Influence of preparation depths on the fracture load of customized zirconia abutments with titanium insert

PURPOSE

This study evaluated the fracture load of customized zirconia abutments with titanium insert according to preparation depths, with or without 5-year artificial aging.

MATERIALS AND METHODS

Thirty-six identical lithium disilicate crowns (IPS e.max press) were fabricated to replace a maxillary right central incisor and cemented to the customized zirconia abutment with titanium insert on a 4.5×10 mm titanium fixture. Abutments were fabricated with 3 preparation depths (0.5 mm, 0.7 mm, and 0.9 mm). Half of the samples were then processed using thermocycling (temperature: 5-55℃, dwelling time: 120s) and chewing simulation (1,200,000 cycles, 49 N load). All specimens were classified into 6 groups depending on the preparation depth and artificial aging (non-artificial aging groups: N5, N7, N9; artificial aging groups: A5, A7, A9). Static load was applied at 135 degrees to the implant axis in a universal testing machine. Statistical analyses of the results were performed using 1-way ANOVA, 2-way ANOVA, independent t-test and multiple linear regression.

RESULTS

The fracture loads were 539.28 ± 63.11 N (N5), 406.56 ± 28.94 N (N7), 366.66 ± 30.19 N (N9), 392.61 ± 50.57 N (A5), 317.94 ± 30.05 N (A7), and 292.74 ± 37.15 N (A9). The fracture load of group N5 was significantly higher than those of group N7 and N9 (P<.017). Consequently, the fracture load of group A5 was also significantly higher than those of group A7 and A9 (P<.05). After artificial aging, the fracture load was significantly decreased in all groups with various preparation depths (P<.05).

CONCLUSION

The fracture load of a single anterior implant restored with lithium disilicate crown on zirconia abutment with titanium insert differed depending on the preparation depths. After 5-year artificial aging, the fracture loads of all preparation groups decreased significantly.     

The effect of resin cements and primer on retentive force of zirconia copings bonded to zirconia abutments with insufficient retention

PURPOSE

The purpose of this study was to investigate the effect of resin cements and primer on the retentive force of zirconia copings bonded to zirconia abutments with insufficient retention.

MATERIALS AND METHODS

Zirconia blocks (Lava, 3M ESPE, St. Paul, MN, USA) were obtained and forty sets of zirconia abutments and copings were fabricated using CAD/CAM technology. They were grouped into 4 categories as follows, depending on the types of resin cements used, and whether the primer is applied or not:Panavia F2.0 (P), Panavia F2.0 using Primer (PRIME Plus, Bisco Inc, Schaumburg, IL, USA) (PZ), Superbond C&B (S), and Superbond C&B using Primer (SZ). For each of the groups, the cementation was conducted. The specimens were kept in sterilized water (37℃) for 24 hours. Retentive forces were tested and measured, and a statistical analysis was carried out. The nature of failure was recorded.

RESULTS

The means and standard deviations of retentive force in Newton for each group were 265.15 ± 35.04 N (P), 318.21 ± 22.24 N (PZ), 445.13 ± 78.54 N (S) and 508.21 ± 79.48 N (SZ). Superbond C&B groups (S & SZ) showed significantly higher retentive force than Panavia F2.0 groups (P & PZ). In Panavia F2.0 groups, the use of primer was found to contribute to the increase of retentive force. On the other hand, in Superbond C&B groups, the use of primer did not influence the retention forces. Adhesive failure was observed in all groups.

CONCLUSION

This study suggests that cementation of the zirconia abutments and zirconia copings with Superbond C&B have a higher retentive force than Panavia F2.0. When using Panavia F2.0, the use of primer increases the retentive force.     

