Prettau Zirconia Research Articles

Impact of different CAD/CAM materials on internal and marginal adaptations and fracture resistance of endocrown restorations with: 3D finite element analysis

PurposeTo assess and compare the impact of various computers aided design/manufacturing (CAD/CAM) materials on internal and marginal discrepancies, fracture resistance and failure probability of Endocrown restorations with 3D Finite Element analysis.Material and methodsForty devitalized human maxillary first molars were collected. After endodontic treatment, they classified into 4 groups (n = 10) based on the materials used for endocrown fabrication. Group V (Vita-Enamic), Group N (Nacera Hybrid), Group T (Translucent Prettau Zirconia) and Group P (Pekkton ivory). All samples were exposed to artificial aging method simulating one year of clinical service. Silicone replica technique and stereomicroscope (25X) utilized to evaluate the marginal and internal gaps of endocrowns at different areas. Fracture resistance test used for cemented specimens followed by qualitative investigation utilizing Stereomicroscopy. Four models representing four endocrown systems used for restoration of severely-damaged endodontically treated upper first molar were generated for finite element analysis (FEA). Axially and centrally static occlusal compressive load was applied. Modified Von Mises and maximum principal stress values on the remaining tooth structure, cement lines and restorative materials were assessed independently. Resulted data were statistically analyzed at P-value ≤ 0.05.ResultsIn the current study, the highest mean values of internal and marginal discrepancies (μm) among studied groups were reported for Zirconia group (100.300 and 102.650) respectively, while the lowest mean value of internal discrepancy (μm) was observed for Nacera group (69.275) and the lowest mean value of marginal discrepancy (μm) was observed for PEKK group (78.4750). Regarding internal discrepancy, Vita-Enamic and PEKK groups did not exhibit any statistically significant differences (P = 0.293), however zirconia and the other tested groups exhibited statistically significant differences in the mean values of the marginal gap region (p 0.05).On the other hand, PEKK group showed the highest mean value of fracture resistance (1845.20 N) and the lowest value was observed for Vita-Enamic group (946.50 N). Regarding to stress distributions through 3D FEA, and according to modified von Mises (mvM) analysis, the greatest possible stress values were noticed in PEKK model in relation to tooth structure, cement line, and flowable composite as the following: (93.1, 64.5, 58.4 MPa) respectively, while Zirconia revealed lower maximum stress values (11.4, 13.6, 11.6 MPa) respectively.ConclusionsStatistically excellent marginal and internal fit was observed for PEKK in relation to other used endocrown materials. Also, PEKK material explained fracture resistance comparable to zirconia value while the lowest value was detected for Vita Enamic material.

Effectiveness of ceramics chair-side polishing – 2D and 3D roughness evaluation

Objectives: Considering the need for intraoral polishing of zirconia restorations, this in vitro study aimed to 1) evaluate the 2D and 3D surface roughness of different types of ceramic after their finishing and polishing and 2) compare three polishing techniques using three different polishing kits. Methods: Seventy-two specimens were obtained from two types of 3Y-TZP zirconia. After sintering, a layer of a glass-based fluorapatite veneering ceramic was applied over 24 specimens of one of the zirconia ceramics. Thus, three ceramic surfaces were set: Prettau Anterior, Prettau Zirconia, and IPS e.max Ceram. The specimens were polished with a universal or specific polishing kit (n=12). After polishing, the specimens were analyzed using white-light interferometry. Kruskal-Wallis and Mann-Whitney U tests were used (α=0.05). Results: The polishing kit used did not significantly (p=0.514) affect the surface roughness of Prettau Anterior. Regarding Prettau Zirconia, the zirconia-specific polishing kit allowed a higher Sa and Ra than the universal kit (p=0.004 and p<0.001). Regarding glass-based ceram- ic, the specific kit led to a higher Ra (p<0.001), but no significant results were found in 3D. Conclusions: The universal polishing set showed the best results for Prettau Zirconia and glass-based ceramic, but no differences were found for Prettau Anterior.

