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Aim: This study aimed to investigate the influence of titanium base (ti‐base) abutment macro‐ and micro‐geometry on the mechanical stability of polymer‐infiltrated ceramic network (PICN) screw‐retained implant‐supported single crowns (iSCs). Materials and Methods: Twelve specimens per group were used, comprising six different implant/ti‐base abutment combinations restored with PICN iSCs: Nb‐T (gingival height [GH]: 1.5 mm, prosthetic height [PH]: 4.3 mm), CC (GH: 0.8 mm, PH: 4.3 mm), CC‐P (GH: 0.8 mm, PH: 7 mm), Nb‐V (GH: 1.5 mm, PH: 6 mm), St (GH: 1.5 mm, PH: 5.5 mm), and Th (GH: 0.5 mm, PH: 9 mm). The specimens underwent thermo‐mechanical aging, and those that survived were subsequently subjected to static loading until failure. The data were analyzed using a one‐way ANOVA test followed by Tukey post hoc test (α =.05). Results: All specimens survived thermo‐mechanical aging without complications, namely, visible cracks, debonding, or screw loosening. Th group demonstrated the highest strength values among all the groups, with significant differences compared to Nb‐T (p <.05), CC (p <.001), and St (p <.001). Additionally, CC‐P group exhibited significantly superior fracture strength results compared to CC (p <.05) and St (p <.05). Conclusion: The choice of ti‐base, particularly prosthetic height, had a significant influence on fracture resistance of PICN iSCs. Nevertheless, the height or geometrical features of the ti‐base did not exhibit a significant influence on the mechanical behavior of the iSC/ti‐base assembly under thermomechanical loading, as all specimens withstood the aging without complication or failure. [ABSTRACT FROM AUTHOR]

Objectives: To simulate the replacement of a premolar with an implant‐supported cantilever fixed dental prosthesis (ICFDP) and how the fracture load is affected by implant type, positioning within the zirconia blank, and aging protocol. Materials and Methods: Seventy‐two ICFDPs were designed either within the enamel‐ or dentin layer of a 4Y‐PSZ blank for bone‐level and tissue‐level titanium‐zirconium implants. Fracture load was obtained on the cantilever at baseline (no aging) or after aging in a chewing simulator with the load applied within the implant axis (axial aging) or on the cantilever (12 groups with n = 6). A three‐way ANOVA was applied (α =.05). Results: A three‐way ANOVA revealed a significant effect on fracture load values of implant type (p =.006) and aging (p <.001) but not for the position within the zirconia blank (p =.847). Fracture load values significantly increased from baseline bone level (608 ± 118 N) and tissue level (880 ± 293 N) when the implants were aged axially, with higher values for tissue level (1065 ± 182 N) than bone level (797 ± 113 N) (p <.001). However, when the force was applied to the cantilever, fracture load values decreased significantly for tissue‐level (493 ± 70 N), while values for bone‐level implants remained stable (690 ± 135 N). Conclusions: For ICFDPs, the use of bone‐level implants is reasonable as catastrophic failures are likely to be restricted to the restoration, whereas with tissue‐level implants, the transmucosal portion of the implant is susceptible to deformation, making repair more difficult. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate load‐bearing capacity and wear performance of experimental short fiber‐reinforced composite (SFRC) and conventional lithium‐disilicate CAD/CAM fabricated fixed partial dentures (FPDs). Two groups (n = 12/group) of three‐unit CAD/CAM fabricated posterior FPDs were made. The first group used experimental SFRC blocks, and the second group fabricated from lithium‐disilicate (IPS e.max CAD). All FPDs were luted on a zirconia testing jig with dual‐curing resin cement. Half of FPDs per group were quasi‐statically loaded until fracture. The other half experienced cyclic fatigue aging (100.000 cycles, Fmax = 500 N) before loading quasi‐statically until fracture. Fracture mode was examined using SEM. Wear test was performed using 15,000 loading cycles. Both material type and aging had a significant effect on the load‐bearing capacity of FPDs. Experimental SFRC CAD without fatigue aging had significantly the highest load‐bearing capacity (2096 ± 149N). Cyclic fatigue aging decreased the load‐bearing capacity of the SFRC group (1709 ± 188N) but increased it for the lithium‐disilicate group (1546 ± 155N). Wear depth values of SFRC CAD (29.3μm) were significantly lower compared to lithium‐disilicate (54.2μm). Experimental SFRC CAD demonstrated the highest load‐bearing capacity before and after cyclic fatigue aging, and superior wear behavior compared to the control material. [ABSTRACT FROM AUTHOR]

Purpose: To assess the effect of CAD‐CAM technique (monolithic, CAD‐on, or CAD‐on cemented) and thermomechanical fatigue on the marginal discrepancy and fracture load of ceramic crowns. Material and methods: A total of 90 brass master dies were fabricated to investigate marginal adaptation and fracture load. A mandibular first molar crown's median measurements were loaded into CAD software and divided into 2 crown design groups: Monolithic (M)(IPS e.max zirCAD)(n = 30) or CAD‐on core (IPS e.max zirCAD) and lithium disilicate veneer (IPS e.max CAD) (n = 60). The crowns and cores were milled, seated on their respective dies, and marginal discrepancy values were measured by using microcomputed tomography. After veneers were milled, the cores in the veneer groups were divided into 2 groups; veneers bonded with fusion glass‐ceramic (IPS e.max CAD Crystal) in CAD‐on group (CO) and CAD‐on cemented group (CO‐C) where veneers were cemented (RelyX U200) onto cores (CO‐C). The marginal discrepancy measurements were remade and the crowns were subjected to thermomechanical fatigue (TMF) by using a chewing simulator and thermocycling (5‐55°C, 1,200,000 cycles). Marginal discrepancy measurements were repeated and the crowns were subjected to fracture load test by using a universal test device. Data were analyzed statistically by analysis of variance (ANOVA) and Tukey's honestly significant difference test (α = 0.05). Results: All crown groups had similar marginal discrepancy before veneering. Veneering and cementation on die increased the marginal discrepancy of crowns in cemented CAD‐on group. Thermomechanical fatigue increased the marginal discrepancy of both CAD‐on groups. Monolithic crown group had the lowest marginal discrepancy after thermomechanical fatigue (p < 0.001), and the highest fracture load (p < 0.001) Conclusions: Fabrication technique affected the marginal fit and fracture load of CAD‐CAM crowns after thermomechanical fatigue. All crowns survived the thermomechanical fatigue test without dislodgement or fracture. Monolithic crowns had the best fit and highest fracture load after fatigue testing. The CAD‐on systems had similar marginal discrepancies, and static loading reproduced veneer chipping. [ABSTRACT FROM AUTHOR]