Influence of implant abutment angulations on the fracture resistance of overlaying CAM-milled zirconia single crowns

Background: An in vitro study was performed to assess the effect of three implant abutment angulations and three core thicknesses on the fracture resistance of overlaying computer‐aided manufacturing (CAM) milled zirconia (Cercon^® system) single crowns. Methods: Three groups, coded A to C, with different implant abutment angulations (group A/0°, group B/15° and group C/30° angulation) were used to construct 15 crowns for each angulation. Forty‐five overlay restorations were milled using the Cercon^® system with zirconium core thicknesses of 0.4, 0.6 and 0.8 mm using five crowns for each angulation. The final restorations were prepared and stored in distilled water at mouth temperature (37 °C) for 24 hours prior to testing. The restorations were cemented using Temp Bond^®. The load required to break each crown and the mode of failure were recorded. All the results obtained were statistically analysed by the ANOVA test (level of significance p < 0.05). Tested crowns were examined using a stereomicroscope at 40X and selected crowns (five randomly selected from each group were further examined by scanning electron microscopy) to reveal the zirconia–ceramic interface and to determine the fracture origin. Results: Implant abutment angulations significantly (p < 0.05) reduced the fracture resistance of overlaying CAM‐milled zirconia single crowns. The fracture loads of Cercon^® crowns cemented onto abutment preparations with a 30° angulation were the lowest of the groups tested. The core thickness (0.4 to 0.8 mm) did not significantly (p > 0.05) affect the fracture resistance of the CAM‐milled zirconia single crowns. SEM showed that the origin of the fracture appeared to be located at the occlusal surfaces of the crowns and the crack propagation tended to radiate from the occlusal surface towards the gingival margin. Conclusions: The implant angulation of 30° significantly (p < 0.05) reduced the fracture resistance of overlaying CAM‐milled zirconia single crowns. Reducing the core thickness from 0.8 mm to 0.4 mm did not affect (p > 0.05) the fracture resistance of overlaying CAM‐milled zirconia single crowns.     

The effect of preparation taper on the resistance to fracture of monolithic zirconia crowns

ObjectiveMonolithic zirconia crowns have become a viable alternative to conventional layered restorations. The aim of this study was to evaluate whether the taper, and thus wall thickness, of the abutment or pre-defined cement space affect the fracture resistance or fracture mode of monolithic zirconia crowns.MethodsA model tooth was prepared with a taper of 15° and a shallow circumferential chamfer preparation (0.5 mm). Two additional models were made based on the master model with a taper of 10° and 30° using computer-aided design software. Twenty monolithic 3rd generation translucent zirconia crowns were produced for each model with pre-defined cement space set to either 30 μm or 60 μm (n = 60). The estimated cement thickness was assessed by the replica method. The cemented crowns were loaded centrally in the occlusal fossa at 0.5 mm/min until fracture. Fractographic analyses were performed on all fractured crowns.ResultsThe load at fracture was statistically significant different between the groups (p < 0.05). The crowns with 30° taper fractured at lower loads than those with 10° and 15° taper, regardless of the cement space (p < 0.05). The fracture origin for 47/60 crowns (78%) was in the cervical area, close to the top of the curvature in the mesial or distal crown margin. The remaining fractures started at the internal surface of the occlusal area and propagated cervically.SignificanceThe fracture resistance of the monolithic zirconia crowns was lower for crowns with very large taper compared to 10 and 15° taper even though the crown walls were thicker.     

Effect of span length on the fit of zirconia framework fabricated using CAD/CAM system

PURPOSE

The purpose of this study was to evaluate the effect of the span length on the fit of zirconia framework fabricated using CAD/CAM system.

MATERIALS AND METHODS

Abutments for single, 4-unit and 6-unit fixed partial prostheses were fabricated. Ten zirconia frameworks were fabricated for each group. The marginal and internal gap were presented by means of replica technique and measured by measuring microscope (AXIO®, Carl Zeiss, Rochester, NY) and software (I-solution®, IMT i-solution Inc., Vancouver, BC, Canada). The results were statistically analyzed by multivariate analysis test and Dunnett T3 test for post hoc test (α=.05).

RESULTS

There were statistically significant differences at 2, 4, 7, 8 points (mesio-distal section) and b, d, e, f, g (labio-lingual section). In some marginal reference points of 6-unit group (P<.05), the marginal gap were larger than 120 µm.

CONCLUSION

Span length of zirconia core may have an influence on marginal and internal fit. Within the limitation of this study, the increase of span length of zirconia framework of 6 or more-unit fixed partial denture may decrease the marginal and internal fit.     

