milling system (Amann Girrbach). All FDPs were bonded with a universal resin cement (Rely X Universal, Solventum Dental Solutions) and evaluated 4 weeks after cementation (baseline) and after 1, 2, and 3 years. The primary objective was to assess the survival and complication rates of the restorations. Furthermore, the quality of the restorations was evaluated based on selected and modified FDI (World Dental Federation) criteria, which encompass functional, aesthetic, and biological parameters. FDI criteria were analyzed using the Fisher-Freeman-Halton exact test.

RESULTS

Twenty-one patients were examined at 1 year, 2 years, and 3 years. The survival rate was 100%. No mechanical complications were observed. A total of 3 biological complications occurred. These were successfully managed without any residual functional impairment. All FDI criteria were found to be clinically acceptable or better.

CONCLUSIONS

Monolithic shade-graded zirconia FDPs demonstrated 100% survival at 3 years with a low complication rate.

CLINICAL RELEVANCE

Fixed 3-unit FDPs made of high-translucent monolithic zirconia might be a viable treatment option in the posterior region, preventing the chipping phenomenon and providing favorable aesthetics while allowing for an efficient digital workflow.

Microplastics as an Emerging Potential Threat: Toxicity, Life Cycle Assessment, and Management

The pervasiveness of microplastics (MPs) in terrestrial and aquatic ecosystems has become a significant environmental concern in recent years. Because of their slow rate of disposal, MPs are ubiquitous in the environment. As a consequence of indiscriminate use, landfill deposits, and inadequate recycling methods, MP production and environmental accumulation are expanding at an alarming rate, resulting in a range of economic, social, and environmental repercussions. Aquatic organisms, including fish and various crustaceans, consume MPs, which are ultimately consumed by humans at the tertiary level of the food chain. Blocking the digestive tracts, disrupting digestive behavior, and ultimately reducing the reproductive growth of entire living organisms are all consequences of this phenomenon. In order to assess the potential environmental impacts and the resources required for the life of a plastic product, the importance of life cycle assessment (LCA) and circularity is underscored. MPs-related ecosystem degradation has not yet been adequately incorporated into LCA, a tool for evaluating the environmental performance of product and technology life cycles. It is a technique that is designed to quantify the environmental effects of a product from its inception to its demise, and it is frequently employed in the context of plastics. The control of MPs is necessary due to the growing concern that MPs pose as a newly emergent potential threat. This is due to the consequences of their use. This paper provides a critical analysis of the formation, distribution, and methods used for detecting MPs. The effects of MPs on ecosystems and human health are also discussed, which posed a great challenge to conduct an LCA related to MPs. The socio-economic impacts of MPs and their management are also discussed. This paper paves the way for understanding the ecotoxicological impacts of the emerging MP threat and their associated issues to LCA and limits the environmental impact of plastic.

Influence of different cutting instruments and rotational speeds on heat generation and cutting efficiency when sectioning different types of zirconia

PURPOSE

The purpose of this study was to evaluate the temperature generated on the intaglio surface and efficiency when cutting different types of zirconia with different rotary instruments and rotational speeds.

METHODS

A conventional diamond rotary instrument (Brasseler, grit size 107 μm) and special diamond rotary instrument marketed to cut zirconia (4 ZR, Brasseler, grit size 126 μm) were tested on 3Y-TZP and 4Y-TZP zirconia with a rotation speed of 100,000 rpm and 200,000 rpm. Zirconia specimens were cut under water cooling (110 mL/min) in a custom-made holder attached to a universal testing machine. The temperature was recorded with infrared sensors pointing at the intaglio surface of the zirconia specimens.

RESULTS

A rotation speed of 200,000 rpm resulted in significantly shorter cutting times, but also in significantly higher temperatures at the intaglio surface of the zirconia specimens compared with a rotation speed of 100,000 rpm. Significantly shorter cutting times were observed for the conventional diamond rotary instrument than for the special rotary instrument marketed to cut zirconia. Using the special rotary instrument, significantly longer cutting times were recorded for 3Y-TZP than for 4Y-TZP.

CONCLUSIONS

A conventional diamond rotary instrument was more efficient than a special rotary instrument. However, to avoid high temperatures when cutting zirconia clinically, a rotation speed of 100,000 rpm is recommended.

Clinical performance of zirconia-based tooth-supported fixed dental prostheses: A systematic review and meta-analysis

OBJECTIVES

This study aimed to investigate the clinical performance of zirconia-based fixed dental prostheses (FDPs) in comparison to metal-ceramic (MC) FDPs.

METHODS

A comprehensive search on MEDLINE (PubMed), Web of Science (Core Collection), Scopus up to June 2024 was conducted. Studies that compared the success, survival and complication rates between zirconia based FDPs and MC FDPs were eligible for inclusion.

RESULTS

Thirty-one articles were identified, of which 22 were included for systematic review and 7 RCTs were included for meta-analysis. 10, 9 and 3 studies were classified to mean follow-up ≤ 5 years, 5 years < mean Follow-up ≤ 10 years, mean Follow-up >10 years, respectively. In the pooled analysis, 180 bilaminar zirconia (ZC) FDPs and 206 MC FDPs were included. ZC FDPs were significantly associated with more failures (RR=3.64, p = 0.009) and more Ceramic Chipping (RR=2.92, p < 0.0001) when compared to MC FDPs. Higher risks of Framework Fracture (RR=4.57, p = 0.18), Loss of Retention (RR=4.79, p = 0.17), Secondary Caries (RR=1.25, p = 0.68), Endodontic complications (RR=1.30, p = 0.74) and Marginal Integrity (RR=1.07, p = 0.88) were also found in ZC FDPs when compared to those of MC FDPs, but with no statistical difference.

CONCLUSION

The current evidence continues to support the preference for traditional MC FDPs over ZC FDPs. Studies indicate that ZC FDPs have higher failure rates and more complications compared to MC FDPs, with ceramic chipping being a significant concern. There is lack of long term (>10 years follow-up) evidence of the clinical performance of ZC FDPs and monolithic zirconia FDPs.

CLINICAL SIGNIFICANCE

The study suggests that despite the growing popularity of zirconia, evidence shows MC FDPs may still be considered preferable to ZC FDPs.