Purpose: To compare the biomechanical behavior of vertebrae with vertebral compression fractures (VCF) treated by a novel system with pedicular anchorage (dowelplasty) versus balloon kyphoplasty. Methods: Four cadaveric spines (T12-L5) were harvested, cleaned from soft tissues, and separated into vertebrae. Axial compressive loads were applied to each vertebra until a VCF was generated. Half of the vertebrae (n = 11) were instrumented using the "dowelplasty" system, consisting of a hollow titanium dowel anchored into the pedicle, through which a cannulated titanium nail is inserted and locked and through which cement is injected. The other half (n = 11) were instrumented using balloon kyphoplasty. Axial compressive loads were re-applied to each vertebra until fracture. Fracture load and fracture energy were calculated from load–displacement data for the pre- and post-treatment states. Results: Compared to balloon kyphoplasty, dowelplasty granted greater net change in fracture load (373N; 95%CI,-331–1076N) and fracture energy (755Nmm; 95%CI,-563–2072Nmm). A sensitivity analysis was performed without L4 and L5 vertebrae from the dowelplasty group, since the length of the cannulated nails was too short for these vertebrae: compared to balloon kyphoplasty, dowelplasty granted an even greater net change in fracture load (680N; 95%CI,-96–1457N) and fracture energy (1274Nmm; 95%CI,-233–2781Nmm). Conclusion: Treating VCFs with dowelplasty grants increased fracture load and fracture energy compared to the pre-treatment state. Furthermore, dowelplasty grants greater improvement in fracture load and fracture energy compared to balloon kyphoplasty, which suggests that dowelplasty may be a good alternative for the treatment of VCF. Level of evidence: level IV. [ABSTRACT FROM AUTHOR]

Objective: Zirconia implants are assumed to satisfy the esthetic requirements that titanium implants cannot meet, however, there are not enough studies in the literature about narrow‐diameter and angled zirconia implants that can be preferred especially in the anterior region. This in vitro study aimed to evaluate the fatigue resistance and fracture strength of narrow‐diameter zirconia implants with angled abutments. Materials and Methods: Forty‐eight one‐piece experimental zirconia implants and monolithic zirconia crowns were produced from 3‐YTZP blanks. The implant diameters (3.0 or 3.7 mm) and the restoration types were determined according to three intraoral regions (upper central incisors, lower central incisors, and upper canine), and abutments were designed as straight or 15° angled. The samples were subjected to chewing simulation corresponding to 5 years of clinical performance and then the static loading test. The survival rates of groups were measured by the Kaplan–Meier log‐rank test, and the fracture load values were estimated by using Kruskal–Wallis and Mann–Whitney U tests (p < 0.05). Results: All 3.0 mm diameter implants failed the fatigue test. The fatigue resistance of the implants with angled abutments was significantly lower than the straight abutments, and different crown designs were found to affect survival rates significantly. The fracture strengths of the surviving groups were above the maximum physiological chewing forces, and the differences were not significant. Conclusions: The implant diameter, abutment angle, and restoration type have a significant effect on the fatigue behavior of zirconia implants. Clinical Significance: The fracture strengths of the one‐piece zirconia implants with a 3.7 mm diameter and a 15° abutment angle are above the chewing forces for the anterior intraoral region. [ABSTRACT FROM AUTHOR]

Objective: To compare four different types of monolithic zirconia crowns in terms of survival rate and fracture resistance after thermocycling and/or thermo‐mechanical loading in a chewing simulator. Methods: Partially stabilized zirconia (PSZ) crowns with fiber‐reinforced resin die assemblies (n = 80) were fabricated using: multi‐yttria‐layered 5Y‐PSZ/3Y‐PSZ, multi‐yttria‐layered 5Y‐PSZ/4Y‐PSZ, monolithic 4Y‐PSZ, and monolithic 3Y‐PSZ as control (n = 20). Half of the samples in each group were subjected to thermo‐mechanical loading under 110 N, 1.4 Hz, 1.2 million cycles with simultaneous thermocycling (10,000 cycles, 5–55°C). The other half were subjected to thermocycling alone. The samples were loaded to failure to measure their fracture resistance. The data were analyzed using by two‐way ANOVA and Tukey's HSD post‐hoc test (α = 0.05). Results: All specimens survived the aging protocols. The yttria content significantly affected the fracture resistance of the crowns (p < 0.0001). The mean fracture resistance, from highest to lowest: 3Y‐PSZ, 4Y‐PSZ, followed by the two multi‐yttria‐layered systems. The mean difference between the two multi‐yttria‐layered systems were not statistically significant (p = 0.98). The mechanical loading protocol did not affect the mean fracture resistance within each group (p = 0.18). Conclusions: Within each group, there was no difference in fracture resistance after thermocycling alone and thermo‐mechanical loading. However, increasing the yttria concentration at the occlusal third of the crown decreased its fracture resistance. Clinical Significance: The term "monolithic zirconia" alone without specifying the actual yttria content is misleading. This term represents different materials with different mechanical properties. The yttria content has an inverse relationship with the fracture resistance of zirconia crowns. The fracture resistance of multi‐layer zirconia crowns is determined by the amount of the weaker zirconia phase at the occlusal part of the restoration rather than enforced by the stronger zirconia at the cervical part of the crown. [ABSTRACT FROM AUTHOR]