数字化口腔修复（18）--CAD／CAM全瓷冠与个性化基台的适合性

目的：比较不同计算机辅助设计和制造（ computer aided design／manufacture,CAD／CAM）全瓷冠与氧化锆个性化基台的边缘和内部适合性。方法：用CAD／CAM分别设计和加工氧化锆个性化基台和全瓷冠3组（ IPS e． max、Enamic和Suprinity）,每组各5个全瓷冠。通过微机断层扫描（ micro computed tomography,micro?CT）测量全瓷冠与氧化锆个性化基台的绝对边缘差异（ absolute marginal discrepancy,AMD）、轴面间隙（ axial gap,AG）、咬合间隙（ oc?clusal gap,OG）,比较不同材料全瓷冠与氧化锆个性化基台的边缘和内部适合性。结果：Enamic组分别与IPS e． max组和Suprinity组AMD之间的比较差异均具有统计学意义（P＜0．05）;而IPS e． max组与Suprinity组AMD之间的差异则无统计学意义（P＞0．05）。 Suprinity组分别与IPS e． max组和Enamic组AG之间的比较差异均具有统计学意义（P＜0．05）;IPS e． max组与Enamic组AG之间的差异不具有统计学意义（P＞0．05）。 Suprinity组、IPS e． max组和Enamic组3组OG之间的比较差异具有统计学意义（P＜0．05）。结论：不同的CAD／CAM全瓷冠材料影响其边缘和内部适合性。 Suprinity和IPS e． max陶瓷材料的边缘适合性优于Enamic材料,Suprinity材料全瓷冠的轴面间隙和咬合间隙最小。     

Fracture loads and failure modes of customized and non-customized zirconia abutments

Objective

This study aimed to evaluate the fracture load and pattern of customized and non-customized zirconia abutments with Morse-taper connection.

后牙四单位氧化锆固定桥抗折性的实验研究

目的:研究后牙四单位氧化锆固定桥基底支架的抗折性能。方法:运用CAD/CAM系统设计并制作后牙四单位氧化锆固定桥基底支架,利用一侧第一前磨牙和第二磨牙来修复第二前磨牙和第一磨牙,根据不同基底冠厚度设计分为0.6 mm组和0.7 mm组,每组6个。将所有后牙四单位氧化锆固定桥基底支架粘固于模型上,进行力学加载至断裂。记录所有固定桥的临界载荷,将两组临界载荷数据进行单因素方差分析。结果:两组不同厚度的后牙四单位氧化锆固定桥基底支架临界载荷分别为:0.6 mm组为(1 070.5±139.3)N,0.7 mm组为(1 217.3±120.5)N,经统计学分析两组临界载荷值无明显差异(P>0.05)。结论:两组后牙四单位氧化锆固定桥基底支架的临界载荷均大于口腔最大咬合力(888 N),抗折性能可靠。     

Effect of cementation,cement type and vent holes on fit of zirconia copings

Objectives

To investigate the effect of cementation, cement type and vent-holes on the marginal and internal fit of Zirconia (Zr) Copings.

The effect of fatigue loading on the screw joint stability of zirconium abutment

PurposeThis study evaluated the effect of fatigue loading on the screw joint stability of a zirconium abutment connected to an external hexagon implant in vitro.Materials and methodsFifteen titanium and 15 zirconia abutments of 3 different heights (5, 8, and 11 mm) were connected to external titanium implants with titanium screws. A torque gauge was used to measure the reverse torque values before and after loading. An air cylindrical loading device was used to simulate mastication at a 45-degree angle to the longitudinal axis of the implant.ResultsThere were significant differences (P < 0.05) before and after the loading of titanium (5 mm) and zirconia (5, 8, and 11 mm) abutments.ConclusionZirconia abutments for external hexagon implants had durability rates similar to those of titanium abutments after repeating load on the reverse torque of the abutment screw, indicating that the zirconia abutment could be reliably used instead of the titanium abutment.     

