Monolithic Zirconia Restorations Research Articles

Translucency and Color Difference of Monolithic Zirconia Restorations: The Effect of Surface Finishing on Background Color

Aim: This study evaluates the effect of different surface finishing procedures on the color and translucency values of monolithic zirconia materials on three different colored composite backgrounds. Materials and Methods: Sixty monolithic zirconia blocks of three different translucency levels were prepared in vitro using computer-aided design/computer-aided manufacturing (CAD/CAM) systems. The correlation between repeat measurements was 0.5, resulting in a sample size of nine samples per group to detect a medium effect size, f = 0.25. Half of the zirconia blocks in each group were subjected to glazing, while the other half were polished ( n = 10). Composite blocks of three different colors were prepared to simulate dental substrates, and the zirconia specimens were placed on these composite backgrounds. The color parameters of the specimens were measured using a spectrophotometer on gray, black, and white backgrounds. Three-way repeated measure ANOVA was used to assess the interaction between the three independent variables (zirconia brand, surface finishing technique, and background color) and the effects of each tested variable on the changes in color and translucency. Results: The surface finishing techniques had a significant effect on the color and translucency of the monolithic zirconia materials. Glazing resulted in higher color differences and lower translucency values compared to polishing. For backgrounds of the same color, no significant differences were detected between the glazed zirconia groups for the same condition ( p > .016). Conclusion: Overall, the study demonstrated the importance of selecting the appropriate surface finishing technique and translucency property of the monolithic zirconia materials to obtain the optimal esthetic results in dental restorations.

Effects of Coloring Liquid Dipping Time and Surface Finishing Procedures on the Optical Properties of Monolithic Zirconia.

Monolithic zirconia restorations can be produced from self-colored or uncolored blocks. The coloring procedure of uncolored blocks and surface treatments may affect the appearance of the restoration. The purpose of this study is to evaluate the effect of liquid coloring and surface treatments on optical properties of translucent monolithic zirconia. All specimens were cut from zirconia blocks with a thickness of 1 mm. Specimens were dipped in the coloring liquids for 3 min, 5 min, and 7 min and then divided into groups of 10 specimens for surface treatments. Glaze and mechanical polishing were applied, and the color of the specimens was measured under the D65 lighting condition with a spectrophotometer device. Color values obtained from the CIE Lab formula and the translucency parameter (TP), opalescence parameter (OP), and contrast ratio (CR) were calculated. The normality of the data was confirmed with the Shapiro-Wilk test. A three-way analysis of variance (ANOVA) was used to assess the effect of dipping time, liquid shade, and surface treatments. The effect of liquid shade and dipping time on the TP, OP, and CR parameters were statistically significant, and the TP values were reduced with the application of coloring liquid. Mechanical polishing groups had higher OP values and lower TP values than glazed groups. In cases where high translucency is required, it may be advisable to use self-colored blocks and apply glaze as a surface treatment to achieve the desired optical properties.

Influence of screw channel angulation on reverse torque value and fracture resistance in monolithic zirconia restorations after thermomechanical cycling: an in-vitro study

BackgroundWhile the concept of angled screw channels has gained popularity, there remains a scarcity of research concerning the torque loss and fracture strength of monolithic zirconia restorations with various screw channel angulations when exposed to thermomechanical cycling. This in-vitro study aimed to evaluate the reverse torque value and fracture resistance of one-piece screw-retained hybrid monolithic zirconia restorations with angulated screw channels after thermomechanical cycling.MethodsOne-piece monolithic zirconia restorations, with angulated screw channels set at 0°, 15°, and 25° (n = 6 per angulation) were fabricated and bonded to titanium inserts using a dual-cure adhesive resin cement. These assemblies were then screwed to implant fixtures embedded in acrylic resin using an omnigrip screwdriver, and reverse torque values were recorded before and after thermomechanical cycles. Additionally, fracture modes were assessed subsequent to the application of compressive load. One-way ANOVA and Bonferroni post hoc test were used to compare the groups (α = 0.05).ResultsThe study groups were significantly different regarding the fracture resistance (P = 0.0015), but only insignificantly different in the mean percentage torque loss (P = 0.4400). Specifically, the fracture resistance of the 15° group was insignificantly higher compared to the 0° group (P = 0.9037), but significantly higher compared to the 25° group (P = 0.0051). Furthermore, the fracture resistance of the 0° group was significantly higher than that of the 25° group (P = 0.0114).ConclusionsOne-piece hybrid monolithic zirconia restorations with angulated screw channels can be considered an acceptable choice for angulated implants in esthetic areas, providing satisfactory fracture strength and torque loss.