Evaluation of Physical Changes and Bond Properties of Monolithic Zirconia Following Surface Treatment with Alumina and Synthetic Diamond Particles: A Comparative X-ray Diffraction Analysis

AIM

The aim of this study was to compare and evaluate the phase transformation and effect on the bond strength and fracture toughness of monolithic zirconia after surface treatment with alumina and synthetic diamond particles.

MATERIALS AND METHODS

Forty samples of monolithic sintered zirconia discs (Y-TZP) were divided into two groups of 20 samples each. Group A - air abrasion with alumina particles (n = 20); group B - air abrasion with synthetic diamond particles (n = 20). Pretreatment phase and posttreatment of each zirconia sample from group A and group B were evaluated using an X-ray diffraction machine. The surface roughness of each zirconia sample was evaluated using a profilometer. Composite discs were fabricated and bonded to the air-abraded surface of each zirconia sample from group A and group B using a dual-cured resin cement, respectively. These samples were mounted in an acrylic block to determine the bond strength of zirconia with resin cement using a universal testing machine. This was followed by a fracture toughness test of the samples using a Vickers indentation hardness tester. The results were subjected to statistical analysis using a t-test, and relevant statistical conclusions were drawn.

RESULTS

The mean ± SD of monoclinic content in group A (alumina particles) and group B (synthetic diamond particles) was 0.82 ± 0.010% and 0.76 ± 0.015%, respectively. The mean ± SD of surface roughness in group A (alumina particles) and group B (synthetic diamond particles) was 0.507 ± 0.106 and 0.513 ± 0.116 µm, respectively, and the mean ± SD of bond strength in group A (alumina particles) and group B (synthetic diamond particles) was 6.11 ± 1.47 and 6.49 ± 0.83 MPa, respectively. The mean ± SD of fracture toughness in group A (alumina particles) and group B (synthetic diamond particles) was 2.63 ± 0.46 0.5 and 5.70 ± 1.03 MPam0.5, respectively. p < 0.05 was considered statistically significant.

CONCLUSION

The distribution of mean monoclinic content was significantly higher in zirconia samples abraded by alumina (Group A) as compared to synthetic diamond particles (Group B). The mean surface roughness and bond strength results were statistically insignificant between both groups. The distribution of mean fracture toughness was significantly higher in group B compared to group A.

CLINICAL SIGNIFICANCE

Synthetic diamond particles for air abrasion of Y-TZP can be a promising alternative to alumina as they cause minimal changes in the structural integrity without compromising the bond strength. How to cite this article: Kazi AI, Dugal R, Madanshetty P, et al. Evaluation of Physical Changes and Bond Properties of Monolithic Zirconia Following Surface Treatment with Alumina and Synthetic Diamond Particles: A Comparative X-ray Diffraction Analysis. J Contemp Dent Pract 2024;25(12):1110-1117.

Exploring physical and mechanical properties of hydrothermally processed recycled non-sintered dental zirconia wastes

BACKGROUND AND AIM

The present investigation explored the potential for recycling residual blocks obtained from the machining processes under hydrothermal conditions. Furthermore, the study examined the recycled samples' various physical and mechanical properties to assess their viability for further use.

MATERIALS AND METHODS

In this in vitro study, Aman Girbach blocks were collected, half of which underwent a hydrothermal process, while the other half did not. The blocks were then subjected to ball milling. Uniaxial and isostatic pressed blocks were prepared, and 10 samples were obtained from each type of recycled block. These samples were compared to a commercial material, and four groups were formed based on the powder type and pressing method used. The quality control analysis of the recycled samples included assessing particle size distribution, identifying crystalline phases, analyzing color differences, examining microstructure, and evaluating mechanical properties. Statistical tests such as normal distribution calculations (k-s test), one-way ANOVA, Brown-Forsythe, Tukey HSD, and Games-Howell tests were used to compare the four groups and perform pairwise comparisons.

RESULTS

The flexural strength and density of the control commercial group were significantly higher than the other experimental groups (P = 0.000). Linear shrinkage of recycled isostatic pressed experimental bodies was significantly lower than that of others (P = 0.000). Qualitative evaluation of microstructure and crystalline phase by FESEM and XRD showed no significant difference in grain size and crystalline phase between different groups.

CONCLUSION

The hydrothermal process is a promising way to recycle zirconia ceramic with lower energy consumption. Recycled waste demonstrates potential as a cost-effective and viable option for ceramic prostheses in situations with low to medium stress levels.

Tribological aspects of enamel wear caused by zirconia and lithium disilicate: A meta-narrative review

The contact between enamel and an antagonist surface is the primary factor in tooth wear. Loss of tooth structure can cause changes in occlusion, chewing functionality, dental sensitivity, and appearance. However, enamel wear caused by opposing restorations is multifactorial and there is a lack of consensus regarding its behavior. This meta-narrative review assesses the multiple factors that affect enamel wear when using two common indirect restorative materials, lithium disilicate and zirconia. PubMed, Google Scholar, MEDLINE, and CINAHL databases were searched using keywords "zirconia," "lithium disilicate," "antagonistic tooth wear," and "enamel wear" to identify studies related to enamel wear caused by zirconia and lithium disilicate restorations. The Realist and Meta-narrative Evidence Syntheses: Evolving Standards (RAMESES) publication standard was used to report this meta-narrative literature review. Four broad categories of influencing factors were identified and reviewed: (1) mechanical and physical properties, (2) wear behavior and microstructural characteristics, (3) surface state, and (4) environmental factors. We conclude that well-polished zirconia is a more favorable indirect restorative material than lithium disilicate in terms of tribology because of its microstructure and surface integrity during wear. This review will enable clinicians to better comprehend the intricate nature of tooth wear caused by dental restorations.

