Zirconia Copings Research Articles

Impact of Digital Manufacturing Methods on the Accuracy of Ceramic Crowns.

The purpose of this study was to assess the accuracy of full coverage crowns produced by two manufacturing methods: additive 3D printing and subtractive milling utilizing three different predefined cement spaces. Six groups were allocated based on the manufacturing method and the predefined cement space: printed wax with a 20 µm space (PW1); printed wax with a 50 µm space (PW2); printed wax with a 100 µm space (PW3); milled wax with a 20 µm cement space (MW1); milled wax with a 50 µm cement space (MW2); milled wax with a 100 µm cement space (MW3); milled zirconia coping with a 20 µm cement space (MZ1); milled zirconia coping with a 50 µm cement space (MZ2); milled zirconia with a 100 µm cement space (MZ3). All fabricated specimens were scanned using an Identica Blue 3D scanner and saved as standard tessellation language (STL) files. A triple scan method was performed using 3-matic software to assess accuracy. The discrepancy values were recorded in micrometers, and the analysis was conducted using one-way ANOVA. The wax printing method, with a cement gap design of 100 μm, demonstrated a significant improvement in the accuracy compared to the other methods (P<.01). In contrast, the zirconia milling method exhibited significantly lower accuracy relative to the other techniques (P<0.01). Moreover, different cement spaces resulted in various accuracy levels but the only statistically significant difference was observed for the 100 µm cement space in the printed wax group. The additive 3D printing method exhibited greater accuracy than the subtractive milling approach. Furthermore, altering the cement gap was found to impact the accuracy of both techniques, albeit without statistical significance. The accuracy of each CAM technique was investigated in this study, highlighting the promising accuracy of 3D-printed patterns for the lost-wax technique over direct crown milling. However, all methods produced reliable and accurate crown restorations.

Evaluation of tensile bond strength of two different cements used for luting zirconia coping to one-piece zirconia implant - An in vitro study

Aim: The purpose of this in vitro study was the evaluation of the tensile bond strength of two different cements used for luting zirconia coping to one-piece zirconia implant. Settings and Design: The study was designed in an in vitro study setting. Materials and Methods: A one-piece zirconia implant was scanned on laboratory scanner, and thirty zirconia implants were milled by computer aided manufacturing (CAM). Subsequently, the abutment surface of each zirconia implants were scanned in laboratory scanner and coping with a hole was designed by computer-aided designing software, which was used for milling by computer-aided manufacturing (CAM). After various surface treatments of abutment and intaglio surface of coping, fifteen sets were cemented by glass ionomer cement (Group I) and the other fifteen sets by adhesive resin cement (Group II). All thirty samples after thermocycling were dried and pulled out in a universal testing machine, and tensile retention force is noted in pounds per square inch (psi). Statistical Analysis Used: Values for tensile retention force were tabulated for both the groups. Mean and standard deviation are calculated. Independent t-value and P value were calculated. Results: The least tensile retention force was reported in Group I (165.86 ± 25.74 psi). Maximum tensile retention force was received for Group II (396.81 ± 78.32 psi). Independent t-test was applied from which t-value calculated was 10.85 and P value obtained was 0.001, which means that there exists a very high difference in tensile bond strength of cement in Group I and Group II. Conclusions: Better tensile retention forces were observed in samples cemented with adhesive resin cement when compared to samples cemented with glass ionomer cement.

Effects of cementation technique and cement thickness on the retention and amount of excess cement in implant-supported restorations