Purpose: Additive manufacturing (AM) technologies are capable of fabricating complex geometries with different porosities. However, the effect of such porosities on mechanical properties of stereolithography (SLA) AM zirconia with different porosities is unclear. The purpose of this in vitro study was to investigate the mechanical properties namely flexural strength, and flexural modulus of AM zirconia with different porosities. Materials and Methods: A bar (25 × 4 × 3 mm) for flexural strength test (ISO standard 6872/2015) was designed by CAD software program and standard tessellation language (STL) file was obtained. The STL file was used to fabricate a total of 80 bars in four groups. Three experimental groups each containing 20 samples were manufactured using an SLA ceramic printer (CeraMaker 900; 3DCeram Co) and zirconia material (3DMix ZrO2 paste; 3DCeram Co) with different sintering post processing to achieve different porosities including 0%‐porosity (AMZ0), 20%‐porosity (AMZ20), and 40%‐porosity (AMZ40). The same STL file was used for subtractive manufacturing or milling of 20 zirconia bars as control group (CNCZ) with the same dimensions using a commercial zirconia. Three‐point bending tests were performed for all groups following ISO standard 6872/2015 specification using a universal testing machine. Outcomes measured included load at fracture, mean flexural strength, and flexural modulus and they were compared across the experimental groups using a one‐way ANOVA. Post hoc pair wise comparison between each pair of the groups were performed using Tukey test. Results: There was a significant difference between the four groups, in terms of fracture load, flexural strength and flexural modulus using one‐way ANOVA. AM zirconia with 0% porosity (AMZ0) showed the highest value for fracture load (1132.7 ± 220.6 N), flexural strength (755.1 ± 147.1 MPa) and flexural modulus (41,273 ± 2193 MPa) and AM zirconia with 40% porosity (AMZ40) showed the lowest fracture load (72.13 ± 13.42 N), flexural strength (48.09 ± 8.95 MPa) and flexural modulus (7177 ± 506 MPa). Tukey's pairwise comparisons detected a significant difference between all the possible pairs for all variables except flexural modulus between AMZ0 and CNCZ. The Weibull moduli presented the lowest value for AMZ20 (4.4) followed by AMZ40 (6.1), AMZ0 (6.1), and the highest value was for CNCZ (8.1). Conclusion: AM zirconia with 0% porosity showed significantly higher flexural strength and flexural modulus when compared to milled and AM zirconia with 20% and 40% porosities. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the fracture resistance behaviors of titanium‐zirconium, one‐piece zirconia, and two‐piece zirconia implants restored by zirconia crowns and different combinations of abutment materials (zirconia and titanium) and retention modes (cement‐retained and screw‐retained zirconia crowns). Material and Methods: Three research groups (n=12) were evaluated according to combinations of abutment material, retention mode, and implant type. In the control group (TTC), titanium‐zirconium implants (∅ 4.1 mm RN, 12 mm, Roxolid; Straumann USA, Andover, MA) and prefabricated titanium abutments (RN synOcta Cementable Abutment, H 5.5 mm; Straumann USA) were used to support cement‐retained zirconia crowns. In the second group (ZZC), one‐piece zirconia implants (PURE Ceramic Implant Monotype, ∅ 4.1 mm RD, 12 mm, AH 5.5 mm; Straumann USA) were used to support cement‐retained zirconia crowns. In the third group (ZTS), two‐piece zirconia implants (PURE Ceramic Implant, ∅ 4.1 mm RD, 12 mm) and prefabricated titanium abutments (CI RD PUREbase Abutment, H 5.5 mm) were used to support screw‐retained zirconia crowns. All zirconia crowns were manufactured in the same anatomic contour with a 5‐axis dental mill and blended 3 and 5 mol% yttria‐stabilized zirconia (LayZir A2). Implants were inserted into specimen holders made of epoxy resin‐glass fiber composite. All specimens were then subject to artificial aging in an incubator at 37°C for 90 days. Fracture resistance of specimen assemblies was tested under static compression load using the universal testing machine based on ISO14801 specification. The peak fracture loads were recorded. All specimens were examined at the end of the test microscopically at 5× and 10× magnification to detect any catastrophic failures. Comparisons between groups for differences in peak fracture load were made using Wilcoxon Rank Sum tests and Weibull and Kaplan‐Meier survival analyses (α = 0.05). Results: The TTC group (942 ± 241 N) showed significantly higher peak fracture loads than the ZZC (645 ± 165 N) and ZTS (650 ± 124 N) groups (p < 0.001), while there was no significant difference between ZZC and ZTS groups (p = 0.940). The survival probability based on the Weibull and Kaplan‐Meier models demonstrated different failure molds between titanium‐zirconium and zirconia implants, in which the TTC group remained in the plastic strain zone for a longer period before fracture when compared to ZZC and ZTS groups. Catastrophic failures, with implant fractures at the embedding level or slightly below, were only observed in the ZZC and ZTS groups. Conclusions: Cement‐retained zirconia crowns supported by titanium‐zirconium implants and prefabricated titanium abutments showed superior peak fracture loads and better survival probability behavior. One‐piece zirconia implants with cement‐retained zirconia crowns and two‐piece zirconia implants with screw‐retained zirconia crowns on prefabricated titanium abutment showed similar peak fracture loads and survival probability behavior. Titanium‐zirconium and zirconia implants could withstand average intraoral mastication loads in the incisor region. This study was conducted under static load, room temperature (21.7°C), and dry condition, and full impacts of intraoral hydrothermal aging and dynamic loading conditions on the zirconia implants should be considered and studied further. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the effect of endodontic access hole preparation on fracture resistance of translucent zirconia (5Y) and conventional zirconia crowns (3Y) with varying occlusal thicknesses. Materials and Methods: Polymethylmethacrylate (PMMA) dies, representing a prepared tooth, were milled. Zirconia crowns with 1 mm thick axial walls and varying occlusal thicknesses were milled from 3Y (Cercon HT) or 5Y (Cercon XT) zirconia discs and sintered. 160 crowns were divided into 16 groups (n = 10 per group) based on the zirconia type (3Y, 5Y), occlusal thickness (0.5, 1.0, 1.5, 2.0 mm), and access hole preparation (with access hole, control). Crowns were cemented on the PMMA dies with resin‐modified glass ionomer cement (Rely X Luting Plus) under constant weight (500 g) and thermocycled for 10,000 cycles. In half of the samples, following 5000 cycles of thermocycling, a uniform endodontic access hole was created using a diamond bur and restored immediately with resin composite (Filtek Supreme Ultra, 3M ESPE). The fracture resistance of the specimens was tested on an Instron 5566 universal testing machine with a stainless steel ball indenter (9.0 mm dia.) and the maximum load before failure was recorded as fracture load (N). Three‐way ANOVA testing examined the effect of zirconia type, occlusal thickness, and access hole preparation on fracture loads of the crowns. Statistical tests were two‐sided and significance level was set at 95% (α = 0.05). Results: Fracture load was significantly affected by the type of zirconia, occlusal thickness, and access hole preparation (p < 0.001). Pairwise comparisons revealed that access hole preparation significantly reduced the fracture load of 3Y crowns with 0.5 or 1.0 mm of occlusal thickness and 5Y zirconia crowns with 0.5, 1.0, or 1.5 mm of occlusal thickness (p < 0.05). Increasing occlusal thickness reduced the effect of access hole preparation on fracture load. Conclusion: Type of zirconia, occlusal thickness, and access hole preparation had significant effects on the fracture load of zirconia crowns. The effect of endodontic access was significant on the 3Y and 5Y zirconia crowns with ≤1.0 and ≤1.5 mm occlusal thicknesses, respectively. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate, in vitro, the fracture load of IPS e.max CAD occlusal veneers at thicknesses of either 0.3 or 0.6 mm luted to enamel or dentin. Materials and methods: Fifty human molars were randomly distributed into five groups (n = 10): G1 ‐ healthy teeth (control); G2‐0.3‐mm‐thick veneers luted to enamel; G3‐0.6‐mm‐thick veneers luted to enamel; G4‐0.3‐mm‐thick veneers luted to dentin; and G5‐0.6‐mm‐thick veneers luted to dentin. After the luting procedures, the specimens were immersed in distilled water at 37°C for 24 hours and then subjected to mechanical loading (106 cycles at 200 N load). The specimens were subjected to a fracture load test in a universal testing machine. Two‐way ANOVA and Tukey's test (α = 0.05) were used to analyze data. Results: Only the thickness factor was significant (P =.002). Values of fracture load followed by distinct letters represent significant differences (P <.05): G1 (3204 N ± 730)ab; G2 (3144 N ± 729)ab; G3 (2489 N ± 606)b; G4 (3591 N ± 776)a; and G5 (2770 N ± 598)ab. Conclusion: IPS e.max ultrathin occlusal veneers luted to enamel or dentin obtained fracture load comparable to that of the healthy tooth. Clinical significance: IPS e.max CAD ultrathin occlusal veneers at 0.3 or 0.6‐mm‐thick seem to provide good perspectives in relation to the clinical use. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate mechanical stability (survival and complication rates) and bending moments of different all‐ceramic monolithic restorations bonded to titanium bases (hybrid abutment‐crowns) or to customized titanium abutments compared to porcelain‐fused‐to‐metal crowns (PFM) after thermo‐mechanical aging. Material and Methods: Sixty conical connection implants (4.3 mm‐diameter) were divided in five groups (n = 12): PFM using gold abutment (GAbut‐PFM), lithium disilicate crown bonded to customized titanium abutment (TAbut+LDS), lithium disilicate abutment‐crown bonded to titanium base (TiBase+LDS), zirconia abutment‐crown bonded to titanium base (TiBase+ZR), polymer‐infiltrated ceramic‐network (PICN) abutment‐crown bonded to titanium base (TiBase+PICN). Simultaneous thermocycling (5°–55°C) and chewing simulation (1,200,000‐cycles, 49 N, 1.67 Hz) were applied. Catastrophic and non‐catastrophic events were evaluated under light microscope, and survival and complication rates were calculated. Specimens that survived aging were loaded until failure and bending moments were calculated. Results: Survival rates after aging were 100% (TAbut+LDS, TiBase+LDS), 91.7% (GA‐PFM), 66.7% (TiBase+ZR) and 58.3% (TiBase+PICN) and differed among the groups (p =.006). Non‐catastrophic events as screw loosening (GA‐PFM) and loss of retention or micro‐/macro‐movement (TiBase groups) were observed. Complication rates varied among the groups (p <.001). TiBase+PICN had lower bending moment than all the other groups (p <.001). Conclusions: Hybrid abutment‐crowns made of lithium disilicate can be an alternative to PFM‐based restorations, although concerns regarding the bonded interface between the titanium base and abutment‐crown can be raised. PICN and zirconia may not be recommended due to its inferior mechanical and bonding outcomes, respectively. Titanium customized abutment with bonded lithium disilicate crown appears to be the most stable combination. [ABSTRACT FROM AUTHOR]