Polishing systems for modern aesthetic dental materials: a narrative review

Objectives To review the current literature surrounding chairside polishing systems for resin composites, zirconia and lithium disilicate restorations.Methods A literature search was undertaken and databases were hand-searched for the most relevant articles.Discussion The current marketplace contains a wide variety of polishing systems, each with different abrasive compounds and number of steps. Current efforts are aimed at reducing the number of steps required for polishing to improve clinical effectiveness. Reduced step systems showed some comparable results to the more traditional multi-step protocols, but the most effective results were achieved with the use of polishing paste as an additional step.Conclusions Based on the current available literature, the use of material-specific polishing systems is effective for chairside polishing of direct and indirect restorative materials. However, it is important to emphasise that, for optimum outcomes, it is essential to follow manufacturers' recommendations for each step, with particular considerations of the handpiece speed, time spent per step and use of adjunct water coolant.

Effect of placement strategies and connector designs in CAD/CAM technology on fracture resistance of multilayered monolithic zirconia fixed dental prostheses: An in vitro study

This study evaluated fracture resistance of monolithic fixed dental prostheses (FDPs) fabricated using different placement strategies of various connector designs in multilayered zirconia disc. Monolithic FDPs were placed in translucent and dentin layers of multilayered zirconia disc and fabricated with V-shaped and U-shaped connector designs gained by sharp and blunt millings. The FDPs were cemented on abutment models made of polymer material, underwent thermal cycles, and loaded to fracture using the universal testing machine. Fracture loads and modes were analyzed using two-way ANOVA, Tukey's post hoc test, and Fisher exact test (p≤0.05). The chosen placement strategy and connector designs gained by different milling procedures in computer-aided design/computer-aided manufacturing technology affect fracture resistance of monolithic FDPs made of multilayered zirconia materials. Placing the connector in translucent layer rather than dentin layer of multilayered zirconia disc and using sharp milling significantly reduces fracture resistance of monolithic multilayered zirconia FDPs.

Clinical assessment of monolithic zirconia crowns fabricated using an intraoral scanner

Background

This in vivo study assessed the accuracy of single-tooth monolithic zirconia crowns made using an intraoral scanner (IOS) and computer-aided design/computer-aided manufacturing (CAD/CAM) technology.

Methods

Thirty patients requiring single posterior crowns were selected. The teeth were prepared with a deep chamfer finish line with a 1-mm extension subgingivally and a 1-mm reduction in all surfaces by one prosthodontist. The gingival margins were retracted using a gingival retraction paste before making impressions using a Trios scanner. All the digital impression files were sent to one laboratory using the dental designer software (3Shape, Copenhagen, Denmark). After completing the milling and sintering processes, the crowns were dyed and glazed. After removing the temporary crown, the qualitative assessment of proximal contacts of definitive monolithic zirconia crowns was performed according to the CDA criteria. Data were analyzed with Friedman's two-way analysis and independent t-test at α=0.05.

Results

The difference in axial and total gaps between premolar and molar teeth was not significant; however, the mean marginal gap of molars was higher than that of the premolars (P=0.043). Furthermore, the comparison of the axial, total, and marginal gaps between the upper and lower jaws showed no significant difference (P>0.05). The distribution of occlusal and proximal contacts indicated 60% and 66.7% proper contacts and no contacts in 6.7% and 10% of cases, respectively.

Conclusion

Using IOSs could result in accurate monolithic zirconia crowns in terms of adaptation. Also, most occlusal and proximal contacts did not need any adjustments.

Effect of artificial aging on fracture toughness and hardness of 3D-printed and milled 3Y-TZP zirconia

PURPOSE

This study aimed to evaluate the impact of artificial aging on the fracture toughness and hardness of three-dimensional (3D)-printed and computer-aided design and computer-aided manufacturing (CAD-CAM) milled 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP).

MATERIALS AND METHODS

Forty bar-shaped specimens (45 × 4 × 3 mm) were prepared using two manufacturing technologies: 3D printing (LithaCon 3Y 210, Lithoz GmbH, Vienna, Austria; n = 20) and milling (Initial Zirconia ST, GC, Japan; n = 20) of 3Y-TZP. The chevron-notch beam method was used to assess the fracture toughness according to ISO 24370. Specimens from each 3Y-TZP group were divided into two subgroups (n = 10) based on the artificial aging process (autoclaving): nonaged and aged. Nonaged specimens were stored at room temperature, while aged specimens underwent autoclave aging at 134°C under 2 bar-pressure for 5 h. Subsequently, the specimens were immersed in absolute 99% ethanol using an ultrasonic cleaner for 5 min. Each specimen was preloaded by subjecting it to a 4-point loading test, with a force of up to 200 N applied for three cycles. Further 4-point loading was conducted at a rate of 0.5 mm/min under controlled temperature and humidity conditions until fracture occurred. The maximum force (Fmax) was recorded and the chevron notch was examined at 30 × magnification under an optical microscope for measurements before the fracture toughness (KIc) was calculated. Microhardness testing was also performed to measure the Vickers hardness number (VHN). A scanning electron microscope (SEM) coupled with an energy dispersive X-ray unit (EDX) was used to examine surface topography and chemical composition. X-ray diffraction (XRD) was conducted to identify crystalline structure. Data were statistically analyzed using two-way ANOVA and Student's t-test with a significance level of 0.05.

RESULTS

The nonaged 3D-printed 3Y-TZP group exhibited a significantly higher fracture toughness value (6.07 MPa m1/2) than the milled 3Y-TZP groups (p < 0.001). After autoclave aging, the 3D-printed 3Y-TZP group maintained significantly higher fracture toughness (p < 0.001) compared to the milled 3Y-TZP group. However, no significant differences in hardness values (p = 0.096) were observed between the aged and nonaged groups within each manufacturing process (3D-printed and milled) independently.

CONCLUSION

The findings revealed that the new 3D-printed 3Y-TZP produced by the lithography-based ceramic manufacturing (LCM) technology exhibited superior fracture toughness after autoclave aging compared to the milled 3Y-TZP. While no significant differences in hardness were observed between the aged groups, the 3D-printed material demonstrated greater resistance to fracture, indicating enhanced mechanical stability.