Effect of sintering process on microstructure, 4-point flexural strength, and grain size of yttria-stabilized tetragonal zirconia polycrystal for use in monolithic dental restorations

Statement of problemModifications have been made in the microstructure and sintering parameters of monolithic zirconia to improve esthetics qualities and avoid chipping of 2-layer restorations. However, how these modifications affect the physical and mechanical properties of zirconia is unclear. PurposeThe purpose of this in vitro study was to compare the influence of different sintering parameters on the microstructure, 4-point flexural strength, density, and grain size of 2 commercially available zirconia advocated for the fabrication of monolithic dental prostheses and 1 commercially available zirconia for use as a core material. Material and methodsThree presintered blocks (Ceramill Zolid, Prettau, and IPS e.max ZirCAD) were used. Specimens were cut and sintered as per the manufacturer's recommendation or as per a modified heating protocol. Ceramill Zolid (Z1450) was sintered at 1450 °C, Prettau (P1600) was sintered at 1600 °C, and IPS e.max ZirCAD (I1530) was sintered at 1530 °C by following the manufacturer's heating protocol. Groups Ceramill Zolid Z1530 and Z1600 were sintered at temperatures higher than the manufacturer's recommendation. Specimens from each group (n=13) were analyzed with X-ray diffraction (XRD), density calculus, average grain size measurement, and 4-point flexural tests. Data were compared by using ANOVA (α=.05). ResultsXRD analysis showed the presence of a tetragonal metastable phase in all groups before and after sintering. No significant differences were found in relative density values for the 3 Ceramill groups (5.98 g/cm3). Groups I1530 (6.03 g/cm3) and P1600 (6.03 g/cm3) had similar density results greater than 6.00 g/cm3. The average grain size of all groups remained lower than 1 μm. P1600 had the highest grain size (0.817 μm), and Z1450 presented the lowest grain size (0.465 μm). P1600 showed the most homogeneous flexural strength and the highest Weibull modulus (m=8.22). Z1530 presented the lowest Weibull modulus (m=4.58). IPS e.max ZirCAD (I1530) had the highest flexural strength (1057.41 ±150.54 MPa), and Ceramill Zolid Z1450 had the lowest (621.01 ±138.08 MPa). ConclusionsThe flexural strength, microstructure, crystal phase, and grain size of the analyzed zirconia varied as per the sintering processing. The IPS e.max ZirCAD had the highest flexural strength (1057.41 ±150.54 MPa), followed by Prettau zirconia (864.18 ±118.21), with a statistically significant difference (P<.05). The Ceramill Zolid zirconia presented the lowest flexural strength, as well as the lowest reliability for all sintering parameters used (Z1450: 621.01 ±138.08 MPa and m=5.42; Z1530: 713.10 ±175.44 MPa and m=4.58; Z1600: 630.15 ±112.08 MPa and m=6.87). At a lower heating rate (8 °C/min), the final density increased and excessive grain growth in group Z1530 was prevented.

Ceramic Printing - Comparative Study of the Flexural Strength of 3D Printed and Milled Zirconia.

To determine and compare the mechanical properties of 3D-printed yttriastabilized zirconia to milled isostatic pressed yttria-stabilized zirconia, with the following hypotheses: (1) The flexural strength of 3D-printed yttria-stabilized zirconia is comparable to milled yttria-stabilized isostatic pressed zirconia; and (2) thermocycling and chewing simulation do not affect the flexural strength of 3D-printed yttria-stabilized zirconia. A total of 30 bars of an experimental 3D-printed 3 mol% yttriastabilized zirconia (LithaCon 3Y 230, Lithoz) and 10 bars of milled isostatic pressed zirconia (Prettau Zirconia, Zirkonzahn) were utilized. The printed zirconia bars were divided into three groups (n = 10 bars per group): (1) untreated (control); (2) thermocycled; and (3) tested after chewing simulation. A flexural strength test was performed on all samples using a three-point bend test in an Instron Universal testing machine. One-way analysis of variance on ranks was used to compare milled to printed zirconia. The effects of thermocycling and load cycling on 3D-printed zirconia were also determined. The flexural strength values for milled and printed zirconia were 936.3 ± 255.0 MPa and 855.4 ± 112.6 MPa, respectively. There was no statistically significant difference in flexural strength between the milled and printed zirconia (P = .178). No statistically significant differences were observed between the control 3D-printed zirconia group and the thermocycled (888.4 ± 59.3 MPa) or load-cycled printed zirconia (789.6 ± 133.8 MPa; P = .119). Printed 3 mol% yttria-stabilized zirconia has comparable flexural strength to milled yttria-stabilized isostatic pressed zirconia. The thermocycling and chewing simulation used in this study did not significantly alter the flexural strength of the printed 3 mol% yttria-stabilized zirconia. These results indicate a promising role for 3D printing in the fabrication of zirconia restorations. Additional studies are needed to explore the full potential of this technology.