Effect of Different Sintering Procedures on Marginal and Internal Fit, Color, and Fracture Load of Monolithic Zirconia Fixed Partial Prosthesis.

The aim of this in vitro study is to investigate the effects of different sintering procedures on the fit, color parameters, and fracture load of monolithic fixed partial prosthesis. Metal model was scanned and fixed partial prosthesis was designed. Groups were created by fabricating fixed partial prosthesis by using four different sinterization procedures (Prettau-Standard (PST), Prettau-Slow (PSL), Ice-Speed (IS), Ice-Standard (IST), n=10). PST-PSL (Group P, N=20) and IS-IST (Group I, N=20) were colored with different coloring liquids. The marginal and internal fit were measured using the silicone replica method. CIELAB values of the samples were measured using a spectrophotometer. Then, for each sample, the die was obtained from polymethyl methacrylate. The specimens were cemented into dies and tested in a universal testing machine for fracture load. One-way ANOVA were performed to assess the effect of the sintering procedure on the marginal and internal fit, fracture load, and ∆E00, ∆L', ∆C', and ∆H' values of fixed partial prosthesis. PSL and PST groups showed significantly smaller internal and marginal fit compared to the IS group. Additionally, IST group internal fit values were significantly higher than Prettau groups. Sintering time reduction led to a decrease in ∆E00 values. Fracture loads values were not statistically significantly affected by the different sintering procedures in both brands. Different sintering procedures did not have a clinically significant effect on fit and fracture load. Different sintering procedures were found to have an impact on the color change of monolithic zirconia restorations.

Fracture resistance of hybrid ceramic abutments with different restoration lengths: A pilot study.

In this pilot study, the fracture resistance of hybrid abutments with different restoration lengths was investigated. Sixteen monolithic zirconia restorations of an upper right incisor were designed to fit a titanium base abutment. Eight central incisors had a crown length of 8 mm (T1) and the other half a length of 12 mm (T2). All crowns were cemented on the titanium base using a resin cement. After cementation, the samples were placed in a thermocycler for 5000 cycles. Fracture strength was measured using a universal test machine. Deformations and fractures of the samples were investigated. The mean fracture resistance of T1 was 515 N (SD 96 N, 339-650) and 305 N (SD 57 N, 234-408) for T2 (p < 0.001). Both groups showed deformation of the titanium base, with no significant difference between both groups (p = 0.200). A difference in fracture type (p = 0.013) was observed, with significantly more screw fractures occurring in group T1 (p = 0.026). Within the limitations of this study, hybrid restorations with standard titanium base abutments can withstand forces that have been associated with chewing, irrespective of the crown length. However, the shorter crowns demonstrated more fatal fractures.

Repair of monolithic zirconia restorations with different direct resin composites: effect on the fatigue bonding and mechanical performance