Effect of rapid cooling on residual stress and surface fracture toughness of dental zirconia

Short-time sintering of dental zirconia not only improves manufacturing efficiency of zirconia prosthetics, but also enables an attractive situation in which prosthetic treatment can be completed within a single visit. Although many studies have clarified the effects of heating rate and dwell time on the properties of dental zirconia during short-time sintering, there are only a few studies on rapid cooling. In this study, we investigated the effect of cooling rate on dental zirconia. It was found that the cooling rate had no effect on the three-point flexural strength, but a fast cooling rate improved fracture toughness at the material surface. Raman piezo-spectroscopy showed that a compressive stress layer formed in the neighborhood of the zirconia surface and that its thickness increased with increasing cooling rate. From the above results, it was concluded that the compressive stress layer formed on the surface by rapid cooling improved the apparent fracture toughness at the material surface.

Qualitative surface roughness of lithium disilicate endo-crown for pulpotomized primary molars

Rehabilitation of pulpotomized primary molars with an appropriate restoration is essential for recovering function and safeguarding the durability of the treatment. This study aimed to assess and compare the surface roughness of stainless steel (ST) crowns, zirconia (ZR) crowns, fiberglass (FG) crowns, and lithium disilicate (LD) endo-crowns as a restoration for pulpotomized primary molars also, evaluating the surface roughness of their antagonists. Sixty pulpotomized primary mandibular first molars were used for qualitative surface roughness evaluation and divided into four groups (n = 15/group) according to the crown type (group-ST, group-ZR, group-FG, group-LD). While the other sixty sound, unprepared primary maxillary first molars were used for evaluation of their surface roughness against the tested crowns. Specimens' preparation and cementation were carried out according to each crown type and manufacturer's instructions. The surface roughness was done using a two-body wear test. The data were statistically analyzed. All tested crowns showed an increased change in surface roughness, except group-ZR, which had the least change in surface roughness after mechanical wear with no statistically significant difference(P = 0.681). All crown types significantly increased the surface roughness of their antagonists after mechanical wear, except group-ST which showed insignificant affection (p ≥ 0.05). Zirconia crowns and lithium disilicate endo-crowns had the least change in surface roughness compared to other groups while SSCs showed the least tooth loss in the antagonist enamel.

Evaluation of Hardness and Wear of Conventional and Transparent Zirconia Ceramics, Feldspathic Ceramic, Glaze, and Enamel

The aim of the study was to compare the hardness, coefficient of friction, and wear experienced by four different ceramic samples: 3Y-TZP zirconium oxide ceramics-Zi-Ceramill Zi (Amman Girrbach), 5Y-PSZ transparent zirconium oxide ceramics-Zol-Ceramill Zolid (Amman Girrbach), Sak-feldspathic ceramics-Sakura Interaction (Elephant), and Glaze (Amman Girrbach). The Vickers hardness of the samples was measured. Friction tests ball-on-disc were performed between the discs of four ceramics and a zirconia ceramic ball, then a premolar tooth as a counter-sample. The mass loss and the friction coefficients of the ceramic samples were determined. The tooth counter-samples were 3D scanned, and enamel attrition depths and mass were measured. The following hardness values (HV1) were obtained: 1454 ± 46 HV1 for Zi, 1439 ± 62 HV1 for Zol, 491 ± 16 HV1 for Sak, 593 ± 16 HV1 for Glaze, and 372 ± 41 HV1 for enamel. The mass losses of the teeth in contact with ceramics were 0.1 mg for Zi, 0.1 mg for Zol, 5.5 mg for Sak, and 4 mg for Glaze. Conventional and transparent zirconium oxide ceramics are four times harder than enamel and three times harder than veneering ceramics. Zirconia ceramics exhibit lower wear and a more homogenous, smoother surface than the other ceramics. Tooth tissues are subject to greater attrition in contact with veneering ceramics than with polished zirconium oxide ceramics.

An Approach to Improve Specimen Processing for the Flexural Strength Testing of Zirconia

Measuring the flexural strength of restorative materials such as zirconia is crucial for providing proper indications for clinical applications and predicting performance. Great variations in specimen preparation for flexural strength measurements exist among laboratories. The aim was to evaluate how the processing method, surface treatment, and test method of the specimens affect the flexural strength of zirconia. Zirconia specimens (VITA YZ HT) (n = 270) were processed using CAD/CAM or were conventionally milled with three different surface treatments (machined, ground, polished) and were measured with three-point bending (non-chamfered/chamfered) or biaxial flexural strength test. Weibull statistics were conducted. The mean flexural strength values ranged from 612 MPa (conventional, machined, three-point bending non-chamfered) to 1143 MPa (CAD/CAM, polished, biaxial flexural strength). The highest reliability is achieved when specimens are prepared using thoroughly controllable processing with CAD/CAM and subsequently polished. Higher strength values are achieved with the biaxial flexural strength test method because the stress concentration in relation to the effective volume is smaller. Polishing reduces surface microcracks and therefore increases the strength values.

Effect of different surface treatments on the bonding potential and physical and mechanical properties of ultratranslucent zirconia

STATEMENT OF PROBLEM

Studies to determine a suitable surface treatment that improves bonding without compromising the strength or translucency of ultratranslucent zirconia are scarce.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of different surface treatments on translucency, surface topography, phase transformation, biaxial flexural strength, bond strength, and durability.

MATERIAL AND METHODS

A total of 169 ultratranslucent zirconia disks were randomly divided into 4 groups according to the surface treatment applied: airborne-particle abrasion (APA) (n=46), tribochemical silica airborne-particle abrasion (TS) (n=46), nonthermal oxygen plasma (NTP) (n=46), and no treatment, control (C) (n=31). The translucency parameter (ΔTP00) was evaluated with a spectrophotometer (n=15), phase transformation was assessed with an X-ray diffractometer (n=5), surface topography was evaluated with a scanning electron microscope (SEM) (n=3), and biaxial flexural strength (BFS) was tested with a universal testing machine (n=15). For the microshear bond strength (μSBS) test, 40 composite resin specimens were attached to 8 disks and tested with a universal testing machine; 20 specimens were tested after 24 hours, and 20 specimens after hydrothermal aging in a thermocycler (TC). The data were analyzed with ANOVA followed by the Tukey post hoc test (α=.05). Weibull analysis was performed for the flexural strength and μSBS results.