Purpose: To assess the effect of yttria mol% concentration and material thickness on the biaxial fracture load (N) of zirconia with and without mastication simulation. Materials and methods: Disk‐shaped specimens (N = 120) of 3 mol% yttria‐partially stabilized zirconia, 3Y‐PSZ (Katana High Translucent, Kuraray Noritake), 4 mol% yttria‐partially stabilized zirconia, 4Y‐PSZ (Katana Super Translucent Multi Layered) and 5 mol% Yttria‐partially stabilized zirconia, 5Y‐PSZ (Katana Ultra Translucent Multi Layered) were prepared to thicknesses of 0.7 and 1.2 mm. For each thickness, the biaxial fracture load (N) was measured with and without mastication simulation with 1.2 million cycles at a 110‐N load and simultaneous thermal cycling at 5°C to 55°C. The data were analyzed by three‐way Analysis of Variance (α = 0.05) and Tukey‐Kramer adjusted multiple comparison test. Results: Yttria mol% concentration and material thickness had a statistically significant effect on the mean biaxial fracture load (F = 388.16, p < 0.001 and F = 714.33, p < 0.001 respectively). The mean biaxial fracture load ranged from the highest to the lowest; 3Y‐PSZ, 4Y‐PSZ, and 5Y‐PSZ (p = 0.012). The mean biaxial fracture load of the 1.2 mm thickness groups was significantly higher than 0.7 mm thickness at any given condition (p = 0.002). Not all specimens survived the mastication simulation protocol. Fifty percent of the 0.7‐mm‐thick 4Y‐PSZ specimens, 70% of the 0.7‐mm‐thick 5Y‐PSZ specimens and 20% of 1.2‐mm‐thick 5Y‐PSZ specimens fractured during mastication simulation. Mastication simulation had no statistically significant effect on the biaxial fracture load (F = 1.24, p = 0.239) of the survived specimens. Conclusions: Lowering yttria mol% concentration and increasing material thickness significantly increases the fracture load of zirconia. At 0.7 mm thickness, only 3Y‐PSZ survived masticatory simulation. A minimum material thickness of 1.2 mm is required for 4Y‐PSZ or 5Y‐PSZ. [ABSTRACT FROM AUTHOR]

Purpose: To compare in vitro fracture load, surface wear, and roughness after thermal cycling and cyclic mechanical fatigue loading among cemented microhybrid resin‐based composite and ceramic occlusal veneers fabricated at two thicknesses (1.5 and 2.5 mm). Materials and methods: Sixty‐four extracted premolars without root canal treatment were prepared and restored with occlusal veneers of two thicknesses (1.5 and 2.5 mm), using four different materials: microhybrid composite (MC), fiber‐reinforced microhybrid composite (FMC), heat‐pressed lithium disilicate ceramic (HPC), and computer‐aided design/computer‐aided manufactured lithium disilicate ceramic (CCC). The specimens underwent thermal cycling and cyclic mechanical fatigue loading, and were then subjected to fracture testing, with loads at failure recorded as fracture load. Wear and surface roughness were recorded before and after fatigue loading. Results were analyzed using one‐way ANOVA, two‐way ANOVA (α = 0.05). Results: All specimens survived thermal cycling and cyclic mechanical fatigue loading. At 1.5‐mm thickness, the mean fracture load of FMC was highest (3926.48 ± 556.54 N), while that of CCC was highest (3066.45 ± 559.94 N) at 2.5 mm. Regardless of thickness, the fracture load of CCC was higher than that of HPC (p = 0.004 and p = 0.023). The wear of MC and FMC was significantly higher than those of HPC and CCC (p ≤ 0.001), but was similar in terms of the wear rate of tooth enamel. HPC exhibited the lowest surface roughness after fatigue loading (p ≤ 0.001). Conclusion: All tested occlusal veneers exhibited a fracture load considerably exceeding the maximum occlusal force in the posterior dentition. When the attainable space for restoration varies, different occlusal veneer materials should be considered. The surface wear and roughness also need to be considered when selecting materials. [ABSTRACT FROM AUTHOR]