Acoustic properties of fracture of dental restorative materials and endocrown restorations under quasi-static loading

Objectives(1) To investigate the properties of acoustic emission (AE) signals from fracture of dental materials and endocrown restorations during quasi-static compression using the continuous wavelet transform analysis. (2) To determine by the parameters of AE signals in which structural element of tooth-endocrown system the fracture starts. MethodsFive restorative materials (zirconium dioxide (Prettau zirconia), ceramics (IPS e.max Press), metal ceramics (GC Initial MC+Nicrallium N2 BCS), composite resin (Nano Q), luting cement (Relyx™ U200)) were manufactured into discs, 13mm diameter, 5mm thick, which were divided into 5 groups (Group B, C, D, E, F, respectively) and included into Type 1. Twenty-five extracted human molars were divided into 5 groups and included into Type 2: Group A (control, no restoration); BE (tooth restored by zirconium dioxide endocrowns); CE (restored by ceramic endocrowns); DE (restored by metal ceramic endocrowns); EE (restored by composite resin endocrowns). An increasing load was applied to the center of the samples with a hard steel ball until a fracture occurred. The loading rate was 0.12mm/min. Two-channel AE detection system was used to record the AE activity during testing. The parameters including the peak frequency, bandwidth, duration time and energy of AE signals were analyzed. ResultsThe restorative materials (Type 1) differ from each other by acoustic properties such as the peak frequency main bands and energy of AE signals. The detected AE signals correspond to the different fracture types. The dominant fracture mechanism of Group C, E and F specimens was the macrocracking (brittle fracture), and of Group D specimens was the microcracking, which alternated with the plastic deformation and macrocracking. For the number of events corresponding to the brittle fracture, statistically significant differences (p<0.05) were found between all group pairs. AE signals were not released during compression test of the zirconium dioxide samples, thus the fracture was not detected.All the AE signals detected during compression test of the different endocrown systems (Type 2) had two peak frequency bands. The fracture of Groups A, BE, CE and DE samples characterized by alternating the micro- and macrocracking with plastic deformation, and the brittle fracture was the dominant fracture mechanism. The restorations of Group EE fractured without plastic deformation. For the number of events corresponding to the brittle fracture, statistically insignificant differences (p>0.05) were found between Groups A vs CE and A vs EE, and statistically significant differences (p<0.05) were found between Groups A vs BE and A vs DE. SignificanceThe initiation of fracture in the restorations with endocrowns made from different materials begins with the tooth damage. The metal ceramic endocrown restoration showed the highest fracture resistance, what is especially important for clinical use.

Changes in properties of monolithic and conventional zirconia during aging process

This study aimed to evaluate and compare the change in the various properties between monolithic and conventional zirconia during hydrothermal aging process.Four zirconia ceramics (KaVo Everest ZS-Blank: Group CE, Lava Frame Zirconia: Group CL, BruxZir: Group MB, Prettau Zirconia: Group MP) were investigated. Ninety disk-shaped specimens (diameter 15.0, thickness 1.2 mm) of each group were fabricated and randomly divided into six subgroups (n = 15). All specimens were autoclaved (134 °C, 0.2 MPa) for 0, 1, 2, 3, 4, 5 h, respectively. Confocal laser scanning microscopy, atomic force microscopy, X-ray diffraction, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy were used to analyze the surface properties. Biaxial flexural strength (BFS), nanoindentation hardness, elastic modulus, and Vickers hardness were measured for the analysis of mechanical properties. All data were statistically analyzed using ANOVA and multiple comparison Scheffé test (α = 0.05).During aging, all groups exhibited a significant increase in surface roughness (Ra, Sa, and Sq) and grain boundary height. The monoclinic phase (m-phase) of all groups increased gradually relative to the tetragonal phase. Groups MB and MP were more sensitive to aging than the others. SEM images of Groups MB and MP showed microcracks and grain push-out, which increased gradually with aging. Oxygen levels in all groups increased with aging, whereas zirconium and yttrium levels decreased. All groups showed a decrease in BFS, but no significant differences between groups were found. The elastic modulus and nanoindentation hardness values decreased significantly in all groups with aging. Vickers microhardness values of Group MB and MP decreased significantly, but those of Group CE and CL did not.Both monolithic and conventional zirconia exhibited similarities in terms of their elastic modulus, nanoindentation hardness, m-phases, and oxygen levels. However, monolithic zirconia was more prone to aging in terms of surface roughness.