RESULTS

Significant ΔTP00 differences were found among all groups and were highest for the APA group (7.33) and lowest for the NTP group (4.79). The NTP group had a significantly higher monoclinic weight fraction value (4.54%) than other groups. The NTP group had significantly higher BFS (581.31) than other groups, while the APA group showed significantly lower values than other groups (340.43). The APA group had significantly higher μSBS values after 24 hours (13.51 MPa) and after TC (13.68 MPa) than the other groups (P<.05).

CONCLUSIONS

Although APA and TS are effective techniques for improving resin-zirconia bonding, they result in significantly higher deterioration of translucency and strength. NTP significantly improved the BFS of zirconia; however, it showed lower bond strength values than other methods.

Effect of non-thermal plasma treatment and resin cements on the bond strength of zirconia ceramics with different yttria concentrations

OBJECTIVES

To investigate the effect of different surface treatments and resin cements on the shear bond strength of zirconia ceramics with different yttria concentrations.

METHODS

Zirconia blocks characterized by different yttria concentrations [Vita YZ HT (HT), Vita YZ ST (ST) and Vita YZ XT (XT)] were used to prepare disc-shaped specimens (n=252). Specimens prepared to investigate shear bond strength (SBS), water contact angle and surface roughness (Ra) were divided into four subgroups; control (C), sandblasting (S), sandblasting + nonthermal plasma treatment (SNTP) and nonthermal plasma treatment (NTP). For SBS testing, specimens were further divided into two groups (n=108) according to the luting cement used [Panavia F2.0 (P) and Rely X U200 (R)]. The water contact angles were determined by sessile drop technique and Ra was analyzed with optical profilometer. SBS tests were performed in a universal testing machine at a crosshead speed of 0.5 mm/min. The data sets were statistically analyzed with two and three-way ANOVAs followed by post-hoc comparisons (α=0.05).

RESULTS

The water contact angle and Ra data were significantly affected by surface treatments. The mean Ra values of ST and XT were significantly lower than HT for the surface treatment groups of C and NTP. The SBS values were significantly different among the groups subjected to different surface treatments. The mean SBS values of surface treatment groups (S, SNTP and NTP) when cemented with R were significantly higher than the groups of C (p<0.05).

CONCLUSIONS

For the tested zirconia ceramics with different yttria concentrations, non-thermal plasma activation helps to improve SBS and is a promising tool in practical use.

Dielectric probing of low-temperature degradation resistance of commercial zirconia bio-ceramics

OBJECTIVES

To investigate the effect of the stability of oxygen vacancies on the low-temperature degradation (LTD) resistance of two kinds of commercial zirconia-based materials (3Y-TZP ceramics and Ce-TZP/Al2O3 composites) via the dielectric probing methods.

METHODS

The commercial 3Y-TZP ceramics and Ce-TZP/Al2O3 composites were prepared via conventional solid-state methods. Density, phase content, microstructure, strain, and biaxial flexural strength (BFS) of two materials were investigated using Archimedes method, XRD, SEM, strain-electric field (S-E) loops and ball-on-ring methods, respectively. The concentration of oxygen vacancies before and after LTD of two materials were evaluated using dielectric probing and XPS methods.

RESULTS

The XRD analysis revealed that compared to the 3Y-TZP ceramics, the Ce-TZP/Al2O3 composites showed better LTD resistance, without clear LTD. The greater LTD resistance for Ce-TZP/Al2O3 composites was associated with their stability of oxygen vacancies, by higher activation energy based on the dielectric measurements and XPS results. For the 3Y-TZP ceramics that underwent the tetragonal to the monoclinic phase transition during the LTD treatment, the concentration of their oxygen vacancies decreased after LTD. In addition, the Ce-TZP/Al2O3 composites exhibited higher flexural strength and potential fracture toughness based on the BFS testing and strain vs electric field measurement results, indicating a great potential for use in fixed restorative dental applications.

SIGNIFICANCE

This work suggested the stability of oxygen vacancies played a key role in the resistance to LTD. Optimizing the stability of the oxygen vacancies is key to the development of more reliable zirconia- based dental biomaterials with greater resistance to LTD.

Comparative assessment of flexural strength of monolithic zirconia with different thicknesses and two sintering techniques

OBJECTIVES

This study aimed to compare the flexural strength of monolithic zirconia with different thicknesses and two sintering techniques.

MATERIALS AND METHODS

This in vitro, experimental study was conducted on 28 monolithic zirconia discs with 10 mm diameter and 0.5 (n = 14) and 1.2 mm (n = 14) thickness. Each group was divided into two subgroups (n = 7) for fast (60 min) and conventional (120 min) sintering at 1450°C. After sintering, the specimens were thermocycled and their flexural strength was measured by piston-on-3-balls technique in a universal testing machine (0.5 mm/min, 1.2 mm pin diameter). Data were analyzed by the Weibull test, one-way analysis of variance, and Tukey's test (α = .05).

RESULTS

The flexural strength of specimens with 1.2 mm thickness was significantly higher than that of specimens with 0.5 mm thickness (p < .05). The flexural strength of 1.2 mm/120-min group was slightly, but not significantly, higher than that of 1.2 mm/60-min group (p > .05). The flexural strength of 0.5 mm/120-min group was slightly, but not significantly, higher than that of 0.5 mm/60-min group (p > .05).

CONCLUSION

The increase in thickness of monolithic zirconia increases its flexural strength; however, increasing the sintering time appears to have no significant effect on the flexural strength of monolithic zirconia.

Fracture characteristics and translucency of multilayer monolithic zirconia crowns of various thicknesses

OBJECTIVES

Multilayer monolithic zirconia (M-Zr) crowns can be engineered to achieve gradational translucency and color intensity. However, this modification may compromise the mechanical strength, raising concerns regarding the ability of M-Zr crowns to withstand occlusal stresses. The effects of M-Zr crown thickness on translucency and ability to endure occlusal forces were investigated at different tooth positions (incisors, premolars, and molars). The objective was to determine the minimal thickness of M-Zr crowns used in tooth preparation to meet aesthetic and functional demands.