Objective: This study evaluated the loading capacity of CAD/CAM‐fabricated anterior feldspathic ceramic crowns bonded to one‐piece zirconia implants with different cements. Material and methods: Fifty one‐piece zirconia implants were embedded in epoxy resin. The abutment aspect of one implant was optically scanned and a standardized upper canine was designed with CAD‐software. Fifty feldspathic ceramic crowns were milled, polished, and mounted on the implants either without any cement, with a temporary cement or with three different composite resin cements after surface pretreatment as recommended by the manufacturers (n = 10). After storage in distilled water at 37°C for 24 hr, specimens were loaded until fracture on the palatal surface of the crown at an angle of 45° to the long axis of the implant and loads until fracture were detected and compared. Compressive strength of the investigated cement materials was determined. Statistical analyses were done with One‐way ANOVA followed by post hoc Fisher LSD test (α = 0.05). Results: The cements revealed significantly different compressive strength values (temporary cement: 37.1 ± 7.0 MPa; composite resin cements: 185.8 ± 21.3, 277.9 ± 22.1, and 389.0 ± 13.6 MPa, respectively). Load‐at‐fracture values had an overall mean value of 237.1 ± 58.2 N with no significant difference among the composite resin cements (p > 0.05). Fracture load values with the temporary cement or without cement were significantly lower (p < 0.002). Conclusions: CAD/CAM‐fabricated anterior feldspathic ceramic crowns bonded to one‐piece zirconia implants provide sufficient resistance to intraoral forces. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the influence of static (not preloaded) and thermomechanical loading on the load to fracture of metal‐ceramic, monolithic and veneered zirconia computer‐aided design/computer‐aided manufacturing (CAD/CAM) posterior fixed partial dentures (FPDs). Materials and Methods: One hundred standardized specimens with 2 abutments screwed onto a platform were prepared from stainless steel to receive a posterior 3‐unit FPD with an intermediate pontic. Specimens were randomly divided into 5 groups (n = 20): Metal‐ceramic (control group), Lava Zirconia system, Vita In‐Ceram YZ, IPS e.max ZirCAD, and Lava Plus. Half of the specimens of each group (n = 10) underwent no preloading, and the other half were subjected to thermomechanical loading in a masticatory simulator, and then all FPDs were loaded until fracture using a universal testing machine at a 1 mm/min crosshead speed. The load to fracture of the veneering ceramic and the load to fracture of framework (total fracture) were recorded for each specimen. Data were statistically analyzed using 2‐way ANOVA, Tukey's HSD post‐hoc test, Student's t test, and Weibull statistics, α = 0.05. Results: Significant differences were recorded between the metal‐ceramic and veneered zirconia groups for the veneering ceramic load (p < 0.001; f = 36.62; f = 57.76) in no preloading and thermomechanical loading subgroups, respectively, but no differences were observed between the static and thermomechanical loading conditions. No differences were observed among the veneered zirconia groups. For the total load to fracture, significant differences were observed according to the material (p < 0.001; f = 500.8), between the metal‐ceramic and Lava Plus group and the other zirconia groups in no preloading subgroup, and between metal‐ceramic and the other groups (p < 0.001; f = 303.33) in thermomechanical loading subgroup. For the type of preloading, significant differences were observed (p = 0.02; f = 5.24) between the Lava Plus group and the other groups. Thermomechanical loading significantly decreased the fracture load of the Lava Plus group (p = 0.005). The Weibull statistics corroborated the results. Conclusions: Monolithic zirconia restorations provided the highest load to fracture values among the zirconia groups tested; however, the results indicate that they must be used in the oral environment with caution, because their load to fracture was influenced by the aging simulation. [ABSTRACT FROM AUTHOR]

Abstract: This paper provides a methodology for the prediction of fracture loads in notched materials that combines the equivalent material concept with the theory of critical distances. The latter has a linear‐elastic nature and requires material calibration in those cases where the non‐linear material behaviour is significant. The calibration may be performed by fracture testing on notched specimens or a combination of fracture testing and simulation. The proposed methodology sets out to define an equivalent linear‐elastic material on which the theory of critical distances may be applied through its basic formulation and without any previous fracture testing and/or simulation. It has been applied to PMMA single edge notch bending specimens containing U‐notches, providing accurate predictions of fracture loads. [ABSTRACT FROM AUTHOR]

Objectives: To investigate the fracture behavior and marginal gap region of CAD/CAM fabricated lithium disilicate (L) and zirconium dioxide (Z) crowns using palatal venting (PV), pre‐cementation with custom analogs (CA), or conventional cementation technique (SP) with adhesive cement (A) or resin‐modified glass ionomer cement (B). Material and methods: Twelve groups (n = 6) were set according to material (L, Z), cement (A, B), and technique (PV, CA, SP). Specimens were thermo‐mechanical aged (TML), loaded until fracture (LF) and fracture patterns recorded. Marginal gap width and quality were assessed and compared to replicas obtained before and after TML. Results: Crown material significantly influenced LF with a mean of 1037.6 ± 282.4 N in L and 5356.3 ± 1207.0 N in Z groups (p < .001). Neither cement material nor cementation method affected the outcome. Fractures occurred along the mesial‐distal central fissure in both materials. Gap width before TML was 22.04 ± 13.42 μm for L and 19.98 ± 12.72 μm for Z specimens, with overall no influence of crown material, cement type, or method. Marginal cleanliness just below the polished implant shoulder reached 66.7%–88.9% with A, and 91.7%–100% with B, and tended to increase in all groups during TML indicating a decrease in excess cement. Implant‐crown junctions were cleaner with B compared to A (p ≤ .001) and along Z crown surfaces compared to L (p ≤ .007). Conclusions: Crown venting of lithium disilicate and zirconium dioxide crowns did not affect the fracture load and patterns. Complete cement removal was rare, and the observed particle ablation requires further clinical attention, particularly with submucosal margins. [ABSTRACT FROM AUTHOR]

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The objective of this study was to quantify natural eating behavior of soft solid foods and identify a mechanical property of food that has the strongest influence on mastication in humans. Electromyography (EMG) of both masseter and suprahyoid muscles was performed to quantify the muscle effort required to naturally masticate five gellan gels. The gels were categorized into two groups; those with (1) similar fracture strain and three different fracture loads (F1 < F2 < F3), and (2) similar fracture load and three different fracture strains (S2 < F2 < E2). True stress of these gels was evaluated using video imaging during an instrumental compression test. EMG variables corresponding to masticatory effort increased with fracture load and with decreasing fracture strain under similar fracture loads of the gellan gels. Fracture load affected the natural eating behavior of the gels more than fracture strain. True stress, in particular true fracture stress, was a better indicator of mastication requirement than load. According to texture, human subjects changed their method of oral processing for the consumption of a small piece of gel from compression between the tongue and hard palate to mastication using the teeth. Once the method was chosen based on the mechanical properties under small deformation before fracture, muscle effort for oral processing highly correlated with true fracture stress but did not significantly correlate with modulus or fracture strain. Practical Applications The requirements for appropriate care food that can be consumed using compression by the tongue and hard palate without using the teeth have increased because the numbers of elderly people with poor mastication performance has increased in an aging society. The oral method changed from compression between the tongue and hard palate to mastication by the teeth with increasing true fracture stress of gels. Mastication effort quantified by electromyography highly correlated with the true fracture stress, but inferior correlation was observed with fracture load and no correlation with other mechanical properties, such as modulus and fracture strain. A simple compression test with video imaging can successfully measure the true stress of food samples. True fracture stress from the compression test was the best single parameter that explained the mastication effort during the natural eating behavior of soft gels. [ABSTRACT FROM AUTHOR]