Micro- Computed Tomographic Evaluation of Marginal Fit of Different Monolithic all Ceramic Crowns Fabricated Using Two CAD/CAM Systems.

the objective of the present in vitro study was to evaluate the effect of two different CAD/CAM systems on the marginal fit of three commercially available dental ceramics using micro-computed tomography. Materials and Methods: one human natural premolar was selected, received a standardized all ceramic preparation and duplicated using two types of die materials. PMMA dies were used for construction of E.max CAD and Vita Enamic monolithic crowns while zirconia dies were used for zirconia crowns. A total of thirty monolithic all-ceramic crowns (N=30) were constructed on the fabricated working dies. These were equally divided into 2 groups (n=15) according to the CAD/CAM system used as follows: group (I): Everest system and group (II): Zircon Zhan system. Each group was further subdivided into 3 subgroups (n=5) according to the ceramic material used into subgroup (E): E.max CAD glass ceramic, subgroup (Z): ice prettau zirconia and subgroup (V): Vita Enamic hybrid ceramic. Each sample was scanned for fit analysis using a quantitative micro-computed tomography scanner then were analyzed. Results: Everest CAD/CAM system showed statistically significantly lower mean marginal gap distance than ZirconZahn. Either with Everest or ZirconZahn; E.max CAD showed the statistically significantly highest mean vertical marginal gap distance followed by Zirconia while Vita Enamic showed the statistically significantly lowest mean vertical marginal gap distance.Conclusions: Micro-CT technology presents a reliable tool for evaluation of the dental restorations fit. Also, superior marginal fit is achievable with monolithic CAD/CAM hybrid ceramic compared to both zirconia based and glass ceramics

Evaluation of the Fracture resistance of Machinable Versus Copy Milling Zirconia Restoration after Cyclic Loading

Purpose: To evaluate the influence of, layering and mechanical fatigue on the Fracture resistance of Zirconia crown produced using CAD/CAM and copy milling systems. Materials and Methods: One metallic die was fabricated to simulate prepared upper premolar tooth (Tooth 24: with anatomic occlusal reduction,). Using universal milling machine Twenty crowns were fabricated using Prettau zirconia blank with a luting space settings of 60 μm. The fabricated crowns were grouped according to fabrication system in to CAD CAM and copy milling (N=20) as well as each group were divided again in to monolithic and by layered (n=10) Crowns were cemented using Panavia resin cement, then the fracture resistance were measured for half of samples using a instron device,. The other half of samples were subjected to cyclic loading (50 N load, 3700 cycles) and fracture resistance. Data were submitted to three-way ANOVA, and statistical significance was set at p < 0.05. Results: In monolithic groups (MO, CO), the highest fracture resistance was recorded with the CAD/CAM non-loaded samples, (1200.48±41.98N), while the lowest fracture resistance was recorded with the copy milled cyclic loaded samples, (1043±28.04N). In veneered groups (MV, CV), the highest fracture resistance was recorded with the CAD/CAM non-loaded samples, (800±41.57N), while the lowest fracture resistance was recorded with the copy milled cyclic loaded samples, (711±122.89N). Conclusion: CAD/CAM groups recorded statistically significant higher fracture resistance than copy milling groups. Monolithic groups recorded statistically significant higher fracture resistance than veneered groups. The cyclic loading (at 37,000 cycles) has no effects on the fracture resistance in all groups.

Clinical advantages of cad-cam-fabricated full-arch fixed implant-supported monolithic zirconia dental prosthesis with digital modelling of the occlusion surfaces

The purpose of the study was to assess the quality of the functionality of CAD-CAM full-arch fixed implant-supported monolithic zirconia dental prostheses with digital modelling of the occlusal surface. We conducted a clinical (external examination, examination of the oral cavity and prostheses, muscle palpation) and paraclinical examination of 20 patients (of them men - 61.3%, women - 38.7%) aged 41-77 years (57.19±9.05). Prostheses were based on 237 implants Nobel Replace/Select/Groovy, Nobel Parallel CC. The number of supports for one prostheses was from 6 to 10, which averaged 7.64±1.08. ZICERAM, PRETTAU ZIRCONIA were used for creating CAD-CAM full-arch fixed implant-supported monolithic zirconia dental prostheses. To record the biopotentials of the masticatory muscles, the electroneuromyographic system "Synapsis" with surface electrodes was used. Electronic registration of movements of the mandible was carried out on an electronic axiograph "CADIAX 3 diagnostic", using the software "Gamma Dental Software". Statistical processing of the data was carried out using a PC in an Excel 2016 using the IBM SPSS Statistics 23 statistical software package. The survival rate was 100% for implants and prostheses. Additional in vitro and clinical studies will be required for more scientific analysis of the criteria for design of this type of prosthesis to minimize all types complications.