METHODS

M-Zr samples (Vita A1) with four thicknesses (0.5, 1.0, 1.5, and 2.0 mm) were prepared and subjected to translucency testing using a digital colorimeter by 3-third and 9-square division methods. Crown-shaped M-Zr samples with three thicknesses (1.0, 1.5, and 2.0 mm) and three tooth positions (incisor, premolar, and molar) were digitally designed, and 2.0 mm metal abutments were fabricated. The samples were bonded to the abutments; their fracture characteristics were evaluated using a universal testing machine, and their fracture surfaces examined using an optical microscope. Statistical analyses included the Shapiro-Wilk test, Pearson correlation, and one-way and two-way ANOVA with a post hoc Tukey HSD test (α = 0.05).

RESULTS

Color analysis results revealed a significant negative correlation between thickness and translucency (r < -0.96, P < 0.01), with the highest values in the incisal region. Cross-sectional profiles confirmed the uniform thickness and morphology of the digitally designed M-Zr crowns. The results of fracture strength analysis showed position-dependent variability, a strong positive correlation with thickness (r > 0.96, P < 0.01), and fracture strengths consistently exceeding 1200 N across all tooth positions. Fracture patterns indicated that thinner crowns at the incisors and molars were more prone to cracking, whereas those at the premolars demonstrated significantly higher strength (4872.51 N, P < 0.05), only with crack or even no fracture occurring at 2.0 mm.

CONCLUSIONS

Thickness significantly influenced both the translucency and fracture strength of M-Zr, with the tooth position playing an additional role, albeit to a lesser extent. Although thinner crowns exhibited lower strength at each tooth position, even at a thickness of 1.0 mm, fracture strength exceeding 1200 N was maintained, surpassing the typical occlusal forces. Thus, it can be asserted that M-Zr crowns with a minimum thickness of 1.0 mm can meet both aesthetic and functional requirements.

Effect of cement spacer on fit accuracy and fracture strength of 3-unit and 4-unit zirconia frameworks

BACKGROUND

Cement spacer is essential for compensating deformation of zirconia restoration after sintering shrinkage, allowing proper seating and better fracture resistance of the restoration. Studies assessing the effect of cement spacer on fit accuracy and fracture strength of zirconia frameworks are missing in the literature. Therefore, the aim of this study was to evaluate the effect of different cement spacer settings on fit accuracy and fracture strength of 3-unit and 4-unit zirconia frameworks.

METHODS

Sixty standardized stainless-steel master dies were manufactured with 2 prepared abutments for fabricating 3-unit and 4-unit zirconia frameworks. The frameworks were assigned into 6 groups (n = 10) according to cement spacer setting (30 μm, 50 μm, and 80 μm) as follows: 3-unit frameworks; 3u-30, 3u-50, 3u-80, and 4-unit frameworks; 4u-30, 4u-50, and 4u-80. The frameworks were assessed for fit accuracy with the replica method. The specimens were cemented to their corresponding dies, and the fracture strength was measured in a universal testing machine. The Weibull parameters were calculated for the study groups and fractured specimens were inspected for failure mode. Two-Way ANOVA followed by Tukey test for pairwise comparison between study groups (α = 0.05).

RESULTS

The cement spacer had a significant effect on both fit accuracy and fracture strength for 3-unit and 4-unit frameworks. The 50 μm spacer had significantly better fit accuracy followed by 80 μm, and 30 μm spacers. Both 50 μm and 80 μm spacers had similar fracture strength, and both had significantly better strength than 30 μm spacer.

CONCLUSIONS

For both 3-unit and 4-unit zirconia frameworks, 50 μm cement spacer can be recommended over 30 μm and 80 μm spacers for significantly better fit accuracy and adequate fracture strength.

Effect of Acid Surface Treatments on the Shear Bond Strength of Metal Bracket to Zirconia Ceramics

The surface treatment of zirconia prior to bonding remains controversial and unclear. This study aimed to compare the shear bond strength (SBS) of metal brackets to zirconia under surface treatments with either 4% HF or 37% PA in both immediate loading (IML) and artificial aging by thermocycling (TMC). Methods: Eighty-four zirconia were randomly assigned to six groups based on the surface treatment and artificial aging by TMC: (1) No surface treatment (NT); (2) NT + TMC; (3) HF (4% HF for 2 min); (4) HF + TMC; (5) PA (37% PA for 2 min); and (6) PA + TMC. After bracket bonding, only the TMC groups were thermocycled for 5000 cycles. The SBS and adhesive remnant index (ARI) of all groups were analyzed (p < 0.01). Results: TMC significantly lowered the SBS more than the IML in all acid surface treatment groups (p < 0.01). The ARI score after TMC was significantly higher than the IML in all acid surface treatment groups (p < 0.001). No significant differences in the SBS values or ARI scores were observed among the surface treatments (p > 0.01). Conclusions: Two-minute simple etching methods, using either 4% HF or 37% PA, showed an insufficient SBS of metal orthodontic brackets to zirconia after TMC.

Anterior Esthetic Rehabilitation with Computer-Aided Design/Computer-Aided Manufacturing Zirconia: A Case Report

In layered zirconia prosthesis, the choice of zirconia composition, framework design, and shade is closely related to the properties of the abutments. This interdependence emphasizes how crucial it is to take a deliberate and tailored approach to meet the unique needs of every therapeutic circumstance. To successfully treat anterior teeth and achieve restorations that look natural, challenges such as incorrect size and shape, atypical gingival contour, and unsightly hues need to be resolved. Ceramodetal restorations have occasionally allowed for the most appealing, authentic replication of natural teeth, despite its proven strength, endurance, and improved aesthetics. Due to their superior cosmetic results, metal-free materials have been used for anterior rehabilitation. Materials like dental zirconia, which offers excellent aesthetics and desired mechanical characteristics, have emerged in response to the increased need for visually appealing and metal-free alternatives. In this case study context, experiences in the clinic using multilayer zirconia prostheses intended exclusively for anterior teeth are discussed.

Flexural Strength of Two Multilayered and Monochromatic High Yttria Containing Zirconia Materials Following Different Sintering Parameters

OBJECTIVES

 Sintering parameters influence the properties of zirconia. This study examined the effect of altering sintering temperature and time of monochrome and multilayer 5 mol% yttria-partially stabilized zirconia (5Y-PSZ) on flexural strength.

