A Total of 1,132 All-Ceramic Single-Tooth Restorations Show Acceptable Survival Rates up to 15 Years in a Non-University Setting.

PURPOSE: To evaluate the long-term survival of IPS Empress 2 and IPS e.max (Ivoclar Vivadent) restorations in a non-university setting. MATERIALS AND METHODS: A retrospective study design was used to evaluate the survival rate of 1,132 Empress 2 and IPS e.max restorations placed in 251 patients with regard to patient age, gender, tooth type, tooth vitality, material, restoration form (inlay vs partial crown vs crown), cementation mode (self-adhesive vs non-self-adhesive), and bruxism activity. Kaplan-Meier and regression analyses were used for statistical analyses. RESULTS: Of the 1,132 restorations, a total of 15 (IPS e.max = 3, Empress 2 = 12) failed. The overall survival rate for all restorations was 98.7% after 15.4 years. A significantly reduced survival rate was found for nonvital teeth (P = .002), patient age > 60 years (P = .002), crowns (vs inlays and partial crowns; P = .002), and self-adhesive resin materials (P = .018). CONCLUSION: Within the limitations of this study, glass-ceramic single-tooth restorations made of Empress 2 and IPS e.max show good survival rates up to a period of 15 years.

In vitro evaluation of the influence of titanium nitride coating on the retention force between components of two-part abutments.

BACKGROUND: Two-part abutments are typically made up of a base composed of titanium and a ceramic build-up. The long-term outcomes are affected by the mechanical durability. The purpose of the present investigation was to evaluate and compare the retention force of two-part abutment systems with titanium or titanium nitride bases-as fixed with zirconia components and with various surface treatments. METHODS: A total of 60 two-part abutments were investigated-with a titanium base (n = 30) or titanium nitride coated bases (n = 30) and bonded with zirconia ceramic build-ups. The bonding surfaces were treated with aluminium oxide blasting, with an average particle size of 110 µm. The titanium bases were then pretreated with Alloy Primer or Clearfil Ceramic Primer. The ceramic build-ups were only treated with Clearfil Ceramic Primer. For twenty test specimens, no chemical pretreatment was performed. Test specimens were classified into six groups in accordance with the pretreatment (A-F; n = 10). A resin-based luting agent was employed to attach the two parts. Specimens were then subjected to artificial thermal aging (104 cycles with 5 °C/55 °C). The retention force between the two parts was then investigated with a pull-off test. The findings were analyzed by ANOVA statistics. Fracture patterns were examined by electron microscopy. RESULTS: In the absence of primer, titanium nitride coated bases gave significantly greater retention forces than other samples (p < 0.05). Chemical preconditioning with silane coupling agents did not effect on the retention force of coated bases. CONCLUSIONS: The results of the current study suggested that modifying metal surfaces by coating the base with titanium nitride not only has esthetic and biological advantages, but also enhances the mechanical properties of the adhesive bond of two-part abutments.

Fitting accuracy of ceramic veneered Co-Cr crowns produced by different manufacturing processes.

PURPOSE: The purpose of this in vitro study was to evaluate the fitting accuracy of single crowns made from a novel presintered Co-Cr alloy prepared with a computer-aided design and computer-aided manufacturing (CAD/CAM) technique, as compared with crowns manufactured by other digital and the conventional casting technique. Additionally, the influence of oxide layer on the fitting accuracy of specimens was tested. MATERIALS AND METHODS: A total of 40 test specimens made from Co-Cr alloy were investigated according to the fitting accuracy using a replica technique. Four different methods processing different materials were used for the manufacture of the crown copings (milling of presintered (Ceramill Sintron-group_cer_sin) or rigid alloy (Tizian NEM-group_ti_nem), selective laser melting (Ceramill NPL-group_cer_npl), and casting (Girobond NB-group_gir_nb)). The specimens were adapted to a resin model and the outer surfaces were airborne-particle abraded with aluminum oxide. After the veneering process, the fitting accuracy (absolute marginal discrepancy and internal gap) was evaluated by the replica technique in 2 steps, before removing the oxide layer from the intaglio surface of the crowns, and after removing the layer with aluminum oxide airborne-particle abrasion. Statistical analysis was performed by multifactorial analysis of variance (ANOVA) (α=.05). RESULTS: Mean absolute marginal discrepancy ranged between 20 µm (group_cer_npl for specimens of Ceramill NPL) and 43 µm (group_cer_sin for crowns of Ceramill Sintron) with the oxide layer and between 19 µm and 28 µm without the oxide layer. The internal gap varied between 33 µm (group_ti_nem for test samples of Tizian NEM) and 75 µm (group_gir_nb for the base material Girobond NB) with the oxide layer and between 30 µm and 76 µm without the oxide layer. The absolute marginal discrepancy and the internal gap were significantly influenced by the fabrication method used (P<.05). CONCLUSION: Different manufacturing techniques had a significant influence on the fitting accuracy of single crowns made from Co-Cr alloys. However, all tested crowns showed a clinically acceptable absolute marginal discrepancy and internal gap with and without oxide layer and could be recommended under clinical considerations. Especially, the new system Ceramill Sintron showed acceptable values of fitting accuracy so it can be suggested in routine clinical work.