Effects of an etching solution on the adhesive properties and surface microhardness of zirconia dental ceramics

Statement of problemConventional approaches to adhesive bonding are not applicable to zirconia restorations. Recently, an etching solution, Zeta Etching Solution (ZES), has been introduced for etching the surface of zirconia. The effects of this etching solution on the bond strength and mechanical properties of zirconia are unknown. PurposeThe purpose of this in vitro study was to examine the effects of ZES on the bond strength and surface hardness of zirconia. Material and methodsTwo different types of partially stabilized tetragonal polycrystalline zirconia (TZP), Prettau zirconia (group P) and anterior Prettau (group AP), were evaluated with and without ZES etching. Each group was bonded to a zirconia substrate by using an adhesive resin cement. After 24 hours of storage in distilled water, the bond strength of the zirconia was analyzed. Vickers hardness was determined by using a microhardness tester. Scanning electron microscopy was used to analyze the surface microstructure and determine the mode of failure for each specimen. Results were analyzed and compared using 1-way ANOVA and Student t tests (α=.05). ResultsScanning electron microscopy analysis showed that etching the surface of zirconia with ZES etching solution for 60 minutes changed the morphological characteristics and microstructure of zirconia, making the surface more irregular. The changes were more pronounced for AP specimens. Etching with ZES significantly increased the shear bond strength of zirconia (P<.05) in AP specimens. The bond strength of Prettau (P group) specimens after ZES etching did not increase significantly (P>.05). An adhesive failure mode was observed for P zirconia specimens, whereas zirconia specimens exhibited a cohesive mode of failure. No significant decrease (P>.05) was observed in the mean Vickers hardness numbers. ConclusionsWithin the limitations of this in vitro study, it was concluded that etching in ZES for 30 minutes significantly enhanced the shear bond strength of highly translucent anterior Prettau (AP) zirconia restorations. Moreover, etching with ZES did not adversely affect the surface hardness of the zirconia specimens tested.

Features of fracture of prosthetic tooth-endocrown constructions by means of acoustic emission analysis

ObjectiveThe study aims at comparing the fracture resistance of different restorative materials used in dental endocrown restorations and respective endocrown restorations under a quasi-static compressive load using acoustic emission (AE) method. MethodsFive restorative materials were used in this study. The restorative materials were manufactured into discs 13mm in diameter and 5mm thick, which were then divided into 5 groups and included into Type 1: Group B: zirconium dioxide (Prettau zirconia); Group C: ceramics (IPS e.max Press); Group D: metal ceramics (GC Initial MC+Nicrallium N2 BCS); Group E: composite resin (Nano Q); Group F: luting cement (RelyX™ U200). Twenty-five extracted human molars were divided into 5 groups and included into Type 2: Group A: control, no restoration; Group BE: restored by zirconium dioxide endocrowns; Group CE: restored by ceramic endocrowns; Group DE: restored by metal ceramic endocrowns; Group EE: restored by composite resin endocrowns. An increasing load was applied to the center of the samples with a hard steel ball until a fracture occurred. The loading rate was 0.12mm/min. An AE system was used to monitor the fracture of the samples. The load corresponding to the first AE event and the final fracture load were used to evaluate the fracture resistance of the restored teeth. The data were analyzed using ANOVA and Tukey’s post hot test (α=0.05). ResultsA lower threshold of 220μV was selected to exclude spurious background signals. For the initial fracture load of Type 1 samples, Group F (0.029kN)<Group E (0.039kN)<Group D (0.056kN)<Group C (0.253kN)<Group B (intact). The same trend was found for the final fracture load, i.e., Group F (1.289kN)<Group E (1.735kN)<Group D (3.362kN)<Group C (6.449kN)<Group B (intact). For the initial and final fracture load, statistically significant differences (p<0.05) were found between group C and the others groups. For the initial fracture load of Type 2 samples, Group EE (0.069kN)<Group DE (0.072kN)<Group CE (0.148kN)<Group BE (2.511kN). For the final fracture load, Group EE (1.533kN)<Group CE (2.726kN)<Group BE (3.082 kN)<Group DE (3.320kN). The initial fracture load of the ceramic samples is somewhat higher than that for the endocrown restorations with the endocrowns made of this material (0.253 and 0.148kN, respectively). At the same time, for the metal ceramic and composite resin samples, the initial fracture loads are somewhat lower than in case of compression of the endocrown restorations with the endocrowns made of these materials (0.056 and 0.072kN; 0.039 and 0.069kN, respectively). The final fracture load of all the samples of the dental materials exceeds the strength of the respective endocrown restorations. The final fracture loads of the endocrown restorations with zirconium dioxide and ceramic endocrowns (3.082 and 2.726kN, respectively) are significantly lower than the final fracture load of the respective endocrown materials (intact and 6.449kN, respectively). SignificanceDental restorations should be made of high-strength materials. Zirconia displayed the highest fracture strength, while composite resin had the lowest fracture strength out of the materials used for the endocrowns. For teeth restored with endocrowns, the use of metal ceramics as endocrown material may lower the risk of failure during clinical use.