MATERIALS AND METHODS

 Three hundred specimens (width × length × thickness = 10 × 20 × 2 mm) were prepared from monolayer (ZX) and multilayer (ZM) 5Y-PSZ and randomly sintered at decreasing (TD: 1,450°C), regular (TR: 1,500°C), and increasing (TI: 1,550°C) sintering temperature, with extremely short (HE: 10 minutes), ultrashort (HU: 15 minutes), short (HS: 30 minutes), and regular (HR: 135 minutes) sintering time (n = 15/group). The precrack was induced on the tension side before testing for flexural strength (σ).

STATISTICAL ANALYSIS

 Analysis of variance and Tukey's test were used for significant differences of σ at p < 0.05. The microstructure and crystalline (monoclinic; m, tetragonal; t, cubic; c) phase were evaluated by scanning electron microscope (SEM) and X-ray diffractometer (XRD).

RESULTS

 ZXTIHS indicated the highest σ for ZX (315.81 ± 18.91 MPa), whereas ZMTIHS indicated the highest σ for ZM (335.21 ± 36.18 MPa). There was no significant difference for σ between ZX and ZM (p > 0.05). Sintering zirconia at TI or HR indicated significantly higher σ than sintering at TD or TR or with HS, HE, or HU for both ZX and ZM (p < 0.05). There was no significant difference for σ between TRHR and TIHS, TIHU, and TIHE (p > 0.05). SEM indicated intergranular and transgranular fractures. XRD revealed predominately c- and t-phases and minor amounts of m-phase.

CONCLUSION

 Increasing sintered temperature with decreasing time offers acceptable strength to regular sintering. Raising sintering temperature with decreasing time is suggested to facilitate chairside restorative reconstruction.

Effects of multiple firings on the translucency, crystalline phase, and mechanical strength of highly translucent zirconia

This study aimed to clarify the effects of multiple firings on the translucency, crystal structure, and mechanical strength of highly translucent zirconia. Four types of highly translucent zirconia (LAVA Esthetic, LAVA Plus, KATANA Zirconia STML, and KATANA Zirconia HTML) were fired three times at three different temperatures, and the translucency, crystal structure, and flexural strength were evaluated before and after firing. The translucency was statistically compared using repeated-measures analysis of variance; the zirconia phase composition was assessed using X-ray diffraction followed by Rietveld analysis; and the biaxial flexural strength was assessed using Weibull analysis. The translucency of LAVA Esthetic and KATANA Zirconia HTML decreased significantly after firing, and the crystal composition of LAVA Plus and KATANA Zirconia HTML changed after multiple firings, whereas multiple firings did not affect the biaxial flexural strength of any samples. Thus, multiple firings may affect the optical properties of highly translucent zirconia.

Effect of Surface Treatment with Alkaline Agents at Two Different Temperatures on Microshear Bond Strength of Zirconia to Composite Resin

Background

Zirconia, with its excellent mechanical properties, has become a popular choice for esthetic and durable restorations due to the increasing demand of patients. It has overcome most of the limitations of all ceramic restorations. However, bonding to zirconia remains a challenge.

Objectives

This study is aimed at assessing the effect of surface treatment with alkaline agents at two different temperatures on microshear bond strength (μSBS) of zirconia to composite resin.

Materials and Methods

This in vitro, experimental study was conducted on zirconia blocks measuring 2 × 4 × 8 mm. The blocks were sandblasted with alumina powder and randomly assigned to 5 groups (n = 16 each). The blocks in groups 1 and 2 underwent surface treatment with sodium hydroxide (NaOH) and groups 3 and 4 with zirconium hydroxide (Zr(OH)4) at room temperature and 70°C. Group 5 served as the control group and did not receive any surface treatment. After the application of bonding agent and its light-curing, composite cylinders in plastic tubes were bonded to the surface of each block and cured. After incubation, they underwent μSBS test. Data were analyzed by one-way ANOVA and Tukey's test (alpha = 0.05).

Results

The μSBS was significantly higher in all intervention groups than that in the control group (P < 0.05). The μSBS in Zr(OH)4 groups was significantly higher than that in NaOH groups (P < 0.05). The mean μSBS of heated groups was slightly, but not significantly, higher than the corresponding room temperature groups (P > 0.05).

Conclusion

Surface treatment of zirconia with NaOH and Zr(OH)4 alkaline agents can increase its μSBS to composite resin; Zr(OH)4 was significantly more effective than NAOH for this purpose, but heating did not have a significant effect on μSBS.

Flexural Strength of Translucent Zirconia Materials Produced with Different Multilayer Technologies: An In Vitro Study

Objective

To evaluate the flexural strength of two translucent multilayered zirconia materials produced with different multilayer technologies. Methodology. Eighty bar-shaped zirconia specimens were prepared from two different multilayered zirconia materials (IPS e.max® ZirCAD Prime and KATANA™ Multilayered Zirconia HTML) and divided into eight groups (n = 10) based on the materials used and the individual layers of the disc for each material: Dentin Prime, Transition Prime, Translucent Prime, Multilayered Prime, Dentin HTML, Transition HTML, Translucent HTML, and Multilayered HTML. The bar-shaped zirconia specimens were cut to include all the layers from translucent to dentin In Multilayered Prime and Multilayered HTML groups. All specimens were fully sintered after cutting from multilayered zirconia discs and subjected to three-point flexural strength test using the universal testing machine.

Results

The specimens made of HTML zirconia material showed significantly (P < 0.001) higher flexural strength than those made of IPS e.max® ZirCAD Prime material, with no significant difference (P > 0.05) compared to the specimens in the Dentin Prime group. The Dentin Prime specimens had the highest flexural strength (743 ± 116 MPa) compared to those in the Translucent Prime (514 ± 120 MPa), Transition Prime (575 ± 102 MPa), and Multilayered Prime (531 ± 132 MPa) groups. The flexural strength of the specimens from the individual layers of HTML zirconia material was not significantly different (P > 0.05) among the Dentin HTML (763 ± 56 MPa), Translucent HTML (791 ± 106 MPa), Transition HTML (816 ± 85 MPa), and Multilayered HTML (793 ± 102 MPa) groups.