Two-part implant abutments with titanium and ceramic components: Surface modification affects retention forces-An in-vitro study.

OBJECTIVES: Two-part abutments consist of titanium base and ceramic coping. Their long-term success is largely determined by the mechanical stability. The aim of the present study was to investigate the retention forces of two-part implant abutments. The study included zirconia and lithium disilicate ceramics copings, with different surface treatments and resin-based luting agents. MATERIAL AND METHODS: The analysis of retention forces was based on a total of 70 test specimens. Seven surface modifications and three resin-based luting agents were employed for the bonding of components in the seven groups (n = 70). All surfaces of titanium bases-except for a control-were pretreated with aluminum oxide blasting, either alone or in combination with surface activating primers. Surfaces of ceramic copings were also treated mechanically by sandblasting, either alone or with acid etching or different primers. All specimens underwent thermal aging (104 cycles, 5°C/55°C). The retention forces between the two parts were measured with a pull-off test. The results were analyzed by two-way ANOVA statistics. Fracture patterns were evaluated by light and scanning electron microscopy. RESULTS: No mechanical pretreatment of the titanium (group 2) base resulted in the lowest retention. The combination with Monobond plus leads to the highest pull-off forces for both ceramic materials. CONCLUSIONS: Surface modifications and resin-based agents influence the retention of components of two-part abutments. Lithium disilicate ceramic copings reached comparable results of retention to the typically used zirconia copings.

Fracture Strength of Ceramic Posterior Occlusal Veneers for Functional Rehabilitation of an Abrasive Dentition.

PURPOSE: To evaluate the load at fracture and influence of artificial aging of posterior teeth occlusal veneers ("table tops") made of two different ceramics. MATERIALS AND METHODS: A total of 80 table tops were produced from feldspathic ceramic (VM) and zirconia-reinforced lithium silicate ceramic (CD) using computer-aided design/computer-assisted manufacturing (CAD/CAM). Half of the specimens from each ceramic were aged prior to the load test. RESULTS: Mean ± standard deviation (SD) load at fracture was significantly higher for CD (1,571.1 N ± 297.0 N) than for VM (573.6 N ± 86.4 N) (P < .001). After aging, load at fracture increased significantly to 1,819.0 N (± 310.6 N) for CD and to 745.2 N (± 168.3 N) for VM. CONCLUSION: The use of zirconia-reinforced lithium silicate ceramic for molar nonprep table tops should be uncomplicated according to the high load-at-fracture values. Mechanical stability of either ceramic is not compromised by aging.

Stress Distribution in All-Ceramic Posterior 4-Unit Fixed Dental Prostheses Supported in Different Ways: Finite Element Analysis.

INTRODUCTION: The purpose of this finite element analysis (FEA) was to complement results of previously published studies that investigated the influence of abutment resilience on the load-bearing capacity of zirconia posterior 4-unit fixed dental prostheses (FDPs) with static load tests. MATERIALS AND METHODS: Duplicates of 3 different physical specimens were modeled for FEA. The first virtual specimen was supported by teeth with periodontal resilience, the second by the combination of tooth and implant, and the third by implants only. The center of the FDP was loaded, vertically to the occlusal plane. The highest maximum principal stresses (MPSs) were computed. DISCUSSION: The highest MPS in each model occurred in the basal region of the middle framework connector. Comparison between the 3 models showed that the tensile stresses were lower when the support of the FDP was more rigid. Numerically determined highest MPSs in the FDPs correlated well with experimentally observed load-bearing capacities. CONCLUSION: The FEA is well suited to confirm the in vitro study mentioned and complement the results with stress distributions in all-ceramic posterior 4-unit FDP.