ObjectiveThe study aims to evaluate the shear bond and flexural strength fatigue behavior of yttrium-stabilized zirconia (4YSZ) repaired using different resin composites.Materials and methodsCylindric specimens of 4YSZ were obtained for the bond strength (Ø = 6 mm, 1.5 mm of thickness) and biaxial flexural strength (Ø = 15 mm, 1 mm of thickness) fatigue tests and divided into 3 groups according to the repair resin composite: EVO (nanohybrid), BULK (bulk-fill), and FLOW (flowable). The zirconia surface was air-abraded with alumina particles, a 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) primer was applied, and the resin composite was build-up over the zirconia. Fatigue shear bond strength and flexural fatigue strength tests were performed (n = 15). One-way ANOVA and Tukey post hoc tests were carried out for both outcomes, besides scanning electron microscopy and finite element analysis.ResultsThe repair material affected the fatigue shear bond strength of zirconia ceramic. The BULK group (18.9 MPa) depicted higher bond strength values than FLOW (14.8 MPa) (p = 0.04), while EVO (18.0 MPa) showed similar results to both groups. No effect was observed for the mechanical behavior (p = 0.53). The stress distribution was similar for all groups.ConclusionThe repair of yttrium-stabilized zirconia (4YSZ) ceramics with bulk-fill resin composites was the best option for high fatigue bond strength. However, the fatigue mechanical performance was similar regardless of the applied repair material.Clinical relevanceThe repair of yttrium-stabilized zirconia (4YSZ) monolithic restorations may be performed with nanohybrid and bulk-fill resin composites in order to promote longevity in the treatment.

Influence of glazing and aging on the marginal, axial, axio-occlusal, and occlusal fit of 3-unit monolithic zirconia restorations fabricated using additive and subtractive techniques

Studies are sparse on how glazing and aging influence the fit of additively fabricated monolithic zirconia restorations. The purpose of this in vitro study was to assess the effect of glazing and aging on the fit of 3-unit monolithic zirconia restorations fabricated using different techniques. A total of 32 monolithic zirconia restorations were fabricated for a typodont model by using 4 distinct techniques (subtractive fabrication [SF], stereolithography [SLA], digital light processing [DLP], and lithography-based ceramic manufacturing [LCM]). The silicone replica approach was adopted to measure the discrepancy values for premolar and molar abutments after sintering, glazing, and 1 year of aging. The silicone replicas were sliced into mesiodistal and buccopalatal cross-sections, and digital micrographs of the cross-sections were made with a ×80 stereomicroscope. An inherent measuring program was run to record the discrepancy values (µm). Repeated-measures 2-way ANOVAs with the Bonferroni post hoc test were used to statistically analyze the acquired data. (α=.05). From the repeated measures 2-way ANOVAs, both the glazing×fabrication technique and the aging×fabrication technique interactions were not statistically significant (P>.05). Glazing significantly influenced premolar abutment marginal (P=.022) and occlusal (P=.007) discrepancy values, as well as molar abutment marginal discrepancy values (P=.047). Aging had a statistically significant effect on premolar abutment marginal (P=.008) and occlusal (P=.011) discrepancy values, as well as molar abutment occlusal discrepancy values (P=.039). In both the glazing and aging data, for all areas of interest, statistically significant differences were detected among the fabrication techniques (P<.05). The LCM group had the lowest discrepancy values, followed by the SLA, SF, and DLP groups. The LCM and SLA groups outperformed the other groups in terms of fit accuracy. The glazing and aging procedures altered the discrepancy values. The marginal discrepancy values of all groups were below the threshold of clinical acceptability (<120µm).

Vertical Marginal Discrepancy of a Monolithic Zirconia Crown with Different Cement Spaces

The long-term clinical success of indirect restorations highly depends on their marginal integrity. The cement space is an element that might affect the marginal integrity, but it can be altered during the configuring of the computer-assisted designing/computer-aided manufacturing (CAD–CAM) restoration. However, there is controversy in the literature regarding the effect of the cement space on the precision of zirconia crown marginal adaptation. The aim of this study was to measure the vertical marginal discrepancies between different cement thickness settings for CAD–CAM monolithic zirconia restorations. Material and Methods. An artificial mandibular right molar tooth mounted on a typodont was prepared for a zirconia crown using the standard method. The study sample consisted of 30 zirconia crowns (Zenostar Zr Translucent Zirconia, Weiland Dental, Germany) milled using an (iMes-iCore) milling machine. Each group of 10 crowns was designed with 30–50 and 70 μm spacer thicknesses. The vertical marginal adaptation at the center of the four different planes (mesial, distal, buccal, and palatal) was measured under a microscope at 40x magnification. A one-way analysis of variance test was used for statistical analysis. Results. The mean of Group 30 was 27.45; of Group 50 was 22.22; and of Group 70 was 22.90. There was no statistically significant difference between the groups ( p ≥ 0.5 ). Conclusions. The increase in the cement space up to 70 μm did not influence the vertical marginal adaptation of the monolithic zirconia crowns.