PurposeTo assess the amount of excess cement and the retentive strengths of two different cementation techniques (conventional cementation and practice abutment) using copings fabricated with three different cement thicknesses (20 μm, 35 μm, and 50 μm). Materials and methodsThirty zirconia copings were fabricated on screw retained abutments and randomly divided into three equal groups (n = 10) according to the cement thickness (20 μm, 35 μm, and 50 μm). Each group was cemented with tow cementation techniques. Cementation was performed with provisional cement (Temp-Bond). In the conventional cementation technique, cement was applied until each coping was approximately half filled, and the copings were subsequently placed on the implant–abutment assembly. Then, the copings were cleaned and cemented using the practice abutment cementation technique to remove excess cement prior to the process. Each technique was performed using copings with three different cement thicknesses (20 μm, 35 μm, and 50 μm). The specimens with the cemented copings were weighed on a high-precision analytical balance before and after removing the extruded cement, and the differences between the two measurements were calculated. Then, each specimen was subjected to a pullout test using a universal testing machine. The load required to dislodge the coping was recorded. The data were analyzed using two-way and one-way analysis of variance and independent sample t tests at a significance level of 0.05. ResultsThe highest retention values were obtained for 20 μm cement thickness in the conventional technique and the practice abutment cementation technique. The amount of excess cement was the highest for the 50 μm cement thickness obtained for both cementation techniques, whereas the lowest mean values were recorded for the 20 μm cement thickness. ConclusionThe conventional cementation technique is recommended over the practice abutment technique to increase the retention of crowns cemented with provisional cement. However, care must be taken to remove the extruded cement. A cement thickness of 20 μm is preferable for enhancing the retention of cemented crowns and for reducing the amount of excess cement when applying both conventional and practical abutment cementation approaches.

Effect of Luting Materials on the Accuracy of Fit of Zirconia Copings: A Non-Destructive Digital Analysis Method.

The marginal accuracy of fit between prosthetic restorations and abutment teeth represents an essential aspect with regard to long-term clinical success. Since the final gap is also influenced by the luting techniques and materials applied, this study analyzed the accuracy of the fit of single-tooth zirconia copings before and after cementation using different luting materials. Forty plaster dies with a corresponding zirconia coping were manufactured based on a single tooth chamfer preparation. The copings were luted on the plaster dies (n = 10 per luting material) with a zinc phosphate (A), glass-ionomer (B), self-adhesive resin (C), or resin-modified glass-ionomer cement (D). The accuracy of fit for each coping was assessed using a non-destructive digital method. Intragroup statistical analysis was conducted using Wilcoxon signed rank tests and intergroup analysis by Kruskal-Wallis and Mann-Whitney U tests (α = 0.05). Accuracy of fit was significantly different before/after cementation within A (0.033/0.110 µm) and B (0.035/0.118 µm; p = 0.002). A had a significantly increased marginal gap compared to C and D, and B compared to C and D (p ≤ 0.001). Significantly increased vertical discrepancies between A and B versus C and D (p < 0.001) were assessed. Of the materials under investigation, the zinc phosphate cement led to increased vertical marginal discrepancies, whereas the self-adhesive resin cement did not influence the restoration fit.

Surface Wear and Retention Force of Zirconia and PEKK Implant-retained Crowns.

The aim of this study was to evaluate the surface wear and retention force of telescopic attachments made of zirconia primary crowns and poly-ether- ketone -ketone (PEKK) secondary crowns for 2-implant retained mandibular complete overdentures. Ten healthy completely edentulous patients aged 55-60 years were selected for this study. Each patient received two implants in the mandibular canine regions. Maxillary conventional complete dentures were constructed against implant-retained mandibular overdentures for all patients. Zirconia- PEKK telescopic attachments were fabricated to retain the overdentures where primary copings were constructed of zirconia and secondary ones were constructed of PEKK. Retention force and surface wear were evaluated at the time of overdenture insertion (T0), and after 6 months of overdenture use (T6). The results revealed less wear of zirconia copings compared to PEKK ones at T0 and T6. However, both materials showed insignificant wear after 6 months of overdenture use. A significant increase in retention force was observed after 6 months of overdenture use. Within limitations of this study, PEKK may be considered a promising alternative material for telescopic secondary crowns construction combined to zirconia primary ones, regarding the wear resistance and the satisfactory retention forces.

Effect of Plasma Treatment on Tensile Bond Strength of (5) Yttrium Zirconia Coping Fixed on Titanium Implant Abutment

Effect of Plasma Treatment on Tensile Bond Strength of (5) Yttrium Zirconia Coping Fixed on Titanium Implant Abutment

Effect of clinical and laboratory techniques of cementation on the assessment of marginal and internal fit of prosthetic elements