Three-Dimensional Nonlinear Finite Element Analysis and Microcomputed Tomography Evaluation of Microgap Formation in a Dental Implant Under Oblique Loading.

PURPOSE: Since bacterial leakage along the implant-abutment interface may be responsible for peri-implant infections, a realistic estimation of the interface gap width during function is important for risk assessment. The purpose of this study was to compare two methods for investigating microgap formation in a loaded dental implant, namely, microcomputed tomography (micro-CT) and three-dimensional (3D) nonlinear finite element analysis (FEA); additionally, stresses to be expected during loading were also evaluated by FEA. MATERIALS AND METHODS: An implant-abutment complex was inspected for microgaps between the abutment and implant in a micro-CT scanner under an oblique load of 200 N. A numerical model of the situation was constructed; boundary conditions and external load were defined according to the experiment. The model was refined stepwise until its load-displacement behavior corresponded sufficiently to data from previous load experiments. FEA of the final, validated model was used to determine microgap widths. These were compared with the widths as measured in micro-CT inspection. Finally, stress distributions were evaluated in selected regions. RESULTS: No microgaps wider than 13 µm could be detected by micro-CT for the loaded implant. FEA revealed gap widths up to 10 µm between the implant and abutment at the side of load application. Furthermore, FEA predicted plastic deformation in a limited area at the implant collar. CONCLUSION: FEA proved to be an adequate method for studying microgap formation in dental implant-abutment complexes. FEA is not limited in gap width resolution as are radiologic techniques and can also provide insight into stress distributions within the loaded complex.

Retention Forces between Titanium and Zirconia Components of Two-Part Implant Abutments with Different Techniques of Surface Modification.

BACKGROUND: The adhesive connection between titanium base and zirconia coping of two-part abutments may be responsible for the failure rate. A high mechanical stability between both components is essential for the long-term success. PURPOSE: The aim of the present in-vitro study was to evaluate the influence of different surface modification techniques and resin-based luting agents on the retention forces between titanium and zirconia components in two-part implant abutments. MATERIALS AND METHODS: A total of 120 abutments with a titanium base bonded to a zirconia coping were investigated. Two different resin-based luting agents (Panavia F 2.0 and RelyX Unicem) and six different surface modifications were used to fix these components, resulting in 12 test groups (n = 10). The surface of the test specimens was mechanically pretreated with aluminium oxide blasting in combination with application of two surface activating primers (Alloy Primer, Clearfil Ceramic Primer) or a tribological conditioning (Rocatec), respectively. All specimens underwent 10,000 thermal cycles between 5°C and 55°C in a moist environment. A pull-off test was then conducted to determine retention forces between the titanium and zirconia components, and statistical analysis was performed (two-way anova). Finally, fracture surfaces were analyzed by light and scanning electron microscopy. RESULTS: No significant differences were found between Panavia F 2.0 and RelyX Unicem. However, the retention forces were significantly influenced by the surface modification technique used (p < 0.001). For both luting agents, the highest retention forces were found when adhesion surfaces of both the titanium bases and the zirconia copings were pretreated with aluminium oxide blasting, and with the application of Clearfil Ceramic Primer. CONCLUSION: Surface modification techniques crucially influence the retention forces between titanium and zirconia components in two-part implant abutments. All adhesion surfaces should be pretreated by sandblasting. Moreover, a phosphate-based primer serves to enhance long-term retention of the components.

Interfacial adhesion of zirconia/veneer bilayers with different thermal characteristics.

The aim of this study was to investigate how changes in the thermal characteristics of veneer ceramics with almost identical chemical and mechanical properties but with different coefficients of thermal expansion (CTE) can modify their interfacial adhesion to zirconia. 48 bilayers made of one Y-TZP ceramic and four veneer ceramics were fabricated (n=12). Thermal residual stresses were calculated on the basis of the CTE and glass transition temperatures. After defined notching all specimens were loaded in a four-point bending test and the critical loads were recorded which induced stable crack extension at the adhesion interface. The strain energy release rate (G, J/m(2)) was calculated and was taken as a measure of interfacial adhesion. The CTE of the veneer ceramics were significantly correlated with their adhesion to Y-TZP (p<0.001). Interfacial adhesion in zirconia/veneer bilayers is predominantly affected by the thermal characteristics of the veneer ceramic.