Longevity of extrinsic stains on monolithic zirconia restorations: An in vitro study

Three-mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) has been commonly used for fixed prosthodontic restorations. The opacity of 3Y-TZP may be masked with external staining, although the longevity of extrinsic stains applied to monolithic zirconia is unclear. The purpose of this in vitro study was to analyze the color and surface roughness of extrinsically stained zirconia specimens after thermocycling and toothbrushing. Monolithic Ø12.5×1.25-mm zirconia disks were milled from 3Y-TZP blocks, sintered according to manufacturer instructions, and then divided into 3 groups (C, J, and O; n=16) for application of stain and glaze. All specimens underwent 10 000 thermocycles in distilled water before being further divided into 2 dentifrice groups (n=8): normal grit, low relative dentin abrasivity (RDA) (Subgroup N) and abrasive grit, high RDA (Subgroup A). Specimens were brushed in a multistation brushing machine under 1.47N of force using a 5:8 toothpaste and distilled water slurry for 10 000 cycles with a straight (American Dental Association Standard) toothbrush to simulate 1 year of toothbrushing. Color and surface roughness measurements were obtained at 3 time points: baseline, after thermocycling, and after brushing. A 2-way repeated measures ANOVA was used to independently assess changes in color and surface roughness with respect to thermocycling and brushing (α=.05). Group J displayed no significant change in color for either dentifrice system (P>.05). However, a significant change in surface roughness was observed for both dentifrice subgroups (P<.001). Group C specimens displayed significant changes in color (P<.001) and surface roughness (P<.001) for both dentifrice systems. Group O specimens displayed significant changes in color (P<.025) for both dentifrice systems and significant changes in surface roughness (P<.004) for subgroup A, but no significant changes for subgroup N (P=.075). Artificial aging of monolithic zirconia resulted in changes in color and surface roughness that did not surpass the thresholds for perceptibility and acceptability. This study failed to establish durability limits for extrinsic stains applied to 3Y-TZP.

Fatigue resistance of 3D printed anatomic post-and-core after mastication simulation

Rigid post-and-core systems have traditionally been used in the restoration of endodontically treated teeth and are regarded by many as the standard treatment. Flexible materials, including nanoceramic resins, are being increasingly implemented as post-and-core systems, but data supporting their use are lacking. The purpose of this in vitro study was to compare the fatigue resistance of conventional cast metal and nanoceramic 3-dimensionally (3D) printed resin post-and-core systems with teeth without posts. Thirty freshly extracted human maxillary premolars were endodontically treated and divided into 3 subgroups (n=10) according to the restorative procedure: cast metal post-and-core (CM), nanoceramic 3D printed resin post-and-core (3DR), and without a post (0P). The CM post-and-core group was fabricated conventionally, while the 3DR group was printed using a 3D resin printing material. For the 0P group, the teeth were restored with a composite resin foundation after root canal obturation. Complete coverage 3-mol% monolithic zirconia restorations were cemented on all specimens. The specimens were exposed to simultaneous mastication simulation (1.2 million cycles) and thermocycling (10 000 cycles at 5 ºC to 55 ºC) and analyzed based on the failure of specimens. Data were analyzed using the Kruskal-Wallis survival analysis and the Wilcoxon rank sum test (α=.05). The Kruskal-Wallis test indicated statistically significant differences among the cycles needed to reach failure for each of the 3 groups (P<.001). At 1.2 million cycles, there were no CM failures. The 3DR group failed at a median value of 950 000 cycles, while the 0P group failed at a median value of 222 500 cycles (P<.001). All the endodontically treated teeth that received CM survived the 1 200 000 simulated mastication cycles. Both 3DR and 0P specimens fractured at the crown cervical third during mastication simulation.