In vitro investigation of fracture load and aging resistance of high-speed sintered monolithic tooth-borne zirconia crowns

ObjectivesThe purpose of this study was to evaluate the fit, fracture load and aging resistance of the monolithic zirconia tooth-borne crowns with conventional and high-speed sintering.MethodsThe Y-TZP block was machined and sintered with conventional and high-speed sintering furnace. The marginal and internal gap between the crown and abutment was measured using a microscope and a fit checking material. A total of 28 crowns were further divided into an undegraded and a degraded group. An accelerated aging test was carried out on the degraded group. The crown was cemented and a fracture resistance was tested. X-ray diffraction was used to evaluate the crystalline structure. The data were analyzed with Student’s t-test, and a one-way ANOVA and Tukey’s multiple comparison test.ResultsThere was no significant difference in mean marginal gap between the two groups. The mean internal gap was significantly greater in the speed sintering than in the conventional sintering (P <0.001). The mean fracture load of the conventional sintering crowns was not significantly different from that of speed sintering crowns after aging. The occurrence of monoclinic crystals of degraded crown was significantly higher than that of undegraded crown both in the conventional (P <0.001) and speed-sintering group (P <0.001).ConclusionsIt was concluded that the monolithic zirconia crowns produced by high-speed sintering showed no significant difference in the marginal gap and the fracture load after aging compared to conventional sintering. Therefore, the high-speed sintering seems a valid method of producing tooth-borne monolithic zirconia crowns.     

Effect on in vitro fracture resistance of the technique used to attach lithium disilicate ceramic veneer to zirconia frameworks

Objectives

This in vitro study should assess the fracture resistance of veneered zirconia-based crowns with either luted or fused veneer.

Methods

Thirty-two identical zirconia frameworks (IPS e.max ZirCAD; Ivoclar/Vivadent), were constructed (inLab 3.80; Sirona Dental Systems). All frameworks were veneered with CAD/CAM-fabricated lithium disilicate ceramic (IPS e.max CAD; Ivoclar/Vivadent). For half the crowns (n = 16) the veneer was luted to the framework (Multilink Implant; Ivoclar/Vivadent); for the other it was fused (IPS e.max Crystall./Connect; Ivoclar/Vivadent). Half of the specimens were then loaded until failure without artificial aging; the other half underwent artificial aging before assessment of the ultimate load. To compare the two techniques further, finite element analysis (FEA) and fractographic assessment using SEM and EDX analysis were conducted. Statistical assessment was performed by use of non-parametric tests.

Results

Initial fracture forces were higher in the fusion group (mean: 1388 ± 190 N versus 1211 ± 158 N). All specimens were insensitive to artificial aging. FEA showed that tensile stresses in the veneer at the frame–veneer interface were much higher for crowns with luted veneer; this may be the reason for their lower fracture resistance. Fractographic analysis revealed that both fused and luted specimens had cohesive and adhesive fracture patterns which resulted in partial delamination of the veneer.

Significance

Fused crowns are superior to luted crowns. Comparison of fracture resistance with the maximum loads which may occur clinically (F_max = 600 N on one tooth) suggests both techniques might be used clinically, however.     

切口角度和深度对氧化锆陶瓷切口强度的影响

目的比较研究切口角度和深度对氧化锆陶瓷切口强度的影响。方法制作尺寸为4.4mm×2.2mm×18mm的氧化锆陶瓷试样,将试样分成6组,每组10个,制备与试样的长轴方向夹角分别为30°、60°及90°,深度分别为1mm和2mm的切口。将试样置于万能力学测试机上,采用三点弯曲方式加载,记录并计算切口试样的断裂强度,即切口强度。结果当切口深度为1mm时,切口角度为60°的试样切口强度最大;当切口深度为2mm时,切口角度为90°的试样切口强度最大,随着角度减小,切口强度也随之减小;在切口角度相同时,切口深度为1mm的试样切口强度大于切口深度为2mm的试样。结论切口的角度和深度影响氧化锆陶瓷试样的切口强度。     

Evaluation of intaglio surface trueness,wear, and fracture resistance of zirconia crown under simulated mastication: a comparative analysis between subtractive and additive manufacturing