Machining human dentin by abrasive water jet drilling.

The aim of this experimental in-vitro study was to investigate the machining of human dentin using an abrasive water jet and to evaluate the influence of different abrasives and water pressures on the removal rate. Seventy-two human teeth had been collected after extraction and randomly divided into six homogeneous groups (n=12). The teeth were processed in the area of root dentin with an industrial water jet device. Different abrasives (saccharose, sorbitol, xylitol) and water pressures (15 or 25 MPa) were used in each group. Dimensions of dentin removal were analysed using a stripe projection microscope and both drilling depth as well as volume of abrasion were recorded. Morphological analyses of the dentin cavities were performed using scanning electron microscopy (SEM). Both drilling depth and volume of abrasion were significantly influenced by the abrasive and the water pressure. Depending on these parameters, the drilling depth averaged between 142 and 378 µm; the volume of abrasion averaged between 0.07 and 0.15 mm3. Microscopic images revealed that all cavities are spherical and with clearly defined margins. Slight differences between the abrasives were found with respect to the microroughness of the surface of the cavities. The results indicate that abrasive water jet machining is a promising technique for processing human dentin.

Influence of lubricant on screw preload and stresses in a finite element model for a dental implant.

STATEMENT OF PROBLEM: Loosening or fracture of the abutment screw are frequent complications in implant dentistry and are detrimental to the long-term success of the restorations. However, little is known about the factors influencing the stability of the screw-abutment complex. PURPOSE: The purpose of this study was to investigate the influence of lubricant action during implant assembly on screw preload and stresses in a dental implant-abutment complex. MATERIAL AND METHODS: A dental implant was modeled for finite element stress analysis. Different friction coefficients (µ=0.2 to 0.5) were chosen for the interfaces between implant components to simulate lubricant action or dry conditions. The stress analyses were each divided into 2 load steps. First, the abutment screw was virtually tightened with a torque of 25 Ncm. This was achieved by applying an equivalent preload calculated according to the different friction coefficients chosen. Second, the construction was externally loaded with a force of 200 N inclined by 30 degrees relative to the implant axis. RESULTS: The screw preload increased with the decreasing friction coefficient. In all components, stresses increased with decreasing friction coefficient. Plastic deformation was observed at the implant neck in an area that expanded with decreasing friction coefficient. No plastic deformation occurred in the abutment. CONCLUSIONS: The results of this study indicated that screw preload should be included in the finite element analysis of dental implants for a realistic evaluation of stresses in the implant-abutment complex. The friction coefficient significantly influenced the screw preload value and modified the stresses in the implant-abutment complex.

Enhancement of the adhesion between cobalt-base alloys and veneer ceramic by application of an oxide dissolving primer.

OBJECTIVES: Uncontrolled formation of an oxide layer on base metal alloy surface impairs adhesion between the alloy and veneer ceramic. The aim of this study was to investigate the influence of an oxide dissolving primer on the adhesion between cobalt-base alloys and a veneer ceramic. METHODS: Combinations of two cobalt-base alloys (Bärlight/BL, Cara Process/CP) and one veneering ceramic (HeraCeram) were investigated. 40 rectangular specimens of each alloy were covered with the veneer ceramic; half of the alloy samples were treated with an oxide dissolving primer (NP-Primer) prior to veneering (n=20). Subsequently, the veneering surface was ground flat and notched using the single-edge V-notched-beam method. Then specimens were loaded in a four-point bending test and the critical load to induce stable crack extension at the adhesion interface was determined, in order to calculate the strain energy release rate (G, J/m(2)). Finally, fracture surfaces of the specimens were evaluated by scanning electron microscopy (SEM). RESULTS: Strain energy release rates averaged between 24.1J/m(2) and 28.8 J/m(2). While application of the primer statistically significantly increased adhesion between alloy and ceramic with the BL specimens (p=0.035), no significant influence was found for the CP specimens (p=0.785). For both material combinations, SEM analysis revealed enhanced wetting of the alloy surfaces with ceramic after application of the primer. SIGNIFICANCE: Application of an oxide dissolving primer increases the wettability of cobalt-base alloy surfaces and thus improves adhesion to veneering ceramics. This may enhance the long-term stability of bilayer restorations made from these materials.