Aim: The aim of this in vitro study was to compare machine and manual cementation of prosthetic elements by measuring internal and marginal fits. Methods: Eighteen anatomic prefabricated abutments were used to manufacture zirconia copings in the Ceramill (n=9) and Lava systems (n=9). The copings were cemented with a fluid consistency addition silicone using a machine (n=18) and manually (n=18) according to the replica technique. They were then cut in the buccal-palatal and mesial-distal directions. The film thickness was photographed using an optical microscope and measured in the internal and marginal regions. The data collected were analyzed by repeated measures ANOVA and Bonferroni’s multiple comparison test (∂=.05). The Bland-Altman test was performed to evaluate the agreement between the methods. Results: In the evaluation of the internal and marginal misfits, the mean values observed for the cementation performed with the aid of a machine and manually, were as follows: angular regions, 76.7 μm and 76.2 μm; linear regions, 60.6 μm and 60.7 μm; incisal region, 144.8 μm and 145.2 μm; marginal region, 40.1 μm and 40.2 μm; and overall mean, 80.4 μm and 80.6 μm, respectively. No significant differences were found between the 2 methods, for any of regions and systems (P&gt;.05). The Bland-Altman test showed agreement between the methods (P&gt;.05) and that the limits of agreement found were clinically acceptable. Conclusions: Within the limitations of this in vitro study, we can conclude that cementation using manual techniques or mechanical aid produces the same cement films.

Evaluation of the Marginal Fit and Fracture Resistance of Polyetheretherketone (PEEK) and Zirconia Copings: An In-vitro Study

Introduction: In dentistry, there has been an increasing demand for aesthetics and biocompatible restorations with low plaque affinity. The success of any restoration is based on three main factors: marginal fit, fracture resistance, and aesthetics. Polyetheretherketone (PEEK) is a polymeric material that has emerged as a novel thermoplastic material with wide applications. Aim: To evaluate the marginal fit and fracture resistance of PEEK and zirconia copings fabricated using Computer-aided Design (CAD)/Computer-aided Manufacturing (CAM) technology. Materials and Methods: The present in-vitro study was conducted in the Department of Prosthodontics, MM College of Dental Sciences and Research, Mullana, Ambala, Haryana, India, from November 2022 to March 2024. The present study compared the marginal fit and fracture resistance of PEEK and zirconia copings fabricated using CAD/CAM technology. All-ceramic tooth preparations were performed on extracted maxillary first premolars, and the prepared teeth were scanned. Using three dimensional (3D) printing technology, 20 resin dies were obtained. These dies were divided into two groups: 10 for PEEK and 10 for zirconia. Ten copings for zirconia and PEEK were fabricated using CAD/CAM technology, and two reference points were marked on the copings. The copings were luted with resin cement on the dies, and marginal fit and fracture resistance were recorded. The observations were statistically analysed using a two-way Analysis of Variance (ANOVA) test and a two-sample t-test. Results: The lowest mean marginal discrepancy values (18.469±6.55 μm for the palatal aspect and 17.116±6.34 μm for the buccal aspect) were observed for the zirconia copings. These values were significantly better compared to the PEEK copings (23.941±7.73 μm on the palatal aspect and 22.338±7.89 μm on the buccal aspect). In terms of fracture resistance, PEEK copings demonstrated a higher load-bearing capacity (523.11±117.27 N) and significantly better results compared to zirconia copings (395.4±150.93 N). Conclusion: The results revealed that, when comparing both PEEK and zirconia copings, zirconia copings demonstrated a better marginal fit compared to PEEK copings. However, for fracture resistance analysis, PEEK copings exhibited better load-bearing capacity than zirconia copings.

Evaluation of the effect of surface roughness and modification of implant abutment axial wall on the retention of zirconium oxide copings before and after thermocycling.

The purpose of this study was to determine the effect of one-wall elimination of the abutment and also the surface treatment of the abutment on the retention of cement-retained, implant-supported zirconium oxide copings. In this experimental study, four straight abutments were connected to four implant analogs (DIO, UF, Busan, Korea) with 35 Ncm torque. They are mounted vertically in resin blocks. Abutments were prepared as following groups: A) abutment was used in its intact standard form as a control group. B) 4 mm of the flat wall was removed to produce an abutment with 3 walls. C) The abutment surface was abraded with 50 µm AL2O3 powder. D) 4 mm of a flat wall of the abutment was removed, then the abutment surface was abraded with 50 µm AL2O3 airborne particle.10 zirconium oxide copings were made. Samples were cemented with temp bond NE to abutments. The retention of copings was measured before and after incubation using the universal testing machine. T-test, one-way ANOVA, and Post Hoc Tukey Test were used for statistical analysis of data. In all groups, retention was decreased after thermocycling (P ≤0.001). 3 wall abutments had less retention than the control group before thermocycling. A significant difference was detected between 3 wall abutments and 4 walls of sandblasted abutments before thermocycling. After thermocycling, no difference in retention was seen between groups. Thermocycling significantly reduces the retention of implant-supported ceramic copings. Sandblasting abutments with 50 µm AL2O3 air-borne particles did not increase the retention of ziconium oxide copings which were cemented with temp bond NE. One wall elimination of abutment decreased the retention of zirconia copings. Key words:Retention, crown, abutment, zirconia coping, sandblasting.