PURPOSEThis in-vitro analysis aimed to compare the intaglio trueness, the antagonist’s wear volume loss, and fracture load of various single-unit zirconia prostheses fabricated by different manufacturing techniques.MATERIALS AND METHODSZirconia crowns were prepared into four different groups (n = 14 per group) according to the manufacturing techniques and generations of the materials. The intaglio surface trueness (root-mean-square estimates, RMS) of the crown was measured at the marginal, axial, occlusal, and inner surface areas. Half of the specimens were artificially aged in the chewing simulator with 120,000 cycles, and the antagonist’s volume loss after aging was calculated. The fracture load for each crown group was measured before and after hydrothermal aging. The intaglio trueness was evaluated with Welch’s ANOVA and the antagonist’s volume loss was assessed by the Kruskal-Wallis tests. The effects of manufacturing and aging on the fracture resistance of the tested zirconia crowns were determined by two-way ANOVA.RESULTSThe trueness analysis of the crown intaglio surfaces showed surface deviation (RMS) within 50 µm, regardless of the manufacturing methods (P = .053). After simulated mastication, no significant differences in the volume loss of the antagonists were observed among the zirconia groups (P = .946). The manufacturing methods and simulated chewing had statistically significant effects on the fracture resistance (P < .001).CONCLUSIONThe intaglio surface trueness, fracture resistance, and antagonist’s wear volume of the additively manufactured 3Y-TZP crown were clinically acceptable, as compared with those of the 4Y- or 5Y-PSZ crowns produced by subtractive milling.     

Comparison of two fracture toughness testing methods using a glass-infiltrated and a zirconia dental ceramic

PURPOSE

The objective of this study was to compare the fracture toughness (K_Ic) obtained from the single edge V-notched beam (SEVNB) and the fractographic analysis (FTA) of a glass-infiltrated and a zirconia ceramic.

MATERIALS AND METHODS

For each material, ten bar-shaped specimens were prepared for the SEVNB method (3 mm × 4 mm × 25 mm) and the FTA method (2 mm × 4 mm × 25 mm). The starter V-notch was prepared as the fracture initiating flaw for the SEVNB method. A Vickers indentation load of 49 N was used to create a controlled surface flaw on each FTA specimen. All specimens were loaded to fracture using a universal testing machine at a crosshead speed of 0.5-1 mm/min. The independent-samples t-test was used for the statistical analysis of the K_Ic values at α=0.05.

RESULTS

The mean K_Ic of zirconia ceramic obtained from SEVNB method (5.4 ± 1.6 MPa·m^1/2) was comparable to that obtained from FTA method (6.3 ± 1.6 MPa·m^1/2). The mean K_Ic of glass-infiltrated ceramic obtained from SEVNB method (4.1 ± 0.6 MPa·m^1/2) was significantly lower than that obtained from FTA method (5.1 ± 0.7 MPa·m^1/2).

CONCLUSION

The mean K_Ic of the glass-infiltrated and zirconia ceramics obtained from the SEVNB method were lower than those obtained from FTA method even they were not significantly different for the zirconia material. The differences in the K_Ic values could be a result of the differences in the characteristics of fracture initiating flaws of these two methods.     

氧化锆个性化基台与钛基边缘适合性研究

目的比较不同品牌的CAD/CAM氧化锆个性化基台与钛基之间的适合性。方法用CAD/CAM分别设计和加工3种氧化锆个性化基台(日进、爱尔创和卡瓦),每种5个。通过扫描电子显微镜,测量氧化锆个性化基台与钛基之间的边缘间隙(MG),比较3种氧化锆个性化基台与钛基之间的边缘适合性。结果卡瓦组(7.19±2.98)μm与日进组(10.25±6.25)μm和爱尔创组(9.87±5.48)μm的边缘间隙的差异具有统计学意义(P<0.05);爱尔创组与日进组的边缘间隙的差异无统计学意义(P>0.05)。结论不同的材料直接影响个性化基台与钛基之间的适合性。在个性化基台与钛基的边缘适合性方面,卡瓦氧化锆明显优于日进及爱尔创氧化锆。     

Influence of implant abutment angulations and two types of fibers on the fracture resistance of ceramage single crowns