Load-bearing capacity of screw-retained CAD/CAM-produced titanium implant frameworks (I-Bridge®2) before and after cyclic mechanical loading.

UNLABELLED: Implant-supported screw-retained fixed dental prostheses (FDPs) produced by CAD/ CAM have been introduced in recent years for the rehabilitation of partial or total endentulous jaws. However, there is a lack of data about the long-term mechanical characteristics. OBJECTIVE: The aim of this study was to investigate the failure mode and the influence of extended cyclic mechanical loading on the load-bearing capacity of these frameworks. MATERIAL AND METHODS: Ten five-unit FDP frameworks simulating a free-end situation in the mandibular jaw were manufactured according to the I-Bridge®2-concept (I-Bridge®2, Biomain AB, Helsingborg, Sweden) and each was screw-retained on three differently angulated Astra Tech implants (30º buccal angulation/0º angulation/30º lingual angulation). One half of the specimens was tested for static load-bearing capacity without any further treatment (control), whereas the other half underwent five million cycles of mechanical loading with 100 N as the upper load limit (test). All specimens were loaded until failure in a universal testing machine with an occlusal force applied at the pontics. Load-displacement curves were recorded and the failure mode was macro- and microscopically analyzed. The statistical analysis was performed using a t-test (p=0.05). RESULTS: All the specimens survived cyclic mechanical loading and no obvious failure could be observed. Due to the cyclic mechanical loading, the load-bearing capacity decreased from 8,496 N±196 N (control) to 7,592 N±901 N (test). The cyclic mechanical loading did not significantly influence the load-bearing capacity (p=0.060). The failure mode was almost identical in all specimens: large deformations of the framework at the implant connection area were obvious. CONCLUSION: The load-bearing capacity of the I-Bridge®2 frameworks is much higher than the clinically relevant occlusal forces, even with considerably angulated implants. However, the performance under functional loading in vivo depends on additional aspects. Further studies are needed to address these aspects.

Load-bearing capacity of screw-retained CAD/CAM-produced titanium implant frameworks (I-Bridge®2) before and after cyclic mechanical loading

Implant-supported screw-retained fixed dental prostheses (FDPs) produced by CAD/ CAM have been introduced in recent years for the rehabilitation of partial or total endentulous jaws. However, there is a lack of data about the long-term mechanical characteristics. OBJECTIVE: The aim of this study was to investigate the failure mode and the influence of extended cyclic mechanical loading on the load-bearing capacity of these frameworks. MATERIAL AND METHODS: Ten five-unit FDP frameworks simulating a free-end situation in the mandibular jaw were manufactured according to the I-Bridge®2-concept (I-Bridge®2, Biomain AB, Helsingborg, Sweden) and each was screw-retained on three differently angulated Astra Tech implants (30º buccal angulation/0º angulation/30º lingual angulation). One half of the specimens was tested for static load-bearing capacity without any further treatment (control), whereas the other half underwent five million cycles of mechanical loading with 100 N as the upper load limit (test). All specimens were loaded until failure in a universal testing machine with an occlusal force applied at the pontics. Load-displacement curves were recorded and the failure mode was macro- and microscopically analyzed. The statistical analysis was performed using a t-test (p=0.05). RESULTS: All the specimens survived cyclic mechanical loading and no obvious failure could be observed. Due to the cyclic mechanical loading, the load-bearing capacity decreased from 8,496 N±196 N (control) to 7,592 N±901 N (test). The cyclic mechanical ...

The influence of simulated aging on the mechanical properties of orthodontic elastomeric chains without an intermodular link.