Retrospective clinical study of 1472-unit monolithic zirconia restorations with feather-edge margins realized with digital workflow.

To evaluate the clinical performance of monolithic zirconia restorations with feather-edge margins fabricated by digital impressions. All participants that present monolithic zirconia restorations with feather-edge margins realized with digital workflow were evaluated during scheduled periodontal maintenance between February and September 2022 according to predetermined inclusion criteria. Clinical performance was assessed using the modified USPHS and periodontal parameters. Overall survival was calculated for monolithic zirconia restorations. Technical and biologic complications were reported. Descriptive statistical analysis and life-table analyses were performed for all data. A total of 1472 monolithic zirconia FDPs (1279 on abutments and 193 on pontics) placed in 1189 patients (982 males and 490 females) from February 2017 to September 2020 were analyzed. The mean follow-up was 44 months (range 36-61 months), and the overall survival rate was 98.5%. There were 931 single crowns, 96 were 3-unit FDPs, 33 were 4-unit FDPs, 11 were 5-unit FDPs, and 6-unit FDPs. Three single crowns had irreparable cracks, and 6 single crowns and one 4-unit FDP were fractured. One 3-unit FDP failed due to tooth fracture and 5 single crowns failed due to endodontic failure. The loss of retention was noted in 25 monolithic zirconia FDPs and hypersensitivity in 44 single crowns. Biologic complications were uncommon. Based on the results and its limitations, the monolithic zirconia FPDs and digital impressions represent a favorable prosthetic treatment similar to that reported with other margin designs CLINICAL RELEVANCE: Monolithic zirconia restorations on vertical-margin abutments fabricated using a digital workflow demonstrate excellent clinical performance. The digital clinical workflow without the use of a cast means a reduction in costs, steps, and operating time.

Illuminant metamerism between natural teeth and zirconia restorations evaluated with a chromatic adaptation transform

Little is known about the effect of illuminant metamerism between natural teeth and zirconia restorations, despite their increasing clinical popularity. The purpose of this in vitro study was to compare illuminant metamerism between pairs of natural teeth and layered zirconia restorations and pairs of natural teeth and monolithic zirconia restorations under 10 different illuminants and analyze their metameric potential. Spectral reflectance factors were obtained from 10 pairs of extracted natural teeth and layered zirconia restorations and 28 pairs of extracted natural teeth and monolithic multilayer zirconia restorations. Each pair showed a color match that was within the visual threshold for clinical acceptability (CIEDE2000≤1.8). A special index of metamerism for the change of illuminant (Milm) was calculated from the CIEDE2000 color difference equation. Descriptive statistics and the one-sample t test were used to analyze the results for the Milm and for both groups of layered and monolithic zirconia restorations (α=.05). Layered zirconia restorations reached a mean ±standard deviation value for Milm=0.3 ±0.2 and Milm=0.5 ±0.4 for monolithic zirconia restorations (P<.01). The effect of illuminant metamerism between natural teeth and zirconia crowns was weak and generally within the clinical acceptability limit.

Performance of posterior third-generation monolithic zirconia crowns in a complete digital workflow: A three-year prospective clinical study

Background/purposeTranslucent monolithic zirconia restorations have recently introduced. The purpose of this study was to evaluate the clinical behavior and the survival rate of the posterior third-generation monolithic zirconia crowns (MZCs) during three years of clinical service. Materials and methodsTwenty-four patients who needed thirty crowns were enrolled in this study. Digital impressions were made, and the crowns were milled and cemented with a resin cement. The crowns outcomes were assessed using the California Dental Association's (CDA) criteria. Gingival index (GI), plaque index (PI), and periodontal probing depth (PPD) for MZCs and contralateral natural teeth (control) were assessed. Margin index (MI) for MZCs was also assessed. Data analysis was conducted using the Wilcoxon signed-rank and the Friedman tests. ResultsThe 3-year survival rate was 100%. All MZCs were rated as satisfactory throughout the follow-up period, and no biological or mechanical complications were observed. No differences were recorded when GI, PI and PPD at 3-year of follow-up were compared to baseline. No differences were recorded between crowned and control teeth. The MI remained stable throughout the study period. ConclusionThe third-generation monolithic zirconia appears to be a good treatment option for the rehabilitation of posterior single teeth.