Purpose To evaluate the fracture load of 3-unit zirconia-based posterior fixed dental prostheses (FDPs) before and after veneering the frameworks. Materials and Methods Forty standardized stainless-steel master dies were fabricated (height: 5 mm, convergence: 6º, chamfer: 1 mm) and randomly screwed in pairs onto metal bases. The bases were randomly divided into two groups (n = 20 each) according to the zirconia CAD/CAM system used for constructing 3-unit structures for FDPs: group 1 (L): Lava All-ceramic, group 2 (Z): IPS e.max ZirCAD. Half of the zirconia structures per group were randomly selected and veneered, while the remaining half was left unveneered. The specimens were luted in standard fashion onto the stainless steel master dies using conventional glass ionomer cement. All specimens were tested for fracture load (FL). Specimens were subjected to a three-point bending test until fracture by applying an axial compressive load at the central fossa of the pontics with a universal testing machine at a 0.5 mm/min crosshead speed. Wilcoxon's rank-sum test and Weibull statistics were used for statistical analysis (α = 0.05). Results L structures recorded significantly higher values of load to fracture than the Z group both before and after veneering. Within each ceramic group, no differences were found between unveneered and veneered frameworks. Conclusions Although further studies are necessary to corroborate these findings, both zirconia systems could be recommended for restoring posterior teeth on the basis of the fracture load values recorded in this experiment (>1000 N). The veneering procedure did not affect the overall load to fracture in any group. [ABSTRACT FROM AUTHOR]

Objective Sandblasting with subsequent acid etching is a potential procedure to generate microstructured surfaces on zirconia implants. The aim of the study was to systematically analyze the effect of these process steps on surface morphology and mechanical strength of the implants. Materials and methods Zirconia implant blanks (ceramic.implant, VITA) were sandblasted (105-μm alumina, 6 bar), subsequently HF-etched, and finally heat-treated at 1250°C. Surface topographies were documented by SEM. Surface roughness Ra ( n = 4), monoclinic volume fraction in the surface layer ( n = 1), and static fracture load ( n = 4) were measured. Results Surface roughness Ra reached a maximum of 1.2 μm after 4× sandblasting. Scratches and sharp edges dominated the surface aspect. Fracture load increased with the number of sandblasting cycles with a gain of 30% after 20 cycles. HF etching did not change the Ra values, but sharp edges were rounded and small pits created. A minor decrease in fracture load with increasing etching time was observed. Heat treatment of 1 h reduced the fracture load by 1/3. Longer heat treatment had no further effect. The roughness Ra was not modified by heat treatment. Fracture load was strongly correlated with the monoclinic fraction except for the results obtained directly after acid etching, where a constant monoclinic fraction was observed. Conclusions Sandblasting with 105-μm alumina followed by 1 h HF etching at room temperature and 1 h heat treatment at 1250°C is a reliable and tolerant process to create a surface roughness of about Ra = 1.2 μm on zirconia implants. [ABSTRACT FROM AUTHOR]

Purpose The purpose of part II of this in vitro study was to compare the fracture load of two-piece zirconia custom abutments with different thicknesses and angulations. Materials and Methods Forty zirconia custom abutments were divided into four groups as follows: group A1: 0.7 mm thickness and 0° angulations; group A2: 0.7 mm thickness and 15° angulations; group B1: 1 mm thickness and 0° angulations; group B2: 1 mm thickness and 15° angulations. As in part I, in all groups, implant replicas were mounted in self-cure acrylic jigs to support the abutments. The zirconia custom abutments were engaged in the implant replicas using a manual torque wrench. All jigs were secured and mounted in a metallic vice and subjected to shear stress till failure using a universal testing machine with a 0.5 mm/min crosshead speed with the force transferred to the lingual surface of the zirconia custom abutments 2 mm below the incisal edge. The test specimens used in this study did not include a crown. The universal testing machine was controlled via a computer software system, which also completed the stress-strain diagram and recorded the breaking fracture load. The fracture loads were recorded for comparison among the groups and subjected to statistical analysis (two-way ANOVA and Kolmogorov-Smirnov). Results The mean fracture load of zirconia custom abutments across the groups (A1 to B2) ranged from 432 ± 97 N to 746 ± 275 N. The angulated zirconia custom abutment exhibited the highest fracture load, which was statistically significant ( p = 0.045). The thickness of the zirconia custom abutment also had a positive influence on the strength of the specimens ( p = 0.005). Conclusions In this study, the 15° angulated zirconia custom abutments showed the highest fracture load of those investigated. The 1 mm thick zirconia custom abutments also exhibited significantly higher fracture load compared to 0.7 mm abutments. Clinical Implications The results of this in vitro study will help dental practitioners with their decision-making process in selecting the type of custom abutment to be used clinically. [ABSTRACT FROM AUTHOR]

To evaluate the in vitro fracture load of extensively damaged vital teeth after either direct or indirect restauration, severe tooth substance loss was simulated for 96 molars. Subsequently, two cavities were prepared with little (design 1) or more substantial (design 2) residual tooth support. All molars were provided with a 2-mm ferrule design and then divided into 12 test groups based on their occlusal surface size. They were restored with composite or with either of two types of single crown (cast metal or milled zirconia). After thermal ageing (10 000 cycles at 6·5 and 60 °C), 1·2 million cycles of chewing simulation were applied (64 N). Maximum fracture load was determined with a loading angle of 45°. Statistical analysis was performed by use of Kaplan-Meier modelling, Student's t-tests, one-way anova, post hoc Tukey's HSD tests and linear regression analysis. Regarding mean fracture load without ageing, the indirect restorations outperformed composite (design 1: direct: 508 ± 123 N, indirect: 741 ± 248 N; design 2: direct: 554 ± 167 N, indirect: 903 ± 221 N). After artificial ageing, however, these differences were no longer significant (design 1: direct: 328 ± 189 N, indirect: 506 ± 352 N; design 2: direct 399 ± 208 N, indirect 577 ± 292 N). Instead, the fracture load of the aged composite restorations was comparable with that for zirconia (design 1) and cast metal (design 2) crowns. Fracture loads of direct composite restorations after artificial ageing might fulfil clinical requirements. [ABSTRACT FROM AUTHOR]