OBJECTIVE: Orthodontic elastomeric chains are a main component in orthodontic therapy with fixed vestibular or lingual appliances. The objective of this study was to investigate the influence of artificial aging on the mechanical properties of orthodontic elastomeric chains (power chains, PCs) without an intermodular link using a test setup according to DIN EN ISO 21606:2007. MATERIAL AND METHODS: In this study, 11 types of PCs supplied by seven manufacturers were investigated. Four groups with 10 specimens each were randomly generated for each type. Samples were separately mounted in a universal testing machine and extended by 300% (four times their initial length) at a crosshead rate of 100 mm/min and were held at this position for five seconds. The chain length was then reduced to three times the initial length (extension by 200%) and kept for 30 s. Then, within the control group (t = 0) and the force Fmin was recorded before extension until failure was performed and force (Fmax) and length (Lmax) at failure were determined. After prestretching, specimens of the three other groups were stored in water at 37°C with its three times initial length for one day (t = 1), 14 days (t = 2), and 28 days (t = 3), respectively. The specimens were then placed in the universal testing machine and the residual force (Fmin) measured, so as to subsequently extend them until failure at Fmax and Lmax. Data were statistically analyzed by one-way analysis of variance; the level of significance was set at p = 0.05. RESULTS: Statistical analysis revealed significant differences in Fmax, Fmin, and Lmax in each group (t = 0 to t = 3) between the various manufacturers (p < 0.001). Moreover, artificial aging significantly influenced Fmax, Fmin, and Lmax (p < 0.001). CONCLUSION: The orthodontist should consider both the mechanical properties of PCs and the duration of these appliances' application when treating patients. Artificial aging had a significant influence on the parameters we determined (p <0.001).

Load-bearing capacity of artificially aged zirconia fixed dental prostheses with heterogeneous abutment supports.

Aim of this in vitro study was to investigate the effect of artificial ageing and differential abutment support on the load-bearing capacity of zirconia posterior four-unit fixed dental prostheses (FDPs). Thirty-six FDPs were fabricated using CAD/CAM technology and divided into three groups. Specimens in the first group were cemented onto tooth analogues with simulated periodontal resilience, in the second group onto a dental implant and a tooth analogue, but in the third group only onto implants. Half of the samples in each group underwent artificial ageing. Afterwards, all FDPs were loaded until bulk fracture in a universal testing machine. Load-displacement curves and forces at fracture were recorded and results were statistically analysed using ANOVA. Load-bearing capacities within the different test groups averaged as follows (control/artificially aged): tooth-tooth supported (2,009/1,751 N), tooth-implant supported (2,144/1,935 N) and implant-implant supported (2,689/2,484 N). Artificial ageing as well as differential abutment support did have a significant influence on the fracture strength of the zirconia FDPs. Implant-retained prostheses demonstrated the highest load-bearing capacity, while resilient support was demonstrated to be unfavourable. According to these in vitro results, zirconia four-unit prostheses may be promising for application in posterior areas with all three support scenarios (implant-assisted, tooth-retained, or implant-tooth-interconnected prostheses). However, the restorations' mechanical strength may expected to be significantly influenced in situ by ageing of the material on the long term.

Effect of thermal expansion mismatch on the Y-TZP/veneer interfacial adhesion determined by strain energy release rate.

PURPOSES: The aim of this study was to assess the effect of differences in the thermal expansion behaviour of veneering ceramics on the adhesion to Y-TZP, using a fracture mechanics approach. METHODS: Seven veneering ceramics (VM7, VM9, VM13, Lava Ceram, Zirox, Triceram, Allux) and one Y-TZP ceramic were investigated. Thermal expansion coefficients and glass transition temperatures were determined to calculate residual stresses (σ(R), MPa) between core and veneer. Subsequently, the veneering ceramics were fired onto rectangular shaped zirconia specimens, ground flat and notched on the veneering porcelain side. Then specimens were loaded in a four-point bending test and load-displacement curves were recorded. The critical load to induce stable crack extension at the adhesion interface was evaluated to calculate the strain energy release rate (G, J/m(2)) for each system. RESULTS: Residual stresses ranged from -48.3±1.5MPa (VM7) to 36.1±4.8MPa (VM13) with significant differences between all groups (p<0.05). The strain energy release rate of the Y-TZP/veneer specimens ranged from 8.2±1.7J/m(2) (Lava Ceram) to 17.1±2.8J/m(2) (VM9). Values for G could not be obtained with the VM7, Allux and VM13 specimens, due to spontaneous debonding or unstable crack growth. Except for Triceram and Zirox specimens, strain energy release rate was significantly different between all groups (p<0.05). CONCLUSION: Thermal residual stresses and strain energy release rates were correlated. Slight compressive stresses in the region of -20MPa were beneficial for the Y-TZP/veneer interfacial adhesion. Stresses higher or lower than this value exhibited decreased adhesion.