Evaluation of Marginal and Internal Adaptation of Crowns Fabricated with Three Different Zirconia CAD/CAM Materials.

Marginal and internal adaptation are key factors that determine the clinical success of dental restorations. The aim of this study is to evaluate the marginal and internal fit of crowns fabricated with three different CAD-CAM zirconia materials; two monolithic zirconia materials and one veneered zirconia copings in comparison with conventional metal-ceramic crowns. Ninety-six extracted molars (n = 96) were selected. Teeth were randomly divided into four groups (n = 24), and the following restorations were fabricated: Metal-ceramic crowns (Control group) (Group CG); monolithic zirconia crowns (GC initial) (Group MZ1); monolithic zirconia crowns (InCoris TZI),(Group MZ2); bilayered zirconia crowns, cores (InCoris ZI) veneered with a low-fusing glass-ceramic (IPS Emax Ceram),(Group BZ). Internal and marginal adaptations were evaluated using the silicone replica technique. A total of 20 points were recorded for every tooth under the light microscope at 20x magnifications. Results were compared using one-way analysis of variance (ANOVA) and the posthoc Tukey's test at a significance level of 0.01. Marginal, marginal-internal, axial, and occlusal gaps between CG, MZ1, MZ2, and BZ crowns showed statistically significant differences (P < 0.01). Monolithic zirconia groups showed better marginal adaptation compared with the veneered zirconia crowns.

Experimental Study to Evaluate the Internal Fit between Computer Aided Designing/Computer Aided Manufactured (CAD-CAM) Zirconia Coping and Pressable Ceramic Coping

Marginal fit of the dental restoration is important to prevent microleakage and periodontal problems so as to avoid secondary caries around the abutment teeth. The purpose of the study was to compare and evaluate the internal fit of copings manufactured using a CAD/CAM-system and laboratory-made heat-pressed ceramics. For this research, typodont mandibular left first molar was prepared about 1.5mm occlusal reduction and 6˚ taper both mesiodistally and buccolingually with shoulder finish line of 1.0mm width to receive all ceramic crown which was duplicated in silicone impressions and the respective working casts were formed using Type IV die stone and the restorations were made by CAD-CAM system for zirconia coping and wax pattern for heat-pressable lithium disilicate ceramics. Total of 20 dies were made and divided into Group I- zirconia copings and Group II - heat pressable lithium disilicate ceramics, in which 10 crowns were made in each group. The crowns were cemented to the respective dies with cyanoacrylate cement using finger pressure. The samples were then sectioned facio-lingually and the three zones measured were 2mm above the marginal finish line in both lingual and buccal side and one in the center of the occlusal surface. The mean horizontal and the vertical internal adaptation discrepancies statistically analyzed using Mann-Whitney test. It was concluded that CAD-CAM milled zirconia copings showed closer adaptation in the axial walls than heat pressed ceramic copings. But in the mid occlusal level where the adaptation was closer in heat pressed ceramic copings than the CAD-CAM milled zirconia copings.