Effect of adhesive resin cements on bond strength of ceramic core materials to dentin.

The aim of the present study was to evaluate the effects of self-etch and self-adhesive resin cements on the shear bond strength of ceramic core materials bonded to dentin. Extracted, caries-free, human central maxillary incisor teeth were selected, and the vestibule surfaces were cut flat to obtain dentin surfaces. Ceramic core materials (IPS e.max Press and Prettau Zirconia) were luted to the dentin surfaces using three self-etch adhesive systems (Duo-Link, Panavia F 2.0, and RelyX Ultimate Clicker) and two self-adhesive resin systems (RelyX U200 Automix and Maxcem Elite). A shear bond strength test was performed using a universal testing machine. Failure modes were observed under a stereomicroscope, and bonding interfaces between the adhesive resin cements and the teeth were evaluated with a scanning electron microscope. Data were analyzed with Student's t-test and one-way analysis of variance followed by Tukey's test (α = 0.05). The type of adhesive resin cement significantly affected the shear bond strengths of ceramic core materials bonded to dentin (P < 0.05). Significant differences were noted between the ceramic core materials when the specimens were luted with self-adhesive resin cements (P < 0.05). The specimens luted with RelyX Ultimate Clicker had the highest shear bond strengths. The self-etch adhesive resin cements exhibited better shear bond strength than the self-adhesive resin cements, except for Panavia cement in the IPS e.max Press group. However, shear bond strengths of the self-adhesive resin cements were dependent on the nature of the ceramic core materials.

Effect of Thermo-Mechanical Aging on The Marginal Fit of Two Types of Monolithic Zirconia Crowns With Two Finish Line Designs

OBJECTIVES: The purpose of this study was to compare the marginal fit of two CAD/CAM monolithic zirconia crowns with two finish line designs after thermo-mechanical aging. MATERIALS AND METHODS: A total of 20 zirconia crowns were divided into two groups Bruxzir and Prettau zirconia (n=10). Each type of zirconiacrowns was divided into two groups according to the finish line design chisel (CH) and deep chamfer (DC) groups (n=5) After cementation of crowns to their correspondingdies, the vertical marginal gap was measured then the all crowns of both groups were subjected to thermo-mechanical aging then the vertical marginal gap was measured again. RESULTS: Statistical analysis showed that. The thermo-mechanical aging significantly increased the vertical marginal gap where DC non-aged Bruxzir recording the lowest mean value (31.41±5.9) and the CH aged Bruxzir recorded the highest mean value (95.28±9.2) as indicated by three-way ANOVA test (F= 23.0741,p=<0.0001<0.05). CONCLUSIONS: Thermo-mechanical aging significantly increasedthe vertical Marginal gap and the deep chamfer finish line preparation is preferredfor construction of monolithic zirconia crowns.

Effect of Glazing on Flexural Strength of Full-Contour Zirconia.

Objective The purpose of this study was to evaluate the effect of glazing on flexural strength of highly translucent zirconia materials. Materials and Methods Specimens of three brands of zirconia bars (Prettau Zirconia, Zirkonzahn; inCoris TZI, Sirona; and Zirlux FC, Pentron Ceramics) were prepared and polished according to manufacturers' instructions. Final specimen dimensions were 20 × 4 × 2 mm. The specimens from each brand were divided into 3 groups (N = 10): control, heat-treated, and glazed. Heat-treated specimens were fired without the application of the glaze material. The glaze material was applied to the glazed specimens before being fired. A three-point bending test (15 mm span) was performed in an Instron universal testing machine (ISO 6872). Data were analyzed by ANOVA and Tukey's HSD post hoc test (α = 0.05). Results Two-way ANOVA showed a significant influence of surface treatments on flexural strength of zirconia materials (P ≤ 0.05). There was no significant difference in flexural strength among the different brands of highly translucent zirconia (P ≥ 0.05). Tukey's HSD post hoc test showed that specimens in the “glazed” group had significantly lower flexural strength than the control and heat-treated groups (P ≤ 0.05). Conclusion Within the limitations of the study, external glazing decreased the flexural strength of highly translucent zirconia.