Objectives To study the surface properties of polyetheretherketone (PEEK) and its bond strength with two veneering resins after different conditioning methods as well as fracture load of PEEK three-unit fixed dental prostheses (FDPs). Methods Two hundred and twenty five PEEK specimens were fabricated and divided into five groups: no treatment (A), etching with 98% sulfuric acid for 1 min (B), air-abrasion for 10 s with either 50 or 110 μm alumina (C and D, respectively), and silica coating using the Rocatec System (E). On 15 specimens of each conditioning method, contact angle and surface roughness were determined. The remaining 150 specimens of each conditioning method were divided into two groups for the veneering procedure with the composites Gradia (GC Europe) and Sinfony (3M ESPE). Shear bond strength (SBS) was measured and failure types were assessed. In addition, 15 FDPs were milled and the fracture load was tested. Data were analyzed using descriptive statistics, one-way ANOVA (Scheffé test), two sample Student's t-test, and Weibull statistics ( p < 0.05). Results Silica-coated PEEK surfaces showed the highest wettability. The highest roughness and lowest contact angles were observed for 110 μm air-abraded and silica-coated PEEK surfaces. The highest SBS values were, however, achieved in the acid-etched group. PEEK three-unit FDPs showed a mean fracture load of 1383 N with a plastic deformation starting approximately at 1200 N. Conclusions Acid etching should be applied when PEEK is used as substructure material and composite veneering material is applied. In this combination, PEEK might be a suitable material for FDPs, especially in load-bearing areas. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 101B: 1209-1216, 2013. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the fracture load and failure types of veneered zirconia crowns that were air-abraded on either the veneering or cementation surface. Fracture loads were determined before and after chewing simulation. Standardized Y-TZP frameworks ( n = 360) for canines were fabricated and divided into one control group ( n = 72) and 12 test groups ( n = 24). The test groups were air-abraded using alumina powder (10 s, 2 bar, distance: 10 mm) with particle size of 50 μm resp. 110 μm and veneered with one of the veneering ceramics: Triceram, Zirox, or VITA VM9. The crowns were cemented on their corresponding CoCr abutment. The initial fracture load was measured in one half of each group ( n = 12), and the other half ( n = 12) was subjected to chewing cycling. The data were analyzed using three-way and one-way ANOVA, a post-hoc Scheffé test, two sample Student's t-test, and Weibull statistics ( p < 0.05). Thus, nonaged, air-abraded groups of two veneering ceramics (Triceram, VITA VM9) showed higher mean fracture load compared to control groups. After chewing simulation, air-abraded groups showed lower mean fracture load compared to control groups. Aging decreased the Weibull modulus of all tested groups, and air-abraded groups showed lower Weibull moduli compared to control groups. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 100B: 1683-1690, 2012. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this study was to evaluate the effect of different types and design of zirconia frameworks as well as the effect of different veneering ceramics on the fracture strength of crowns. The importance of different abutment materials was also evaluated. Materials and methods: Eighty cores, 40 in a fully-sintered zirconia material and 40 in a pre-sintered zirconia material were made. Twenty cores of each material were made with a core of even thickness shape (ES) and 20 were made with a core with anatomical shape (AS). The cores were divided into subgroups and veneered with one of two different veneering ceramics: a porcelain and a glass-ceramic material. In total eight groups of 10 crowns were made. They were all cemented onto abutments made of resin. One extra group of 10 AS, pre-sintered zirconia cores veneered with glass-ceramic were made and cemented onto titanium abutments. All crowns underwent thermocycling and mechanical pre-load and were finally loaded until fracture. Results: AS crowns withstood significantly higher loads than ES crowns ( P-value <0.001), and crowns with titanium abutments withstood significantly higher loads than crowns supported by abutments made of inlay pattern resin ( P-value <0.001). Three types of fracture were noted: minor and major fracture of the veneering ceramic, and complete fracture through core and veneer. ES crowns showed significantly more major fractures of the veneering ceramic than AS crowns. Conclusions: This in vitro study indicates that the design of the core, as well as the abutment support, significantly influences fracture load and fracture mode of yttria-stabilized tetragonal zirconia polycrystals crowns. To cite this article: Larsson C, El Madhoun S, Wennerberg A, Vult von Steyern P. Fracture strength of yttria-stabilized tetragonal zirconia polycrystals crowns with different design: an in vitro study. Clin. Oral Impl. Res. 23, 2012; 820-826. doi: 10.1111/j.1600-0501.2011.02224.x [ABSTRACT FROM AUTHOR]

ABSTRACT One of the most powerful criteria to predict the critical fracture load in plates with notches is the strain-energy density averaged over a well-defined control volume ahead of the notch tip. Although the averaged strain-energy density (ASED) criterion has been proposed for homogeneous materials, it has been shown in this paper that this criterion can also be applied for non-homogeneous materials, especially for functionally graded materials (FGMs). A numerical method has been used to evaluate the control volume boundary, the averaged strain-energy density over the control volume, and also the critical fracture load in FGMs under mode I loading. A new set of experimental results on fracture of blunt V-notched samples made of austenitic-martensitic functionally graded steel under mode I loading have been provided. [ABSTRACT FROM AUTHOR]

Summary The aim of this study was to analyse the strength and failure mode of teeth restored with fibre posts under retention and flexural-compressive loads at different stages of the restoration and to analyse whether including a simulated ligament in the experimental setup has any effect on the strength or the failure mode. Thirty human maxillary central incisors were distributed in three different groups to be restored with simulation of different restoration stages (1: only post, 2: post and core, 3: post-core and crown), using Rebilda fibre posts. The specimens were inserted in resin blocks and loaded by means of a universal testing machine until failure under tension (stage 1) and 50º flexion (stages 2-3). Half the specimens in each group were restored using a simulated ligament between root dentine and resin block and the other half did not use this element. Failure in stage 1 always occurred at the post-dentine interface, with a mean failure load of 191·2 N. Failure in stage 2 was located mainly in the core or coronal dentine (mean failure load of 505·9 N). Failure in stage 3 was observed in the coronal dentine (mean failure load 397·4 N). Failure loads registered were greater than expected masticatory loads. Fracture modes were mostly reparable, thus indicating that this post is clinically valid at the different stages of restoration studied. The inclusion of the simulated ligament in the experimental system did not show a statistically significant effect on the failure load or the failure mode. [ABSTRACT FROM AUTHOR]

Objective: In in vitro tests, metals and resins are frequently used as substitutes for human teeth. This study aims at determining the suitability of various materials for substituting human incisors in load capability tests. Method: Veneering composite (Adoro; n = 16) and non‐precious CoCr‐alloy (NPA; n = 16) were used for manufacturing 32 identical specimens based on the model of a maxillary central incisor resin tooth (Morita). Sixteen human incisors served as a control group. After root canal treatment, all specimens were restored with fiber‐reinforced composite posts and core build‐ups. For each group, eight specimens were chosen randomly and restored either with identical NPA crowns or with all‐ceramic crowns. Specimens were exposed to thermal cycling and mechanical loading (TCML) until failure. Statistical analysis was conducted using the Kruskal–Wallis test and the Bonferroni‐adjusted Mann Whitney U‐test. Results: In ceramic crowns, the highest median fracture resistance was found in alloy tooth substitutes (430 N) and natural incisors (426 N), which both showed a significantly higher fracture resistance than composite tooth substitutes (162 N). In alloy crowns, alloy tooth substitutes exhibited the highest fracture resistance (348 N), but no statistically significant difference could be detected between natural incisors (158 N) and composite tooth substitutes (117 N). No artificial tooth substitute showed fracture patterns similar to those of natural incisors. Significance: Mechanical parameters are significantly influenced by the type of restoration and the restorative material used. In in vitro tests, the range of artificial tooth substitutes suitable for the replacement of human incisors is limited by load capability. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 2009 [ABSTRACT FROM AUTHOR]