Influence of exposure of customized dental implant abutments to different cleaning procedures: an in vitro study using AI-assisted SEM/EDS analysis

PurposeDental implant abutments are defined as medical devices by their intended use. Surfaces of custom-made CAD/CAM two-piece abutments may become contaminated during the manufacturing process in the dental lab. Inadequate reprocessing prior to patient care may contribute to implant-associated complications. Risk-adapted hygiene management is required to meet the requirements for medical devices.MethodsA total of 49 CAD/CAM-manufactured zirconia copings were bonded to prefabricated titanium bases. One group was bonded, polished, and cleaned separately in dental laboratories throughout Germany (LA). Another group was left untreated (NC). Five groups received the following hygiene regimen: three-stage ultrasonic cleaning (CP and FP), steam (SC), argon–oxygen plasma (PL), and simple ultrasonic cleaning (UD). Contaminants were detected using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) and segmented and quantified using interactive machine learning (ML) and thresholding (SW). The data were statistically analysed using non-parametric tests (Kruskal–Wallis test, Dunn’s test).ResultsSignificant differences in contamination levels with the different cleaning procedures were found (p ≤ 0.01). The FP–NC/LA groups showed the most significant difference in contamination levels for both measurement methods (ML, SW), followed by CP–LA/NC and UD–LA/NC for SW and CP–LA/NC and PL–LA/NC for ML (p ≤ 0.05). EDS revealed organic contamination in all specimens; traces of aluminum, silicon, and calcium were detected.ConclusionsChemothermal cleaning methods based on ultrasound and argon–oxygen plasma effectively removed process-related contamination from zirconia surfaces. Machine learning is a promising assessment tool for quantifying and monitoring external contamination on zirconia abutments.Graphical

The Influence of Alumina Airborne-Particle Abrasion with Various Sizes of Alumina Particles on the Phase Transformation and Fracture Resistance of Zirconia-Based Dental Ceramics.

The surface of zirconia-based dental ceramic restorations require preparation prior to adhesive cementation. The purpose of this study was to assess the influence of airborne-particle abrasion with different sizes of alumina particles (50 μm, 110 μm, or 250 μm) on the mechanical strength of zirconia-based ceramics' frameworks and on the extent of phase transformations. A fracture resistance test was performed. The central surface of the frameworks was subjected to a load [N]. The identification and quantitative determination of the crystalline phase present in the zirconia specimens was assessed using X-ray diffraction. The Kruskal-Wallis one-way analysis of variance was used to establish significance (α = 0.05). The fracture resistance of zirconia-based frameworks significantly increases with an increase in the size of alumina particles used for air abrasion: 715.5 N for 250 μm alumina particles, 661.1 N for 110 μm, 608.7 N for 50 μm and the lowest for the untreated specimens (364.2 N). The X-ray diffraction analysis showed an increase in the monoclinic phase content after air abrasion: 50 μm alumina particles-26%, 110 μm-40%, 250 μm-56%, and no treatment-none. Air abrasion of the zirconia-based dental ceramics' surface with alumina particles increases the fracture resistance of zirconia copings and the monoclinic phase volume. This increase is strongly related to the alumina particle size.

Influence of Vertical versus Horizontal Margin Configuration on Fracture Resistance of Zirconia Copings Restorations with Varied Occlusal Thickness

Influence of Vertical versus Horizontal Margin Configuration on Fracture Resistance of Zirconia Copings Restorations with Varied Occlusal Thickness

In Vitro Evaluation of marginal adaptation of polyether ether ketone and zirconia copings.

Polyether ether ketone (PEEK) has emerged as a new thermoplastic material with potential applications as a restorative material. Aim: This study aimed to evaluate the marginal adaptation of PEEK copings compared to zirconia copings using field emission scanning electron microscopy. A freshly extracted maxillary central incisor was prepared for a full-coverage restoration following standard principles of tooth preparation. The tooth was sent to a laboratory for fabrication of samples using computer-aided design and manufacturing (CAD/CAM). Twenty samples of polyether ether ketone (PEEK) copings (group A) and 20 of zirconia copings were fabricated (group B). The copings were scanned under a field emission scanning electron microscope and measurements were taken at four distinct points. The marginal adaptation over the buccal, lingual, mesial, and distal margins for both groups was evaluated. One-way analysis of variance (ANOVA) and independent t test were applied. Our findings indicate that PEEK showed better marginal adaptation than zirconia at all measurement points. The mean marginal gap value of the PEEK group was 33.99 ± 8.81 μm and of the zirconia group was 56.21 ± 15.07 μm. On comparing marginal adaptation among the mesial, distal, buccal, and lingual aspects, PEEK showed better adaptation on all four margins, with the best adaptation on the buccal margin that had the lowest mean gap value of 29.27 ± 6.07 μm. The zirconia group adapted best at the distal margin, with a lowest mean gap value of 53.58 ± 15.25 μm (P ≤ 0.05). PEEK copings had better marginal adaptation and fit compared to zirconia copings. It may have applications as a restorative material in fixed prostheses.