Influence of coloring techniques on the surface characteristics and color stability of a monolithic zirconia ceramic

The color of monolithic zirconia restorations is obtained by presintering or postsintering coloring techniques. However, studies on the differences in surface characteristics and their influence on color stability are lacking. The purpose of this in vitro study was to evaluate the influence of shading and staining techniques for a zirconia ceramic on the surface characteristics and colorimetric parameters (color difference, translucency, and whiteness index) after exposure to coffee or red wine and then polishing. Ceramic disks (N=30; Ø10×1mm) were allocated into 3 groups: preshaded-shaded by the manufacturer (IPS e.max ZirCAD MT, shade A2); manually shaded-unshaded zirconia (IPS e.max ZirCAD MT, bleaching shade-BL) colored by the brushing technique, before sintering; stained-unshaded zirconia (IPS e.max ZirCAD MT BL) colored by the staining technique, after sintering. Spectrophotometric color assessments ensured the same initial perceived color (Vita Classical A2) for specimens included in the study (∆E00<1.77 acceptability threshold). Surface characteristics were assessed by scanning electron microscopy and atomic force microscopy. The specimens were immersed in coffee (n=5) or red wine (n=5) for 12 and 24 days and subsequently polished. The data were statistically and descriptively analyzed for color differences (∆E00), translucency parameters (TP00), and whiteness indexes for dentistry (WID), considering acceptability and perceptibility thresholds. The shaded groups found an irregular ceramic surface with uniformly sized zirconia crystals. The stained group found a glass-covered smoother surface. Significant alterations in color parameters (∆E00, TP00, WID) were observed with immersion in pigmenting beverages (P<.001) both after 12 days, and after 24 days. The shaded specimens had greater color alterations after immersion but benefited from the polishing procedure, which reduced color differences below an acceptable threshold in comparison with the baseline. Stained specimens had lower color alterations after immersion, but the polishing protocol was detrimental as it whitened the ceramic by subsurface exposure. The coloring technique influences the surface characteristics of zirconia ceramic and also the color parameters after exposure to colored beverages and polishing.

Http://journals.khalijedental.com.ly/index.php/ojs/article/view/55

Background and objectives. Many dental practitioners have always struggled with obtaining aesthetic restorations while preserving the remaining dental structure. The purpose of this study is to investigate the relationship between the occlusal thickness and fracture resistance of CAD/CAM monolithic zirconia restorations to determine the feasibility of reducing the occlusal thickness, particularly in the posterior area, where inter-occlusal space is typically limited and high biting forces are applied. Methods. Four experimental groups were created using thirty-two CAD-CAM monolithic zirconia crowns with different occlusal thicknesses: 2.0 mm (group 1), 1.5 mm (group 2), 1.0 mm (group 3), and 0.5 mm (group 4). Self-adhesive resin cement was used to cement the restorations to human molars. Loading the specimens until fracture occurred, and the fracture resistance and mode of failure were recorded. The data were statistically analyzed using a one-way ANOVA followed by Fisher's exact test. Results. All specimens' fracture resistance values exceeded the maximum physiological occlusal loads in molar areas, and all of the crowns had consistent microcracks. A complete fracture was only interested in one crown with a thickness of 0.5 mm. Conclusion. The occlusal thickness of CAD-CAM monolithic zirconia crowns can be decreased to 0.5 mm while still being strong enough to sustain occlusal loads.

Stress Distribution of Monolithic and Veneered 3-unit Zirconia FDPs - Finite Element Analysis.