Purpose: A common problem associated with implant-supported prostheses is the fracture of denture teeth. This study was designed to compare the fracture modes of three denture teeth by compressive load at a 30° off-axis angle. Material and Methods: Three denture teeth (Vident Duostat, Ivoclar Vivadent, and Dentsply Trubyte) processed to two denture base processing systems [injection-molded (IM) SR-Ivocap system and compression-molded (CM) denture base resin] were evaluated. Each specimen was processed to a metal framework. Ultimate failure strength of each system when point loaded at a 30° off-axis angle was recorded, along with a visual inspection of each specimen. Results: The average load fracture for each group was (in N): Vident CM 1106.97 ± 223.20, Vident IM 1168.18 ± 322.52, Dentsply CM 1098.08 ± 286.32, Dentsply IM 1023.80 ± 282.45, Ivoclar CM 1616.98 ± 204.87, and Ivoclar IM 1373.54 ± 282.58. There was a significant difference between the groups and the Ivoclar CM group. The Ivoclar CM group had the highest average load force, and the Dentsply IM group had the lowest average load force. On average, the teeth within the groups fractured at a higher compression force than the average maximum occlusal force in natural dentition. Dentsply and Vident denture teeth fractured more horizontally, and the Ivoclar denture teeth fractured more vertically within the groups. There was no significant difference among the groups between the IM and CM processing methods. Conclusions: In the present in vitro study, all specimens were able to withstand 30° off-axis loading with the exception of one specimen. With these results, this would indicate that these denture teeth are able to withstand normal occlusal forces. [ABSTRACT FROM AUTHOR]

This study evaluated the fracture loads of three-unit all-ceramic bridges on implants; the core frameworks of the bridges were made of zirconium oxide. Three core framework designs were fabricated according to the design of the bars between the retainers: (i) straight, (ii) curved in the occlusal direction, or (iii) curved in the gingival direction. A static load was applied at the centre of the pontic, and the mean initial crack and final fracture loads were measured and compared. The core framework curved in the occlusal direction had the highest final fracture loads; there were significant differences ( P < 0·05) in the mean final fracture load, whereas initial fracture load, which fractured of veneered porcelain, did not show significant differences among three designs. The all-ceramic bridges on the implants made with Procera zirconium core frameworks had high final fracture load. The core framework design that curved in the occlusal direction helped the framework withstand the occlusal load, which results in reliable prostheses, especially in the molar region. [ABSTRACT FROM AUTHOR]

The aim of this in vitro study was to evaluate the fracture load and marginal accuracy of crowns made from a shrinkage-free ZrSiO4 ceramic cemented with glass–ionomer or composite cement after chewing simulation. Thirty-two human mandibular molars were randomly divided into two groups. All teeth were prepared for and restored with shrinkage-free ZrSiO4 ceramic crowns (Everest HPC®, KaVo). The crowns of group A ( N = 16) were luted to the teeth using KetacCem® and group B ( N = 16) were adhesively cemented using Panavia®21EX. Measurements of the marginal accuracy before and after cementation were made using replicas and an image analysis system. All specimens were exposed to 1·2 million cycles of thermo-mechanical fatigue in a chewing simulator. Surviving specimens were subsequently loaded until fracture in a static testing device. Fracture loads (N) were recorded. All specimens survived chewing simulation. The mean fracture loads (±s.d.) were Group A, 1622 N (±433); group B, 1957 N (±806). There was no significant difference between the two groups ( P > 0·05). The marginal gap values before cementation were (mean ± s.d.): Group A, 32·7 μm (±6·8); group B, 33·0 μm (±6·7).The mean marginal gap values after cementation were (±s.d.): Group A, 44·6 μm (±6·7); group B, 46·6 μm (±7·7). The marginal openings were significantly higher after cementation for both groups ( P < 0·05). All test groups demonstrated fracture load and marginal accuracy values within the range of clinical acceptability. [ABSTRACT FROM AUTHOR]

The strength and fracture pattern of posterior CAD/CAM-generated crown copings with 0·4 mm wall thickness were evaluated in vitro hypothesizing that fracture resistance of YTZP-zirconia copings might be independent of mode of cementation whether resin-bonded or cemented because of the high strength of YTZP-zirconia. Two sets of copings ( n = 15) each were fabricated using CEREC inLab CAD/CAM from (i) lithiumdisilicate glass–ceramic, (ii) infiltration ceramic as controls and (iii) YTZP-zirconia. Copings ( n = 15) of ceramics (i), (ii) and (iii) each were (a) zinc–phosphate cemented, (b) adhesively seated on resin-based composite dies and loaded until fracture. Load (N) data was analysed usinganova and Scheffé tests. Crack pattern was evaluated on additional three sample cross-sections for each group at fracture-start. Radial cracks originated early at the cementation interfaces and cone cracks were observed finally at the loading sites. Mean load (N) values (±s.d.) of A-copings at fracture-start/-end (i) 804 ± 195/862 ± 162, (ii) 923 ± 180/975 ± 147, (iii) 697 ± 110/1607 ± 145, were all significantly ( P < 0·01) lower when compared with their B-crown coping analogs (i) 1183 ± 318/1919 ± 326, (ii) 1621 ± 165/1820 ± 211, (iii) 731 ± 115/1973 ± 287 except for A3 and B3 at fracture-start. This confirmed our hypothesis at fracture-start ( P > 0·05) but rejected it at fracture-end ( P < 0·01). The A3 fracture-end data, even if significantly ( P < 0·01) lower, came close to the B3 values by 18%. A3 was significantly ( P < 0·001) stronger by 86/74% than A1/A2 at fracture-end. The data indicates that YTZP-zirconia copings have the potential to provide support for all-ceramic core crowns, which may be adequate for non-adhesive cementation. [ABSTRACT FROM AUTHOR]

A carbon fibre post system, three non-palladium and one palladium metal post systems, two ceramic post systems, and a metal post system with a ceramic core were studied in vitro. The control group consisted of root-filled test teeth without posts. The test teeth were identical artificial roots of an upper central incisor made from a posterior composite whose module of elasticity was similar to that of natural dentine. All posts were cemented in the roots using PanaviaTM 21 TC. Subsequently, standardized full crowns were cemented onto all roots. On a universal testing machine, the test teeth were loaded palatally at monotonously increasing loads until root fracture. The highest mean fracture loads were found for the carbon fibre post system (312·5 ± 58·8 N). The fracture load of non-palladium metal posts (242·3–300·4 N) did not differ significantly from that of the Perma-dorTM post (265·9 N), which does contain palladium. Values of 300·3 ± 89·3 N (aluminium oxide ceramics) and 193·5 ± 57·0 N (zirconia ceramics) were found for the ceramic posts. The control group exhibited a fracture load of 228·8 ± 35·7 N. The mean distance between the vestibular end of the fracture gap and the point of force application was between 10·1 ± 2·3 and 14·7 ± 1·2 mm. [ABSTRACT FROM AUTHOR]