Comparative Effect of No Finish Line, Heavy Chamfer, and Shoulder Marginal Designs on the Fracture Resistance of Zirconia (Cercon) Ceramic Restoration: An In Vitro Study.

Background Because all-ceramic crowns are more aesthetic and biocompatible than metal-ceramic crowns, they have grown in popularity among patients and dentists. Poor finish line layout can result in restoration margin fracturing, hence, finish line arrangement is critical to maintaining the restoration's marginal integrity. The goal of this in-vitro study is to evaluate zirconia's resistance to fracture (Cercon) ceramic restorations with three marginal designs (no finish line, heavy chamfer, and shoulder). This study is important in contributing to the ongoing debate about the optimal finish line design for zirconia restorations. Methodology Three different finish lines, namely, biologically oriented preparation technique (BOPT) with a marginal width of less than 0.3 mm, heavy chamfer with a marginal width of up to 0.3 mm, and shoulder with a marginal width greater than 0.3 mm, were made on 10 extracted maxillary first premolar tooth to make 30 epoxy resin dies on which zirconia (Cercon) coping was done using CAD/CAM technology, and marginal discrepancies were measured using a three-dimensional scanner. All the copings were affixed to their respective dies using GIC luting cement, and fracture resistance was measured using a digital universal testing machine. Results The Kruskal-Wallis test revealed that the mean fracture resistance was more in the heavy chamfer finish line, followed by the no finish line (BOPT) and the shoulder finish line. No statistically significant difference was seen between the no finish line and the heavy chamfer finish line. There was a significant difference between the heavy chamfer and shoulder finish lines (p = 0.004). Conclusions To increase the biomechanical performance of posterior single zirconia restorations, heavy chamfer margins are indicated.

The effect of different methods of cleansing temporary cement (with and without eugenol) on the final bond strength of implant-supported zirconia copings after final cementation: An in vitro study.

The temporary cement remaining inside the dental prosthesis can act as a source of microbial colonization and contamination and decrease the final cement retention. Consequently, complete removal of temporary cement before permanent cementation is suggested. This study aimed to assess the effect of different cleaning methods for removing temporary cement on the tensile bond force (TBF) of permanently cemented implant-supported zirconia copings. In this in vitro study fifty titanium abutments were screwed onto 50 analogs with 30 Ncm torque into in acrylic resin blocks. Each abutment was scanned separately, and 50 zirconia copings were designed and milled. Permanent resin cement was used to cement copings of control group (N = 10). Copings were divided into two temporary cementation types that in each group, two cleansing methods were used: Temp-S (temporary cement with eugenol and sandblasted after debonding), Samples of the control group were placed in the universal testing machine, and the TBF values were recorded. Samples of the test groups after debonding and cleaning the abutments were subjected to cement with permanent resin cement, aging, and removing. Levene test, two-way analysis of variance (ANOVA), and Tamhane post hoc tests were applied. α = 0.05. The highest and lowest TBF values were found for the TempNE-SU (554.7 ± 31.5 N) and Temp-S (492.2 ± 48 N) groups, respectively. The two groups of isopropyl alcohol baths in ultrasonics in combination with sandblasting showed statistically higher TBF values than the other two groups that used only sandblasting (P < 0.001) and had similar values compared to the control group. Sandblasting combined with immersion in an ultrasonic bath containing isopropyl alcohol resulted in statistically similar values to the values of cementation with resin cement from the beginning. However, cleaning the inside of the copings only by sandblasting method reduced the values of the final retention force in comparison to cement with permanent resin cement from the beginning.

Marginal Accuracy of Monolithic and Veneered Zirconia Crowns Fabricated by Conventional and Digital Workflows.