To evaluate the effect of restoration design on fracture resistance and stress distribution of veneered and monolithic 3-unit zirconia fixed partial dentures (FDPs) using finite element analysis (FEA). Identical epoxy resin replicas of mandibular second premolar and second molar (to serve as abutment for the 3-unit bridge) were divided into four groups (n = 10): monolithic zirconia (MZ) restorations; conventional layering veneering technique (ZL), heat-pressed technique (ZP), or CAD/CAM lithium disilicate glass ceramic (CAD-on). Specimens were subjected to compressive cyclic loading on the mesio-buccal cusp of the pontic (load range 50 to 600 N; aqueous environment; 500,000 cycles) in a universal testing machine. Data were statistically analyzed at 5% significance level with Fisher exact test and Kaplan-Meier survival analysis. 3D models were constructed in accordance with experimental groups. The stress distribution in each model was analyzed and evaluated according to the location and magnitude of the maximum principal stresses (MPS) using ANSYS software. Specimens from ZL and ZP groups failed at different stages of the 500,000 cycles fatigue, while CAD-on and MZ restorations survived fatigue test. Statistically, there was a significant difference between the groups (P < .001). The MPS were located under the mesial connector in both monolithic and bilayered 3-unit zirconia FDPs. These stresses were found to be higher in monolithic geometries compared to bilayered zirconia FDPs. Monolithic 3-unit zirconia and CAD-on zirconia frameworks resulted in superior fracture resistance. Restoration design significantly affected the stress distribution of 3-unit zirconia FDPs.

The Success and Complications of Complete-Arch Implant-Supported Fixed Monolithic Zirconia Restorations: A Systematic Review

In full-arch rehabilitation with implant-supported fixed prostheses, using monolithic zirconia seems to have several advantages regarding function and esthetics. However, the current scientific evidence is still limited. Thus, the aim of this investigation was to systematically review the literature on monolithic zirconia restorations for full-arch rehabilitation, particularly pursuing the survival rate and mechanical and biological complications. This study’s protocol was registered in PROSPERO (CRD42022301799). The primary literature search was performed in PubMed/MedLine and Web of Science, and a manual search was performed (checking cross-references). The focused question was, “In an adult population with one or both edentulous arches (P), the oral rehabilitation with implant-supported fixed-monolithic zirconia (full arch) (I), compared with oral rehabilitation using fixed-metal-ceramic prosthesis on implants (C), did show superior clinical results (O) in a minimum follow-up of 1 year (T)?” Inclusion and exclusion criteria were defined. Joana Briggs Institute tools were used to evaluate the quality of the studies. Meta-analysis was performed for the variable survival rate (%), applying the specific continuous moderator (follow-up). Data heterogeneity (I2) was assessed. From the initial search, 327 references were obtained. After eliminating duplicates and applying the inclusion/exclusion criteria by reading the titles, abstracts, and full text, seven articles were included. All included articles were observational longitudinal retrospective studies, with a number of prostheses between 7 and 2039. The mean age was 60 years, and the mean follow-up was 49.7 months. They had mandibular, maxillary, or bimaxillary rehabilitations, always with screw-retained retention, with an average survival rate of 97.23%. The number of implants ranged between four and eight. The quality of the articles was over 70%, and the heterogeneity was considered low (I2 = 28.64%). Within a mean follow-up of around four years, full-arch implant-supported monolithic zirconia rehabilitations had a high survival rate and minimal complications.

Surface roughness and translucency of glazed versus polished cubic ultra-translucent multi-layered zirconia: An in-vitro study