Conclusion

Multilayered zirconia materials produced with different yttria contents by layer have lower flexural strength than those produced with gradient shade technology and the same yttria content for each layer. Therefore, various factors such as the type of prostheses, nesting strategies of prostheses within the zirconia disc, and the desired aesthetical requirements should be considered when selecting the multilayered zirconia materials.

Clinical performance of monolithic lithium disilicate hybrid abutment crowns over at least 3.5 years

PURPOSE

Hybrid abutment crowns (HACs) made from monolithic ceramics represent an efficient option for single restorations on implants. However, long-term data are scarce. The purpose of this clinical trial was to evaluate the survival and complication rates of CAD-CAM fabricated HACs over a time period of at least 3.5 years.

MATERIALS AND METHODS

Twenty-five patients with a total of 40 HACs made of monolithic lithium disilicate ceramic bonded to a titanium base CAD-CAM abutment were retrospectively evaluated. All implants and screw-retained restorations were placed and manufactured in the same department of a university hospital. Only crowns that had been in service for more than 3.5 years were included in the study. HACs were evaluated regarding technical and biological complications. Functional Implant Prosthodontic Scores (FIPS) were obtained.

RESULTS

The mean observation time was 5.9 ± 1.4 years. Implant survival was 100%, and HAC survival was 97.5%. Over the observation period, one crown fracture was observed, necessitating refabricating of the restoration. Three minor biological complications were found. The overall mean FIPS score was 8.69 ± 1.12 points.

CONCLUSIONS

Within the limitations of this study, monolithic screw-retained HACs milled from lithium disilicate ceramics and bonded to titanium bases appeared to be a reliable treatment option over more than 3.5 years due to their low biological and technical complication rates.

Full-ceramic resin-bonded fixed dental prostheses: A systematic review

Despite the development of implant-supported prostheses, there are still patients for whom conservative treatments such as resin-bonded fixed dental prostheses (RBFDPs) are more appropriate. This study's objective was to analyze the available research on full-ceramic RBFDPs. In this study, Web of Science, MEDLINE/PubMed, Scopus, Embase, Cochrane Library, and Google Scholar databases were searched for articles published in English between 2010 and 2020. A total of 14 studies were reviewed based on the eligibility criteria. The results showed that using a cantilever design with one abutment had an advantage over two abutments. Additionally, it was proposed that preparations designed with retentive aids, such as a proximal box, groove, and pinhole, could improve RBFDP survival rates. IPS e.max ZirCAD, In-Ceram alumina, and zirconia CAD/CAM were the most commonly used framework materials. Most studies used air abrasion, salinization, or hydrofluoric acid for surface treatment. Adhesive resin cements were the most frequently used type of cement. The survival rate of In-Ceram ceramics (85.3%-94.8%) was lower than that of In-Ceram zirconia and IPS e.max ZirCAD. Debonding, followed by framework fracture, was the leading cause of failure. Following 3-10 years follow-up, the survival percentage of all-ceramic RBFDPs ranged from 76% to 100%. Although RBFDPs have demonstrated satisfactory success as a conservative treatment, long-term follow-ups and higher sample sizes in clinical research are required to gain more reliable outcomes on the clinical success rate of various RBFDP designs.

Mechanical characteristics of zirconia produced additively by 3D printing in dentistry - A systematic review with meta-analysis of novel reports

OBJECTIVES

This study was aimed at comparing the mechanical parameters of ceramics made using the addition and subtraction technique.

METHODS

A search was performed on four search engines on 5th April 2023. Quality assessment was performed using study type-specific scales. Where possible, a meta-analysis was performed.

SOURCES

Data were extracted from four search engines: PubMed, PubMed Central, Embase, Web of Science, Scopus.

STUDY SELECTION

The search strategy identified 686 potential articles. 19 papers were subject to qualitative analysis, and data from 11 papers were meta-analysed. The included studies were of high or medium quality. All included papers were in-vitro studies. No clinical trials were found in the literature.

SIGNIFICANCE

Ceramics made in the additive technology in terms of mechanical parameters can compete with ceramics made in the milling technology. There are no clinical studies yet that would indicate the use of this type of material for permanent restorations in patients. Studies presented in the literature vary greatly in terms of study design and reporting of results. The research did not receive external funding.

A comparative study of the cutting efficiency of diamond rotary instruments with different grit sizes with a low-speed electric handpiece against zirconia specimens

STATEMENT OF PROBLEM

The use of zirconia in dentistry has increased. However, little attention has been given to the difficulty experienced by clinicians when cutting zirconia restorations intraorally. Evidence for which grit size and type of rotary instrument is best for cutting zirconia intraorally is lacking.

PURPOSE

The purpose of this in vitro study was to identify the most efficient diamond rotary instrument grit size for cutting zirconia intraorally.

MATERIAL AND METHODS

Efficiency was measured by comparing the cutting depth of each rotary instrument into zirconia, analyzing zirconia specimens for surface damage after cutting, and measuring instrument deterioration. Thirty zirconia specimens of the same measurements were used as test specimens and cut with 30 diamond rotary instruments with different grit sizes. An electric handpiece was used with constant force (1.7 N), speed (40 000 rpm), time (1 min), and water flow rate (25 mL/min) to produce comparative data. The mean cutting efficiency values were compared by analysis, and the median values were compared by the nonparametric Kruskal-Wallis test (α=.05). Each test was followed up with pair wise comparisons of the mean or median values if significance was indicated.

RESULTS

The greatest cutting depth was achieved with a fine-grit instrument with a mean cutting depth of 5.79 mm compared with 4.54 mm for the coarse-grit instrument (P=.032). The greatest damage to zirconia was done by the coarse- and supercoarse-grit instruments (both 33%), with no substrate damage by the superfine-, fine-, and medium-grit instruments. The greatest instrument deterioration was found on the supercoarse rotary instruments (9.05%). With only 3 exceptions, the power calculations were all sufficient and above 83%.

CONCLUSIONS

The fine grit rotary instrument (between 40 and 50 µm) was the most efficient, achieving the greatest cutting depth, with no detectable macroscopic damage to the zirconia and minimal instrument deterioration.