Purpose: To assess the effect of three implant abutment angulations and two types of fibers on the fracture resistance of overlaying Ceramage single crowns. Materials and Methods: Three groups, coded A to C, with different implant abutment angulations (group A/0°, group B/15°, and group C/30° angulation) were restored with 45 overlay composite restorations; 15 Ceramage crowns for each angulation. Groups A, B, and C were further subdivided into three subgroups (n = 5) coded: 1, crowns without fiber reinforcement; 2, crowns with Connect polyethylene reinforcement; and 3, crowns with Interlig glass reinforcement. All crowns were constructed by one technician using the Ceramage System. The definitive restorations (before cementation) were stored in distilled water at mouth temperature (37°C) for 24 hours prior to testing. Before testing, the crowns were cemented using Temp Bond. The compressive load required to break each crown and the mode of failure were recorded. The speed of testing was 1 mm/min. The results were statistically analyzed by two‐way ANOVA (p < 0.05). The tested crowns were examined using a stereomicroscope at 40×, and selected crowns (five randomly selected from each group) were further examined by scanning electron microscopy (SEM) to reveal the composite–fiber interface. Results: Fracture resistance of single crowns was not affected (p > 0.05) by the different abutment angulations chosen (0°, 15°, 30°) or fiber reinforcement (Connect and Interlig fibers). Crowns in group A exhibited average loads to fracture (N) of A1 = 843.57 ± 168.20, A2 = 1389.20 ± 193.40, and A3 = 968.00 ± 387.53, which were not significantly different (p > 0.05) from those of groups B (B1 = 993.20 ± 327.19, B2 = 1471.00 ± 311.68, B3 = 1408.40 ± 295.07), or group C (C1 = 1326.80 ± 785.30, C2 = 1322.20 ± 285.33, C3 = 1348.40 ± 527.21). SEM images of the fractured crowns showed that the origin of the fracture appeared to be located at the occlusal surfaces of the crowns, and the crack propagation tended to extend from the occlusal surface towards the gingival margin. Conclusions: Implant abutment angulations of 0°, 15°, and 30° did not significantly (p > 0.05) influence the fracture resistance of overlaying Ceramage single crowns constructed with or without reinforcing fibers. The two types of fibers used for reinforcement (Connect and Interlig) had no effect (p > 0.05) on the fracture resistance of overlaying Ceramage single crowns.     

Influence of residual thermal stresses on the edge chipping resistance of PFM and veneered zirconia structures: Experimental and FEA study

Objective

Chipping fractures of the veneering porcelain are frequently reported for veneered all-ceramic crowns. In the present study, the edge chipping test is used to measure the toughness and the edge chipping resistance of veneered zirconia and porcelain-fused-to-metal (PFM). The aim is to describe an edge chipping method developed with the use of a universal testing machine and to verify the accuracy of this method to determine the influence of residual thermal stresses on the chipping fracture resistance of veneering porcelain. A finite element analysis (FEA) was used to study the residual stress profiles within the veneering porcelain.

Fatigue and fracture resistance of zirconia crowns prepared with different finish line designs

Purpose: The aim of this study was to evaluate the effect of finish line design on the fatigue, fracture resistance, and failure type of veneered zirconia restorations. Materials and Methods: A CAD/CAM system (Cercon) was used to prepare zirconia frameworks (0.5 mm thick) for a maxillary central incisor. Three finish line designs were evaluated: a complete narrow chamfer, a narrow chamfer with a lingual ledge, and a complete ledge. The prepared frameworks were veneered using a press‐on ceramic (Ceram Press) and were cemented on the corresponding prepared teeth using a resin cement (Panavia F2.0). The cemented specimens were thermocycled, subjected to dynamic fatigue, and finally loaded till fracture. Fractured specimens were examined under a scanning electron microscope to assess fracture type. One‐way ANOVA and Bonferroni post hoc tests were used to analyze the data (α= 0.05). Results: The finish line design did not have any significant statistical influence on the fracture resistance (F = 1.9, p= 0.346) or on the failure type of the tested specimens. Adjusted R squared value (R = 0.049) indicated a weak correlation between finish line design and fracture load of the tested specimens. All specimens failed due to cracking and fracture of the veneer ceramic. Meanwhile, the framework remained entirely intact. Three narrow chamfer finish line specimens demonstrated adhesive fracture of the veneer ceramic during dynamic fatigue testing, related to overextension of the veneer ceramic during the layering procedure. Conclusion: Within the limitations of this study, the finish line design did not influence the fatigue or the fracture resistance of veneered zirconia crowns. Selection of any of the finish line designs should be based on the clinical condition of the restored tooth.