EFFECT OF FINISH LINE DESIGN AND THERMO-MECHANICAL AGING ON THE FRACTURE RESISTANCE OF TWO TYPES OF MONOLITHIC ZIRCONIA CROWNS

Objectives: The purpose of this study was to compare the fracture resistance of two types of CAD/CAM monolithic zirconia crowns with two finish line designs after thermo-mechanical aging. Materials and methods: A total of 40 zirconia crowns were milled and divided into two groups Bruxzir and Prettau zirconia (n=20). Each type of zirconia crowns was divided into two groups according to the finish line design, chisel (CH) and deep chamfer (DC) groups (n=10) After cementation of crowns to their corresponding dies, half of each group was subjected to thermo-mechanical aging, then fracture resistance was measured. Results: Statistical analysis showed the highest fracture resistance mean±SD value was recorded with Bruxzir non-aged CH group (3432.22±462.4), while the lowest fracture resistance mean±SD values was recorded with Prettau aged DC group (2658.97±417.2) as indicated by three-way ANOVA test (F= 11.8806, p= 0.0087<0.05).Conclusion: Within the limitations of this study, fully contoured zirconia crowns showed high resistance to failures and a minimally invasive preparation design should be determined as the optimal choice.

Complications and Clinical Considerations of the Implant-Retained Zirconia Complete-Arch Prosthesis with Various Opposing Dentitions

To evaluate the performance of the implant-retained zirconia complete-arch prosthesis with various opposing dentitions. The 40 patients included in this retrospective case series study were treated with one or two implant-retained zirconia complete-arch prostheses (ZIRCAP) using the Zirkonzahn protocol. Prettau zirconia frames were created with strategic cutbacks in the structure to extend zirconia incisal coverage of the esthetic anterior sextants and complete monolithic zirconia in the molar areas; subsequent layers of porcelain were applied to nonfunctional and esthetic areas. Patients had three possible occlusal scenarios: (1) maxillary ZIRCAP and mandibular ZIRCAP, (2) maxillary ZIRCAP and mandibular natural dentition, and (3) maxillary ZIRCAP and mandibular conventional hybrid prosthesis. Complications were recorded during follow-up appointments 3, 6, and 12 months after definitive prosthesis delivery. The mean treatment observation period was 33 months. Eight prosthetic complications were noted for the 40 implant-retained zirconia complete-arch prostheses (18.18%), including six cases of minor porcelain chipping and two cases of debonding of the metal insert from the zirconia framework. Maxillary ZIRCAP opposing mandibular ZIRCAP and maxillary ZIRCAP opposing mandibular natural dentition occlusal scenarios presented the same complication ratio of 4. No complications were seen in the maxillary ZIRCAP opposing mandibular conventional hybrid prosthesis group, yet 16 complications were found as denture tooth fractures in 12 mandibular conventional hybrid prostheses (ratio of 0.75). The results indicate that the implant-retained zirconia complete-arch prosthesis offers acceptable performance for use as an alternative to the conventional titanium framework acrylic veneer prosthesis for complete edentulism with a lower incidence of prosthetic complications and fewer maintenance appointments. Chipping of veneering porcelain was the most common complication, but a low incidence was observed in this study. Acrylic denture teeth may represent the weakest link when restoring complete edentulism with a maxillary ZIRCAP and mandibular conventional hybrid prosthesis.

Outcome of zirconia partial fixed dental prostheses made by predoctoral dental students: A clinical retrospective study after 3 to 7 years of clinical service

Statement of problemZirconia has an established role in fixed prosthodontics, especially for single crowns. Whether it is durable enough for fixed dental prostheses (FDPs) in the long term is yet unclear. PurposeThe purpose of this retrospective study was to evaluate the outcome of FDPs made by predoctoral students after 3 to 7 years of clinical service. Material and methodsA total of 102 patients received 120 zirconia FDPs (range, 3-12 units; mean, 4.5 units) between 2007 and 2010. Materials used were Zirkonzahn Zirconia (Zirkonzahn), NobelProcera Zirconia (Nobel Biocare), and Prettau Zirconia (Zirkonzahn). Veneering porcelain was hand-layered on Zirkonzahn Zirconia (GC Initial Zr; GC Europe) and Nobel Procera Zirconia (VITA VM 9; VITA Zahnfabrik). Prettau Zirconia was monolithic and had no veneering porcelain. Success and survival rates were calculated using Kaplan-Meier survival analysis. Ethics approval was obtained from the Ethical Committee of the Northern Ostrobothnia Hospital District (100/2013). ResultsThe 76 participants examined (75%) had received 88 zirconia FDPs. The mean follow-up period was 4.9 years (range, 3-7 years). The most common complication was chipping of the veneering porcelain in 13 of 88 FDPs (14.7%). The success rate of the zirconia-based partial FDPs after 4.9 years was 89%, and the survival rate was 100%. ConclusionsThe success rate of the zirconia-based partial FDPs after 4.9 years was 89%, and the survival rate was 100%.