To compare the marginal accuracy of zirconia crowns fabricated by different workflows (conventional and digital) and designs (monolithic and veneered). A prepared maxillary first molar was used for the study. Four workflow combinations were evaluated: (1) intraoral scanning and monolithic zirconia (IOS-M), (2) intraoral scanning and veneered zirconia (IOS-V), (3) conventional impression and monolithic zirconia (IMP-M), and (4) conventional impression and veneered zirconia (IMP-V). All of the specimens had similar designs. The veneered groups had a buccal cutback for esthetic veneer application. A total of 10 crowns were produced in each workflow. The vertical and horizontal marginal accuracies were measured with a traveling microscope. Depending on the normality of the data, one-way analysis of variance test or Kruskal-Wallis test were applied to evaluate the differences among the groups (α = 0.05). The most superior vertical marginal accuracy was observed for IOS-V (mean= 22.5μm; SD = 6.7μm), followed by IMP-V (mean= 23.9μm; SD = 7.8μm), IOS-M (mean = 28.7μm; SD = 10.3μm), and IMP-M (mean = 39.8μm; SD = 22.0μm), respectively (p < 0.001). The IOS-M had the greatest mean horizontal discrepancies (mean = 23.9μm; SD = 4.3μm) followed by IMP-M (mean = 21.3μm; SD = 5.7μm), IMP-V (mean = 19.2μm; SD = 5.3μm) and IOS-V (mean = 17.6μm; SD = 5.7μm) (p < 0.001). Monolithic zirconia crowns fabricated digitally had superior marginal accuracy than monolithic zirconia crowns fabricated conventionally. Esthetic buccal veneering of predominantly monolithic zirconia copings improved the vertical and horizontal marginal accuracies.

Evaluating the Bond Strength of a Polymer Infiltrated Ceramic Network to Zirconia Using the Crossbeam Push-Off Method.

Porcelains and glass-ceramics have been used to produce CAD-milled veneers and crowns for zirconia copings and implant-abutments. This study evaluated the bondstrength of a polymer-infiltrated-ceramic-network to zirconia using two adhesive cement systems: Panavia 21 and Multilink Automix. Lithium disilicate and feldspathic porcelain were also tested as reference CAD-On materials. Long beams (3x6x40 mm³) of zirconia and short beams (3x6x15 mm³) of the CAD-On materials were prepared. Zirconia and each CAD-On material were bonded in a crossbeam arrangement and subjected to a modified tensile bond-strength test. Half of the samples in each group (n=10) were tested 5 days after bonding (baseline) and the remaining (n=10) underwent aging (50,000 thermocycles at 5°C and 55°C) prior to bond-strength testing. The effects of material, cement, and aging on the tensile bond-strength were tested using a three-way ANOVA. The reference lithium disilicate/Multilink system showed no significant differences in bond strength compared to polymer-infiltrated-ceramic-network and porcelain. The long-term retention of polymer-infiltrated-ceramic-network was not statistically different compared to the baseline values and the two reference materials. With comparable bond strength between all materials, polymer-infiltrated-ceramic-network is the favorable choice for CAD-On to zirconia copings and implant-abutments due to its superior resistance to fatigue fracture relative to porcelain.

In Vitro Comparative Evaluation of Bond Strength of CAD/CAM Monolithic Zirconia Copings Influenced by Luting Agents and Finish Line Design

The aim of the in vitro study was to comparatively evaluate the bond strength of CAD/CAM monolithic zirconia copings using three luting agents and two different finish lines. For the evaluation of bond strength, 60 extracted human maxillary first premolars were prepared to receive CAD/CAM monolithic zirconia copings. They were randomly divided into six groups of 10 samples each to receive CAD/CAM monolithic zirconia copings to bond with three different luting agents on two different finish lines. The luting agents used were RelyX U200, RMGIC, and Maxcem Elite with finish lines which were incorporated were 90° shoulder and radial shoulder finish lines. The tensile bond strength for all 60 samples was tested using the universal testing machine. Between and within the group differences in tensile bond strength were analyzed using one-way ANOVA test of significance with Tukey's post-hoc analysis. The statistical analysis revealed that the CAD/CAM zirconia copings used a combination of 90° shoulder and RelyX U200 as the luting agent (Group II) which offered the maximum bond strength. Within the constraints of this study, it could be concluded that CAD/CAM monolithic zirconia copings luted with RelyX U200 cement on a 90° shoulder finish line is the preferred method, taking the bond strength into consideration. The results of this study can be extrapolated into a clinical scenario to help the clinician decide the most apt combination of finish line design and the luting agent to achieve superior bond strengths in CAD/CAM zirconia crowns and fixed dental prosthesis.