Influence of the interface design on the yield force of the implant-abutment complex before and after cyclic mechanical loading.

PURPOSE: The aim of this in vitro study was to evaluate the implant-abutment assembly of Astra Tech (AST), Bego (BEG), Camlog (CAM), Friadent (FRI), Nobel Biocare (NOB) and Straumann (STR) with respect to yield force before and after cyclic fatigue, using a static overload test with a test set-up according to ISO 14801. METHODS: Ten specimens of each type were split into two homogenous groups: one half was tested for static yield force without any further treatment (control), whereas the other one underwent one million cycles of mechanical loading with 100N as the upper load limit. For load-to-failure testing, specimens were then placed in a stainless steel jig and loaded in a universal testing machine under an angle of 30° with respect to the implant axis until failure. Load-displacement curves were analyzed and the yield forces at which non-linear behaviour set in (Fp) were recorded. Statistical analysis was performed using one-way ANOVA and t-test, respectively, with the level of significance set at 0.05. RESULTS: Statistical analysis revealed that the type of implant-abutment connection has a significant influence on Fp (p<0.001). Furthermore, dynamic loading proved to significantly influence Fp of BEG and CAM (p<0.001). CONCLUSION: None of the implant-abutment types tested would be expected to fail under clinically relevant forces, but the type of implant-abutment connection significantly influences the yield force Fp.

Low-temperature degradation of different zirconia ceramics for dental applications.

The aim of this investigation was to determine the influence of simulated ageing on the tetragonal-to-monoclinic phase transformation and on the flexural strength of a 3Y-TZP ceramic, compared to alumina toughened zirconia (ATZ) and ceria-stabilized zirconia (12Ce-TZP). Standardized disc specimens of each material were hydrothermally aged in steam at 134°C and 3bar for 0, 16, 32, 64 or 128h. The phase transformation was determined by X-ray diffraction (XRD) and atomic force microscopy. Scanning electron microscopy was performed to estimate the depth of the transformation zone. The flexural strength was investigated in a biaxial flexural test. XRD revealed a significant increase in the monoclinic phase content for 3Y-TZP and ATZ due to ageing, although this increase was less pronounced for ATZ. In contrast, the monoclinic phase content of 12Ce-TZP was not influenced. For 3Y-TZP and ATZ, a transformation zone was found of which the depth linearly correlated with ageing time, while for 12Ce-TZP no transformation zone could be observed. Changes in flexural strength after ageing were heterogeneous: while 3Y-TZP showed a significant decrease in strength - from 1740 to 1169 MPa - with ATZ there was a considerable increase - from 1093 to 1378 MPa. The flexural strength of 12Ce-TZP remained unaffected at the low level of about 500 MPa. These results indicate that both alumina and ceria, as stabilizing oxides, reduce the susceptibility of zirconia to hydrothermal degradation; the alternative use of these oxides may enhance the clinical long-term stability of dental zirconia restorations.

Effect of implant-abutment connection design on load bearing capacity and failure mode of implants.

PURPOSE: In this in vitro study, six implant-abutment connection designs were compared and evaluated regarding load bearing capacities and failure modes. MATERIALS AND METHODS: Five implants of Astra Tech, Bego, Camlog, Friadent, Nobel Biocare, and Straumann were separately embedded in stainless steel tubes using polyurethane, for a total of 30 specimens. Specimens were statically loaded under an angle of 30° with respect to the implant axis in a universal testing machine using a test setup according to ISO 14801. Failure was indicated by a load drop of 100 N in force. Load-displacement curves were analyzed, and maximum force and force at which permanent deformation occurred were recorded. Statistical analysis was performed using one-way ANOVA with the level of significance set at 0.05. RESULTS: Statistical analysis revealed that the type of implant-abutment connection design has a significant influence on load bearing capacity (p < 0.001). The mean maximum forces ranged between 606 N (Straumann) and 1129 N (Bego); the forces where plastic deformation set in ranged between 368 N (Friadent) and 955 N (Bego). Failure modes differed between the various implant-abutment connection types tested. CONCLUSIONS: Implant-abutment connection design has a significant influence on load bearing capacity and failure mode of implants; however, all implant-abutment connection designs tested would be expected to withstand clinically relevant forces.