EVALUATION OF INTERNAL ADAPTATION OF FULL CONTOUR ZIRCONIA CROWNS VERSUS VENEERED ZIRCONIA CROWNS – IN VITRO STUDY

Purpose: To evaluate the internal adaptation of full contour zirconia crowns to veneered zirconia with two different finish line designs (shoulder and deep chamfer). Materials and Methods: Twenty four dies were received twelve full contour zirconia crowns (Prettau) and twelve veneered zirconia crowns (ICE Zirconia). Each group will be subdivided into two equally subgroups: with Shoulder finish line and with Deep chamfer finish line. Measurements of internal fitness were recorded Results: The lowest overall mean value of internal adaptation was recorded with Ice zirconia crowns with deep chamfer finish line design (74.6µm ± 19.14), then with shoulder finish line design (93.40 µm ± 9.99), followed by Prettau zirconia crowns with deep chamfer finish line design (157µm ± 27.25) and finally Prettau zirconia crowns with shoulder finish line design (181µm ± 24.86). Conclusions: The ice zirconia crowns recorded better overall internal adaptation values than Prettau crowns with both finish line designs.

Effect of colouring green stage zirconia on the adhesion of veneering ceramics with different thermal expansion coefficients

This study evaluated the adhesion of zirconia core ceramics with their corresponding veneering ceramics, having different thermal expansion coefficients (TECs), when zirconia ceramics were coloured at green stage. Zirconia blocks (N=240; 6 mm×7 mm×7 mm) were manufactured from two materials namely, ICE Zirconia (Group 1) and Prettau Zirconia (Group 2). In their green stage, they were randomly divided into two groups. Half of the specimens were coloured with colouring liquid (shade A2). Three different veneering ceramics with different TEC (ICE Ceramic, GC Initial Zr and IPS e.max Ceram) were fired on both coloured and non-coloured zirconia cores. Specimens of high noble alloys (Esteticor Plus) veneered with ceramic (VM 13) (n=16) acted as the control group. Core–veneer interface of the specimens were subjected to shear force in the Universal Testing Machine (0.5 mm⋅min−1). Neither the zirconia core material (P=0.318) nor colouring (P=0.188) significantly affected the results (three-way analysis of variance, Tukey's test). But the results were significantly affected by the veneering ceramic (P=0.000). Control group exhibited significantly higher mean bond strength values (45.7±8) MPa than all other tested groups ((27.1±4.1)−(39.7±4.7) and (27.4±5.6)−(35.9±4.7) MPa with and without colouring, respectively) (P<0.001). While in zirconia–veneer test groups, predominantly mixed type of failures were observed with the veneering ceramic covering <1/3 of the substrate surface, in the metal–ceramic group, veneering ceramic was left adhered >1/3 of the metal surface. Colouring zirconia did not impair adhesion of veneering ceramic, but veneering ceramic had a significant influence on the core–veneer adhesion. Metal–ceramic adhesion was more reliable than all zirconia–veneer ceramics tested.

Comparative study of fracture strength depending on the occlusal thickness of full zirconia crown

Purpose: The purpose of this study was to compare the fracture strength of traditional metal-ceramic crowns and full zirconia crowns according to the occlusal thickness. Materials and methods: A mandibular first molar resin tooth was prepared with 1.5 mm occlusal reduction, 1.0 mm rounded shoulder margin and 6� taperness in the axial wall. Duplicating the resin tooth, 64 metal dies were fabricated. 48 full zirconia crowns were fabricated using Prettau zirconia blanks by ZIRKONZAHN CAD/CAM and classified into six groups according to the occlusal thickness (0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm). 16 metal-ceramic crowns were fabricated and classified into two groups according to the occlusal porcelain thickness (1.0 mm, 1.5 mm). All crowns were cemented on each metal die and mounted in a universal testing machine. The load was directed at the functional cusp of each specimen until catastrophic failure occurred. One-way ANOVA, Tukey multiple comparison test ( α =.05) and t-test (α =.05) were used. Results: The results were as follows. 1. The test 1 group (646.48 N) showed the lowest fracture strength (P .05). The value of test 6 group (1781.24 N) was significantly higher than those of the other groups (P<.05). 2. There were no significant differences of the fracture strength of metal ceramic crowns according to occlusal porcelain thickness 1.0 mm (2515.71 N) and 1.5 mm (3473.31 N) (P<.05). Conclusion: Full zirconia crown needs to be 1.0 mm or over in occlusal thickness for the posterior area to have higher fracture strength than maximum bite force. (J Korean Acad Prosthodont 2013;51:160-6)