Statement of the problem: The final surface finish after sintering or after adjustment procedure of monolithic zirconia restorations is an important issue. Currently, there is lack of evidence based recommendations regarding the best surface finishing protocols for achieving optimal surface roughness and translucency of cubic multi layered ultra-translucent monolithic zirconia. Aim: The purpose of this in vitro study was to assess the effect of surface finish protocols (glazing versus polishing) on the surface roughness and translucency of cubic ultra-translucent multi-layered zirconia. Materials and Methods: CAD/CAM fabricated ultra-translucent multi-layer cubic zirconia cylinders were cut into disc-shaped samples and sintered to end up with (16) discs of uniform dimensions 11mm diameter and 0.6mm thickness. Disc samples were divided into two equal groups according to the surface finish protocols. Group G: glazing surface finish. Group P: polishing surface finish. Surface roughness (Ra) was assessed by a non-contact profilometer and translucent parameter (TP) was assessed by spectrophotometer. Results: Surface roughness of studied samples of group 1 recorded (0.253±0.0009 µm) and (0.251±0.0024 µm) before and after glazing respectively. While for group 2 revealed (0.2547±0.0002 µm) and (0.2545±0.001 µm) respectively. While for translucent parameter of group 1 revealed (16.0553±2.659) and (15.3714±9.773) before and after glazing respectively. While for group 2 revealed (16.0553±2.659) and (14.242±8.325) respectively. There was a significant difference between both groups showing that glazing gave a smoother surface and more translucency than a polishing surface finish protocol. Conclusions: Glazing of cubic ultra-translucent multi-layered zirconia is better than polished surface finishing protocol regarding surface roughness and translucency.

Influence of Layer and Sintering Temperature on the Optical Properties of Multilayered Zirconia Materials.

To evaluate the translucency and color difference of the individual layers of two multi-layered zirconia materials at different sintering temperatures and to compare them with lithium disilicate. Multi-layered zirconia systems with four distinct layers were selected for this study: DD cube ONE ML (4Y-TZP), DD cubeX2 ML (5Y-TZP); and compared with IPS e.max CAD HT (LS2). Plate-shaped A2-shade specimens were obtained from LS2 and individual layers of both zirconia materials. Individual layers were then divided equally into three different sintering temperatures:1300°C, 1450°C, and 1600°C. The TP and ΔE were determined by a spectrophotometer. SEM images were taken. Data was analyzed using SPSS 24.0 software with a p-value ⟨0.05. A significant difference was found in TP and ΔE values amongst all types of ceramic materials. Different sintering temperatures yielded distinct TP and ΔE values when both zirconia materials were tested and compared with LS2. Finally, TP and ΔE values were different amongst the zirconia layers. Sintering temperature, type of ceramic material and different zirconia layers significantly affected the optical properties. Multi-layered zirconia materials possess a unique gradient effect that could efficiently enhance the esthetics of monolithic zirconia restorations. However, the sintering condition should be optimized.

Screw-retained internal connection zirconia CAD-CAM abutments in single implant reconstructions: Results of a 1-year prospective case series study.

To evaluate the clinical and radiographic outcomes of single-tooth implant restorations using one-piece, internally connected, screw-retained, computer-aided design and computer-aided manufactured monolithic zirconia restorations fabricated on regular diameter implants. Following a 2-stage surgical procedure, 22 implants placed in anterior and posterior areas in 21 partially edentulous patients (mean age of 55 years; 9 males/12 females) were evaluated in terms of plaque index, pocket probing depth, bleeding on probing, level of oral hygiene (OH), signs of mucositis/peri-implantitis, esthetic score (ES), gingival zenith position (GZP), papilla index score, the thickness of peri-implant gingiva, radiographic marginal bone loss, and technical complications. Implants and restorations were prospectively followed from the insertion of the restoration (baseline), up to 12-months post-loading. A 100% implant survival rate resulted after loading; one implant was lost before loading. Clinically, patients performed an adequate OH, and tissues were kept healthy. Probing depth showed a slightly lower value at baseline compared to any follow-up examination (2.26 [0.94] at baseline vs. 2.53 [0.66]mm at 12 months). ES, GZP, and the thickness of the peri-implant gingiva improved throughout the course of the study. Radiographically, average marginal bone level (MBL) was 0.40 (0.40)mm after 1-year follow-up with no differences in average MBL at all time points. Technically, after 1 year of clinical function, neither abutment fracture nor any other serious complications occurred. Hence, prosthetic reconstruction survival rate was 100%. Clinical outcomes of single-tooth implant restorations using internally connected, screw-retained, computer-aided design and computer-aided manufacturing monolithic zirconia abutments can be considered a reliable treatment alternative after 1-year clinical observation.